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Oceanus 

The International Magazine of Marine Science 

Volume 21, Number 3, Summer 1978 



Peter MacLeish, Editor 

Paul R. Ryan,/4ssoc/ate Editor 

Deborah Annan, Editorial Assistant 



Editorial Advisory Board 

Edward D. Goldberg, Professor of Chemistry, Scripps Institution of Oceanography 

Richard L. Haedrich,/\ssoc/afe Scientist, Department of Biology, Woods Hole Oceanographic Institution 

John A. Knauss, Dean of the Graduate School of Oceanography, University of Rhode Island 

Robert W. Morse, Associate Director and Dean of Graduate Studies, Woods Hole Oceanographic Institution 

Allan R. Robinson, Gordon McKay Professor of Geophysical Fluid Dynamics, Harvard University 

David A. Ross, Associate Scientist, Department of Geology and Geophysics, Woods Hole Oceanographic Institution 

John C. Sclater,/4ssoc/afe Professor, Department of Earth and Planetary Sciences, Massachusetts Institute of Technology 

Allyn C. Vine, Senior Scientist, Department of Geology and Geophysics, Woods Hole Oceanographic Institution 



Published by Woods Hole Oceanographic Institution 

Charles F. Adams, Chairman, Board of Trustees 
Paul M. Fye, President of the Corporation 
Townsend Hornor, President of the Associates 



John H. Stee\e,Directorofthe Institution 



The views expressed in Oceanus are those of the authors and do not necessarily reflect 
those of Woods Hole Oceanographic Institution. 

Editorial correspondence: Oceanus, Woods Hole Oceanographic Institution, Woods Hole, 
Massachusetts 02543. Telephone (617) 548-1400. 

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Postmaster: Please send Form 3579 to Oceanus, Woods Hole, Massachusetts 02543. 



Contents 




THE FUTURE OF DEEP-OCEAN DRILLING 

byJ.R. Heirtzlerand A.E. Maxwell 

Scientists and government officials are assessing the International Program of Ocean Drilling -a 

major oceanographic effort now 10 years old - to determine whether the program should continue, 

and if so, what direction it should take. 




HELIUM ISOTOPES FROM THE SOLID EARTH: UP, UP, UP, AND AWAY 

by William J. Jenkins 

Oceanographers are tracing the path of the primordial isotope helium-3 to determine the rate at 

which the oceans and atmosphere are still forming. 




THE SCANNING ELECTRON MICROSCOPE IN MARINE SCIENCE 

by Susumu Honjo 

Scanning electron micrographs are allowing oceanographers in varied disciplines to unravel some of 

the mysteries surrounding the structure of marine organisms, microfossils, and the reactions of 

minerals in seawater. 1 O 



SEAGRASSESAND THE COASTAL MARINE ENVIRONMENT 

by Ronald C. Phillips 

Threatened by a variety of man's activities, seagrass meadows offer protection against coastal erosion 

and the potential of a vital food resource. 



Cover Micrographs 



RED TIDE AND PARALYTIC SHELLFISH POISONING 
by Barrie Dale and Clarice M. Yentsch 
Researchers studying "red tide" are coming up with 
some new theories about how shellfish become 
poisonous. A 1 



THE GREEN SEA TURTLE OF THE CAYMAN ISLANDS 
by James L. Considine and John J. Winberry 
The green sea turtle - once considered the world's most 
economically valuable reptile until threatened with 
extinction - is being revived as a resource at an 
experimental station in the Cayman Islands. C/l 



FRONT COVER: Scanning electron micrograph of the comb-like spines (V on a primitive crustacean, 
Cephalocarida (picture of the animal above, adult size about 3 millimeters, was photographed from 
model at Smithsonian Institution -circles indicate areas of cover photographs). 4,000x. BACK: the tip 
of the tentacles (2) of the same animal. 500x. Cover photographs by Susumu Honjo (see article page 
19). 

Copyright 1978 by Woods Hole Oceanographic Institution. Published quarterly by Woods Hole 
Oceanographic Institution, Woods Hole, Massachusetts 02543. Second-class postage paid at 
Falmouth, Massachusetts, and additional mailing points. 




The Future of 




Deep-Ocean Drilling 




by J. R. Heirtzler and A. E. Maxwell 

I he International Program of Ocean Drilling 
(IPOD) a joint research effort that has just 
completed a decade of important work is at a 
critical juncture in its development. The marine 
scientific community is pausing to assess the many 
accomplishments of the program as well as 
objectives not obtained. In short, it is trying to 
determine whether drilling should continue, and if 
so, how and at what cost. Among the significant 
results of the program which has been compared 
in importance with the first Challenger Expedition 
(1872-1876) that ushered in modern oceanography 

- have been data that support the theory of 
sea-floor spreading or plate tectonics, and 
indications of oil and metal deposits in the 
sediments at various coring sites. In addition, 
important information has been gathered relating 
to past climate periods for example, it has been 
established that Antarctic glaciation has lasted more 
than 20 million years, or more than four times the 
age previously accepted. ButtheC/omarCha//enger 

-the ship specially built for the project that has 
been used to drill more than 703 holes at 466 sites (as 
of Leg 61), along with sampling, measuring, and 
charting that has filled 42 volumes with data on 
underwater structure and sediment and basement 
rock composition is generally felt not adequate to 
meet the deeper and more demanding drilling of 
the 1980s. And so thought is turning to use of a 
larger vessel probably the salvage ship Clomar 
Explorer to conduct the major drilling efforts of 
the next decade (Figure 1). Thus it is appropriate 
here to review the early years of the program, 
addressing the questions relevant to its future 
direction. 

When the IPOD was implemented under its 
original name of Deep Sea Drilling Project (DSDP), 
its goals were to obtain samples of sediments from 
the world's ocean basins, and in the process, 
hopefully provide evidence to support the newly 
proposed plate tectonic or sea-floor spreading 
theory (see Oceanus, Winter 1974). On the early 
cruises of the Clomar Challenger, fossil-laden 



The Glomar Challenger a 10,500-ton vessel, 400 feet 
long, with a beam of 65 feet and a loaded draft of 20 feet. 
The drilling derrick stands 194 feet above the waterline. 
She is owned by Clobal Marine of Los Angeles, California. 



sediment cores tended to support the theory, 
convincing many land geologists, stratigraphers, 
and micropaleontologists who had been hitherto 
wary of the idea. In the course of collecting and 
analyzing core sediments, much was learned about 
the processes inherent in ocean basin 
development, the structure and composition of the 
oceanic crust, and the age and history of the earth. 

In fact, a major discovery occurred on the 
first voyage to the Gulf of Mexico: oil was found in 
sediment cores brought up from about 180 meters 
below the ocean floor. On later cruises, traces of 
hard minerals iron, copper, chromium, and 
vanadium were found. These discoveries have 
obvious significance as possible future energy and 
mineral sources. On the 13th cruise in 1970, another 
startling discovery was made. Salt deposits found in 
core samples, along with other data, led 
oceanographers to theorize that the Mediterranean 
six million years ago was not a sea, but a desert. But 
this was just the beginning: the data continued to 
accumulate, giving rise to several new concepts. 

Deep-Sea Drilling as a Scientific Tool 

It may not be immediately apparent that the 
processes that form the sea floor are more orderly 
and simple than those that shape and form the dry 
land. However, that is apparently the case. Since 
complex atmospheric forces have not disturbed it 
and man has not been there to change it artificially, 
the ocean floor geologic formations can be 
decoded to determine the earth's history. 

During the last 50 years, the ocean floor has 
been studied with remote acoustic sensing 
equipment, with bottom instruments on cables, 
and with short corers that penetrate a few meters 
into the bottom. All of these provided a first 
impression of the nature of the ocean bottom/ocean 
water interface as it now exists. 

In some places, the ocean floor is eroded, 
revealing older sediments, but if one really wants 
information on the nature of the bottom, such as 
underlying rock formation, drilling is required. 
Drilling on the continental shelf in water depths of 
200 meters or less has been undertaken by oil 
companies si nee the 1940s, butdrillingin thousands 
of meters of water has only been attempted 
recently. 

Deep-sea drilling began with Project 
Mohole, proposed in 1957 as an attempt to drill to 
the Mohorovicic discontinuity, which represents 
the boundary between the earth's crust and mantle. 
The project, funded by the National Science 
Foundation in 1961 , drilled off the California coast, 
penetrating 300 meters of sediment in 1 ,000 meters 
of water. In later drilling off Guadalupe Island, 
samples of basaltic basement rock were recovered 
from under 183 meters of sediment in 3,570 meters 
of water. This represented the first successful 




400' 



GLOMAR CHALLENGER 




618 



GLOMAR EXPLORER 

Figure 7. The Clomar Explorer can handle more than 10 
kilometers of drill pipe in contrast to the 7. 6 kilometers for 
the Glomar Challenger. In addition, the Explorer can 
operate in waves that are 72 meters high and in winds of 65 
knots, as well as in ice-covered polar seas. It is too large, 
however, to pass under bridges or to go through the 
Panama Canal. 



attempt to explore the sea floor, utilizing deep-sea 
drilling techniques. 

While in the processof choosinga sitetodrill 
to "Mono" northeast of Hawaii in 1966, the U.S. 
Congress discontinued funding for the project 
because of escalating costs. At this point, $25 
million had been spent, and it was estimated that 
another $100 million would be needed to complete 
the job. Despite its early demise, the project 
produced technical developments that later proved 
useful to the Deep Sea Drilling Project as well as the 
offshore oil industry. 

Two years prior to the Congressional action 
on Project Mohole, an organization was established 
called the Joint Oceanographic Institutions for 
Deep Earth Sampling (JOIDES). In 1965, this 
organization drilled 14 holes in the Blake Plateau - 
a large bottom feature off the southeast coast of the 
United States (see Oceanus, Winter, 1978). The 
success of this venture, undertaken at less cost than 
Project Mohole combined with the potential for 
significant scientific returns, was one of the chief 
factors that led the National Science Foundation to 
back the Deep Sea Drilling Project formally 
proposed by JOIDES in 1966. The Glomar 
Challenger was then ordered from Global Marine, 



Continental Drift and Sea-Floor Spreading 




150 TO 200 MILLION YEARS AGO 




80 TO 120 MILLION YEARS AGO 




Mid - oceanic ridge 




The Deep Sea Drilling Project core results have provided support for the concepts of continental drift and sea-floor 
spreading. Note above the jigsaw puzzle fit that can be made of the Atlantic coastlines of Africa and South America. In 
1885, Eduard Suess suggested that all the southern continents had once been joined as a supercontinent that he called 
"Gonwanaland." Some 30 years later it was proposed that there had been two continental masses, Laurasia in the 
north and Conwanaland in the south. Over the years, however, many scientists remained skeptical because of alack 
of clear-cut evidence. Supporting evidence for the continental drift theories began to emerge in the 1950s and 1960s 
with the discovery of rocks in Brazil that nearly matched others found in Gabon, West Africa. About the same time, 
sedimentary rocks, about 200 million years old, were found in Antarctica that contained fossil amphibians and reptiles 
found in other Gonwanaland continents. One of the problems with the continental drift concept was that no one had 
determined a reasonable mechanism for the movement of the continents. Thus the theory of sea-floor spreading 
(above) and plate tectonics emerged. Volcanic material is brought up in the center of the ridge, cools, and is forced 
away on either side by newer lava rising along the rift. The older crust is forced down again into the mantle in the deep 
oceanic trenches where it becomes part of a plate system. These plates are in motion relative to one another, either 
slowly moving apart with the creation of new crust, moving together with the destruction of old crust, or moving past 
one another. 



Inc., beginning her first cruise in the Gulf of Mexico 
in July, 1968. 

The JOIDES group initially consisted of four 
oceanographic institutions the Lament 
Geological Observatory of Columbia University 
(now Lamont-Doherty), the Institute of Marine 
Science of the University of Miami (now the 
Rosenstiel School of Marine and Atmospheric 
Science), the Scripps Institution of Oceanography 
of the University of California, and the Woods Hole 
Oceanographic Institution. Later, five more U.S. 
institutions were added the departments of 
oceanography at the University of Rhode Island, the 
University of Washington, Oregon State University, 
and Texas A & M, and the Institute of Geophysics at 
the University of Hawaii. In 1974, the project 
became an international one when the Soviet 
Union, West Germany, France, Britain, and Japan 
signed up, each making a direct contribution of $1 
million a year, plus much larger indirect ones. 
Beginning in November 1975, the DSDP was 
renamed the International Program of Ocean 
Drilling (IPOD). The title DSDP, however, was 
retained to identify the Scripps portion of the 
operations. 

In 1976, the member institutions from the 
United States incorporated to form Joint 
Oceanographic Institutions (JOI). This was done to 
allow the group to enter into formal contracts with 
the government in connection with the program. 
JOIDES, including its foreign members, continued 
as a subgroup of JOI. 

The Project 

The funding, organization, and operation of this 
program is an interesting example of a joint 
international research effort. Financial 
contributions from foreign members are received at 
the National Science Foundation, where the funds 
are added to the U.S. contribution. Utilizing this 
international funding base, the NSF contracts with 
the DSDP office at Scripps for the ship operation, 
preparation of initial reports, and core repositories. 
The funds are also used to support the JOIDES 
advisory structure through a contract with JOI. 
However, each country separately funds surveys of 
proposed drill sites and the post-cruise study of 
samples. 

The JOIDES advisory group consists of 250 
members, who make up 23 committees and panels. 
This body drafts the scientific part of the IPOD 
proposals, definingdrill shipobjectiveson each leg. 
It also appoints special committees, recommends 
sites to be surveyed and reviews safety factors, 
works out the drill ship schedule and provides for 
cruise staffing, recommends purchase of scientific 
equipment and special studies of samples, and 
oversees initial reports and matters relating to the 
curation of samples. While this may give the 
impression of administrative bureaucracy, 



Table 1 . Record as of Leg 60, May 1 978. 

1 . Completed 60 cruises of two months' duration in all 
oceans except the Arctic. 

2. Drilled a total of 1 96,652 meters below sea floor at 
466 sites (703 holes). 

3. At single locations, penetration up to 1,741 meters 
of sediment, 700 meters of basaltic basement rock. 

4. Longest drill string used 7,060 meters. 

5. Recovered a total of 54,408 meters of cores, stored 
in two repositories. 

6. More than 800 scientists have requested more than 
90,000 samples. 

7. More than 480 scientists have participated in 
Glomar Challenger cruises. 

8. Forty-two volumes of initial reports have been 
published, deposited in 393 libraries worldwide. 

academic marine scientists rate this project 
(according to a recent study conducted by the 
University of Connecticut) first in quality of all 
marine geological and geophysical work funded by 
Federal funding agencies. Table 1 lists some of its 
accomplishments. 

Few geological scientists doubt the success 
of the past decade of drilling, nor would they 
probably quarrel about the cost. However, the 
future requires a basic reappraisal. Among the 
questions that need to be answered are: Have the 
scientific results been worth the investment? Are 
future scientific achievements through continued 
drilling likely to provide significant advancement of 
the knowledge of the sea floor? Is present drilling 
technology adequate to meet future scientific 
requirements? What will the costs be? What priority 
does scientific drilling merit? These and similar 
questions must be answered by the scientific 
community to the satisfaction of government 
officials before any decision will be made about 
future drilling. Past successes have heavily 
depended on the availability of geological and 
geophysical information that was collected over 
many years in all areas of the oceans. These data 
allowed scientists to formulate many hypotheses 
concerningtheage, structure, and history of the sea 
floor. Subsequent drilling data permitted 
geophysical measurements to be correlated with 
geological reality, thusconfirmingor modifyingthe 
earlier hypotheses. However, this reservoir of data 
has been virtually consumed during the decade. 
Therefore, future studies must give high priority to 
gathering new geophysical and geological data. 
With additional geophysical information, specific 
scientific objectives can be defined that can be only 
resolved by drilling (Figure 2). 

A meeting was convened by JOIDES at 
Woods Hole, Massachusetts, in March, 1977, to 



identify more clearly the need and priorities for 
future deep-sea drilling and to assess new drilling 
technology. Participants included scientists from 
JOIDES and non-JOIDES institutions, 
representatives from industry and government, and 
members of foreign governments and institutions. 
At the meeting, scientific objectives were listed 
under four topics: passive margin, active margin, 
ocean crust, and paleoenvironment. It was stressed 
that drilling itself was not the objective, but merely a 
means to an end that future drilling should 
attempt to solve specific scientific problems. In 
addition, the meeting determined that many future 
objectives would be unattainable using the Clomar 
Challenger. For example, the ship does not have the 
capability of handling riser pipe, thus providing for 
return circulation; or setting blowout preventers, 
essential when drilling in areas of potential 
hydrocarbon accumulation; or working in high 
latitudes with ice cover. In examining other 
availabledrillingships, includingthose operated by 
industry, the meeting recommended that the 
government-owned Clomar Explorer be converted 
and used for drilling (Figure 1). TheExp/orer, 187 
meters in length with a displacement nearly five 
times that of the Challenger, has a significantly 
better capability; it can handle about 4,000 meters 
of riser, has blowout prevention equipment, and 
can suspend nearly 12,000 meters of drilling pipe, 
compared with a maximum of 7,600 meters now 
possi ble with the Challenger ( Figu re 3). The Explorer 
also can be easily strengthened to work at 
anticipated sites in the South Atlantic that have ice 
conditions. 

Participants at the meeting also 
recommended several alternative drilling programs 
for the future, which included various 
combinations of Challenger and Explorer drilling. 
Foran optimum scientific program, it was suggested 
that the Challenger continue to drill through 1983, 
overlapping with an Explorer program, running 
from 1981 through 1987. In addition, the meeting 
recommended strong geophysical and sample 
analysis programs. The group stressed that 
continued drilling was dependent upon adequate 
support in this area. The estimated total cost of such 
a program was $396 million, excluding inflation and 
Explorer conversion costs estimated at $52 million. 

The recommendations of the meeting at 
Woods Hole were subsequently approved and 
published by JOIDES in a document entitled "The 
Future of Scientific Ocean Drilling," which will 
serve as the basis for future planning. This has set 
the stage for a much broader evaluation of the 
program. The National Science Foundation has 
established scientific and engineering review 
panels. Similarly, there are committees within the 
National Academy of Sciences that are examining 
the program with a view to other scientific 
priorities. When these reviews are complete, their 




25Ni -=* 



85 



80 75 70 65W 

COASTAL PLAINS a CONTINENTAL SHELVES 
CONTINENTAL SLOPES 
CONTINENTAL & OUTER RISES 



Figure 2. Continental shelves, slopes, and rises off eastern 
North America. Other plateaus, rises, and abyssal plains 
are unshaded. Dots indicate holes drilled in the area. The 
triangle is where six companies are now drilling for oil and 
gas off New Jersey. Elongated dashed areas represent the 
East Coast Magnetic Anomaly (toward the west) and the 
Blake Spur Magnetic Anomaly (toward the east). The edge 
of the North American continent is thought to lie 
somewhere between these two anomalies. (After K. O. 
Emery, in preparation) 



recommendations likely will be key factors in 
decisions relating to any future drilling. 

The review process, too, will extend to other 
bodies beyond just the scientific community. A 
reappraisal of costs based on the Woods Hole 
recommendations puts a more realistic price tag on 
the program $693 million in 1978 dollars, 
escalated at 7 percent per year for the period 1979 to 
1988. Averaging out at about $70 million per year, 
this represents more than 75 percent of the present 
combined earth and ocean sciences research 
budgets of the National Science Foundation, or 
about 10 percent of the entire Foundation budget. 
The program thus requires new funds so as not to 
squeeze out other research programs. 
Consequently, the Office of Science and 
Technology Policy, the Office of Management and 



r 



East coast anomaly 



INTERNAL VELOCITIES 

in km/sec 




100 150 200 

DISTANCE (KM) 



250 



300 



Figure 3. Geophysical profiles across the continental shelf, slope, and rise southeast from Cape Cod. Drilling with an 
Explorer-type vessel could reach structures down to 10 kilometers. 



Budget, and the Congress all have begun their own 
investigations into the merits of the program. 

Scientific Results Thus Far 

The scientific accomplishments of the past decade 
of drilling fall under the topics of passive margins, 
active margins, ocean paleoenvironment, ocean 
crust, and downhole measurements. 

Passive Margins 

Passive conti nental margins are those where there is 
no spreading motion between the ocean and the 
adjoining continent. They are distinct from active 
margins, where the ocean floor goes under the 
continent, causing deep-sea trenches, 
earthquakes, and volcanoes. Both the North and 
South Atlantic margins are examples of passive 
margins. The North Atlantic margins are believed to 
have been created when a protocontinent rifted 
(split) and then spread about 180 million years ago. 

The purpose of drilling on the passive 
continental margins is to determine how this initial 
rifting and spreading occurred and to understand 
the subsequent hiatuses in sediment deposition 
caused by climate, ocean circulation, sea-level 
changes, and the geology of the adjacent 
continents. Holes have been drilled in the Atlantic 
off eastern North America, Africa, the European 
continent near the Bay of Biscay, and the Rockall 



Plateau. The results were especially valuable where 
the sediments werethin and prograding (advancing 
on) the continent/ocean boundary. An example is 
on the Rockall Plateau, where we found evidenceof 
subaerial (above sea level) relief during rifting. 
Lower Miocene hiatuses found on the Rockall 
Plateau (seeOceanus, Winter 1978) and in the Bay of 
Biscay correlate with deep boundary current 
seawater overflowing the Iceland-Faeroes Ridge. In 
both these drill sites, the carbonate content of the 
sediments relates to worldwide changes in the 
calcium carbonate compensation depth (the level 
below which the rate of calcium carbonate solution 
exceeds the rate of calcium carbonate deposition) 
and to transgressions and regressions on land. 

Off northwest Africa and the eastern United 
States, the sediments are thicker than off Rockall 
and Biscay, frequently in excess of 10 kilometers 
near the continental margins. Because the Clomar 
Challenger does not have blowout prevention 
equipment, that ship can not drill on the conti nental 
shelf, which contains thick sediment basins 
probably formed during rifting and initial 
spreading. On both sides of the North and South 
Atlantic, these areas are being drilled by petroleum 
companies. The Challenger has drilled on the outer 
continental margin and found rich organic layers. 
The possibility of petroleum deposits on the outer 
margin and beyond is thought to be good. 



8 



Active Margins 

The drilling of active margin sites is a relatively 
recent activity. It requires a longer drill string for the 
greater depths of water found near the active 
trenches and margins. The sediment found on the 
landward side of the trenches is also of greater 
thickness. 

The first major active margin drilling 
occurred in late 1977 in a traverse across the Japan 
Trench east of the island of Honshu. Some holes 
were not far from where a large earthquake 
occurred on June 11, 1978. Somewhat surprisingly, 
initial analyses of the cores had not revealed any 
oceanic sediments on the continental side of the 
trench, but revealed sediments with continental, 
rather than oceanic, affinities. It had been assumed 
that oceanic-type sediments would have been 
scraped off the oceanic basement rock as it was 
subducted under Japan. Not finding this prompted 
the overzealous/apan Times to run the headline 
"IPOD Survey Team Finds No Evidence Supporting 
Plate Tectonics Theory" - which, while true, does 
not disprove the plate tectonics theory. This voyage 
also determined that much of the sea floor west of 
the Japan Trench was once at or above sea level, 
emphasizing the great amount of vertical tectonics 
that occurs near active margins. 

A second major traverse across an active 
margin occurred in the late winter and springof this 
year. In this case, a traverse was made across the 
Mariana Trench westward to the South Philippine 
Sea basin. The analyses from these cruises were not 
completed at this writing. Other traverses will be 
made across the Middle America Trench off 
southern Mexico and Guatemala during the spring 
of 1979. 

Ocean Paleoenvironment 

Factors that influenced the oceans of the past 
include drifting continents, uplift and subsidence of 
the sea floor, and climatic changes. These factors, in 
turn, altered the biological, chemical, and physical 
oceanographic regimes of the oceans. While there 
is some discussion about which are the causes and 
which are the effects among some of these factors, 
the observational record is being rapidly filled in 
from the deep-sea drill cores. The lithologic and 
micropaleontologic records have revealed a 
number of highlights. 

The oldest sea floor is early Mesozoic in age 
(somewhat more than 150 million years old). Most 
of the microorganisms that provide the basis for 
marine biostratigraphy (the correlation of structure 
by biological means) first appeared in the oceans at 
this time. Establishment of the continuity of 
evolving forms and the integration of them into 
biostratigraphic units has resulted from the core 
studies. In fact, because of the usefulness of the 
microfossils from the deep-sea drilling collection, 
paleontological reference centers have been 



established in Bern, Switzerland, and Lajolla, 
California. Additional centers are being considered 
worldwide. 

Two central problems being studied through 
the use of this data are the changes from a warm 
ocean bottom water in the Early Cenozoic era to a 
colderocean more recently (Figure4), and achange 
from poor to well oxygenated water. There has been 
a very distinct cooling since the Late Eocene epoch 
(about 60 million years ago). Prior to that time, the 
high latitudes were warmer as was the ocean 
bottom (more than 10 degrees Celsius). Near the 
Eocene-Oligocenestratigraphic boundary there are 
widespread deep-sea unconformities and a rapid 
deepening of the calcium carbonate compensation 
depth by about 2 kilometers. This is probably 
related to changes in circumAntarctic currents due 
to the drift of Australia away from Antarctica and 
other continental reconfigurations. 

Drilling has shown that the 3,800-kilometer 
long Ninetyeast Ridge in the Indian Ocean was 
originally an ocean island and seamount chain, but 
has sunk nearly 3,000 meters since the Cretaceous 
period. This, too, probably had a major influence on 
circumpolar seawater circulation. 

Ocean Crust 

Among the earliest successes of the Deep Sea 
Drilling Project was the verification and calibration 
of the magnetic reversal time scale for the last 70 



MILLIONS 
OF YEARS AGO 



EPOCHS 



17 

21 


\ 


MID MIOCENE 
EARLY MIOCENE 


28 


/ 


MID-LATE 
OLIGOCENE 


31 


'^ 


MID OLIGOCENE 


37 


/__ 


EARLY OLIGOCENE 




J 




40 


"?" 


LATE EOCENE 


45 


*%- 


MID EOCENE 


49 


V ~~ N -^ 7 . 


MID- EARLY 
EOCENE 


55 
57 


_.-'' 


EARLY EOCENE 

LATE 
PALEOCENE 



5 10 15 C 

BOTTOM WATER TEMPERATURE 



Figure 4. A record of T-kilometer deep bottom water for 40 
million years in an area south ofNewZealand. This curve is 
based on oxygen isotope ratios (which give temperature) 
for benthic foraminifera from Leg 29 of the Deep Sea 
Drilling Project. (After Shackleton and Kennett, 1975) 



Dynamic Positioning and Re-entry 




u 




The Glomar Challenger uses "dynamic positioning" to hold station while drilling. Two thrusters forward and two aft, 
along with the vessel's two main propellers, are computer-controlled to hold position without anchors in water depths 
up to 6,000 meters so that drilling and coring can be accomplished. When a drill bit is worn out, the drill string is 
retracted, the bit changed and then returned to the same bore hole through a re-entry funnel placed on the ocean 
floor. High resolution scanning sonar is used to locate the funnel and to guide the drill string over it, which is 
maneuvered by a water jet. Operational re-entry was first achieved on Christmas Day, 1970, during Leg 75 in the 
Caribbean Sea. The relative position of bit and funnel are displayed at the surface on a Drill String Position Indicator 
Scope. The DSDP developed the re-entry technique because of being stopped short of scientific goals at many bore 
holes in the Atlantic and Pacific when the bit hit beds of flint-like rocks that dulled the bit and forced early 
abandonment of drill sites. 



million years. This was accomplished by a series of 
drill holes in the South Atlantic, which allowed 
dating of the sediments lying immediately above the 
basaltic basement rock by means of biostratigraphy, 
thereby determining the age of the crust. These 
ages could then be correlated with magnetic 
anomalies to yield a time scale that can be used to 
determine the worldwide rate of sea-floor 
spreading. 

One of the major new challenges at the 
beginning of the International Program of Ocean 
Drilling in 1975 was to drill a kilometer or more into 
the basaltic basement rock or ocean crust. Up to 
that time, only a few tens of meters of basement 
rock had been recovered. 

Recognizing that the generation of new 
ocean crust at the mid-ocean ridges was one of the 
fundamental geologic processes on earth, a 
program was devised to identify and study the 
igneous processes involved in formation, the 
possible modification of the crust by hydrothermal 
circulation, the nature of the magnetized rocks that 
give rise to linear magnetic anomalies, the aging of 
the crust away from the ridge axis, and other key 
problems about which there was no direct 
knowledge. 

Six cruises have been made in the Atlantic 
and one in the Pacific to study these problems. 
Crust from about 10 to 110 million years of age was 
drilled in the Atlantic where sea-floor spreading is 
slow and young crust was drilled in the Pacific 
where spreading is faster. From the very beginning, 
this drilling program produced surprises. 

The first discovery was that it was impossible 
to drill more than about 700 meters into the crust 
with the Glomar Challenger, because the crust was 
highly fractured with some layers broken down to 
sand-size pieces. The broken pieces bind the drill 
bit and prevent drilling. Fortunately, this is less of a 
problem in the older crust where cracks are filled. 
There also appears to be some evidence of 
hydrothermal circulation through the fragments 
(even away from the ridge axis). Future voyages will 
study these problems. 

Study of the rocks has shown that in a single 
hole several primitive magma types can be present, 
which are not related to each other by crystal 
fractionation. Magnetization of the rocks is 
consistent only over depths of a few tens of meters: 
it varies down the hole, and the direction of 
magnetization is rarely what might be expected 
from the analysis of sea-level magnetic anomalies. 
Furthermore, the petrology and magnetic signatu re 
with depth may vary from one hole to another even 
when the holes are only 50 to 150 meters apart 
(FigureS). 

These new findings have precipitated new 
models of crustal genesis with a large statistical 
element built into them. The simplistic models that 
were originally proposed for global sea-floor 



MAGNETIC INCLINATION () 



R N R N 

-80 *80 -80 *80 



R N 

-80 *80 



8] 



' ' ' ' 


4 


1111 ' * * 


























_ 


~ 











* 


200 *~ 





























300 

_ 
















- 



500 - 



600 

Hole 332A 



Hole 332B 



Hole 333A 



Figure 5. Observed magnetic inclinations from basement 
rock specimens from three nearby holes on Leg 37 of the 
Deep Sea Drilling Project in 7975. Hole 332B is only WO 
meters from 332A and hole 333A is less than 10 kilometers 
from either of the other two. Note that rocks from the same 
depth are magnetized differently even though the holes 
are relatively close to each other. This illustrates the great 
heterogeneity of the basement. 

spreading now need to be modified to include local 
variability. The use of submersibles to study rocks at 
mid-ocean spreading centers such as in Project 
FAMOUS, the Cayman Trough and Galapagos 
projects (see Oceanus, Summer 1977) has been 
of great assistance in trying to understand the 
spatial relationships of the newly determined 
geologic units. 

Downhole Measurements 

It is frequently difficult to relate the findings from a 
drill hole to the regional geology because the 
drilling provides such a small core sample. 
Accordingly, a downhole measurements program 
has been instituted to extend the base of knowledge 
out from the drill hole to tie in with regional 
geophysical surveys. 

This program includes measuring the in situ 
acoustic wave velocity, density, porosity, 
temperature, electrical resistivity and radioactivity 
along the length of the hole. These measurements 
give continuity to the study of samples down the 
hole when recovery is incomplete and give average 



11 



values for the sediments and rocks surrounding the 
hole (up to a few meters). 

Another group of experiments has been 
undertaken to sense even further from the drill 
hole. Oblique seismic experiments using a 
geophone down the hole and firing explosive shots 
nearby have led to a better knowledge of local 
average seismic velocities and their anisotropy. 
Electrical experiments with widely separated 
electrodes are being made to extend the range of 
resistivity information. These and other 
experiments will be compared with the 
measurements previously mentioned and with 
similar measurements made on land in comparable 
geologic environments. 

A third type of downhole experiment is 
presently being proposed. It includes instruments 
to be left in holes after the drilling ship departs. 
These include seismic sensors, strainmeters, and 
temperature and magnetic sensors. The 
experiments could also be expanded to include data 
on the diffusion of radioactive wastes. These 
instruments presently are all limited by battery life 
and the rate of data relay. The challenges should 
attract some of our best technical minds in the next 
few years. 

A Summing Up 

The JOIDES International Program of Ocean Drilling 
has completed its first decade. During this period, 
there have been notable achievements. Foremost 
are the scientific contributions to our 
understanding of the sea floor. This has allowed us 
to come to an understanding of the origin of mineral 
and petroleum resources. In addition, the program 
has been a model of international cooperation. It 
has brought together scientists from six countries in 
a unique management structure to provide 
scientific guidance to a complicated and expensive 
program. All six countries have participated in its 
financial support. Scientists from many countries 
have contributed to the results. 

As the program enters its second decade, 
there are critical decisions to be made. Should the 
drill ing continue in the face of the high 
technological costs that will be required to meet 
scientific objectives? Nearly $150 million has been 
spent and some $700 million will be needed for the 
next decade. In hindsight, the $125 million 
estimated to carry out the Mohole Project in 1966 
does not seem unreasonable. 



Earthquake and Crust Monitor 



The National Science Foundation recently 
announced a plan to monitor earthquakes and 
study the earth's crust by installing a seismic 
device in a hole drilled 450 meters below the 
ocean floor. 

The device, if successful, could be the start 
of a network of similar instruments placed at 
scattered undersea sites throughout the world. At 
present, there is a large land network of such 
devices called the Worldwide Seismic Net; the 
undersea project would be an extension of this 
network, giving scientists a type and quality of 
data not possible before. 

The hole is scheduled to be drilled in 
November by the Glomar Challenger. The device, 
an instrument package containing sensors and 
electronics, is the first of its kind to be placed 
under the sea floor. The hole will be drilled at a 
depth of 1,200 meters at the mouth of the Gulf of 
California, a site chosen because it is a small ocean 
basin being formed by a rifting of continental crust 
of the peninsula of Baja California away from the 
mainland of Mexico. 

The instrument package will be 10.1 
centimeters in diameter and 4.5 meters long, an 
adaptation of seismic devices that have been placed 
on the ocean bottom in the past. The instruments in 
the hole will be wired to a recorder on the ocean 
bottom; the recorder can be brought to the surface 
for data recovery without disrupting the sensors. 



In the final analysis though, the future of the 
drilling program will depend upon the quality of the 
science proposed and its economic and social 
implications. 

]. R. Heirtzler, a Senior Scientist in the Department of 
Geology and Geophysics at the Woods Hole 
Oceanographic Institution, has been involved in the Deep 
Sea Drilling Project since 7969, and A. E. Maxwell, Provost 
of the Institution, since its inception. Heirtzler is presently 
Chairman of the JOIDES Planning Committee and Maxwell 
is Chairman of the organization's Executive Committee. 



12 



OUTER SPACE 



Pb + He 4,000,000,000 yrs 




Figure 7. The geochemical cycle of helium. Long-lived radioactive substances, namely uranium and thorium isotopes, 
are continually decaying in the solid earth, becoming lead isotopes, but in the process producing helium atoms as a 
by-product. This helium escapes from the solid earth to the sea, then to the atmosphere, and eventually is lost into 
outer space. The numbers given are representative of the time which a given helium atom might spend in each stage 
of the cycle. 

Up, Up, Up, and Away 

by William J. Jenkins 

H elium is the second lightest element. It is also the abundance, it is one of the rarer elements in the 

second most abundant element in the universe. In earth. Forexample,ouratmosphereconsistsof only 

fact, next to hydrogen (the lightest element), it is the five parts per million helium; whereas, if it were 

major constituent of stars. Yet despite its cosmic present in its cosmic proportions, we would be 



13 



breathing air that was more than 99.9 percent 
helium! Now, we could explain part of this 
deficiency by postulating that helium was 
inefficiently lost when the earth was formed. Since 
helium is chemically inert (it is the lightest of the 
noble* gases), it would not have been tightly tied to 
the small particles that combined to form the earth, 
and so a small amount of heating could have caused 
it to "boil" off and be lost forever. However, there is 
another process that accounts for the scarcity of 
helium. 

Due to its light mass, helium tends to 
evaporate from the top of the earth's atmosphere, 
and is lost into interplanetary space. That is, a 
certain fraction (actually an incredibly small, but 
important fraction) of helium atoms achieve 
velocities in excess of the escape velocity** for the 
earth. These atoms obtain these speeds by a 
number of complicated processes; however, it is 
possible to calculate these effects, and thereby 
determine how rapidly we lose helium from our 
atmosphere. When these calculations are 
performed, we obtain the rather curious result that 
the residence timeof helium in the atmosphere (the 
amountof helium in theatmospheredivided by the 
loss rate) is about 10 million years. This may sound 
I ike a long time, but when we consider that the earth 
is4.5b/7//onyearsold, then this loss rate reduces the 
atmospheric helium inventory by a factor of 10~ 200 (a 
way of visualizing this figure is to consider that 10 2 
- 1/100 and 10 3 = 1/1 ,000, and so on). We thus are 
faced with the problem of explaining why we still 
havesomuc/7 helium! 

To understand this embarrassment of riches, 
wemustturn tothesolid earth. When theearth was 
formed, it inherited a number of long-lived 
radioactive elements. It is ultimately these 
radioisotopes that provide the heat for the earth's 
volcanoes and global tectonics. What is important 
for our story is that most of these elements (thorium 
and uranium isotopes), in the process of radioactive 
decay, produce alpha particles (helium atoms) as a 
by-product. It is the leakage of this radiogenic 
helium from the solid earth that serves to maintain 
what little atmospheric helium inventory we have 
against loss into outer space. Figure 1 shows the 
geochemical cycle of helium. Helium atoms are 
produced by the decay of uranium and thorium in 
the solid earth. The bulk of the helium leaks into the 
oceans, primarily by upwellingof mantle material at 



*The "noble" or "inert" gases (helium, neon, argon, 
krypton, and xenon) are a group of elements that have no 
chemical affinities and therefore do not become involved 
in chemical reactions of bonding. 

**As with rockets, or any projectile, there is a critical 
speed above which the projectile is travelling so fast that it 
will escape the gravitational pull of the earth. 



sea-floor spreading centers and eventually (by bulk 
fluid motion and gas exchange) enters the 
atmosphere. The ultimate fate of this helium, once 
in the atmosphere, is evaporation into outer space. 

So we have, at least in principle, an 
understanding of the geochemical cycle of helium. 
Or rather, most of the helium. Actually, helium 
consists of two isotopes. (The chemical nature of an 
element is governed by the number of protons in its 
nucleus. Hydrogen has one proton, helium two, 
lithium three, and so on. However, it is possible to 
have varying numbers of neutrons without 
changing the atom's chemical nature. Different 
atoms with different neutron numbers, but the 
same proton numbers are called isotopes.) We were 
dealing with helium-4 ( 4 He), which constitutes 
about 99.9999 percent of all helium. The remaining 
one millionth consists of the lighter isotope 
helium-3 ( 3 He two protons and only one 
neutron). Itmayseem pointless to worry aboutsuch 
a small fraction, but this isotope has important 
consequences. 

Although there is a process in the solid earth 
that produces a small amount of helium-3, there are 
none that produce significant amounts. This means 
that what helium-3 we see escaping from the earth 
must be primordial that is, it was trapped when 
the earth was formed. This is of great interest to 
geochemists for two reasons. First, this is very clear 
evidence that the earth isstill losingvolatiles that 
is, the earth's atmosphere and oceans are still in the 
process of formation. How rapidly the earth is 
degassing is the subject of considerable debate; we 
will discuss this later. Second, it is possible to 
determine the magnitude of this helium-3 flux. 
Once we know what the flux is, we can use it to 
calibrate other geochemical fluxes. 

The question is: how does one measure the 
helium-3 flux? There is little doubt that such a flux 
exists. Excess helium-3 has been detected in hot 
springs, geothermal wells, fumaroles (vents), 
volcanoes, and in basaltic magmaextruded onto the 
ocean floor. More importantly, this excess helium-3 
has been seen in seawater throughout the entire 
Pacific and in all the other oceans. Recalling Figure 
1 , one realizes that the oceans act as an integrator 
for the helium flux. Since the oceans circulate on a 
time scale of about a thousand years, the deep 
waters will pickup many centuries worth of helium. 
In fact, we have used the oceans as a clock to time 
and amplify the helium-3 flux. This is done by using 
the observed distribution of excess helium-3 in the 
oceans coupled with what we have learned about 
the circulation of the oceans from radioisotopes, 
such as carbon-14. This flux calculation gives an 
estimated terrestrial helium-3 flux of about 4 atoms 
per square centimeter per second. This estimate is 
in very good agreement with independent, 
theoretical estimates of the loss rate of helium-3 
from the atmosphere a loss rate that must balance 



14 



the terrestrial input. Dividing this flux into the 
atmospheric inventory gives the residence time of 
helium-3 in the atmosphere to be about a million 
years. This shorter residence time (relative to 
helium-4, which is about 10 million years) is a result 
of the fact that helium-3 is lost at a 
disproportionately higher rate than helium-4, due 
to its lower mass. Of course, if helium-3 is lost at a 
disproportionately higher rate than its more 
abundant sibling, then it must begained at a 
disproportionately greater rate. This is to say, the 
isotopic ratio ( 3 He/ 4 He) of helium coming from the 
deep earth is much higher (about 10 times higher!) 
than the atmospheric ratio. This way we can seevery 
clear isotopic signatures where natural variations in 
the amount of helium might mask the primordial 
flux. 

An additional flux of helium comes from the 
continental crust. As we understand it, the 
continental crust was created by magma that has 
worked its way up from the deep earth , cooling and 
degassing at the surface. Thus these rocks have 
given up their original helium-3 signal. However, 
the uranium and thorium isotopes concentrated in 
these rocks are continuously producing almost 
pure helium-4, so what helium is released from 
these rocks has an isotopic ratio ( 3 He/ 4 He) from 10 to 
100 times lower than the atmosphere. That there is 
any helium-3 at all is the result of a secondary 
reaction on lithium nuclei caused by the 
radioactivity of the uranium and thorium isotopes. 

So what we see in nature are three 
characteristically different kinds of helium, with 
very different isotopic ratios (see Table 1). The fact 
that they differ by factors of 10 (whereas we can 
measure these isotopic ratios to less than a percent) 
makes their detection very easy. 

Helium From the Galapagos 

We had learned from measuring the distribution of 
this primordial helium-3 excess in deep waters that a 
lot of the helium appeared to be coming from the 
eastern equatorial Pacific. This was not particularly 
surprising since this area was known to contain the 
fastest spreading ridges in the world. In keeping 
with this high tectonic activity, such as sea-floor 
spreading, it is natural to expect to see a lot of 
primordial helium. Consequently, when/4/wn 



500 - 



400 



300 



I 



200 



i 



100 



3 He/ 4 He =1 08 .OZxICT 5 ^?. 



VENT AREAS 

GARDEN OF EDEN 

* CLAMBAKE 

O OYSTER BED 
D DANDELIONS 




10 20 30 40 50 60 

4 He CONCENTRATION ( 10' 8 cc(STP)g-') 

Figure 2. Observed 3 He and 4 He concentrations in the 
Calapagos submarine hydrothermal springs. Note the tight 
correlation about a straight line despite the nearly five-fold 
variation in concentrations. Compare the massive 
enrichment to background (ambient) concentrations in 
the darkened rectangle. The other trend line shows what 
would happen if the helium came from the atmosphere. 



made its historic dives to the Galapagos submarine 
hot springs last year (see Oceanus, Summer 1977), 
we made sure to take samples for measurement of 
helium isotopes. 

We were not disappointed. We found 
enormous enrichments of primordial helium in 
these samples (Figure 2). Some of the samples we 
analyzed were almost 100 times enriched in 
helium-3 and more than 10 times enriched in 



Table 1 : The kinds of helium seen in nature. 



Type of Helium 



Typical Places Observed 



Isotopic ( 3 He/ 4 He) Ratio 



Primordial 

Atmospheric 
Continental 



Volcanoes, hot springs, 
spreading ridges 

In the air 

Natural gas wells, 
uranium mines 



1.5x10* 

1.4x10* 

1 x 1 8 to 1 x 1 7 



15 



helium-4 over background seawater. It happens 
that even the background seawater was almost 50 
percent supersaturated in helium-3 the highest 
enrichments seen in ocean waters to date. To get 
the perspective, note the small black rectangle in 
Figure 2, which represents the contents of 
background seawater. 

As we expected, the isotopic ratio of this 
superabundance of helium was almost 10 times 
atmospheric. For comparison, a trend line is shown 
(Figure 2), which the helium data would follow if 
what we added was air. 

The water from which this helium came also 
was noticeably warmer than surrounding seawater. 
This, too, is no surprise, since the helium is being 
carried up from below by molten rock. What was 
encouraging was the very distinct correlation 
between the temperature of the water and the 
amount of excess helium-3 in it (Figure 3). To see 
how useful this could be, we must digress a 
moment. 

When new oceanic crust is formed by 
upwelling magma, it cools and spreads outward as it 
is displaced by more new magma: hence the 
concept of sea-floor spreading or plate tectonics. It 
is possible from simple models to predict the 
amount of heat yielded by this spreading crust, and 
the rate at which it is conductively cooled. 
However, when scientists measure the heat flow 
from the ocean floor, especially near the axis of this 
spreading, they see substantially lower levels of 
conducted heat (Figure 4). Because of this, it has 
been suggested, and subsequently shown, that this 
missing heat is carried away by hydrothermal 
convection of seawater. As the rocks form and cool, 
thermal stresses are set up that crack and fracture 
them. Seawater penetrates these cracks, pervading 
(some scientists believe) as deep as five kilometers. 
The seawater is heated by the upcoming hot magma 
and the surrounding rocks, and begins to rise - 
issuing forth on the ocean bottom as hot springs. 
Isotope and chemical data from the Galapagos 
expedition indicate that the rocks exchange heat 
and chemicals with the water at temperatures 
around 300 degrees Celsius, but by the time the 
water reaches the ocean floor, it has entrained and 
mixed with so much cold seawater that it is a tepid 20 
degrees Celsius or so. A few meters above the 
ocean floor these plumes of hydrothermal water are 
so dilute that their temperatures are only a few 
thousandths of a degree above normal. Thus it is 
very difficult to see their impact by standard 
oceanographic sampling techniques. 

Despite this anonymity, these quiet springs 
do carry a substantial fraction of heat away from the 
spreading ocean crust. Now, since we know the 
helium-3 flux (we can see it throughout the world 
oceans), we can use the observed heat/helium-3 
ratio in the hydrothermal waters to extrapolate to a 
global scale convective hydrothermal heatflux. This 



400 



300 






^ 200 
I 



100 



D 
O D 



O 



VENT AREAS 

GARDEN OF EDEN 

A CLAMBAKE 
O OYSTER BED 
a DANDELIONS 



4 6 8 (0 12 

CORRECTED TEMPERATURE (C) 



14 



Figure 3. Observed heat/ 3 He correlation in the Galapagos 
submarine hydrothermal waters. The trend is definite, 
although scattered. The scatter is largely due to 
uncertainties in the temperature of the water, and to local 
variations in the heat/ } He ratio. 




a) A hypothetical oceanic spreading ridge 



s Theoretically predicted 

S v*^heat - flow 




b) Theoretical (dashed line) and observed (solid line) heat flow 
curves for a) 

Figure 4. The difference between the observed (solid line) 
and theoretically predicted (dashed line) heat flow for a 
spreading ridge. The heat deficit, the area between the two 
lines, is the convective hydrothermal heatflux. This heat is 
carried away by seawater which permeates through 
fractured and cracked rocks andconvects upward. It is this 
process that also carries chemicals to and from the freshly 
formed oceanic crustal rocks. 



16 



seems a rather brash thing to do, for we are dealing 
with only one small corner of the world, but, in 
defense of this, we pose the following argument. In 
such a situation, there is always enough seawater 
around. In addition, the processes that do transport 
the heat namely convection and permeation - 
are likely self-limiting. That is, if less water reached 
the heat source, it would become hotter. But what 
water did penetrate would not only cause more 
fracturing (due to the greater thermal shock), but 
would be more violently convected, causing more 
water to be drawn in and balancing the system. 

Returning to the data, we use the observed 
heat/helium-3 ratio (7.6 x 10' 8 calories per atom of 
helium-3) and the observed helium-3 flux (2 x 10 19 
atoms per second) for the entire earth to estimate 
the convective hydrothermal heat flux to be 5 x 10 19 
calories per year. Various scientists have estimated 
this heat flux by subtracting their observed 
conductive heat flow data from the theoretical 
curve (Figure 4) and they obtain estimates from 4 to 
6 x 10 19 calories per year. Therefore, this represents 
the first experimental proof of their estimates. 

Moreover, we can use the helium-3 data to 
look at chemical fluxes from the deep earth. 
Evidence from sedimentary records clearly 
indicates that the oceans are approximately in a 
chemically steady state that is the relative 
abundanceof dissolved chemicals in theoceans has 
not changed substantially in the last few hundreds 
of millions of years despite the fact that sediment is 
forming from the dissolved chemicals and that 
materials are being carried to the oceans by winds 
and rivers. What this means is that the fluxes into 
and out of the oceanic reservior must balance. 
Geochemists have been occupied with looking at 
these fluxes and trying to balance the oceanic 
budgets for each element. This works well for most 
elements: the river flux, as measured by the river 
water flow and the amount of chemicals contained 
in that flow, quite closely matches the sedimentary 
flux, as determined by measuring the rate of 
sedimentation and chemical composition of the 
sediments. Scientists have long recognized, 
however, that for certain elements (notably 
magnesium [Mg] and calcium [CaJ) the oceanic 
budgets need an additional source (for Ca) or sink 
(for Mg) to balance out. It has been suggested, and 
indeed determined by observation, that cooling 
rocks take up magnesium from seawater in return 
for calcium and other elements (see Oceanus, 
Summer 1977). Until now, it had not been possible 
to quantify these exchanges, but by correlating the 
observed chemical anomalies with the helium-3 
anomalies in the same way as we did for heat, we 
can compute these chemical fluxes. The results 
(chemical measurements are still in progress at the 
Massachusetts Institute of Technology) are 
encouragingly close to what we need to balance the 
budgets, but with a few interesting surprises. 



The Degassing of the Earth 

As mentioned before, the presence of primordial 
helium-3 is the first real evidence that the earth is 
still degassing. Also, the measured helium-3 flux is 
the first hard number for the rate of degassing. You 
may ask whyan oceanographerwould be interested 
in such a thing, but it is by this process that the 
oceans and atmosphere were formed. All today's 
water and air used to be inside the solid earth, and 
were released in the process of the formation of the 
crust that is, degassing. It then becomes of 
interest to ask ourselves: is it over? If not, how 
rapidly is this formation process taking place? How 
rapidly did it take place in the past? 

The answers to these questions, and many 
more, are tied upinthegeochemical budgets of not 
just helium, but many other elements; and in the 
complex physics and chemistry of the entire earth, 
solar system, and even the stars. To compound the 
difficulty, we are looking at the present a relative 
snapshot and trying to guess what has happened 
over the last four and a half billion years. 
Nonetheless, we do have some information 
available. We know the helium isotope fluxes, and 
we therefore know a good deal about the helium 
budgets. From global heat-flow measurements, we 
can learn something about the abundances of the 
radioactive elements, for it is these elements that 
provide the heat energy, and helium-4for the 
earth's volcanism and tectonics. Thus we can set up 
a number of budgets which we must satisfy in order 
to explain the degassing of the earth. Then we test 
different theories on how the oceans evolved. 

First, we suppose that the earth's degassing 
rate has been constant over all geologic time. When 
we try to balance the budgets, we find that we 
cannot simultaneously satisfy both the uranium and 
the helium budgets. What this tells us is that the rate 
at which the earth is degassingmusf have varied 
over the earth's history. 

This is not surprising at all. The radioactive 
substances that produce the heat which drives the 
degassing process are themselves disappearing, 
and decreasing in concentration with time. As a 
result, we would quite naturally expect a decrease 
in degassing activity with time. When we apply a 
time varying (exponentially decreasing) degassing 
with time, we find a very good balance for our 
budgets. What is encouraging is that the time 
dependence which results quite naturally from this 
analysis is fairly similar to the time-dependence of 
the radioactive heat production (Figure 5). 

This might be expected, as the earth will try to 
"thermostat" itself. If there is a great amount of heat 
production in a parcel of mantle material, it will 
become very warm and expand. As with 
Archimedes' principle,* it will try to float (or at least 

*A body floating in a fluid displaces a weight of fluid equal 
to its own weight. If the density of the body is lighter than 
that of the fluid, the body will feel an upward force, or 
buoyancy. 

17 



I 

K-. 
<o 



k 

* 



a) Terrestrial heat production 
over geologic time 



fc 



to 5 



ki 



4 present 
TIME (billions of years ) 

b) Terrestrial degassing 



4 present 
TIME (billions of years) 




c) Accumulation of the 
oceans and atmosphere 



4 present 

TIME (billions of years) 



Figure 5. The degassing of the earth. The theoretical 
calculations of the helium and uranium budgets produce 
a degassing curve for the earth (b), which looks quite 
similar to the heat production curve (a). Figure (c) shows 
the growth of the oceans and atmosphere that would result 
from the calculated degassing curve (b). 



rise). In addition, the material will become less 
viscous, so that the motion will be enhanced. 
Consequently, a higher heat production will lead to 
more vigorous convection and hence more rapid 
degassing. So what we see, or at least predict, is a 
more rapid accumulation of the oceans in the first 
half of the earth's history coupled with a more 
gradual, butstill on-going accumulation in the latter 
half. 

We can test this theory against an additional 
budget: that of argon-40 ( 40 Ar). This is the third most 
abundant gas in our atmosphere (about 1 percent of 
air by volume is argon), and is almost totally derived 
by the decay of potassium ( 40 K). Unlike helium, 
argon-40 cannot escape the atmosphere once it is 
degassed from the solid earth, so that it represents 
an integrator of the degassing process. When we do 
try to balance the argon-40 budget, we find we must 
accountfor the portion produced in the continental 



crust, for not all of it is retained in the rocks where it 
is formed (about half escapes). When we do this, we 
find remarkably good agreement with what we see. 
This tells us that we are indeed on the right track. 

Unfortunately, the story does not end here, 
because inevitably we will have to balance and 
explain the budgets of all the elements, resolving 
our predictions with the physics and chemistry of 
the earth. There may never be an ultimate answeror 
test to our questions, for we are delving into a highly 
speculative and uncertain area of geochemistry. But 
perhaps that is what makes it so rewarding. 



William ]. Jenkins is an Assistant Scientist in the Chemistry 
Department at the Woods Hole Oceanographic 
Institution. 



18 















... 






' 



A f / ^Si 



\ . The Scanning m 
Electron Microscope 

% 'n Marine Science > ^ 

./ .1 "" 5^J 

' > :. "-M- 



by Susumu Honjo 

I he scanning electron microscope (SEM) 
is an important tool for ocean scientists. 
They use it to study minute plankton, 
bacteria, and suspended particles - 
unraveling the mysteries of the complex 
relationship these organisms have to the 



A scanning electron micrograph of the 
surface skeleton of a primitive crustacean, 
Cephalocarida (see cover photographs, 
contents page, and Figure 9). 20,000x. 
(Photo by Author) 



^ 








Light Microscope 



environments they inhabit. The SEM also is a 
sensitive instrument for assessing the slow but 
important chemical reactions of seawater with 
minerals, and the path of surplus nutrients from the 
surface layer to the deep ocean floor. Ocean 
micropaleontologists use it to study microfossils in 
the deep-sea sediment, reconstructing past climate 
epochs and estimating future changes. In a sense, 
the user of the SEM is an explorer, seeking to 
uncover the fine details of the world of marine 
matter. In addition to revealing this ultrastructure, 
the photographs produced by the scanning 
electron microscope often are exquisitely abstract 
in an artistic sense. 

There are three basic types of microscopes - 
the light microscope, the conventional electron 
microscope (often referred to as the transmission 
electron microscope), and the scanning electron 
microscope. It should be stressed that these 
instruments do not compete with each other, but, 
in fact, complement each other by supplying the 
scientist with different kinds of information. One of 
the major features that sets the scanning electron 
microscope apart from the light microscope and the 
conventional electron microscope is that it 
produces three-dimensional images, whereas the 
two other microscopes generally produce 
two-dimensional ones. 

The light microscope first built in the 16th 
century presents an image in two dimensions 
because it has a very limited depth of field, focusing 
sharply in only one plane. In essence it is limited by 
the fundamental nature of light, which imposes a 
limit on the resolution of images. This means that it 
cannot separate dots that are closer together than 
2,000 or 3,000 angstroms (1 angstrom is 1/10,000 of a 
micrometer). The light microscope works best with 
thin samples viewed by transmitted light, or with 
flatter samples, viewed by reflected light. 

The technical development of the 
conventional electron microscope gave scientists 
clearer access to the world between the cellular and 
molecular realms of existence. The best 
transmission electron microscopes have a 
resolution of between two and five angstroms, so 
that the maximum effective magnification exceeds a 



million diameters. Although the physical concepts 
upon which electron microscopy are based can be 
traced to the 19th century, two important events in 
the early 1900s led directly to the building of the 
electron microscope. The first was de Broglie's 
theory that a moving electron might have the 
properties of a light-like wave. The second was a 
demonstration by Busch that suitably shaped 
magnetic or electrostatic fields could be used as 
true lenses to focus an electron beam to produce an 
image. 

It was not, however, until the mid-1930s 
when scientists were studying the functions of the 
cathode ray tube that the electron beam was 
harnessed for use in the electron microscope. The 
shorter the wavelength used in microscopy, the 
higher the potential resolution. The transmission 
electron microscope achieves much higher 
resolution than the light microscope because 
electrons when subjected to high voltage (say 
100,000 volts) have wavelengths several orders of 
magnitude shorter than visible light. Actually the 
function of an electron microscope is the same as 
the light microscope. The latter makes use of glass 
lenses to focus light, while the former incorporates 
electromagnetic coils to deflect the electron beam. 

One feature of the transmission electron 
microscope is that the inside of the scope has to be 
kept in a very high vacuum to prevent the beam 
from being intercepted by air molecules. This is also 
one of the disadvantages of the microscope in that 
any sample has to go into the high vacuum area, 
exposing it to the bombardment of the electron 
beam. The transmission electron microscope 
requires thinner samples than the light microscope 
because only those electrons that emerge from the 
specimen with a narrow range of energies can be 
focused in a single image plane by the magnetic 
field of the objective lens. In most cases, it is the 
electrons that have been deflected but not changed 
in energy that are utilized to form the image. The 
thicker the specimen, the more likely is an electron 
to lose energy as it passes through. This is why the 
sample for transmission electron microscopy must 
be very thin, usually not more than 800 angstroms 
thick. It must be completely dehydrated, with all 
volatile matter removed. This severely limits the 
kinds of objects that can be observed without 
preparation and special preservation in our case 
microskeletons of marine organisms, such as 
diatoms and coccoliths, which are essentially made 
of hard minerals. The resulting image produced by 
the transmission electron microscope tends to be a 
"shadow graph," a map, in effect, of the mass 
density of the specimen (Figure 1). 

Diatoms are microscopic algae. Since the 
19th century, their regularly spaced siliceous 
frustules have been used to check the resolution of 
the light microscope. The diatom also was the 
common object used by physicists and engineers in 



20 



Figure 7. Transmission 
electron "shadow graph" of 
a valve of a diatom, 
Thalsassiosira, suspended 
at 3, 000 meters in the 
central Pacific. 
Magnification 2,000x. 
(Photo by Author) 




the early stages of electron microscope 
development. Systematic studies of diatoms and 
coccoliths (minute calcite scales of marine algae) 
also were accomplished shortly after this period. It 
was not, however, until the development of a 
complex replication technique that sedimentary 
rock could be brought under the electron 
microscope. The process involves replicating 
samples with a thin film of carbon by vacuum 
evaporation. It has been a standard technique for 
manyyears (Figures 2 and 3). 

The scanning electron microscope 
developed rapidly in theyears after World War II. By 
themid-1960s, itwas ready to serve applied science. 
The microscope is able to provide 
three-dimensional images because generally it 
records not the electrons passing through the 
sample but the secondary electrons that are 
released from the specimen as a result of its 
interaction with the primary electron beam. 



Usually, only those secondary electrons originating 
near the surface of the specimen are seen; the 
sample therefore can be of any size and thickness 
that will fit in the instrument's evacuated sample 
chamber. The secondary electrons are not focused 
but are simply collected in a device known as an 
electron detector where they are amplified, 
producing a signal that is relayed to the cathode ray 
tube to create the image. With the scanning 
electron microscope, a microscopist can start from 
a tangible image at hand-lens range and zoom up to 
a magnification of 100,000x, with a routinely 
obtainable resolution of 100 A. Ordinary electron 
microscopes are incapable of operating at less than 
a few hundred magnifications. Because thin 
specimen slices are not required, the preparation of 
samples for the scanning electron microscope is 
generally much simpler than it is for the light 
microscope or the transmission electron 
microscope. 



Figure 2. Transmission 
electron micrograph of 
carbon film replication of 
coccoliths, 

Syracosphaera, from the 
central Pacific. 
Magnification 10,000x. 
(Photo by Hisatake Okada) 




21 



How the SEM Works 

In scanning electron microscopy, the sample is 
scanned by a focused electron beam and the image 
that results is formed by a technique similar to that 
used in television sets. There are two major 
differences. First, the standard TV picture is made 
up of 525 horizontal lines, whereas the SEM image 
can be adjusted from 100 lines to more than 1 ,000. 
This finer scan is used to produce the micrograph. 
Second, the rate of the SEM scan is often slower than 
the scanning rate in television. Thus the resulting 
micrograph is an image produced by a slow-moving 
electron beam. While one can speed up the 
scanning pattern for visual inspection, a time 
exposure of several minutes is often needed to 
obtain high-resolution micrographs of the best 
quality. A diagram of the instrument is shown in 
Figure 4. Electron lenses (L) focus the primary 
electron beam (PE) down to a diameter of 
approximately 50 to 100 A on the surface of the 
specimen. This beam is deflected by two pairs of 
coils (C) in combination with the deflection control 
(DC) to perform a square scanning motion by 
moving line after line across the specimen surface 
(between 1 ,000 and 2,500 lines per frame). When the 
surf ace of the spec! men is hit by the electron probe, 
it generates what is known as "slow" (low energy) 
secondary electrons (SE) that belong to the surface 
of theobject. Atthe same time, "fast" (high energy) 
backscatter electrons (BE) are generated. Both types 
of electrons are collected in an electron detector 
(D). The slow secondary electrons are attracted by 
the positive field of the detector and are accelerated 
in the detector. The electrons impinge on the 
surface of a scintillator (SO and generate photons. 
These are directed into a photomultiplier (PM) by 
means of a light guide (LC), where they release 
electrons that are instantly multiplied. The 
photomultiplier signal is then put into an amplifier 
system (A), whose output governs the intensity of 
the electron beam of the display cathode ray tube 
(CRT). On the video screen of the CRT, an image 
is built up in synchronism with the scanning 
movement of the initial electron beam on the 
specimen surface. The image represents the 
projection of the specimen surface as seen from a 
perspective along the center of the electron beam. 
Every location on the surface is represented by an 
image point on the video screen. Areas of high 
secondary electron emission are light and vice 
versa. The resolution of the picture is defined by the 
size of the primary electron beam; to a certain 
point, the smaller the diameter of the electron 
probe, the better the resolution. The magnification 
is changed by scanning different size areas of the 



Figure 3. Electron micrograph of plastic-carbon film 
replication of Miocene fine-grain carbonate rock 
deposited in the deep-sea environment off the northwest 
Spanish coast. 5,000x. (Photo by Author) 




CRT 



DC 



A 




SC 



Figure 4. The scanning electron microscope. A = signal 
amplifier; C = scanning coils; CRT = cathode ray tube with 
video screen; D = electron detector; DC = deflection 
control; E = emitted electrons; C = electron gun; L - 
electron lenses; LC = light guide; M = magnification 
control; PE = primary electron beam; PM = 
photomultiplier; SC = scintillator; SP = specimen. (After 
C. Pfefferkorn, 1975) 




The author, right, and assistant examine scanning electron 
micrograph in SEM facility at the Woods Hole 
Oceanographic Institution. 

specimen and displayingthe signal on the same size 
video tube. 

Examples of Research Projects 

The deep sea is a severe environment. It is a world of 
total darkness, constant low temperatures, and 



23 





Figures. At left, scanning electron micrograph of sediment gathered by sediment trap experiment in Sargasso Sea at 
5, 300 meters. Oval object is the fecal pellet of a small zooplankton produced in surface waters. It contains coccoliths, 
clay minerals and a large amount of undigested organic matter from phytoplankton. 400x. At right, acloseupofafecal 
pellet. 4,000x. (Photos by Margaret Goreau) 



great pressures. Despite this, a large number of 
animals live there. All their energy needs depend on 
food produced in shallow or surface waters. But 
how does this food get to the bottom? It has been 
found that the surplus of food contained in the 
feces of zooplankton plays an important role in 
transporting energy from the productive surface 
waters to the abyss (see Oceanus, Winter 1978). 

Through the use of electron microscopes at 
the Woods Hole Oceanographic Institution, the 
contents of these "fecal packages" have been 
exposed in detail (Figure 5). First, large numbers of 
nutrient-rich submicroscopic plant pigments were 
found. In some areas of the ocean, such as the 
Sargasso Sea, these pigments are the major source 
of nutrients and energy in the deep sea. 

The remains of coccoliths (submicroscopic 
calcite discs produced by marine algae in surface 
water) are abundant in abyssal sediments (Figure 6). 
In some areas it has been estimated that nearly half 
of the sediment is made up of the remains of 
coccoliths. For a long time, geologists did not 
understand how this coccolith ooze was deposited 
at the deep-sea bottom. The discs are so small that it 
would take them tens of years to reach the bottom 
in several thousands meters of water. Seawater 
below a few thousand meters in the Atlantic and 
several hundred meters in the Pacific is 
undersaturated in respect to calcite. Thus it would 
seem that coccoliths, enroute to the bottom for 
burial in waters deeper than the saturation depth, 
could notsurvivethedissolution process. Butquite 
the contrary is true: the coccoliths found in the 



deep sea are often well preserved, showing little or 
no sign of dissolution on their delicate architecture. 

How coccoliths get from the surface to the 
bottom is now known, thanks to the scanning 
electron microscope. Zooplankton fecal pellets are 
often packed with coccoliths. The animals graze on 
phytoplankton and the indigestible coccoliths are 
wrapped into the pellet, which sinks quickly (within 
a few weeks) to the bottom. We have also found that 
the pellets contain clay minerals that are 
transported from arid lands by winds in the 
atmosphere and then deposited in the surface 
waters of the ocean. 

The other major materials found in coccolith 
ooze on the bottom are tiny planktonic foraminifera 
shells, usually the source of calcium carbonate. 
These protozoan remains are relatively numerous in 
surface waters and sink rapidly by themselves. As 
coccoliths also apparently sink fast via fecal pellets, 
we have reached an important conclusion: the 
dissolution of carbonates does nottake place in the 
water column, as previously thought, but occurs 
after arrival on the deep ocean floor. The 
dissolution of coccolith and foraminifera particles 
provides the natural lime that neutralizes the excess 
acidity of seawater. Information concerning where 
and how rapidly these particles dissolve has a 
bearing on the global climate situation, specifically 
the increased carbon dioxide levels in the 
atmosphere, which have been attributed to the 
burning of fossil fuels and the worldwide 
destruction of forests. The scanning electron 



24 








Figure 6. Scanning electron micrograph ofcoccolith ooze 
from the Rio Grande Rise in the South Pacific at 2, 000 
meters. 3,000x. (Photo by Margaret Coreau) 




Figure 7. Dissolution on a calcite crystal deployed at 5,000 
meters for three months in the Sargasso Sea, using taut 
mooring line. Magnification 3,000x. (Photo by Margaret 
Goreau) 



microscope is a very sensitive method for assessing 
the rate of dissolution or precipitation of minerals in 
the ocean (Figure 7). Samples are collected at 
various depths through the use of mooring devices. 

A variety of plastic filters have been devised 
to observe the many microscopic particles that 
seawater contains. For example, when a liter of 
water is collected from the Sargasso Sea (where the 
water is regarded as the cleanest in the world), it is 
passed through a filter with a pore size of 0.5 
micrometers. The number of particles that remain 
on the filter usually exceeds 10,000. The weight of 
the particles is as small as 10' 10 to 10 12 grams but they 
fall within a "comfortable range" for observation 
with the SEM. Clay particles, coccoliths, and debris 
from organisms are the major constituents of the 
suspended particles in the open sea (Figure 8). 
Nearshore waters contain greater numbers and 
varieties of particles. The species composition of 
suspended particles is more or less uniform 
throughout the deep-water column. This suggests 
that many particles are transported rapidly from the 
surface by large objects, such as fecal pellets. Their 
disintegration on the way down results in the 
suspension of small particles. Thus a particle found 
at extreme depth is not necessarily older than one 
from shallow water and vice versa. 

Quite often particles are found whose origin 
is hard to determine even when using the scanning 
electron microscope. For example, a piece of 
molted shell from a small crustacean looks very 
much like a clay particle. However, the energy 
dispersive X-ray microprobe, a common accessory 



of SEM, can reveal the elemental composition of an 
object almost instantaneously. When the primary 
electron beam bombards the object's surface, it 
emits a fluorescent X-ray radiation along with the 
secondary electrons. The pulse of this X-ray 
emission is then converted to electrons by a 
semiconductor detector. The pulses are measured 
and counted by a computer called a multichannel 
analyzer. The result the buildup of a spectrum 
count versus X-ray energy is either displayed on a 
TV screen or printed out. This technique allows the 
scientist to semiquantitatively analyze areas on the 
surface of an object as small as 0.1 micrometers 
square while still observing the image of the area as 
a whole. 

The computer processing of the scanning 
electron microscope image also has enabled 
scientists to make an efficient statistical analysis of 
an object. Information relating to the number, 
projected area, and morphological details of 
suspended particles collected on a filter, for 
example, can be automatically gathered during the 
viewing process with the aid of a computer 
connected to the final display circuit. When this 
method is combined with the energy dispersive 
X-ray analysis through a computer editing process, 
what results is a large, high quality data bank on the 
composition of suspended particles in the ocean. 

Marine biologists have been turning more 
and more to the SEM in their study of zooplankton, 
phytoplankton, and bacteria (Figure 9). But 
for a long while they were stymied in the 
preparation of samples for the instrument. 



25 



^m ^m ^H^^ A ^ 

s 01 suspended Particles 



3*5 






Dinoflagellate. l,000x. 



r 



ll^ 




f k : TV C . 

Acantharia skeleton. 2,500x. 








Sponge particle. 3,000x. 




Trumpet-shaped coccolith. 5,000x. 



' 









Unusual diatom. l,000x. 



Part of diatom at left. 3,000x. 






from the Western Pacific Ocean <Fi g , 



I 




Silicaflagellate skeleton. 3,000x. 




Surface of unicell plankton. 4,000x. 




Unidentified particle. 2,000x. 







Diatom. 2,500x. 






Clay particle. 5,000x. 



Spiral coccolith. 3,000x. 




L 



Figure 9. A scanning electron micrograph of part of the mouth of a primitive crustacean, Cephalocarida (see cover 
photographs, contents page, and first page of this article). 1,000x. (Photo by Author) 



Generally speaking, marine organisms are 
separated from the surrounding seawater by a thin 
membrane of delicate tissues. To observe them 
under the SEM, they have to be completely 
dehydrated. So the problem was how to view the 
specimen as if it were still in its natural habitat, 
seawater. When seawater evaporates, the specimen 
is affected by high surface tension as great as several 
hundred kilograms per square meter, usually 
resulting in surface distortion. In the early 1950s, a 
technique called the critical point drying method 
was developed to solve the problem. Essentially, 
the method avoids the distortion that is produced 
by the passageof an air/liquid interface through the 
specimen. After critical point drying, the specimen 
is usually coated with a thin layer of metal either by 
evaporation or a technique known as sputtering. 



The purpose of the coat is two-fold: one, it renders 
the surface of the specimen conductive so that no 
excess electrical charge is built up; and, two, it 
enhances the production of secondary electrons, 
which are harnessed to form the image. 

Future Trends 

The engineering development of the scanning 
electron microscope is still growing rapidly. High 
resolution instruments capable of resolving objects 
as small as 30 A are already on the market. And with 
the aid of microelectronics, the operation of the 
SEM is becoming simpler and more efficient. Some 
manufacturers have marketed a semi-portable 
microscope as small as a medium-sized television 
set. 

In the marine science field, the method has a 



28 





At left, an unusual radiolarian skeleton from the Sargasso Sea. 3,000x. Right, two species ofcoccolithophorids from 
the central South Pacific. 3,000x. (Photos by Tadashi Otaka) 



bright future. Although there are still technical 
difficulties to overcome, there are also some 
exciting challenges to meet. For example, a device is 
being developed that will allow the deep 
submersible vessel Alvin, operated by the Woods 
Hole Oceanographic Institution, to collect 
sediment samples at the sediment/water interface 
for a multi-discipline deep-sea research project 
called Low Energy Benthic Boundary Layer 
Exploration (LEBBLE). The technique calls for human 
observation (through the submersible's portholes) 
of the sampling process, which involves partly 
preparing specimens in situ (at 4,000 meters in the 
Panama Basin) for the scanning electron 
microscope. This will provide ocean scientists a 



chance to see what the bottom of the abyss looks 
like under great magnification, which in turn will 
provide important information to answer the basic 
question of how it is formed. 



Susumu Honjo is an Associate Scientist in the Department 
of Geology and Geophysics at the Woods Hole 
Oceanographic Institution. 

The majority of research programs being conducted at the 
Electron Microscope Facility of the Woods Hole 
Oceanographic Institution are supported by the 
Oceanography Section of the National Science Foundation. 



29 



l>| early half the population of the United States is 
living adjacent to coastal waters or to the shores of 
the Great Lakes. This percentage almost certainly 
will continue to increase during the 1980s. The 
coastal environment, however, really constitutes a 
very small area. It has been estimated that all 
harbors, estuaries, and nearshore coastal waters of 
the world make up no more than 1 percent of the 
surface area of the world's oceans. Yet it is this 
nearshore fringe that is colonized by one or more of 
the most highly productive ecosystems in the 
world. These ecosystems are dominated by 
submerged or semi-submerged plants. Only in the 
Arctic or Antarctic are these ecosystems absent. 
Because these vascular plants exist in relatively 
shallow water along the coastal fringe, they are 
subject to increasing stresses caused by man and his 
growing, diversified needs. The continued 
multiplicity of demands upon estuarine and coastal 
environments as producers of food, avenues of 



transportation, receptacles of wastes, living space, 
and sources of recreational or aesthetic pleasure 
makes it imperative that we understand the 
functioning of these nearshore ecosystems, with 
their attendant frailties and strengths. This 
knowledge is essential if we are to manage these 
ecosystems wisely so that we can derive maximum 
benefits from them. 

Coastal Ecosystems 

Several different coastal ecosystems exist in the 
tropics and temperate zones of the world. In the 
tropics, for example, extensive mangrove systems 
are present, whereas in temperate zones one finds 
massive kelp and marsh systems. Beyond the 
coastal fringe that supports the mangrove and 
marsh systems are vast meadows of one or more 
species of grass-like plants. These are rooted in soft, 
sandy, or muddy bottoms. Horizontal stems in the 
sediment, known as rhizomes, send erect, leafy 



Figure 1. Eelgrass, Zostera marina, in Puget Sound, Washington. Note the snails, which eat the leaves. (Photo by 
Author) 




t 








a/rme 




mxronment 



by Ronald C. Phillips 



shoots into the water. The stalks are often dense, 
with leaves so long that they resemble vast 
meadows of waving wheat or oats. These plants are 
called seagrasses (Figures 1 and 2). 

There are few parts of the world's coastal 
zone where one or more species of seagrasses do 
not grow (Figure 3). It is becoming clear that 
seagrass meadows form one of the most productive 
natural ecosystems on earth (Table 1), and that they 
contain a wide variety of marine life. Bostwick 
Ketchum of the Woods Hole Oceanographic 
Institution has estimated that 80 to 90 percent of the 
commercial and sport fishes depend on estuaries 
for part or all of their life cycle. Estuaries typically 
support large seagrass meadows. The problem is 
that until recent years the presence and importance 
of these meadows wentvirtually unrecognized. This 
was due in large measure to the training of marine 
scientists, who usually viewed the ocean as a 
deep-water mass. Marine biologists, who have 



worked in and around seagrass meadows, mainly 
have been interested in particular algae or animals 
that live there. Fishery biologists have been 
interested largely in the shellfish or fish stocks 
directly or indirectly associated with the meadows. 
It has only been since the mid-1960s that 
oceanographers have begun to include the shallow 
benthic coastal zone as a part of the ocean system. It 
is now known that seagrasses form a discrete 
ecosystem that traps material from the land and 
exports great quantities of plant and animal 
products to the open sea. These products range 
from whole leaf and rhizome material, to particulate 
detritus, to dissolved organic matter that is used to 
support oceanic phytoplankton. This latter 
component forms the base of the food chain of the 
oceanic offshore fisheries. 

The leaves and rhizomes of turtle grass, 
Thalassia testudinum, for example, have been 
transported to deep trenches, such as those off 



Figure 2. Turtle grass, Thalassia testudinum, in Panama. These grasses are commonly eaten by Diademat/iaf move off 
adjacent coral reefs at night to eat blades, then move back to the reefs at daybreak. The urchins cause a "halo zone" of 
closely cropped leaves around the base of the reef. (Photo by Author) 





Halodula, Tholossio 
Halophila 



Zosterello 
Zostero 



40 



Figure 3. The distribution of selected genera ofseagrasses. These genera have distributions so broad that they exceed 
the more restricted distribution of lesser genera. (Adapted from C. den Hartog, 1970) 



Puerto Rico, and have been found down to 8,900 
meters. This material is eaten by a variety of 
isopods, amphipods, annelids, gastropods, and 
bivalves. Thus the seagrass ecosystem may be 
described as a trap or filter, as well as a pump that 
links the land to open oceanic masses. 

The Seagrass Ecosystem 

There are approximately 45 species of seagrasses in 
the world's oceans, falling into two families and 12 
genera. All are monocots (having a single seed in a 
leaf). The family Potamogetonaceae contains 9 
genera and 34 species. The family Hydrocharitaceae 
contains 3 genera and 11 species. Most seagrasses 
have submerged flowers, with pollination occurring 
underwater. 

By their presence on a landscape of relatively 
uniform relief, seagrasses create a diversity of 
habitats and substrates, providing a structured 
habitat from a structureless one. In 1937, R.C. 
Stauffer subdivided the eelgrass invertebrate 
communityintofourcategories: Don the plants; 2) 
among the plants; 3) on the mud surface; and 4) in 
the mud. Only the two latter categories of animals 
would be present withoutthe plants. Since many of 
the animals in these categories are either protected 
from wave action by the plant cover or are 
associated with the roots, it is probable that the 
species list in categories three and four would be 
considerably reduced if seagrasses were absent. 



Because of their structure and physiology, 
seagrasses perform a wide assortment of biological 
and physical functions in the coastal environment. 
These functions were summarized in 1969 by E.J.F. 
Wood, W.E. Odum, and J.C. Zieman: 

1 . Eelgrass, a north temperate seagrass, has a 
high growth rate, producing on the average 
about 300 to 600 grams dry weight per square 
meter per year, not including root production. 

2. The leaves support large numbers of 
epiphytic organisms (other plants attached to 
the eelgrass, not growing parasitical ly but using 
them for support), with a total biomass 
approach ing that of the plants themselves. This 
diversity is possible because of the abundance 
of oxygen, nutrients, and food provided by the 
plants. Thus seagrass meadows provide a 
stable, benign, and predictable environment in 
which a great variety of organisms can grow. 

3. Although a few organisms may feed directly 
on the eelgrass and several may graze on the 
epiphytes, the major food chains are based on 
eelgrass detritus and its resident microbes. 

4. The organic matter in the detritus and in 
decaying roots indicates sulfate reduction and 
maintains an active sulfur cycle. 

5. The roots bind the sediments together, and, 
with the protection afforded by leaves, surface 



32 



Table 1 : Comparative average productivities of selected seagrasses and crop plants. (After McRoy and 
McMillan, 1977; Odum, 1959) 



Species 



Locality 



Productivity 
(g C/nWday) 



Annual Productivity 
(g C/m>) 



Seagrasses 
Thalassia testudinum 

(assume growing season 

of 250 days) 

Halodule wrightii 

(assume growing season 
of 120 days) 



Puerto Rico 
Florida 
Texas 

North Carolina 



2.4-4.5 

0.35-16 

0.9-9.0 

0.48-2.0 



600-1125 

88-4000 

225-2250 

72-240 



Zoster a marina 


Denmark 


2.0-7.3 


240-1095 


(assume growing season 


Rhode Island 


0.4-2.9 


60-435 


of 120 days) 


North Carolina 


0.2-1.7 


30-255 




Washington 


0.6-4.0 


90-600 




Alaska 


3.3-8.0 


495-1200 


Cultivated Crops 








Wheat 


World Average 


0.94 


344 


Corn 


World Average 


1.13 


412 


Rice 


World Average 


1.36 


497 


Hay 


U.S. Average 


1.15 


420 


Sugar Beets 


World Average 


2.10 


765 


Sugar Cane 


World Average 


4.73 


1725 



erosion is reduced, thereby preserving the 
microbial flora of the sediment and the 
sediment/water interface. Since seagrass 
rhizomes form a dense, interlacing mat, and 
the leaves form a dense baffle, the plants are so 
effective in their hold on the bottom that they 
persist during tropical hurricanes, despite wave 
action caused by 150-knot winds. 

6. The leaves retard currents and increase 
sedimentation of organic and inorganic 
materials around the plants. 

7. Eelgrass absorbs nutrients through the 
leaves and roots; nitrogen and phosphorus can 
be returned to the water column from 
sediments via seagrasses. 

Ecology of Seagrasses 

Seagrasses tolerate a wide range of salinities from 
6 %o (parts per thousand) to 60 /oo (they even will 
tolerate fresh water for short periods). For eelgrass 
in the north-temperate zone, Zostera marina, the 
optimum range appears to be 10 to 30 %o. For turtle 
grass in the tropics, Thalassia testudinum, the range 
is 20 to 35 /no. For shoal grass in the tropics, 
Halodule wrightii, a pioneering and more adaptable 
species, the salinity range extends from 20 to 60 %o. 

Seagrasses also tolerate a wide range of water 
temperatures, varying from to 40 degrees Celsius. 



The optimum temperature for growth and 
development of a species seems to depend on its 
specific location. It is likely that seagrasses form 
biotypes adapted to a local suite of salinity, 
temperature, nutrient, and weather conditions. 
Thus in Puget Sound, Washington, eelgrass grows, 
flowers, and develops seeds in a water temperature 
range of 6 to 13 degrees Celsius, whereas in 
Beaufort, North Carolina, the range is to 33 
degrees Celsius. The same is true for the two North 
American tropical species, Thalassia and Halodule. 
In the northern Gulf of Mexico, the temperature 
range is 7 to 32 degrees Celsius, whereas in 
southern Florida it varies between 17 to 32 degrees 
Celsius. At St. Croix, U.S. Virgin Islands, the range is 
23 to 30 degrees Celsius. 

The depth distribution of seagrasses 
depends on many interrelated factors depth, 
waves, currents, substrate, turbidity, and light 
penetration. The plants usually occur from low tide 
down to about 10 meters. In the temperate zone, 
eelgrass maintains limited intertidal stocks, 
whereas in the tropics only shoal grass grows in 
sparse amounts in the intertidal zone. In some 
areas, eelgrass (San Diego Trench) and turtle grass 
(Bahamas) have been observed at depths of 30 
meters. This lower limit is probably established by a 
combination of minimum light intensities and 
suitable substrate. Seagrasses may be restricted to 



33 



less than 1 meter where waves stir up a muddy 
bottom. 

Almost all species occur on unconsolidated 
muddy sand substrates, thus occupying a habitat 
virtually uncontested by benthic algae. In the 
tropics, species of the green algal families 
Codiaceae and Caulerpaceae grow on a muddy sand 
substrate. These algae are often abundant in a 
dense seagrass meadow. Only species of 
Phyllospadix in the North Pacific and Posidonia in 
Australia and Tasmania grow attached to rocky 
substrates. The substrates vary from coarse sand to 
almost liquid mud. The normal substrate is a 
reducing one beneath an oxidized surface layer. 
Cuts made by boat propellers in shallow-water 
meadows show how the union between seagrasses 
and theirsubstratecan bedisrupted. In someareas, 
such cuts are still noticeable up to 15 years after the 
act. 



Seagrass Productivity 

Aprobable key to the diversity of plants and animals 
in seagrass meadows is their productivity (Table 1 ). 
Representative values of annual production of 
Thalassia in the Caribbean range from 88 to 4,000 
grams of carbon per square meter. Annual values 
forZosfera range from 6 to 1 ,200 grams of carbon 
per square meter. Thus seagrasses can grow as fast 
as cultivated corn or rice, hayfields, or tall grass 
prairies (corn annually produces 412 grams of 
carbon per square meter and rice, 497). On an areal 
basis, seagrass production rates can be higher than 
phytoplankton production off Peru, one of the most 
productive areas in the world's oceans. Since 
seagrasses are located in the nearshore coastal 
fringe, which also supports other shallow-water 
ecosystems, seagrass production is supplemented 
by that of benthic microalgae, macroalgae, 
epiphytes, phytoplankton, marshes, mangroves, 
and (in some areas) coral reefs. 

Several components of the seagrass 
ecosystem have been found to be contributors to 
carbon cycling. The epiphytic flora on seagrasses 
can be diverse and very abundant, causing leaves to 
break or to be shaded from sufficient light, 
preventing photosynthesis. C. den Hartog 
published a list in 1970 of up to 200 algal species 
epiphytic on eelgrass alone. This productivity was 
measured at 20 percent of the mean annual net 
production of Thalassia in Florida (200 grams of 
carbon per square meter per year) and at about 25 
percent of the annual production of Zostera in 
North Carolina. In addition, seagrasses excrete a 
considerable quantity of dissolved organic carbon 
(DOC) into the water mass, which is then available 
for uptake by other local plants or for export 
offshore. It was found that eelgrass and its 
epiphytes contributed almost 15 percent of the total 
DOC in the estuarine system near Beaufort, North 



Carolina. The conclusion was that these plants are 
an important part of the carbon cycle in an estuary. 

Seagrasses produce and consume great 
quantities of oxygen. A study done in Holland in 
1935 showed a supersaturation of the waters over 
the plants of 260 percent in mid-afternoon. At night 
the waters became anoxic. In Florida, Thalassia 
leaves during the day swell as much as 200 to 250 
percent of their early morning volume due to the 
internal production of oxygen. Since the leaves lack 
stomata, the oxygen is forced out of the leaves at the 
edges in long streams. Moreover in a shallow, calm 
meadow, with little water flow, it is possible to hear 
a hissing from the rapid bubbling. The appearance, 
as described by one researcher, is akin to that of a 
"newly opened bottle of beer! " 

Animal Diversity 

Some of the earliest studies conducted on animal 
life in the seagrass ecosystem were done at the 
Biological Station in Copenhagen, Denmark. The 
first was a report by C.G.J. Petersen in 1891, stating 
his belief that fish abundance in Denmark was due 
to eelgrass. Other Danish scientists, working from 
the same station, concluded that the eelgrass belt 
was faunistically the richest in their fjords. The 
water over the plants teemed with small 
crustaceans, molluscs, and fish. Outside this plant 
belt the fauna was much poorer. Much the same 
findings have been reported for eelgrass meadows 
in the United States and Japan. A typical animal list 
would include ciliates and flagellates, hydroids, 
polychaetes, coelenterates, snails, clams, scallops, 
shrimp, amphipods, isopods, bryozoans, 
opistobranchs, crabs, copepods, nematodes, 
echinoderms (such as sea urchins and starfish), 
lamellibranchs, ostracods, and pycnogonids. A 
diversity of fish and wildfowl also inhabit eelgrass 
meadows. Tropical meadows support the same 
diversity and abundance of animals. In addition, 
tropical turtle-grass meadows often support 
populations of green, loggerhead, and hawksbill 
turtles, as well as dugongs and manatees, all of 
which eat the seagrasses (Figure 4). 

Many animals occupy a seagrass meadow as 
larvae only (crabs, scallops, and fish), while others 
pass through either as zooplankton or as migrating 
fish. A number of animals, many of which are food 
animals, live in the seagrass beds throughout their 
life, such as clams, shrimp, crabs, and various fish 
(FigureS). 

The importance of seagrass systems, 
however, does not lie only in their direct food value 
to animals. They also provide a habitat for the 
growth of both commercial and noncommercial fish 
and invertebrates, while providing protection from 
predators (Figures 6 and 7). Thus seagrass meadows 
act as a nursery, as well as being one of the most 
valuable marine resources in terms of overall 
coastal ecology and fisheries production. In 1918, 



34 




Figure 4. Loggerhead turtle caught in eelgrass meadow at 
Puenta Chueca in the Gulf of California. (Photo by Tom 
Backman) 



Petersen, summarizing the work of three other 
scientists on the eelgrass ecosystem in the Kattegat 
region of Denmark, reported that detritus formed 
from eelgrass served as the basis for several 
invertebrate communities, and that this ultimately 
led to several species of food fish important to the 
Danish economy. These conclusions were 
challenged in 1931 , when a massive die-off of 90 to 
100 percent of the eelgrass in the North Atlantic 
occurred. Exactly why the eelgrass died out is still a 
matter of conjecture. 

Following the die-off, most of the animals 
associated with eelgrass such as scallops, clams, 
crabs, and waterfowl disappeared. In some areas, 
black brant geese populations diminished by up to 
90 percent. Fish populations fell off sharply but not 
as drastically as Petersen might have predicted. It is 
now believed that the rich organic sediment built up 
by the eelgrass system over the years, but devoid of 
the plant cover, began to release nutrients into the 
water mass, thus cushioning an immediate impact 
on the fisheries. 

Food Chains 

The most important role of seagrasses in the food 
chain is the death and decomposition of the living 
plants to form detritus (Figure 8). A variety of 
investigators, including several of the early Danish 
group to more contemporary scientists working in 
the northeastern United States, California, and 
Japan, have concluded that detritus is probably the 
single most important item at the base of food 
chains in intertidal and shallow subtidal 
communities. 



Evidence is accumulating, however, that 
detritusper se is not the primary source of food 
when it is ingested by the teeming masses of clams, 
oysters, worms, and crustaceans the detritivores. 
Other researchers have shown that detritus is a 
substrate for large numbers of bacteria, which are 
the real food for detritivores, allowing many marine 
invertebrates to live almost indefinitely on an 
exclusive diet of bacteria. 

A general food chain is shown in Figure 9. 
The bacterivorous fauna include zooflagellates 
(protozoans), and some species of ciliates and 
rotifers, while the carnivorous microfauna include 
ciliates, rotifers, and turbellarians. The detritus 
feeders include amphipods, gastropods, bivalves, 
polychaetes, and oligochaetes. These chains are 
long and complex. It appears that many of the food 
animals gathered in the inshore coastal 
environment result from detritus food chains that 
are associated with seagrass meadows. 

There is an important relationship between 
seagrass detritus formation and nutrient cycling 
within and across ecosystem boundaries. The plants 
themselves absorb phosphorus, nitrogen, sulfur, 
and carbon through the roots and, to some extent, 
through the leaves, pumping them into the water 
mass where they can be used by epiphytes and 
phytoplankton. Particulate detritus is poor in 
essential nutrients, while bacteria contain very high 
amounts of phosphorus and nitrogen. Bacteria 
absorb nutrients from the water and, while acting 
on the detritus, enrich it with nitrogen and 
phosphorus. Mineral nutrients cycle between 
bacteria and animals, the latter remineralizing the 
nutrients by digesting the bacteria. At the same 
time, the seagrass plants are excreting dissolved 




Figure 5. Dungeness crab, Cancer magister, found in 
eelgrass meadow in Puget Sound. (Photo by Author) 



35 




Figure 6. Simpson's sunstar, Solastersimpsonii, /nee/grass 
meadows in Puget Sound, Washington. This starfish 
forages for dams among the plants. (Photo by Author) 



organic carbon (DOC) and matter (DOM) into the 
water column. These are available to epiphytes on 
the seagrasses, benthic macroalgae and microalgae 
in the meadows, as well as phytoplankton in and 
outside the ecosystem. 

The detritus is involved in a complex 
chemistry of nutrient cycling in the substrates of a 
seagrass meadow. Because of the quantity of dead 
leaf material fall ing from the plants and the rate of its 
decomposition by bacteria, sediments in a meadow 
become reducing below a very shallow oxidized 
layer. In turn, because of this and an abundance of 
sulfur bacteria, the sediments tend to be dominated 
by the sulfur cycle. This is related to a rich 
microflora and microfauna. 

Sediment Stabilization 

All research indicates that seagrass leaves in a 
meadow act as a baffle that increases the rate of 
particulate sedimentation, preferentially 
concentrating the finer particle sizes and stabilizing 
the underlying sedimentary deposits. This occurs 
through the entrapment of water-borne particles by 
the leaf blades, the formation and retention of 
particles produced within the meadows, and the 
binding and stabilization of the substrate by the 
rhizome and root systems. These effects can be 
local or widespread. Two examples of the 
long-term, widespread influence of seagrasses on 
sedimentation and stabilization are the carbonate 
bank along the eastern margin of Shark Bay in 
Western Australia, and the grass-bound "mattes" 
on the Mediterranean coast of France. 

The effect of seagrass meadows on sediment 
stabilization is well documented. When theeelgrass 




Figure 7. Sand dollars, Dendraster sp., are often found on 
sand adjacent to meadows in Puget Sound, where they 
dig, undercut, and uproot the eelgrass. If the animals are 
excluded by cages, the eelgrass returns to the denuded 
patch. (Photo by Author) 



disappeared in 1931 , sand banks formerly covered 
by the grass in Salcombe Harbor, England, were 
lowered by 30 centimeters or more almost 
overnight. Many species of filter-feeding 
invertebrates and molluscs, and several flatfish also 
disappeared. Several people have observed that 
Thalassia meadows suffer little damage from 




Figure 8. Detached seagrass leaves often pile up on a 
beach, where they are mechanically ground up into 
particulate matter called detritus. This detritus and other 
dissolved materials released in the process float back to 
sea and form the basis of long, complex food chains. 
(Photo by Author) 



36 



HERBIVORE 



WATER SURFACE 




>ISCIVORE 

ZOO- 
PLANKTON 



MICROHERBIVORE 
MICROCARNIVORE 



VATER MASS 



AS<? ^ 





CARNIVORE 



EPIZOAN 

SUSPENSION FEEDERS 



ZOO- 
PLANKTON 







DOM- 
DOC 




HERBIVORf 



: 

CARNIVORE 



y 









SCAVENGER 



CARNIVORE 






HERBIVORE 



CARNIVORE 



SUBSTRATE LEVEL 



INFAUNAL 
SUSPENSION FEEDER 



Figure 9. Generalized food chain forseagrasses. (Adapted from J. C. Ogden, in press. Drawing by Irish Pettigrew) 



hurricanes (some of which produce 150-knot winds) 
in Florida and Texas. Bottom areas recover quickly 
due to a rapid growth rate of leaves (up to 
25-millimeter increments per week), and the 
sediment remains intact. Up to 10 to 20 centimeters 
of sediment have eroded from unvegetated sand 
banks following a single storm in Chesapeake Bay, 
Maryland, while little, if any, disappeared from 
within an eelgrass meadow. 

Sediment stability is a function of density and 
the species of seagrass. Thalassia (wide, flat blade) is 
more effective at binding sediment than is 
Syringodium (narrow, terete blade). Observations 
indicate there is a decreasing density of plants and 
an increasing amount of sediment removed by 
turbulent water as one moves closer to the edge of 
an eelgrass meadow. Also there is a positive 
correlation between sediment stability and 
invertebrate diversity. 

Strengths and Frailties 

Almost all species of seagrasses grow on 
unconsolidated substrates. There is evidence that 



the plants function not only to stabilize the physical 
milieu of their environment, but that they also 
originate, drive, and coordinate a great diversity of 
chemical and biological events. The very dense mat 
of roots and rhizomes binds sediments, while the 
dense meadow of leaves acts as a baffle to surges 
and currents. This promotes and accelerates 
sedimentation of plankton, epibiota, and seagrass 
detritus. In turn, this leads to complex chemical 
cycles of gases and nutrients, trophic webs, and a 
high level of primary and secondary productivity. 

Despite the ability of seagrasses to adapt to a 
fluctuating environment, several human-related 
activities threaten these hearty plants. Dredging 
poses the greatest danger. Not only are the plants 
removed, butthe physical, biological, and chemical 
structures of the ecosystem are changed. 
Sediments may bury plants, but can also reduce 
plant density. This could result from sediment 
accumulation alone or in concert with an increased 
water turbidity. Sediment textures change from a 
mixture of sand and fine silts to sand, while 
chemistry changes from a reduced to a highly 



37 



oxidized state. Lacking a cover to reduce erosion, 
the water over unconsolidated substrates turns 
from crystal clear to very turbid. The influence of 
turbid water on seagrass growth appears to be the 
same for all seagrasses. Where very turbid water 
prevails, Thalassia andZostera are limited to a 
maximum depth of 3 meters, while populations of 
both have been observed down to 30 meters where 
the water is clear. Several studies have documented 
the drastic reduction in fauna, macroinvertebrates, 
and fishery products in both tropical and temperate 
seagrass meadows following dredging. 

The reasons for dredging in the inshore 
coastal environment are varied. Since shipping and 
boating are necessary, maintenance dredging must 
bedoneto keepchannelsopen. When this happens 
near seagrasses, large quantities of silt are 
deposited over indigenous seagrass meadows 
accompanied by turbid water over the plants. The 
greatest amountof dredging, however, involves the 
creation of new real estate. This became a serious 
problem in Florida in the mid-1950s; in the Tampa 
Bay area, for example, vast acreage was dredged 
and smothered by silt. More recently, dredging in 
seagrasses near coral reefs in southern Florida has 
increased. In fact, dredging has increased on a 
broad scale worldwide. Seagrass meadows and 
coral reef systems are currently being threatened in 
several areas where ports are planned to receive oil 
supertankers. Channels that are normally 35 feet 
deep for most shipping must be lowered to 70 feet. 
These channels also must be greatly lengthened, 
which results in continuous maintenance dredging. 

The use of the hydraulic clam dredge also is 
increasing. It is indeed an economical method of 
harvesting clams from a seagrass meadow, but a 
destructive one since it blasts sediments to a depth 
of 45 centimeters. Most seagrass rhizome mats are 
located at a maximum depth of 15 centimeters. This 
type of dredging has been done in Thalassia and 
Zostera meadows in such diverse areas as Florida 
and Washington, respectively. 

Thermal effluents also have a critical effect on 
seagrasses. All seagrasses appear to have upperand 
lower temperature tolerance levels. The upper level 
for eelgrass is 30 degrees Celsius; turtle grass 
approaches 35 degrees. Above such levels, leaf kill 
and plant death set in. jay Zieman of the University 
of Virginia and AnitraThorhaug of Florida 
International University have documented the 
extensive damage done to Thalassia in Biscayne Bay 
by heated effluents from two fossil fuel and two 
nuclear power plants at Turkey Point. Water near 
the plants in Biscayne Bay was raised uptoS degrees 
Celsius above the ambient temperature. All plants 
in an area of about 9.3 hectares off the mouth of the 
discharge canal disappeared, while those in an area 
30 hectares farther.out declined by about 50 
percent. The animal communities associated with 
these meadows also disappeared. Sediments off the 



fossil fuel plants also contained much higher levels 
of nickel, copper, vanadium, lead, cadmium, zinc, 
and iron than those not affected by the thermal 
plumes in Biscayne Bay. 

In recent years, humans have dumped 
increasingly greater amounts of heavy metals, oil 
products, synthetics (such as DDE, DDT, and 
chlorinated hydrocarbons), solid wastes, domestic 
pollution, pesticides, detergents, fertilizers, and 
Pharmaceuticals into the shallow waters of our 
inshore coastal areas. There has been little concern 
about the presence or absence of plant 
communities in these areas or for the impacts of 
these pollutants on them. 

Solid wastes and domestic sewage adversely 
affect seagrass ecosystems by increasing 
sedimentation too quickly and by decreasing light 
penetration in the water. Studies are lacking on 
turtle grass and eelgrass but a team of scientists in 
England has determined that Zostera noltii can only 
tolerate changes of 7 centimeters per year or 3 
centimeters per week. Meadows can be smothered 
by too much silt caused by upland erosion and 
runoff ordredging. Forexample, eelgrass meadows 
in Newport Bay, California, were reduced to 
isolated patches after dredging caused the plants to 
be smothered. 

There is accumulating evidence that oil 
spilled in the sea damages both seagrasses and the 
surrounding community. This is presently the 
subject of on-going research. Certainly, oil kills 
seabirds and interferes with the development of 
animals, such as marsh crabs and some fish. Crude 
oil spillage on the south coast of Puerto Rico 
resulted in severe and long-lasting damage to 
tropical meadows of Thalassia. Following a crude oil 
spill at Santa Barbara, California, on January 28, 
1969, it was reported that heavily coated leaves of 
Phyllospadix torreyi, a rock-inhabiting seagrass, 
were killed when oil made direct contact with 
air-exposed leaves at low tide. Plants located in 10 
centimeters of water were protected from the 
damaging effects of the oil. Another study found 
that oil adhered to the leaves of this seagrass, 
subsequently killing them. It was also reported that 
the oil moved into the sediments, where it had a 
severe effect on the invertebrates, consequently 
moving up the food chain to humans. New leaves 
grew when the oil in the water was removed. Thus, 
exceptforthe long-term residual effect of oil on the 
benthic animal community and its passage through 
the food chains, there was little noticeable effect of 
spilled oil on the seagrasses themselves. 



Restoration of Seagrasses 

Following the massive die-off of eelgrass in the 
North Atlantic in 1931 , experimental work began on 
restoration methods to accelerate the normal 
30-year period required for recovery. Early attempts 



38 




Figure 10. Eelgrass fixed serially to an iron rod and 
transplanted from the intertidal to a subtidal site in Puget 
Sound, Washington, in February, 7965. (Photo by Author) 



Figure 11. The same site as Figure 10, but in September 
7965. (Photo by Author) 



in the 1940s were not successful. It is compelling 
and necessary that new attempts be made, since 
human activities that affect seagrasses are 
increasing. 

Before any successful large-scale 
applications can be made, basic experimental work 
must be done on seagrass transplantation to discern 
phenotypic plasticity, biotype formation, and the 
range of adaptational response of a seagrass 
species. Seagrass transplantation has two major 
objectives: 1) to stabilize bottom sediments and to 
prevent erosion, and 2) to increase productivity in 
an area that has lost a seagrass cover. 

There are two basic transplantation methods 
presently under investigation. One uses seeds and 
seedlings. It has achieved success in restoring 
Thalassia growth following its decimation by 
thermal effluents from the Turkey Point energy 
plant in Biscayne Bay, Florida. The other method 
involves the transplantation of vegetative material 
(Figures 10 to 13). Both methods have certain 
advantages. Vegetative material results in rapid 
seagrass growth, especially when planted intact as 
turfs or plugs in the original sediment, but large 
quantities of such material can be difficult to 



transport over long distances. Seeds are much 
easier to transfer in quantity, but germination rates 
at ambient salinities are low as is survival in thefield. 
Vegetative material provides for greater survival 
chances aftertransplantation, as well as offeringthe 
full range of adaptive responses to the 
environment. 

The only large-scale field project using the 
vegetative method was tried on North American 
seagrasses growing on dredge spoil banks at Port St. 
Joe, Florida. The U.S. Army Corps of Engineers 
sponsored the experiment, which involved 
transplanting a pioneering species of shoal grass, 
Halodule wrightii, in the sand. After a year, the 
plugs became fully established, demonstrating that 
transplantation of seagrasses on dredge spoil is 
feasible. Within a year, animals (crabs, birds, fish) 
found in local shoal grass meadows began to invade 
the new plants. 

Thus seagrass restoration projects are 
possible. They can be used to stabilize spoil bank 
sediments and to restore seagrass growths that have 
disappeared, and even to enhance the productivity 
of meadows that suffer natural or human 
perturbations. 



Figure 12. Eelgrass transplanted as 20-centimeter plugs 
(plants intact in original sediment) on December 19, 1974. 
Note flatfish moving over newly transplanted seagrasses. 
(Photo by Author) 



Figure 13. Same site as Figure 12, but on March 4, 1977. The 
plants from the original plugs have grown enormously and 
have greatly expanded their coverage over the bottom. 
(Photo by Author) 




Past, Present, and Future Studies 

The earliest seagrass studies in the United States 
were done by William A. Setchell from 1920 to 1935. 
These represent fundamental phenological and 
taxonomic studies and underlie most of the later 
work. From 1935 to about the mid-1950s, seagrass 
studies in the United States centered around the 
cataloguing of plant and animal changes resulting 
from the eelgrass epidemic of the 1930s. 

In 1973, with the aid of the National Science 
Foundation (NSF) and the International Decade of 
Ocean Exploration (IDOE), C. Peter McRoy of the 
University of Alaska formed a steering committee 
that convened an International Seagrass Workshop 
at Leiden, The Netherlands. This workshop was 
attended by 38 investigators from 11 countries. The 
purpose was to assess past studies and to formulate 
future research needs. Following this workshop, 
the NSF/IDOE funded a Seagrass Ecosystem Study, 
utilizing a team approach to seagrass research. This 
study, currently underway, should prove useful in 
explaining and predicting patterns of development 
and activity in seagrass and epiphyte productivity, 
animal phenology, and the patterns of nutrient 
cycling in the seagrass ecosystem. 

With research conducted thus far, we 
are able to intelligently advise governmental 
agencies that have control over our nearshore 
coastal ecosystems, thus reducing adverse 
impacting of seagrass ecosystems. In the past, these 
impacts (such as dredging, thermal and sewage 
effluent dumping, and oil spills) have damaged 
these ecosystems, reducing or decimating fish 
catches, oyster harvests, and clam and shrimp 
landings. 

Future research work should concentrate 
more intensively on nutrient and heavy metal 
cycling between seagrasses, the sediments, and 
water masses. More work also is needed on 
seagrass productivity and the factors that reduce 
and increase it; harvesting procedures and 
nutritional analysis; the use of seeds; temperature 
tolerances and the daily requirements of plants 
from different areas; and research on certain 
vigorous strains that might produce higher yields. 

I recently received a letter from a Peace 
Corps volunteer in Ghana who was interested in 
using eelgrass as a substitute for bacterial 
cultivation that could then be used as a nutritional 
supplement for underfed people. Since the 
seagrass ecosystem is a detritus-based system and 
bacterial films on seagrass detritus are the 
fundamental food items at the base of the food 
chain, it would be interesting to follow up on the 
nutritional aspects of seagrass cultivation. 

Thus there are many directions for future 
applied research to take. As I have indicated, it 
can relate to the use of seagrasses or their seeds for 
food, or the use of associated bacteria for food. 
Perhaps the leaves can be used for carbohydrate 



and/or protein extracts; new meadows can be 
created by transplantation in coastal ponds, which 
in turn can be used to generate food animals; and 
transplantation can also serve to reduce or stop 
coastal erosion, thus saving millions of dollars. 
Then, too, when we know enough, we can preserve 
ournatural, existing seagrass meadows. In this way, 
we would make the highest, most advanced use of 
our research knowledge in a predictive 
management program. 

Ronald C. Phillips is Professor of Biology at Seattle Pacific 
University, Seattle, Washington. He has been involved in 
seagrass research since 7957. 



This material is based upon work supported in part by the 
National Science Foundation under grants OCE76-01307, 
OCE76-84259, and OCE77-25559. 



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sedimentary processes. Chesapeake Bay Institute, The Johns 

Hopkins University, Ref. 73-12. Spec. Rept. 33, pp. 1-32. 
Stauffer, R.C. 1937. Changes in the invertebrate community of a 

lagoon after disappearance of the eelgrass. Ecology 18: 427-31. 
Thayer, C.W., D.A. Wolfe, and R.B. Williams. 1975. The impact of 

man on seagrass systems. Amer. Sci. 63(3): 288-96. 
Wood, E.J.F., W.E. Odum, and J.C. Zieman. 1969. Influence of 

seagrass on the productivity of coastal lagoons. Lagunas 

Costeras. Un SimposioMem. Simp. Intern. UNAM-UNESCO, 

Mexico, D.F. Nov. 1967. pp. 495-502. 



40 



Red Tide 




by Barrie Dale and Clarice M. Yentsch 






cm- 





ropean settlers in North America noted that coastal Indians had taboos and 



legends associated with eating shellfish. On the East Coast, Marc Lesc^rbot, a 
much traveled French lawyer, wrtang in 1609, stated that Indiansat Port Royal, 
Nova Scotia, would not eat mussels even wrren starving. They 




2S -> : ';..*%* 



**"" 




/w/7 



" more ^ o /i /* e fo 

8j BILL r^jHn f"^ 

Wthurti <'>lf(l}fln ui/t~. j.. . 



Si-ZS5Lr!l? fcr<i 

and ih f , r n r,_. _*?** * (w " al ' "- 



Figure 1. Boston area 
newspaper articles, many 
of which were published 
after the September 1972 
outbreak of PSP. 



v\ \ v ^4 *^<y* A ** **>^ t ^T^ \ lo ^^k * tndu.1^ ^ "^t^ 

%SSJ!^ 



W but rtf ii -'"t H wueto -ttv t. 

\\wS," to ""~"-- -ML,' 

.SS38S 5= 



**"- 



would eat their dogs and the bark from trees 
instead. On the West Coast, some Indian tribes 
maintained a nightly lookout for bioluminescence* 
in the sea, and they would not eat shellfish when the 
sea was "glowing." From the Alaskan Coast, there is 
a legend that Indians disposed of a group of 
troublesome Russian settlers by inviting them to a 
feast of shellfish near the islands of Baranov and 
Chichagof.** The passage between these islands is 
to this day called Peril Straits, a name that puzzles 
mariners who can see no obvious navigational 
hazards. It is probably no mere coincidence that 
scientists recently discovered extremely toxic 
shellfish in this vicinity. Examples such as these 
suggest that the Indians were aware of what 
scientists today generally call paralytic shellfish 
poisoning (PSP), and what the lay person calls red 
tide. These early records establish an important 
point that PSP is a natural phenomenon that 
occurred centuries before the modern industrial 
world developed. 



*Production of light by numerous minute marine and 
other organ isms, for example fireflies, bacteria, and fungi. 
The light is due to an enzyme-catalyzed chemical reaction, 
which produces very little heat. In the sea, the 
phenomenon is most pronounced when the water is 
disturbed. Many dinoflagellates, some of which produce 
toxins, are bioluminescent. 

**lronically, when U2 pilot Gary Powers was captured by 
the Russians in 1960, he carried a suicide vial of saxitoxin. 



Why Red Tide? 

Theterm red tide means differentthings to different 
people. To the oceanographer, it may mean 
concentrations (blooms) of planktonic organisms 
that discolor the sea. In the temperate oceans, 
blooms of algae occur seasonally and the plankton 
ecosystem is regulated by their occurrence. On the 
other hand, the lay person usually associates the 
term red tide with adverse effects. For example, on 
the coast of Florida, red tide generally signals fish 
kills, and the spectacle of dead fish on beaches. In 
northeastern and northwestern North America, the 
lay person associates red tide with toxic shellfish, 
and the dangers of paralytic poisoning (Figure 1). 

Discolored water as the term is used here 
- results from the absorption of light by the 
pigmentation in planktonic organisms. However, 
the term red tide is inadequate when used with 
reference to PSP: red water is often the result of the 
activities of nontoxic organisms. For example, the 
larvae of many marine invertebrates swarm, turning 
the water a rust-red color. Also, there are nontoxic 
algae that can discolor-water. The terminology 
problem is further complicated by the fact that toxic 
dinoflagellates may not always be of sufficient 
abundance to discolor the water,* although they 
may be numerous enough to toxify shellfish. 



*This was not the case in 1972 when the entire 
Massachusetts, New Hampshire, and Maine coastlines 
were closed to shellfishing; red patches were in evidence. 



42 




/. Gonyaulax catenella 

2. Gonyaulax polyedra 

3. Gymnodinium sp. 



4. Gonyaulax excavata 

5. Gymnodinium breve 

6. Pyrodinium bahamense (in bays) 



7. Gonyaulax polygramma 

8. Unidentified. 



Figure 2. World distribution of PSP incidents. Numerals in hatched areas indicate approximate total numbers of 
human poisonings in the four major areas affected; dots represent individual outbreaks. (After Prakash, Medcof, and 
Tennant, 1971; and B. Sweeney, 1976) 



Hence, the misnomer "red tide." In fact, there is no 
accurate general term that applies to 
dinoflagellate-borne toxicity. 

Inthelast20years, research has solved some 
of the mysteries of PSP, but it also has raised 
important new questions. Disturbing evidence* 
that PSP may be increasing in intensity and 
spreading to new areas has spurred scientific efforts 
in the lastfewyears. In viewof thisand the meeting 
of the Second International Conference on Toxic 
Dinoflagellate Blooms in Florida October 31 to 
November 5, 1978, it is appropriate to review what 
we know and do not know about PSP. 



*ln 1972, parts of southern Massachusetts having no 
previous history of PSP were affected, and in 1976 PSP was 
reported off northern Spain for the first time. 



The Nature of PSP 

PSP is a food poisoning that occurs when toxins 
accumulated in shellfish are passed on to humans. It 
is known to have caused at least 300 fatalities 
worldwide (Figure 2). The symptoms of the ailment 
are summarized in Table 1 . There is evidence that 
individuals who habitually eat shellfish containing 
low levels of toxin can build up a limited immunity. 
However, it is not only the tourist visiting the coast 
who succumbs to PSP, but the local person as well 
(hospital records have even included the name of a 
coastal warden!). A major difficulty with clinical 
diagnosis is that the symptoms are often interpreted 
as those associated with drunkenness (in 
combination with alcohol, the toxins are known to 
accentuate these symptoms). In at least one state, 
Maine, the local medical association has launched a 
major effort to make physicians and public health 



Table 1 . Symptoms of PSP. 



Tingling sensation or numbness around lips, gradually 
spreading to face and neck. Prickly sensation in 
fingertips and toes. Headache, dizziness, nausea. 

Incoherent speech. Progression of prickly sensation to 
arms and legs. Stiffness and noncoordination of limbs. 
General weakness and feeling of lightness. Slight 
respiratory difficulty. Rapid pulse. 

Muscular paralysis. Pronounced respiratory difficulty. 
Choking sensation. 



MILD 



SEVERE 



EXTREME 



43 



officials in coastal areas aware of PSP symptoms. 
One of the most dangerous myths is that cooking 
denatures the toxins; although cooking slightly 
reduces the toxins, it is not an adequate precaution. 
Once determined or suspected toxic, shellfish 
should be destroyed. 

In the body, these toxins act on the nerves. 
As neurotoxins, they inhibit the sodium/potassium 
pump that controls the electrical conduction in the 
nerve. The prevention of nerve impulses to the 
diaphragm may cause death by respiratory paralysis 
within 24 hours after ingestion. Efforts to discover 
an antidote forthetoxins have been unsuccessful. A 
patient suffering severe symptoms has his stomach 
pumped and is given artificial respiration in an iron 
lung. Fortunately, once the toxins have worn off, 
there are no known lasting effects. For this reason, 
they are referred to as "clean" toxins and are used in 
some types of neural and coronary therapy. 

For public health protection, the PSP 
problem is costly. Officials face two choices: to 
monitor shellfish toxicities, or to close the coast to 
shellfishing altogether (Figure 3). A dramatic 
example of the latter is the vast coastline of Alaska, 
which has been closed to harvesting clams and 
mussels since 1947, following severe outbreaks of 
PSP. Alaskan shellfish represent an important 
financial resource, and there is great pressure to 
reopen the coastline in some areas. 

Most shellfishing areas in the United States 
run toxicity monitoring programs, which regularly 
test shellfish from representative locations.* The 
standard mouse test was developed in 1937 and has 
remained virtually unchanged. A liquid fraction is 
extracted from macerated shellfish meats and 
injected intraperitoneally into laboratory mice 
(Figure 4). The times of death of the mice are related 
to the toxin level. Typical toxicity levels are shown in 
Table 2. The "total consumed" level can be the 
result of eating 12 clams weighing 100 grams at toxin 
levels of 80 micrograms per 100 grams of tissue, or 
one clam weighing 100 grams at 1 ,000 micrograms 
per 100 grams of tissue. 

Toxic Dinoflagellate Ecology 

Together with diatoms and coccolithophores, 
dinoflagellates are major components of marine 
phytoplankton. They are microscopic, one-celled, 
and motile (propelled by two flagella). Many 
dinoflagellates, including those producing shellfish 
toxins, are bioluminescent, which is probably why 
the West Coast Indians learned to associate 
shellfish toxicity with light flashes in the sea. An 
important feature of dinoflagellates in the context 



*Several European countries have or are considering 
setting up a monitoring program following the 1976 
outbreak of PSP off the coast of northern Spain . 



THIS AREA 

CLOSED 

TO ALL DIGGING 

OF 

CLAMS, MUSSELS, QUAHOGS 

Because of 
PARALYTIC SHELLFISH POISON 

IT HAS BEEN CERTIFIED BY THE STATE OF- MAINE DEPARTMENT OF MARINE RESOURCES 
THAT CLAMS, OLIAHOCS AND MUSSELS IN THIS AREA, "t LOSED AREA NUMBER J7CII " 

\RE AFFECTED WITH PARALYTIC POISON AND DO NOT CONFORM WITH PUBLIC HEALTH 
STANDARDS AND REGULATIONS AS ESTABLISHED BY THE STATE OF MAINE AND THE FOOD 
AND DRUG ADMINISTRATION 



CLOSED AREA NUMBER 



Commissioner of 
Marine Resources 



Figure 3. Warning sign for PSP. 




Figure 4. The mouse test, the standard method for 
determining levels of toxin in shellfish. The mouse is 
injected with liquid from the affected shellfish, and the 
toxicity level determines the death time. 



Table 2. Typical toxicity levels, based on mouse test 
results. 

Toxin level 

expressed as micrograms 
per 100 grams tissue 

Limits of mouse test 

sensitivity. 58 

Closure level in United 

States for shellfish. 80 

Moderate symptoms in 

human adult. 1,000 

Lethal level in 

human adult. 10,000 

Highest level in mussels 

at Monhegan, Maine, in 1 975. 22,000 



44 



of red tide is their ability to reproduceasexuallyata 
rate from once every five days to twice a day in some 
cases. This allows a population with relatively few 
cells to develop quickly into a large concentration 
(bloom). 

It takes concentrations of nearly 1 ,000,000 
cells per liter to discolor seawater. Such 
concentrations are obtained in two principal ways: 
1) accelerated biological growth, which is 
dependent on specific environmental factors, such 
as temperature, light, and certain nutrients, and 2) 
physical (hydrography) mechanisms that 
concentrate the dinoflagellates. These mechanisms 
are triggered by meteorological events, such as 
wind and rain. Most situations are a combination of 
the two. 

Most areas of red tide occu rrence are located 
between the extremes of active upwelling and 
passive concentrating mechanisms. In some cases, 
such as off the coasts of Britain, fronts are identified 
as the zones where red tides are most likely to 
occur. These frontal zones, or discontinuities 
between water masses, are formed by tides, winds, 
and/or the density of seawater. 

The majority of the scientific observations of 
discolored water have been made by chance 
encounter. Some evidence suggests that red tides 
are noticed only when the bloom is in its final 
stages. Thus the initiation and maintenance of the 
bloom are "history" by the time of observation. This 
has handicapped studies of bloom formation. An 
analogy has often been drawn to studies of cancer: 
once it is observed, it is difficult to reconstruct the 
historical causes. 

Until recently, the process leading to 
shellfish toxicity was thought to involve a very 
restricted group of dinoflagellates producing the 
toxin saxitoxin. These were Conyaulax catenella 
and/or C. acatenella on the west coast of North 
America, and C. tamarensis in northwestern Europe 
and on the east coast of North America and Japan. 
Under certain environmental conditions such as 
reduced salinity and high organic runoff from land, 
these species developed large bloom populations. 
Shellfish were found to toxify as they ingested these 
motiledinoflagellatecells, particularly under bloom 
conditions. For many years, scientists have studied 
the dinoflagellates implicated in PSP, both in 
laboratory cultures and in nature. The main 
objectives behind this work have been to identify 
the species responsible for producing the toxins, to 
document their growth requirements, and to 
identify any particular environmental factors 
contributing to shellfish toxin development. It has 
been hoped that this might lead to the development 
of a predictive index, giving public warning of 
approachingshellfish toxicity. Suggestionsforsuch 
an early warn ing system included monitoring motile 
dinoflagellates in the water and looking for 
developing blooms. 



Taxonomy and Life History Aspects 

In recent years, taxonomists have taken a closer 
look at the small, related group of dinoflagellates 
producing the toxins responsible for PSP. They have 
come across a problem common to dinoflagellate 
studies: how to effectively use minute, 
morphological details to identify these organisms. 
Such problems, which were difficult enough using 
ordinary light microscopy, have become more 
complicated with the introduction of the scanning 
electron microscope (SEM). It is now clear that 
within what used to be called C. tamarensis there 
are several different organisms, based on minute, 
morphological and physiological details.* As yet, 
there is no consensus as to whether these should be 
regarded as different species, strains, forms, or 
varieties; but work is proceeding on at least 
recognizing and identifying them (Figure 5). It will 
be important to establish whether these forms have 
environmental preferences, and particularly 
whether they have different inherent toxicities, or 
whether the toxicity is induced by various 
environmental factors. Obviously, if they all behave 
similarly, classification can be treated as a minor 
academic problem. However, evidence suggests 
that both in laboratory cultures and in nature at least 
one form is nontoxic, posing problems for the 
microscopist trying to monitor toxic dinoflagellates 
in plankton (see page 19). 

A rapidly developing area for research 
concerns the life histories of these dinoflagellates. 

*The New England organism is now referred to as 
Conyaulax tamarensis by some and Conyaulax excavata by 
others. 




Figure 5. Scanning electron micrograph of Gonyaulax 
excavata, which was isolated off Gloucester in the 7972 red 
tide occurrence. The diameter of the cell is 36 microns. 
(Courtesy Alfred and Laurel Loeblich, University of 
Houston, Texas) 



45 



environmental suitability 
(hours) 



MOTILE environmental stress^ 


CELL 

bioluminescent 
toxic 


( minutes / hours ) 




MOTILE 

CELL 

bioluminescent 
toxic 



fusion 
(gametes) * 




(zygote) 




TEMPORARY 
CYSTS 

non-motile 
toxic 
30-40 jj 
rounded 




Figure 6. Probable life 
history cycle of Gonyaulax 
excavata. 



RESTING CYST 

non-motile 
highly toxic 
25 X 40 jj 
elongated with 
gelatinous covering 



increase 
temperature 



mandatory dormancy 
(months) 



It has been shown that in addition to the familiar 
motile stage, present in New England waters from 
mid-April to mid-October, C. excavata produces at 
least two other nonmotile stages (Figure 6). One is 
called a temporary cyst, since it is easily induced in 
cultures of motile cells subjected to unfavorable 
conditions, and since it quickly (within hours) 
reestablishes a motile population on return to 
favorable conditions. So far, temporary cysts have 
been seen only in laboratory cultures. We think that 
their role in nature might be to provide a method for 
overcoming temporary environmental setbacks. 

A second type of nonmotile cyst the 
resting cyst (Figure 7) is probably a zygote 
produced in sexual reproduction. These cysts, 
equipped with food storage products, sink to the 
bottom of the water column and accumulate in the 
flocculant layer at the sediment/water interface. 
There they overwinter. They appear to require at 
least a four-month resting period. We recently 
measured toxicity levels in cysts several months at 
rest, and found them to be at least 10 times higher 
than in motile stages. There is a suggestion that 
toxicity decreases with time after formation, such 
that resting cysts when first formed may be as much 
as 1 ,000 times more toxic than the motile cell. 

Cysts behave as fine silt particles within the 
sedimentary regime; some areas act as "sinks" for 
collecting them, while other areas remain relatively 
cyst-free. We are discovering large concentrations 
of toxic resting cysts in bottom sediments along the 
Maine coast, and they have been reported as far 
south as Woods Hole, Massachusetts. This calls for 
a new approach to the shellfish toxicity problem. 
Resting cysts probably account for shellfish toxicity 



where there is no obvious link with motile 
dinoflagellates (forexample, in deeper waters, or in 
winter), and they probably contribute significantly 
to toxicity following blooms. If so, then the 
monitoring of plankton for shellfish toxicity will 
have to be broadened to include benthic resting 
cysts and the sedimentary process. 

Recent Work with Trace Metals 

Considerable evidence has accumulated to 
implicate organic materials and trace metals in the 
regulation of growth and distribution of 
phytoplankton. Early experiments showed that 
growth was enhanced, particularly in dinoflagellate 
cultures, by adding soil or seaweed extracts, or 
other organic chelating* compounds to seawater 
and growth media. In the 1960s, the correlations 
were good enough that some investigators 
proposed a river runoff index for the Bay of Fundy, 
and an iron runoff index for the Peace River in the 
Gulf of Mexico. These have not stood up 
completely, probably because of an oversimplified 
approach. Recently, more sophisticated 
experiments by D. Anderson and F.M.M. Morel at 
the Massachusetts Institute of Technology have 
shown that when the metals in the growth medium 
are carefully manipulated, C. tamarensis will grow 
well only when the concentrations of cupric ion are 
at exceedingly low levels. In other words, C. 
tamarensis appears to be several orders of 
magnitude more sensitive to trace metals (for 



*A combining of large molecules with ions. 



46 



Figure 7. Resting cysts 
collected in January 7977 at 
WO meters depth off 
Monhegan Island, Maine. 
Bar equals 10 microns. 
(Photo by Barrie Dale) 




example, cupric ion) than are other members of the 
summer phytoplankton community. 

Howmightthis work in the real world? Based 
on their culture data, the MIT authors suggest that 
the normal ambient levels of cupric ion along the 
coast of New England would be sufficient to 
suppress the rapid division and growth of C. 
tamarensis, while permitting other phytoplankton 
to flourish. However, after a heavy rain and flush ing 
of organic material from intertidal seaweeds as well 
as estuaries, or a mixing of organic materials from 
the shallow bottom, the copper would be reduced 
to nontoxic levels and then C. tamarensis could 
divideand bloom. Another aspectofthis hypothesis 



is that with increased organic material, there is 
greater availability of iron compounds, which 
dinoflagellates require in larger quantities than the 
amount needed by other members of the 
phytoplankton community. Accordingly, increased 
chelation would improve both the copper and iron 
status for C. tamarensis and other dinoflagellates. 

This work needs field testing. Unfortunately, 
the methodologies that can be used in seawater to 
detect the speciation of these trace metals have 
limitations. However, some data and circumstantial 
information support the hypothesis. There was an 
apparent correlation of iron levels with a bloom of 
dinoflagellates at Monhegan Island off the Maine 



47 



O <80>jg/IOOg tissue 
80-499 



igneous rocks undivided 
exposed at seacoasi 




Monhegon Island 



Figure 8. Peak shellfish toxin levels, off the Maine coast, for 
7975. 

coast in 1976. Field measurements for the 1977 
season indicated that the copper levels were too 
high and the iron levels too low to support growth 
of C. tamarensis. Blooms of the organism were not 
observed duringthe summer of 1977. In contrast, 
field data of the upwelling system off Peru showed 
extremely low levels of cupric ion. Correlated with 
this were immense blooms of the dinoflagellate 
Gymnodinium splendens and a ciliate with a 
dinoflagellate-like symbiont, Mesodinium rubrum. 

Consistent too with this hypothesis is the 
presence and absence pattern of shellfish toxin 
along the Maine coast (Figure 8). The area where no 
toxin has been detected is composed of igneous 
rocks, including those from abandoned copper 
mines. Analysis of seaweeds that are known to 
accumulate metals reveals that they are twice as 
high in copper levels in this area as seaweeds from 
other areas of the Maine coastline. Preliminary data 
also suggest that there may be fewer benthic resting 
cysts of C. tamarensis in this area. 

The Chemistry of the Toxins 

For several years, the causative toxin was 
considered to be pure saxitoxin in species of 
Gonyaulax found along the coasts of North 
America. Accordingly, the mouse test was, and still 
is, standardized with saxitoxin. More elaborate 
recent testing has revealed that there are at least 
seven toxins associated with saxitoxin in Gonyaulax 
tamarensis. The associated toxins are structurally 
similar to saxitoxin (Figure 9) and have been named 



Gonyautoxins by Y. Shimizu and coworkers at the 
University of Rhode Island. Their potency is similar 
to saxitoxin, one of the most potent toxins known. 
In crystalline form, toxin the size of an aspirin tablet 
(350 milligrams), if split and consumed by 35 
persons, would theoretically be a lethal dosage for 
all; or if subdivided among 350 persons, would 
result in moderate poisoning of all. 

A unique aspect of the toxins is that they are 
very high in nitrogen. Some researchers are 
investigating the possibility that the toxins may 
serve as a nitrogen pool for the organism in the 
motile stage as well as the encysted stage. 

Future Work 

Important objectives in future shellfish toxin 
research include: how to insure safety for public 
health; how to better utilize the shellfisheries; and 
how to investigate the apparent spread of shellfish 
toxin, along with the possibility that it may be 
aggravated by human activities. 

A new replacement test for measuring 
toxicity would help with the first two objectives. The 
mouse injection is too cumbersome to be used by 
Alaskan fishermen on board ship, when 
considering whether to harvest a particular bed of 
clams, or by the local shellfish warden who must 
send samples to a central processing laboratory. It is 
hoped that new chemical work on the toxins will 
eventually lead to a test suitable for use as a 
preliminary guide in the field. 

It will be useful to develop a new predictive 
i ndex for the monitoring of PSP. This index will have 
to take into account several of the factors that we 
have mentioned in this article. The original concept 
of monitoring dinoflagellates in the plankton is 
unsatisfactory in view of the knowledge that there 
are blooms of nontoxic dinoflagellates that are 
indistinguishable from the toxic forms under the 
conventional light microscope. Added to this is the 
fact that highly toxic cysts in sediments may cause 




Figure9. Chemical structure of saxitoxin. (From Schantz, et 
al., 1975, in First International Conference Proceedings) 



48 



Figure 10. Motile cells 
developing into cysts, and 
their role in perpetuating 
shellfish toxin, leading to 
PSP in humans. 




PSP 



shellfish toxicity without any accompanying 
build-up of a plankton bloom. 

To address the possible role of spreading, we 
need to understand more about the bloom 
phenomenon. We know that some dinoflagellates, 
including those implicated by PSP, appear to be 
present every year in small numbers, although they 
only bloom in particular years when they reach 
enormous concentrations, whereas other species 
occur every year, without ever blooming. Trace 
metals and chelation appear to be likely factors 
causing some species to bloom, but we do not know 
yet the natural incidence rate of these blooms. 
Caution therefore is needed in presuming that 
shellfish toxicity is spreading to new areas. In such 
areas as southern Massachusetts and northern 
Spain, where there have been recent outbreaks of 
PSP, a probable explanation is that the toxic 
dinoflagellates were there many years before, but 
apparently never bloomed. The important question 
then becomes: are these recent blooms natural, 
long-term events whose scale falls outside our 
records, or is this in some way due to man's 
activities? 

One area of immediate concern arises from 
the discovery of large concentrations of highly toxic 
cysts in bottom sediments. Those engaged in 
projects such as artificial seeding of shellfish beds, 
shellfish culturing, and marinedredgingoperations 
should be alerted to possible dangers that might 
arise from such activities. Dredged sediment could 
well contain toxic cysts that could be carried far 
from the source after dumping at sea, likely settling 
at or near the sediment/water interface. Caution 
also should be used when transferring shellfish 
from one area to another; microscopic cysts could 
easily be carried with them. It should be 
emphasized that once introduced into a new area, 



cysts may directly contaminate shellfish. They also 
may establish a more permanent local toxic 
dinoflagellate population by acting as "seed beds" 
(Figure 10). 

One fact is evident: we need to improve our 
data collecting, especially on a worldwide scale. The 
establishment of an international rapid 
communication network for red tides and toxic 
dinoflagellate blooms will be addressed at the 
Second International Conference on Toxic 
Dinoflagellate Blooms. 

Barrie Dale is a Visiting Investigator at the Institute for 
Marine Biology and Limnology, University of Oslo, 
Norway. Clarice M. Yentsch is a Research Scientist at the 
Bigelow Laboratory for Ocean Sciences, West Boothbay 
Harbor, Maine. 



Suggested Readings 

Anderson, D.M., and F.M.M. Morel. 1978. Copper sensitivity of 
Gonyaulax tamarensis. Limnol. and Oceanogr. 23: 283-95. 

Dale, B., C.M. Yentsch, and ).W. Hurst. 1978. Toxicity in resting 
cysts of the red tide dinoflagellate Gonyaulax excavata from 
deeper water sediments off the Maine coast. Science, In Press. 

LoCicero, V., ed. 1975. Proceedings of the First International 
Conference on Toxic Dinoflagellate Blooms. Wakefield, 
Mass.: Massachusetts Science and Technology Foundation. 

Oshima, Y., L. ). Buckley, N. Alam, and Y. Shimizu. 1977. 

Heterogeneity of paralytic shellfish poisons. Three new toxins 
from cultured Gonyaulax tamarensis cells, Mya arenaria and 
Saxidomusgiganteux. Comp. Biochem. and Physiol. 57: 31-34. 

Prakash, A., J.C. Medcof, and A.D. Tennant. 1971 . Paralytic 

shellfish poisoning in eastern Canada. Bulletin 177, Fisheries 
Research Board of Canada. 

Pingree, R.D., P.R. Pugh, P.M. Holligan, and G.R. Forster. 1975. 
Summer phytoplankton blooms and red tides along tidal fronts 
in the approaches to the English Channel. Nature 258: 672-77. 

Tyler, M. A., and H.H. Seliger. 1978. Annual subsurface transport of 
a red tide dinoflagellate to its bloom area: water circulation 
patterns and organism distributions in the Chesapeake Bay. 
Limnol. and Oceanogr. 23: 227-46. 



49 




Green <$ea 

by James L. Considine 
and John J. Winberry 




ver-exploitation of ocean resources is nota new 
phenomenon, but with the world population and 
the demand for calories and protein increasing, the 
sea is a potentially important food source. The 



annual worldwide catch of all species as of 1976 was 
72 million tons, and some of these are now 
threatened with extinction. Unless current methods 
of exploitation are modified, the number of species 




of the Cayman Islands 



threatened will continue to increase. Such is the 
case with the green sea turtle, Chelonia mydas 
mydas also called the Atlantic Green Turtle. It has 
been called theworld's most economically valuable 




reptile because of the many products derived from 
it. These include meat; the white calipee (the 
unossified undershell) and calipash (the 
cartilaginous greenish gelatin that lines the shell), 
used for soup; and eggs. Nonfood articles include 
oil, skins, and shells. Since the 17th century, the 
green sea turtle has been intensively hunted by 
man, and the result has been the near annihilation 
of the species in American and Asian waters. 

Si nee the middle of this century we have seen 
the application of plant genetics to increase the 
productivity of wheat and rice and to improve the 
nutritiveness of sorghum advances that have 
quelled, at least for the present, the 
food/population threat. Of equal importance is 
research applied to the productivity of the sea. If 
species can be domesticated and their reproduction 
controlled, exploitation of the oceans will change 
from a hunting/gathering process to sophisticated 
husbandry. Not only would production be more 
efficient, but major inroads could be made in the 
protein shortages of the tropical world. 

The green sea turtle has been the subject of 
such research since 1968, much of it carried out on 
the Caribbean island of Grand Cayman (Figure 1 ). 
Turtle fishing long a major part of the island's 
economy was made illegal in 1970, after a process 
of over-exploitation and virtual extinction. 

History of Turtle Hunting 

Apparently there was no permanent pre-Columbian 
Indian settlement in the Cayman Islands, but bands 
of Arawaks or Caribs probably visited the islands 
occasionally. Archaeological and ethnographic 
evidence in the Caribbean indicates that turtles 
were hunted for food, but whether this was the 
reason for such stays in the Caymans is not known. 

On May 10, 1503, Christopher Columbus, 
returning from his fourth voyage, passed the Lesser 
Cayman Islands and named them "Las Tortugas," 
but the discovery of Grand Cayman is unrecorded. 
All three islands appear on 16th-century charts, and 
Europe-bound Spanish vessels probably stopped 
there for supplies, specifically turtles and water. By 
1562, English ships also were anchoring in the 
Caymans, and through the 16th and early 17th 
centuries, the islands were frequented by French 
and Dutch vessels as well. In 1655, England 



Figure 1. Green sea turtle range in the Caribbean. (Photo 
Russ Kinne, PR) 



51 



conquered Jamaica and brought the Caymans 
within her Caribbean sphere. As a result, the 
frequency of English visits to the Caymans increased 
as well as the representation of these islands in 
colonial documents. In the early 1660s, Jamaicans 
settled the Lesser Caymans for the purpose of 
hunting turtles.* 

At first, hunting was a haphazard, unplanned 
affair. A vessel would stop at an island in hopes of 
discovering a fleet of turtles on the beach. If nesting 
turtles were found, large numbers were easily 
captured. Though graceful in the water, the green 
sea turtle is slow and awkward on land easily 
being turned on its back. Unable to right itself, the 
turtle was killed and salted or taken on board alive 
to provide fresh meat during the voyage. By the 
1600s, turtle fishing in the Cayman Islands had 
undergone changes. Instead of depending on 
random encounters, hunters began searching 
systematically for nesting herds. In addition to 
setting up shore camps during nesting season, they 
also netted swimming turtles, finding that the ones 
mating offshore were easy prey. These practices, 
though rudimentary, were devastating. As early as 
the 18th century these hunting methods, which 
focused on killing the females and collecting their 
eggs, threatened the green sea turtle population. 

In 1734, a small English colony was 
established on Grand Cayman. Initially, it relied on 
agriculture and privateering, but turtling grew in 
importance. By the late 18th century, Georgetown 
had become the capital of Grand Cayman and, with 
the rise of turtle fishing, served as a major market 
for turtle products. In the 1790s, six small turtling 
vessels operated out of Grand Cayman; the meat 
was sold to merchant ships ret urn ing to Europe and 
to buyers from Jamaica. Methods for capturing 
turtles changed little over a span of 150 years, but 
the systematic and indiscriminate hunting 
eventually caused the virtual disappearance of the 
turtle population in Cayman waters. 

Cayman turtle hunters then sought new 
fishingareas, securing permission from Spain in the 
early 1800s to fish off Cuba's southern coast. The 
Cuban sea turtle population was quickly decimated 



*The Grand Cayman turtle fishery is distinct from that of 
the Lesser Cayman Islands. The Lesser Caymans, or 
Cayman Brae, though semi-permanently settled as early as 
the 1660s, had long been deserted and were recolonized 
from Grand Cayman only in 1833. The inhabitants of 
Cayman Brae developed their own turtle fishery, relying 
on the hawksbill turtle, Eretmochelys imbricata. Although 
the hawksbill was valued primarily for its shell, the people 
of Cayman Brae developed a taste for what had been 
hitherto thought of as unpalatable meat. Interestingly, 
when the turtle industry of Cayman Brae declined, the 
former turtlers became involved with tourism and turned 
to making handicrafts. They abandoned their traditional 
economy in order not to infringe on Grand Cayman's 
fishery. 



Behavioral Aspects 

The green sea turtle (Chelonia mydas), which 
gets its name from the greenish color of its 
body fat, has been known to migrate long 
distances - in some cases 1,000 miles or more. 

They are strong swimmers, having been 
observed cruising at a speed of 0.88 to 1 .4 
miles per hour. Physiological studies (Berkson 
1 966, 1 967) indicate that the green sea turtle in 
prolonged dives can survive up to 5 hours with 
no measurable oxygen in the trachea or in the 
blood of the carotid artery and that as long as 9 
minutes may elapse between heartbeats. 

In the past, wild green turtles have been 
weighed in at more than 1,000 pounds. Today 
the largest are about 4-foot long and weigh in 
the vicinity of 500 pounds. Most are under 100 
pounds. The adults feed largely on seagrasses in 
shallow water, although they have also been 
known to feed on algae, mollusks, jellyfish, and 
small crustaceans. 

Mating occurs off the nesting beaches, 
usually close to shore. Several males may 
simultaneously court and attempt to mate with 
a single female. Males have been known to 
fight with one another during the breeding 
season. During copulation, which occurs 
usually at the surface, the male's claws have 
been observed cutting into the female's 
carapace, leaving deep, bleeding wounds. 
Nesting occurs on the beach at night. 

The nearly spherical, soft, white eggs 
are 35 to 58 millimeters in diameter and weigh 
44 to 65 grams. The average number of eggs 
per clutch or nest is in the vicinity of 1 10. The 
incubation period is anywhere from 30 to 72 
days. Hatching rates vary widely. 



through the use of nets set over feeding grounds 
and coral reefs. By 1850, fishing shifted to the waters 
off Honduras and Nicaragua, especially the Miskito 
Cays. During the latter half of the 19th century, the 
turtle catch of the Cayman fleet now numbering 
12 vessels was sold to passing ships or at markets 
in Jamaica. By 1900, the market for green sea turtles 
included Europe and the United States. Theturtling 
fleet grew to 25 vessels, but the industry's success 
held the seeds of its decline. By 1940, the fleet 
fishing Nicaraguan waters was down to 15 vessels, 
and by 1950 only 10 were active. The number of 
turtles caught, however, remained constant, 
though generally they were smaller and of poorer 
quality. 

The 1960s were difficult years for Cayman 
turtle hunters. The population of turtles in Central 
American waters had declined to near extinction, 
and the remaining reptiles were protected by an 
international agreement. The era of Cayman turtle 



52 






Farm worker amid 
approximately 800 turtles 
in a Mariculture holding 
tank. (Photo James 
Considine) 







fishing ended in 1970. No legally registered 
schooners left for Nicaraguan waters that year, 
although some Cayman vessels continued to hunt 
turtles illegally or bought them from poachers. 

Domestication of the Sea Turtle 

Since turtling grounds were closed due to 
conservation regulations, an artificial method of 




Farm worker holding an 8-month-old turtle. (Photo James 
Considine) 



dealing with the green sea turtle was implemented. 
Prior to 1945, there had been several attempts to 
establish turtle ranches in the Caymans, but limited 
knowledge of the reptile's habits doomed them. In 
the 1950s, a ranch for 500 green sea turtles was 
attempted, but it also failed. In the late 1960s, a 
program aimed at domesticating the green sea 
turtle was proposed by a company called 
Mariculture, Ltd., to the Grand Cayman 
government. The program had two general 
purposes: to produce turtle meat and products and 
to relieve pressure on wild species. Commercially, 
theturtle has a high market potential (virtually every 
part is salable). Its food to meat conversion ratio is 
approximately 2: 1 half that of chicken or hog and 
less than an eighth of cattle. This is because the 
turtle is a cold-blooded animal and uses no food 
energy to maintain body heat. At that time, 
however, littlewas known aboutthe turtle's biology 
and behavior, especially about its ability to breed in 
captivity. 

In August, 1968, Mariculture began 
operations. Initial experiments sought to answer 
questions about feeding, growth rates, behavior, 
and stock survival. Eggs were collected on Costa 
Rican beaches, hatched, and the turtles reared 
under controlled conditions for about a year. They 
werethen released into a natural water body to feed 
on seagrasses. Despite expectations that young 
turtles would not migrate after a year in captivity, 
they still wandered. The idea of an open range had 
to be abandoned. At this juncture, it was decided to 
raise the turtles in enclosed pens. This required a 
more complex operation than the few holding pens 
used for hatch I ings prior to their control led release. 

In 1971 , Mariculture moved toa new location 
and constructed large permanent pens for the 
turtles that were in effect artificial environments. 
The new site was closer to clear ocean water needed 



53 




caff 




Artificial breeding pond 
and nesting beach. (Photo 
James Considine) 



for filling the pens and for expelling effluent. The 
company at this point also shifted its emphasis from 
gathering research data on the turtles to applying 
the knowledge gained toward production for profit. 

The new complex is located at Goat Rock in 
the northeastern corner of Grand Cayman Island, 
and includes concrete pens, tanks, and a breeding 
and stock pond. It can accommodate more than 
100,000 sea turtles, which are grouped into the 
various holding pens according to size and weight. 
An artificial beach that can hold about 80 nesting 
turtles has been constructed adjacent to the 
breeding pond. 

The ultimate goal of Mariculture is to 
establish a complete turtle breeding cycle on the 
farm. At present, however, the company purchases 
eggs collected from nesting beaches in the 
Caribbean and Atlantic. It agrees to return 
approximately 1 percent of the hatched turtles to 
the natal beaches when they areayearold. Because 
only one or two tenths of 1 percent of the hatched 
turtles reach adulthood, this more than 
compensates for a reduction of population due to 
egg collection. The eggs are gathered several times 
annually, and are flown to Grand Cayman. After 
nine egg collections, the company averaged an 80 
percent hatching rate. Of these, 85 percent reached 
one year of age. As the turtles grow, they are shifted 
to larger tanks, and a weight/volume formula 
determines the optimum number per tank. After 
three years, each turtle weighs approximately 100 
pounds and is ready for processing. 

Though much of the reproduction cycle has 
been realized under artificial conditions, it has not 
been perfected. Successful mating and subsequent 
egg laying on the artificial beach at Goat Rock are 
crucial to the venture because without both, 
domestication of the species and the industry's 
self-sufficiency are impossible. Various husbandry 
experiments have been performed in an effort to 



establish a breeding cycle. Sporadic nestings by 
fertilized females from the wild and numerous 
copulations in the breeding pond have occurred. 
Mating in 1973 at the farm resulted in some 12,000 
eggs; in 1974, the figure was 10,000. Once captive 
breeding is established and better understood, 
genetic and growth experiments can be attempted. 
Then, the venture will become an aquaculture one, 
and not a ranch, relying on turtles in the wild to 
replenish the stock. 

Future of Mariculture 

If a successful aquaculture venture can be 
established, it will revive the market for turtle 
steaks, stew meat, soup stock, lower-grade meat, 
flippers, leather, oil, and shell. The company has 
marketed meat in Georgetown since 1972, also 
selling it in the United States, Canada, Australia, and 
Western Europe. But there are still basic problems 
to overcome. The turtle's complete biological cycle 
has yet to be established. As well, certain problems 
with disease must be addressed.* Furthermore, the 
problem of turtle conservation has not been solved. 
Though this had been a highly desired by-product 
of the venture, the fact that Mariculture has not 
increased production substantially means that 
natural populations are still threatened. 

Based on present results of the experiment, 
production of the sea turtle could potentially 
increase some 650-fold over natural conditions. 
Such a result would be an extremely important 
development for man if it could be extended to 

*Parasitism has been minimal. The most frequently 
observed pathology thus far has been infections resulting 
from bite lesions, which are treated with gentian violet. 
The crowd ing of turtles in pens and tanks, however, poses 
the possibility of severe bacterial or viral epidemics. Any 
microbial agents of serious disease that might be endemic 
should be identified. 



54 



other sea creatures. Areas of protein deficiency in 
theThird World could benefit from expanded turtle 
husbandry. 

Once there is a breakthrough in 
domestication of the green sea turtle, cultivation 
would not entail large-scale equipment or high 
capital investment.* Many coastal communities 
could establish small-scale farms for domestic meat 
production. The development in the tropics of 
larger farms could also be undertaken. 

The potential of turtle farming is great, but it 
requires additional research and development for 
ultimate success. When the major goal of 
domesticating the green sea turtle has been fully 
realized, perhaps the creature will regain its 
position as the world's most economically valuable 
reptile, pointing the way to further advances in 
aquaculture. 

James L. Considine is Assistant Planning Director of the 
Adams County Board of Commissioners, Brighton, 
Colorado. John J. Winberry is Associate Professor of 
Geography at the University of South Carolina. 

This has been questioned in a general study of 
aquaculture practices by Weatherly and Cogger, 1977. 
Although the green sea turtle feeds naturally on various 
seagrasses that could be readily and cheaply harvested, 
current feeding practices at Mariculture emphasize 
animal-protein feed pellet supplements that are imported 
from the United States. 

Selected Readings 

Brown, L.R., and G.W. Finsterbusch. 1972. Man and his 

environment: food. N.Y.: Harper and Row. 
Bustard, H.R. 1972. Turtle farmers of Torres Strait. Hemisphere 16: 

24-28. 
Carr, A. 1967. So excellent a fishe: A natural history of sea turtles. 

Garden City, N.Y.: The Natural History Press. 
. 1969a. Sea turtle resources of the Caribbean and Gulf of 

Mexico. I UCN Bulletin, New Series 2(10): 74-75,83. 
. 1969b. Survival outlook of the west Caribbean green turtle 

colony. IUCN Publications, Suppl. Paper No. 20: 13-16. 
. 1970. Green sea turtles in peril. National Parks 

Conservation Magazine 44: 19-24. 
Ehrenfeld, D.W. 1974. Conserving the edible sea turtle: can 

mariculture help?/\m. So. 62: 23-31. 
Emery, K.O., and C. O'D. Iselin. 1967. Human food from ocean and 

land. Science 157: 1279-81. 
Hendrickson, J.R. 1974. Marine turtle culture an overview. In 

Proceedings of the Fifth Annual Meeting of the World 

Mariculture Society. Baton Rouge: Louisiana State University 

Press. 
Lewis, C.B. 1940. The Cayman Islands and marine turtle. In The 

herpetologyofthe Cayman Islands, ed. by C. Grant. Kingston, 

Jamaica: Inst. of Jamaica. 
Parsons, J.J. 1962. The green turtle and man. Gainesville, Fla.: Univ. 

of Florida Press. 
Reiger, G. 1975. Aquaculture: has it been oversold? International 

Wildlife 5: 21-24. 
Ryther, J.H. 1975. Mariculture: how much protein and for whom? 

In The oceans and man, ed. by J.B. Ray, pp. 29-45. Dubuque: 

Kendall/Hunt. 
Thompson, E.F. 1945. The fisheries of the Cayman Islands. 

Development and Welfare in the West Indies, Bull. No. 22, 

Advocate Bridgetown. 
Weatherly, A. H., and B.M.G. Cogger. 1975. Fish culture: problems 

and prospects. Science 197: 427-30. 



!-: 
















Two Atlantic green turtles engaged in mating behavior. 
(Photo Cordon S. Smith from National Audubon 
Society, PR) 




In the article "Strategies for Protecting 
Marine Mammal Habitats" by G. Carleton 
Ray, James A. Dobbin, and Rodney V. Salm 
that appeared in the Spring issue (Vol. 21 , 
Number 2, 1978), the wrong map appeared 
in Figure 2 at the top of page 61 . The correct 
map appears above. 



55 




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SEA-FLOOR SPREADING, Vol. 17:3, Winter 1974 Plate tectonics is turning out to be one of the most 
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ENERGY AND THE SEA, Vol. 17:5, Summer 1974 One of our most popular issues. There is extractable 
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MARINE POLLUTION, Vol. 18: 1 , Fall 1974 Popular controversies, such as the one over whether or not the 
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FOOD FROM THE SEA, Vol .18:2, Winter 1975 Fisheries biologists and managers are dealing with the hard 
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DEEP-SEA PHOTOGRAPHY, Vol. 18:3, Spring 1975 A good deal has been written about the use of 
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MARINE BIOMEDICINE, Vol. 19: 2, Winter 1976 Marine organisms offer exciting advantages as models for 
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SOUND IN THE SEA, Vol. 20:2, Spring 1977 Beginning with a chronicle of man's use of ocean acoustics, 
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ESTUARIES, Vol. 19:5, Fall 1976 Of great societal importance, estuaries are complex environments 
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SOUND IN THE SEA, Vol. 20:2, Spring 1977 Beginning with a chronicle of man's use of ocean acoustics, 
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GENERAL ISSUE, Vol. 20:3, Summer 1977 The controversial 200-mile limit constitutes a mini-theme in this 
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OIL IN COASTAL WATERS, Vol. 20:4, Fall 1977 From a standing start a decade or two ago, scientists have 
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MARINE MAMMALS, Vol. 21:2, Spring 1978 Attitudes toward marine mammals are changing worldwide. 
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SEAWARD EXPANSION, Vol. 19:1, Fall 1975 

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