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FWS/OBS-81/01
March 1982
THE ECOLOGY OF who/
NEW ENGLAND TIDAL FLAT$: document
A Community Profile y collection
Fish and Wildlife Service
U.S. Department of the Interior
The Biological Services Program was established within the U.S. Fish
and Wildlife Service to supply scientific information and methodologies on
key environmental issues that impact fish and wildlife resources and their
supporting ecosystems. The mission of the program is as follov/s:
• To strengthen the Fish and Wildlife Service in its role as
a primary source of information on national fish and wild-
life resources, particularly in respect to environmental
impact assessment.
• To gather, analyze, and present information that will aid
decisionmakers in the identification and resolution of
problems associated with major changes in land and water
use.
• To provide better ecological information and evaluation
for Department of the Interior development programs, such
as those relating to energy development.
Information developed by the Biological Services Program is intended
for use in the planning and decisionmaking process to prevent or minimize
the impact of development on fish and wildlife. Research activities and
technical assistance services are based on an analysis of the issues, a
determination of the decisionmakers involved and their information needs,
and an evaluation of the state of the art to identify information gaps
and to determine priorities. This is a strategy that will ensure that
the products produced and disseminated are timely and useful.
Projects have been initiated in the following areas: coal extraction
and conversion; power plants; geothermal , mineral and oil shale develop-
ment; water resource analysis, including stream alterations and western
water allocation; coastal ecosystems and Outer Continental Shelf develop-
ment; and systems inventory, including National Wetland Inventory,
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The Biological Services Program consists of the Office of Biological
Services in Washington, D.C., which is responsible for overall planning and
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certain Fish and Wildlife Service research facilities, who conduct in-house
research studies.
FWS/OBS-81/01
March 1982
THE ECOLOGY OF
NEW ENGLAND TIDAL FLATS:
A Community Profile
by
Robert B. Whitlatch
University of Connecticut
Department of Marine Sciences
Marine Research Laboratory
Noank, Connecticut 06340
Project Officer
Martha W. Young
National Coastal Ecosystems Team
U.S. Fish and Wildlife Service
1010 Gause Boulevard
Slidell, Louisiana 70458
Performed for
National Coastal Ecosystems Team
Office of Biological Services
Fish and Wildlife Service
U.S. Department of the Interior
Washington, D.C. 20240
Library of Congress Number 82-600534
This report should be cited as follows:
Whitlatch, R.B. 1982. The ecology of New England tidal flats: a community
profile. U.S. Fish and Wildlife Service, Biological Services Program, Washinaton,
D.C. FWS/OBS-81/01. 125 pp.
PREFACE
To many, the thought of walking along
the coastline of New England produces
visions of the rocky shores of Maine or
the sandy beaches of Cape Cod. Intertidal
sand and mud flats, conversely, are typi-
cally viewed as physically uninviting if
not repellent habitats filled with sticky
muds, foul odors, and singularly uninter-
esting organisms except, possibly, for the
soft-shell ("steamer") clam. This view is
probably due to a lack of understanding
and appreciation of these habitats. While
tidal flats appear at first glance to be
rather inhospitable portions of the coast-
line, they play an important role as habi-
tats for commercially and recreational ly
important invertebrates and fishes as well
as serving as feeding sites along the New
England coast for a variety of migratory
shorebirds.
The purpose of this report is to
provide a general perspective of tidal
flats of New England, the organisms
commonly associated with them, and the
importance of tidal flats to the coastal
zone viewed as a whole. The approach is
taxonomically based although there is also
attention paid to the flow of organic
matter through the tidal flat habitat.
The method of presentation is similar to
that of Peterson and Peterson (1979) who
have described the tidal flat ecosystems
of North Carolina. The reader, therefore,
has the opportunity of comparing and
contrasting the physical and biological
functioning of the two regions. Chapter 1
begins with a general view of the physi-
cal, chemical, and geological character-
istics of tidal flat environments followed
by a discussion of organic production and
decomposition processes vital to these
systems (Chapter 2). The next three chap-
ters deal with the benthic invertebrates
(Chapter 3), fishes (Chapter 4), and birds
(Chapter 5) common to New England tidal
flats. The coverage within each chapter
reflects the published information avail-
able at the time of writing in addition to
the author's perception about the struc-
ture, function, and importance of each of
the taxonomic groups to the overall tidal
flat system. The last chapter (Chapter 6)
considers the response of tidal flats to
environmental perturbation as well as
their value to the New England coastal
zone.
The reader should be aware that this
report is not intended to be an exhaustive
survey of the literature pertaining to New
England tidal flats. Rather, the approach
and philosophy used has been to provide an
overall impression of the characteristics
of the various players and their roles
within the habitat. If there has been a
goal in the writing, it is to provide a
better understanding and appreciation of
these habitats.
This report is part of a series of
"community profiles" of coastal habitats
of the United States. Sand and mud flats
are identified as habitats by the U.S.
Service, National Wet-
classification system
Wetlands and Deepwater
United States, by Cowardin
Cowardin et al. placed
Fish and Wildlife
lands Inventory
(Classification of
Habitats of the
et al. 1979).
flats in the "unconsolidated shore" class,
the intertidal subsystem, of the marine
and estuarine systems. These landforms
are produced by erosion and deposition by
waves and currents and are alternately ex-
posed and flooded by tides (see Figure 1).
Comments or requests for this publi-
cation should be addressed to:
Information Transfer Specialist
National Coastal Ecosystems Team
U.S. Fish and Wildlife Service
NASA-SI idell Computer Complex
1010 Cause Boulevard
SI idell, LA 70458
(504) 255-G511, FTS 685-6511
m
Aside from their aesthetic value, tidal flats represent important areas in the
coastal zone for a variety of invertebrate and vertebrate species. Photo by
Robert E. DeGoursey, University of Connecticut.
IV
CONTENTS
Page
PREFACE iii
FIGURES vii
TABLES viii
ACKNOWLEDGhENTS ix
CHAPTER 1. GENERAL FEATURES OF TIDAL FLATS 1
1.1 INTRODUCTION 1
1.2 THE NEK ENGLAND COASTAL ENVIRONMENT 1
1.3 GEOLOGICAL, PHYSICAL, AND CHEMICAL CHARACTERISTICS
OF TIDAL FLATS 4
CHAPTER 2. PRODUCERS, DECOMPOSERS, AND ENERGY FLOW 9
2.1 INTRODUCTION 9
2.2 PRODUCERS 9
2.2.1 Microalgae 9
2.2.2 Macroflora H
2.2.3 Phytoplankton H
2.2.4 Photosynthetic and CheTOSynthetic Bacteria 12
2.3 THE DECOMPOSERS 12
2.4 ENERGY FLOW AND FOOD WEB RELATIONSHIPS 14
CHAPTER 3. BENTHIC INVERTEBRATES 18
3.1 INTRODUCTION 18
3.2 BENTHIC EPIFAUNA 18
3.3 BENTHIC INFAUNA 25
CHAPTER 4. FISHES 36
4.1 INTRODUCTION 36
4.2 TROPHIC RELATIONSHIPS 36
4.3 GEOGRAPHIC DISTRIBUTION PATTERNS 37
4.4 MIGRATORY PATTERNS 38
4.5 REGIONAL PATTERNS 38
4.5.1 South of Cape Cod 38
4.5.2 Gulf of Maine . 44
4.6 THE DEPENDENCE AND ROLE OF FISH ON TIDAL FLATS 47
CONTENTS (continued)
Page
CHAPTER 5. BIRDS 49
5.1 INTRODUCTION 49
5.2 SHOREBIRDS 49
5.3 GULLS AND TERNS 54
5.4 HERONS AND OTHER WADING BIRDS 59
5.5 WATERFOWL AND DIVING BIRDS 61
5.6 RAPTORS 64
5.7 DEPENDENCE ON TIDAL FLATS 65
CHAPTER 6. TIDAL FLATS: THEIR IMPORTANCE AND PERSISTENCE 66
6.1 INTRODUCTION 66
6.2 RESPONSE OF TIDAL FLATS TO ENVIRONMENTAL PERTURBATIONS 66
6.3 THE IMPORTANCE OF NEW ENGLAND TIDAL FLATS 68
REFERENCES 70
APPENDIX I. COMMON INFAUNAL INVERTEBRATES ASSOCIATED WITH
NEW ENGLAND TIDAL FLATS 84
APPENDIX II. COASTAL FISHES OF NEW ENGLAND 92
APPENDIX III. BIRD SPECIES THAT UTILIZE NEW ENGLAND TIDAL FLATS ... 119
VI
FIGURES
Number 1^21
1 Diagrammatic representation of a tidal flat 2
2 Map of the New England coast 3
3 Monthly surface seawater temperatures at four localities
along the New England coastline 3
4 Particulate characteristics of tidal flat sediment 5
5 Vertical distributions of some dominant groups of
meiofaunal organisms _ 26
6 Some representative New England sand flat benthic
invertebrates 28
7 Some representative New England mud flat benthic
invertebrates ^^
8 Intertidal zonation patterns of major groups of benthic
invertebrates 30
9 Vertical distributions of major groups of tidal flat
macroinvertebrates 31
10 Percentages of different temporal components of fish
species alono the northeast Atlantic coastline 37
11 Seasonal migration patterns of New England coastal fish
populations 39
12 Examples of major groups of fish that occupy tidal flats
and adjacent coastal habitats in southern New England .... 40
13 Seasonal movements of fish in the Gulf of Maine inshore
environment ^^
14 Mew England tidal flat bird guilds 50
15 Vertical feeding depths of some common New England
shorebirds 52
vn
TABLES
Number Page
1 Different types and relative abundances of living and
non-living particulate types found in sorr,e New England
tidal flat sediments 6
2 Primary production of benthic microalgae in some
temperate intertidal and shallow subtidal habitats 16
3 Phytoplankton primary production in some temperate
estuarine areas 16
4 Sources and contributions of organic carbon to some
southern New England coastal ponds and estuaries 17
5 Common epifaunal invertebrates inhabiting New England
tidal flats 20
6 Number of coastal nesting pairs of colonial waterbird
species in 1977 55
vm
ACKNOWLEDGMENTS
I wish to thank a number of people
for valuable assistance with this project.
Robert DeGoursey and Peter Auster helped
to collate much of the fish literature and
served as sounding boards and reviewers of
Chapter 4. Steven Malinowski gathered
information on coastal birds and wrote the
lion's share of Chapter 5. Members of the
Manomet Bird Observatory, Manomet, Massa-
chusetts, were instrumental in identifying
pertinent references and in providing
access to unpublished reports of their
work. An informative conversation with
Les Watling helped to clarify questions
regarding the mud flats of Maine. Barry
Lyons supplied information about mud flat
chemistry. Steven Edwards and Barbara
Welsh provided access to unpublished
data on tidal flat macrophytes. Sarah
Malinowski expertly drew all the figures
from sketches and verbal descriptions of
what benthic invertebrates, fish, and bird
communities "really" look like. I appre-
ciate the thoughtful and extensive reviews
of Ralph Andrews, Bill Drury, Eric Mills,
Don Rhoads, and Peter Larsen. Martha
Young initiated the project, provided
editorial assistance and logistic support,
and most importantly, allowed (relatively)
unimpeded time to think and write. Joyce
Lorensen typed portions of an early draft
and Ann Whitlatch expertly typed, edited,
and quietly suffered through the final
draft. Preparation and publication of
this report were supported by the U.S.
Department of Interior, Fish and Wildlife
Service, National Coastal Ecosystems Team.
To all , I am grateful .
This report is dedicated to A.C.
Redfield and H.L. Sanders. Dr. Redfield's
pioneering studies provided the initial
stimulus for my working in the most
beautiful salt marsh-tidal flat system
in New England. Howard Sanders not only
provided the opportunity to undertake
this project, but his encouragement and
insightful and provocative outlook on
marine ecology have been a constant source
of professional stimulation.
IX
CHAPTER 1
GENERAL FEATURES OF TIDAL FLATS
1.1 INTRODUCTION
Intertidal sand and mud flats are
soft to semi-soft substrata, shallow-water
habitats situated between the low and high
tidal limits. Tidal flats are found where
sediment accumulates and are, therefore,
associated with coastal embayments, behind
spits and barrier beaches, and along the
margins of estuaries. The occurrence and
extent of tidal flats varies according to
local coastline morphology and tidal
amplitude. These habitats are sometimes
bordered landward by salt marshes and sea-
ward by tidal channels and/or subtidal
eel grass (Zostera marina) beds (Figure 1).
Tidal flats are common features of the New
England coastline, especially in Maine,
New Hampshire, and parts of Massachusetts
where increased tidal amplitude exposes
more of the tidal flats at low tide. For
example, tidal flats represent about 48%
of the intertidal habitats of Maine (Fefer
and Schettig 1980).
Tidal flats are not static, closed
ecological habitats, but are physically
and biologically linked to other coastal
marine systems. It is generally recog-
nized, for example, that organisms inhab-
iting tidal flats rely heavily upon
organic materials (e.g., plankton, detri-
tus) imported from adjacent coastal, estu-
arine, riverine, and salt marsh habitats.
In addition, many species of estuarine and
coastal fishes migrate over tidal flats
with the incoming tide to feed on the
organisms found on and in the sediments.
1.2 THE NEW ENGLAND COASTAL ENVIRONMENT
Climatic conditions of the New Eng-
land coastal region exhibit pronounced
seasonal temperature fluctuations, a char-
acteristic of temperate environments.
Extremes in seawater temperatures, warmest
in August through September and coolest in
December to March, are among the greatest
in the world (Sanders 1968). The region
is commonly divided, for convenience, into
two areas: the Gulf of Maine extending
from Cape Cod, Massachusetts, to the Bay
of Fundy, Nova Scotia, Canada, and the
areas south of Cape Cod ranging to western
Connecticut including Long Island Sound
(Figure 2). This division is based largely
on differences in annual water temperature
variation in the two regions. Waters in
the Gulf of Maine are continually well-
mixed by tidal, current, and wind action
(Brown and Beardsley 1978) and in the sum-
mer do not become as warm as the waters
south of Cape Cod. On the south side of
Cape Cod, the influence of the Gulf Stream
coupled with a shallower coastal plain
produces more abrupt increases in summer
temperatures. The net effect is that the
annual range of seawater temperatures
along the coast of New England is closely
related to latitude (Figure 3). For
instance, in the northern portion of the
Gulf of Maine there is a 10°C (50°F)
annual temperature range while in portions
of Long Island Sound the annual range is
about 20°C (68°F).
Cape Cod is a transition zone rather
than a discrete physical barrier separat-
ing warm and cool New England coastal
water masses. Water associated with embay-
ment and estuarine environments is gener-
ally shallow and is more likely to be
influenced by atmospheric and terrestrial
conditions than deeper water areas. Spring
runoff from rivers, thermal warming of mud
and sand flats with subsequent heat
transfer to shallow waters, and low flush-
ing rates of water in some estuarine
habitats all contribute to warmer water
temperatures. Warm water embayments north
of Cape Cod do occur (e.g., Barnstable
Harbor, Massachusetts; upper reaches of
some estuaries in New Hampshire and
Maine), but in autumn shallow water
habitats respond quickly to the cooler
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Figure 2. Map of the New England coast. The marine waters are often separated into
two areas: Gulf of Maine (north of Cape Cod, MA) and Mid-Atlantic Bight (south of
Cape Cod, MA).
JFAAAJ J A50ND
Figure 3. Monthly surface seawater temperatures at four localities along the New
England coastline. Note differences in summer temperatures north (Sandwich, MA,
and Penobscot Bay, ME) and south (Woods Hole, MA, and Mystic, CT) of Cape Cod, MA.
atmospheric conditions and influence of
associated land masses, and the waters
become cooler than nearby coastal waters.
Buildup of seawater ice on New Eng-
land tidal flats, both north and south of
Cape Cod, commonly occurs in winter. The
appearance and extent of the ice is de-
pendent upon tidal fluctuation, location,
and severity of the winter. Because of
tidal action, the ice moves back and forth
across the flats resulting in appreciable
geomorphological effects upon the sediment
through accretion, erosion, and transport.
Boulders weighing several tons have been
transported considerable distances by ice
at Barnstable Harbor (Redfield 1972). Salt
marsh turf may also be transported onto
tidal flats by ice movement. Shortly after
breakup of the ice in early spring, ero-
sional scars in the sediment are evident.
Most of the scars are quickly removed by
tidal and wave action. Although ice
occurs regularly on New England tidal
flats, relatively little is known about
its effects on the biota. Ice scouring
can remove or displace infaunal and epi-
faunal organisms. Freezing of the sedi-
ments to a depth of 5 to 10 cm (2 to 4
inches) may also occur, although little is
known about what effect this has on the
organisms living in the sediment. During
periods of severe and prolonged ice build-
up on tidal flats, birds that use the
areas as feeding sites may have to forage
elsewhere.
Storms that pass through New England
also affect the sedimentary features of
tidal flats. Both northern and southern
New England normally experience three to
five major storms each year, usually in
fall and winter. Winds in New England are
predominantly from the southwest but dur-
ing winter are likely to shift to the west
or northwest. Occasionally winds come
from the northeast and are typically asso-
ciated with the most severe storms (the
classic "nor 'easter"). Hurricanes occur
in New England - the last major storm hit
the coastline in 1954.
Fog is common in the coastal zone
especially in northern New England. Fog
occurs at any time of the year although
dense fog is associated with the warmer,
summer months. The presence of fog on
the tidal flats acts to insulate organisms
living on or in the sediments from desic-
cation and allows less hardy organisms to
survive in intertidal areas during periods
of intense solar heating.
1.3 GEOLOGICAL, PHYSICAL, AND CHEMICAL
CHARACTERISTICS OF TIDAL FLATS
On a geologic timescale, coastal ma-
rine environments of New England represent
systems that have continually changed.
Since the last Pleistocene glaciation epi-
sode, the coastline has slowly subsided
and sealevel has progressively risen. The
net effect is a slow migration of the sea
into the lowlands, altering coastal habi-
tats. Historical reconstructions of many
New England estuarine systems show the
transitional nature of tidal flat habi-
tats. Flats develop as depositional fea-
tures expanding at the expense of tidal
channels and eelgrass beds and they in
turn are invaded by the progression of
salt marsh vegetation (Redfield 1967).
The formation of tidal flats and
their sedimentary characteristics are pri-
marily dependent upon the physical and
biological environment (e.g., tidal cur-
rents, wave action, and biologically-
induced sediment mixing), the nature and
source of available materials, and the
glacial history of New England. Vast
deposits of coarse-grained sediments left
by glacial activity are responsible for
the general restriction of sand flats to
Cape Cod and southward. Mud flats, more
commonly found in northern New England,
are derived from land-based sources, and
transported by river systems. Sediments
are also deposited on tidal flats by cur-
rents from offshore sources or through the
erosion of adjacent tidal flats or shore-
lines.
Sediments of tidal flats can be
characterized in various ways. Geologists
prefer to use the bulk properties of the
sediment (e.g., median grain size, percent
silt-clay fraction). Sandy sediments are
those having less than 5% of their weight
composed of silt-clay-sized material
(particles less than 62 jjm in diameter),
while muddy-sands and sandy-muds consist
of 5% to 50% and 50% to 90% silt-clay.
respectively. Muds are sediments with
greater than 90% silt-clay fraction. Biol-
ogists, on the other hand, have attempted
to view sediments with a higher degree of
resolution. Sediments are described by
biologists according to their particulate
constituents: these consist of a complex
array of organic and inorganic forms,
varying in size, shape, and qualitative
nature (Table 1; Figure 4). Most of the
sediments found in New England tidal flats
are dominated by siliceous sands, clay
minerals, and organic-mineral aggregates
(detritus). The abundance and variety of
particle types vary spatially and verti-
cally within the sediment (Johnson 1974;
Whitlatch 1981). A larger variety of par-
ticle types is usually found in the upper
layers of the surface than in deeper lay-
ers. Muddy sediments have a greater pro-
portion of organic-mineral aggregates than
sandy sediments.
Examination of the surface of tidal
flats reveals undulations and ripples
formed by waves and currents sweeping over
the flats. Large grains tend to accumulate
on the front of the ripples while smaller
grains tend to concentrate on the back
side of the ripple marks. Sand and mud
flats may or may not be dissected by chan-
nels. When they occur, the channels form
meandering depressions roughly perpendicu-
lar to the creeks that border the flats
and are more common on the lower portion
of the flat (Figure 1 ).
Tidal action is responsible for sedi-
ment movement and control of sediment tex-
ture as currents continually resuspend and
transport sediments. In exposed areas
where there are high current velocities
and turbulence, sediments are generally
composed of coarse, unstable sands and
cobble. In more protected areas, reduced
Figure 4. Viewed microscopically, tidal flat sediments are a complex array of organic
and inorganic particulate material. The large (0.2 mm) plant fragment from cordgrass,
Spartina alterniflora, is the source of much of the detritus entering many New England
tidal flat ecosystems. Photo by R.B. Whitlatch, University of Connecticut.
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water flow results in the deposition of
finer-grained, more stable sediments. On
a larger scale, coarser-grained sandy sed-
iments are found in channels, on beaches,
and near the mouths of inlets, while
finer-grained sediments are associated
with increasing distance from the mouths
of inlets and at higher intertidal eleva-
tions. Redfield (1S72) described these
sediment distribution patterns at Barn-
stable Harbor, Massachusetts, noting a
decrease in grain size proceeding from
the mouth of the harbor to the vegetated
salt marsh.
Wind-generated waves and currents
also affect mixing and redistribution of
sediments on some tidal flats. The
magnitude of wind impact is largely
dependent upon the size and depth of the
waterbody over which the wind passes.
Large shallow embayments in some southern
states, for example, can be influenced
considerably by wind-generated waves
(Peterson and Peterson 1979). In New
England, embayments are comparatively
smaller and shallower; wind action is
generally less significant than tidal
action. Most wind effects on tidal flats
are probably concentrated in periods of
storm activity when resuspension and
redistribution of sediments occur.
The New England coast has semi-
diurnal tides (e.g., two high and two low
tides per tidal day). Channel constric-
tions and bottom topography alter the
magnitude of the tidal range although the
mean tidal range south of Cape Cod is
about 1 to 1.5 m (3 to 5 ft) while mean
tides north of Cape Cod range 3 to 4 m (10
to 13 ft). The twice daily inundation and
exposure contributes in an important man-
ner to the spatial and temporal complexity
of the tidal flat habitat. When tidal
flats are submerged, they share many of
the same physical and chemical character-
istics of the water found in adjacent
coastal and/or estuarine systems. When
exposed, tidal flats are affected by cli-
matic variations of air temperature, pre-
cipitation, and wind. Organisms living in
these environments, therefore, must be
well adapted to the physically rigorous
environmental conditions.
While the physical conditions of the
water over the tidal flats may change con-
siderably during a tidal cycle, physical
features of the sediments are less vari-
able. Even at low tide, small amounts of
water are retained in the sediments; this
helps prevent desiccation. Sediments also
tend to buffer temperature and salinity
fluctuations (Sanders et al. 1965; Johnson
1965, 1967). The net result is that
organisms living within tidal flat sedi-
ments are normally able to withstand
greater environmental fluctuation than
exposed organisms attached to or living on
the sediments (Alexander et al. 1955).
Chemical properties of the sediments
vary vertically in tidal flats and it is
possible to view this stratification by
examining sediment samples in cross-
section. In muddy sediments, two or three
distinctly colored zones commonly exist.
The uppermost is light-brown, extending 1
to 5 mm below the sediment surface. This
is the zone of oxygenated sediment. Below
this thin layer is a black zone where oxy-
gen is absent and the sediments smell of
hydrogen sulfide ("rotten egg" gas). The
black color is due primarily to the pres-
ence of iron sulfides. In some muddy
sediments a third, gray-colored zone may
exist below the black zone due to the
presence of iron pyrite.
The boundary between and position of
the oxygenated and black anoxic zone
(termed the redox potential discontinuity,
or redox zone) varies with depth, depend-
ing on the amount of organic matter in the
sediment, sediment grain size, and the
activities of organisms burrowing through
the sediment or disturbing the surface.
Oxygen diffusion may extend 10 to 20 cm
(4 to 8 inches) below the sediment-water
interface in sandy sediments due to
increased percolation of water through the
sediments and small amounts of organic
material. On many sandy flats it may be
difficult to find a black zone and the
sediments may not smell of hydrogen
sulfide. In muddy sediments containing
greater amounts of organic material,
the redox zone is usually within sev-
eral millimeters of the surface. Rhoads
(1974) noted that activities of burrowing
organisms greatly increased the diffus- nematodes. Larger organisms (e.g., anne-
ibility of oxygen into muddy sediment and lids) that also live in the anoxic zone
extended the redox layer further below the tend to build tubes or burrows to the sur-
surface. Despite the lack of oxygen, face that bring oxygenated water to the
black reducing sediments contain a variety organism,
of small organisms such as bacteria and
CHAPTER 2
PRODUCERS, DECOMPOSERS, AND ENERGY FLOW
2.1 INTRODUCTION
Estuaries and coastal embayments are
well -recognized for their high primary and
secondary productivity. High production
by New England tidal flats is reflected in
their abundant and diverse populations of
invertebrates (Chapter 3) and vertebrates
(Chapters 4 and 5) that utilize the habi-
tat as nursery grounds and feeding sites.
In addition, many New England tidal flats
support large populations of commercially
and recreational ly important shellfish and
baitworms. The high productivity of tidal
flats is attributed, in part, to the
diverse variety of primary food types
(e.g., benthic microalgae, phytoplankton,
imported particulate organic materials -
"detritus") that are available to the
organisms of the flat.
2.2 PRODUCERS
2.2.1 Microalgae
New England tidal flats support a
large and diverse microflora. These assem-
blages typically appear as brownish or
greenish films or mats on the sediment
surface and tend to be dominated by ben-
thic diatoms, euglenoids, dinof lagellates,
and blue-green algae.
The depth of microalgal distributions
in tidal flat sediments is affected by the
ability of light to penetrate the sedi-
ments. Fenchel and Straarup (1971) found
that the photic zone (depth of light pene-
tration) of fine sands was about half the
thickness of that found in coarse sand.
Although the majority of microalgae are
concentrated in the upper several centime-
ters of the sediment, pigmented cells are
commonly found below the photic zone. When
exposed to light, these cells actively
photosynthesize and it has been hypothe-
sized that they provide a reservoir of
potential benthic primary producers if the
upper several centimeters of the sediment
are eroded by wave action (Van der Eijk
1979).
By virtue of their location, benthic
microalgal species composition, abundance,
and spatial distribution patterns are
strongly influenced by near-surface phy-
sical, chemical, and biological processes.
These groups of organisms exhibit pro-
nounced spatial and temporal variation in
abundance. Exposed tidal flats generally
have lower abundances of microalgae than
protected flats. Marshall et al. (1971)
noted that benthic microflora were most
abundant from May to August in several
southern New England shallow estuaries
probably as a result of temperature and
illumination cycles. While summer peaks
in abundance are typical throughout New
England, Watling (L. Watling; University
of Maine, Walpole; February 1981 ; personal
communication) has observed dense surface
films of diatoms on a tidal flat in Maine
during winter, possibly a consequence of
decreased grazing activities by benthic
invertebrates at this time of the year.
Most of the academic study of the
benthic microflora of tidal flats has been
concentrated on the diatoms. Diatoms are
ordinarily divided by specialists into two
categories: the episammic (non-motile)
and epipelic (motile) forms. Most studies
have concentrated on the epipelic form
since the method commonly used to collect
diatoms (e.g., Eaton and Moss 1966)
depends on the movement of microalgae into
layers of fine netting placed on the sedi-
ment surface.
The benthic epipelic diatom tidal
flat communities of New England are domi-
nated by pennate forms such as Navicula,
Hantzschia, and Nitzchia (Moull and Mason
1957; Connor 1980). ^These forms can
migrate vertically through sediments by
extruding mucus threads. The extent of
movement is variable and species-specific,
ranging from diurnal ly migrating forms
such as Hantzschia to relatively immobile
forms such as Amphora (Round 1979). Ver-
tical movements are thought to be depend-
ent upon cycles of illumination with
diatoms appearing at the sediment surface
at low tide and burrowing into the sedi-
ment at flood tide (Palmer and Round
1967). The downward migration into the
sediments is considered to be either an
active response to compensate for dis-
placement by tidal action or a mechanism
for increasing nutrient availability
(Pomeroy 1959). While the non-migratory
forms are most commonly attached to sand
grains, some species are capable of
limited mobility.
Although episammic forms are not
as intensively studied as the epipelic
diatoms because they become more easily
buried in unstable tidal flat sediments
(Williams 1962; Sullivan 1975; Pace et al.
1979), these forms may be important
benthic primary producers. Riznyk (1973)
found that when sampling methods were used
to collect both motile and non-motile
forms, the latter group was more abundant
on an Oregon tidal flat.
Occasionally algal mats are present
in the higher elevations of tidal flat
habitats. The mats consist of tightly
intertwined groups of species of green and
blue-green algae. The mats form a dark-
green or blue-black crust on the sediment
surface and are found in protected areas.
The principle species found in a Massa-
chusetts salt marsh by Brenner et al.
(1976) were Lyngbya aestuari, Microcoleus
chthonoplastes, and Calothrix contarenii.
In cross-section, many of the mats form
Epipelic pennate diatoms (this specimen is approximately 0.2 mm long) are commonly seen
in the upper several centimeters of tidal flat sediments. When very abundant, benthic
diatoms form brownish films on the sediment surface. Photo by R.B. Whitlatch, Univer-
sity of Connecticut.
10
alternating layers of dark-green organic
matter and lighter colored sedirent 1 to
10 cm (0.4 to 4 inches) deep. Algal mats
are known to accelerate rates of sediment
accretion on tidal flats by mucilagenous
trapping of fine-grained sediments.
The formation of algal mats is prob-
ably restricted to the high intertidal
zone because of the reduced activities of
grazing and burrowing organisms in these
areas. Experimental removal of the
surface-grazing periwinkle, Littorina
littorea, and the mud snail, Ilyanassa
obsoleta, from the mid-intertidal portions
of a Barnstable Harbor, Massachusetts,
sand flat resulted in the formation of a
1 to 2 mm thick algal mat within several
weeks. Replacement of the snails in these
plots resulted in the quick destruction of
the mats (Whitlatch unpublished data).
Other organisms such as amphipods and fish
are also known to feed on the mats and
probably help to control their distribu-
tion on tidal flats.
2.2.2 Macroflora
Because of the fine-grained and un-
stable nature of tidal flat sediments and
their regular exposure to salt water at
high tide and desiccation at low tide,
macroalgae and rooted vegetation are rela-
tively uncommon. While these factors may
preclude the establishment of stable
macrophytic communities on tidal flats,
several species of ephemerals (short-lived
species) are occasionally found in the New
England region. These species (notably
Ul va spp. - sea lettuce, and Enteromorpha
spp. - green algae) are often associated
with protected areas, the upper portions
of sand flats, or with eutrophic condi-
tions (e.g., sewage outfalls). They
appear in early spring, continue to thrive
throughout the summer, and rapidly decline
during fall and winter.
In some parts of New England, dense
populations of Ul va spp. have been docu-
mented. Welsh (1980) reported quantities
up to 185 g/m2 and several centimeters
thick at the Branford Cove, Connecticut,
mud flat. Edwards (S. Edwards; University
of Rhode Island, Kingston; June 1980;
personal communication) found that more
than 75% of this same tidal flat was
covered by Ul va during the summer. This
dense coverage resulted in the establish-
ment of anaerobic conditions at the sedi-
ment surface and contributed to the reduc-
tion of microalgae through shading as well
as decreased abundance of meio- and macro-
fauna. Others (e.g., Woodin 1974; Watling
1975) have also found that dense stands of
Ulva can create anaerobic conditions at
the sediment-water interface that alter
infaunal species abundance and composi-
tion. Inhibitory effects of Ulva on tidal
flat animial populations may also extend to
fish species. In a series of laboratory
experiments, Johnson (198G) demonstrated
that mortalities of post-larval winter
flounder (Pseudopleuronectes americanus)
were greatly increased in the presence of
Ulva. She offered the hypothesis that the
increased fish mortality rates were the
result of a harmful algal exudate.
Other species of large plants are
commonly transported onto New England
tidal flats from adjacent salt marshes
(e.g., cordgrass-Spartina spp., rush-
Juncus sp.), from eelgrass beds (Zqstera
marina), and from rocky coastlines (e.g.,
fucoids, Codium in southern New England).
These species are most abundant on flats
following storm activity or during the
fall when they begin to die and decompose.
When very abundant, these plant remains
form strand or "wrack" lines on the higher
elevations of the flats and provide food
and protection for small crustaceans.
Most of the biomass of these plants,
however, is not used by herbivores but
is broken down by microorganisms and
by physical and biological fragmenta-
tion, becoming part of the tidal flat
detritus-based food web (see section
2.3).
2.2.3 Phytoplankton
Phytoplankton are temporary tidal
flat components and are present only when
water is covering the flat. Phytoplankton
are influenced by nutrient concentration,
water temperature and circulation pat-
terns, and by grazing; pronounced spatial
and temporal variability in species com-
position and abundance exist along the
New England coastline (see TRIGOK-PARC
1974 and Malone 1977 for reviews). Typi-
cally, phytoplankton concentrations are
reduced during winter because of cold
water temperatures and low light levels.
11
Growth rates increase in spring and may
remain high throughout the summer in
shallow waters. Primary production,
therefore, tends to be higher in near-
shore than oceanic waters because the
shallower waters are continuously well-
mixed and the phytoplankton have a con-
stant supply of nutrients from the sedi-
ments. Growth rates are also higher in
southern New England than northern New
England probably due to higher water
temperatures and the presence of larger
amounts of anthropogenic nutrients in
southern areas.
Phytoplankton species composition
varies along the New England coast. Dia-
toms are most abundant in northern waters
while the warmer, southern waters have
higher concentrations of dinoflagellates.
Hulburt (1556, 1963) found that several
central New England shallow estuaries
exhibited large concentrations of one or
two species of phytoplankton and that
species diversity was generally lower than
in more oceanic waters. These patterns
are assumed to reflect the more physically
unstable inshore conditions that favor
motile species (e.g., dinoflagellates)
that do not sink to the bottom in shallow
waters.
Occasionally, outbreaks of the dino-
flagellate, Gonyaulax excavata, occur in
New England nearshore waters. This "red
tide" organism produces a toxin that is
harmful to marine species when ingested
(e.g., suspension-feeding clams, mussels).
If the toxin accumulates in shellfish in
sufficient quantities, it may be fatal to
the host organism as well as to humans
when contaminated shellfish are eaten.
The intensity and duration of red tide
outbreaks are variable in New England, but
massive outbreaks create a severe health
problem and economic impact upon the
shellfish industry.
2.2.4 Photosynthetic and Chemosynthetic
Bacteria
Although photosynthetic bacteria are
commonly found in the sediments of New
England tidal flats, relatively little is
known about their ecology or role in the
tidal flat food web. These organisms are
restricted to the upper few millimeters of
the sediment and appear as purplish films
especially during the warmer months of the
year. Chemosynthetic bacteria, on the
other hand, tend to be most abundant in
the redox layer of tidal flat sediments
and derive energy from the oxidation of
inorganic compounds such as sulfide,
nitrite, and ammonia. While relatively
little is known about these bacterial
types, recent studies in New Hampshire
tidal flats (Lyons and Gaudette 1979) and
a Massachusetts salt marsh (Howarth and
Teal 1980) have shown that chemosynthetic
bacteria may contribute significantly to
primary production. How much of this
energy is transferred to higher trophic
levels within the tidal flat ecosystem is
not known.
2.3 THE DECOMPOSERS
While considerable attention has
focused on coastal embayments and estuar-
ies as areas of high primary production,
much of the organic material entering
these systems is in the form of organic
detritus (e.g., dead and decomposing salt
marsh plants, eelgrass, phytoplankton).
Recent evidence points to in situ utili-
zation of the bulk of detritus (Haines
1977; Woodwell et al. 1977) as well as
importation of additional detritus into
shallow water from adjacent coastal water.
Combining these organic inputs with those
coming from terrestrial and aquatic
sources and human activities (e.g.,
Kuenzler et al. 1977; Welsh et al. 1978),
it appears that the utilization of detri-
tus in inshore waters outweighs the con-
sumption of the products of primary pro-
duction.
Decomposition processes become in-
creasingly important to the fauna on tidal
flats because of (1) a high relative
proportion of shallow water areas that
promotes the occurrence of autochthonous
(indigenous) detrital producers (e.g.,
benthic micro- and macroalgae), (2) low
velocity current regimes that increase the
probability of organic particles settling
out from the water column, and (3) an
increase in the ratio of length of shore-
line to volume of water resulting in
increased amounts of allochthonous (trans-
ported) detrital material entering from
12
freshwater, terrigenous salt marsh and
eelgrass sources.
The organisms primarily responsible
for the initial decomposition of detrital
material on tidal flats are a wide variety
of microorganisms, mainly fungi and bacte-
ria. Fungi are associated with decompos-
ing vascular plant material and breakdown
cellulose by extending their hyphae into
the detrital fragments. Fungi adhering to
other particles, such as organic-encrusted
mineral grains, are less common in tidal
flat sediments (Johnson 1?74). Bacteria
are associated with the interstitial water
found in sediments as well as the external
surface of detrital particles and the con-
cave surfaces of mineral grains (Johnson
1974). Studies have shown that bacterial
standing stock is inversely correlated
with particle size in marine sediments
(e.g.. Dale 1974). Presumably such a rela-
tionship exists because of the increased
surface-to-volume ratio of the smaller
particles resulting in increased area per
unit volume of sedimenc for bacterial
colonization and growth. Finer-grained
sediments, therefore, have more abundant
bacterial populations than coarser-grained
sediments. Bacteria are also more abun-
dant at the surface of sediments than at
depth (Rublee and Dornseif 1978) probably
because of the greater amount of detrital
material found in near-surface sediment
layers (Whitlatch 1981).
Decomposition rates of detritus are a
function of the type and source of the
organic substrate, physical and chemical
conditions, and the density and type of
organism feeding upon the matrix of living
and non-living organic material. Detrital
material entering tidal flats from terres-
trial sources is more resistant to decom-
position than much marine-derived detrital
material. Terrestrial plants build more
structural polymers (e.g., lignins) than
marine plants and are much more resistant
to bacterial decomposition (MacCubbin and
Hodson 1?80). Larger organisms (e.g.,
invertebrates) feeding upon detrital mate-
rial have been shown to accelerate the
decomposition process through the reduc-
tion of particle size, exposure of grazed
surfaces to microbial activity, and
selective foraging upon fast-growing
microbial cells (Fenchel 197C, 1972;
Fenchel and Harrison 1976; Lopez et al.
1977).
The decomposers perform several vital
functions in marine coastal habitats.
First, microbial decomposition of plant
material serves as the primary link be-
tween primary and secondary production
(Cdum and de la Cruz 1967). Many studies
have demonstrated that only small percent-
ages of plant material are consumed while
plants are living but that after death and
physical-biological fragmentation, plant
material serves as an energy source for
the microbial and fungal populations in
the sediment. The resultant microbial
activity breaks down detritus and enhances
its nutritive value as a food source for
many other species of organisms. Second,
during the decomposition process, the
microbiota convert dead organic material
into nutrients that can be utilized by
primary producers. Loder and Gilbert
(1980), for example, calculated that 7% of
the dissolved phosphate entering Great Bay
Estuary, New Hampshire, came from the
estuarine sediments. Zeitzschel (1980)
recently suggested that 30% to 100% of the
nutrient requirements of shallow-water
phytoplankton growth comes from the sedi-
ments. Release of nutrients from the
sediment may also be important for tidal
flat macroalgal production (B.L. Welsh;
University of Connecticut, Avery Point,
Groton; February 1981; personal communica-
tion). Bacteria can also convert dissolved
organic materials from the water column
into particulate biomass. While the impor-
tance of dissolved organic material in
shallow-water marine environments is not
fully understood, many types of marine
invertebrates can utilize these substances
as a food source (Stephens and Schinske
1961; Stephens 1975). Tidal flat inverte-
brates have well-developed digestive sys-
tems for the ingestion of particulate
material and it is thought that bacteria
can outcompete many of these organisms for
dissolved organic material in marine sedi-
ments (Fenchel and J0rgensen 1977). Last,
the net effect of having bacteria and
fungi at the base of the decomposer food
web is a stabilization of energy transfer
to higher trophic levels within the tidal
flat habitat. The availability of food for
consumers is not restricted to the growing
season of a temperate climate. The energy
tied up in the primary detrital fraction
is slowly released depending on the rate
of microbial degradation to become avail-
able to higher trophic levels throughout
the year.
13
2.4 ENERGY FLOW AND FOOD WEB RELATIONSHIPS
Organic materials in marine ecosys-
terris are channeled through two types of
food webs: one based on grazing, which
starts with the utilization of the pro-
ducts of primary production; and another
based on the consumption of detrital pate-
rial and associated microbial populations.
While these two food webs exist in tidal
flat habitats, they are not well-defined.
The trophic structure of New England tidal
flats includes a number of primary food
types and an intricately connected food
web of generalized feeders. Many organisms
interact and feed at different trophic
levels at the same time and are able to
utilize both living plant and detrital
materials. Also, many tidal flat organisms
change their trophic status with increas-
ing size. Nost fish, for example, begin
their lives as planktivores, pass through
a detritus-feeding stage, and finally
become predaceous as adults.
Because detrital material is so
conspicuous in the guts of many species
associated with tidal flats (Whitlatch
1S76; Tenore 1977), food webs in these
habitats are considered to be detrital ly
driven. The grazing food web apparently
contributes less to tidal flat energy. One
of the more striking examples of the lack
of utilization of the products of primiary
production is the scarcity of organisms
feeding on Ul va and Enteromorpha. While
these microphytes may densely carpet por-
tions of New England tidal flats, only a
few species (e.g., the snail, Littorina,
nereid polychaetes, some gammaridean
anphipods, and birds) feed upon them
directly. Occasionally dense populations
of birds or snails deplete these macro-
phytes locally, but probably 90% to 95%
are consumed after death and entry into
the detrital food web (Mann 1972). Grazing
on microalcae by herbivorous snails and
some tube-dwelling amphipods is more
common although to what extent these
organisms rely exclusively upon the micro-
algae as food has yet to be determined.
Although detritus appears to be the
major food source of n.any tidal flat or-
ganisms, there are uncertainties regarding
exactly what fractions of the detrital
materials are utilized by detritivorcs.
The microbial portion (the "living" frac-
tion) of the detrital particle is easier
to digest and is more nutritious than the
structural ("non-living") portion. Fungi,
bacteria, and protozoans associated with
detrital particles are efficiently removed
by detritivores (Fenchel 1972; Hylleberg
1975; Lopez and Levinton 1978), and stud-
ies have shown that these living materials
are more easily digested than the non-
living fraction (Kofoed 1975; Wetzel
1977). When comparing the ingestion rates
of various detritivores, Cammen et al.
(1978) found that the microbial portion of
detritus accounted for only about 10% of
their metabolic demands. This apparent
contradiction suggests some possibilities
about the importance of the living versus
the non-living fractions of detritus to
detritivores. First, detritivores may be
able to derive most of their nutrition
from the non-living fraction. Second,
energy obtained from other sources, such
as dissolved organic materials or small
meiofaunal organisms (see section 3.3) may
figure significantly in a detritivore's
nutritional requirements. Last, organisms
may be selectively feeding on the living
portion of the detrital particle. Selec-
tivity for high organic food items has
been shown in several species of detriti-
vores (e.g., Whitlatch 1974; Connor 1980)
and selective ingestion of microbial ly-
enriched fecal material (termed coproph-
agy) is common (Johannes and Satomi 1966;
Frankenberg and Smith 1967). While more
information is needed to test the various
alternative explanations, it is becoming
increasingly apparent that inshore detri-
tal food web dynamics are more complex
than previously considered.
Many ecologists believe that tidal
flat ecosystems are "energy subsidized",
iving the bulk of their energy from
salt n,arshes, seagrass
estuaries, and
adjacent salt n,arshes, seagrass beds,
estuaries, and coastal waters as detrital
carbon. It has been difficult in actual
practice to assign a relative importance
tn thp rnntn'hnt i nnc nf nrnanir ni;^tori;il
14
macroalgae, but photo- and chemosynthetic
bacterial productivity have yet to be
estimated. There are several estimates
of benthic microalgal production in tem-
perate, shallow-water habitats (Table 2),
but only Marshall et al. (1971) deal spe-
cifically with the New England region.
Table 2 shows large regional differences
in primary production, probably dependent
upon local biological, physical, and chem-
ical conditions, and the time of the year
of the measurements. In addition since
it appears that microalgal production is
lower at higher latitudes, the estimates
by Marshall et al. (1971) cannot be used
to generalize for the whole New England
region. Phytoplankton productivity in
several temperate estuarine environments
is given in Table 3. As in the case of
benthic microalgae, large regional differ-
ences in productivity exist for phyto-
plankton making general statements of
little value. No estimate of phytoplankton
production on New England tidal flats is
available and conflicting evidence exists
as to whether tidal flat production levels
are higher or lower than production levels
in deeper coastal waters. Phytoplankton
productivity above the flats may be low
because these areas are covered by water
only a portion of the day and the water
over the flats Is turbid because of tidal
action. Conversely, primary production
may be stimulated by the increased warmth
of water over the flat and the closer
proximity of nutrients available in the
sediments.
Few studies have attempted to deter-
mine organic sources and estimate input
and utilization rates of organic matter in
New England coastal environments. The few
data available, while not specifically
from tidal flat habitats, suggest that the
flats rely on external sources of organics
transported by tidal action. Nixon and
Oviatt's (1973) comprehensive study on a
smiall Rhode Island coastal embayment
demonstrated that the system depended
heavily on imports of organic matter from
adjacent salt marsh grasses and micro-
algae. Welsh (1980) found a western
Connecticut mud flat to be a nutrient
importer in which mud flat sediment
scavenged nutrients derived from both an
adjacent salt marsh and tidal creek. In
fact, the sediments were so effective in
trapping passing nutrients that very
little were transported to the adjacent
open estuarine environment. The periodic
contribution of detrital material to the
sediment of Barnstable Harbor, Massachu-
setts sand flats was related to the
annual productivity-decay cycles of
Spartina alterniflora (Whitlatch 1981).
Other data support the view that detritus
imported from salt marshes, eel grass beds,
and phytoplankton contribute significantly
to the annual budget of organic matter
entering shallow water estuarine systems
(e.g., Day et al. 1973; DeJonge and Postma
1974; Wolff 1977).
Data are available that contradict
the "energy subsidy" thesis. In a variety
of southern New England coastal ponds and
estuaries, Marshall (1970) found that most
of the organic matter contributed to the
sediment came from sources within the sys-
tem (Table 4). While it is difficult to
extrapolate directly from these data to
tidal flat habitats, they do point to ben-
thic micro- and macrophyte production as
significant contributors of organic car-
bon. Marshall (1972) later pointed out
that the rates at which organic matter was
added to those systems he studied was less
than the rates at which it was being uti-
lized. He suggested that rapid recycling
of organic materials within the habitats
could explain the imbalanced carbon bud-
get. In addition, there is a debate
regarding the importance of salt marshes
as energy subsidizers of estuarine and
coastal environments (see Nixon 1980 for a
review). Early studies suggested that
marsh grasses were exported in large quan-
tities to become the major contributor of
detritus to the coastal zone. More recent-
ly, studies have indicated that much of
the detritus associated with Georgian
estuaries is not derived from marsh grass
but comes from algal sources (e.g., Haines
1977; Haines and Montague 1979). Produc-
tion of organic materials by chemosynthe-
tic bacteria has been overlooked and may
contribute appreciably to the tidal flat
carbon budget (see section 2.2.4). In any
event, it is obvious that more research
carried out with a holistic (whole system)
perspective will be needed to clarify this
situation. The contribution of salt marsh
organic materials to tidal flat habitats,
for instance, may be determined by hydro-
graphic characteristics (e.g., flushing
rates, topographic conditions) of the
individual systems and the proximity of
the salt marshes to the tidal flats.
15
Table 2. Primary production by benthic niicroalgae in
some temperate intertidal and shallow subtidal habitats.
Area
Production
gC/m2/yr
Reference
Danish Wadden Sea
Dutch Wadden Sea
False Bay, Washington^
Ythan estuary, Scotland
Southern New England shoals
115-178
35-435
143-226
31
81
Gr0ntved 1962
Cadee and Hegeman 1 974
Pamatmat 1968
Leach 1970
Marshall et al. 1971
a 14
Estimated by oxygen method, all others C.
Table 3. Phytoplankton primary production in some temperate estuarine areas.
Area
Production
gC/m2/yr
Reference
380
Riley 1956
190
Piatt 1971
70
Wood et al. 1973
100-200
Cadee and Hegeman 1974
13-55
Cadee and Hegeman 1974
146-200
Vegter 1977
135-145
Cadee and Hegeman 1979
Long Island Sound
St. Margaret' s Bay,
Nova Scotia
Loch Etive, Scotland
Wadden Sea, Netherlands
Ems estuary, Netherlands
Grevelingen estuary,
Netherlands
Marsdiep Inlet, western
Wadden Sea, Netherlands
Estimated by oxygen method, all others C.
16
Table 4. Sources and contributions of organic carbon to some southern
New England coastal ponds and estuaries (Marshall 1970).
Source
Production
gC/m2/yr
Percentage of
total organic
carbon
Macrophytes (e.g., eel grass,
macroalgae)
125
45-47
Benthic microalgae
90
33-34
Phytoplankton
50
18-19
Allochthonous materials (e.g.,
tidal marshes, terrestrial and
coastal sources)
0-10
0-4
Dissolved organic materials
No
estimate avai
lable
Photosynthetic and chemosynthetic
bacteria No estimate available
17
CHAPTER 3
BENTHIC INVERTEBRATES
3.1 INTRODUCTION
Living in close association with
tidal flat substrata are a variety of
benthic invertebrates. These organisms
may be extremely abundant and play major
roles in the tidal flat habitat. The
benthos are, for instance, a major link in
the coastal detritus-based food web. Many
species feed on detrital materials and
associated microorganisms and, by doing
so, accelerate the decomposition of
organic materials deposited on the sedi-
ment surface (see Chapter 2). Many of
these same species then serve as food for
bottom-dwelling fishes (Chapter 4), birds
(Chapter 5), as well as commercially
important species of crabs. In addition,
as the mobile benthos forage on or burrow
through the sediment, they promote sedi-
ment mixing. Biologically-induced sediment
mixing (bioturbation) has the potential of
greatly modifying the biological, physi-
cal, and chemical properties of the sedi-
ments. Such activities alter sediment
stability, vertical profiles of sedimen-
tary materials, movements of organic and
inorganic materials across the sediment-
water interface, and the distribution and
abundance patterns of other benthic spe-
cies. In a recent review, Zeitzschel
(1980) estimated that between 30% to 100%
of the nutrient requirem.ents of shallow
water phytoplankton populations were
derived from sediments with the benthos
playing a major role in promoting regen-
eration and recycling of inorganic nu-
trients from the sediments to the water
column. And last, several benthic inver-
tebrate species are commercially and
recreational ly important in New England
(Chapter 6).
By convention, benthic invertebrates
have been divided into generalized groups
based upon life mode. Organisms living on
the surface of the sediment are termed
epifauna and most are actively mobile mem-
bers of the phyla, Arthropoda and Mol-
lusca. The infauna consist of organisms
that live in the sediments. These species
include a taxonomical ly broader group of
organisms ranging from small nematodes and
ostracods to larger annelids, crustaceans,
and molluscs. Categorization of benthic
organisms as "infaunal" and "epifaunal"
remains somewhat arbitrary. Many infaunal
species spend certain portions of time
foraging and reproducing on the sediment
surface or have been found swimming in the
water column in inshore areas (e.g.,
Thomas and Jelley 1972; Dean 1978a, b;
Dauer et al. 1980). While the latter
behavior may be related to reproductive
and feeding activities or environmental
cues (e.g., changes in salinity, tempera-
ture, and light), much of the migrational
activity into and out of the sediments
remains unexplained and may result from
overcrowding or habitat degradation.
3.2 BENTHIC EPIFAUNA
Because of its general lack of suit-
able substrate for settlement of larvae,
there are few permanently attached organ-
isms living on tidal flats. Unlike some
areas along the Atlantic coast (Bahr and
Lanier 1981), extensive intertidal oyster
(Crassostrea virginica) reefs do not occur
in New England. Overexploitation coupled
with pronounced environmental variability
in New England probably control the upper
limit of intertidal distribution of the
oyster. The only significant populations
of this bivalve are found in subtidal,
commercially maintained areas. Blue mussel
(Mytilus edulis) beds, however, are found
throughout New England tidal flats (espe-
cially in Maine) and occur in the lower
elevations of the intertidal zone in dense
concentrations. Along some parts of the
Maine coast, mussel densities are high
18
enough to be conrercially harvested. The
initial formation of these beds on tidal
flats is dependent upon the existence of a
hard substrate such as stones, mollusc
shells, or other debris. After establish-
ment, other mussels settle and the bed
spreads laterally forming a copiplex mat of
sediment, shell debris, and animals. The
mussel beds provide a stable substrate
upon which other sessile epifauna attach
as well as serving as protection for
mobile epifauna and infauna. Lee (1975)
found many species of annelids, molluscs,
and crustaceans associated with mussel
beds in Long Island Sound. New England
tidal flat mussel beds have not been well-
studied and in some areas may be ephemeral
features of the habitat. Field (1923)
indicated that many beds in Long Island
Sound only last two to three years. Be-
cause of the limited availability of firm
substrate for attachment, physical dis-
turbance such as ice, storm waves, and
accreting sediment contribute to the tem-
poral instability of mussel beds.
The mobile invertebrate epifauna com-
prise two taxonomic groups — arthropods and
molluscs (Table 5). Both groups exhibit
low habitat specificity although predatory
gastropods are found in sandy areas where
their preferred prey items (bivalve mol-
luscs) reside. Distribution and activity
patterns of these epifauna are affected by
seasonal changes in water temperature. As
water temperature declines in the fall,
all the crustacean species migrate into
deeper water where many burrow into the
subtidal sediment and become semi-torpid.
The gastropods are apparently less sensi-
tive than arthropods to low temperatures
and tend to remain on tidal flats until
the beginning of ice formation. In rela-
tively mild winters, some species do not
migrate into deeper water.
The receding tide may reveal large
populations of gastropods on New England
tidal flats. In high intertidal areas,
concentrations of common (Littorina lit-
torea) and rough (Littorina saxatilis)
periwinkles are often found. These gas-
tropods are herbivorous and are often seen
scraping the sediment surface for micro-
algae or grazing on pieces of Ulva and
Enteromorpha. Another species found in
this area is Hydrobia totteni . This minute
gastropod browses upon sediment particles
consuming microalgae and associated micro-
organisms. Although abundant on many tidal
flats, it is often overlooked because of
its small (2 to 4 mm) size.
Extremely large and often dense
aggregations of the mudsnail, Ilyanassa
obsoleta, frequent New England tidal
flats. This species displays catholic
feeding behavior ranging from strict her-
bivory to carnivory (Brovm 1969; Connor
1980). Aside from the snail's impact on
the benthic microalgal community (Chap-
ter 2), several authors have documented
the effects of its feeding and sediment
disruption upon the benthic infauna. Move-
ments by Ilyanassa reduce the abundance of
nematodes (Nichols and Robertson 1979) and
the infauna associated with amphipod tubes
(Grant 1965). Snail enclosure experiments
conducted at Barnstable Harbor, Massachu-
setts, resulted in pronounced decreases in
the infauna particularly newly settled
juveniles of near-surface dwelling poly-
chaetes (Whitlatch unpublished data).
Boyer (1980) has shown that the mudsnail
decreases stability of the sediment-water
interface. Ilyanassa migrates into deeper
waters during the winter and reappears
each spring. Brenchley (1980) feels that
this migratory pattern may be altered by
the presence of Littorina littorea which
may also interfere with the reproductive
activities of Ilyanassa.
Several species of mollusc-eating
gastropods are common in southern New Eng-
land. The most abundant is the moon snail,
Polinices duplicatus ; this active predator
leaves distinctive circular bore holes in
the shells of its victims. Edwards and
Huebner (1977) concluded that Pol in ices
eats only living prey items and prefers
the soft-shelled clam, Mya arcnaria.
Wiltse (1980) demonstrated the influence
of the snail's foraging activities on the
infauna using caging experiments in the
field. When snails were excluded from
cages, increased numbers and diversity of
both prey (molluscs) and non-prey (anne-
lids, sipunculids) species were found
inside the cages. The snail's influence
was both through direct consumption of
prey items and indirect disruption of the
upper few millimeters of the sediment sur-
face as it plowed along in search of food.
Boyer (1980) found that the foraging
behavior of Polinices destroyed blue-green
19
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22
Dense aggregations of the mudsnail, Ilyanassa obsoleta, typically overwinter subtid-
ally during New England winters. As water temperature increases in the spring, the
snails begin mass migrations back onto tidal flats where they begin reproducing and
feeding. Snails are approximately 2 cm in length. Photo by R.E. DeGoursey, Univer-
sity of Connecticut.
algal mats and microalgae, decreased
sediment stability, and contributed to
increased erosion of the sediment-water
interface. Another species of naticid
snail, Lunatia heros, is occasionally
found on tidal flats in northern New Eng-
land although it is more abundant in sub-
tidal, sandy substrates. The whelk,
Busycon canal iculatum, also forages inter-
tidal ly in southern New England but is a
rare inhabitat of tidal flats.
The mobile bay scallop (Aequipecten
irradians) is sometimes seen on tidal
flats. Settling juveniles prefer to attach
themselves by threads to eel grass (Zostera
marina) or other subtidal macroalgae. As
scallops grow, they drop to the sediment
surface in the vicinity of eel grass beds
and may move onto tidal flats at high
tide.
Several species of epifaunal arthro-
pods are common to New England tidal
flats. Unlike the gastropods, this group
migrates on and off the flats with the
tidal cycle. The most common species
throughout New England is the green crab,
Carcinus maenas. Like all large crabs,
this species feeds by crushing its prey.
Feeding rates and preferred prey are re-
lated to crab size (Elner and Hughes 1978;
Elner 1980) with a tendency to specialize
on bivalves (e.g., ^1ya arenaria, Mytilus
edulis). Ropes (1968) noted that these
crabs ingest annelids, detritus, and
Spartina blades as well. Other large crab
species are also present but are less
abundant than the green crab. The blue
crab, Callinectes sapidus. so very abun-
dant in the middle and southern portions
of the eastern seaboard, is less so in
New England, found only south of Cape Cod.
23
■,.'>. .
ve
The gastropod, Polinices duplicatus (shell approximately 8 cm in width), bulldozing
through the sediments in search of molluscan prey. Photo by P. Auster, University of
Connecticut.
This species is found in estuaries and its
distributional pattern varies seasonally,
with the sexes, and with the stage of
development of the crab (Van Engel 1958).
Virnstein (1977) has documented the impact
of this species on the benthic infauna of
Chesapeake Bay. Blue crabs are voracious
predators as well as active diggers in the
sediment and can significantly alter both
species composition and abundance of the
infauna. The rock (Cancer irroratus) and
Jonah (C^. boreal is) crabs, commonly found
in estuaries on mud bottoms and rocky out-
crops respectively, are more often found
intertidally in northern New England than
in southern New England (MacKay 1943) and
probably have similar effects upon the
infauna as the blue crab.
In spring, Limulus polyphemus, the
horseshoe crab, appears intertidally to
initiate spawning activities. These crabs
dig distinctive pits about 3 to 6 cm (1 to
2 inches) deep on the sediment surface
while searching for bivalves and polychae-
tes. VJoodin (1978) demonstrated that this
digging activity reduced the abundance of
several infaunal invertebrates on a Mary-
land tidal flat. She noted that high
spring-summer densities of Limulus re-
sulted in feeding pits that covered 50% to
70% of her study site. New England popu-
lations of Limulus are not as large and
tend to be more spatially variable than
those described in Maryland. Occasionally
this species is used as bait for eel fish-
eries and uncontrolled harvesting may have
led to reduced population levels in some
New England areas.
Several other species of
also frequent tidal flats,
shrimp, Palaemonetes pugio,
found in southern than in
England eelgrass beds. The
Crangon septemspinosus , i n
the only common shallow-water
crustaceans
The grass
is more often
northern New
sand shrimp,
contrast, is
species
between Cape Ann and the Bay of Fundy.
24
This species can often be seen following
the leading edge of flood tides over tidal
flats feeding on resuspended detrital
material and carrion. The hermit crabs,
Paqurus longicarpus and P_. pol licaris,
are abundant locally, Paqurus longicarpus,
found occupying Ilyanassa and Littorina
shells, and P^. pol licaris, preferring
Polinices shells, are omnivores scavenging
on living and non-living animal material
as well as detrital material on the sedi-
ment surface. The lady crab. Ova li pes
ocellatus, is frequently seen on the sand
flats of Cape Cod where it hides buried in
sand with only its eyestalks exposed.
Spider crabs (Libinia emarginata and L^.
dubia) and fiddler crabl (Uca pugilator
and L[. pugnax) are also locally abundant,
although the former two species are more
characteristic of eelgrass beds, while the
latter two species are in greatest abun-
dance near or in salt marsh habitats. Var-
ious smaller amphipods and isopods also
occur in both mud and sand flats. These
species typically burrow slightly below
the sediment-water interface and have been
categorized as infaunal organisms (see
Appendix I).
3.3 BENTHIC INFAUNA
Broad designations, based on organism
size, are used to distinguish among groups
of infaunal organisms. Confusion arises
because of this approach although size
groupings tend to correspond to taxonomic
groupings. Organisms that pass through a
64 ^m mesh sieve are termed microfauna,
those retained on a 300 to 500 um mesh are
called macrofauna, and all others are
designated as meiofauna. In addition to
the arbitrariness of sieve-size selection
in determining the various infauna groups,
many organisms pass from the meiofauna!
category to the macrofaunal category as
they grow.
Because of the small size of micro-
and meiofauna and difficulties in sampling
them, our knowledge of these groups is
fragmentary and speculative. Microfauna
include the protozoans, especially the
ciliates and foraminiferans. They are
abundant, particularly in fine sands
with strong reducing properties and numer-
ous sulfur bacteria (Fenchel 1967). Most
microfauna are found within several centi-
meters of the sediment surface although
Fenchel (1969) noted distinct species-
specific vertical distribution patterns
related to the redox-discontinuity layer.
Relatively little is known about the role
of microfauna in coastal ecosystems al-
though Barsdate et al. (1974) found that
detrital decomposition was apparently
stimulated and phosphorus cycling in-
creased in the presence of grazing proto-
zoans. Other workers have questioned the
overall importance of the microfauna in
the recycling of detrital materials
(Fenchel and J^rgensen 1977) recognizing
that microfauna may be a food source for
meio- and macrofauna.
Meiofaunal populations comprise a
taxonomically broader group of organisms.
Tietjen (1969), for example, found that
nematodes, ostracods, harpacticoid cope-
pods, and turbellarian flatworms were
abundant in two shallow subtidal sites in
southern New England. Meiofaunal dis-
tributions are apparently controlled by
sediment composition. Turbellarians dom-
inate coarser sandy sediments and nema-
todes are in greater numbers in muddy
sediments, presumably because of the
increased amounts of detrital material and
microorganisms in muds. Most meiofauna
occur in the upper, well -oxygenated layers
of the sedim,ent (Figure 5) although nema-
todes have been recorded at greater
depths.
As more information accumulates on
the marine meiofauna, biologists share a
greater appreciation for the ecological
importance of these organisms in soft-
sediment environments. In addition to
accelerating decomposition and recycling
of detrital materials (see Chapter 2),
these effects may be transmitted to higher
trophic levels in the detritus-based food
web (Tenore et al. 1977). A high degree
of interest has focused on the trophic
position of the meiofauna--questioning
whether they represent a trophic dead end,
are competitors with macrofauna for shared
food materials, or are a major food source
consumed by macrofauna. Recent evidence
points to the last hypothesis. Gerlach
(1978) estimated that foraminifera and
meiofauna represent 12% to 30% of the liv-
ing biomass in many marine sediments and
25
zo eo (oo
PERCENT
20 bO 100
20 60 100
HARPACTICOID
COPEPODS
05TRAC0DS
NEMATODES
Figure 5. Vertical distributions of some dominant groups of meiofaunal organisms (from
Tietjen 1969; Whitlatch unpublished data).
Nematodes (this specimen is approximately 0.3 mm in length) are very common members of
the benthic meiofauna of New England tidal flats. Photo by R.B. Whitlatch, University
of Connecticut.
26
are fed upon by a wide range of benthic
macrofaunal invertebrates. Many species
of juvenile fishes are also known to
ingest large numbers of meiofauna (e.g.,
gobies, Smidt 1951; flatfish, Bregnballe
1961; salmonids, Feller and Kaczinski
1975). The transfer of meiobenthic bio-
mass to higher trophic levels may be
limited to areas where the meiobenthic
densities are high enough to be readily
consumed by bottom- feeding invertebrates
and vertebrates (Coull and Bell 1979).
The macrofauna are the most well-
studied group of infauna because of their
relatively large size and the fact that
several species are commercially and
recreational ly important along the New
England coast (see Chapter 6). Annelid
worms, bivalve molluscs, and amphipod
crustaceans are usually the most numerous
although other taxonomic groups such as
echinoderms, hemichordates, sipunculids,
and nemerteans are also relatively common
on tidal flats. The macrofauna are often
divided into three generalized trophic
groups: (1) suspension feeders, organisms
that obtain food materials (e.g., plank-
tonic diatoms, suspended sediment) from
the overlying water column, (2) deposit
feeders, organisms dependent upon the
organic fractions within the sediment for
food, and (3) scavenger-predators, organ-
isms that feed mostly on dead and living
animal materials. These trophic groupings
are complicated by the feeding plasticity
exhibited by most species of infauna
(e.g., Sanders etal. 1962; Fauchald and
Jumars 1979; Taghon et al. 1980). Many
species tend to be generalized feeders
whose diet is primarily limited by the
size of the food particles they are able
to ingest (Whitlatch 1980).
One feature of macrofaunal communi-
ties is the long recognized association of
particular species or assemblages of spe-
cies with particular sediment types. The
scientific literature often refers to
"mud" and "sand" communities rather than
mentioning specific species names (see
Figures 6 and 7). Spatial variation among
such species assemblages is primarily
correlated with sediment particle size
(Sanders 1958; Fager 1964; Bloom et al.
1972). Other factors directly or indi-
rectly influencing the composition of
bottom sediments can also affect the
distribution patterns of macrofauna (e.g.,
sedimentation rates, sediment stability,
food availability).
The intimate association of infauna!
organisms with sediment features is a
consequence of the animals' reduced mobil-
ity. Infauna rely on sediments not only
for shelter, protection, and areas to
reproduce, but also for food. Deposit
feeders usually dominate in fine-grained
muddy sediments because of the increased
availability of detrital material and
microorganisms. Suspension feeders, con-
versely, must retain contact with the
sediment-water interface to feed and are
usually found in stable sedimentary envi-
ronments where there is less resuspended
sediment to clog their filtering struc-
tures. This complementary trophic group
separation of the benthic habitat by feed-
ing type while apparently true of New
England subtidal habitats (Sanders 1958;
Rhoads and Young 1970), may be less so
intertidally. While Whitlatch (1977) found
trophic separation by sediment type in
Barnstable Harbor, Massachusetts, Larsen
et al. (1979) found deposit feeders to
be abundant in both sand and mud flats
in Maine. Only unstable sandy beach
substrates were dominated by suspension-
feeding amphipods.
In addition to conditions in the sed-
iment, other physical factors limit the
distribution of New England macrofauna.
On a geographic basis, distribution pat-
terns of macrofauna can be divided into
three generalized categories: (1) species
that occur throughout the New England
coast, (2) species more restricted to the
cold Gulf of Maine waters, and (3) species
found in warmer southern New England
waters (Appendix I). Cape Cod is recog-
nized as a biogeographical boundary and
several studies have noted distinct groups
of subtidal benthic species occurring only
north or south of Cape Cod (Yentsch et al.
1966). Nearshore, where water tempera-
tures exhibit pronounced fluctuation,
these categories are less distinct. North
of Cape Cod, warm water embayments and
estuaries do occur and one occasionally
finds warm water species in these areas
(e.g., the quahog, Mercenaria mercenaria).
Representatives of the cold water group
inhabit southern New England waters espe-
cially during winter. Depending upon
27
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nOLLUSCS ARTHROPODS P0LYCHAETE5
I Ms
OuJ CO -1 % °-
■ cc o 5 O
LlI (J CL U
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Figure 8. Intertidal zonation patterns of major groups of benthic macrofauna
inhabiting a New England muddy sand flat (Whitlatch unpublished data, Barn-
stable Harbor, MA, June 1975).
30
of Penobscot
species are
distribution
local environmental features, members of
both groups may occupy the same habitat
reproducing at different times of the year
at water temperatures appropriate for each
species (Whitlatch 1977). It has been
hypothesized that a third biogeographic
boundary exists northeast
Bay, Maine, where boreal
limited in their southern
by warm summer water temperatures (Bous-
field and Laubitz 1972 cited in Fefer and
Schettig 1980).
On a more local scale, the structure
of New England tidal flat macrofaunal
communities is also determined by temporal
and spatial variations in temperature.
Green and Hobson (1970) found that small
differences in tidal range influenced the
density of several species of infauna and
affected the growth rate of the small bi-
valve, Gemma gemma. Since tidal flats are
gently sloping habitats, zonation patterns
are not as pronounced as those observed in
rocky intertidal areas. Figure 8 shows an
example of infaunal zonation on a muddy-
sand flat in Massachusetts. Broadly de-
fined, species-specific patterns are prob-
ably related to physiological tolerances,
desiccation, and temperature as well as
certain biological interactions (e.g.,
competition and predation). Larsen (1979)
suggested the importance of temporally and
spatially variable hydrographic features
affecting nearshore zonation of infauna.
In northern New England regions, winter
ice and spring thaw can alter patterns of
salinity for brief periods. In areas with
restricted water flow (e.g., glacially-
incised estuaries), this yearly event may
have profound effects on infaunal distri-
bution patterns (Larsen 1979).
New England tidal flat macrofauna
display high temporal and spatial varia-
bility; numbers of species and total num-
bers of organisms may vary by several
orders of magnitude within and between
years. This high degree of variability,
coupled with the effects of latitudinal
variation in physical properties of the
region, make it difficult to describe a
"typical" tidal flat infaunal association.
Figures 6 and 7 and Appendix I illustrate
some of the more common macrofaunal organ-
isms found in sand flats and mud flats.
Not all species will always occur together
in any one particular habitat. Rather,
the species are representative of those
associated with the two different sediment
types.
Most macrofauna live in the upper
layers of the sediment, probably reflect-
ing the greater amount of food and oxygen
in this zone (Figure 9). Amphipods and
20 bO
BURROWING
^i POLYCHAETES
BIVALVES
Figure 9. Vertical distributions of major groups of tidal flat macroinvertebrates
(Whitlatch unpublished data, Barnstable Harbor, MA, 1974 to 1977).
31
bivalves are more restricted to the near-
surface layers than are the burrowing an-
nelids. The deposit feeders exhibit a wide
range of feeding and mobility patterns
although three general life styles or
guilds are apparent. First is the surface-
feeding species. These organisms either
live in vertical tubes (e.g., spionid and
terebellid polychaetes) or burrow slightly
below the surface (e.g., some gammaridean
amphipods) feeding with appendages on or
slightly above the sediment-water inter-
face. The deposit-feeding clam, Macoma
balthica, an abundant species on northern
New England mud flats, also feeds off the
sediment surface with a long inhalent
siphon. The surface-feeding guild is the
most abundant group of organisms in tidal
flat habitats. Second in abundance are
the organisms that burrow through the sed-
iment, much like earthworms. This group
has the largest number of species (e.g.,
members of the polychaete worm families
Capitellidae, Nereidae, Syllidae, Lumbri-
nereidae, Orbiniidae, Nepthyidae). Several
species build temporary burrow-like struc-
tures to the surface. Since many worms
live in anaerobic sediments, the burrows
aide in transport of oxygenated water to
the organism from the sediment surface.
Last are the "conveyor-belt species"
(Rhoads 1974), organisms that live head
down in the sediments (e.g., the polychae-
tes, Pectinaria gouldii and Clymenella
torquata) feeding at depth and depositing
egested sedimentary materials on the sur-
face. While this feeding group is less
diverse and abundant than the other two,
the members are interesting because of
their impressive bioturbation activities.
Dense populations of Clymenella are known
to completely bioturbate (turn over) sedi-
ments to a depth of 20 cm (8 inches)
annually. One noticeable effect of this
extensive feeding activity is described by
Sanders et al. (1962) who state that the
presence of Clymenella on the Barnstable
Harbor, Massachusetts, tidal flats could
be detected by walking over areas and
feeling a spongy sediment underfoot.
Suspension-feeding organisms include
bivalve molluscs and some species of
amphipods and polychaetes. Probably the
most abundant suspension feeder on New
England tidal flats is the small bivalve.
Gemma gemma . Densities exceeding 300,000
per m2 have been recorded and individuals
are often found packed valve to valve in
fine-grained tidal flats. Even though
these are small organisms (about 3 mm), at
these high densities they are able to
effectively exclude other species of
suspension-feeding bivalves and surface-
feeding polychaetes from their habitats
(Sanders et al. 1962; Whitlatch unpub-
lished data). The clam, Mya^ arenaria, is
also abundant, especially in Maine, New
Hampshire, and parts of Massachusetts.
This species tends to be associated with
silty-sand sediments and is not usually
found in areas dominated by G. gemma. The
hard-shelled clam, Mercenaria mercenaria,
is generally restricted to sand flats in
southern New England. Abundant assemblages
of suspension-feeding amphipods are found
in northern New England (Croker 1977)
where they are primarily associated with
sandy beach habitats.
New England tidal flat infaunal asso-
ciations are highly dynamic and many stud-
ies have noted pronounced seasonal changes
in species occurrence and abundance (e.g.,
Whitlatch 1977; Dobbs 1981). Large fluc-
tuations in population size are attribut-
able to the short life span of most infau-
nal species (probably 1 to 3 years), sea-
sonal reproductive cycles, predation by
vertebrates and benthic invertebrates, and
large-scale habitat heterogeneity. Sea-
sonal patterns of population and community
change are reflected as sudden rises in
the densities of certain species or groups
of species followed by declining densities
over a period of weeks to months. Specific
patterns of seasonal change in New England
are tied to latitude, and increased infau-
nal abundance may be a response of benthic
organisms to seasonally-induced variations
in food supplies. Natural selection favors
individuals that reproduce at about the
time that food for juveniles (e.g., plank-
tonic plants and animals) is increasing in
abundance. The result of such a response
is temporal acceleration of birth rates in
response to seasonally-induced increases
in the availability of prey and/or nutri-
ents. Seasonal reduction in abundance of
tidal flat benthos begins about July in
Massachusetts (Green and Hobson 1970;
Whitlatch 1977) and slightly later in
Maine (L. Watling; University of Maine,
Walpole; February 1981; personal communi-
cation) and Nova Scotia (Levings 1976).
Seasonal decreases in benthic organism
32
^
Small spionid polychaetes (this species is Spio setosa, approximately 1 mm
body width) are common inhabitants of New England tidal flats. They construct
vertically positioned tubes in the sediment and feed on surface deposits with
a pair of grooved, ciliated palps. Photo by K.W. Kaufman, Johns Hopkins Uni-
versity.
33
abundance begin before July south of Mass-
achusetts (Duncan 1S74; Dobbs 1981). These
declines in population abundance are prob-
ably the result of biotic interactions
such as competition for food and space and
the seasonal appearance of vertebrate and
invertebrate predators (e.g., fish, epi-
faunal gastropods, crabs, and birds).
While seasonal change in the physi-
cal and chemical components of benthic
systems contributes to the highly variable
spatial-temporal abundance of organisms
in tidal flats, several studies have noted
the existence of consistent year-to-year
trends in benthic community structure
in New England and elsewhere (Grassle
and Smith 1976; Whitlatch 1977; Coull and
Fleeger 1978). The cycle may be attrib-
uted to seasonally-programmed reproduc-
tive activities of organisms found in dif-
ferent geographic areas (Whitlatch 1977)
or to the seasonal occurrence of benthic
invertebrate and vertebrate predators
(e.g., demersal fishes, epifaunal crusta-
ceans and gastropods). Other studies have
failed to find repeatable seasonal trends
in community structure (e.g., Levings
1976; Dobbs 1981). The existence of such
patterns may be the result of the specific
characteristics of the local biotic and
abiotic environment controlling the struc-
ture of the infaunal populations and com-
munities.
Infaunal interactions result in
alterations of their abundance and distri-
bution patterns on tidal flats. These
interactions may take several forms but
may be conveniently separated into direct
and indirect effects. The most common
form of indirect interaction is habitat
modification by one species or trophic
group resulting in an adverse impact upon
another species or trophic group. The
best documented example of this type of
interaction is called trophic group amen-
salism (Rhoads and Young 1970). First
described in subtidal, muddy sediments of
Buzzards Bay, Massachusetts, this phenom-
enon involves the destabi lization of the
surficial sediment by the burrowing and
feeding activities of deposit feeders
which results in increased sediment resus-
pension and subsequent interference with
the filtering activities of suspension
feeders. This type of interaction is most
likely to occur in muddy sediments where
deposit feeders are abundant and fine sed-
iments are easily resuspended, but Myers
(1977a, b) has recently reported trophic
group amensalism in a shallow water sandy
habitat. Biological destabilization of
the sediment-water interface by demersal
fishes, large epifaunal invertebrates, and
meiofauna has also been reported (e.g.,
Yingst and Rhoads 1978; Boyer 1980), but
the predicted effect upon suspension feed-
ers has yet to be determined.
Direct interactions can be either
adult-adult or adult-larval effects.
Adult-larval interactions occur when
infaunal assemblages of adult organisms
are dense enough to prevent or restrict
recruitment of larvae. Woodin (1976) sug-
gested that these interactions occur when
suspension and deposit feeders ingest
settling larvae or when deposit feeders,
through their feeding activities, bury or
smother settling larvae. Dense popula-
tions of infauna are common in New England
tidal flats (e.g., Sanders et al. 1962;
Whitlatch 1977; Dobbs 1981) and there is
evidence that adult-larval interactions
occur. At present, however, we lack con-
trolled field studies to document the
importance and magnitude of adult-larval
interactions in the New England region.
Adult-adult interactions involve
predatory interactions and infaunal organ-
isms competing for either space (lateral
or vertical) and/or food. Whitlatch (1980)
found a general relationship between food
and space overlap and sediment organic
matter suggesting the importance of ex-
ploitive competition for food by deposit-
feeding species. In habitats with high
levels of organic matter, species that
were similar in resource utilization were
able to coexist and species numbers were
high. In less productive habitats, eco-
logically similar species were excluded
and species number declined. Grassle and
Grassle (1974) documented intraspecif ic
effects on egg production in the poly-
chaete, Capitella capitata, related to
competition for food. Other studies have
noted the importance of exploitive inter-
actions in limiting the distributional
patterns of infaunal organisms (e.g.,
Levinton 1977; Weinberg 1979). Competi-
tion between species for space within sed-
iments has been shown in a variety of
suspension- and deposit-feeding species
34
(Woodin 1974; Levinton 1977; Peterson deposit-feeding. The more important pred-
1977; Peterson and Andre 1S80). There are ators live outside the infaunal coinrrunity.
relatively few infaunal predators on the Epifaunal invertebrates, demersal fishes,
macrobenthos. Nemerteans and the preda- and birds consume significant fractions of
ceous polychaete annelids. Nereis virens the infauna and can alter species dis-
and Glycera dibranchiata, are the most tribution and abundance patterns (see
common species although the latter two Peterson 1979 for a review),
species also supplement their diets by
35
CHAPTER 4
FISHES
4.1 INTRODUCTION
Fishes migrate onto tidal flats dur-
ing flood tides and retreat during ebb
tides. A few species, such as stickle-
backs and mummichogs, remain in tidal
creeks during ebb tide. It is difficult,
therefore, to identify which species of
fish actually are representative of tidal
flat habitats since they may utilize these
areas only during portions of their life
cycle (e.g., as a nursery ground), on a
daily or seasonal basis for spawning or
pursuing preferred prey items, or through-
out their entire life span. In addition,
tidal flats are not closed ecological sys-
tems; rather, they are bounded by and
intricately linked to other coastal habi-
tats such as salt marshes, estuaries, and
eelgrass beds. Actively moving organisms
such as fishes can and do readily move
from habitat to habitat during the course
of feeding and reproducing. Few species
are exclusive inhabitants of tidal flats
but are more often found in other habitats
adjacent to tidal flats (e.g., deeper
waters, rocky outcrops) that afford more
protection. Generally, fish utilizing
tidal flats are estuarine species, juve-
nile and adult fishes from deeper marine
waters that use the sites as nursery
grounds and feeding sites, and diadromous
species that cross the habitat during
migrations to and from spawning sites or
wintering areas.
The approach taken to describe the
fishes associated with New England tidal
flats has focused on those representative
species one would be most likely to
encounter when sampling. Commercially
important species (for which the most life
history information is available) and non-
commercial species (for which there are
sporadic sampling and life history data)
are viewed collectively. In many publica-
tions, the two groups have been treated
separately.
Appendix II gives names and related
life history information for fish species
common throughout the tidal flats of the
New England coastal zone. Species were
selected from Bigelow and Schroeder
(1953), Leim and Scott (1966), and Thomson
et al. (1971) who provide extensive inven-
tories for the regions they cover. Scien-
tific and common names are those cited by
Robins et al. (1980). Distributional
patterns, spawning periodicity, and food
habits have been accumulated for each spe-
cies from several sources and are as gen-
eral or specific as the cited authors have
reported.
4.2 TROPHIC RELATIONSHIPS
A broad spectrum of trophic roles is
displayed by fishes inhabiting the New
England coastal zone and it is possible to
divide them into generalized feeding cate-
gories (e.g., demersal feeders, predators,
planktivores). Aside from menhaden (an
exclusive herbivorous planktivore) and
several species of omnivores and grazers,
most fish appear to be carnivorous. Al-
though Appendix II shows that many species
display wide dietary preferences, several
studies have demonstrated that food selec-
tion does occur on a community level.
Demersal and pelagic fishes apparently
select food by size and type as well as
forage at different times or in different
habitats (Richards et al. 1963; Tyler
1972; Maurer 1976). A change in food
preference with age (size) appears to be
the general rule (Appendix II) with many
of the juvenile stages feeding as plank-
tivores regardless of later dietary
specialization. This feature is particu-
larly germane to a discussion of trophic
relationships on tidal flats because many
fish inhabiting these areas are juvenile
forms. There have been several expla-
nations for age- or size-related changes
in feeding behavior. Changing dietary
36
preference may reduce the effects of
intra- and interspecific competitive
interactions in food-limited habitats.
Second, there are probably age- or size-
related changes in the energy requirements
of fish. Possibly the metabolic demands
of species change with age, necessitating
shifts in dietary preference. Many near-
shore individuals are juveniles that, as
they grow, tend to move into deeper waters
(Haedrich and Hall 1976). 011a et al.
(1974) described differences in habitat
preference in the tautog. Large tautog
foraged at greater distances from resting
sites than small individuals. Also, older
fish migrated offshore during colder
months while younger fish remained near-
shore and became torpid. Finally, broad
dietary preference may reflect the unpre-
dictable nature of food supplies in marine
temperate environments. Pronounced sea-
sonal and local variations in primary and
secondary productivity may favor general-
ized feeding habits.
4.3 GEOGRAPHIC DISTRIBUTION PATTERNS
Fish communities north and south of
Cape Cod show distinctive differences in
species composition, apparently related to
seasonal differences in water temperature
(see Chapter 1). Fish communities north
of Cape Cod tend to be dominated by
boreal, non-migratory forms while those to
the south primarily consist of warm-water,
migratory species (Colton 1972; Colton
et al. 1979). Species composition on a
large scale, therefore, is determined by
temperature.
Temperature effects on a more local
scale have also been observed in northern
Atlantic coast fish communities. Tyler
(1971a), working in a deep, nearshore site
in Passamaquoddy Bay, New Brunswick, and
Maine, classified four broad types of
demersal fish according to their residence
patterns: year-round residents, winter
residents, summer residents, and occa-
sional species. The fish community
reflected patterns of temperature fluctua-
tion throughout New England. Areas exhib-
iting greater annual temperature fluctua-
tion (e.g., south of Cape Cod) had more
temporary residents and fewer year-round
species (Figure 10).
bO
I-
2
UJ
o
U
a
iO
20
SEASONAL5
A
V
"t^<^
v^
9
r
>
<0'
nJ
.o-^
o
,^"
^'
Figure 10. Percentages of
poral components in fish
the northeast Atlantic coastline (modified
from Tyler 1971).
different tem-
species along
Recksiek and McCleave (1973), working
in the Sheepscot River-Back River estuary
at Wiscasset, Maine, found pelagic fish
assemblages corresponding to Tyler's com-
munity structure groups. The relatively
warm Back River estuary had a summer
pelagic component consisting mostly of
alewives, blueback herring, and Atlantic
menhaden, while the relatively cooler and
oceanic Sheepscot River estuary had a sum-
mer migrant pelagic component of Atlantic
herring, Atlantic mackerel, and spiny dog-
fish. Rainbow smelt was the only year-
round resident and Atlantic herring was
the only winter resident species. It ap-
pears, therefore, that although pelagic
and demersal fish assemblages can be
divided into similar residency patterns,
species composition varies with tempera-
ture regime both within and between lati-
tudes along the New England coastline.
37
4.4 MIGRATORY PATTERNS
The structure of New England fish
communities is dynamic and the species
are, for the most part, constantly shift-
ing position in the coastal zone. Many
movements can be linked predictably to
patterns of foraging, local and regional
variations in water temperature, or repro-
ductive activities. The frequency and
magnitude of migrational activities, how-
ever, appear to be both species- and
regionally-specific.
Species in the resident (non-migra-
tory), nearshore fish assemblage make
inshore-offshore movements over small
distances, moving into slightly deeper
water to avoid extremes in water tempera-
ture (e.g., tomcod). Movements are also
linked to tidal cycles where fish move out
of areas that are exposed at low tide or
are very shallow and reoccupy the areas as
the tide floods (e.g., murrmichogs). Dusk
feeding movements are also common to many
species. Herring move to the surface to
feed at dusk (Sindermann 1979a), juvenile
pollock move inshore, and striped bass
also rise to the surface to feed at dusk
following their preferred prey items.
Coastal fish migrations occur on
a regional scale in New England; Fig-
ure 11 sumn;arizes these general patterns.
Bluefish, mackerel, and menhaden are
examples of spring-summer northward mi-
grants. These species move along the
coastline and inshore to southern New Eng-
land and the Gulf of Maine as water tem-
perature increases. The timing of these
migrations is probably also a response to
increasing food supplies since during the
warm months pelagic and demersal food
organisms are abundant in coastal areas.
In fall and winter, the fish reverse
direction in response to declining water
temperature. Southward migrating fish do
not always follow the coastline, but may
move offshore to the warrrier continental
slope waters off southern New England
(Figure 11). Many inshore migrant species
(including red hake, silver hake, scup,
butterfish, summer flounder, and goose-
fish) winter there (TRIGOM-PARC 1974).
Some species, such as the winter flounder,
reside in cooler offshore waters during
the summer and move inshore in winter.
Because of differences in water tempera-
ture variation, southern New England con-
tains few permanent fish residents and is
characterized by a continuously shifting
fish species composition. The Gulf of
Maine, conversely, is typified by more
resident species and less pronounced sea-
sonality in species composition.
4.5 REGIONAL PATTERNS
Since New England coastal fish commu-
nities are strongly influenced by water
temperature variation, more detailed com-
munity descriptions can be made by exami-
nation of both regional and seasonal dif-
ferences using Cape Cod as a biogeographic
boundary. Regional patterns of community
structure have been separated into spring-
summer and fall-winter periods. It is im-
portant to realize that within-region
physical and biological conditions vary,
and that these will in turn affect the
distribution and abundance patterns of the
fishes. The generalized patterns described
below are intended to convey overall
trends in seasonal shifts of species
composition and not, necessarily, the
dynamics of specific, localized fish
community structure.
4.5.1 South of Cape Cod (Figure 12)
During spring, anadromous species
such as lampreys, striped bass, and large
schools of certain herring (e.g., ale-
wives, bluebacks, and shad) begin ascend-
ing river systems to spawn in brackish and
freshwater. Although larger rivers such
as the Hudson, Connecticut, and Thames
support major spawning runs, anadromous
fish also enter many smaller rivers and
streams. Lampreys, sturgeon, and herrings
have spawning populations along the entire
northeast coast while for the striped
bass, the Hudson River marks the northern
limit of a major spawning population.
(Recent anadron:ous fish restoration pro-
jects to re-establish successful spawning
populations of the Atlantic salmon and
shad have been initiated in many New Eng-
land rivers.) Adults of some species die
following spawning (e.g., lampreys);
others descend rivers and feed actively to
regain body stores lost during spawning
(e.g., herrings, striped bass). In south-
ern New England, adults of most anadromous
38
SPRING-SUnAER
ATLANTIC BfCHT
FALL- WINTER
C-B<GHT
Figure 11. Seasonal migration patterns of New England coastal fish populations.
See text for details (modified from TRIGOM-PARC 1974).
39
ANADRO/^OUS
LArtPBtV
STUOaCON
LANTiC SALMON
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ESTUARINE
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AMERICAN £EL
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ROCn GUMNCL
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SEA BAVEW
SEA Snails
iHANKlV
ROCKY OUTCROPS
Figure 12. Examples of major groups of fish which occupy tidal flats and adjacent
coastal habitats in southern New England. Upper figure refers to movements during the
spring-summer period; lower figure refers to movements in fall-winter months. Arrows
indicate direction of movement for fish that migrate. Fish depicted without arrows are
either restricted in home range or undertake only localized movements, both moving
alongshore and into the substrate. The figure depicts these groups for an extended
period (approximately six months) and does not show the location of particular species
at any one time. These individuals or groups are found at different times (for the
most part sequentially, see text) throughout the period considered. The fish are
typical representatives of groups found in each habitat.
40
An extensive restoration effort has been undertaken to re-establish populations of the
anadromous Atlantic salmon, Sal mo salar, in New England's major river systems. This
individual (approximately 60 cm) was photographed durings its spawning migration in the
Salmon River, Connecticut. Photo by R.E. DeGoursey, University of Connecticut.
species have moved from nearshore areas by
midsummer. Exceptions include striped
bass that may remain in coastal waters
until late October or early November, and
fall spawners (e.g., salmon) that begin to
move into the estuaries in late winter and
early spring and are found in the river
systems until early winter. Following
spawning, adults return to the open ocean
to overwinter. Rainbow smelt remains in
the lower estuaries throughout the winter
and ascends to freshwater to spawn as soon
as the ice begins to break up on upper
estuaries (usually February to March).
Juveniles of most anadromous species
occupy estuarine and nearshore water
through late spring and summer, then move
offshore with declining water temperatures
in fall.
Another group of fish is more typi-
cally associated with estuarine conditions
in southern New England. Tomcod are win-
ter spawners that move from brackish to
more saline waters in the spring. White
perch and hogchokers move from the lower
estuary where they overwinter to more
brackish waters to begin feeding and
spawning. They remain active in estuaries
throughout the warmer months. Winter
flounder are also found abundantly in
estuaries and bays in early spring. They
spawn in late winter and early spring in
lower portions of the estuaries. Tyler
(1971b) reported that this species concen-
trates feeding in soft substrate habitats
of the intertidal zone. Adult winter
flounder begin moving into deeper waters
during the summer to avoid elevated water
temperatures in the shallows, while juve-
nile fish remain in relatively shallow,
heavily vegetated, muddy bottoms through-
out the year where they feed on benthic
invertebrates.
41
In early spring, fish communities of
eelgrass beds and marsh tidal creeks con-
sist of year-round residents (e.g., killi-
fishes, sheepshead, sticklebacks, pipe-
fish, and toadfish) that emerge from a
torpid overv/intering state and begin to
feed actively in preparation for spawning
in mid- and late spring and early summer.
Schools of the planktivorous Atlantic sil-
verside (Menidia menidia) also move into
tidal wetlands and shallow bays to spawn
in spring. The year-round residents and
the juveniles of many spring spawners are
found in wetlands and marshes throughout
summer and early fall and are able to tol-
erate severe stress of heated water and
reduced oxygen levels. These species are
active until late fall and early winter
when it is believed the majority hide
beneath vegetation and some species burrow
into mud to avoid extremely cold water
temperatures. They also may move into
slightly deeper waters (e.g., eels, killi-
fishes, and sticklebacks). Silversides are
apparently an exception since they have
been observed feeding and schooling in
early winter and early spring in southern
New England. Their whereabouts during the
middle of winter has not been determined.
In late spring, anchovies (Anchoa
mitchil li ) move northward along the New
England coast and into small, shallow bays
and inlets where they often school in tre-
mendous numbers. They remain in coastal
waters throughout the summer and move
southward and offshore during the fall.
Although they are seasonally abundant, no
commercial fishery for anchovies presently
exists in southern New England.
Skates, dogfish, windowpane, and win-
ter flounder are abundant on sand and mud
flats in early spring. In late spring and
The winter flounder, Pseudopleuronectes americanus, is a common inhabitant of New
England tidal flats. This demersal fish (actual size) consumes large amounts of
benthic infaunal invertebrates. Photo by R.E. DeGoursey, University of Connecticut.
42
early summer (June to July), spawning
aggregations of searobins, which inhabit
sandy substrates, move into coastal
waters. During the same period, schools of
scup move from offshore waters into bays
and inlets to spawn. Both scup and sea-
robins begin to migrate offshore by Octo-
ber. Also during the summer months, dense
schools of the sand lance are found inhab-
iting inshore sand flats, often burrowing
into the sediment. This species is an
important food item for many pelagic and
demersal fish, as well as finback whales,
porpoises, and terns. Most of these fish
species begin moving offshore by mid- to
late September and disappear from the
coastal zone by mid-October. Only little
skate and windowpane flounder remain
through the fall and winter.
With declining fall temperatures some
offshore species migrate into nearshore
sand and mud flats. From October to
December, sea ravens move inshore to spawn
and are commonly observed in water 1 to
2 m (3.2 to 6.5 ft) deep. Goosefish enter
coastal waters in October and November to
feed, and sculpin, which are winter spawn-
ers, move inshore in late fall. The
grubby sculpin is frequently found in very
shallow water during this period.
Summer southern migrants that enter
southern New England waters include the
summer flounder, black seabass, and king-
fish. Their occurrence is predictable but
the overall abundance of each species
varies from year to year, possibly because
of the abundance of specific year-classes.
In som.e years, a particular species may be
abundant in certain areas while in suc-
ceeding years it may be scarce due to
natural population fluctuations and/or
increasing fishing pressure.
From May to October, rocky inshore
habitats adjacent to tidal flats are
dominated by two labrids, the tautog
(Tautoga onitis) and the cunner (Tautogo-
labrus adspersus) . Both species spawn in
A large 55 en' rale tautog, Tautoga onitis, emerges from a rock crevice in the spring
to resume actively feeding after overwintering in a torpid state. Tautog prefer rocky
habitats and adults feed almost exclusively on the blue mussel, Kytilus edulis. Al-
though tautog are most abundant south of Cape Cod, they also range into the Gulf of
Maine. Strictly a coastal fish, they are seldom found more than 1-2 km from shore.
Photo by R.E. DeGoursey, University of Connecticut.
43
the spring and remain in or directly adja-
cent to rocky outcrops, pilings, or debris
to feed throughout summer and fall. They
appear to have restricted territories and
are seldom found more than a few kilome-
ters from the coastline. The young of
both species feed on small invertebrates
while the adults feed mainly on mussels
(Mytilus edulis). Other smaller, more
cryptic species also inhabit these areas
(Figure 12) and their abundance and occur-
rence may be more widespread than the
current literature suggests. For example,
gobies, rock gunnel, and juveniles of
tropical migrants are missed by conven-
tional fishing methods (R. DeGoursey; Uni-
versity of Connecticut, Noank; February
1981; personal communication; Munroe and
Lotspeich 1979). In late October, the
labrids occupy crevices in which they
overwinter in a torpid state, or may move
to slightly deeper areas. The rock gun-
nel, a winter spawner, remains active and
in certain localities moves into shallower
waters to spawn.
The pelagic component of fishes in
southern New England is found strictly
during the summer and is composed of
schooling fishes that enter nearshore
waters either as southern migrants (e.g.,
young weakfish, bluefish) or offshore spe-
cies moving inshore from the continental
shelf (e.g., mackerel, butterfish). Some
species are oceanic spawners (e.g., blue-
fish and menhaden) that enter coastal
waters in late spring to feed. Menhaden
form tremendous schools that often can be
seen moving in and out of bays and har-
bors. Since menhaden form such large
aggregations and often enter shallow
embayments in summer months, elevated
water temperatures and low dissolved
oxygen concentrations occasionally cause
mass mortalities (e.g., in Long Island
Sound).
Pelagic predators, such as the blue-
fish and weakfish, enter coastal waters in
southern New England in late spring and
early summer to feed. Young bluefish,
known as "snappers", often form large
schools that move through the coastal
waters chasing prey such as silversides,
sand lance, and juveniles of many other
fish species. The Atlantic mackerel is
usually the first to appear in coastal
waters in early spring to spawn, and also
one of the first species to abandon those
areas in mid- and late summer to over-
winter offshore.
A group of warm water, tropical
migrants also moves into coastal waters of
southern New England and sometimes into
the Gulf of Maine in mid- and late summer.
These tropicals occur sporadically and in
small numbers often first entering the
shallow bays in Long Island Sound and
eventually appearing in Connecticut and
Rhode Island and further north in late
summer. Primarily juveniles of most spe-
cies have been collected although adults
are sometimes recorded. No comprehensive
study has been undertaken to determine the
seasonal abundance and distribution of
these tropical species, so existing data
probably underestimate their numbers in
southern New England. The more common
migrants include the mullets, jacks,
drums, triggerfish, filefish, and needle-
fishes. The behavior of these migrants
during declining temperatures in the fall
is not known. It is not known whether
they move offshore, return to warmer
southern waters during the winter, or
whether a significant proportion experi-
ences winter mortality. None of the trop-
ical migrants have been collected in New
England during the winter.
4.5.2 Gulf of Maine
Figure 13 shows that many of the
seasonally-related movement patterns of
fish that exist in southern New England
also are found in the Gulf of Maine
inshore waters. For example, the anadro-
mous and resident marsh-eelgrass species
are similar, although spawning activities
of the former group occur later in spring.
A major difference between the two New
England regions is that fewer migratory
species are found in the Gulf of Maine;
this contributes to lower summer species
diversity when compared to southern New
England. In addition, a greater number of
gadids (e.g., cod, hakes, pollock, tomcod,
haddock) are found in the inshore Gulf of
Maine waters. All but the hakes, which
are summer migrants, are year-round resi-
dents of these waters. The tomcod is the
most common inshore gadid found at the
mouths of streams and estuaries.
44
«^^-
RIVER
sntLT
ESTUARY
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STURGEON
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HERRINGS V
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ESTUARY ^\ljj|J^|^'"'-^8Ac«
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jp\. ^^^
SnOOTW FLOUNDER [ ^--^"''^ >
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BOULDER OUTCROP6
Figure 13. Seasonal movements of fish in the Gulf of Maine inshore environment;
upper figure refers to movements in the spring-summer months; lower figure refers
to fall -winter movements (see Figure 12 for further details).
45
The spotfin butterf lyfish, Chaetodon ocel latus, is one of a group of tropical species
which migrate northward along the east coast and enter New England waters during mid-
and late summer. Many of these summer southern migrants (such as the fish pictured)
are juveniles (about 4 cm). These fish probably perish with the onset of declining
water temperatures. There is no evidence to suggest that they are capable of return-
ing south or of overwintering in New England. Photo by R.E. DeGoursey, University of
Connecticut.
As in southern New England, flounders
and skates are the common demersal species
found on muddy and sandy bottoms. Both
groups feed actively on benthic inverte-
brates and the skates make noticeable
depressions in the sediment surface as
they forage for crustaceans, bivalves, and
polychaete annelids. Flounders represent
a major inshore groundfishery in the Gulf
of Maine and winter flounder is the most
abundant species. Other species of floun-
der are also found in the Gulf of Maine
(see Appendix II), although the smooth
flounder, windowpane, and American plaice
are associated more with the bays and
estuaries of northern New England.
Many species of pelagic fishes
inhabit northern New England waters. The
pelagic predators are similar to those
found in southern New England, although
bluefish, weakfish, and striped bass are
all reduced in number when compared to
warmer New England waters. Striped bass
is a popular sport fish, although spawning
populations have not been located north of
Cape Cod. All these species are summer
migrants. The Atlantic herring, another
member of the pelagic fish component, is
commercially the most important fish in
the Gulf of Maine. This species is found
offshore during fall (when it spawns) and
winter, but is seen in nearshore waters
during summer (Targett and McCleave 1974).
The tropical migrant species are only
found sporadically in the Gulf of Maine,
restricted to those summers with unusually
warm water temperatures.
46
In winter, many species remain part
of a year-round resident population
(Figure 13). The winter and smooth
flounder remain in the estuaries, with the
winter flounder, in particular, moving
into shallower parts of the area during
fall and winter. White perch move from
their habitat upstream in slightly brack-
ish and freshwater to more brackish and
oceanic conditions in estuaries during the
winter. Some boreal-Arctic species (e.g.,
alligatorfish) migrate southward into
these waters in the winter.
There are three major differences
between the fish communities north and
south of Cape Cod: a greater proportion
of the fish in the Gulf of Maine are year-
round resident species, so that during the
summer, lacking migrants from the south,
fish species diversity is generally lower
than in southern New England; gadids are
more common to the inshore Gulf of Maine
region, while in southern waters their
distribution is largely restricted to
offshore waters; migration and spawning
activities tend to occur later in northern
waters because Gulf of Maine water temper-
atures increase later than those in south-
ern New England.
4.6 THE DEPENDENCE AND ROLE OF FISH ON
TIDAL FLATS
Many fish utilize shallow-water
coastal habitats as feeding and nursery
grounds. The reproductive activities of
these species coincide with periods of
maximum food production, and predation
rates on juvenile fish are apparently
lower in shallow-water than adjacent
deeper water areas. As the fish grow.
The longhorned sculpin, Myoxocephalus octodecemstinosus, (this specimen ZU cm long) is
distinguished from the other western North Atlantic sculpins by a long, sharp spine on
the preopercular bone. In the northern part of its range it is a year-round resident
moving into deeper waters in cold weather and back inshore in spring. In the southern
part of its range, it remains in deeper water during the warmer months and moves
inshore with declining water temperatures. Longhorned sculpins are winter spawners in
New England, laying adhesive egg clumps on vegetation. Photo by R.E. DeGoursey, Uni-
versity of Connecticut.
47
they begin moving into deeper waters.
Haedrich and Hall (1S76) hypothesize that
these ontogenetic habitat shifts and the
general absence of adults in an estuarine
environment act as mechanisms to reduce
competitive interactions within species as
well as to allow the juvenile stages
access to the more productive marine
habitats.
Age-related changes in the use of
inshore environments by fish and their
subsequent effects on a tidal flat habitat
is largely species- or group-specific
(i.e., resident vs. migratory species).
Those fish most dependent upon tidal flats
for feeding are the demersal species
(e.g., flatfishes, skates) and small bait-
fishes (e.g., silversides, killifishes,
and menhaden), while most of the pelagic
fishes are probably less dependent upon
tidal flats for food items.
Juvenile fish dominate coastal waters
and because of their abundance can consume
large quantities of benthic invertebrates
and have a conspicuous effect upon the
structure of benthic communities. Many
demersal fishes form schools (e.g., scup)
or may be found in loosely aggregated pop-
ulations (e.g., winter flounder) and have
caused localized, short-term reductions in
the population abundance of polychaetes,
small crustaceans, and bivalves. The
reported seasonal population decline of
infaunal invertebrates in a Massachusetts
salt marsh habitat was probably due to the
appearance of invertebrate predators
(e.g., epibenthic crustaceans) and fish
predators (Schneider 1978). Tyler (1971b)
found that adult winter flounder fed over
a Bay of Fundy intertidal flat and sug-
gested that destruction of the habitat
would reduce the productivity of the fish
populations. Others have also noted the
presence of large populations of demersal
fishes associated with intertidal zones
(Hancock and Urquhart 1965; Edwards and
Steele 1968). Virnstein (1977) demon-
strated experimentally that the effect of
demersal fish on the benthos was highly
species-specific. Some species like the
hogchoker had a minimal ef'fect on benthic
population abundance while other species
such as the spot (Leiostomus xanthurus)
reduced both the abundance and species
diversity of the infauna in a Chesapeake
Bay subtidal site. The relative magnitude
of such impact is dependent upon the
degree of disturbance associated with for-
aging on the bottom (e.g., excavating
activities) as well as feeding rates.
Species such as skates that can disturb
large areas of the bottom when foraging
have more pronounced effects on the ben-
thos (Van Blaricom 1970) than species that
only browse on the sediment surface.
48
CHAPTER 5
BIRDS
5.1 INTRODUCTION
To the casual observer, the avifauna
is the most conspicuous component of the
tidal flat biota. Since birds are compar-
atively large bodied with high metabolic
rates, their impact on the tidal flat as
predators is often considerable (Schneider
1978). Collectively, coastal birds take
on a wide variety of trophic roles and
occupy numerous positions in the coastal
food web (Figure 14), ranging from primary
consumers that feed on vegetation, to top
level carnivores that prey exclusively on
fish. Few are themselves preyed upon and
therefore, regardless of where each spe-
cies or group fits into the food web,
their trophic level is necessarily a ter-
minal one in the tidal flat ecosystem.
Appendix III lists the species of
birds that commonly use tidal flats in New
England during some portion of their life
history. The list is not exhaustive and
does not include all those species that
might be seen on a tidal flat or all spe-
cies of coastal birds. The birds that
have been included vary considerably in
terms of their use of and dependence on
the tidal flat environment. For some,
such as the herons and shorebirds, tidal
flats are an absolutely essential habitat,
while for others such as the diving ducks,
the tidal flat at high tide is just one of
many potential foraging areas and often
not even a primary one. The geographical
ranges of most of New England's tidal flat
avifauna extend beyond the boundaries of
New England and much of what we know about
their ecology is based on studies done
elsewhere. This literature has been
included because, in most cases, it
applies to New England birds as well.
Various methods may be used to organ-
ize a discussion of this highly diverse
assem,blage of organisms. The following
scheme is based on trophic groups and is
convenient since there are fairly consis-
tent relationships within the taxonomic
groups concerning ecology and distribu-
tional status. The major groups are: (1)
shorebirds, which are largely migratory
and feed on invertebrates, (2) gulls and
terns, which feed on fish and large inver-
tebrates and commonly breed in New Eng-
land, (3) herons, which also breed in New
England and consume small fish and large
crustaceans, (4) waterfowl, cormorants,
and diving birds, which are primarily
migratory and as a group eat a wide vari-
ety of prey, and (5) raptors, which breed
in New England and, while over the tidal
flats, feed on fish and birds. In addi-
tion to these five major groups, the king-
fisher and fish crow have been included in
Appendix III. The kingfisher is a year-
round resident of much of New England.
The fish crow is a year-round resident of
Connecticut and Rhode Island and feeds on
intertidal invertebrates and the eggs of
unguarded tern and heron nests.
The following is a group-by-group
discussion elaborating on the functional
roles and other important biological
information about each of the five cate-
gories.
5.2 SHOREBIRDS
Shorebirds that appear on the New
England coast belong to the families
Charadriidae (plovers), Scolopacidae
(sandpipers), and Haematopodidae (oyster-
catchers). Although several shorebird
species breed and/or winter in New England
(Appendix III), most are hemispheric
travelers, appearing only during spring
and fall migrations. The semipalmated
sandpiper is the most abundant shorebird
in North America. Because this species
has a yearly migratory pattern character-
istic of many migratory shorebirds, it
will be used as an example of the typical
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yearly schedule of events in the lives of
shorebirds that frequent New England tidal
flats. From its Arctic breeding range,
which extends from Alaska to eastern
Canada, the sandpiper migrates thousands
of miles to its wintering grounds along
the U.S. Gulf coast and the West Indies,
south to northern Chile and Paraguay
(Palmer 1967). During migrations, the
birds stop at various resting and feeding
areas along the eastern coast of North
America. In Plymouth, Massachusetts, a
minor staging area, peak counts of these
birds occur in late July and early August
with stragglers present until early Octo-
ber (Harrington and Morrison 1S79). While
at these stopover areas, the birds do
little more than rest and eat, accumulat-
ing sufficient reserves of subcutaneous
fat to fuel what may be a nonstop flight
to the wintering areas in South America
(McNeil and Burton 1973) where they remain
for 6 to 7 months. In April, the birds
start on a return migration to their
breeding ranges (Palmer 1967), a trip that
takes many to their fall stopover areas.
Others take an inland route along the
Mississippi Valley. The spring migration
occupies less time than the fall migration
and after arriving on their Arctic breed-
ing ranges, they spend about a month pro-
ducing young. They then accumulate in
large flocks at major staging areas such
as James Bay, Ontario, Canada, and Bay of
Fundy, first adults and later juveniles.
Soon they depart from the northeast coast
and repeat this yearly cycle of events.
Shorebirds feed primarily on inverte-
brates (molluscs, crustaceans, polychae-
tes) that are captured on beaches and sand
and mud flats. Their daily activity pat-
terns and specific foraging sites are
often dictated by the tides. During the
early part of the ebb tide, foraging
begins on the beaches and as the tide con-
tinues to recede, many species then move
to tidal flats (Burger et al. 1977). Con-
nors et al. (1981) related these movements
to the peak availability of prey items in
these two habitats. During high tide, the
birds usually rest on adjacent beaches and
upland areas (Harrington et al. 1974).
Although there are a few large sand-
pipers, the majority are among the small-
est birds to frequent tidal flats. These
exquisitely camouflaged shorebirds often
go unnoticed by even well -trained eyes.
They are probers that often feed in small
flocks. Many plovers are larger, m.ay
assume a more upright posture in alarm,
frequently feed solitarily or in loose
groups, and are considerably more active
than most sandpipers. Only a single spe-
cies of oystercatcher is found in New Eng-
land. The American oystercatcher is con-
spicuous with a long, bright orange bill.
As the name implies, these birds feed
almost exclusively on large molluscs and
are only infrequently seen.
A tidal flat may be exploited by a
large number of shorebirds of many differ-
ent species. Their effects may deplete
prey populations (Schneider 1978). Since
tidal flats appear to be a physically uni-
form habitat, severe competition for food
between predator species may be expected.
How is it that so many seemingly similar
bird species can all exploit the inverte-
brates of the same tidal flats and con-
tinue to coexist? There are several pos-
sible explanations. Due to their migra-
tory nature, shorebirds may not deplete
resources to the critically low levels
that would result in severe competition.
When resources are severely depleted,
however, we must look for alternative
explanations. Among these is the possi-
bility that a tidal flat may not be as
physically uniform an environment as it
appears. If the tidal flat actually
represents a collection of discrete micro-
habitats, then different species may
exploit different habitats with the result
that competition is reduced. Differences
in sediment grain size, patches of algae,
depressions, shellfish beds, cobbles and
larger rocks create surficial, horizontal
discontinuities while segregation by depth
of water and sediments of different prey
items represents a vertical habitat divery
sity. Superimpose on these variables the
temporal component of tidal fluctuations
and there exists a wide variety of differ-
ent habitats within a single tidal flat.
If bird species differ in microhabitat
preferences, then foraging individuals may
be separated in either space or time,
reducing direct competition. In addition,
morphology (e.g., bill shape and size),
feeding tactics, and prey preferences may
prevent even those species that forage in
the sam.e areas simultaneously fron actu-
ally competing for food.
51
There is evidence that bird species
differ with respect to substrate prefer-
ences. Sander! ings prefer sandy substrates
and dowitchers are more often found over
siltier areas (Harrington and Schneider
1S78) while ruddy turnstones most fre-
quently forage on barnacle-covered rocks
and in accumulations of tidal wrack
(Groves 1?78). Other species, such as
black-bellied plovers, opportunistically
feed in any of several habitats with no
noticeably strong preferences (Harrington
and Schneider 1978). Burger et al. (1977)
found that larger species prefer muddier
algal zones while smaller species frequent
drier nicrohabitats.
Temporal segregation may occur as the
tides recede--when a wave of species, each
oriented to preferred distances from the
water's edge, sequentially use the same
areas of the tidal flat. Sanderlings and
semipalmated sandpipers characteristically
follow the water's edge as the tide ebbs
while semipalmated plovers restrict their
foraging to the middle areas of the tidal
flats (Harrington et al. 1974). Knots and
dunlins also follow the receding tide and
although they occur together, both spa-
tially and temporally, competition is
avoided since knots prefer molluscs while
dunlins eat polychaetes (Evans et al.
1979). Dowitchers also follow the tide
but feed deeper in the sediments. The form
of the bill and leg length influence the
type of potential prey items available to
a species (Figure 15).
Ten;poral segregation may occur on a
broader, seasonal scale. As shorebirds
arrive in fall or spring, peak densities
of different species may be staggered in
time, reducing competition, particularly
between ecologically similar species
(Recher 1966). Even subtle differences in
migration schedules may have profound ef-
fects on resource availability. Harrington
and Schneider (1978) mention that shrimp
that feed on the juveniles of infaunal
invertebrates may not arrive on the flats
until late in the shorebird migratory sea-
son. Shorebirds that prey on crustaceans,
such as black-bellied plovers and sander-
lings, are later fall migrants than short-
billed dowitchers and semipalmated sand-
pipers that consume infaunal prey.
VERTICAL FEEDING RANGE
B C
SEDIMENT
SURFACH
BILL LENGTH
o Cinches)
14
Figure 15. Vertical feeding depths of some comnon New England shorebirds (modified
from Recher 1966). Bill lengths are an average of the ranges given by Palmer (1967).
A = species foraging between the water and sediment surface (heights of bars refer to
water depths); B = species primarily feeding on the sediment surface; C = species
mainly feeding below the sediment-water interface (the willet feeds below the sediment
surface as well as in shallow water).
52
In addition to habitat selection and
bill and leg morphology, variability in
foraging behaviors between bird species is
also a critical factor in determining
potential shorebird food resources (Baker
and Baker 1973). Behavioral patterns may
be stereotyped to the extent that not only
may species identifications be possible by
observations of behavior, but also it has
been suggested that behavioral as well as
morphological attributes may reflect
evolutionary relationships (Matthiessen
1967). The erratic run and peck foraging
behavior of the plovers easily distin-
guishes them from the slower, more method-
ical probing sandpipers. Pearson and
Parker (1973) found behavioral uniformity
within each group and an inverse relation-
ship between bill length and stepping
speed suggesting that birds that peck
the surface for prey are more active then
those that probe deeper in the sediments.
The active audio/visual hunting by plovers
requires increased activity, quick move-
ments, and intermittent pauses for search-
ing and stalking. The probing sandpipers
locate their prey primarily by tactile
methods, walking slowly and continually
thrusting their bill into the sediment.
These 'i/ery different hunting techniques
may result in the consumption of different
prey species or different-sized individ-
uals of the same species or a more effi-
cient prey-capture time. For example, the
semipalmated plovers that forage on the
middle regions of the tidal flats search
for prey in areas that have been previ-
ously exploited by the probing sanderlings
and semipalmated sandpipers. All three
species may consume the same species of
prey but the later-arriving and visually
hunting semipalmated plovers are more
successful per unit time (Harrington
et al. 1974). Most probing shorebirds
will also respond to visual cues and peck
at prey items. Often the pecking or prob-
ing alternative may be a function of habi-
tat type and prey availability.
Since migrating shorebirds may often
occur in high densities, aggressive inter-
actions in the form of displays and chases
are quite common among many species,
particularly those that feed primarily
by visually active hunting tactics (Burger
et al. 1979). Probers frequently occur
in foraging flocks and only rarely do
aggressive interactions occur, as in the
case of knots that most commonly feed in
tight groups (Bryant 1979). Species such
as the sanderling that feed by both visual
and tactile methods will show little
aggression and feed in flocks but maintain
intraspecif ic distances while foraging
solitarily (Harrington et al. 1974). In
general, among shorebirds, intraspecific
aggressions are more frequent than inter-
specific interactions (Burger et al. 1979)
and when interspecific aggression does
occur, it is most common among similar
species such as between the least and
semipalmated sandpipers (Recher and Recher
1969b) that avoid each other by marked
habitat segregation (i.e., mud flats vs.
grassy marsh and seaweeds).
A remaining question is what role
shorebirds play in the New England tidal
flat community. Although the majority are
transients, their role as major consumers
of invertebrate production is a substan-
tial one during migrations. They may be
best described as removers. Other than
the nutrients in their feces, no form of
the energy they consume is returned to
the tidal flats. During the fall migra-
tion, in just a few weeks they may deplete
large portions of their prey populations.
Schneider (1978) found the average harvest
by foraging shorebirds was 5C% and 70% of
invertebrate populations during two suc-
cessive years of study. In Massachusetts,
dowitchers have been reported to remove
nearly one half of available food re-
sources during July and August (Harrington
and Schneider 1978). Wintering species
may have a more dramatic effect as seen in
a study done in England where shorebirds
were responsible for removing 90% of the
Hydrobia (snail) population and 80% of the
nereid polychaetes (Evans et al. 1979).
Stomach contents of dunlins in Sweden
revealed an average of 152 Nereis (poly-
chaete worm) jaws per individual (Bengston
and Svensson 1968). Site selection among
foraging shorebirds is not a random, pas-
sive process. Favorable feeding areas
with a high density of prey can be recog-
nized and exploited. Harrington and
Schneider (1978) found that semipalmated
plovers shifted their habitat usage to
coincide with peak densities of nereid
worms and that extremely high densities of
knots could be correlated with an unusual-
ly heavy set of My til us (mussels).
53
Shorebirds, such as this semi pal mated
England tidal flats in spring and fall,
to provide the necessary fat reserves
to wintering areas in South America.
Wildl ife Service. )
sandpiper, concentrate in large numbers on New
They consume great quantities of invertebrates
for long migrations from Arctic nesting grounds
(Photo by J.M. Greeny; courtesy U.S. Fish and
Since shorebird predation nay be
intense and focused in areas where prey
species are most abundant, these birds
probably play an important, if temporary,
role in structuring the invertebrate com-
munities of tidal flat environments. On
Long Island, New York, Schneider (1978)
found that such predation resulted in
wider spatial distributions of prey spe-
cies. By concentrating their foraging on
the most abundant prey, shorebirds prevent
single species of invertebrates from domi-
nating areas of the tidal flats at the
expense of others.
5.3 GULLS AND TERNS
Eight species of gulls and six spe-
cies of terns (family Laridae) occur com-
monly in New England. Seven of the four-
teen species nest in colonies on the New
England coast, and two species, the her-
ring and great black-backed gulls, appear
year-round. The distribution of nesting
pairs of colonial wstprhirHt: fhri — ' — ^
New England is
waterbirds throughout
given in Table 6.
Gulls will drop to the surface from
flight (plunge diving, Ashmole 1971) when
54
Table 6. Number of coastal nesting pairs of colonial waterbird
species in 1977 (Maine-Connecticut), showing occurrence by
state (from Erwin and Korschgen 1979).
Species
ME
NH
MA
RI
CT
Double-crested Cormorant
Phalacroxorax auritus
15
,333
Great Blue Heron
Ardea herodias
903
Green Heron^
Butorides striatus
Little Blue Heron
Florida caerulea
4
Great Egret
Casmerodius albus
Snowy Egret
Egretta thula
90
Louisiana Heron
Hydranassa tricolor
1
Black-crowned Night Heron
Mycticorax nycticorax
117
Glossy Ibis
Plegadis falcinellus
75
Common Eider
Somateria mollissima
22
,390
Great Black-backed Gull
Larus marinus
9
,847
Herring Gull
Larus argentatus
26
,037
Laughing Gull
Larus atricilla
231
Common Tern
Sterna hirundo
2
,095
Arctic Tern
Sterna paradisaea
1
.640
Roseate Tern
Sterna dougallii
80
Least Tern
Sterna albifrons
21
24
91
1,760
1
19
1 +
4,670
200
4,475
73
1,327
1,551
2
35
22
540
350 25,845 6,016
47
15
1
20
459
180
50
1
1,958
517
406
112
160
10
164
3,134
589 1,479
120
'included only when found at mixed species heronries.
55
feeding on schools of small fish. More
frequently they paddle slowly on the sur-
face dunking their heads (surface dipping,
Ashirole 1971), fly a few feet up from this
position and make short plunges in shallow
water (surface plunging, Ashmole 1971), or
forage over exposed tidal flats or inter-
tidal rocky substrates. Some of their
feeding techniques show remarkable ingenu-
ity. They paddle in shallow water, creat-
ing a current that moves away sediments to
expose infaunal prey. It is not uncommon
to see gulls cracking mollusc shells by
dropping them from the air onto docks,
boulders, parking lots, or any other large
hard object.
flost New England terns are smaller
than the gulls. Some kinds with forked
tails are aptly called sea swallows. Their
speed and flight patterns, particularly
when being pursued by one of their own
kind, are remarkable to watch. They are
most famous for their group feeding "fren-
zies" when they plummet head first from
the sky to capture schooling fish and
crustaceans. More gracefully, on calm
days they can swoop down and snatch a
minnow without making a ripple. While
searching for food, they may be seen hov-
ering or "stilling". Their relatively
small feet serve to orient them but pre-
vent them from being good swimmers. Prey,
usually small fish or crustaceans, are
generally captured by plunge diving.
At the turn of the century, no one
would have predicted that "sea gulls"
would become a symbol of the New England
seashore. During the last two hundred
years, the breeding populations of New
England gulls and terns have fluctuated
greatly. Surveys have been made at fre-
quent intervals during this century and
there is good documentation for recent
periods of both declines and expansions.
The following discussion of the historical
trends in these populations is summarized
from Drury (1973) and Nisbet (1973).
During much of the 18th and 19th cen-
turies, the larger gulls were exploited
for their food value and nearly extermi-
nated in New England, and in the later
decades of the 19th century, the millinery
trade inflicted hunting pressures on terns
as well. By 1900, both gull and tern
populations were at low levels, and some
conservationists feared these species were
on the verge of disappearing from the New
England coast. A conscious effort to save
these birds resulted in the passage of
several bird protection laws and the
response of the bird populations has been
good to spectacular for terns and gulls
respectively.
The New England herring gull breeding
population numbered only about 10,000
pairs at the turn of the century, with the
great majority restricted to islands off
the Maine coast. Both the number and
range of gulls have increased tremendously
in the last 75 years. From 1900 to the
1960's, the population appears to have
increased by a factor of 15 to 30, dou-
bling every 12 to 15 years (Kadlec and
Drury 1968). As early as the 192C's, there
was concern that the rapidly increasing
herring gull population threatened farm
and blueberry crops in eastern Maine as
well as the continued survival of the
terns; in the 1930's, a gull control
program was initiated in the form of egg
spraying. This was originally focused in
Maine and the gulls responded in part by a
southwestward expansion into Massachusetts
(Kadlec and Drury 1968). During the 1940's
to early 1950's, the control program was
conducted on most colonies from Maine to
Massachusetts, but was eventually aban-
doned as ineffective. Although gulls col-
onized islands at the eastern end of Long
Island Sound by 1933, it was not until
1950 that herring gulls colonized the
shores of Connecticut. By 1960, they had
expanded their range as far south as North
Carol ina.
The common tern has been the most
abundant tern nesting on the northeastern
coast of the United States, although the
Arctic tern may now be more numerous in
Maine (W.H. Drury; College of the Atlan-
tic; Bar Harbor, Maine; April 1981; per-
sonal commiunication). Historical popula-
tion estimates indicate a period of
increase early in this century followed by
a more recent period of decline in popula-
tion numbers. Peak populations occurred
during the 1940's and since then, the pop-
ulation has been reduced by about one
half. One author suggests that the
decline of these birds may be due in part
to decreased breeding success that has
resulted from the displacement of breeding
56
Gulls of several species are the rpost abundant and conspicuous birds on New England
tidal flats. They feed on a wide variety of fish and invertebrates and scavange hurran
waste. (Photo by L.C. Goldman; courtesy U.S. Fish and Wildlife Service)
birds from preferred areas by herring
gulls (Nisbet 1973), and also from winter
predation pressure by residents of the
Guianas on the northern coast of South
America (W.H. Drury; College of the
Atlantic; Bar Harbor, Maine; April 1981;
personal communication).
Most gulls and terns are highly gre-
garious. They are colonial breeders and
often gather in large groups where food is
concentrated. It is impressive to witness
the accumulation of a group of feeding
gulls. Initially only one or two nay be
within sight, but within a few minutes
there may be one hundred or more. Group
feeding techniques in gulls have been
examined by Frings et al. (1955). They
found that food finding and the accumula-
tion of feeding groups resulted from the
combination of auditory and visual cues.
There is a constant visual surveillance of
all parts of the coast by individuals or
small groups of birds. A bird that has
spotted food flies a characteristic figure
eight flight pattern in an attempt at prey
capture and emits a characteristic call.
Gulls within sight respond to the flight
pattern and those within earshot respond
to the call. Terns may also form feeding
groups via auditory and visual cues (Erwin
1977).
Colonies may serve as information
centers and be an important aid in food
finding, particularly for species that
feed in groups on a patchy resource (Ward
and Zahavi 1973; Erwin 1978). Davis (1975)
found that the nests of gulls that consis-
tently fed together at fish docks were not
randomly dispersed in the breeding colo-
nies, but were clumped, suggesting that
57
gulls may follow each other to foraging
sites. Among different species of terns,
Erwin (1978) suggests that those species
which feed closer to the breeding colonies
are more gregarious while feeding and have
larger colony sizes. While feeding on
exposed tidal flats where food is patchy,
herring gulls may establish territories
that are defended by calls and posturing.
These territories may be maintained by the
same birds for many years (Drury and Smith
1968).
The displacement of nesting terns by
gulls can be explained in part by review-
ing some aspects of the biology of these
species. Herring gulls
opportunistic foragers,
almost any large piece
rial, living or dead,
capitalized on a subsidy
are general and
They will eat
of organic mate-
and have thus
in the form of
tons of organic wastes produced each year
by the northeastern coastal human popula-
tion which has increased spectacularly
during this century. The effect has been
to tremendously increase the carrying
capacity of their environment which has
released the population growth rate of the
gulls from dependence on food resources;
the New England herring gull population is
now dependent on human refuse. Perhaps
the greatest impact on the species has
been to increase the survival of wintering
yearlings that feed on refuse. Harris
(1965) estimated that in England as much
as two-thirds of the food remains of her-
ring gulls were attributable to human
waste and Kadlec and Drury (1968) sug-
gested that only 12% of New England gulls
make an "honest" living by consuming food
other than that generated by man. Hunt
(1972) studied Maine islands of varying
The least tern is one of four species of terns that feed on small fish of the New
England tidal flats and nest on nearby beaches and islands. (Photo by L.C. Goldman;
courtesy U.S. Fish and Wildlife Service)
58
distances from refuse sources and observed
that fledging success was greatest at the
near islands. Since there is little dif-
ference between the fledging success of
two and three egg clutches (Kadlec and
Drury 1P68), when chick mortality does
occur, it is generally not because of
insufficient food, but rather due to
parental neglect (Drury and Smith 1968;
Hunt 1972). If gull chicks are left
unattended for long periods of time, they
may wander into adjacent territories and
may be attacked by neighboring adults
(Hunt and McLoon 1975).
Another potential control on popula-
tion growth is available breeding space.
During the last 75 years of rapid expan-
sion, the density of nests in herring gull
colonies has reipained unchanged (Kadlec
and Drury 1568). As the number of birds
in the New England gull population has
grown, new nesting pairs have established
new colonies, expanding the breeding
range. Most breeding colonies occur on
nearshore islands, the same type of
islands used by breeding terns. Kadlec
and Drury (1968) have estimated that
approximately 15% to 30% of adult herring
gulls are nonbreeders in any given year.
There is a tendency for gulls that find no
space in existing colonies to establish
territories on islands that support tern
colonies and, in time, to displace the
terns (Drury 1974).
Terns are much more selective in
their feeding than gulls, preferring small
fish and crustaceans. Unlike the herring
gulls, their population growth is food-
limited. During the breeding season, adult
males may hunt for food up to 14.5 hours
per day (Nisbet 1973). There is evidence
that the number of chicks that survive to
fledging may be a function of food avail-
ability. LeCroy and Collins (1972) found
that both roseate and common tern produc-
tivity in Long Island Sound, as measured
by successful fledgings, fluctuated year-
ly, and the authors suggested that these
fluctuations were related to food avail-
ability. These workers also examined the
relationship between clutch size and chick
survival. Common and roseate terns may
lay either two or three egg clutches and,
unlike the herring gulls, the survival
from hatched egg to fledging is much
greater in two egg clutches than three.
This evidence suggests that (1) dur-
ing this century, we have increased the
carrying capacity of New England for the
herring and great black-backed gull popu-
lations, (2) tern populations are limited
by natural controls, and (3) both groups
overlap considerably in their preferred
breeding areas. Collectively then, this
evidence implies that the dense coastal
hum.an population of the northeast is
threatening the continued coexistence of
these two groups of birds.
5.4 HERONS AND OTHER WADING BIRDS
For many people, the most conspicu-
ously beautiful and aesthetically pleasing
birds that frequent tidal flats are the
herons and egrets. These long-legged and
slender-necked wading birds are elegant as
they take off and land with broad wings
beating in slow motion. At other times as
they pursue prey with feet splashing, head
jerking, and wings flapping, they seem
clumsy. Like the gulls and terns, herons
and other wading birds are colonial breed-
ers that often nest on islands. Table 6
shows the relative abundance of coastal
breeding herons in New England. Most spe-
cies frequent the New England coast only
during the warmer months, but the great
blue and the black-crowned night herons
may remain all winter. After young are
fledged, there is a general dispersion
northward and then a southward migration
in the fall. In New England, herons are
primarily tree nesters. Until the 1950's,
most kinds of wading birds nested only in
more southern states. Since then there
has been a steady "invasion" into New Eng-
land (R. Andrews; U.S. Fish and Uildlife
Service, Newton Corner, Massachusetts;
April 1981; personal communication). In
the south, dense multispecies breeding
and feeding assemblages frequently occur.
Each species has a characteristic foraging
behavior and the collective repertoire of
the feeding behaviors of this group has
been studied extensively.
Soon after arriving from wintering
areas, pairs of herons establish well-
defended breeding territories. At least
one member of the pair always occupies the
territory (Jenni 1969). Nest site selec-
tion is species-specific. Snowy egrets
have a tendency to nest in exposed areas
59
around the periphery of the colony, while
little blue herons prefer more protected
locations (Jenni 1969).
Egg destruction occurs as the result
of predators such as raccoons or crows
(Teal 1965). During the first few weeks
after hatching, chick mortality may be
high. Jenni (1969) suggested that snowy
egret chick loss was largely due to star-
vation. He found that mortality rates
were Zl% per nest of four, 23% per nest of
three, and 10% per nest of two. In a mixed
species heronry in Georgia, 10% of the
nestlings died of starvation (Teal 1965).
Nest success varies from species to spe-
cies. Teal (1965) found that only black-
crowned night herons fledged more than 50%
of the eggs laid. He attributed this to
pugnacious behavior of the chicks who
vigorously defend their nest. He suggested
that the smaller and less fierce species
(snowy egret and Louisiana heron) were the
least successful.
After fledging, high mortality rates
may be sustained through the first year of
life. Kahl (1963) found that 76% of the
common egrets alive on July 1 died during
their first year, and mortality rates of
71% (Owen 1959) were reported for the
great blue heron. Most of the first year
mortality for both common egrets and great
blue herons occurs between July and Decem-
ber and may be due to the unfamiliarity of
inexperienced young of the year with
migratory territories (Kahl 1963). It
takes time for young birds to become pro-
ficient hunters. Although feeding behav-
iors appear to be innate components of a
heron's biology and similar techniques are
used by both adults and juveniles, success
rates are much higher for adult birds.
Recher and Recher (1969a) found that for
each minute spent foraging, adult little
blue herons obtained more prey by weight
than the juveniles. Similarly, adult great
blue herons were found to be successful in
62% of strikes while juveniles captured
prey in only 33% of their attempts (Quin-
ney and Smith 1980).
While it appears that food is a lim-
iting resource particularly during the
breeding season. Teal (1965) concluded
that there is a surplus of food, but this
food is not sufficiently available to even
the adult birds since they are relatively
inefficient predators. This is not sur-
prising since the primary prey are mobile
fish and large crustaceans, making food
finding and foraging techniques critical
factors in heron ecology.
The role of colonies as information
centers has been studied extensively in
heron breeding colonies. Krebs (1974)
specifically addressed this problem in a
study of the great blue heron. To illus-
trate the advantage of gregariousness, he
showed that while the birds exploited a
patchy food supply, individuals were not
behaving independently, and birds that
foraged in groups had a higher rate of
food intake than those feeding solitarily.
Feeding areas were highly variable from
day to day and the colony tended to switch
in unison from one feeding site to anoth-
er. Departure from the breeding colonies
to foraging areas generally occurred in
groups and birds from neighboring nests
frequently fed in the same areas. Finally,
Krebs (1974), who put styrofoam models of
foraging herons in the field, found indi-
viduals flying overhead were attracted to
them, landed, and began foraging.
During foraging, the herons may be
either solitary and defend feeding terri-
tories or gregarious and form small
flocks. Great blue herons have their
highest rate of feeding success at a flock
size of about twenty birds and Krebs
(1974) suggests that flocks may buffer the
risk of birds being unsuccessful in feed-
ing on the short term, which may be criti-
cal when rearing chicks. Even when great
blues feed alone, colonies may still play
a role as information centers in locating
the position of food resources relative to
the colony (Ward and Zahavi 1973).
As a group, the herons use a diverse
array of foraging behaviors and within the
tidal flat environment, may segregate
themselves according to habitat prefer-
ences and morphology. As a result, the
overlap in prey items between species may
be reduced. In Florida, Meyerriecks
(1962) has seen as many as nine species of
herons feeding on the same shoal; he
claims that their ability to coexist while
using a common habitat results from their
use of different feeding methods. Kushlan
(1976) provides a good descriptive sum-
mary of heron feeding behaviors. The major
60
categories of foraging tactics are stand
or stalk feeding, disturb and chase feed-
ing, and aerial and deep water feeding.
VJithin each of these major categories,
there are several variations. The stand
and wait feeding behavior is the most
typical and is common to all species of
herons (Allen 1962).
Depending on the habitat, which in-
cludes prey density, predator density,
water depth, and plant cover, species use
their own unique hunting tactics (Kushlan
1976). In his study of heron feeding in
southern New Jersey, Willard (1977) sum-
marized the foraging behaviors of many of
the herons seen in New England. He found
that great blue herons and common egrets
hunt in deeper water than the smaller
species. Great blue herons used stand
and wait and slow wading techniques to the
same extent. Active pursuit was rare,
probably related to the large and highly
mobile fish species in the diet. Great
egrets also used slow wading techniques
but their pace was faster than the great
blue herons, and when feeding in flocks,
they used the stand and wait technique.
Snowy egrets showed the greatest variety
of feeding behaviors and of habitat selec-
tion. They were the only species to fre-
quent exposed mud flats where they would
take large polychaetes. Slow wading was
the nost frequent hunting technique, but
foot stirring and active pursuit were also
common. The foot stirring behavior re-
sulted in a larger portion of benthic
crustaceans in the snowy egret's diet.
The Louisiana herons also relied on active
pursuit, but the most common feeding
behavior was to crouch and strike hori-
zontal to the water's surface. This was
the only species in which slow wading was
not the preferred technique. Little blue
herons commonly waded slowly and peered
around banks and vegetation. The green
heron and black-crowned night heron were
not studied by Willard (1977). Both these
species can be commonly seen crouched
overlooking the water's surface where they
wait motionless for prey to wander by.
5.5 WATERFOWL AND DIVING BIRDS
This group is composed of a wide
variety of families, including the loons
(Gaviidae), grebes (Podicipedidae), cormo-
rants (Phalacrocoracidae), and the ducks,
geese, and swans (Anatidae). The majority
are migrants, present in New England only
during spring and fall, or they are winter
residents. Exceptions are the double-
crested cormorant, common loon, gadwall,
wood duck, and red-breasted merganser that
breed in some areas of New England and the
pied-billed grebe, Canada goose, black
duck, mallard, and mute swan that are
year-round residents. With only a few
exceptions (the geese, swan, and dabbling
ducks), all these birds dive for their
food which is usually fish, molluscs, or
crustaceans. Although many species are
capable of dives to great depths (over
70 m or 230 ft for the common loon), most
forage in shallower water, usually less
than 10 m (33 ft) deep. Some have become
extremely well-adapted to an aquatic
existence, can barely walk on land, and
can only take off from the water.
Two species of loons (common loon and
red-throated loon) are often found along
the New England coast during the winter.
Although they do not concentrate their
foraging on tidal flats, at high tide,
they may be seen over these shallow areas
diving for fish. Common loons are soli-
tary, even during migrations, and occur
singly or in pairs, while the red-throated
loons accumulate in large flocks, particu-
larly during migrations (Terres 1980).
Because the loons require up to several
hundred meters of water "runway" to become
airborn, when approached, they will dive
rather than fly as a means of escape.
Grebes, like the loons, may use tidal
flats at high tide as one of several of
their feeding areas. They are extremely
well-adapted for their primarily aquatic
existence where they feed, sleep, court,
and carry their chicks on their backs in
the water. Of the three species seen along
the New England coast, the horned and red-
necked grebes breed in Canada but winter
in coastal New England. The pied-billed
grebe breeds throughout New England and
winters as far north as Massachusetts.
Their diets consist of small fish and
crustaceans.
Cormorants are related to pelicans
and feed almost entirely on fish that they
61
Young double-crested cormorants in nest. Cormorants are specialists that feed on fish
and have been increasing along the New England coast. (Photo by R.G. Schmidt; courtesy
of U.S. Fish and Wildlife Service.)
capture by diving beneath the water's sur-
face. Double-crested cormorants are colo-
nial breeders, present in New England only
from April to November. They nest on rocky
islands, along the Maine and Massachusetts
coast, although they have been reported to
nest in trees at many locations in New
England (Drury 1973). An historical review
of the status of this species in New Eng-
land has been provided by Drury (1973).
After being completely extirpated on the
New England coast during the last century,
double-crested cormorants made a dramatic
comeback during the early part of the
1900's. Between 1925 and 1S45 the popula-
tion grew to about 13,000 nesting pairs
along the Kaine coast and since then, has
expanded its range along the New England
coast as far south as the entrance to Long
Island Sound (although the majority of
breeding pairs occurs north of boston,
Massachusetts). In the mid 1940's, Maine
fisherman declared this species a menace
to the commercial fishery and an egg
spraying program was initiated by the U.S.
Fish and Wildlife Service but was termi-
nated in 1953. Since then, the population
has continued to expand despite some indi-
cations that cormorants may have been
affected by toxic chemical poisoning
(Drury 1S74).
As the double-crested cormorant
leaves the New England coast each year
during the fall migration, it is replaced
by the larger and more northerly breeding
great cormorant that is a winter resident.
Both species consume fish that they pursue
underwater. Double-crested cormorants
appear to be the least wary and maritime
of the two and frequently feed over tidal
flats at high tide but can pursue fish to
great depths. Feeding i;,ay occur solitar-
ily or in groups. Bartholomew (1942)
has reported observations of orderly
flock-feeding on San Francisco Bay. During
62
flock-feeding, cormorants exploit school-
ing fishes. Active fishing is confined
almost exclusively to the front line of
birds, and as many as one quarter to one
half of the birds may be underwater at one
time.
Peak densities of wintering waterfowl
on the Atlantic coast occur in the mid-
Atlantic states, but large numbers of
several species are found on the New Eng-
land coast, some of which use tidal flats.
North American migratory waterfowl that
pass through or winter along the New Eng-
land coast use the Atlantic flyway, which
is one of the four great North American
migratory flyway systems (Lincoln 1935,
cited in Gusey 1977). Unlike the long,
nonstop migratory flights of shorebirds,
waterfowl often follow the coast, stopping
occasionally to rest and feed. Flocks even
take up residence in areas for extended
periods. For example in Massachusetts,
oldsquaw may appear during the middle part
of October, remain until the middle of
November, and then fly farther south
(MacKay 1892).
Geese (Canada geese and brant) fre-
quent the New England coast primarily dur-
ing the winter, although a small number of
introduced Canada geese breed in New Eng-
land as well. As herbivores, Canada geese
forage on submerged eel grass (Zostera
marina) and algae in shallow coastal areas
by reaching down into the water with their
long necks, often tilting their tails
straight up in the air. Brant are true
sea geese with well -developed salt glands
that enable them to drink salt water. Al-
though they are usually herbivorous, brant
also eat crustaceans, molluscs, and poly-
chaetes (Bent 1937). Before the 1930's,
brant fed almost exclusively on eelgrass.
After a blight destroyed much of the eel-
grass in the northeast, the brant popula-
tion declined dramatically. Since then,
brant have switched their foraging prefer-
ence to Ulva (sea lettuce) and although
the population is reduced compared to that
in the 1930's, its numbers have increased
in recent years.
The majority of wintering ducks and
mergansers in New England belong to only a
few species. Diving ducks and mergansers
use tidal flats at high tide as one of
several habitats for catching small fish
and invertebrates, while the dabblers are
more restricted to shallow coastal areas
and may feed extensively on tidal flats at
high and low tide. Stott and Olson (1972)
found all wintering species in New Hamp-
shire (scoters, goldeneye, red-breasted
merganser, oldsquaw, and bufflehead) to be
within 450m (1,476 ft) of the shoreline.
Competition between these wintering birds
appears to be reduced as a result of
species-specific habitat and food prefer-
ences. Many species of sea duck studied
were consistent in their habitat usage
from arrival in the fall until departure
in the spring (Stott and Olson 1973).
Within the study area, there were sandy
beaches, rocky outcrops, and bays. The
scoters preferred to feed in areas adja-
cent to the sand beaches, while goldeneyes
and red-breasted mergansers most often
foraged closer to the rocky headlands.
Oldsquaws showed no consistent habitat
preferences and buffleheads were almost
exclusively restricted to the quieter
bays. All these species are divers.
Ninety percent of the scoter's diet con-
sisted of molluscs of which the Atlantic
razor clam (Ensis di rectus), Arctic wedge
clam (Mesodesma arctatum), and blue mussel
(Mytilus edulis) were the most abundant
species. Although the goldeneyes and red-
breasted mergansers overlapped in habitat
preference, the goldeneyes ate small crus-
taceans, with some gastropods and poly-
chaetes, while the mergansers were fish
eaters, consuming killifish and silver-
sides. Small sand shrimp comprised 90% by
volume of the buffiehead's prey items.
Nilsson (1969) found similar habitat
segregation among wintering ducks in
southern Sweden, but in his study he found
goldeneyes to feed mainly over mud bot-
toms.
Waterfowl are the only group of
coastal waterbirds that constitute a com-
modity harvested for recreational use.
The bulk of each year's harvest in New
England is dabbling ducks; the major spe-
cies taken are black ducks, mallards, and
geese. Eiders and oldsquaw are also taken
in numbers along the coast of Maine (W.H.
Drury; College of the Atlantic; Bar Har-
bor, Maine; April 1981; personal communi-
cation). The dabbling ducks are mainly
herbivorous but omnivorous in that they
eat whatever their feeding techniques
catch in shallow submerged vegetation.
63
Both mallards and black ducks are year-
round residents of New England. The black
duck is currently more abundant, but there
is evidence that it is hybridizing with
and being replaced by the northward spread
of the closely related mallard. Black
ducks use tidal flats, especially in
northern New England, more than any other
species of this group. Breeding in
freshwater swamps, marshes, and streams
throughout New England, black ducks
migrate to the coast in the fall and rely
heavily on tidal flats during the winter.
Winter feeding may be regulated by tidal
rhythms and' weather and although these
ducks are mainly herbivorous, their diet
includes intertidal invertebrates such as
the blue mussel (Myti lus edulis), soft-
shelled clam (My a arenaria), and sand worm
(Nereis virens) and various amphipods and
isopods (Hartman 1963). During severe
winter weather, black ducks remain in
groups in open water kept free of ice by
tidal currents (Spencer et al. 1980).
5.6 RAPTORS
As consumers of large fish and shore-
birds, the hawks and eagles (family Accip-
itridae), and osprey (family Strigidae)
occupy the highest level in the nearshore
food chain. Of these raptors, the osprey,
and bald eagle exceed all others in terms
of their dependence on the coastal zone.
Ospreys eat a variety of coastal pelagic
fish and often hunt over shallow water
where they can take more demersal varie-
ties. Prey species weigh up to 2 kg
(4 lb) (Bent 1937) and there have been
reports of these birds being drowned while
attempting to capture large fish. The
osprey soars 30 m (100 ft) or more above
the water, where with its keen eyesight,
it may locate even the most camouflaged
species such as flatfish. When prey is
detected, the soaring is often interrupted
by hovering which may last up to ten
seconds and is usually followed by a
spiral plunge into the water. Prey is
captured with specialized talons and car-
ried in flight always with the head point-
ing forward to reduce frictional drag
(Terres 1980). Hovering is an important
behavioral adaptation. Although an ener-
getic cost is involved, dives from hovers
are 50% more successful than those started
from a glide (Grub 1977).
Ospreys nest along most of the Maine
coast and at several locations in southern
New England, often forming loose colonies.
Telephone poles, trees, channel markers,
duck blinds, chimneys, and man-made nest-
ing platforms are all acceptable locations
for their huge nests that may weigh up to
455 kg (1000 lb) (Abbott 1911, in Terres
1980). These birds are protected by law
and although presently on the increase,
their numbers in New England have reached
precariously low levels during this cen-
tury. The decline of the osprey is due to
coastal development, human disturbance,
and eggshell thinning and embryo mortality
as a result of poisoning by DDT and other
chlorinated hydrocarbons. Puleston (1975)
reviewed the historical status of the spe-
cies on Gardiner's Island in Long Island
Sound. In 1932, there were 300 nests on
the island, representing what was probably
the world's greatest concentration of
nesting ospreys. In the 1940 's, the
colony seemed to be in good health; the
productivity of each nest averaged two
fledgings. A decline began in 1948 so
that by 1965 there were only 55 to 60
nests that were producing 0.07 young per
nest. Since then and coinciding with a
nationwide ban on many pesticides, fledg-
ing success has increased, and in 1974, a
total of 26 young were produced from 34
nests. Puleston (1975) believes that the
current modest increases in the New Eng-
land osprey population will continue.
The bald eagle nests and winters in
Maine. Coastal areas support 75% of the
resident breeding and wintering popula-
tions and are used by spring and fall
migrants (Famous et al. 1980). Most eagle
nests are close to bays or estuaries where
the birds can obtain their preferred diet
of fish (tomcod, sculpin, alewives, blue-
black herring, and American eels) (Famous
et al. 1980). During the winter, eagles
depend increasingly on birds as their
major prey. The remains of 20 different
species of seabirds have been recorded as
eagle prey, of which black ducks and gulls
constitute more than 50% (Famous et al.
1980). Like the ospreys, the terminal
position of the eagle in the food chain
has resulted in decreased breeding success
due to toxic chemical poisoning. Studies
of Maine bald eagle eggs from 1967 to
1979 indicated an average shell thickness
15% less than normal and no significant
64
reduction in the levels of DUE, PCBs, or
mercury during this period. It is diffi-
cult to assess recent trends in bald eagle
numbers in Maine, but the current levels
of recruitment per nest remain below that
necessary to sustain a stable population
(Famous et al . 1980).
Several other raptors dre included in
Appendix III because they may consume
shorebirds. Of these, the peregrine fal-
con preys most heavily on shorebirds and
often follows migratory shorebird flocks
(E.L. Mills; Dalhousie University, Hali-
fax, Nova Scotia; April 1981; personal
communication). In a study conducted on
the west coast of the United States, Page
and Whitacre (1975) found that raptors
consume a large portion of wintering
shorebirds. At the study site, a variety
of hawks and owls removed 20.7% of the
dunlins, 11.9% of the least sandpipers,
and 13.5% of the sanderlings. New England
tidal flats are migratory stopover areas
for most shorebirds and such large remov-
als do not occur. Most of the raptors
studied on the west coast occur in New
England also and occasionally consume
shorebirds.
5.7 DEPENDENCE ON TIDAL FLATS
The major groups of coastal birds
differ in their dependence on tidal flats.
For the shorebirds that feed extensively
on exposed flats and the wading birds that
feed in shallow waters, tidal flats are
essential sources of food. The migratory
and winter habitat and feeding behavior
among shorebirds and the feeding behavior
of wading birds suggests a dependence
relationship that has persisted on an
evolutionary time-scale. Tidal flats
differ in their importance as feeding
sites, with those areas having dense popu-
lations of infaunal invertebrates being
more attractive. Also, migration routes
differ among species of shorebirds and a
relatively few coastal areas support large
numbers of shorebirds (Morrison and Har-
rington 1979). The wading birds are more
evenly distributed, especially in southern
New England. Since many nest there, the
ability to successfully fledge young is a
function of how well tidal flats can pro-
vide energy for their metabolic demands.
The terns and particularly the gulls
are the most persistent and common birds
of New England tidal flats, but this habi-
tat is only one of many used by this
group. Deeper waters are suitable for
hunting pelagic fishes and gulls feed as
well in rocky intertidal areas and terres-
trial refuse sites. Gulls make greater
use of the exposed tidal flats than the
fish-eating terns. This is true especially
in winter when the terns migrate south and
many fish leave the coastal area. Exposed
flats become particularly important to
wintering gulls that feed on sedentary
invertebrates and organic materials left
by the tides.
Although waterfowl and diving birds
often forage over tidal flats at high
tide, they are not restricted to these
areas. Many species prefer rocky sub-
strates and those that forage in or over
soft substrates often do so in deeper
water. Exceptions are the omnivores that
do not dive, such as several species of
dabbling ducks, geese, and the mute swan.
For these species, foraging occurs in
shallow water where they can reach benthic
vegetation by "tipping up" without diving.
Raptors, other than the osprey and
the eagle generally feed over terrestrial
areas and, except for peregrines and mer-
lins, only occasionally hunt shorebirds on
tidal flats. Ospreys are especially de-
pendent on the flats in the spring when
pelagic schooling species of fish are
rare.
65
CHAPTER 6
TIDAL FLATS: THEIR IMPORTANCE AND PERSISTENCE
6.1 INTRODUCTION
It has been recognized since the late
1950's that nearshore marine habitats,
particularly estuaries and coastal embay-
ments, are vitally important as nursery
and spawning grounds for fishes and as
habitats for shellfish. Tidal flats func-
tion in many of the same ways as deeper-
water, coastal habitats in addition to
providing resting and feeding sites for
coastal birds. Because the coastal zone
is heavily used for other land- and
marine-based recreational and commerical
purposes, tidal flats frequently are sub-
jected to reversible and irreversible man-
induced environmental impacts. Conflicting
demands on the use of tidal flats necessi-
tate legislative participation in the man-
agement of these areas and it is important
to address questions such as: How valu-
able are tidal flats relative to other
coastal habitats and how resistent or
resilient are tidal flat organisms to
environmental perturbation? In other
words, can we afford to lose tidal flat
habitats without experiencing unacceptable
alterations in the productivity of marine
biota?
6.2 RESPONSE OF TIDAL FLATS TO ENVIRON-
MENTAL PERTURBATIONS
The majority of man-induced impacts
on tidal flats can be categorized as
follows: (1) dredging and channelization
to maintain navigable waterways and the
construction and maintenance of water-
dependent industries or businesses (e.g.,
marinas), (2) discharge of pollutants from
waste disposal and industrial outfalls or
non-point sources (e.g., sewage, chemi-
cals, oil), (3) building of dams and jet-
ties resulting in altered inorganic depo-
sition, (4) spoil disposal for the crea-
tion of salt marshes, or landfill for
residential and/or commercial purposes.
and (5) overexploitation of commercially
important tidal flat shellfish.
The response of tidal flat organisms
and their ability to recover from man's
activities depends upon the type, magni-
tude, and frequency of the impact. Envi-
ronmental impacts can be classified as
those which are (1) destructive (e.g.,
dredging and spoil disposal) and result in
changes in habitat quantity or (2) those
that alter habitat quality (e.g., exces-
sive organic pollution) and result in the
degradation of the habitat.
The most easily detected effects upon
tidal flats are those that lead to habitat
destruction. Generally these impacts are
incremental and vary widely. Dredging
and spoil disposal, for instance, can
result in dramatic changes in the physi-
cal, chemical, and biological nature of a
tidal flat. When these perturbations are
taken to extremes, the result is irrevers-
ible habitat loss or modification. Dredg-
ing eliminates feeding sites for shore-
birds and spoil deposition destroys ben-
thic invertebrates and feeding sites for
vertebrates.
The response of tidal flat popula-
tions to severe habitat alteration has
usually been studied by examining change
in species ^ composition and abundance
following perturbation. Field studies may
involve monitoring the patterns of repopu-
lation by benthic organism.s following
spoil disposal (e.g., Rhoads et al. 1978)
or after experimental elimination of the
fauna in relatively small areas (e.g.,
Grassle and Grassle 1974; McCall 1977;
Zajac 1981). Despite differences in the
type of disturbance, environmental charac-
teristics, and species composition consid-
ered, there are common trends in benthic
community re-establishment and develop-
ment. Early colonizers of a disturbed
habitat are small species, predominately
66
polychaete worn;s. These species have sim-
ilar life histories, such as prolific
reproduction (often with several broods
per year), early rraturation, and high mor-
tality rates (e.g., the classic pollution
indicator species, the polychaete worms,
Capi tella capi tata and Streblospio bene-
dicti). These so-called "opportunists"
are gradually replaced by slightly larger,
taxonomical ly more diverse assemblages
that typically exhibit slower growth
rates, lower mortality rates, delayed
reproduction, and reduced reproductive
rates. Rhoads et al. (1978) have also
noted changes in benthic infaunal life
mode during the recolonization of dis-
turbed subtidal soft-bottom habitats.
Early colonists on spoil disposal sites
tended to live in the upper layers of the
sediment and to isolate themselves from
the surrounding sediment through tube-
building activities. As the sediments
were increasingly affected by bioturba-
tion, (e.g., by organisms burrowing and
feeding), larger, subsurface burrowing
animals invaded the spoil site.
Patterns of temporal change reported
in the literature correlate recovery rates
of disturbed shallow-water areas with
habitat, type of disturbance, and the size
and degree of isolation of the affected
area. In one study, over 3 years were
needed to establish a stable number of
benthic species (Dean and Haskins 1964),
while Sanders et al. (1980) found that
complete recovery of a benthic community
following a small oil spill had not oc-
curred over a period of more than 5 years.
On a smaller scale, recolonization may
take weeks to months (Grassle and Grassle
1974; McCall 1977; Zajac 1981). Recruit-
ment by benthic organisms into soft-
bottoms can be accomplished by planktonic
larval settlement as well as migration of
adults from surrounding areas. This colo-
nization is relatively rapid when compared
to marine rocky substrate systems (Osman
1977) in which repopulation of disturbed
sites is almost exclusively planktonic.
Life histories of infaunal species
inhabiting New England tidal flats include
a range of strategies. Niany species dis-
play life histories characteristic of the
earliest stages of recolonization. Tem-
perate tidal flat environments are con-
tinually exposed to extremes of natural
physical and biological change (See Chap-
ters 1 and 3). The organisms inhabiting
flats, therefore, are well-adapted to
withstand natural perturbations and per-
sist by recovering rapidly. Other species
have life histories more similar to those
found in the later stages of recoloniza-
tion. These organisms are more sensitive
to disturbance and do not inhabit tidal
flat areas that are continually exposed to
environmental fluctuation. In Maine, dense
populations of Mya arenaria are commonly
found in areas that are not abraded by ice
scouring (L. Watling; University of Maine,
Walpole; February 1981; personal communi-
cation).
Fish and birds respond differently to
habitat perturbations. They are more
mobile and move from the impacted area.
Fish and birds may not be affected by the
loss of small portions of a tidal flat,
but a bigger loss of that habitat would
have an effect upon species abundance and
composition. The remarkable recovery of
many populations of New England coastal
birds following near annihilation in the
last century was almost certainly depend-
ent upon the existence of undisturbed
feeding and nesting sites. Inshore fish
communities also appear resistant to small
habitat losses or modifications (e.g.,
Nixon et al. 1978) but more pronounced
alterations of these habitats would un-
doubtedly result in decreased abundance of
certain fish species. Spinner (1969), for
example, reported the decline in menhaden
population abundance after loss of estua-
rine nursery areas in Connecticut.
The effects of more subtle habitat
degradation can readily be seen on both a
regional and historical basis in New
England. The southern New England coast-
line is more heavily populated than north-
ern New England and many tidal flats are
exposed to residential, municipal, and
commercial pollutant discharges. Increased
pollution (e.g. from sewage, heavy metals,
bacteria) has drastically reduced tidal
flat shellfisheries in southern New Eng-
land. In upper Narragansett Bay, Rhode
Island, oyster populations were once so
abundant that they were used to fatten
pigs by early New England colonists.
While the upper bay supported a viable
oyster industry for many years (peaking in
the early 1900's), no oysters have been
67
harvested there since 1957 primarily
because of pollution and overfishing
(Robadue and Lee 1980). The soft-shell
clam fishery in upper Narragansett Bay is
apparently experiencing a similar fate.
In 1949, approximately 296,600 kg (650,000
lb) of clams were harvested while in 1979
commercial landings declined to about
3,650 kg (8000 lb). Abundant populations
of clams have been reported in the upper
bay but many areas have been closed to
shellfishing because of organic pollution
(Robadue and Lee 1980). In Connecticut,
approximately 90% of tidal flats are
closed to shellfishing because of pollu-
tion. Urbanization and its associated
impacts on northern New England tidal
flats have not yet been as severe. Al-
though approximately 20% of Maine's tidal
flats are closed annually to soft-shell
clamming because of water pollution, over-
exploitation of the shellfisheries may
pose a greater threat to clam populations
than habitat degradation (Doggett and
Sykes 1980).
The effects of changing habitat qual-
ity extend to other groups of organisms
using tidal flats. Haedrich and Hall
(1976) suggested that the degree of sea-
sonal change in New England fish communi-
ties (see Chapter 4) is a convenient indi-
cator of estuarine environmental "health".
Environments unaffected by pollution
should exhibit high annual diversity of
fish species and pronounced seasonal turn-
over in species composition. Where unfav-
orable habitat change has occurred, the
most sensitive species will be eliminated
and only those best-adapted to inhospit-
able conditions will remain. The net
effect upon fish communities, therefore,
is an overall reduction in the variety of
species that utilize the habitat.
Other sources of pollution are also
responsible for damage to New England
tidal flats. One of the more severe and
long-lasting impacts is from oil spills.
In a well -documented study of a relatively
small spill in Wild Harbor, Massachusetts,
Sanders et al. (1980) observed an almost
complete elimination of benthic organisms
at several oiled sites. The effects of
oil on the biota were still detectable at
this site 5 years after the spill, in part
because oil remained in the sediments and
did not degrade or disperse.
Not all responses to environmental
degradation are as dramatic as these.
Sindermann (1979a), in reviewing pollu-
tion-associated diseases in fish, sug-
gested that many effects are subtle (e.g.,
fin rot and fin erosion) and due to
chronic exposure of fish to a polluted
inshore environment. Since many fish
inhabiting inshore waters are juveniles,
they may be even more sensitive to these
chronic effects than adults.
The New England region provides a
well -documented historical case study of
environmental degradation and destruction
of tidal flats and their resident organ-
isms. These changes in New England should
provide an impetus for developing manage-
ment criteria for tidal flat habitats. To
begin such an undertaking, however, the
tidal flat's importance to the coastal
zone must be well-understood.
6.3 THE IMPORTANCE OF NEW ENGLAND TIDAL
FLATS
In the past, legislation protecting
marine coastal habitats was based on a
series of suppositions regarding the role
of these habitats in the overall coastal
zone (e.g., Oviatt et al. 1977). The sup-
positions focused on a habitat's role as
wildlife, fisheries, and storm-control
areas in addition to its potential for
exporting organic materials to stimulate
or enhance production in adjacent marine
systems. While much attention has been
directed toward identifying the function-
ing of specific coastal habitats, it has
been more difficult to assign a "value" to
individual systems. Early efforts to
evaluate habitats converted primary pro-
duction values for salt marshes into aver-
age dollar value per calorie produced by
the marsh (Gosselink et al. 1974). This
approach remains subjective because many
of the functions or roles of salt marshes
lie outside recognized monetary systems
and do not have an agreed monetary value
(Shabman and Batie 1980). In addition,
adequate evaluation of coastal zone habi-
tats must include values associated with
incremental changes (i.e., with time) in
these habitats and not be restricted to
the worth of an "average" salt marsh,
tidal flat, or estuary. Alternative
approaches to value assessment of coastal
68
zone habitats have been formulated (e.g.,
Kennedy 1980) although no generally
accepted method presently exists.
Unlike salt marshes that are recog-
nized for their potential for exporting
the primary production of grasses to
adjacent marine habitats, tidal flats
function as sites for the conversion of
plant production into animal biomass. The
most tangible evidence of the value of New
England tidal flats to human consumers is
the shellfish and baitworm fisheries. All
New England coastal states exploit tidal
flat shellfish populations. The extent of
these fisheries varies widely between
states and harvestable catch is largely
dependent upon habitat quality. In south-
ern New England, urbanization of the
coastal zone and associated pollution has
resulted in the closure of many tidal
flats to shellfishing. In Connecticut
only a few hundred pounds of shellfish are
harvested annually and virtually all of
the common tidal flat shellfish (e.g., Mj^
arenaria and Mercenaria mercenaria) sold
commercially are imported from outside the
State. In northern New England, where
coastal urbanization is not as extensive,
tidal flat shellfish and baitworm fisher-
ies are extremely important industries.
In Maine soft-shell clam (Mya^ arenaria)
and baitworm (Nereis virens and Glycera
dibranchiata) fisheries rank third and
fourth in economic value after the exten-
sive lobster and (now diminished) shrimp
fisheries. While soft-shell clams and
baitworms are not restricted to tidal flat
habitats, their abundance is greatest in
these areas and destruction or degradation
of these habitats would eliminate the
fisheries. Other species of economically
valuable invertebrates (e.g., crabs) are
also found on New England tidal flats.
Crabs do not depend entirely on flats, but
use them as important feeding sites.
The value of tidal flats to coastal
fish populations is more difficult to
assess. Most fish frequenting flats are
juveniles and are known to consume tidal
flat food items (especially benthic inver-
tebrates). Relatively little is known
about the degree of dependence of juve-
nile fish on flats and about the contribu-
tion of these populations to commercial
catches. Probably demersal fishes (e.g.,
winter flounder) rely most heavily on
tidal flats for feeding, but to what
extent remains conjecture. Tyler (1971b)
has suggested that the destruction of
tidal flats in the Bay of Fundy would
reduce the winter flounder populations.
Shallow water coastal habitats provide
juvenile fish a refuge from their preda-
tors in addition to serving as sheltered
feeding areas.
Many species of shorebirds rely heav-
ily (and some species exclusively) upon
tidal flats for feeding and resting sites.
Without productive benthic invertebrate
populations on flats some bird species
would probably suffer population declines.
A recent study (Goss-Custard 1977) that
has addressed the importance of tidal
flats to shorebird populations, however,
has failed to define the degree to which
the birds are limited by tidal flat habi-
tat availability. Other groups of birds
(e.g., gulls, terns, waterfowl), while not
as dependent on tidal flats for feeding
sites, are commonly present and are known
to consume benthic invertebrates.
One of the major difficulties in
attempting to assign specific values to
tidal flat habitats centers on the lack of
information about the magnitude of their
primary and secondary productivity and
about how much of that production is chan-
neled to higher trophic levels within the
coastal food web. Examination of the
sources and amounts 9f organic materials
entering the flats from other systems, the
rates at which these organics are utili-
zed, and the amounts passed to different
trophic levels requires detailed informa-
tion about energy flow, life history char-
acteristics of resident and transient
organisms, as well as insight into abiotic
and biotic processes affecting tidal flat
populations. This lack of knowledge, of
course, does not diminish the importance
of tidal flats to the coastal zone. More
information about ecological processes and
interrelationships on tidal flats is
required before planners, managers, and
legislators will be able to develop a com-
prehensive and rational basis for the pre-
servation, utilization, and management of
tidal flats.
69
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118
Appendix III. Bird species that regularly utilize New England tidal flats.
Residency status
(Peterson 1980)
Diet
(Terres 1980)
Shorebirds
American Oystercatcher
Haematopus palliatus
Black-bellied Plover
Pluvial is squatarola
Lesser Golden Plover
Pluvial is doniinica
Breeds locally north to
Massachusetts
Migrant; a few present
in summer and winter
Migrant; rare
Primarily bivalves,
some crustaceans and
echinoderms
Crustaceans, polychaetes,
molluscs
Molluscs, crustaceans
Ruddy Turnstone
Arenaria interpres
Semipalmated Plover
Charadrius semipalmatus
Piping Plover
Charadrius melodus
Kill deer
Charadrius vociferus
Short-billed Dowitcher
Limnodromus griseus
Long-billed Dowitcher
Limnodromus scolopaceus
Willet
Catoptrophorus semipalmatus
Greater Yellowlegs
Tringa melanoleuca
Lesser Yellowlegs
Tringa flavipes
Stilt Sandpiper
Micropalma himantopus
Migrant; prefers
rocky coasts
Migrant
Breeds locally along
New England coast in
very small numbers
Breeds throughout New
England; generally inland;
on flats in fall
Migrant
Fall migrant
Breeds locally north to
southern Maine and Nova
Scotia; more common as
migrant
Migrant; occasionally
winters north to
Massachusetts
Migrant; uncommon in
spring
Migrant; rare in spring
Crustaceans, polychaetes
Polychaetes, crustaceans,
molluscs
Polychaetes, crustaceans,
molluscs
Crustaceans, insects
Molluscs, crustaceans,
polychaetes
Molluscs, crustaceans,
polychaetes
Polychaetes, crustaceans,
molluscs, some small fish
Fish, molluscs,
polychaetes, crustaceans
Fish, molluscs,
polychaetes, crustaceans
Molluscs, crustaceans
continued
119
Appendix III. (Continued).
Residency status
(Peterson 1980)
Diet
(Terres 1980)
Shorebirds (continued]
Red Knot
Cal idris canutus
Sander ling
Cal idris alba
Pectoral Sandpiper
Cal idris melanotus
Migrant
Migrant
Migrant
Primarily molluscs, some
crustaceans, polychaetes
Primarily molluscs, some
crustaceans, polychaetes
Crustaceans
Spotted Sandpiper
Actitis macularia
Dunlin
Cal idris alpina
Purple Sandpiper
Cal idris maritima
Least Sandpiper
Cal idris minutilla
Fall migrant; breeds
inland
Migrant; some winter
north to southern Maine
Migrant; some winter
throughout New England;
rocky areas
Migrant
Crustaceans
Crustaceans, polychaetes,
mol luscs
Crustaceans, molluscs
Crustaceans, polychaetes,
molluscs
Semipalmated Sandpiper
Cal idris pusilla
Western Sandpiper
Cal idris mauri
White-rumped Sandpiper
Cal idris fuscicollis
Hudsonian Godwit
Limosa haemastica
Marbled Godwit
Limosa fedoa
Migrant
Migrant; may winter in
very small numbers,
rare in spring
Migrant; rare in spring
Migrant
Migrant
Molluscs, polychaetes,
crustaceans
Molluscs, polychaetes,
crustaceans
Polychaetes, molluscs
Molluscs, crustaceans,
polychaetes
Molluscs, crustaceans,
polychaetes
Gul Is and terns
Herring Gull
Larus argentatus
Breeds on islands along
New England coast; winters
throughout New England
Fish, invertebrates,
refuse, sea bird chicks
and eggs
continued
120
Appendix III. (Continued).
Residency status
(Peterson 1980)
Diet
(Terres 1980)
Gulls and terns (continued)
Ring-billed Gull
Larus delawarensis
Great Black-backed Gull
Larus marinus
Laughing Gull
Larus atri cilia
Bonaparte' s Gull
Larus Philadelphia
Least Tern
Sterna albifrons
Arctic Tern
Sterna paradisaea
Common Tern
Sterna hirundo
Roseate Tern
Sterna dougallii
Migrant; winters along
New England coast
Breeds on islands along
New England coast; winters
throughout New England
Breeds locally along
New England coast
Migrant; winters locally
along New England coast
Breeds north to central
Maine
Breeds south to
Massachusetts
Breeds on coast throughout
New England
Breeds locally through
southern New England and
Maine
Fish, refuse
Fish, invertebrates,
refuse, seabird chicks
and eggs
Fish, tern eggs or chicks
Fish, invertebrates
Fish, crustaceans
Fish, crustaceans
Fish, crustaceans
Fish
Waterfowl and diving birds
Common Loon
Gavia immer
Red-throated Loon
Gavia stellata
Horned Grebe
Podiceps auritus
Red-necked Grebe
Podilymbus grisegena
Breeds in interior
New England lakes;
winters along coast
Migrant; also winters
along New England coast
Winters throughout
New England
Winters locally along
New England coast
Fish
Fish
Fish and some shrimp
Fish
continued
121
Appendix III. (Continued),
Residency status
(Peterson 1980)
Diet
(Terres 1980)
Waterfowl and diving birds (continued)
Double-crested Cormorant
Phalacrocorax auritus
Great Cormorant
Phalacrocorax carbo
Mute Swan
Cygnus olor
Canada goose
Branta canadensis
Brant
Branta bernicia
Mallard
Anas platyrhynchos
Black Duck
Anas rubripes
Gadwall
Anas strepera
Canvasback
Aythya valisineria
Redhead
Aythya americana
Greater Scaup
Aythya marila
Lesser Scaup
Aythya affinis
Migrant; breeds on islands
along New England coast,
mostly north of Cape Cod
Winters along New
England coast
Year-round resident
inland and on coast in
Connecticut, Rhode Island,
and Massachusetts
Migrant; also resident
throughout New England
Migrant; some winter
north to southern Maine
Resident; increasing
due to stocking
Resident; most breed inland,
winter along coast
Breeds locally in New
England; some winter
Migrant; especially spring
in southern New England,
some winter
Migrant; especially spring
in southern New England,
some winter
Migrant; winters locally
Migrant; a few winter
north to Cape Cod
Primarily fish, also
crustaceans
Primarily fish, also
crustaceans
Aquatic plants
Primarily aquatic plants,
also molluscs and small
crustaceans
Aquatic marine plants
Aquatic plants, seeds,
grains
Aquatic plants, some
molluscs, crustaceans and
polychaetes during winter
Aquatic plants, invertebrates
Primarily aquatic plants,
also some molluscs
Primarily aquatic plants,
also some molluscs and
crustaceans
Primarily molluscs, also
aquatic plants
Primarily molluscs, also
aquatic plants
continued
122
Appendix III. (Continued),
Residency status
(Peterson 1980)
Diet
(Terres 1980)
Waterfowl and diving birds (continued)
Common Goldeneye
Bucephala clangula
Bufflehead
Bucephala albeola
White-winged Scoter
Melanitta deglandi
Surf Scoter
Melanitta perspicillata
Black Scoter
Melanitta nigra
Oldsquaw
Clangula hyemalis
Common Eider
Somateria mollissima
Harlequin Duck
Histrionicus histrionicus
Red-breasted Merganser
Mergus serrator
Winters along New England
coast
Winters along New England
coast
Migrant; locally common
in winter
Migrant; locally common
in winter
Migrant; locally common
in winter
Migrant; winters locally
offshore
Winters along New England
coast, along Cape Cod and
offshore islands
Winters locally along
coast, prefers rocky areas
Breeds locally in northern
New England; winters along
New England coast
Molluscs and crustaceans
Primarily shrimp, also
other crustaceans and
molluscs
Primarily molluscs
(especially blue mussel),
some crustaceans
Primarily molluscs
(especially blue mussel),
some crustaceans
Primarily molluscs
(especially blue mussel),
some crustaceans
Molluscs and crustaceans
Primarily mussels
Molluscs and crustaceans
Primarily fish, some
crustaceans
Wading birds
Great Blue Heron
Ardea herodias
Breeds locally on Maine
coast and elsewhere in
interior; occasionally
winters north to southern
Maine
Primarily fish, amphibians,
some crustaceans, small
mammals
continued
123
Appendix III. (Continued),
Residency status
(Peterson 1980)
Diet
(Terres 1980)
Wading birds (continued)
Little Blue Heron
Florida caerulea
Great Egret
Casmerodius albus
Snowy Egret
Egretta thula
Black-crowned Night Heron
Nycticorax nycticorax
Breeds locally north to
southern Maine
Breeds very locally north
to Massachusetts
Breeds locally north to
southern Maine
Breeds locally north to
eastern Maine
Fish, crustaceans
Primarily fish, and
crustaceans
Fish, crustaceans,
some polychaetes
Fish, crustaceans,
amphibians, occasionally
heron and tern chicks
Green Heron
Butorides striatus
Glossy Ibis
Plegadis falcinellus
Breeds throughout New
England, coast and interior
Breeds along coast to
southern Maine
Fish, crustaceans
Crustaceans
Raptors
Bald Eagle
Hal iaeetus leucocephalus
Osprey
Pandion haliaetus
Marsh Hawk
Circus cyaneus
Sharp-shinned Hawk
Accipiter striatus
Rough-legged Hawk
Buteo lagopus
Red-tailed Hawk
Buteo jamaicensis
Breeds locally in northern
Maine; some winter on
coast or interior throughout
New England
Breeds locally throughout
New England, coast and
interior, mostly in Maine
Migrant; breeds locally
in New England; winters
north to Cape Cod
Migrant on coast;
resident inland
Migrant; winters throughout
New England
Breeds throughout New
England; winters north
to central Maine and
Nova Scotia
Fish, carrion, birds
Fish
Small mammals, birds
Birds, small mammals
Sma 1 1 mamma 1 s ,
occasionally birds
Small mammals,
occasionally birds
continued
124
Appendix III. (Concluded).
Residency status Diet
(Peterson 1980) (Terres 1980)
Raptors (continued)
Merlin Migrant; occasionally Birds, small mammals
Falco columbarius winters throughout New
England
Peregrine Falcon Rare migrant Birds
Falco peregrinus
Others
Belted Kingfisher Breeds throughout New Primarily fish,
Megaceryle alcyon England; year-round some crustaceans
resident north to
northern Maine
Fish Crow Year-round resident Crustaceans, bird eggs
Corvus ossifragus Connecticut, Rhode Island,
Massachusetts
125
50272-101
REPORT DOCUMENTATION IuRepoRt no.
PAGE FWS/OBS-81/01
4. Title and Subtitle
The Ecology of New England Tidal Flats: A Community Profile
7. Author(s)
Robert B.
Whitlatch
9. Performing Organization Name and Address
University of Connecticut
Department of Marine Sciences
Marine Research Laboratory
Noank, Connecticut 06340
12. Sponsoring Organization Name and Address
National Coastal Ecosystems Team
Office of Biological Services, Fish and Wildlife Service
U.S. Department of the Interior
Washington, DC 20240
3. Recipient's Accession No.
5. Report Date
March 1982
8. Performing Organization Rept. No.
10. Project/Task /Work Unit No.
11. Contract(C) or Grant(G) No.
(C)
(G)
13. Type of Report & Period Covered
15. Supplementary Notes
16. Abstract (Limit: 200 words)
The purpose of this report is to provide a general perspective of tidal flats of New
England, the organisms commonly associated with them, and the importance of tidal flats
to the coastal zone viewed as a whole. The approach is taxonomically based although
there is also attention paid to the flow of organic matter through the tidal flat habi-
tat. The method of presentation is similar to that of Peterson and Peterson (1979) who
have described the tidal flat ecosystems of North Carolina. The reader, therefore, has
the opportunity of comparing and contrasting the physical and biological functioning of
the two regions. Chapter 1 begins with a general view of the physical, chemical, and
geological characteristics of tidal flat environments followed by a discussion of or-
ganic production and decomposition processes vital to these systems (Chapter 2). The
next three chapters deal with the benthic invertebrates (Chapter 3), fishes (Chapter 4),
and birds (Chapter 5) common to the New England tidal flats. The coverage within each
chapter reflects the published information available at the time of writing in addition
to the author's perception about the structure, function, and importance of each of the
taxonomic groups to the overall tidal flat system. The last chapter (Chapter 6) con-
siders the response of tidal flats to environmental perturbation as well as their value
to the New England coastal zone.
17. Document Analysis a. Descriptors
sand flats, mud flats, birds, fishes, benthic invertebrates
b. Identifiers/Open-Ended Terms
c. C0SAT1 Field/Group
18. Availability Statement
Unlimited
19. Security Class (This Report)
Unclass ified
20. Security Class (This Page)
21. No. of Pages
125
22. Price
(See ANSl-239.18)
See Instructions on Reverse
OPTIONAL FORM 272 (4-77)
(Formerly NTIS-35)
Department of Commerce
^U.S. GOVERNMENT PRINTING OFFICE: 1982—571-329 3
4-)
(0
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a
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(D-d)
LEGEND
Headquarters - Office of Biological
Services, Washington, D.C.
National Coastal Ecosystenns Teann,
Slidell. La.
Regional Offices
U.S. FISH AND WILDLIFE SERVICE
REGIONAL OFFICES
REGION 1
Regional Director
U.S. Fish and Wildlife Service
Lloyd Five Hundred Building, Suite 1692
500 N.E. Multnomah Street
Portland, Oregon 97232
REGION 2
Regional Director
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P.O.Box 1306
Albuquerque, New Mexico 87103
REGION 3
Regional Director
U.S. Fish and Wildlife Service
Federal Building, Fort Snelling
Twin Cities, Minnesota 55111
REGION 4
Regional Director
U.S. Fish and Wildlife Service
Richard B. Russell Building
75 Spring Street, S.W.
Atlanta, Georgia 30303
REGION 5
Regional Director
U.S. Fish and Wildlife Service
One Gateway Center
Newton Corner, Massachusetts 02158
REGION 6
Regional Director
U.S. Fish and Wildlife Service
P.O. Box 25486
Denver Federal Center
Denver, Colorado 80225
REGION 7
Regional Director
U.S. Fish and Wildlife Service
1011 E.Tudor Road
Anchorage, Alaska 99503
DEPARTMENT OF THE INTERIOR
U.S. FISH AND WILDLIFE SERVICE
As the Nation's principal conservation agency, the Department of the Interior has respon-
sibility for most of our nationally owned public lands and natural resources. This Includes
fostering the wisest use of our land and water resources, protecting our fish and wildlife,
preserving the. environmental and cultural values of our national parks and historical places,
and providing for the enjoyment of life through outdoor recreation. The Department as-
sesses our energy and mineral resources and works to assure that their development is in
the best interests of all our people. The Department also has a major responsibility for
American Indian reservation communities and for people who live in island territories under
U.S. administration.
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