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THE UNIVERSITY OF ALBERTA

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NAME OF AUTHOR
TITLE OF THESIS

DEGREE FOR WHICH
YEAR THIS DEGREE

Daniel Anton Soluk

LIFE HISTORY AND ECOLOGY OF AQUATIC
INSECTS ASSOCIATED WITH SHIFTING SAND
AREAS, WITH SPECIAL REFERENCE TO THEIR
CONTRIBUTION TO MACROINVERTEBRATE
BIOMASS AND PRODUCTION IN RIVERS.
THESIS WAS PRESENTED Master of Science
GRANTED Fall, 1983

Permission is hereby granted to THE UNIVERSITY OF
ALBERTA LIBRARY to reproduce single copies of this
thesis and to lend or sell such copies for private,
scholarly or scientific research purposes only.

The author reserves other publication rights, and
neither the thesis nor extensive extracts from it may
be printed or otherwise reproduced without the author's
written permission. ^ '

THE UNIVERSITY OF ALBERTA

LIFE HISTORY AND ECOLOGY OF AQUATIC INSECTS ASSOCIATED WITH
SHIFTING SAND AREAS, WITH SPECIAL REFERENCE TO THEIR
CONTRIBUTION TO MACROINVERTEBRATE BIOMASS AND PRODUCTION IN

RIVERS,
by

Daniel Anton Soluk

A THESIS

SUBMITTED TO THE FACULTY OF GRADUATE STUDIES AND RESEARCH
IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE

OF Master of Science

Department of Zoology

EDMONTON, ALBERTA
Fall, 1983

THE UNIVERSITY OF ALBERTA

FACULTY OF GRADUATE STUDIES AND RESEARCH

The undersigned certify that they have read, and
recommend to the Faculty of Graduate Studies and Research,
for acceptance, a thesis entitled LIFE HISTORY AND ECOLOGY
OF AQUATIC INSECTS ASSOCIATED WITH SHIFTING SAND AREAS, WITH
SPECIAL REFERENCE TO THEIR CONTRIBUTION TO MACROINVERTEBRATE
BIOMASS AND PRODUCTION IN RIVERS, submitted by Daniel Anton
Soluk in partial fulfilment of the requirements for the
degree of Master of Science.

ABSTRACT

Benthic macroinvertebrates associated with areas of
shifting sand in a river in central Alberta, Canada, were
studied over two years. The life history and ecology of the
three dominant species (Robacki a demei jerei , Rheosmittia
Sp. , and Pseud i ron central is) were intensively studied.

Larvae of the chironomids R. demei jerei and Rheosmittia
were associated with interstitial environments in shifting
sand, where they often attained densities greater than
50,000 larvae/m2. Robackia demei jerei was univoltine with an
extended emergence pattern; Rheosmittia Sp . was bivoltine.
Laboratory experiments indicated that larvae of both species
actively selected for coarse sand (0.50 to 2.00 mm).
Rheosmitt ia Sp. larvae appeared to feed primarily on
diatoms, while R. demei jerei larvae exhibited uncertain
dietary preferences.

Larvae of the predaceous heptageniid mayfly Pseud i ron
central is were associated with shifting sand areas only in
the later developmental stages, early stage larvae were
associated with marginal areas. P. central is larvae foraged
across the surface of the sediments, feeding primarily on
larvae of two chironmid species. Pseud i ron centralis larvae
occurred in low densities (<4 larvae/m2) and the population
exhibited a random dispersion pattern on shifting sands. The
movement of larvae from marginal areas to shifting sand
areas during development was hypothesized as a mechanism
which allowed either an escape from potential predators or

the exploitation of the abundant and accessible chironomid
fauna of shifting sand.

Overall, macroinvertebrate numbers were high on
shifting sand, although both biomass and production were
relatively low on a unit area basis. Shifting sand areas
occupy a large proportion of the bed in larger rivers, and
it is suggested that these areas make significant -
contributions to functional processes in river ecosystems.

ACKNOWLEDGEMENTS

I thank Dr. Hugh F. Clifford for his support and for
valuable suggestions made during the course of this study. I
extend special thanks to Drs. Jan J.H. Ciborowski, Paul A.
Murtaugh and Mr. Richard J. Casey, for critically reviewing
parts of this study. Thanks to my fellow graduate students
in aquatic ecology Dr. Robert Baker, Jay Babin, Vytenis
Gotceitas, John Richardson, and Edward Riley; all of which
contributed in frank interchanges of ideas.

Thanks to my brother Richard A. Soluk for able and
untiring assistance in the field; also to Teresa Lovell,
Roberta Miller and Elizabeth Thompson for assistance in both
the laboratory and field. Special thanks to Mrs. Gertrude
Hutchinson, both for her patience and technical assistance.

I also acknowledge the use of computing terminals provided
by Drs. F.S. Chia and E.E. Prepas.

Thanks to Dr. John F. Addi'cott for his valuable
insights in both scientific and personal matters. Thanks
also to Dr. Douglas A. Craig for his interest in the
morphology of these psammophi lous invertebrates.

Most especially I would thank my wife Laureen J. Soluk
not only for her untiring technical assistance, but also for
her love and support, without which this study would not
have been possible.

Financial assistance was provided by a NSERC operating
grant to Dr. H.F. Clifford and a Boreal Institute For
Northern Studies grant to the Author.

Table of Contents

Chapter Page

THESIS INTRODUCTION . 1

LITERATURE CITED . 5

I. THE LIFE HISTORY AND ECOLOGY OF Pseud iron
central is McDunnough (EPHEMEROPTERA:

HEPTAGENI IDAE) , A PREDACEOUS MAYFLY ASSOCIATED
WITH SANDY SUBSTRATES IN RIVERS . 7

ABSTRACT . 8

INTRODUCTION . 10

STUDY SITE . 11

MATERIALS AND METHODS . 13

Field Studies . 13

Experimental Studies . 17

RESULTS . 17

Life History . 17

Larval Distribution and Abundance . 21

Larval Biomass and Production . 26

Larval Behavior . 28

Experimental Studies . 33

DISCUSSION . 42

Life History Features . 42

Larval Habitat Associations . 43

Larval Dispersion and Spacing Behavior . 47

CONCLUSIONS . 48

LITERATURE CITED . 50

II. THE LIFE HISTORY AND ECOLOGY OF Robackia
deme ijere i K r u s . and Rheosm ittia sp. , two

RIVERINE CH I RONOM I DAE (DIPTERA) ASSOCIATED WITH
SHIFTING SAND SUBSTRATES IN RIVERS . 54

VI 1

ABSTRACT . 55

INTRODUCTION . 56

STUDY SITE . 57

METHODS . 57

RESULTS AND DISCUSSION . 62

Life Histories . 62

Larval Density and Distribution . 67

Larval Behavior . 74

Substrate Selection Experiments . 75

CONCLUSIONS . 89

LITERATURE CITED . 92

APPENDIX 1 . 95

Construction of the Core-Freezer . 95

III. THE MACRO INVERTEBRATES OF SHIFTING SAND AREAS: A
REEVALUATION OF THEIR CONTRIBUTION TO RIVER
ECOSYSTEMS . 97

ABSTRACT, . 98

INTRODUCTION . 99

STUDY SITE . 101

METHODS . 101

RESULTS . 103

DISCUSSION . 105

LITERATURE CITED . 110

THESIS CONCLUSION . 114

Further Studies . 116

LITERATURE CITED . 119

• • •

VI 1 1

List of Tables

Table Page

1.1 Criteria for identifying the prominent

substrate types in the Sand River . 15

1.2 Number of samples obtained from the

three categories of sandy substrate (SS=

shifting sand; MS= marginal sand; and

GS= gravelly sand) in which P. central is

larvae of particular stages were present

or absent . 22

1.3 The number of samples (collected on one
date from shifting sand areas)
containing particular numbers (A/) of

P. centralis larvae . 27

1.4 Production calculation for P. centralis
larvae, determined by the instantaneous
growth method (G= instantaneous growth

rate, <B>= mean standing crop, and P= product ion ).. 29

1.5 Abundance of three taxa of chironomid
larvae in the guts of three P. central is
larvae. The number in brackets is the
expected number of chironomid larvae
based on the mean benthic densities of
these taxa in the shifting sand (SS)

area . 31

1.6 Number of P. centralis larvae on each
substrate in pairwise comparisons of
seven different particle size
categories: I (0.06-0.12 mm), II
(0.12-0.25 mm), III (0.25-0.50 mm), IV
(0.50-1.00 mm), V (1.00-2.00 mm), VI
(2.00-3.36 mm), and VII (3.36-6.35 mm).

Asterisk indicates significantly

different pairs (binomial test, p<0.05) . 34

I. 7 The total number of larvae on each

substrate type in each run of Experiment 2 . 38

II. 1 Criteria for identifying the four major

substrate types in the Sand River . 58

II. 2 Mean head capsule lengths and widths for
each discernible larval instar of

RobacK i a demejere i and Rheosm ittia sp . 63

Table

Page

11. 3 Mean dry weight of all distinguishable
larval instars of Robackia demei jerei
and Rheosmittia Sp.. Also indicated is
the number of larvae weighed per sample,
and the number of samples weighed to

determine the mean . 64

11. 4 Value of ’F' ratio and the probability
(p) of this value from ANOVAs calculated
for Robackia demei jerei and

Rheosmittia sp. on 10 dates in 1981 . 68

1 1. 5 Mean number and variance of larvae per
cage for each substrate category in each
of the two experiments. The initial

number of larvae per cage was 10 . 78

II. 6 Mean depth in the substrate of the

oxidized (yellow) layer in shifting sand

(SS), marginal sand (MS), and gravelly

sand (GS ) . 88

III. 1 Production (dry weight) by instar and

total annual production (±95% C.I.) for

the two dominant chironomids in shifting

sand areas of the Sand River . 106

III. 2 Macroinvertebrate density and dry weight
biomass estimates reported from unstable
sandy substrates in some large

relatively unpolluted rivers (NR= not reported )... 1 07

List of Figures

Figure Page

1.1 Larval development of P. centralis based
on larval stage (see text). Horizontal
width of bars represents proportion of

larvae in each particular stage . 18

1.2 Larval development of P. centralis based
on mean larval headwidth. Vertical bars

represent one standard error of the mean . 19

1.3 Number of P. centralis larvae obtained
from the three categories of sandy
substrate: shifting sand (SS), marginal

sand (MS), and gravelly sand (GS) . 23

1.4 Mean larval density (±S.E.) of

P. central is in the Sand River based on
weighted estimates from the three types
of sandy substrate . 25

1.5 The mean number of P. central is larvae
per tray, as a function of larval

density in the experimental tank . 41

11. 1 Relative frequency of discernible larval
instars of Robackia demei jerei and

Rheosmitt ia sp. over the study period . 65

1 1. 2 Mean larval density of Robackia
demei jerei on the three substate types
(SS is shifting sands, MS is marginal

sands, and GS is gravelly sand) . 69

1 1. 3 Mean larval density of Rheosmitt i a sp.
on the three substate types (SS is
shifting sands, MS is marginal sands,

and GS is gravelly sand) . 70

11. 4 Mean dry weight (±S.E.) of larval
Robackia demei jerei on the three

substrate types . 72

11. 5 Mean dry weight (±S.E.) of larval

Rheosm i tt i a sp. on the three substrate types . 73

11. 6 Mean particle size distribution by
weight (g) of substrate from the

shifting sand (SS) area . 82

Figure

Page

II .7

Mean particle
weight (g) of
marginal sand

size distribution by

substrate from the

(MS ) area . .

. 83

II .8

Mean particle
weight (g) of
gravelly sand

size distribution by

substrate from the

(GS ) area . .

. 84

II .9

Mean larval density (±S.E.) of
chironomids other than R. demei jerei and
Rheosmitt ia sp. on the three substrate types..,

. 90

11.10

The dimensions

(cm) of the modified

core-freezer for sampling loosely
consolidated sandy substrates (all
diameters are i.d.). ’A' is the adapter;

?Bf is the penetration ring . 96

III.1 Mean dry weight biomass (±S.E.) of three
categories of benthic invertebrates in
the Sand River; all categories are
inclusive of lower categories (Rb= R.
demei jerei and Rh= Rheosmitt ia sp.).

104

List of Plates

Plate Page

1.1 Aerial view of the mouth of the Sand
River (A= Sand River; B= Beaver River).

Study area is indicated by the two

arrows. Insert indicates location in Alberta . 12

1.2 Apparatus used in the second experiment
to examine substrate selection in

Pseud iron centralis larvae . 36

II. 1 Experiment apparatus used to test for
substrate selection in fourth instar
Roback i a deme i jere i and Rheosm itt i a
larvae. In the foreground is one of the
substrate cages (see text) . 76

X 1 1 1

THESIS INTRODUCTION

Rivers have been important to the development and
maintenance of both modern and past civilizations.
Examination of a map of the world quickly confirms that most
of the major cities are located in close proximity. to large
navigable rivers. Despite the importance of these rivers in
transportation, waste disposal, electrical generation,
fisheries, and as sources of freshwater for both human and
agricultural consumption, the biota of these systems has
seldom been studied.

Large lowland rivers exhibit widely fluctuating
discharge, high mean current velocities, and are relatively
deep. These characteristics make studies of the biota of
these rivers both difficult and expensive, and thus most
stream ecologists have focused their research on smaller
headwater streams. There are few quantitative studies of the
lower reaches of river systems, and generalizations about
river ecosystems have often stressed processes that are
important primarily in headwater areas.

Most studies carried out in lowland rivers are
conducted by or for government agencies, usually with the
intent of assessing the impact of some human activity on the
biota of a particular river. Thus, most studies of rivers
usually have relatively narrow objectives and often only
examine organisms that are associated with artificial
substrates or one type of habitat in the river bed. The use
of artificial substrates has often been criticized, because

the relationship between the communities inhabiting these
substrates and those inhabiting natural substrates in the
river bed is only poorly understood (Rosenburg and Resh,
1982). When benthic macroinvertebrate communities are
examined, usually only those found in riffle or silty
backwater areas are considered (Barton, 1980). Although
these areas are certainly prominent habitat types, they
usually occupy only a small proportion of the mainstream
channel of most rivers.

Sand is the dominant substrate material in the bed of
most larger lowland rivers (Leopold et al . , 1964). A variety
of physical and chemical factors, such as the friability of
large stones and the crystal structure of silicates,
contribute to the dominance of sand-sized material (Leopold
et al . , 1 964 ) .

Hynes (1970) distinguishes between two types of sandy
habitats: mixtures of sand and silt, which form a firm
substrate, and shifting sands, which form a loosely
consolidated soft substrate. Sand and silt areas usually
occur marginally as a narrow band roughly paralleling the
river banks, and shifting sand areas usually dominate the
central channel.

Shifting sand areas have generally been considered
hostile environments for benthic macroinvertebrates, and
have been indicated as supporting only a few species and
individuals (Hynes, 1970). This view has generally been
confirmed by most studies that have examined shifting sand

areas in rivers (Berner, 1951; Monakov, 1968; Northcote et
al . , 1976; Seagle et al . , 1976). However, studies of the
fauna of some large rivers in the U.S.S.R. (Zhadin and Gerd,
1961), and intensive studies carried out on the Athabasca
River (Barton and Lock, 1979; Barton, 1980) have indicated
that large numbers of organisms could be found in shifting
sand areas.

My study was undertaken to examine the potential
contribution of shifting sand areas to both
macroinvertebrate biomass and production in river systems.

It was reasoned that if the small macroinvertebrates
associated with shifting sand areas occurred in high
densities and exhibited high generation turnover rates then
these areas could be potential sources of a significant
proportion of the total secondary production in river
systems .

The Sand River in east-central Alberta was used as a
representative river since its moderate size allowed a
relatively intensive quantitative study to be conducted with
a reasonable degree of continuity and effort. Although it is
not a large river, it possesses the macroinvertebrate fauna
typical of large rivers in North America, including many
species considered to be quite rare.

Since little is known of the biology of psammophi lous
invertebrates in rivers, the first two chapters of this work
describe various aspects of the life history and ecology of
the three dominant species of macroinvertebrate found in

shifting sand habitats in the Sand River. In the third
chapter, using data on the life history and patterns of
abundance reported in the first two chapters, I estimate the
potential macroinvertebrate production from shifting sand
areas and attempt to evaluate the contribution and role of
these areas in river ecosystems.

LITERATURE CITED

Barton, D.E. 1980. Benthic macroinvertebrate communities of
the Athabasca River near Ft. Mackay, Alberta.
Hydrobiologia 74:151-60.

_ , and M.A. Lock. 1979. Numerical abundance and biomass of

bacteria, algae and macrobenthos of a large northern
river, the Athabasca. Int. Rev. ges Hydrobiol.

64(3) : 345-59 .

Berner, L.M. 1951. Limnology of
Ecology 32 ( 1 ) : 1 - 1 2 .

the lower Missouri River.

Hynes, H.B.N. 1970. The ecology of running waters. Univ. of
Toronto, Toronto. 555 p.

Leopold, L.B., M.G. Wolman, and J.P. Miller. 1964. Fluvial
processes in geomorphology. Freeman, San Francisco.

522 p .

Monakov, A.V. 1969. The zooplankton and zoobenthos of the
White Nile and adjoining waters in the Republic of
Sudan. Hydrobiologia 33:161-85.

Northcote, T.G. , N.T. Johnston, and K. Tsumura. 1976.

Benthic, epibenthic and drift fauna of the Lower Fraser
River. Technical Report 11, Westwater Research
Institute, University of British Columbia. 227 p.

Rosenburg, D.M. , and V.H. Resh. 1982. The use of artificial
substrates in the study of freshwater benthic
macroinvertebrates, p 175-235, In J. Cairns, Jr. [ed.]
Artificial substrates. Ann Arbour Science, Ann Arbour.
273 p.

Seagle, H.H. , J.C. Hutton, and K.S. Lubinski 1982. A

comparison of benthic invertebrate community composition
in the Mississippi and Illinios Rivers, Pool 26. Jour.
Freshw. Ecol. 1(6): 637—50 •

Zhadin, V.I., and S.V. Gerd. 1961. Fauna and flora of the
rivers, lakes and reservoirs of the U.S.S.R.. (Transl.
[1963] from Russian by Israel Program for Scientific
Translations) Smithsonian Institution and National
Science Foundation, Washington. 626 p.

i. the life history and ecology of Pseud i ron central is

McDunnough (EPHEMEROPTERA: HEPTAGEN 1 1 DAE ) , A PREDACEOUS
MAYFLY ASSOCIATED WITH SANDY SUBSTRATES IN RIVERS.

ABSTRACT

This study examines aspects of the life history,
distribution, abundance, and behavior of Pseud i ron centralis
McDunnough in a river in central Alberta. The population
studied exhibited a univoltine summer life cycle: larvae
hatched in late April, developed rapidly, emerged as adults
in late June and throughout July, and spent the remainder of
the year in the egg stage. Pseud i ron central is larvae were
found in association with three types of substrate in the
river bed: shifting sand, marginal sand, and gravelly sand.
The substrate associations of larvae changed over the course
of development; stage I larvae were associated with marginal
sand areas, and stage III and IV larvae were associated with
shifting sand areas. Larval density was found to be
relatively low (<4 larvae/m2), however, larval mortality
also appeared to be low. Stage III & IV larvae exhibited a
random dispersion pattern on shifting sand substrates.
Secondary production of P. central is larvae was estimated to
be 18.4 and 5.67 mg/m2/yr in 1980 and 1981 respectively.
Pseud i ron central is larvae were active epibenthic predators,
appearing to feed primarily on psammophi lous chironomid
larvae. An experiment examining spacing behavior in P.
central is larvae suggested that interactions between
individuals were probably not important determinants of
larval density or distribution. Substrate selection
experiments indicated that stage III P. central is larvae
avoided gravel, but did not indicate discrimination against

fine sand or silt. Stage I larvae are probably restricted to
marginal sand areas because they cannot cope with the
physical stresses in shifting sand areas. The shift in
association to shifting sand areas is hypothesized to be a
mechanism that allows the animal to exploit either the
greater prey availability or the lower numbers of potential
predators and competitors in these areas.

INTRODUCTION

Sand is a dominant component in the bed of most large
rivers. However, very little is known of the ecology of
organisms and the nature of communities found in sandy
habitats in large rivers.

Several species of Ephemeroptera are associated with
the sandy substrates of large rivers. These species have
been of interest to systematists because many exhibit
aberrant morphologies that make their phylogenetic placement
difficult. Behaviorally , the larvae of many of these species
are distinct from the majority of Ephemeroptera in being
predaceous. One species ( Dolania americana Edmunds and
Traver) has been studied in detail (Tsui and Hubbard, 1979;
Harvey et a7 . , 1980; Sweeney and Vannote, 1982), but
knowledge of most sand-dwelling mayflies is restricted to
anecdotal comments by collectors. Knowledge of the ecology
of these species could contribute greatly toward an
increased understanding of important ecological processes in
one of the dominant habitat types in the lower reaches of
most river systems.

Pseudiron larvae are associated with sandy river beds
in medium to large rivers over much of North America
(Edmunds et al . , 1976). The carnivorous behavior of larval
Pseudiron and some aspects of their foraging behavior were
discussed by Edmunds et a/. (1976). Tsui and Hubbard (1979)
speculated on the nature of habitat partitioning between
Pseudiron meridional is Traver and another predaceous mayfly,

Dolania americana (P. mer id ional i s occupies the surface of
the sand while D. americana burrows beneath it).

There are two described species of Pseud iron: P.
meridional is Traver occurs in the southeastern United
States, and P. central is McDunnough is found in western and
central North America (Edmunds et al . , 1976). Pseud i ron
centralis is found in all major drainage systems in Alberta.

This study examines aspects of the life history and
ecology of P. centralis in a medium-sized river in central
Alberta, Canada. Two approaches were used: (1) a
field-correlative approach was utilized to assess the life
history and to elucidate patterns of distribution and
abundance of this species; and (2) a laboratory-experimental
approach was used to assess some of the proximal
determinants of the observed patterns.

STUDY SITE

The Sand River is located on the southern edge of the
mixed boreal forest of Alberta (Plate 1.1). It drains
approximately 5000 km2 of largely forested land and has its
headwaters in the Department of National Defense Primrose
Lake Air Weapons Range. The Sand River is the major
tributary of the the Beaver River System in Alberta and
supplies approximately 75% of the total discharge. The
Beaver River is a tributary of the Churchill River which
drains into Hudson Bay.

Plate I . 1
Sand River
two arrows

Aerial view of the mouth of the Sand River (A=
; B= Beaver River). Study area is indicated by
. Insert indicates location in Alberta.

the

During the study period the mean discharge of the Sand
River was approximately 12 m3/s with a range from 1.5 to
42.9 m3/s (Environment Canada, 1981; and unpublished data
courtesy of Environment Canada, Water Survey of Canada).

The bed of the Sand River is composed primarily of sand
derived from the extensive deposits of this material found
in Northeastern Alberta. In the mainstream channel, sand
forms moving dunes 6 to 15 cm in height, which may be riding
on larger dunes with very long wavelengths and heights of
over 50 cm. Occasional gravel bars occur in the bed and
there is a narrow marginal band of silty deposits.

The study area (54° 23'N; 111°02'W) was at the mouth of
the Sand River (Plate 1.1). Thalweg current velocities
ranged from 40 to 150 cm/s at the study site, but were
usually about 60 cm/s. Immediately upstream of its mouth,
the Sand River is 30 to 50 m in width with a maximum depth
of 1.5 to 2 m; below its mouth the width' of the flow widens
and the mean depth decreases to between 1 and 1.5m.

At the study site the Sand River is quite warm with an
average summer temperature of approximately 20°C; the
maximumum temperature recorded was 27°C.

MATERIALS AND METHODS

Field Studies

Four major substrate types were recognized: "shifting
sands" (SS), "marginal sands" (MS), "gravelly sands" (GS),

and "silt" (SI). These substrate types were defined using
the visual and tactile criteria presented in Table 1.1.

Data on the distribution and abundance of P. central is
larvae were obtained from samples taken along ten transects
established at 5 m intervals along a 50 m reach at the mouth
of the Sand River. Samples were taken at intervals
determined by the availability of the different substrate
types along each of these transects. Samples were obtained
from the middle area of those substrates that occurred in
narrow bands parallel to the banks and at intervals of
approximately 5, 10, 20, and 30 m from the bank wherever
possible in SS areas.

Sampling was primarily bi-weekly throughout the open
water season (April to November) in 1980, from April to the
end of July in 1981, and on one date in June 1982.

A Surber sampler (mesh 0.243 mm) modified with a handle
and a extra long net bag was the chief sampling device used
throughout the study. The depth and velocities encountered
precluded the use of closed cylinder type samplers. Samples
were collected by disturbing the substrate, within a 930 cm2
area defined by the sampler, with the foot for 30 seconds.
Samples were placed in jars and preserved with 95% ethanol.

In the laboratory, organic material was separated from
inorganic material by elutriation, examined under a
dissecting microscope at 1 2X magnification, and the
P. central is larvae removed. A standard "D" frame dipnet
(mesh size 0.5 mm) was used to collect additional larvae for

Table 1.1 Criteria for identifying the prominent substrate
types in the Sand River.

Substrate Category

Visual and Tactile Criteria

Silt (SI)

soft sticky texture, abundant visible
silt, dark grey or black color

Marginal Sand (MS)

firm fine-grained texture, some visible
silt, few sand particles in active
motion

Gravelly Sand (GS)

firm coarse texture, abundant gravel
apparent, few sand particles in active
motion

Shifting Sand (SS)

soft loose texture, no apparent silt,
actively moving sand dunes

life history analysis, dry weight determinations, and
experimental analysis.

Larval stages were designated using the criteria of
Clifford (1970): stage I larvae lack wing pads, stage II
larvae possess wing pads whose length is less than the
distance between them, stage III larvae have wing pads
longer than the distance between them, and stage IV larvae
have the darkened wing pads characteristic of the last
larval instar. Head capsule widths were measured at the
widest point (just posterior to the eyes). All measurements
were made at 25X or 50X magnification using a eyepiece
micrometer on a dissecting microscope.

The mean dry weight of larvae was determined from
frozen specimens, which were thawed and dried at 60°C for 24
hrs. Weights were measured on a microbalance to the nearest
0.002 mg.

The food habits of P. central is larvae were determined
by examination of the foregut of 20 individuals belonging to
stage II, III or IV. The contents were quantified by direct
counts of the type and number of organisms in the foregut.

To determine fecundity, female subimagoes (reared from
larvae kept for a short period in the laboratory) were
dissected, and all eggs removed and counted. The eggs of
these females were then placed in dechlor inated water and
the dimensions measured at irregular intervals over a 24
hour period to determine egg size.

Observations of the behavior of P. centralis larvae
were carried out in various types of artificial streams.

Experimental Studies

Substrate selection by P. central is larvae was
investigated using three different experimental designs,
described in the results section. The spacing behavior of
these larvae was examined in one experiment. All substrates
used in these experiments were natural mineral substrates
removed from the bed of the Sand River. Before being used,
these substrates were heated to 600°C for 48 hours, dry
sieved into the appropriate size class, and washed with
distilled water.

RESULTS

Life History

Pseud i r on centralis was univoltine in the Sand River
(Figs. 1.1 and 1.2), apparently overwintering in the egg
stage. The relatively large first instar larvae of this
species (headwidth approximately 0.24 mm, bodylength
approximately 0.90 mm) first appeared in late April and were
easy to distinguish because compound eyes, ocelli, and gills
were not apparent. Neither quantitative nor intense
qualitative collecting yielded P. centralis larvae in late
autumn before the formation of ice.

n=6 7 10

15-30 01-15 15-31

19 42 7 6

f 7 * +

Jn Jn Jl Jl

01-15 15-30 01-15 15-31

DATE

Figure 1.1 Larval development of P. centralis based on
larval stage (see text). Horizontal width of bars represents
proportion of larvae in each particular stage.

HEAD WIDTH (mm)

7 6

Figure 1.2 Larval development of P. centralis based on mean
larval headwidth. Vertical bars represent one standard error

of the mean.

After the larvae hatched, subsequent development was
rapid with mature larvae appearing in the population in less
than 8 weeks. The low number of stage IV larvae collected is
likely an artifact due to the relatively short duration (2
to 3 days under laboratory conditions) of this stage. Adult
emergence was not observed at the study site, but the
presence of stage IV nymphs indicated emergence from- late
June to the end of July. This pattern is probably similar
over the entire range of this species; all reported adult
records of P . central is are from June and July (McDunnough,
1931; Burks, 1953). Thus it appears that P. centralis spends
most of the year in the egg stage, its life cycle being best
described, in the terminology of Clifford (1982), as a
univoltine summer cycle

The swarming behavior of adult Pseud i ron spp. has never
been reported, and I was unable to find swarming adults.
However, emerging subimagoes and spent imagoes were
collected from the water's surface at one locality during
mid to late morning.

The fecundity of females appears to be relatively low
compared to those recorded for other large mayflies
(Brittain, 1982), with 624 and 467 being the total number of
eggs encountered in the two females examined. The mean dry
weight of eggs was 0.005 mg (S.D. =0.001) based on the
weights of five groups of ten eggs.

Needham et al . (1935) figure the egg of Pseud i ron sp.
removed from a preserved specimen of an unspecified stage

’

(presumably subimago or imago). The egg was ellipsoid in
shape with dimensions of approximately 0.190 x 0.310 mm. The
size and shape of this egg was similar to that of the
compressed eggs found within the bodies of female subimagoes
of P. central is from the Sand River. However, when I exposed
these eggs to water, they rapidly became more rotund,
attaining dimensions of approximately 0.33 x 0.41 mm.

One egg was collected from the shifting sand area of
the Sand River on Oct. 17, 1981. This egg had approximate
dimensions of 0.35 x 0.41 mm, and a number of sand grains
were firmly adhering to it. Positive identification of the
egg as that of P. central is was possible because the egg
enclosed an almost fully developed first instar larvae.

Larval Distribution and Abundance

Pseud i r on centralis larvae were restricted to the three
types of sandy substrates described in Table 1.1; no larvae
were collected from silt areas. Larval associations with the
sandy substrate types appeared to change during larval
development (Fig. 1.3).

Contingency table analysis (Zar, 1974) was used to
determine whether particular larval stages exhibited
associations with particular substrate types (Table 1.2).
Where significant (p<0.05) associations were indicated,
subdivision of the contingency table (Zar, 1974) was used to
assign particular associations. Data for each stage were
assembled only from dates where the stage in question was

■

Table 1.2 Number of samples obtained from the three
categories of sandy substrate (SS= shifting sand; MS=
marginal sand; and GS= gravelly sand) in which P. central is
larvae of particular stages were present or absent.

Stage I Larvae

Substrate Category

Samples with
larvae :

Total

Absent

136

Present

1 1

Total

157

Stage I I Larvae

Absent

126

Present

Total

140

Stage III & IV Larvae

Absent

Present

Total

125

Percent of Total Larvae Collected

Larval Stage

Substrate Type
[ZJ MS

EZ3 GS
Q ss

Figure 1.3 Number of P. centralis larvae obtained from the
three categories of sandy substrate: shifting sand (SS),
marginal sand (MS), and gravelly sand (GS).

likely to be present (Fig. 1.1); stages III and IV were
considered together. The analysis indicated that stage I
larvae were significantly (p<0.05) associated with MS areas
and stage III and IV larvae were significantly ( p< 0.001 )
associated with SS areas. The low number of stage II larvae
necessitated a pooling of the MS and GS categories; these
larvae exhibited no statistically significant
differentiation between this pooled category and SS.

There did not appear to be substantial changes in
substrate availability during the larval period in either
year of this study; hence, it seems unlikely that the shift
in substrate association can be attributed to changes in
substrate availability.

Pseud i ron centralis larvae occurred at low densities
and much effort was required to collect them. Figure 1.4
illustrates the mean larval densities in the Sand River in
1980 and 1981. These densities were obtained by summing the
density estimates of P. central is on GS, MS, and SS areas
weighted with respect to the proportion of river bed that
they represent. At the study site the proportions were
estimated to be approximately 70% for SS, and 15% each for
both MS and GS areas, based on the occurrence of these
substrates along the transects. The study site was generally
representative of the bed of the Sand River, except that the
GS area was somewhat over-represented.

Densities of P. central is larvae remained relatively
constant throughout the period of larval development,

Density (number of larvae/m

u. o

^ 3. 5
3.0

2.5

2.0

1.5

1 . 0

0.5

0.0

Date

Figure 1.4 Mean larval density (±S.E.) of P. centralis in
the Sand River based on weighted estimates from the three
types of sandy substrate.

suggesting relatively low rates of larval mortality. Despite
the low density of P. central is larvae, individuals were
collected with a high degree of regularity on a per sample
or per unit effort basis. A series of 24 samples were
collected on June 15, 1982 from SS areas to determine the
nature of the dispersion pattern of P. central is larvae on
this substrate. Numbers of larvae in each sample (Table 1.3)
were compared with values that would be expected from a
Poisson distribution utilizing the index of dispersion
(Southwood, 1978). The analysis indicated that P. centralis
larvae were randomly distributed (x2=28.70, p>0.10) over
shifting sand areas.

The larval density in 1982 was higher (10.16 larvae/m2
for all sandy substrates) than during the previous two years
(Fig. 1.4), but this change was not considered large enough
to affect the dispersion pattern of larvae.

Larval Biomass and Production

The regression

log(weight)= 3 . 37 ( log [head width]) - 0.48 (r2=0.97, n=64)

was generated to predict the weight of larvae (mg) based on
head capsule width (mm). This regression was based on the
dry weights of larvae collected on June 15 and 23, 1982 (the
weight of first instar larvae was estimated using the mean
weight of the eggs). The regression was used to interpolate

• • *; ' . • -• 1 v z 1 r 1 1 ; *

Table 1.3 The number of samples (collected on one date from
shifting sand areas) containing particular numbers (A/) of
P. centralis larvae.

Number of Number of

larvae (A/) samples with

"N" larva

the weights of all P. central is larvae collected on
particular dates during the study. These weights were in
turn used with the mean larval densities (Fig. 1.4) to
obtain estimates of standing crop (Table 1.4).

Production of P. central is larvae in the Sand River
were obtained using the instantaneous growth method (Waters
and Crawford, 1973; Waters, 1977). The total annual larval
production of P. central is was found to be 18.40 and 5.67
mg/m2/year for 1980 and 1981 respectively. These estimates
were relatively low on a per unit area basis, when compared
with herbivirous or detr it ivorous mayflies in other habitats
(Waters , 1 977 ) .

Larval Behavior

Examination of foregut contents indicated that
P. central is larvae preyed primarily on chironomid larvae
( Robackia demei jerei and Rheosmitt ia) characteristically
associated with the sandy habitats of the Sand River. The
only other prey items found in the guts of P. central is
larvae were small Baetis and Centroptilum mayfly larvae.

To determine whether P. central is larvae prey more
frequently on particular species of chironomids, I examined
the frequency of occurrence of chironomid taxa in the guts
of three P. centralis larvae collected from the SS area June
9, 1981. Table 1.5 compares the number in each of three
chironomid taxa found in the guts of stage III P. centralis
larvae with that expected to be found based on the the

Table 1.4 Production calculation for P. centralis larvae,
determined by the instantaneous growth method (G=
instantaneous growth rate, <B>= mean standing crop, and P=
production) .

1980

Date

Density

Mean

Standing

<B>

(no./m2 )

Wt. (mg)

crop
(mg/m2 )

(mg/m2 )

1 .72

0.010

0.017

1 .92

0.06

0.12

1.61

0.068

0.109

2.12

0.42

0.90

1.30

0.568

0.738

2.37

7.23

17.15

2.25

6.095

13.714

0.02

11.52

0.23

1.50

6.221

9.332

total

18.40

1981

2.22

0.004

0.009

-0.29

0.01

0.00

0.83

0.003

0.002

4. 18

0.07

0.29

0.69

0.197

0.136

2.49

1 .35

3.37

1.08

2.379

2.569

0.55

3.67

2.01

1.16

4.116

4.775

total

5.67

benthic densities of the chironomid taxa in SS areas on June
9 , 1981 (Chapter 2). Chi-square goodness-of - f i t analysis was
used to determine whether there were significant differences
(p<0.05) between these values. Because of the low numbers
expected in the "other chironomids" category, it was
necessary to pool this category alternately with the other
two categories to use Chi-square analysis. The analysis
indicated that the guts of the P. central is larvae
consistently contained significantly (p<0.025) more
Rheosmitt ia sp. larvae, and less Robackia demei jerei larvae
than would be expected based on the estimated benthic
densities of these chironomids. But the apparent selection
for Rheosmitt ia larvae by P. centralis does not necessarily
imply active discrimination; it may only reflect the
relative availability of the various species.

In laboratory streams, P. centralis larvae foraged
principally along the upstream face of actively moving sand
dunes. Their long maxillary palpi were extended into the
substrate in the same manner as that described for Anal etr i s
eximia by Lehmkuhl (1976). In the presence of sufficiently
high current velocities (high enough to cause significant
movement of sand), P. central is larvae exhibited a unique
foraging behavior. A larva would, with its anterior end
facing the current, rear-up on its prothoracic and
mesothoracic legs, bend the head steeply downward, and
deflect the flow of water at the surface of the sand. This
caused a rapid erosion of the sand in the area beneath the

Table 1.5 Abundance of three taxa of chironomid larvae in
the guts of three P. centralis larvae. The number in
brackets is the expected number of chironomid larvae based
on the mean benthic densities of these taxa in the shifting
sand (SS) area.

Taxa

Larva 1

Larva 2

Larva

Rheosmittia sp.

79(71 )

49(42)

62(54)

Roback i a deme i jere i

2(10)

0(6)

0(7)

other chironomids

2(2)

0(1)

front margin of the head and presumably exposed chironomid
larvae. The P. central is larva would move slowly backwards
along the face of the dune, usually leaving behind a shallow
groove, which was rapidly filled by eroding sand. When a
chironomid larva was encountered, it was rapidly pulled from
the sediment, manipulated by the mouthparts, and engulfed,
either head or caudal end first. The rapid consumption
(large chironomid larvae being consumed in 1 to 3 seconds)
and the presence of intact chironomid larvae in the foregut
of P. central is suggest that little mastication occurs.

Pseud i ron centralis larvae were also observed to use
their heads in a similar manner to aid in avoiding the
direct effects of the current. Using its claws to retain a
hold on the sediment, a larva would rear-up on all legs and
bend the head downward. Water flow was thus deflected
downward causing a cavity to be eroded in the sand between
the legs. The body was then pulled down by the legs into
this shallow cavity. The dorsal surface of the larva was
thus made flush with the surface of the substrate, and much
of the dislodging effect of the current was probably
avoided. In this position, eroding sand grains would roll
over the larva, sometimes burying it beneath a thin layer of
sand. This behavior was frequently observed after a foraging

bout .

Experimental Studies

Experiment 1 The first experiment consisted of a series of
pairwise comparisons between seven substrate particle size
categories ranging from 0.06 to 6.35 mm (Table 1.6). Each of
the two substrate types to be compared was placed in two
trays with dimensions of 16.0 x 5.5 x 1.6 cm, and these
trays were then arranged in a 2 x 2 latin square design. The
four trays were then placed in an artifical stream driven by
a paddle wheel (Ciborowski, 1982); the stream had a width of
11 cm and a water depth of 14 cm. One stage III larva was
placed on the substrate in each of the four trays and the
stream was then run at a surface velocity of 12 cm/s for 15
minutes. This velocity was the maximum velocity that could
be achieved without significant outwash of the finer
substrate particles. After the 15 minutes, the number of
larvae on each of the substrates was counted and recorded.

Four replicates were obtained for each pairwise
comparison. Data were analyzed for each pairwise comparison,
using a two-tailed binomial test (Zar, 1974) to indicate the
presence of significant (p<0.05) differences between the sum
of the four replicates.

Table 1.6 indicates, for each particle size class, the
total of the four replicates in each pairwise comparison.
Particle sizes in the range from 0.063 - 2.00 mm appeared to
be the only sizes actively chosen by larvae of P. central is.
When larvae were given the choice between the two coarsest

Table 1.6 Number of P. central is larvae on each substrate in
pairwise comparisons of seven different particle size
categories: I (0.06-0.12 mm) , II (0.12-0.25 mm), III
(0.25-0.50 mm), IV (0.50-1.00 mm), V (1.00-2.00 mm), VI
(2.00-3.36 mm), and VII (3.36-6.35 mm). Asterisk indicates
significantly different pairs (binomial test, p<0.05).

Particle Size I II III IV V

Category

—

1 1

—

13*

1 1 1

—

14*

1 *

VI I

1 *

VI VI I

15*

1 6*

16*

14*

1 6*

15*

1 6*

1 1

15*

particle size classes (2.00-3.36 and 3.36-6.35 mm), 10 of
the 16 larvae left the substrate and drifted in the water
column after spending only a short time on the substrate. In
contrast, the highest number of larvae drifting in all the
other comparisons was two.

Although discrimination was exhibited between
substrates of nonadjacent size classes, no significant
discrimination was exhibited between adjacent classes. This
suggests that if the experiment had been designed only to
compare adjacent classes then no significant selection would
have been exhibited.

Experiment 2 To clarify some of the ambiguity of the first
experiment, a second experiment was undertaken. The second
experiment tested for selection amongst four substrate size
categories simultaneously. Each category was placed in four
plexiglas trays (6.0 x 6.0 x 2.3 cm), which were randomized
within a 4 x 4 arrangement with the constraints that no
substrate category occurred more than once in any column or

row and all substrate categories contacted all other
substrate categories the same number of times (Plate 1.2).
Two runs were conducted, the first utilizing the substrate
size categories 0.06 - 0.12, 0.12 - 0.25, 0.25 - 0.50, and
0.50 - 1.00 mm; and the second using the categories 0.25 -
0.50, 0.50 - 1.00, 1.00 - 2.00, and 2.00 - 3.36 mm. One
stage III larva was placed on the substrate in each of the
16 trays, and the number of larvae on each of the substrate

Plate 1.2 Apparatus used in the second experiment

to examine

substrate selection in Pseud / r on central is larvae

types was counted after one hour. Each run consisted of four
replicates, all carried out in an air-powered recirculating
stream having a width of 30 cm, a depth of 7 cm, and a mean
velocity of 12 cm/s.

Results are presented in Table 1.7. A chi-square
goodness-of-f i t test was used to analyze each of the runs
separately .

The first run of this experiment examined substrate
selection for the four categories from 0.06 to 1.00 mm. The
chi-square value was 15.19, indicating significant
differences (p<0.005) between the four categories.
Subdivision of the chi-square analysis (Zar, 1974) indicated
that the two smallest size categories (0.06-0.12 and
0.12-0.25 mm) were selected significantly (p<0.05) more
often than were the two larger categories (0.25-0.50 and

O. 50-1.00 mm). In the second run, the chi-square value was
38.96 indicating highly significant differences (p<0.001)
between the categories. Subdivision of the chi-square
analysis further indicated that particle sizes from 0.25 to
1.00 mm were selected significantly more often (p<0.05) than
particle sizes from 1.00 to 3.36 mm.

The results of the two experiments indicate that

P. central is larvae select most frequently for fine to
medium sands (0.06-1.00), selecting coarse sand (1.00-2.00
mm) less often, and generally avoiding substrates with
particle sizes greater than 2.00 mm.

Table 1.7 The total number of larvae on each substrate type
in each run of Experiment 2.

Total Number of Larvae
on Each Category

Particle Size First Run Second Run

Category (mm)

0.06-0.12 25

0.12-0.25 14

0.25-0.50 8 23

0.50-1.00 7 29

1.00-2.00 - 6

2.00-3.36 - 0

Experiment 3 A third experiment was conducted to determin
whether P. central is larvae discriminate between fine sand
(particle size 0.06 - 0.12 mm) and silt (particle size <0.
mm). Four trays (11.5 x 11.5 x 3.0 cm), two containing fin
sand and two containing silt, were arranged in a 2 x 2 lat
square. Two larvae were placed on the substrate in each
tray. After one hour, the number of larvae on each of the
two substrate types was recorded. There were four
replicates. This experiment was run in the absence of
current (a highly artificial situation for P. centralis
larvae), since even the lowest detectable water velocities
caused some outwash of silt. Results of the four replicate
of this experiment were summed to yield counts of 17 and 1
for the fine sand and the silt categories respectively.
Chi-square analysis of these data indicated no significant
(x2=0.32, p>0.50) discrimination between the two substrate
This lack of discrimination was surprising, because
P. central is larvae seem to discriminate strongly against
silt areas in the Sand River.

Experiment 4 The spacing behavior of P. central is larvae
was examined experimentally to determine: (1) whether the
field densities and the random dispersion pattern exhibited
by these larvae might be largely due to interactions between
individuals; and (2) whether interaction between individuals
may have affected the results of the substrate selection
experiments. If P. central is larvae actively space, then, as

numbers increase for .a limited amount of optimal substrate,
the mean density on that substrate should approach an
asymptote with extra individuals being displaced either into
the drift or to less optimal substrates.

Four trays (6.0 x 6.0 x 2.3 cm) containing sand
(particle size 0.25 to 1.00 mm) were placed side by side in
an air-powered flow tank with a velocity of 16 cm/s and a
depth of 7 cm. Eight larvae were introduced upstream of the
substrate trays. After one hour, the number in each tray was
counted and recorded. Another four larvae were then
introduced and the number on each substrate type was counted
again after one hour. This process was repeated until 28
larvae had been introduced into the flow tank.

The results of the experiment are presented in Figure
1.5. There was no apparent tendency toward an asymptote,
except at the highest larval density used in the experiment,
where there was almost no unoccupied space left in the
substrate trays.

Mean Number of Larvae per Tray

Figure 1.5 The mean number of P. centralis larvae per tray,
as a function of larval density in the experimental tank.

DISCUSSION

Life History Features

In the Sand River, P. centralis exhibits a summer type
life cycle, with a relatively short larval period and a long
egg dormancy (approximately 9 months). Overwintering as a
dormant egg appears to be a relatively common strategy in
Ephemeroptera (Clifford, 1982). Long egg dormancies have
been reported for Dolania americana (Harvey et al . , 1980),
and have been suggested for Anal etr i s eximia Edmunds
(Lehmkuhl, 1976), both of which are predaceous mayflies
associated with sandy river beds.

Clifford (1982) indicates that the adaptive
significance of the summer cycle has generally been
attributed to the avoidance of harsh or uncertain conditions
during winter, but suggests that this life cycle may be an
adaptation to shorten the larval period and thereby minimize
the impact of such factors as predation on this stage.

Pseud i ron centralis larvae did not seem to exhibit high
mortality rates, based on the changes in larval density over
time (Fig. 1.4). Also the relatively low fecundity of
females does not suggest high levels of larval or egg
mortality. Thus it seems unlikely that the adaptive
significance of the life cycle pattern of P. centralis is to
minimize larval mortality.

It is apparent that the density of psammophi lous
chironomid larvae remains high throughout the year (see

Chapter 2 and 3). Since P. centralis was the only
macroinvertebrate predator collected on shifting sand areas
in the Sand River, it appears that the chironomid
populations of this habitat remain unexploited for much of
the year. Given the presence of a relatively constant
availability of prey items, the P. central is population,
would be expected to exhibit a more staggered larval growth
and emergence pattern. The absence of this pattern suggests
some overriding factor makes developmental synchrony
advantageous to members of this population.

The large size of P. central is eggs was probably not
simply a function of the duration of the dormancy period and
the food requirements of the embryo, since most other
Ephemeroptera with similar egg dormancy periods do not
possess such large eggs. Pseud i r on centralis larvae may be
large at hatching because of their predaceous habits
(chironomid larvae were found in the guts of even the
smallest stage I larvae examined) , which may impose a
minimum size constraint, below which larvae cannot prey
effectively on chironomids. Alternately, P. centralis larvae
might be constrained to a certain minimum size to cope
effectively with the dynamic nature of the sandy beds on
which they are found.

Larval Habitat Associations

The shift in habitat association exhibited by
P. central is during larval development may in part also be a

reflection of the dynamic nature of sandy river beds.

Pseud i r on central is larvae occupy the surface of the
substrate; thus they are exposed to the current and any
substrate movements that occur. Given the high current
velocities, turbulence, and active movement of substrate
that characterize shifting sand areas in the mainstream of
the Sand River, it seems reasonable that stage I larvae
cannot cope with these stresses and are thus confined to
marginal areas. However, the almost exclusive association of
stage III and IV larvae with areas of shifting sand is more
difficult to explain.

In the laboratory, stage III and IV P. central is larvae
were able to survive for long periods at low current
velocities, and one larva survived for a week in the absence
of significant current. It thus seems unlikely that there is
an immediate physiological necessity to seek out areas with
relatively high current velocities, such as found over
shifting sand substrates.

Results of the substrate selection experiments provide
a possible explanation for the absence of stage III and IV
larvae from gravelly sand areas of the river bed, since they
indicated that P. centralis larvae avoid gravel. However,
there is no indication as to why stage III and IV larvae
were absent from marginal sand areas.

Two hypotheses are advanced to account for the observed
distribution pattern of stage III and IV P. centralis larvae
in the Sand River: (l)predator or competitor pressure is

lower in areas of shifting sands; or (2)food availability
(i.e. chironomid larvae) is greater in shifting sands.

Pseud i r on central is larvae are the only epibenthic
macroinvertebrates occupying shifting sand areas in the Sand
River, and they are much larger than any other
macroinvertebrate in this habitat. Possibly by occupying
this area, they avoid interact ion's with the much more
diverse epibenthic fauna of gravelly sand and marginal sand
areas. Prominent macroinvertebrates associated with GS and
MS areas in the Sand River are the larvae of the family
Gomphidae (Odonata). These predaceous dragonfly larvae have
been suggested to be partially responsible for restricting
the distribution of Dolania americana larvae to shifting
sand areas through competition for food resources (Tsui and
Hubbard, 1979). For P. centralis larvae, predation by
odonates is probably more important as a determinant of
distribution than is competition for food resources. This is
suggested by the rapid decline in the numbers of
P. central is larvae in laboratory streams that contained
gomphid larvae. It is possible that an active foraging
strategy, such as that exhibited by P. centralis larvae, is
incompatible with the presence of a significant number of
’ sit-and-wait 1 predators, such as gomphid larvae. However,
the susceptibility of P. centralis to such predation has not
been determined, and I did not measure the gomphid larval
density; hence this hypothesis could not be tested.

The second hypothesis predicts a greater prey
availability (i.e. chironomid larvae) in shifting sand areas
than in other areas examined. Availability is defined here
as including both the abundance (numerical and biomass) and
the accessibility of chironomid larvae. Chapter 2 reports
the mean total density and biomass of larval Chironomidae on
the various substrate types in the Sand River for the
ice-free season in 1981. Considering only the sampling
intervals when stage III and IV P. central is larvae were
likely present (Fig. 1.2), ANOVA indicated no significant
differences in mean density (F=0.922, p=0.40) or biomass
(F=0.388, p=0.68) of chironomid larvae in the three types of
substrate. This suggests that P. central is larvae occupying
shifting sand areas gained no apparent advantage in terms of
food abundance.

The relative accessibility of chironomid larvae in the
various substrates types was not determined, but the
observed preference of P. central is larvae for the eroding
upstream face of sand dunes suggests that the movement of
the sand may expose chironomid larvae. Since P. centralis
larvae have not been observed to burrow actively after prey,
except in the manner described previously, it is possible
that P. central is may exploit prey items exposed by the
action of the current and the instability of the substrate
in shifting sand areas.

A complicating factor is that changes also occur in the
composition of the chironomid communities associated with

the substrate types. Shifting sands are dominated almost
exclusively by chironomid larvae that live in the
interstices between sand grains (Chapter 2); whereas
marginal sand and gravelly sand areas support large numbers
of tube-dwelling and burrowing forms. The numerically
dominant species in shifting sand areas was also Rheosmitt ia
sp. , which appeared to be a favoured prey item of
P. central is larvae (Table 1.5). This is unlikely, however,
to explain the exclusive association of stage III and IV
P. centralis larvae observed, since Rheosmitt ia sp. larvae
also occurred in substantial numbers in marginal sand areas
(Chapter 2 ) .

Larval Dispersion and Spacing Behavior

The random dispersion pattern of stage III and IV
P. centralis larvae on shifting sand areas greatly
facilitated accurate population estimates. Random dispersion
patterns have seldom been reported for lotic benthic
invertebrates, although they have been found in populations
of species frequenting areas of relatively uniform substrate
composition (Resh, 1979). The presence of a random
dispersion pattern on shifting sands suggests P. central is
larvae might be perceiving this area as a relatively uniform
patch, at least at the population level; and supports the
designation of shifting sand areas as a distinctive habitat
for P. central is.

♦

Observations suggest that P. central is larvae will not
tolerate physical contact with other individuals. Such
contact elicits a response whereby one or both individuals
will rapidly swim or crawl away. The spacing experiment
indicated that P. central is larvae seem to tolerate a mean
density of about six individuals in a 36 cm2 area. This
density could have easily been accommodated in the
substrates used in the substrate selection experiments, and
thus it is unlikely that spacing of individuals had an
appreciable effect on these experiments. Since the density
tolerated by larvae in the spacing experiment corresponds to
a density of 1600 individuals/m2, it seems unlikely that
spacing is an important determinant of field densities, even
given that actively foraging individuals would probably only
tolerate a much lower density.

CONCLUSIONS

Although P. central is larvae and adults are rarely
collected, the species is probably not rare. The low
densities at which P. central is occurs and the difficulties
of sampling the invertebrate fauna near and in the
mainstream of larger rivers have probably combined to give
this impression. This is probably true for the genus
Pseud i ron as a whole. Specimens of Pseud i ron have been
collected in sandy reaches of all major river systems in
North America, with the exception of the St. Lawrence River
and some drainages west of the Rocky Mountains.

Barton (1980) commented on the generalized invertebrate
assemblages associated with the sandy beds of larger rivers
over wide geographic areas. Mayflies of the genus Pseud / r on
appear to be consistent members of these assemblages in
North America.

In the Sand River, and probably in other rivers,

Pseud 7 ron larvae are the only epibenthic invertebrate
predators that occupy areas of actively shifting sand. They
are highly specialized predators on the chironomid fauna of
these areas, and as such may play an important role in the
biological communities associated with shifting sand areas.
Further examination of the biology and ecology of Pseud i ron
is likely to increase our understanding of one of the
dominant habitat types in river ecosystems.

LITERATURE CITED

Barton, D.E. 1980. Benthic macroinvertebrate communities of
the Athabasca River near Ft. Mackay, Alberta.
Hydrobiologia 74:151-60.

Brittain, J.E. 1982. Biology of mayflies. Ann. Rev. Entomol.
27: 1 19-47.

Burks, B.D. 1953. The mayflies, or Ephemeroptera , of
Illinois. Ill. Natur. Hist. Surv. Bull. 26(1).

Ciborowski, J.J.H. 1982. The relationship between drift and
microdistribution of larval Ephemeroptera. Ph.D. Thesis,
University of Alberta. 186 p.

Clifford, H.F. 1970. Variability of linear measurements
throughout the life cycle of the mayfly Leptophlebia
cupida (Say ) (Ephemeroptera : Leptophlebi idae ) . Pan-Pacif.
Entomol. 46 ( 2 ) : 98- 1 06 .

_ . 1982. Life cycles of mayflies (Ephemeroptera), with

special reference to voltinism. Quaest. Ent. 18:15-90.

Edmunds, J.F., Jr., S.L. Jensen, and L. Berner. 1976. The
mayflies of North and Central America. Univ of Minn.,
Minneapolis, 330 p.

Environment Canada, 1981. Surface water data, Alberta 1980.
Inland Waters Directorate, Water Resources Branch, Water
Survey of Canada, Ottawa. 245 p.

Harvey, R.S., R.L. Vannote, and B.W. Sweeney. 1980. Life
history, developmental processes and energetics of the
burrowing mayfly Dolania americana, p. 211-30. In
Flannagan, J.F. and K.E. Marshall [eds.] Advances in
Ephemeropteran biology. Plenum, New York. 552 p.

Hynes, H.B.N. 1970. The ecology of running waters. Univ. of
Toronto, Toronto. 555 p.

Lehmkuhl, D.M. 1976. Additions to the taxonomy,
zoogeography, and biology of Anal etr i s eximia
( Acanthametropodinae : Siphlonur idae : Ephemeroptera ) .
Canad. Entomol. 108:199-207.

McDunnough, J. 1931. New species of North American
Ephemeroptera. Canad. Entomol. 63:82-93.

Needham, J.G., J.R. Traver, and Y.-C. Hsu. 1935. The biology
of mayflies .Comstock , Ithaca. 759 p.

Resh, V.H. 1979. Sampling variability and life history

features: basic considerations in the design of aquatic
insect studies, p. 290-311. In D.M. Rosenberg [ed.]
Proceedings of the Plenary Session, 26th Annual Meeting
of the North American Benthological Society. Jour. Fish.
Res. Board Canada 36:289-345.

Shapiro, J. 1958. The core freezer: a new sampler for lake
sediments. Ecology 39(4) :758.

Southwood, T.R.E. 1978. Ecological methods: with particular
reference to the study of insect populations, 2nd
revised edition. Chapman and Hall, London. 524 p.

Sweeney, B.W., and R.L. Vannote. 1982. Population synchrony
in mayflies: a predator satiation hypothesis. Evolution
36(4) : 8 1 0-2 1 .

Tsui, P.T.P., and M.D. Hubbard. 1979. Feeding habits of the
predaceous nymphs of Dolania amer icana in Northwestern
Florida (Ephemeroptera : Behningi idae ) . Hydrobiologia
67(2) : 1 19-23.

Waters, T.F. 1977. Secondary production in inland waters.
Adv . Ecol. Res. 10:91-164.

_ , and G.W. Crawford. 1973. Annual production of a stream

mayfly population: a comparison of methods. Limnol.
Oceanogr. 18:289-96.

Zar, J.H. 1974. Biostat i st ical analysis. Prentice-Hall, New
Jersey. 620 p.

ii. the life history and ecology of Robackia demeijerei

Krus. AND
(DIPTERA)

Rheosmittia sp., two riverine chironomidae

ASSOCIATED WITH SHIFTING SAND SUBSTRATES IN

RIVERS.

ABSTRACT

Chironomid larvae are often the dominant
macroinvertebrates associated with areas of actively
shifting sand in the beds of larger rivers. This study
examines the ecology of Robackia demei jerei and an
undescribed species of Rheosmitt ia in a river in central
Alberta, Canada. Robackia demei jerei was univoltine with an
extended emergence pattern. Rheosmitt ia sp. exhibited a
bivoltine life cycle with well defined emergence periods.
Larval densities of both species were highest where the sand
was in active motion. Most larvae occurred in the upper 10
cm of substrate. Larvae of neither species constructed tubes
or tunnels in the substrate. The small cross-sectional
diameters of these larvae suggest that they are true
interstitial forms, using the space between sand grains.
Laboratory experiments indicated that larvae of both species
select substrates in the range of 0.50-2.00 mm. This was
consistent with model predictions of accessibility and
suitability of interstitial space for vermiform animals of
given cross-sectional diameters. Separation of substrate
types, using visual and tactile criteria, predicted the
abundance of larvae of both species more accurately than the
particle size distributions of the substrates. There was no
clear relationship between depth of the oxidized layer in
the sediments and larval abundance. A negative relationship
existed between abundance of larvae of other chironomids,
and those of R. demei jerei and Rheosmitt i a sp ..

INTRODUCTION

Chironomid larvae appear to be the dominant
macroinvertebrates occupying areas of unstable shifting sand
in the beds of most large rivers (Berner, 1951; Zhadin and
Gerd, 1961; Barton and Lock, 1979; Barton, 1980; Seagle et
al. 1982), although Oligochaeta sometimes achieve dominance
in heavily polluted systems (Zhadin and Gerd, 1961). The
chironomid fauna of sandy river beds appears to be a highly
generalized assemblage of species, some occurring over wide
geographic and climatic ranges (Saether, 1977; Barton,

1980). This fauna has seldom been studied except in the
course of general taxonomic or ecological surveys.

Robackia demei jerei (Kruseman) is a widely distributed
species in the subfamily Chi ronominae , occurring in most
larger rivers in North America, some rivers in the U.S.S.R.,
and in the beaches of some lakes in North America (Saether,
1977). Barton (1980) indicated that larval R. demei jerei
were chacter i st ically associated with coarse sand in the
Athabasca River. Zhadin and Gerd (1961) suggest that members
of the group to which the genus Robackia belongs are all
predaceous .

Rheosm i tt i a sp. is an undescribed species in the
subfamily Orthocladi inae and was referred to as
"Orthocladi inae B" by Barton (1980) and Barton and Lock
(1979) (D.R. Oliver pers. comm.). Barton (1980) suggests
that this species is probably widespread but has been
overlooked because of its small size. The genus is known

from Europe and North America and until recently was
included in the genus Eukiefferellia (D.R. Oliver pers.
comm. )

My study examines the life history, distribution,
abundance, and behavior of R. demei jerei and Rheosmitt ia in
the sandy substrates of a medium-sized river in central
Alberta .

STUDY SITE

The study was carried out at the mouth of the Sand
River (54°23? N, 1 1 1 ° 2 T W) , located in east-central Alberta.
Above its mouth, the Sand River is approximately 30 m wide
with mean thalweg current velocities ranging from 60-150
cm/s. The mean annual discharge over the study period was
approximately 16 m3/s. The bottom of the Sand River is
composed almost exclusively of sand, with silty areas
occurring near the banks and with an occasional gravel bar
occupying part of the bed. The mean daily summer temperature
(June to September) of the Sand River was approximately
20 °C . A more detailed description of the study area is given
in Chapter 1 .

METHODS

Four substrate types were recognized in the bed of the
Sand River: silt (SI), marginal sand (MS), gravelly sand
(GS), and shifting sand (SS). These substrates were defined
by a series of visual and tactile criteria (Table II. 1).

Table II. 1 Criteria
types in the Sand R

Substrate Category
Silt (SI)

Marginal Sand (MS)

Gravelly Sand (GS)

Shifting Sand (SS)

for identifying the four major substrate
iver .

Visual and Tactile Criteria

soft sticky texture, abundant visible
silt, dark grey or black color

firm fine-grained texture, some visible
silt, few sand particles in active
motion

firm coarse texture, abundant gravel
apparent, few sand particles in active
motion

soft loose texture, no apparent silt,
actively moving sand dunes

Samples were obtained along ten transects, set out at 5
m intervals along a 50 m stretch near the mouth of the Sand
River. Samples were obtained at intervals determined by the
occurrence of the various substrate types along each
transect (silt areas were not sampled). Samples were
obtained from the middle area of those substrates that
occurred in narrow bands parallel with the banks (MS and GS)
and at intervals of 5,10,20, and 30 m from the east bank,
wherever possible in SS areas. A series of samples was
obtained prior to freeze-up in 1980 (November 9) and on a
roughly bi-weekly basis during the ice-free season of 1981
(April 23 to October 28). Additional samples were obtained
on June 23, 1982.

The principal sampling device was a modified version
(see Appendix 1) of the core-freezer described by Shapiro
(1958). A handled Surber sampler (mesh size 0.243 mm) was
used exclusively on Nov. 9, 1980 and, in conjunction with
the core-freezer, on May 7,1981.

Cores were obtained by pushing the corer into the
sediments to a depth of 25 cm, and then pouring a mixture of
dry ice and iso-butyl alcohol into the outer jacket of the
sampler. After approximately 5 minutes the corer was removed
from the sediments and transported to the river bank, where
the dry ice butanol mixture was poured from the outer
jacket. If the core was to be kept intact, the water column
over the core was poured off into a labelled container,
water was poured into the outer jacket, and the intact core

would fall out into another container. If the core was not
to be kept intact, then the core and water column were
collected into one container. All samples were frozen in the
field and stored at -28°C until examination.

Samples were obtained with the Surber sampler by
disturbing the 930 cm2 area defined by the sampler, with the
foot for 30 seconds. This technique disturbed the substrate
down to a level of approximately 10 cm. Samples were placed
in jars and preserved in 95% ethanol until examination.

In the laboratory, samples were thawed where necessary
and the organic material in the samples was separated from
inorganic by elutriation. The organic material was examined
under a dissecting microscope at 12X, and all organisms were
removed, identified, and counted. For the cores, the organic
material remaining after all organisms were removed was
returned to the inorganic fraction, and then the entire
sample was air-dried.

Larvae of R. demei jerei and Rheosmitt ia sp. were
separated by instar and the number in each of the various
instars was recorded. Instar was determined by head capsule
length, which was measured from the hind lateral margin of
the head to the base of the mandibles. Head capsule width
was obtained from the widest part of the head (approximately
at the level of the eyes) in both species. All measurements
were obtained using an eyepiece micrometer, either under a
dissecting microscope at 100X or under a compound microscope

at 200X.

To determine the vertical distribution of R. demei jerei
and Rheosm i tt i a Sp. larvae, cores that had been collected
intact were cut into 5 cm sections. Each of these sections
was then treated as an individual sample and the number of
larvae in each section recorded.

To determine the mean weight of each discernible larval
instar, larvae removed from the cores were dried at 60°C for
24 hours and weighed on a microbalance to the nearest 0.002
mg. Because of the minute size of the early instar larvae,
it was necessary to weigh individuals as groups (Table
II .3) .

The gut contents of larvae were qualitatively examined
in slide mounted specimens that were squashed to spread the
material in the guts. Uncleared specimens and specimens
cleared in 10% potassium hydroxide for 24 hrs at room
temperature were examined under a compound microscope at a
series of magnifications (100-400X).

The particle size distribution of the substrate types
in terms of weight was determined for samples obtained from
two dates (June 9 and August 5, 1981). These samples were
dried for 24 hrs at 60°C, and dry sieved (for 7 minutes
using a mechanical sieve shaker) through a series of eight
brass sieves (mesh sizes: 12.70, 3.36, 2.00, 1.00, 0.50,
0.25, 0.12 and 0.06 mm) to yield nine particle size classes.
The material in each fraction was then weighed to the
nearest 0.1 mg .

i I > f . *

RESULTS AND DISCUSSION

Life Histories

Table II. 2 shows the mean head capsule lengths and
widths for all larval instars of R. demei jerei and all
distinguishable larval instars of Rheosmitt ia Sp. . First and
second instar Rheosmitt ia sp. larvae were not separable by
head width or head length and were treated together.

The mean dry weight of each discernible larval instar
of the two species is given in Table II. 3. Robackia
demei jerei and especially Rheosmitt ia sp. are relatively
small chironomids both in terms of larval head capsule
dimensions and larval dry weight.

Figure II. 1 illustrates the relative proportion of
individual instars for both species in the Sand River during
the study. Rheosmitt ia Sp. appears to exhibit a bivoltine
life cycle in the Sand River, with a winter and a summer
generation. After overwintering as third instar larvae,
Rheosmitt ia sp. larvae develop rapidly in the spring and
appear to pupate and emerge as adults in late May. Eggs laid
by the adults of this winter generation hatch after a short
time, and large numbers of first and second instar larvae
appear in early June. Larvae in this summer generation then
develop over a 6 to 8 week period, pupating and emerging in
late July and early August. Larvae of the next winter
generation first appear in early August and develop as far
as the third larval instar before freeze-up, at which time

Table II. 2 Mean head capsule lengths and widths for each
discernible larval instar of Robackia demejerei and
Rheosmittia sp..

Robackia demei jerei

Instar

Mean Head
Length (jum)

[S.E. ]

Mean Head Width
(Mm) [S.E. ]

69 [ 2 ]

52 [ 2 ]

98 [ 1 ]

64 [ 1 ]

III

1 34 [ 1 ]

87 [ 1 ]

1 94 [ 1 ]

1 30 [ 1 3

Rheosmitt ia

sp.

I+II

55 [ 2 ] -

47 [ 1 ]

1 1

III

74 t 1 3

61 [ 1 ]

91 [2]

80 [ 1 3

Table II. 3 Mean dry weight of all distinguishable larval
instars of Robackia demei jerei and Rheosmitt ia sp . . Also
indicated is the number of larvae weighed per sample, and
the number of samples weighed to determine the mean.

Robackia demei jerei

Instar

no. /sample

no .

samples

mean wt .
(Mg)

S.E.

1.5

0.7

3.5

1 .2

III

104

12.6

5.3

29. 1

13.2

Rheosmitt i a sp.

I+II

0.7

0.3

III

1 .7

•

7.2

2.8

7.6

1.5

development seems to cease until spring.

The life cycle of R. demeijerei (Fig. II. 1) in the Sand
River is difficult to interpret because both emergence and
hatching appear to occur over an extended period. A
comparison between the life cycle exhibited in Figure II. 1
and the density of R. demeijerei larvae during this study
(Fig. II. 2) suggests that this species is univoltine in the
Sand River. First instar larvae appear from late June until
late September, with maximum numbers occurring in late
August. The low number of first instar larvae was probably a
function of either a relatively short time spent in this
stage or reflects utilization of a different habitat by
first instar larvae; both are common strategies exhibited by
other chironomids (Oliver, 1971). Larvae develop throughout
the summer and fall, with most individuals achieving second
or third instar before freeze-up. Overwintering can occur in
either second and third instar and probably is a major
factor contributing to the difficulty of interpreting the
life cycle of this species in the Sand River. Development
appears to stop during winter, but resumes after the
break-up of ice in spring. The presence of first and fourth
instar larvae suggests that adult emergence and egg laying
take place over an extended period, probably from the end of
May to the end of September. Since R. demeijerei pupae were
seldom encountered, it is likely that individuals leave the
substrate after pupation.

Larval Density and Distribution

The densities of R. demei jerei and Rheosmittia sp. on
the three substrate types are presented in Figures II. 2 and
II. 3. The values obtained for Nov. 9, 1980, were based on
estimates obtained with a Surber sampler and have been
corrected for the relative efficiency of this type of
sampler when compared with the freeze-corer. This correction
factor was determined from the comparison of the density
estimates obtained from six pairs of Surber and core-freezer
samples taken in close proximity in the SS area on May
7,1981. The efficiency of the Surber sampler was found to be
approximately 5% (s2 = 1 1 .6) for Rheosmittia sp. and 13%

(s2 = 118.8) for R. demei jerei. These are likely maximal
estimates of sampling efficiency since early instar larvae
were not present on this date (Fig. II. 1).

To determine whether significant differences existed
between the densities of R. demei jerei and Rheosmittia sp.
larvae on the three different types of substrate sampled,
one-way analysis of variance (ANOVA) was conducted on
log(n+1) transformed data from all dates where all substrate
categories were sampled. The probabilities obtained from
these ANOVAs (Table II. 4) were then pooled (Sokal and Rolhf,
1969) to obtain an overall probability. This analysis
indicated that significant differences existed between the
densities of each species in the three substrate types
( X 2 = 38 . 36 , p<0 . 0 1 for R. demei jerei; and X 2 = 68. 72 , p<0.001
for Rheosmittia sp.).

Table II. 4 Value of ’F' ratio and the probability (p) of
this value from ANOVAs calculated for Robackia demei jerei
and Rheosmittia Sp. on 10 dates in 1981.

Roback i a deme i jere i Rheosm ittia sp.

Date F p F p

1 .586

0.242

0.516

0.608

2.299

0.131

0.504

0.202

0.928

0.408

5.261

0.012

1 .543

0.248

0.216

0.808

1 .488

0.247

3.877

0.035

0.611

0.552

9.190

0.001

1.162

0.330

4.012

0.031

2.186

0.147

5.079

0.021

4.640

0.020

10.649

0.001

5.665

0.011

3.629

0.044

Date

Figure II. 2 Mean larval density of Robackia demeijerei on
the three substate types (SS is shifting sands, MS is

marginal sands, and GS is gravelly sand)

Date

Figure II. 3 Mean larval density of Rheosmittia Sp. on the
three substate types (SS is shifting sands, MS is marginal
sands, and GS is gravelly sand).

One-way ANOVAs conducted on an overall pooling of
log(n+1) transformed data from all dates for each species
and each substrate type yielded a similar result (F=8.74 and
F=2 1 . 53 for R. demeijerei and Rheosmitt ia sp. respectively,
p<0.0001 in both cases), indicating significant differences
between the densities of each species in the three substrate
types. Duncan's multiple range test (DMR) (Sokal and Rohlf,
1969) indicated that SS areas supported significantly higher
(p<0 . 05 ) densities of both R. demeijerei and Rheosmitt ia sp.
than did MS or GS areas.

Most (mean=77.4%, S.D.=11.6, n=7) R. demeijerei and
Rheosmitt ia sp. larvae were found in the upper 10 cm of
substrate; however, a few larvae were collected deeper than
15 cm (mean=2.4%, S.D.=4.6, n=7). This is somewhat deeper
than reported depths for chironomid larvae in stream muds
(Ford, 1962), but is shallower than those reported for
coarser substrates (Williams and Hynes, 1974). The results
of this analysis of vertical distribution should be viewed
as tentative, since the core-freezer freezes the sample from
the bottom up; and the chironomids may have moved toward the
surface to escape this freezing.

The mean total biomass (mg/m2 dry weight) for each
species on the various substrate types over the year is
illustrated in Figures II. 4 and II. 5. Biomass was determined
by indirectly assessing the weight of individuals in each
sample from the mean weights (Table II. 3) of the different
larval instars. Total biomass for each sample was the sum of

Weight (mg/m2)

Figure II. 4 Mean dry weight (±S.E.) of larval RobdCkis

deme i jere J on the three substrate types

Figure II. 5 Mean dry weight (±S.E.) of larval

Rheosmitt ia Sp. on the three substrate types

these individual estimates. These data show trends similar
to those indicated by the density estimates.

Larval Behavior

The trophic relations of the two species could only be
assessed qualitatively, given the technique used to examine
the gut contents. The guts of Rheosmitt ia sp. larvae were
tightly packed with diatoms, suggesting that these larvae
directly exploit sources of primary production in the river
bed. The guts of R. demeijerei larvae, although containing
some diatoms were mostly filled with an unidentifiable
amorphous material. Since many predaceous chironomids do not
consume the hard parts of their prey (Oliver, 1971), it was
impossible to determine whether this material was animal
tissue or detritus.

Robackia demeijerei and Rheosmittia sp. larvae are
similar behaviorally and to some extent morphologically. In
the laboratory larvae of neither species constructed tubes,
and there was no evidence that burrows were actively
maintained. The larvae of these species probably exploit the
interstitial space available between sand grains.

When individuals of either species were placed on the
surface of sand sediments or were disturbed, they tended to
respond by producing copious quantities of a sticky silk,
which they attached to nearby sand grains through a vigorous
thrashing motion of the head and body. Similar behavior has
been described for other species of sand-dwelling

chironomids; Wiley (1980) suggested that this action allows
the animal to maintain its position while penetrating the
sediment .

Robackia demei jerei larvae exhibit a relatively
elongated (fourth instar larvae: body width approximately
0.14 mm, body length approximately 5.8 mm) body form that is
somewhat atypical for a chironomid; they superficially
resemble larvae of Ceratopogon idae (Diptera). Larvae of
Rheosmitt ia sp. though somewhat stouter relative to body
width (fourth instar larvae: body width approximately 0.10
mm, body length approximately 2.2 mm), are also relatively
more slender than larvae of most other chironomid species.

Substrate Selection Experiments

Experiments were conducted to determine whether
R. demei jerei and Rheosmitt ia sp. larvae would select
substrates with particular particle size distributions. The
design consisted of sixteen (2. 7x2. 7x2. 9 cm) substrate cages
arranged in a 4x4 matrix inside a 11.8x11.8x3.1 cm tray
(Plate II. 1). Each cage consisted of a bottom plate made of
a 2. 7x2. 7x0. 3 cm piece of plexiglas, and four (0.3x0. 3 cm)
supports with 0.15 mm mesh nylon netting between them. The
0.15 mm netting allowed free passage of even the largest
individuals between cages, while minimizing any leakage of
fine particles if the cage was not unduly disturbed.

The cages were filled with one of four substrate size
classes: <0.12, 0.12-0.50, 0 . 50-2 . 00 , and 2.00-6.35 mm. Each

Plate II. 1 Experiment apparatus used to test for substrate
selection in fourth instar Robackia demei jerei and
Rheosmitt ia larvae. In the foreground is one of the
substrate cages (see text).

of these substrates was made up of equal volumes of
particles from two size classes; hence the median particle
size in each substrate was easily calculated.

Cage position was randomized in the tray with no
substrate class occurring more than once in any row or
column, and every substrate type contacting every other
substrate type the same number of times within the tray as a
whole. The tray was filled with water and ten individuals of
the same species were placed on the substrate surface in
each cage. Animals were then allowed to burrow into the
substrate; after a few minutes, individuals remaining on the
surface were buried. The tray was placed in a recirculating
artificial stream and exposed to a mean current velocity of
10 cm/s for 24 hours. The tray was then removed and the
individual cages placed in separate jars filled with 95%
ethanol. The contents of these cages were sorted at 1 2X
magnification under a dissecting microscope and all
individuals were removed and counted.

The R. demei jerei experiment was repeated three times
with different arrangements of the substrates, the
Rheosm i tt i a sp. experiment was run only once. Fourth instar
larvae were used in both experiments.

Results are presented in Table II. 5. Only the first run
of the R. demei jerei experiment is reported since all three
runs yielded similar results. The large number of
Rheosmitt ia Sp. larvae that left the substrate during the
experiment was due to pupation (the pupae floated near or at

Table II. 5 Mean number and variance of larvae per cage for
each substrate category in each of the two experiments. The
initial number of larvae per cage was 10.

Roback i a deme i jere i Rheosm itt i a sp.

Substrate
size (mm)

mean

no . /cage

s 2

mean

no . /cage

s 2

<0.12

4.50

4.25

1.50

2.25

0.12-0.50

6.75

18.69

4.75

6.19

0.50-2.00

18.00

5.00

8.50

9.00

2.00-6.35

4.75

6.69

2.50

1 .25

the water’s surface in the artificial stream), and does not
represent a normal rate of larval emigration from the
sediments into the water column.

The results of the R. deme 7 jere / experiment were
analyzed using one-way ANOVA; this indicated significant
differences (F=14.25, p<0.001) between the number of larvae
on the different substrate types. DMR indicated that the
substrate in the 0.50-2.00 mm range was selected
significantly (p<0.05) more often than all other types of
substrate .

One-way ANOVA also indicated significant differences
(F=7.04, p<0.01) in the number of Rheosmittia Sp. larvae on
the four substrates. As in the previous case, DMR indicated
that the 0.50-2.00 mm substrate class retained a
significantly (p<0.05) higher number of larvae than all the
other substrates.

Wiley (1981) relates the distribution of some
chironomid larvae to their ability to penetrate sediments
and the probability of being swept from the substrate before
penetration is accomplished. If Robackia demei jenei and
Rheosmittia sp. larvae are interstitial forms, then the
volume of accessible interstitial space within the substrate
should also be a critical factor in substrate suitability.
Crisp and Williams (1971) provide a model for estimating the
accessible interstitial space for vermiform animals in
relatively homogeneous monomorphic substrates. They estimate
that an animal with a cross-sectional diameter equal to 30

to 40% of the grain size would be able to use 50% of the
total volume of interstitial space.

By using Crisp and Williams (1971) model and the mean
head widths of fourth instar larvae of both species (Table
II. 2), I calculated the minimum grain size in which 50% of
the total interstitial space would be available for the
larvae of each species. This analysis indicated that fourth
instar R. demei jerei larvae would require a particle size
greater than 0.32-0.43 mm for more than 50% of the total
void space to be available. Fourth instar Rheosmitt ia Sp .
larvae would require particle sizes greater than 0.20-0.27
mm for access to 50% of interstitial space.

The median particle sizes of the substrates used in the
substrate selection experiments were 0.06, 0.25, 1.00, and
3.36 mm respectively. It seems likely that the selection of
the 0.50-2.00 mm substrate size class over the finer size
classes by fourth instar R. demei jerei larvae was influenced
by the accessibility of suitable interstitial space in this
substrate. There were few individuals in the coarsest
substrate class (2.00-3.36 mm), where theoretically the
greatest volume of interstitial space should have been
available. This might have been due to the difficulty some
interstitial animals have in moving through large openings,
especially if their bodies do not contact more than a small
area of the wall of the opening (Crisp and Williams, 1971).

The association of fourth instar Rheosmitt ia Sp. larvae
with the 0.50-2.00 mm substrate size class is explained in

■

much the same manner as that for R. demeijerei , except that
the 0.12-0.50 substrate size class should also have provided
a significant amount of accessible interstitial space for
these larvae. Crisp and Williams (1971) point out that fine
particles fill the larger interstitial spaces and tend to
greatly reduce the accessibility of interstitial spaces.

Thus the portion of particles below the median value in the
substrates used in my experiments may have decreased the
reliability of estimates of the availability of interstitial
space based on the median particle size.

The results of these experiments suggest that the
distribution of R. demeijerei and Rheosmittia sp. larvae in
the field may have been determined by differences in the
distribution of particle sizes in the three substrate types
sampled. To determine whether substantial differences
existed between the three substrate types, the mean
contribution of nine particle size classes to the total
weight of the substrate types was measured and pooled for
two separate dates (Figures II. 6, II. 7 and II. 8). A
Kruskal-Wall i s non-paramet r ic ANOVA (Daniel, 1978) was used
to determine whether significant (p<0.05) differences
existed in the weight of material in each individual
particle size class among the three substrate types. Dunn’s
test (Daniel, 1978) was used to assign differences between
the substrate types where the previous analysis had
indicated significant differences. The use of actual weights
rather than proportions was justified, because there were no

Mean Percentage of Total Sample Weight (n=18)

40 .

30 .

20 .

10 .

0000 07^0 7^ 6

'°o '°e '*o '°o '°o

Substrate Size Category (mm)

Figure II. 6 Mean particle size distribution by weight (g)
substrate from the shifting sand (SS) area.

Mean Percentage of Total Sample Weight (n=16)

Figure II. 7 Mean particle size distribution by weight (g) of
substrate from the marginal sand (MS) area.

Mean Percentage of Total Sample Weight (n=1l)

40 .

' aO '°& Xp &o °o °o ^ ' >c

Substrate Size Category (mm)

Figure II. 8 Mean particle size distribution by weight (g)
substrate from the gravelly sand (GS) area.

significant differences in the total weight of substrate
obtained from the three substrate types by the core-freezer
( ANOVA , F= 1 . 99 , p=0. 15) .

Significant differences (p<0.05) were observed in only
four of the nine particle size classes. The weight of
substrate in the 12.70-38.10 mm class differed significantly
between all three substrate types, GS (gravelly sand)
possessing the greatest proportion of this class, and MS
(marginal sand) possessing more of this class than SS
(shifting sand). Particle size classes 2.00-3.36 mm and
3.36-12.70 mm were significantly more abundant in GS than in
the other substrate types, and particle size class 0.50-1.00
mm was significantly more abundant in SS than in the other
substrate types. No significant differences were detected
amongst the finer particle size classes

The GS areas exhibited a higher proportion of the
larger particle size classes, and these areas were quite
distinct from the other substrate types. However, the MS
areas would be expected to possess significantly more finer
particles than the other substrates, since the presence of
fine particles on the surface of the sediments is one of the
features used to define this substrate type.

The lack of substantial differences in the distribution
of particle size classes in the three substrate types was
probably due in part to the historical component of the
cores. The sediment collected in each core represents the
depositional history of the point on the bed from which the

core was obtained. With fluctuating discharge, the nature of
the material being deposited will change and, assuming no
major scouring, may cover sediments laid down under very
different conditions. A good example is the significantly
greater weight of gravel in the 12.70-38.10 mm particle size
class obtained from MS when compared to SS (Figures II. 6 and
II. 7). The gravel found in MS was not surficial; it was
contributed by a gravel layer that underlaid the area from
which some MS samples were obtained. This layer occurred at
a depth of approximately 20 to 30 cm below the surface of
the sediment and no macroinvertebrates were obtained from
this layer; however, it had a substantial effect on the
particle size distribution of substrate obtained from MS
areas. In fact, most of the differences between the SS and
MS particle size distributions are attributable to this
gravel layer.

For my objectives, I found qualitative categorization
of substrate types to be a better predictor of the abundance
of R. demei jerei and Rheosmitt \a Sp. larvae than
quantitative measures of particle size distribution. This
suggests that the particle size distribution is only one of
the factors that control the distribution of these
chironomid larvae. Two other factors that might be important
in determining the observed patterns of abundance exhibited
by larvae of R. demei jerei and Rheosmitt ia sp. were: (1)the
depth in the substrate in which sufficient dissolved oxygen
was available, and (2)the presence of other

macroinvertebrates (especially other chi ronomids ) .

Availability of oxygen in the substrate is an important
determinant of the distribution of both marine meiobenthic
fauna (Coull and Bell, 1979) and freshwater hyporheic fauna
(Whitman and Clark, 1982). Fenchel and Riedl (1970) define
three color layers in marine quartzite sands: (1) the
yellow, or oxidized layer, characterized by the presence of
free oxygen and ferric iron; (2) the gray, or redox
potential discontinuity (RPD) layer, characterized by the
presence of both oxygen and reduced compounds; and (3) the
black, or sulfide layer, characterized by the absence of
free oxygen and the presence of H2S and iron sulfides. They
also indicate that these layers can move up and down on a
daily basis. All three of these layers were visible in the
sandy sediments of the Sand River.

To determine the relative depths of the oxidized layers
in the three substrate types, measurements were made of the
depth at which the gray (RPD) layer was first visible in the
sediment frozen to the outside of the corer when it was
removed from the substrate (Table II. 6). The mean depth of
the oxidized (yellow) layer represents only a minimum
estimate since all depths greater than 25 cm (the maximum
depth sampled) were arbitrarily given a value of 26 cm. A
Kruskal-Wallis one way ANOVA by ranks (Daniel, 1978) was
used to test for differences in the depth of the oxidized
layers. This analysis indicated no significant difference
( H=4 . 7 1 , p>0.05) in the depth of the oxidized layer in MS,

■

Table II. 6 Mean depth in the substrate of the oxidized
(yellow) layer in shifting sand (SS), marginal sand (MS),
and gravelly sand (GS).

Substrate

Category

Mean Depth
Oxygenated
Layer (cm)

S.D.

17.5

5.3

21.9

6.0

18.4

6.6

GS, or SS areas. Thus it does not appear that the depth of
the oxidized layer was an important determinant of the
distribution patterns of R. demeijerei and Rheosmittia Sp.
larvae in the Sand River.

Figure II. 9 shows the abundance of chironomids other
than R. demeijerei and Rheosmittia in the three substrate
types. These data were analyzed in the same way as the
R. demeijerei and Rheosmittia sp. data, and they indicated
that significantly (p<0.05) more individuals of all other
chironomids occur in MS and GS areas than in SS areas. This
distribution is the opposite of those exhibited by larvae of
R. demeijerei and Rheosmittia sp. and is consistent with the
conjecture that other chironomid larvae could be exerting a
negative influence on R. demeijerei and Rheosmittia

CONCLUSIONS

Larvae of Robackia demeijerei and Rheosmittia sp. were
primarily associated with areas of unstable shifting sand,
where their small body diameters allow them to exploit the
interstitial spaces between sand grains. Other chironomids
that construct tubes or tunnels in the substrate were scarce
or absent from shifting sand areas, probably because of the
unstable nature of these substrates.

Laboratory experiments suggest that distribution
patterns exhibited by R. demeijerei and Rheosmittia sp.
larvae are affected by the distribution of particle sizes in
the substrate, with particles in the coarse sand size range

Nv 09 Ma 07 Ma 22 Jn 09 Jn 23 J1 09 Jl 23 Au 05 Au 19 Se 08 Se 26 Oc 17 Oc 28

Date

Figure II. 9 Mean larval density (±S.E.) of chironomids other
than R. demeijerei and Rheosmitt ia sp. on the three

substrate types

(0.50 - 2.00 mm) being favoured over both finer and coarser
particles. However, subjective visual and tactile criteria
for the separation of substrate types was a better predictor
of the abundance of these species than quantitative measures
of the particle size distributions of natural substrates.
Other factors, such as the presence of other chironomids and
the level of dissolved oxygen in the substrate, possibly
influence the distribution of R. demei jerei and
Rheosmittia Sp., although my data demonstrated only a
negative relationship with the abundance of other chironomid

larvae .

LITERATURE CITED

Barton, D.E. 1980. Benthic macroinvertebrate communities of
the Athabasca River near Ft. Mackay, Alberta.
Hydrobiologia 74:151-60.

_ , and M . A . Lock. 1979. Numerical abundance and biomass of

bacteria, algae and macrobenthos of a large northern
river, the Athabasca. Int. Rev. ges Hydrobiol.

64(3) : 345-59 .

Berner, L.M. 1951. Limnology of the lower Missouri River.
Ecology 32 ( 1 ) : 1 - 1 2 .

Crisp, D.J., and R. Williams. 1971. Direct measurement of
pore-size distribution on artificial and natural
deposits and prediction of pore space accessible to
interstitial organisms. Mar. Biol. 10:214-26.

Coull, B.C., and S.S. Bell. 1979. Perpectives of marine

meiofa unal ecology, p 189-216. In R.J. Livingston [ed.]
Ecological processes in coastal and marine systems.
Plenum, New York.

Daniel, W.W. 1978. Applied nonparamet r ic statistics.

Houghton Mifflin, Boston. 503 p.

Fenchel, T.M., and R.J. Riedl. 1970. The sulfide system: a
new biotic community underneath the oxidized layer of
marine sand bottoms. Mar. Biol. 7:255-68.

Ford, J.B. 1962. The vertical distribution of larval
Chironomidae (Diptera) in the mud of a stream.
Hydrobiologia 19:262-72.

Oliver, D.R. 1971. Life history of the Chironomidae. Ann.
Rev. Entom. 16:211-30.

Saether, O.A. 1977. Taxonomic studies on Chironomidae:

Nanocl adius, Pseudoch i ronomus , and the Harn ischia
complex. Bull. Fish. Res. Bd. Can. 196.

Seagle, H.H., J.C. Hutton, and K.S. Lubinski. 1982. A

comparison of benthic invertebrate community composition
in the Mississippi and Illinios Rivers, Pool 26. Jour.
Freshw. Ecol. 1 (6) :637 — 50.

Shapiro, J. 1958. The core freezer: a new sampler for lake
sediments. Ecology 39(4) :758.

Sokal, R.R., and F.J. Rohlf. 1969. Biometry. Freeman, San

Francisco.

Wiley, M.J. 1981. An analysis of some factors influencing
the successful penetration of sediment by chironomid
larvae. Oikos 36:296-302.

Whitman, R.L. , and W.J. Clark. 1982. Availability of
dissolved oxygen in interstitial waters of a sandy
creek. HydrobiOlogia 92:651-8.

Williams, D.D., and H.B.N. Hynes. 1974. The occurrence of
benthos deep in the substratum of a stream. Freshw.
Biol. 4:233-56.

APPENDIX 1

Construction of the Core-Freezer

The main body of the core-freezer was constructed of
standard copper water pipe. Figure 11.10 indicates the
dimensions of the corer. The two lengths of copper pipe that
made up the inner and outer walls of the corer were joined
using a standard copper adapter (A) for joining 3.8 cm (1.5
in) diameter pipe to 7.6 cm (3.0 in) diameter pipe. An inner
ridge on the adapter had to be removed to facilitate the use
of the adapter in a backwards position. The pipes were
soldered to the adapter using a high temperature silver
solder. Three spacers made of 0.6 cm (0.25 in) pipe were
soldered in place near the top part of the double-walled
portion to keep the central tube in place. The handle was
made of a solid steel rod (1.3 cm diameter), which was
pushed into place through holes drilled in the outer and
inner pipes. The ring (B) made of masking tape was attached
25 cm from the bottom of the corer and prevented the corer
from penetrating more than 25 cm into the substrate.

*3.8*

*- 7.6 -*

Figure 11.10 The dimensions (cm) of the modified
core-freezer for sampling loosely consolidated sandy
substrates (all diameters are i.d.). 'A' is the adapter; 'B'
is the penetration ring.

III. THE MACRO INVERTEBRATES OF SHIFTING SAND AREAS: A

REEVALUATION OF THEIR CONTRIBUTION TO RIVER ECOSYSTEMS.

ABSTRACT

The abundance and biomass of benthic macroinvertebrates
from shifting sand areas in the bed of the Sand River in
central Alberta, Canada, was examined for one year.
Macroinvertebrate density was relatively high; however,
total biomass was low due to the small size of most
organisms. Total annual secondary production was determined
for populations of the two dominant chironomid species
( Robackia demei jerei and Rheosmitt ia sp.) , and the sum of
these estimates (752 mg/m2/yr) was used as an estimate of
the total secondary production of benthic macroinvertebrates
on shifting sand areas. Although unit area biomass and
production were low relative to values reported for some
other lotic habitat types, shifting sand areas and other
sandy bedforms may be important if the entire river system
is considered.

INTRODUCTION .

Any attempt to study rivers as ecosystems will require
knowledge of the functional relationships within and between
communities of organisms occupying the various habitat types
present in the system. Most studies conducted in streams
have concentrated on organisms and communities associated
with relatively coarse substrates found in riffle areas.
Since large rivers are usually dominated by fine-grained
materials and their characteristic bedforms (Leopold et al . ,
1964; Hynes, 1970), riffles occupy only a small proportion
of the total river bed area in these systems. Sandy
sediments probably form the most common habitat types found
in the beds of large rivers; however, benthic
macroinvertebrates associated with these areas have seldom
been studied quantitatively.

One of the most prominent types of sandy habitat are
areas where the sand is being actively moved by the force of
the water current. These areas are usually characterized by
the presence of sand dunes, although other forms, such as
plane beds and antidunes, are possible given appropriate
current regimes (Leopold et al . , 1964; Smith, 1975). These
dunes are in continuous downstream motion and present a
dynamic substrate for benthic organisms. Despite this, a
well-developed microfauna has been reported from shifting
sand areas (Niewestnova-Shadina , 1935). However, these areas
are usually characterized as unfavourable for benthic
macroinvertebrates, supporting only a few individuals of a

100

few specialized species (Hynes, 1970).

Studies of unstable sand areas have generally supported
the view that these areas support few macroinvertebrate
species. However, there appear to be conflicting views on
whether these areas support significant numbers of
individuals. Studies of the effect of sand on smaller
streams and rivers with predominantly stony bottoms have
supported the view that unstable sands support few
individuals (e.g. Nuttall, 1972; Lenat et al . , 1981).

Studies of the fauna of unstable sands areas in streams with
predominantly sandy bottoms (usually large streams) have
yielded conflicting results, some indicating few individual
macroinvertebrates (Berner, 1951; Zhadin and Gerd, 1961;
Sioli, 1975; Northcote et a/., 1976; Seagle et a/., 1982)
while others indicate large numbers of individuals (Zhadin
and Gerd, 1961; Barton and Lock, 1979; Barton, 1980).

Perhaps more important than number of individuals are
the amounts of biomass and production that shifting sand
areas contribute to river ecosystems. This question has been
partially addressed in only a few studies of large rivers
(Berner, 1951; Zhadin and Gerd, 1961; Monakov, 1969;
Northcote et a/., 1976; Barton and Lock, 1979).

My study was conducted to assess the biomass of benthic
macroinvertebrates on shifting sand and adjacent areas and
to obtain an estimate of annual secondary production for the
shifting sand areas in the bed of the Sand River in Alberta,
Canada. This river is not large, but the thalweg current

101

velocities, nature of the sediments, and the
macroinvertebrate species found in the Sand River are
characteristic of many large lowland rivers in North
America. Thus, I feel that this an appropriate model system
for studying the ecology of shifting sand substrates in
rivers .

STUDY SITE

The study was carried out at the mouth of the Sand
River (54°23' N, 1 1 1 ° 0 2 * W) , in east-central Alberta.
Upstream of its mouth, the Sand River is approximately 30 m
wide with mean thalweg current velocities ranging from
60-150 cm/s. The mean annual discharge over the study period
was approximately 16 m3/s. The bottom of the Sand River is
composed almost exclusively of sand, with silty areas
occurring near the banks and with an occasional gravel bar
occupying part of the bed. Mean daily summer temperature
(June to September) was approximately 20°C. A more complete
description of the study site is given in Chapter 1.

METHODS

Samples were collected along ten transects, set out at
5 m intervals along a 50 m stretch near the mouth of the
Sand River. Samples were obtained in shifting sand areas
along these transects at intervals of 5,10,20, and 30 m from
the east bank, wherever possible. A series of samples was
obtained prior to freeze-up in 1980 (November 9) and

102

approximately bi-weekly during the ice-free season of 1981
(April 23 to October 28).

The principal sampling device was a modified version of
the core-freezer described by Shapiro (1958). A handled
Surber sampler (mesh size 0.243 mm) was used exclusively on
Nov. 9, 1980 and in conjunction with the core-freezer on May
7,1981. Construction of the core freezer and the techniques
used to obtain cores are described in Chapter 2. Techniques
used with the handled Surber sampler are described in
Chapter 1 .

Cores were kept frozen, and Surber samples were
preserved in 95% ethanol for transportation and storage.

Core samples were thawed, and organic material was separated
from inorganic material, for both types of samples, by
elutriation. The organic material was then sorted under a
dissecting microscope at 1 2X magnification and all benthic
macroinvertebrates were removed and counted. Members of the
two dominant chironomid species in the shifting sand areas
(Robackia demei jerei Krus. and Rheosmittia sp.) were
separated by larval instar.

Mean dry weight biomass for larval populations of the
two dominant chironomid species was calculated from the
counts and the mean dry weights for each instar (Chapter 2).
All other macroinvertebrates were separated into two
categories "other chironomids" and "other organisms" and
were weighed as a group to the nearest 0.002 mg on a

microbalance .

103

Surber sampler data for the two dominant chironomids
were corrected using efficiency estimates of 13% and 5% for
R. demeijerei and Rheosmitt ia Sp. respectively (Chapter 2).
Total sample weights were then estimated using these
corrected values.

Production estimates were obtained for larvae of each
of the two dominant chironomids separately and then summed
to estimate annual production for the habitat. Because of
difficulty in defining the cohort structure of Robackia
demeijerei, larval production of this species in the Sand
River was estimated using the size-frequency (Hynes) method
(Waters and Crawford, 1973; Waters, 1977). Rheosmitt ia sp.
production was determined using the same method to maintain
consistency. The 95% confidence intervals for each of the
production estimates were determined using the method of
Krueger and Martin (1980).

RESULTS

The mean biomass of all macroinvertebrates, all
chironomids, and the two dominant chironomids obtained from
shifting sand areas in the Sand River are illustrated in
Figure 1 1 1 . 1 . Total invertebrate biomass was overestimated
because sphaeriid (fingernail clams), which occur in
significant numbers in this area, were weighed in their
shells. Larvae of R. demeijerei and Rheosmitt i a sp.
consistently contributed the majority of the chironomid
(mean=94.6%, S.E.=2.3) and total invertebrate biomass

Dry Weight (mg/m2)

104

600

500

U00

100

. _ All

MocroTnverts.

_ All Chironomlds

_ Rb and Rh

_ I _ I _ 1 _ I _ l _ l _ ! _ 1 _ 1 _ I _ l _ I _ _l_

Nv 00 Ma 07 Ma 22 Jn 09 Jn 23 J1 09 J1 23 Au 05 Au 19 S® 08 S® 26 Oc 17 Oo 28

Date

Figure III.1 Mean dry weight biomass (±S.E.) of three
categories of benthic invertebrates in the Sand River; all
categories are inclusive of lower categories (Rb= R.
demeijerei and Rh= Rheosmitt ia sp .).

105

(mean=80.6%, S.E.=3.7). They were also the numerically
dominant taxa in shifting sand areas of the Sand River
(Chapter 2 ) .

Table 1 contains the production calculations for the
larval populations of each of the two dominant chironomids.
The sum of the annual larval production of R. demei jerei and
Rheosmittia Sp. (752.03 ±144.50 mg/m2/yr) was used as a
minimum estimate of total annual macroinvertebrate
production from shifting sand.

DISCUSSION

Total benthic macroinvertebrate density and biomass on
shifting sand areas in the Sand River was generally higher
than the values reported in most other studies of unstable
sandy substrates in large relatively unpolluted rivers
(Table III. 2). Most of the differences between the values
obtained in my study and those obtained in other studies are
probably attributable to differences in sampling techniques.

Unstable sandy areas tend to be dominated by small
interstitial or burrowing invertebrates, which are very
difficult, especially the early stages, to detect with the
unaided eye. Thus, the hand-picking or live-picking
techniques used by Berner (1951) and Monakov (1969) would
probably greatly underestimate the number of benthic
macroinvertebrates .

Most studies that report mesh sizes used in sample
processing indicate mesh sizes greater than 0.50 mm. Several

♦

Table III.1 Production (dry weight) by instar and total
annual production (±95% C.I.) for the two dominant
chironomids in shifting sand areas of the Sand River.

106

Rheosmittia sp.

Instar

No./m2

Mean wt.

No. loss

Wt . at

Wt . loss

Prod .

(mg )

loss

(mg/m2 )

(mg)

I+II

16464

0.0007

10674

0.0011

11.74

35.22

III

5790

0.0017

4308

0.0045

15.08

45.23

1482

0.0072

1482

0.0072

10.67

32.01

112.46

Annual

Production = 112

.46 x 2 =

224.92

±83.47 mg/m2/yr

Roback i a deme i jere i

346

0.0015

-5922

0.0023

-13.62

-54.48

6268

0.0035

-939

0.0066

-6.20

-24.79

ill

7207

0.0126

5813

0.0191

111.03

444.12

1394

0.0291

1394

0.0291

40.56

162.26

I 527.10

Annual Production = 527 . 10 x 1 = 527. 10 ±61.03 mg/m2/yr

•

107

Table III. 2 Macroinvertebrate density and dry weight biomass
estimates reported from unstable sandy substrates in some
large relatively unpolluted rivers (NR= not reported).

R i ver

Author

Samp 1 er

Mesh Size
(mm)

Dens i ty
(no./m! )

B i omass
(mg/m7 )

Comments

M i ssour i

Berner
( 1951 )

Petersen

grab

0. 19-12. 5‘

Hand

sorted

Amur

Zhadln and
Gerd ( 1961 )

4.1*

Includes
f 1 ne
grave 1 s

Dn 1 eper

It II II II

170'

•l II li ll

Dniester

II It W II

1500

493’

M 11 II II

Lena

II It II II

120-164

20.4-62.9'

•1 II II II

II tl II M

2.2-39. 1 1

II II N II

Vo 1 ga

II II II II

up to 9500

960-1440’

II It It II

Yenisei

It II II II

62.9'

II II II II

White Nile

Monakov
( 1969)

Petersen

grab

0.0-200

1 1 ve
sorted

Fraser

Nor thcote
et al .

( 1976)

Petersen
and Ponar
grabs

0.61

19-979

1 1-146'

Includes
grave 1 1 y
sand areas

Athabasca

Barton and
Lock (1979)

Ekman grab

0.18

1 100-40000

60-200

Athabasca

Barton
( 1980)

Airlift
samp 1 er

0.20

1675-3564

Mississippi

Seagle et
al . ( 1982)

Petersen

grab

0.61

200-300

1 Dry weight approximations from wet weights using conversion factor of
O. 1 7 ( Waters 1978) .

108

studies have indicated the relative ineffectiveness of these
coarse mesh sizes in retaining chironomid larvae and
oligochaetes (Mason et al . , 1975). This situation would be
aggravated by the minute size of most riverine psammophi lous
chironomid larvae. It is significant that the study
reporting the smallest mesh size in sample processing (0.18
mm; Barton and Lock, 1979) also reported the largest numbers
of invertebrates in sand areas. Because most studies have
used large mesh sizes, it seems probable that the abundance
and biomass of chironomidae in unstable sands have been
systematically underestimated.

Although macroinvertebrate densities can be high in
shifting sand areas, macroinvertebrate biomass and
production estimates are usually low relative to those of
many other lotic habitats (Berner, 1951; Zhadin and Gerd,
1961; Mann, 1975; Waters, 1977; Barton and Lock, 1979).

The beds of large lowland rivers are usually dominated
by unstable sandy substrates (Leopold et al . , 1964; Barton,
1980). Zhadin and Gerd (1961) indicate that 90-95% of the
beds of some rivers in the U.S.S.R. are composed of this
type of substrate. In the lower reaches of the Sand River, a
conservative estimate of the proportion of the river bed
composed of shifting sand is 80% (based on aerial
photographs and surface observations). I suggest that,
although shifting sand areas support relatively little
macroinvertebrate biomass or production on a per unit area
basis, these areas by virtue of their large size contribute

109

significantly to the total macroinvertebrate biomass and
production within the entire river system.

Although the role of shifting sand areas in river
ecosystems is poorly known, this generally overlooked
habitat is probably important because of its contribution of
biomass and secondary production. The sensitivity of
macroinvertebrate communities associated with shifting sand
areas is unknown, but possibly some of the differences
observed between my study and those of others are due to the
effects of human- induced perturbations or pollution of many
of the other rivers studied.

LITERATURE CITED

Barton, D.E. 1980. Benthic macroinvertebrate communities of
the Athabasca River near Ft. Mackay, Alberta.
Hydrobiologia 74:151-60.

_ , and M . A . Lock. 1979. Numerical abundance and biomass of

bacteria, algae and macrobenthos of a large northern
river, the Athabasca. Int. Rev. ges Hydrobiol.

64(3) : 345-59 .

Berner, L.M. 1951. Limnology of the lower Missouri River.
Ecology 32( 1 ) : 1—12.

Hynes, H.B.N. 1970. The ecology of running waters. Univ. of
Toronto, Toronto. 555 p.

Krueger, C.C., and F.B. Martin. 1980. Computation of

confidence intervals for the size-frequency (Hynes)
method of estimating secondary production. Limnol.
Oceanogr. 25(4):773-7.

Lenat, D.R. , D.L. Penrose, and K.W. Eagleson. 1981. Variable
effects of sediment addition on stream benthos.
Hydrobiologia 79:187-94.

Leopold, L.B., M.G. Wolman, and J.P. Miller. 1964. Fluvial
processes in geomorphology. Freeman, San Francisco.

522 p.

Mann, K.H. 1975. Patterns of energy flow. p. 248-63 In B.A.
Whitton [ed.] River ecology. Univ. of California,
Berkeley. 725 p.

Mason, W.T., Jr., P.A. Lewis, and P.L. Hudson. 1975. The
influence of sieve mesh size selectivity on benthic
invertebrate indices of eutrophication. Verh. Internat.
Verein. Limnol. 19:1550-61.

Monakov, A.V. 1969. The zooplankton and zoobenthos of the

White Nile and ajoining waters in the Republic of Sudan.
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Niewestnova-Shadina , K. 1935. Zur Kenntnis des rheophilen
Mi krobenthos . Arch. Hydrobiol. 28:555-82.

Northcote, T.G. , N.T. Johnston, and K. Tsumura. 1976.

Benthic, epibenthic and drift fauna of the Lower Fraser
River. Technical Report 11, Westwater Research
Institute, University of British Columbia. 227 p.

Nuttall, P.M. 1972. The effects of sand deposition upon the
macroinvertebrate fauna of the River Camel, Cornwall.
Freshw. Biol. 2:181-6.

Seagle, H.H., J.C.’ Hutton, and K.S. Lubinski. 1982. A

comparison of benthic invertebrate community composition
in the Mississippi and Illinios Rivers, Pool 26. Jour.
Freshw. Ecol. 1 (6) :637 — 50.

Shapiro, J. 1958. The core freezer: a new sampler for lake
sediments. Ecology 39(4):758.

Sioli, H. 1975. Tropical river: the Amazon, p. 461-88 In
B.A. Whitton [ed.] River ecology. Univ. of California,
San Francisco. 725 p.

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Biol. Assn. Scient. Publ. 29.

Waters, T.F. 1977. Secondary production in inland waters.
Adv. Ecol. Res. 10:91-164.

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mayfly population: a comparison of methods. Limnol.
Oceanogr. 18:289-96.

THESIS CONCLUSION

Three species {Pseud iron central is, Robackia
demeijerei, and an undescribed species of Rheosmittia ) of
benthic macroinvertebrates dominated the shifting sand areas
in the bed of the Sand River.

Pseud i ron centralis is a heptageniid mayfly associated
with areas of shifting sand for part of its larval life. In
these areas it preys upon chironomid larvae, which it
captures while foraging across the surface of actively
moving sand dunes. It is univoltine and spends most of the
year (July to April) in the egg stage.

Robackia demeijerei is a relatively small chironomid in
the subfamily Chi ronominae . The larvae utilize the
interstitial environment below the surface of shifting sand
areas. Robackia demeijerei larvae have been suggested to be
predaceous; however, no clear evidence of predatory behavior
was obtained in my study. Robackia demeijerei was found to
be univoltine in the Sand River, with an extended emergence
period .

Rheosmittia sp. is a member of the subfamily
Orthocladi inae . The genus was unrecognized until very
recently, probably due to the habitats frequented by
(rivers) and the small size of most members of this genus.

In the Sand River, larvae of Rheosmittia sp. also appear to
use the interstitial space available between sand grains in
shifting sand areas. Rheosmittia sp. larvae appear to feed
primarily on diatoms, probably obtained from the surface of

sand grains. This species was bivoltine in the Sand River,
with a winter and a summer generation.

Populations of these three species represent more than
80% of the mean macroinvertebrate biomass associated with
shifting sand areas and thus appear to be the major
structural elements of macroinvertebrate communities
associated with these areas in the bed of the Sand River. It
appears that Rheosmitt i a sp. larvae are herbivorous
exploiting psammophilic diatoms; R. demei jerei larvae are
predators or detr itivores , perhaps preying upon Rheosmitt ia
or utilizing the small amounts of organic material entrained
in shifting sands; and P. centralis larvae are predators,
preying upon larvae of both R. demei jerei and Rheosmitt ia
sp. .

Although shifting sand areas in the Sand River
supported high densities of macroinvertebrates, the mean
total biomass in these areas was lower on a per unit area
basis than those reported from many other types of riverine
habitats (Zhadin and Gerd, 1961; Barton and Lock, 1979;
Seagle et a/., 1982). The suggestion that shifting sand
areas could support relatively large amounts of
macroinvertebrate production per unit area was not supported
by my study, primarily because the dominant chironomids in
the Sand River exhibited relatively low generation turnover
rates. Macroinvertebrate production from shifting sands
appears to be generally lower than values reported for
entire faunas or even populations of single species in other

lotic habitats (Waters, 1977; MacFarlane and Waters, 1982).

Although the amounts of biomass and macroinvertebrate
production were low in shifting sand areas, there were
significant amounts. This is contrary to the suggestion that
such areas support few macroinvertebrates (Berner, 1951;
Hynes, 1970; Sioli, 1975) and indicates that these areas
should not be ignored in studies of rivers. This is
especially important if the contribution of shifting sand
areas is assessed for whole reaches of the river or for the
entire river system. Shifting sand areas dominate the beds
of most large lowland rivers, and thus the fauna of these
areas probably makes a major contribution to river
ecosystems .

Further Studies

Little is known about the ecology of the biota of large
rivers. I believe effective management of the river
resources requires a much better understanding of the biota
of these systems. I feel that my work raises some
interesting questions that if addressed would contribute
toward an enhanced understanding of river ecosystems.

The relationships between the three dominant
macroinvertebrates in shifting sand areas of the Sand River
were only briefly examined in this study; however, several
questions were raised. Some of the most interesting ones
involve the nature of food webs in shifting sand
environments. If both P. centralis and R. demejerei larvae

are predaceous, what then is the nature of the interaction
between these two species and their prey? Since P. central is
larvae prey on chironomids in shifting sand habitats for
only a small part of the year, do these chironomid
populations remain unexploited for the rest of the year?

An obvious question is whether the results of my study
can be applied generally to shifting sand areas in all
rivers. In terms of taxonomic composition, the
macroinvertebrate fauna of shifting sand areas in the Sand
River is similar to that found in other sandy rivers in
North America (Chapters 1 and 2). However, given the present
state of knowledge (Chapter 3), it is difficult to assess
objectively whether the density, biomass, and production
estimates obtained for shifting sand areas in the Sand River
are truly representative of these areas in general. Further
study is required to support or refute my view that most
studies have failed to sample macroinvertebrates effectively
in these areas.

I have attempted to compare my results only with
studies of other in relatively unpolluted rivers or in
unpolluted reaches of large rivers. But many of these rivers
have been modified for hydroelectrical generation, flood
control, and navigation. Hence, these rivers, irrespective
of differences attributable to sampling methods, may support
very different communities in shifting sand areas. If this
is true, then the macroinvertebrate fauna of shifting sand
habitats may be a important indicator of the health of a

river system. The usefulness of these animals as
biomonitoring tools is potentially great, if the sampling
problems could be overcome. The uniformity of shifting sand
habitats over long reaches of the river bed facilitates
comparisons above and below sources of human perturbation.
The low diversity and large number of individuals would also
probably aid in sample processing and estimating
macroinvertebrate density.

The shifting sand habitat of rivers is generally
considered an unfavourable habitat, because of the
instability of the substrate; however, this instabilty was
relatively constant and predictable over the life cycle of
the benthic macroinvertebrates examined in the Sand River.
Barton (1980) points out the devastating effects of
fluctuating river discharges on marginal silt and bedrock
areas in rivers. Areas of shifting sand appear to be
relatively unaffected by moderate changes in discharge, and
thus it is difficult to determine whether such areas are
relatively more or less unfavourable than other river
habitats. It would be interesting to determine whether the
low macroinvertebrate diversity of shifting sands is a
function of the physical stresses imposed by the instability
of the substrate in this habitat, or whether it is a
function of the long term predictability and uniformity of
this habitat.

- ■

119

LITERATURE CITED

Barton, D.E. 1980. Benthic macroinvertebrate communities of
the Athabasca River near Ft. Mackay, Alberta.
Hydrobiologia 74:151-60.

_ , and M . A . Lock. 1979. Numerical abundance and biomass of

bacteria, algae and macrobenthos of a large northern
river, the Athabasca. Int. Rev. ges Hydrobiol.

64(3) : 345-59 .

Berner, L.M. 1951. Limnology of the lower Missouri River.
Ecology 32 ( 1 ) : 1 - 1 2 .

Hynes, H.B.N. 1970. The ecology of running waters. Univ. of
Toronto, Toronto. 555 p.

MacFarlane, M.B. and T.F. Waters. 1982. Annual production by
caddisflies and mayflies in a Western Minnesota plains
stream. Can. Jour. Fish. Aquat. Sc i . 39:1628-35.

Seagle, H.H. , J.C. Hutton, and K.S. Lubinski. 1982. A

comparison of benthic invertebrate community composition
in the Mississippi and Illinios Rivers, Pool 26. Jour.
Freshw. Ecol. 1(6): 637—50 •

■

Sioli, H. 1975. Tropical river: the Amazon, p. 461-88 In
B . A . Whitton [ed.] River ecology. Univ. of California
San Francisco. 725 p.

Waters, T.F. 1977. Secondary production in inland waters.
Adv. Ecol. Res. 10:91-164.

Zhadin, V.I., and S.V. Gerd. 1961. Fauna and flora of the
rivers, lakes and reservoirs of the U.S.S.R.. (Transl
[1963] from Russian by Israel Program for Scientific
Translations) Smithsonian Institution and National
Science Foundation, Washington. 626 p.

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