EPA-600/3-77-016
January 1977
Ecological Research Series
THE DYNAMICS OF AN ESTUARY AS A
NATURAL ECOSYSTEM
Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Gulf Breeze, Florida 32561
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into five series. These five broad
categories were established to facilitate further development and application of
environmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ECOLOGICAL RESEARCH series. This series
describes research on the effects of pollution on humans, plant and animal
species, and materials. Problems are assessed for their long- and short-term
influences. Investigations include formation, transport, and pathway studies to
determine the fate of pollutants and their effects. This work provides the technical
basis for setting standards to minimize undesirable changes in living organisms
in the aquatic, terrestrial, and atmospheric environments.
x?>
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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THE DYNAMICS OF AN ESTUARY
AS A NATURAL ECOSYSTEM
by
F. J. Vernberg, R. Bonnell,
B. Coull, R. Dame, Jr., P. DeCoursey,
W. Kitchens, Jr., B. Kjerfve,
H. Stevenson, W. Vernberg, R. Zingmark
Belle W. Baruch Institute for Marine Biology and Coastal Research
University of South Carolina
Columbia, S. C. 29208
Grant No. R 802928
Project Officer
Gerald E. Walsh
Gulf Breeze Environmental Research Laboratory
Gulf Breeze, Florida 32561
U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT
ENVIRONMENTAL RESEARCH LABORATORY
GULF BREEZE .FLORIDA 32561
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DISCLAIMER
This report has been reviewed by the Environmental Research Laboratory,
U.S. Environmental Protection Agency, and approved for publication. Approval
does not signify that the contents necessarily reflect the views and policies
of the U.S. Environmental Protection Agency, nor does mention of trade names
or commercial products constitute endorsement or recommendation for use.
ii
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FOREWORD
To evaluate effects of pollution on estuarine populations, communities,
and ecosystems, it is necessary to understand their structures and functions
under natural, unstressed conditions. Without an understanding of normal
situations, it would be difficult for the Environmental Protection Agency
to carry out its mission in the fields of surveillance and regulation. The
Environmental Research Laboratory, Gulf Breeze conducts field research
programs in an effort to learn natural conditions in estuarine ecosystems
on the eastern and Gulf coasts of the United States.
This report describes ecological research that was done in a two-year
period in a relatively unpolluted salt-marsh ecosystem on the eastern
seaboard. It also describes uses of an artificial salt-marsh ecosystem
for study of aspects that cannot be studied in the field. The data are
being used for construction of mathematical and conceptual models that
describe physical, chemical, and biological aspects of the marsh. The
models will be published in an EPA Ecological Series Report.
Gerald E. Walsh
Research Ecologist
Environmental Research Laboratory
Gulf Breeze, Florida
iii
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ABSTRACT
Although estuaries and marshlands are valuable as a natural resource,
integrative scientific studies leading to the development of predictive
models are practically nonexistent. Such studies are necessary for effective
pollution control and long-term management of the estuarine ecosystem.
A research program was initiated to understand the dynamics of a
relatively undisturbed estuary-marshland ecosystem, the North Inlet Estuary,
near Georgetown, South Carolina. Because of the relative complexity of this
type of study, a five year study was proposed; this report summarizes results
of the first two years.
This study consisted of two separate but interrelated substudies: a
macroecosystem substudy and a microecosystem substudy. The objectives of
the macroecosystem study were: 1) to establish baseline data on an
undisturbed estuary to provide a scientific basis for comparative studies on
effects of various stresses of pollutants on other estuarine environments;
and 2) to develop models of an estuarine ecosystem which would predict
probable effects of environmental perturbation. The principal objective of
the microecosystem study was to develop and test replicate experimental salt
marsh units at the microecosystem level as diagnostic tools for the assess-
ment of both long- and short-term pollution effects on the Spartina
alterniflora salt marsh community.
A conceptual model of energy flow for the entire marsh-estuarine
ecosystem was developed which consisted of three sub-models. A simulation of
the water column submodel and a simulation by a linear systems model of an
intertidal oyster community was completed. Much baseline data needed for
model development is available on primary producers, zooplankton, meiofauna,
benthic macrofauna, decomposers, and relevant physical parameters. An
interdisciplinary team of marine scientists has developed the capability to
work together to solve a common complex problem. This five year study was
designed to be developed in specific phases. Modeling, field work, and an
experimental approach were developed simultaneously. However, the
additional phases need to be studied in order to complete the initial
objectives.
This report was submitted in fulfillment of Grant No. R 802928
by the University of South Carolina, F. John Vernberg, principal investigator,
under the sponsorship of the U.S. Environmental Protection Agency. This
report covers a period from January 14, 1974 to January 13, 1976 and work
was completed January 13, 1976.
iv
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CONTENTS
Foreword
Abstract iv
Figures vi
Tables vii
1. Introduction 1
2. Conclusions 3
3. Recommendations 4
4. Review of Pertinent Estuarine Ecosystem Studies 5
5. Study Site Description 8
6. Overall View 12
7. Substudies 14
Simulation Model for North Inlet Estuary (R. D. Bonnell).. 14
A Linear Systems Model of an Intertidal Oyster Community
(R. F. Dame and S. A. Stevens) 26
Studies on the Phytoplankton and Microbenthic Algae in
in North Inlet Estuary, S. C. (R. G. Zingmark) 35
Composition and Seasonality of the North Inlet
Zooplankton: Establishment of the Baseline
(B. C. Coull) 40
Vertical Migration of Larval Uca in North Inlet Estuary
(P. DeCoursey) 45
Light, Time of Day and Metabolism in Larvae of Uca
pugilator (W. B. Vernberg and D. D. Jorgensen) 48
Energetics of Zooplankton (W. B. Vernberg) 50
The Macrobenthic Fauna of North Inlet: Abundance,
Diversity and Respiration (R. Dame) 53
Decomposers: Microbiological Studies (L. H. Stevenson
and C. W. Erkenbrecher) 56
Radiation Balance in the North Inlet Marsh
(S. J. Crabtree and B. Kjerfve) 59
Hydrography of North Inlet, South Carolina (B. Kjerfve,
M. S. Ivester, L. L. Vansant, M. L. Sloan, R. L. Grout,
and Jeffrey E. Greer) 62
Data Retrieval System (B. Kjerfve, L. L. Vansant,
R. L. Crout, and M. L. Sloan) 65
Salt Marsh Unit Microecosysterns for Assessment of
Pollutant Addition Perturbations (W. Kitchens) 67
8. Summary of Report 72
References 75
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FIGURES
Number Page
1 The Hobcaw Barony. Property of the Belle W. Baruch Foundation 9
2 North Inlet Estuary and marshlands. Stations 1-5: Dr. Dame's
study sites; Station 6: Dr. Stevenson's Station 1; Station 7:
Dr. Stevenson's Station 2; Stations 8-11: Dr. Stevenson's
other study sites; Station 12: radiation balance site 10
3 North Inlet estuarine ecosystem 15
4 Relation matrix - North Inlet Estuary 20
5 Water column submodel 21
6 Signal flow graph for water column submodel 23
7 The system matrix jk for the water column submodel 25
8 A compartment model of energy flow in an intertidal oyster
community 29
9 Sampling site for 1974 vertical migration study (tide phases) 47
vi
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TABLES
Number FaSe
1 Definition of State Variables. All units are
expressed as kcal/m^ 17
2 Standing Crop Values for Water Column Submodel.
Unit is kcal/m2 22
3 System Equations for Water Column Submodel 22
4 System Parameters for Water Column Submodel 24
5 Intertidal Oyster Bed Community Biomass and Numbers 28
6 Values for the Functions in the Intertidal Oyster
Community Compartment Model 30
7 1% Sensitivity of the Linear Systems Model of the
Oyster Community 34
8 Annual Rates of Benthic Algal Productivity as Reported
in the Literature 37
9 Respiratory Rates of Zooplankton from the North
Inlet Estuary 51
10 Respiratory Rates of Meiofaunal Species from the North
Inlet Estuary 52
vii
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SECTION 1
INTRODUCTION
The value of marshlands and estuaries to man as natural resources is
indisputable and has been stressed by numerous national reports. Estuaries
and their surrounding marshlands have served as centers of population and are
heavily utilized for industrial development, shipping, fishing, and recrea-
tion. Furthermore, such usage is destined to increase in the future, with
the predictable result of increased competition for these limited natural
resources. Estuaries have been exploited to varying degrees; in some, almost
the total biota have been ruined. Despite recognition that estuaries are not
an unlimited resource, integrated scientific studies leading to the develop-
ment of predictive models are practically non-existent. Such integrated
studies, rather than isolated studies of individual species, are necessary
for effective pollution control and long-term management of the estuarine
ecosystem. In particular, production, energetics, and the mechanisms of
various processes as influenced by environmental perturbation are poorly
understood, although the knowledge of these factors has obvious economic and
fundamental scientific values.
Great diversity in kinds and shapes of estuaries has been reported in
the scientific literature (Lauff, 1967; Odum et al., 1974). However,
estuaries typically have certain characteristics in common, such as tidal
fluctuation, salinity changes, and high concentrations of nutrients. Differ-
ences between estuaries may be quantitative or qualitative, such as the
amount of wetlands or the amount and types of human habitation bordering
their shores. Therefore, it is important to develop and compare ecosystem-
oriented models of the major estuarine types if we are to assess the univer-
sal nature and differences of estuarine dynamics.
This study was undertaken to understand the ecosystem dynamics of a
relatively undisturbed estuary, the North Inlet Estuary near Georgetown,
South Carolina. This report describes the initial two-year study of what was
designed to be a five-year project. After the project began, the study was
expanded to include a specific section on a microecosystem.
This study consisted of two separate but interrelated substudies, that
of the macroecosystem, and that of the microecosystem. For purposes of
clarity, objectives are presented separately.
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MACROECOSYSTEM STUDY
This was designed to study the dynamics of a relatively undisturbed
marsh-estuarine ecosystem. There were two interrelated objectives of this
study: 1) to establish baseline data on an undisturbed estuary to provide a
scientific basis for comparative studies on effects of various stresses of
pollutants on other estuarine environments; and 2) to develop models of an
estuarine ecosystem which would predict probable effects of environmental
perturbation.
MICROECOSYSTEM STUDY
The prime objective was to develop and test replicate experimental salt
marsh units at the microecosystem level as diagnostic tools for the assess-
ment of both long- and short-term pollution effects on the Spartina alterni-
flora salt marsh community.
Results of this integrated study add significantly to our understanding
of the marsh-estuarine ecosystem. Not only does this study provide better
insight into the functioning of estuarine processes in an undisturbed estuary,
but it also provides a basis for the development and validation of the pre-
dictive models. These models are needed in making decisions on environmental
impact of man's activities in the estuarine environment and in developing
long-term management programs of this vital natural area.
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SECTION 2
CONCLUSIONS
Results in the first two years of a proposed five-year analysis of a
relatively undisturbed marsh-estuarine ecosystem and a salt marsh microeco-
system program have resulted in development of a conceptual model of energy
flow, a simulation of the water column submodel, and simulation by a linear
systems model of an intertidal oyster community. Much baseline data needed
for model development is available on primary producers, zooplankton, meio-
fauna, benthic macrofauna, decomposers, and relevant physical parameters.
An interdisciplinary team of marine scientists has developed the capability
to work together to solve a common complex problem. This five-year study
was designed to be developed in specific phases. Modeling, field work, and
an experimental approach were developed simultaneously. However, the addi-
tional phases need to be studied in order to complete the initial objectives.
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SECTION 3
RECOMMENDATIONS
Since this two-year project was designed as the initial phase of a five-
year project, definitive recommendations are premature. However, we suggest:
1) The study of relatively undisturbed ecosystems is necessary to under-
stand the dynamics of how systems work and to serve as a vital baseline with
which to compare perturbed areas.
2) Since natural environmental units are complex and it takes time and
effort to analyze them, it is recommended that granting agencies recognize
the need for supporting long-term projects. To develop an interdisciplinary
team, such as involved with the North Inlet Estuarlne Study, is difficult
and once assembled it should be allowed to accomplish its initial goals.
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SECTION 4
REVIEW OF PERTINENT ESTUARINE ECOSYSTEM STUDIES
One of the first attempts to construct an energy flow diagram for an
estuarine-marsh ecosystem was that of Teal (1962) for the marshes of Sapelo
Island, Georgia. Teal proposed an energy flow diagram based on the data of
various investigators. During a year the input of solar energy was 600,000
kcal/m^. This energy was estimated to be partitioned as follows: most of
the energy (93.9%) was lost in photosynthetic activity, gross production was
6.1%, and net production was about 1.4% of the incident light energy. Of
the energy available to secondary consumers, 55% was expended in respiration,
while 45% of net production was exported. Since this study, more detailed
energy budgets have been published for various individual species found in
the estuarine-marsh ecosystem (Dame, 1972; Hughes, 1970) and other estuarine
systems have been studied as described below.
Recently, a detailed study of a New England salt marsh was made by Nixon
and Oviatt (1973). The two studies differed in that Teal emphasized energy
flow in the marsh, while Nixon and Oviatt were concerned with energy flow in
marsh creeks and embayments. Since consumption for the embayment exceeded
production based on a yearly energy budget, this aquatic system must depend
on input of energy in the form of organic detritus from marsh grasses. Pro-
duction values of New England marsh grass were similar to those from New
York, but markedly lower than those of southern marshes. This finding may
reflect the substantial difference in climatic conditions between these geo-
graphical regions. Marked seasonal differences in energy flow patterns of
New England ecosystems were observed. The flow of energy is much more com-
plex and values are higher during summer than in winter. Thus, pollutants
introduced at different times of the year might not only have a greater dif-
ferential seasonal effect on northern marshes, but northern marshes might
respond differently than those in southern regions.
To the south, the Newport River estuarine ecosystem is being studied by
the Atlantic Estuarine Fisheries Center, National Marine Fisheries Service,
Beaufort, North Carolina. Much of this work is reported in the numerous
papers of Williams and co-workers (Ferguson and Murdoch, 1975; Thayer, 1971;
Thayer et al., 1974, 1975; Williams, 1966, 1973; Williams and Murdoch, 1966)
beginning about 1965 and in the annual reports of the United States National
Marine Fisheries Service Laboratory, Beaufort, North Carolina. Recently
this group reported on the interaction between major plant producers and epi-
faunal and infaunal invertebrates and fish populations comprising the eel-
grass community, a part of the estuarine system not discussed by Teal or
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Nixon and Oviatt. Unlike the system studied by Nixon and Oviatt, there
appears to be excess food energy for the consumers. Failure of the herbi-
vores and detritivores to expand to the limits of their food reserves sug-
gests that the organisms may be predator-limited: fishes, and shore birds
being the primary predators (Thayer, Adams, and LaCroix, 1975). These authors
suggest that the excess plant production in the system is likely exported to
the adjoining estuary, thus providing food energy, in the form of detritus,
to that system. This ecosystem research program also includes detrital
cycles, microbial activity studies, export of materials from grass beds, and
trace metal studies.
An active program involving Georgia salt marshes has continued since the
earlier work of Teal (1962), and recently Wiegert et al. (1975), presented a
preliminary ecosystem model of a coastal Georgia Spartina marsh. Dr. L. Pomeroy
et al. are continuing studies on the intermediary metabolism of a salt marsh.
The dynamics of energy flow expressed as carbon in an estuarine-marsh
ecosystem, Barataria Bay, Louisiana, was described by Day et al. (1973).
This study differs from the ones described above in that it deals in greater
detail with all parts of the estuarine-marsh complex. Like other marshes,
energy was available to be exported to the water, but unlike the findings of
Nixon and Oviatt, a net community production in the water column was reported.
Models of larger systems that include estuarines and wetlands as sub-
units have been developed. One example is that of Young et al. (1974) which
uses models of energy relationships on a regional basis to develop a manage-
ment plan for development and channelization of the Atchafalaya Basin of
Louisiana.
In January 1974 an ecosystem study of a relatively undisturbed estuary,
the North Inlet Estuary, Georgetown, South Carolina, was formally initiated
by the Belle W. Baruch Institute for Marine Biology and Coastal Research,
University of South Carolina with support from the Environmental Protection
Agency. The North Inlet Estuary is unique in the United States in that it
is sufficiently large to have estuarine characteristics and at the same time
it is sufficiently small to be studied comprehensively. Furthermore, and of
great importance, most of the water and tidelands associated with this estuary
and the adjacent undeveloped highlands are within the property boundaries of
a private foundation, the Belle W. Baruch Foundation. The Foundation has as
one of its stated goals the long-term preservation of this natural area.
Hence this area is ideally situated for long-term study of marsh-estuarine
processes.
Our study differs from those on other southeastern estuaries in that the
North Inlet Estuary is relatively simple and discrete, representing a dif-
ferent type of estuarine system. For example, in North Carolina the Newport
River Estuary represents a large, complex system bordered by industries and
human habitation, while the marshes of Sapelo Island, Georgia are a small
part of a large bay system encompassing numerous islands. Our study repre-
sents a comprehensive, interdisciplinary study involving a number of investi-
gators working simultaneously to understand complex estuarine processes. In
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this manner data collection for various discrete but interacting processes
can be collected at one time, thus providing a comparable data base for inter-
pretation of how these processes function. Some other models have suffered
because the best available data were collected either in distantly located
estuaries or in the same estuary but in different years and for different
purposes.
Because of the complex nature of this study, which directly involved ten
faculty members and two post-doctoral investigators and indirectly a number
of other faculty who were studying related projects funded through other
sources, this report is presented in the following format:
1. Study site description
2. Overview, including a general discussion of the plan of
study involving the various substudies
3. Substudies, including a detailed analysis of the various
interrelated parts of the energy flow model
4. Summary of entire study
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SECTION 5
STUDY SITE DESCRIPTION
The Belle W. Baruch Foundation property referred to as the Hobcaw Barony
is located near Georgetown, South Carolina (Fig. 1). It is unique along
the eastern coast of the United States for marsh-estuarine studies for the
following reasons:
1. The North Inlet Estuary and marshlands are chiefly confined within the
property lines of the Belle W. Baruch Foundation (Fig. 2). The Founda-
tion is dedicated to conservational research and has established its
lands and marshes for long-term studies in marine science.
2. The estuary and marshlands are relatively undisturbed. Their waters are
classified by the South Carolina Department of Health and Environmental
Control as "highest quality." The estuary is sufficiently small to be
studied in detail, but large enough to have distinctive estuarine charac-
teristics. The inlet is approximately 0.88 km wide and the distance
from the inlet to the pier at Clambank is approximately 3.06 km by boat.
The total estuarine and tideland areas cover an area of approximately
28.06 km2.
3. The marshlands and estuary are sufficiently large to permit experimental
manipulation and control of experimental areas, and extensive land hold-
ings provide space for construction of experimental ponds. Extensive
oyster beds are found in this region as well as large populations of
other commercially important species, such as blue crab, shrimp, and
mullet.
4. Study of the biota and physical parameters of the marshes and estuary
has been in progress since January 1970. Although far from being a
complete study, data from these investigations furnish a realistic basis
for future studies.
5. The present staff of 32 associates of the Belle W. Baruch Institute for
Marine Biology and Coastal Research, University of South Carolina, has
demonstrated its ability to work on complex problems in a coordinated
manner.
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/rj|§^
j Hobcaw House
Colonial Cemetery
D
—I \-^4 . -i /••-*•/.. X_^—™r *« v .< ^ ^^
Remains of Colonial Fort
Atlantic Ocean
Figure 1. The Hobcaw Barony. Property of the Belle W. Baruch Foundation.
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GEORGETOWN
CHARLESTON
Figure 2. North Inlet Estuary and marshlands. Stations 1-5: Dr.Dame's
study sites; Station 6: Dr. Stevenson's Station 1; Station 7: Dr. Stevenson's
Station 2; Stations 8-11: Dr. Stevenson's other study sites; Station 12:
Radiation balance site.
10
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GEOLOGIC SETTING
North Inlet waters drain a very large marsh located between Debidue
Beach and North Island and the mainland. The mainland consists of Pleisto-
cene Storm Beach Terrain with ridges oriented in a northeasterly-southwesterly
direction. These ridges intersect the Atlantic Ocean at the north end of
Debidue Beach. These surficial mainland features are underlain by a complex
sequence of older coastal plain sediments, a sequence which is poorly under-
stood in the immediate area at the present time.
Debidue Beach and North Island represent part of a Holocene Barrier
Beach System. This system has migrated southward in recent times, with
principal evidence here being the major spit along the northern entrance to
Winyah Bay, and smaller spit migration land forms along the northern border
of North Inlet.
North Inlet drains numerous tidal creeks and two of these extend back
through the marsh to lie in close proximity to the Pleistocene mainland.
The creeks are very shallow, never exceeding 9.12 m below mean sea level and
commonly show floors which are occupied by sand bars. The marsh areas are
underlaid by silts and clays which extend to an unknown depth.
HABITAT TYPES
There is a number of distinctive habitat types within the North Inlet
Estuary. There are approximately 2,630 ha (6,500 acres) of marshland
dominated chiefly by Spartina alterniflora. Creek bottoms show, in addition
to the sands mentioned above, sandy mud and firm shell substrates. The
substrate of the intertidal zone habitats is also variable. Oyster beds and
reefs are numerous and extensive; other intertidal zone habitats include
open sandy beaches, projected sandy beaches, mud flats showing varying admix-
tures of sand-sized particles, dunes and forest-marsh edge habitats.
Marked seasonal changes in temperature have been recorded; air tempera-
tures range from about -10°C to above 33°C; water temperatures range from
9°C to approximately 32°C. The salinity may range from about 18 °/oo to above
35 °/oo. Typically, the salinity is 30 °/oo or higher. Tidal amplitude is
about 1.82 m.
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SECTION 6
OVERALL VIEW
Since estuarine processes are complex, it is recognized that the develop-
ment of comprehensive estuarine models will take time. The early phase of
this program included development of an energy flow conceptual model of the
North Inlet Estuary. Baseline data were collected on some of the major com-
poments, but not all compartments of the model were studied initially. Where
possible, data from published studies of other estuarine and marshes were
used in model development.
Three major aspects of the estuarine-marsh ecosystem were studied:
1) structural component; 2) functional processes; and 3) synthetic aspects
and modelling. Listed below are the major features of each of these sub-
divisions and the name of the investigator studying this feature.
A. Structural Components
1. Biotic factors (Staff)
a. Communities
1) Spartina marsh
2) Oyster, both subtidal and intertidal
3) Sand beaches, including open and protected sand bars and dunes
4) Benthic, including the channel bottoms
5) Plankton
b. Descriptive aspects of each community
1) Qualitative and quantitative analysis of species composition
2) Temporal relationship of community structure
3) Inter-community comparison of species diversity
c. Specific groups of organisms
1) Bacteria - Stevenson
2) Fungi - Cowley
3) Algae - Zingmark
4) Vascular plants - Staff
5) Meiofauna - Coull
6) Zooplankton - W. Vernberg, Coull, and DeCoursey
7) Macro-invertebrates - J. Vernberg and Dame
8) Fish - Dean
9) Birds - DeCoursey
2. Abiotic factors
a. Sediment (substrate study only) (Colquhoun and Nelson)
1) Source, type, and chemistry of sediments
2) Structural features, physical and biotic features
12
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3) Geometry of substrate masses, including marsh, estuarine
landforms, barrier islands, bars, and the shelf
4) Accumulation rate
b. Water chemistry (Gardner)
1) Chemistry of interstitial water and the water column
2) Interaction between interstitial and column water
c. Hydrology (Kjerfve)
1) Water mass movements
2) Tidal fluctuations
3) Mixing of water masses
4) Temperature
5) Miscellaneous factors, microenvironmental measurements
d. Measurements of environmental factors (Staff)
B. Functional Processes and Environmental Adaptation
1. Ecological energetics
a. Primary producers
1) Algae (Zingmark)
2) Vascular plants (Staff)
b. Consumers
1) Meiofauna and zooplankton (W. Vernberg, Coull, and DeCoursey)
2) Energetics of prominent marsh and estuarine macrofauna
(J. Vernberg, Dame, Dean, and DeCoursey)
c. Decomposers
1) Environmental effects and the role of heterotrophic
bacteria (Stevenson)
2) Fungi as decomposers (Cowley)
2. Nutrient cycling (Kitchens)
3. Role of detritus (Stevenson and Coull)
4. Export-import dynamics (Kitchens, Kjerfve, and Staff)
C. Synthetic Aspects and Modelling
Model development includes instantaneous and temporal aspects of an
estuarine ecosystem (Bonnell and Dame)
Each investigator has written a detailed report which describes his(her)
initial phase of what was designed to be a five-year study. The first
report by Professor Bonnell describes the energy flow model which was devel-
oped by all of the investigators and serves as the unifying framework of the
entire study. Within the framework of the overall model, Dr. Dame developed
a submodel on the intertidal oyster community. The remaining substudies
deal with various compartments of the energy flow model. The final substudy
deals with the salt marsh microecosystem.
13
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SECTION 7
SUBSTUDIES
SIMULATION MODEL FOR NORTH INLET ESTUARY
Ronald D. Bonnell
A comprehensive conceptual energy flow model has been formulated in
order to represent the dynamics of North Inlet Estuary. A functional unit
with recognizable boundaries and large enough to contain a full set of estua-
rine ecosystem processes and their interactions was chosen (Fig. 3). The
conceptual model has three distinct subsystems:
1) Water Column. The aqueous environment above the benthic subtidal
and intertidal marsh zones. Its uppermost boundary is the air-
water interface.
2) Intertidal Marsh Zone. The lower boundary of this zone is defined
as that portion of the benthic region extending landward from the
lower limit of the distribution of creek bank oysters (Crassostrea
virginica), siphon tubes of the stout razor clam (Tagelus plebeius)
and immediately above the upper limit of the normal distribution of
the fire sponge (Microciona prolifera) and the sea pansy (Renilla
reniformia). The upper boundary is the upper limit of the vegeta-
tional assemblage associated with the high tide mark. This is
characterized by the presence of the following species of plants:
Spartina alterniflora, S^. patens, _S_. cynosuroides, Juncus roemeria-
nus, Distichlis spicata, Salicornia spp., and/or Iva frutescens.
3) Benthic Subtidal Zone. The area beneath the water column and sea-
ward of the lower limit of the intertidal marsh. Included in the
benthic sub tidal zone is the material between the sediment-water
interface to a depth of 50 cm.
A linear dynamic system with twenty-two states was chosen as the mathema-
tical model for the system, i.e., jc = A jc + B_ _u, where
A = (22 x 22) system matrix
B_ = (22 x m) input matrix
x(t) = (22 x 1) state vector
_u(t) = (m x 1) input vector
ft = time; m = number of inputs in the input vector]
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boundary of
'ecosystem
Figure 3. North Inlet estuarine ecosystem.
The definitions of the states of the system are given in Table 1. These
states represent the variables which the study team determined were most
important and are included in the ecosystem model.
The relation matrix for the conceptual model is given in Fig. 4. The
high degree of connectivity (approximately 40%) between the states provides
an indication of the complexity of the ecosystem. For example, the system
matrix A, alone has approximately 190 coefficients that must be evaluated.
The conceptual model serves as a framework for combining individual stud-
ies within the ecosystem and can be used to define the scope of the overall
program.
15
-------
WATER COLUMN SUBMODEL
The water column submodel consists of states Xjg through
of energy into the states of the submodel from other states in the overall
model are considered imports, while all flows of energy from the states in
the submodel to other states in the overall model are considered exports.
Other inputs and outputs to the water column submodel are phytoplankton pri-
mary production and respiration of the blotic states and tidal washout. A
compartment model illustrating the interaction between the states of the water
column submodel and all inputs, outputs, imports and exports is given in Fig.
5.
Several observations can be made concerning the system depicted in Fig.
5. The states Xig» %9» sa^i ^20 » corresponding to herbivores, omnivores, and
carnivores respectively, are assumed to be decomposed in the benthic subtidal
and not in the water column. Hence, there are no directed branches from these
three states to the decomposers in the water column state, fyl" Further, the
internal self-loops within the compartments for states X^g and X2Q illustrate
only that in our grouping of species of omnivores and carnivores, some spe-
cies of carnivores feed on other carnivores, etc. However, the total energy
associated with the state X£Q is not affected by the internal self -loop.
Finally, the input to state X^g, FQ ^ is the energy associated with primary
production of phytoplankton and not*solar isolation.
Standing Crop Values for Water Column Submodel
The average standing crops over one year for states X^g through X£2 are
given in Table 2. These values were computed from actual field data for the
year June 1974 through May 1975, Monthly data for the standing crop values
of the states are also available and can be used to validate the water column
submodel with time-varying system parameter, i.e. A.(t) and B(t). However, at
present, the time-varying rate parameters have not~~been evaluated.
System Differential Equations for the Water Column Submodel
The system differential equations for the seven states Xjg through %22
are given in Table 3. Each differential equation was derived by using the
conservation of energy principle for each compartment. The linear flows were
assumed to be donor controlled, i.e., if a flow of energy, J?±j , from state
X-£ to state Xj occurs, then F^j = Aij X-^ where AIJ is the rate constant.
Moreover, lAij is the turn-over rate for the flow F^j and state X^.
Import lij and export E^* are assumed to be constants in the submodel.
For each state, import Ijj was evaluated by the study team and the export
E.J4 was determined by invoking the steady-state average condition X-^ = 0, and
solving for EJ_J. The value of respiration RA is included in Ey A signal
flow graph for the water column submodel is given in Figure 6. From the flow
graph it is clear that the D.O.M. state X.22 serve^ as the "sink" for the
energy in the water column submodel. Also of interest is the outer loop
which encloses all states, the feedback of D.O.M. energy X22» -to energy
associated with phytoplankton X^g.
16
-------
TABLE 1. DEFINITION OF STATE VARIABLES.
All units are expressed as kcal/m^.
X^ - Benthic macroflora. The energy associated with those macroscopic
algae, including filamentous forms, that are attached to a substrate,
but excluding those species of blue-green algae that form mats and
that contribute to the stability of the benthic sediments. Primary
forms: green, red and brown algae.
X2 - Benthic microflora. The energy associated with those microscopic
algae, both unicellular and multicellular, that are primarily asso-
ciated with the upper 1-cm of the marsh mud and sand surfaces, includ-
ing blue-green algae that form mats and contribute to the stability of
benthic sediments. Primary forms: diatoms and blue-green algae.
Xo - Detritus-Benthic subtidal. The energy associated with dead organic
material in or on the bottom below mean low tide, including dissolved
organic carbon in the sediment.
X^ - Decomposers-Benthic subtidal. The total microbial biomass (mgC/m2).
Unit measured was ATP. Luciferin/luciferase and biomass carbon were
calculated using a conversion factor of 250 mgC per 1 mg ATP (method
of Holm-Hansen and Booth, 1966). The biomass of the decomposers
(mgC/m^) was converted to energy (kcal/m2) by literature values to
obtain the energy associated with decomposers-benthic subtidal. The
genera of bacteria (decomposers) are: Pseudomonas, Vibrio, Achromo-
bacter, Aeromonas, and Cytophaga.
Xc - Meiofauna-Benthic subtidal. The energy associated with those benthic
animals living below the mean low tide that pass through a 0.5-mm
sieve and are retained on a 0.063-mm sieve.
X^ - Macrofauna-Benthic subtidal. The energy associated with those benthic
animals living below the mean low tide that are retained on a 0.5-mm
sieve.
XT - Grasses. The energy associated with all rooted vegetation growing
in the intertidal marsh zone. The dominant species are: Spartina
alterniflora, ^. patens, S^. cynosuroides, Juncus roemerianus,
Distichlis spicata, Salicornia virginica, Salicornia sp., Iva
frutescens, and Barrichia frutescens.
Xg - Detritus-Intertidal. The energy associated with the plant and animal
(biogenic) material decomposing in the intertidal marsh.
Xn - Insects, Snails, etc.-Intertidal. The energy associated with inter-
tidal macrofauna larger than 1-mm mesh which consume plant or detrital
material.
^10 ~ Birds. The energy associated with all avian species, both resident
and transient, that feed in the intertidal marsh or in the water
17
-------
Table 1. continued
column. The dominant forms feeding In the water column are: Black
Skimmer, terns, Bay and Sea Ducks, pelican, and ospreys. In the Inter-
tidal marsh: Marsh Wren, rails, Seaside and Sharp-tailed Sparrows.
- Meiofauna-Intertidal. The energy associated with those benthic ani-
mals living between mean low water and mean high water that pass
through a 0.5-mm sieve and are retained on a 0.063-mm sieve.
- Mud crabs-Intertldal. The energy associated with crabs, chiefly
Panopeus, Eurypanopeus, and occasionally Uca, which feed upon other
animals.
- Decomposers-Inter tidal. The total microbial biomass in intertidal
sediment (reported as mgC/m^) measured using ATP techniques. Basic
measurement is ATP (luciferin/luciferase) and biomass carbon is cal-
culated using the conversion factor of 250 mgC per 1 mg ATP (method
of Holm-Hansen and Booth, 1966). The biomass of the decomposers-
intertidal (mgC/m~2) is converted to energy (kcal/nr) by literature
values to obtain the energy associated with decomposers. The
dominant genera of bacteria (decomposers) are: Pseudomonas, Vibrio,
Achromobacter, Aeromonas, and Cytophaga.
- Oysters, Mussels-Intertidal. The energy associated with the inter-
tidal macrofauna which filter microscopic plant, animal, and detrital
material out of the water (filter feeders).
- Mammals. The energy associated with all mammal species (exclusive of
man) that feed in the intertidal marsh. The dominant forms are:
raccoon, otter, feral pigs, Norway Rat, Rice Rat, Cotton Rat, Harvest
Mouse, House Mouse, and Deermouse.
- Phytoplankton. The energy associated with those microscopic algae,
both unicellular and multicellular, that are primarily free-floating
in the water column. Primary forms are: diatoms, dinoflagellates,
and chrysoflagellates.
- Detritus-Water Column. Biogenic particulate organic matter suspended
in the water column. The material retained on micro-fine glass fiber
filters (Whatman GF/C) and converted to C(>2 by combustion at 500°C.
- Herbivores-Water Column. The energy associated with those free-
floating or swimming animals that eat living plant material. Primar-
ily the zooplankton but may include some fishes.
- Omnivores-Water Column. The energy associated with consumers that
utilize both plant and animal matter as energy sources. The dominant
forms are: Mullet, crabs, Fundulus, and shrimp.
18
-------
Table 1. continued
- Carnivores-Water Column. The energy associated with consumers that
utilize herbivores, omnivores, and other carnivores in the water
column as energy sources. The dominant forms are: sharks, dolphin,
rays, trout, flounder, Spot, Croaker, Drum and sea turtles.
- Decomposers-Water Column. The total microbial biomass in the water
column during ebb and flood tide as mgC/m^ measured using ATP tech-
niques. Basic measurement is ATP (luciferin/luciferase technique)
and biomass carbon is calculated using a conversion factor of 250
mgC per 1 mg ATP (method of Holm-Hansen and Booth, 1966). The biomass
of decomposers (mgC/m^) is converted to energy (kcal/m^) by litera-
ture values to obtain the energy associated with decomposers-water
column. The dominant genera of bacteria are: Pseudomonas, Vibrio,
Achromobacter, Aeromonas, and Cytophaga.
X22 - Dissolved Organic Matter (D.O.M)-Water Column. The energy associated
with those dissolved organic chemicals in the water column synthe-
sized by biological processes. These are mainly compounds arising
from excretory and secretory processes.
System Parameters for Water Column Submodel
The system parameters, imports, and exports for the water column sub-
model are given in Table 4. Some of the values are literature values,
others are best estimates from field experinece. Several rate constants in
the water column are unknown at this time, such as the rate constants asso-
ciated with flow of energy from herbivores, omnivores, and carnivores to
D.O.M. in the water column (^18,22» ^19,22» ^20,22)« A "best guess" was
used for these three rate constants. The feeding rates A^g ^9, \2o 19»
^18 20 » ^19,20 f°r t*16 omnivores X^g and carnivores X2Q were very hard to
evaluate and estimates were placed on gut analysis studies.
System Matrix for Water Column Submodel
The system matrix A for the water column submodel is given in Figure
7. Normally, the diagonaTly dominant characteristic of the system matrix A^
insures system stability. However, in the water column submodel, the respira-
tion energy loss of the biotic states was included in the export flows. Hence
the system is not stable unless sufficient energy loss to account for respira-
tion is considered in the export from each state. For the system matrix A. =
the sum of all columns is equal to zero, i.e., ~
7
Z2V • • = n W . — 1 7
"1 *i \J v-»~J.f • « • • y /.
For stability, the sum for each column should be negative.
19
-------
ENERGY
kcal/m~2
N3
O
Ber.thic Hacroflora
Benthlc Microflora
Detritus-lienthic Subtidal
Decomposers
Meiof auria
Macro fauna
Grasses
Detritus-Intertidal
Insects, Snails, etc
Birds
Mciofnuna
Mud Crabs
DC com;.rsers-In tor tidal
Oy.-itrjts, Mussels, etc.
M.ir.innls
Phytoplankton
Cctritus-Water Column
Herbivores
Chmivores
Carnivores
Decocposers-Watcr Column
D.O.M.-Water Column
TO
\FROM
xl
X2
Xl
U
U
1
X2
0
u
1
X3
0
0
0
X,
0
0
0
X5
0
u
1
X6
0
u
1
X7
0
0
1
xfl
(I
(1
.i.
X9
0
0
1
X10
0
0
0
Xll X12 X13 X1U X15 X16 X17 X18 X19 X20 X21 X22
000000000000
oooooooooooo
110101111100
Xj, 1
X5 0
X6 1
X7 0
Xfl 1
X 0
xn o
X1JL 0
Xn 0
Xiu 0
X15_0_
X,a 0
Xl, 1
X20 0
X21 0
1
1
1
0
1
1
0
1
0
0
1
0
0
0
1
0
0>
1
1
1
u
0
1
0
1
0
0
0
0
0
0
1
0
1
0
1
1
0
0
0
0
0
0
0
1
0
0
0
I
0
1
1
1
1
0
u
1
0
1
0
0
0
0
0
0
1
0
0
1
0
1
0
1
1
1
0
1
0
0
1
0
0
1.
1
0
i
0
0
u
1
1
0
0
0
1
0
1
0
0
0
0
0
].
1.
].
0
1
1
(1
1
0
.1
1
0
0
0
1
0
.
0
0
1
0
1
1
1
0
1
1
0
1
0
1
0
1
1
0
.
0
0
0
0
1
0
1
0
0
0
0
1
0
0
0
0
0
.
1
1
1
0
1
1-
0
1
0
1
1
0
0
1
0
1
1
0
.
u
0
0
u
1
0
1
0
1
0
0
1
0
0
1
1
0
u
0
0
u
0
u
0
1
0
0
1
0
0
1
0
0
0
1
1
0
0
u
1
0
1
0
1
1
0
1
0
0
1
1
1
0
0
0
0
1
0
1
0
0
0
0
0
0
0
0
0
0
1
0
0
0
0
0
0
0
0
1
1
0
0
1
1
0
r
1
0
0
0
1
0
0
0
0
1
1
0
0
1
1
0
1
0
0
1
0
1
0
1
0
0
0
0
1
0
0
1
1
u
0
0
1
0
1
0
1
0
0
0
0
1
0
n
0
1
1
0
n
0
1
0
1
0
1
0
0
0
0
1.
0
n
0
1
1
u
n
0
0
0
0
0
0
0
0
0
1
0
u
o
1
u
0
0
o
1
1
1
0
0
1
0
0
1
1
1
0
1
0
0
u
0
1
0
Figure 4. Relation matrix - North Inlet Estuary.
-------
7/4
Figure 5. Water column submodel.
21
-------
TABLE 2. STANDING CROP VALUES FOR WATER COLUMN
SUBMODEL. Unit is kcal/m2.
fs>
ts»
Phytoplankton
Detritus
Herbivores
Omnivores
Carnivores
Decomposers
D.O.M.
X16-
x17-
X18-
X19-
X20"
x21-
X22 "
9.48
16.83
4.20
4.81
1.14
13.14
168.3
TABLE 3. SYSTEM EQUATIONS FOR WATER COLUMN SUBMODEL.
Phytoplankton
Detritus
Herbivores
Omnivores
Carnivores
Decomposers
D.O.M.
X16 ' X22,16 X22 + X0,16 " E16,0 ' X16,17 X16 ' X16,18 X16 " X16,21 X16 ' X16,22 X16
*17 • to, 17 + X16,17 X16 - Bl7,0 - X17,18 X17 ~ X17,21 X17 - X17,22 X17
9
X18 • X16,18 X16 + X17,18 X17 + X21,18 X21 ' E13,0 ' X18,19 X18 ' X18,20 X18 ~ X18»22 X18
g
10.19 * X18.19 X18 + X20,19 X20 " E19,0 " X19,20 X19 ~ X19,22 X19
J0,20 + X18,20 X18 + X19,20 X19 " E20,0 - X20,19 X20 ~ X20,22 X20
10,ZI + X16,21 X16 + X17,21 X17 + X22,21 X22 ~ E21,0 - X21,18 X21
X19 "
X22 "
X16,22 X16 + X17,22 X17 + X18,22 X18 + X19,22 X19 + X20,22 X20 ~ E22,0 -X22,16 X22 ~ X22,21 X22
-------
to
(ji
Figure 6. Signal flow graph for water column submodel.
-------
TABLE 4. SYSTEM PARAMETERS FOR WATER COLUMN SUBMODEL.
Flow Rates (day"1) Imports,I.jj and Exports,!
(kcalm~2 day-1)
*lfi 17 = 2.74 x 10~5 In 1A = 9.01
-LO >X/ UjXO
X16,18 = 2-19 x 10~4 ^.l? = 4'15 x 10~2
X16,21 - !'37 * 10-4 I0)19 = 1.32 x 10-3
X16,22 = 2-19 x 10~4 Io,20 = 6-26 x 10~4
X17,18 = 2'74 x 10"4 rO,21 - 1-84 x 10-2
X17,21 * 5'48 x 10~4 I0,22 = 4'15 x 10~1
X17,22 = 2'74 x 10~5 E16,0 = 9-°°
X18,19 = 6'28 x 10"4 E17,0 - 2'75 x 10"2
X18,20 = 2.74 x 10" Elgj0 - 3.52 x 10~3
X18,22 = 2.74 x 10~5 E19 0 = 2.36 x 10~3
X19,20 " 2-60 x 10"4 E20,0 = 2.56 x 10~3
X19,22 " 1-37 x 10~4 E21>0 - 1.44 x 10'1
X20 19 = 2'74 x 10~4 E22 0 = 3'01 x I0"1
X20,22 - 1-37 x 1C'4
X21,18 « 5.48 x 10~5
\
21,22
= 1.37 x 10
-4
A,, ., = 1.37 x 10 5
22,16
X22 21 = 6*85 x 10
*1=X16,17+X16,18+X16,21+X16,22
*2=X17 ,18"'"X17,21+X17,22
, 20^18,22
*4=X19,20+X19,22
*5=X20,19+X20,22
*6"X21,18
*7=X22,16+X22,21
24
-------
-+!
X16,17
X16,18
0
0
X16,21
X16,22
0
~4>2
X17,18
0
0
X17,21
X17,22
0
0
~3
X18,19
A18,20
0
X18,22
0
0
0
-*4
A19,20
0
X19,22
0
0
0
X20,19
-*5
0
X20,22
0
0
X21,18
0
0
-*6
0
X22,16
0
0
0
0
X22,21
-*7
Figure 7. The system matrix A for the water column submodel.
An obvious improvement in the model would be to model respiration and
tidal washout separate from export. As noted by Mulholland and Keener (1974),
maintenance or stability of life can be viewed as a continual process of
pumping out disorder in the form of heat loss through respiration to provide
internal order within each compartment.
COMPUTER SIMULATION OF WATER COLUMN SUBMODEL
A CSMP-III program used to simulate the system of differential equa-
tions for the water column submodel was developed. A procedure for handling
time-varying rate constants within a CSMP-III program was also developed.
The development of software to simulate the water column submodel was not a
problem since the CSMP-III language is designed for this type simulation.
CONCLUSIONS
A useful conceptual model for North Inlet Estuary has been developed.
A "first attempt" dynamic model for the water column submodel has been formu-
lated mathematically and a simulation program constructed. A great deal of
work, however, is needed in the evaluation of system parameters.
25
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A LINEAR SYSTEMS MODEL OF AN INTERTIDAL OYSTER COMMUNITY
Richard F. Dame and Stuart A. Stevens
ABSTRACT
Verbal, compartmental and mathematical models were developed for
energy flow in the intertidal oyster community. Based on specific
assumptions, simulation of the mathematical model indicated the original
model was near stability. This agrees with field studies on the natural
intertidal oyster communities in the North Inlet area which indicated that
these oyster communities have been stable for the past five years. A 1%
sensitivity analysis of the parameters in the mathematical model suggests
the order in which these parameters should be studied. The linear systems
model offers a first step in development of a resource management model for
intertidal oysters.
INTRODUCTION
Intertidal oyster communities are common to high-salinity estuarine
environments of the southeastern United States. These communities are
dominated by dense concentrations of oysters, Crassostrea virginica, whose
shells tend to give the assemblages a high degree of structural stability.
The intertidal oyster communities or beds are located in the mid- to low-
intertidal zone and usually border or project into tidal creeks. The
oyster community has been compared to an industrialized city in that both
are concentrations of consumers which depend on the flow of fuel and
oxygen into the system and waste out of the system (Odum, 1971).
The intertidal oyster community is economically important as a source
of commercial oysters and as a recreational zone for vacationers and
coastal residents. Ecologically, intertidal oyster populations have been
shown by Bahr (1974) and Dame (1976) to have high rates of energy flow.
High energy flow is indicative of the oyster population's functional
importance to estuarine systems. Because intertidal oyster communities
are important, it is imperative that they be investigated as a system of
interrelated populations interacting with their environment rather than as
monoculture systems. Systems analysis is one approach to quantitative
study of such systems.
26
-------
Systems analysis is becoming more important as a research tool to
ecology and resource management (Patten, 1971; 1972). It has been used
extensively in the U. S. International Biological Program and currently is
being used in the earliest stages of development in the North Inlet
Ecosystem Project near Georgetown, South Carolina. The model and analysis
described here is the first from the North Inlet Ecosystem Project.
The model presented here is only an initial step in which systems
analysis is applied to the intertidal oyster communities of North Inlet.
As more data become available and as our understanding of the North Inlet
ecosystem and intertidal oyster communities improves, the model will
become more sophisticated. The objectives of this first model of the
intertidal oyster community are to summarize and indicate the limits of
available data, point to new directions for research, and increase our
understanding of oyster communities.
In this study, the intertidal oyster community is analyzed using
energy and rates of energy flow as the main components of the model.
Energy was chosen because it is universal in both biological and physical
processes.
MODEL DEVELOPMENT
Every theory describing natural events is by necessity a simplification
of the real world. Usually the first step in model building is a picture or
verbal model of the system under consideration. In the case of the inter-
tidal oyster community, a list of the organisms found in the community
along with their biomass and numbers satisfies a verbal model (Table 5).
Such a verbal model does not sort out the complexity of the intertidal
oyster community: it describes what is there.
The next step in model development entails producing a model which
describes to some extent the processes and structure of the intertidal
oyster community. Since energy and energy flow were the processes and
structural attributes we were most interested in understanding, we
developed a compartmental model of energy flow (Fig. 8). The compartments
describe the standing crops of herbivores (Xi), omnivores (X2>, carnivores
(X3), and decomposers (X4> in kcal/m^. The rates of energy flow into, out
of and between the various compartments in the system are described by
arrows.
Values for the standing crops and rate functions are given in Table 6.
Some of these values are from observation on the North Inlet intertidal
oyster communities while others are best estimates. The sources of the
parameters in Table 6 are described below.
Standing crop values in gdw/m2 (grams dry weight/m2) for the
herbivores, omnivores, and carnivores are from studies currently underway
in North Inlet. These values are the means of seasonal observations during
1974. A value of 5 kcal/gdw was used to convert the dry weight biomass of
27
-------
TABLE 5. INTERTIDAL OYSTER BED COMMUNITY BIOMASS AND NUMBERS.
Species
Amphitrite ornata
Anurlda maritlma
Brachedontes exustus
Chione intaparpurea
Crassostrea virginica
Eurypanopeus depressus
Ganmarldlans
Geukensia denlssus
Glycera aoericana
Heteromastus filiformis
Insect pupae
Marphysa saugulnea
Mellta nitlda
Mercenaria mercenaria
Nereis succinea
Odostona Impressa
Panopeus herbs til
Phyllodocea fragllls
Uca pugllator
I/-2
3
14
741
1
974
61
6
5
1
105
3
5
7
4
102
23
56
7
4
g/»2
0.430
0.611
32,330
0.137
164.870
5.700
0.006
6.580
0.016
0.139
0.012
0.120
0.022
4.580
0.717
0.061
5.890
0.074
0.380
Trophic Level
Herbivore
Omnivore
Herbivore
Herbivore
Herbivore
Carnivore
Omnivore
Herbivore
Omnivore
Omnivore
Omnivore
Omnivore
Omnivore
Herbivore
Omnivore
Carnivore
Carnivore
Omnivore
Omnivore
28
-------
VO
_J LU
-------
TABLE 6. VALUES FOR THE FUNCTIONS IN THE INTER-
TIDAL OYSTER COMMUNITY COMPARTMENT MODEL.
Function
Xl
JC2
*3
X4
F01
F02
F04
*10
*20
So
*40
F14
F24
F34
F12
F13
F23
F10
F20
F30
F40
Kcal/m2/yr
2449
8
58
1
17011
15
100
5989
19
56
808
742
27
39
44
123
6
10113
7
36
100
Definition of Function
Herbivore Standing Crop
Omnlvore Standing Crop
Carnivore Standing Crop
Decomposer Standing Crop
Input of Algae and Detritus
to Compartment X.
Input of Algae and Detritus
to Compartment X_
Input of Detritus to
to Compartment X,
Respiration by Xj
Respiration by X«
Respiration by X
3
Respiration by X,
Mortality of X.
Mortality of X-
Mortallty of Xj
Feeding by X_ on X.
Feeding by X. on X.
Feeding by X- on X-
Export from Xj
Export from X_
Export from X.>
Export from X,
30
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invertebrates into standing crop energy (Cummings, 1962) and the methodo-
logy of Dame (1972; 1976) was used to account for the energy retained in
bivalve shells. No measurements were made of decomposer biomass, so an
estimate of 1.0 kcal/m^ was chosen. This estimate is close to a value of
0.14 g/m^ of decomposers observed by Harvey (1950).
Five years of observations of the intertidal oyster beds in North
Inlet indicate there is little change in biomass and diversity (Dame, 1976;
unpublished data) . It was assumed from these observations that the inter-
tidal oyster community model is at steady state, where inputs to X^ (FQ1)
from algae and detritus was calculated by summing the total outputs from X^
and setting this value equal to FQI. Input of detritus to X2 (Fg2^ was
considered as 25% of the total input required to equal the outputs from
decomposers, therefore input of detritus to X^ (Fg^) was considered equal to
export X^ (F^Q) to achieve a balanced model.
Respiration values were taken from the literature or calculated from
equations using dry body weights. Respiration estimates for oysters and
other bivalve herbivores (RIO) were based on observations of Dame (1972 and
unpublished) . Respiration of carnivorous crabs (R3o) was estimated from
observations of Dame and Vernberg (in prep) while values for the other
macrof auna were computed using the general equation of Pamatmat (1968) .
Decomposer respiration (R4Q) was set equal to the sum of the input of
mortality to this compartment .
Mortality was calculated from turnover time for a given compartment.
Turnover times used were: herbivores - 3.3 years (Dame, 1976), omnivores -
0.3 years (D. M. Dauer, personal communication), and carnivores - 1.5 years
(Dame and Vernberg, in prep).
Feeding by omnivores on herbivores (F]^) was calculated by taking 75%
of the total inputs needed to balance the sum of the outputs from X2-
Feeding by carnivores on herbivores (Fjj) was found by summing the outputs
from X3, taking a feeding input of 50% of the total omnivore production
(F23) » and allowing the remainder of the required input to come from
herbivores .
Export from the system was in the form of feces, pseudofeces, and
feeding by transient carnivores. Production was estimated for the various
components from Dame (1976) , Dame and Vernberg (in prep) and the general
equations developed by McNeil and Lawton (1970) . Utilizing an assimilation
efficiency for oysters of 0.62 (Dame, 1972) export of feces and pseudofeces
was computed. The export of feces and pseudofeces from X2 and X-j was
estimated to be 14% of the standing crop biomass of the respective
compartments. X^ export was set equal to X4 input of detritus as
previously stated. Predation of X-^ by carnivores external to the system
was found by subtracting the remainder of production. Export from X2 to
transient carnivores was equated as 50% of the total omnivore production.
A value of 100% of the carnivore production was used as feeding by
31
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external carnivores on Xg, since there are no predators on this
compartment within the system's boundaries.
The next stage in modeling the system was to develop a mathematical
model which described amounts and rates of energy flow by a set of
ordinary differential equations. Transfer coefficients were computed for
the steady state by dividing the rate of energy leaving a compartment by
the amount of energy contained in the compartment. Transfer coefficients
for the intertidal oyster community model are shown below, the Greek
letters p, A, u, and T stand for respiration, export from the system,
export to decomposers when organisms died, and predation within the system.
= 0.30 T12 = 0.02
= 3.33 T13 = 0.05
= °-67 T23 = 0.72
P4Q = 734.70 X4Q 90.91
By assuming that energy transferred from a donor compartment to a
receiving compartment is directly proportional to energy in the donor
compartment, and by expressing all energy losses and gains from a
compartment in terms of transfer coefficients, the system can be defined
by the following set of differential equations, one equation for each
compartment.
PIO =
P20 =
P30 =
2.4
2.36
0.95
A10 =
A20 =
X30 =
4.13
0.86
0.58
Xx (p10 + X1Q + Vl4 + x12 + TIS) (1)
dX2/dt = F02 + TJ^X!) - X2 (p2Q + X2Q + y24 + T23) (2)
dX3/dt = T13(X1) + T23(X2) - X3(p30 + X3Q + y34) (3)
dX4/dt = F04 + m^) + y24(X2) + M34(X3) - X4 (p40 -I- X4Q) (4)
As previously defined, X^ describes the standing crop energy of a
given compartment and FQ!» ^02 » an<^ F04 are forcing functions for energy
entering an intertidal oyster community system.
The differential equations were solved simultaneously utilizing
Continuous Systems Modeling Program III (CSMP III) as described by Patten
(1971) on an IBM 370/165 digital computer. All compartments of the system
reached steady state within 2.2 years. The herbivores (Xj^) reached a
steady state value of 2449.3 kcal/m2 at 0.225 years. The omnivores (X2)
became stable at 0.650 years with a standing crop of 8.0957 kcal/m2. The
carnivores followed with a time of 2.025 years and a biomass of 58.194
kcal/m2. The decomposers required the most time to stabilize, 2.2 years
with a value of 1.0997 kcal/m2 with caloric charges low and with steady
state quickly reached.
32
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The model was analyzed for statistical sensitivity at steady state.
In this case, sensitivity analysis indicates how the individual compartments
behave if a given rate function is changed 1%. The results of the
sensitivity analysis are shown in Table 7.
The 1% sensitivity analysis of the intertidal oyster community model
shows that the standing crops of all compartments are most sensitive to
changes in energy input (F0l) to the KI compartment. This is expected in
a simple linear model. In addition, all four compartments exhibited a high
level of sensitivity to changes in export (^IQ) and respiration (P^Q) from
X1. All compartments were fairly sensitive to change in their respective
respiration energy losses. Compartment X^, the omnivores, was also
sensitive to energy losses to the decomposers (^134) and external to the
system (X3Q). Finally, the decomposers (X£) were very sensitive to changes
in respiration, energy loss (P^Q) and energy input from the herbivores
(^14)• Using this sensitivity analysis of the intertidal oyster community
model as a guide, it is easy to develop a hierarchy of transfer functions
for future study.
DISCUSSION
The linear systems model of the intertidal oyster community reached
stability in a short period of time (2.2 years) and this seems to describe
the naturally occurring intertidal oyster communities in North Inlet which
have been stable for at least the past five years. We cannot at this time
say that this model is a valid representation of the "real world" inter-
tidal oyster communities until we have manipulated and stressed existing
intertidal oyster beds and simulations of the model have predicted the
changes which our manipulations produce in the real communities.
The linear character of the intertidal oyster community systems model
may have to be changed, especially in respect to the feeding rates of the
herbivores, beyond their needs, the herbivores will not in nature continue
to grow (Tenore and Dunstan, 1973; Winter, 1973). One possibility might be
to model the herbivore feeding rates with some feedback repression in a
manner similar to the procedure described by Wiegert (1975). It can be
argued, particularly by biologists, that a predominantly linear model of
an ecosystem or community is unrealistic, but it should be noted that
linearization may describe ecological systems in their large scale better
than non-linear models (Patten, 1975).
The development of a linear systems model of the intertidal oyster
community has noted shortcomings in that there is a paucity of available
data. There are no quantitative data on the export of energy from the
community by transient predators, although we know that these predators
exist. The feeding rates of most of the organisms in the model are only
vaguely known, if at all. We also need to know the magnitude of detritus
and algal food sources available to the filter feeding herbivores since
their feeding rates are very sensitive to change, the decomposer component
33
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standing crop and the sensitivity of decomposer respiration, and the
importance of the meiofauna of the intertidal zone to intertidal oyster
communities.
The present systems model of the intertidal oyster community forms a
basis for the development of a new type of shellfish management model
which relates all segments of the system to the management process. The
model presented here is only a first step and future models will include
additional observations on many of the energy fluxes not observed to date,
seasonal changes in standing crops and the influences of the environment,
particularly temperature and salinity, on the rates of flow into, out of,
and within the system.
TABLE 7. 1% SENSITIVITY OF THE LINEAR SYSTEMS MODEL OF THE OYSTER COMMUNITY.
Kate
and Xj
Coefficients
F01 1.000
P02
F04
plO 0.352
X10 0.595
y!4 0.04%
T12 0.003
Tl3 C.007
p20
X20
p24
T23
p30
X30
P34
p40
A40
2 Change In Standing
*2
0.752
0.254
0.264
0.446
0.032
0.747
0.005
0.325
0.119
0.046
0.099
Crops
*3
0.977
0.011
0.344
0.581
0.043
0.031
0.007
0.015
0.005
0.002
0.041
0.430
0.263
0.301
*4
0.882
0.082
0.110
0.310
0.524
0.779
0.022
0.006
0.011
0.004
0.002*
0.001
0.018
0.031
0.028
0.879
0.110
34
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STUDIES ON THE PHYTOPLANKTON AND MICROBENTHIC
ALGAE IN THE NORTH INLET ESTUARY, S. C.
Richard G. Zingmark
It is well known that, because of their generally high productivity,
estuaries play a major role in supporting numerous fish and invertebrate
species during at least some phase of their life histories (Lauff, 1967;
McHugh, 1967). It has been estimated that two-thirds to three-fourths of
the carbon fixed in East Coast salt marsh estuaries originates from the
autotrophic production of halophylic spermatophytes such as Spartina
alterniflora, and is utilized by consumers in the form of detritus (Teal,
1962). The remaining carbon is contributed largely by algae on the marsh
mud, phytoplankton in the water column, the "aufwuchs" community on halo-
phytes, and, to a lesser extent, by the macrobenthic algae (Pomeroy, 1959;
Ragotskie, 1959; Schelske and Odum, 1961; Marshall et al., 1971). The
plankton communities associated with the surface film perhaps are also
significant sources of energy to salt marsh estuaries (Gallagher, 1975).
Studies on productivity of phytoplankton in the North Inlet estuary,
S. C. were begun in 1972 because it is a significant trophic component of
this ecosystem. It is essential that an ecosystem model consider all of
the sources and sinks of energy within and without the system. Thus, it
was required that we quantify the energetics of the primary producers in
North Inlet. The major objective of this study was to determine the
annual production of energy by the smaller algae in North Inlet. Annual
variations in biomass and productivity of phytoplankton and benthic micro-
flora were measured.
DISCUSSION
The rate of phytoplanktonic production of 273 g C/m/year, measured
during this study (1974-75), was about one third lower than the rate
measured in North Inlet in 1972-73 (Sellner et al., 1976). As the
techniques used in both studies were identical, the differences in the two
studies are assumed to reflect annual variations in productivity. Both
rates are lower than a few other studies (Riley, 1956; Stross and
Stottlemeyer, 1965; Thomas, 1966), but are significantly higher than
those measured in nearby estuaries to the south (Ragotskie, 1959) and to
the north (Williams, 1966; Williams and Murdoch, 1966; Thayer, 1971). The
reasons why the present data are about 4-5 times larger than those of
35
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estuarine waters,of North Carolina are unclear. The annual ranges of
environmental factors such as temperature, salinity, and pH in North Inlet
were not significantly different from those in North Carolina. This would
allow photosynthesis to occur throughout a deeper water column. Thayer
(1971) showed that the productivity rate on a mr basis was about the same
as an areal (m^) basis. Thus, the depth of the photic zone in Beaufort,
N. C. estuaries must be about 1 M. In North Inlet the depth that receives
one percent of the surface isolation was calculated to be 3.3 m. All
other environmental factors being equal, the increased depth available for
photosynthesis in North Inlet could account for the significant differences
in productivity measured elsewhere. Thus, light may be the most controlling,
limiting factor in southeastern coastal estuaries. However, without
comparative data on nutrient concentrations from the two areas, the
differences can never be fully resolved.
PRODUCTION OF THE BENTHIC MICROFLORA
There were significant differences in the benthic productivity rates
in the shallow creek station from those of the other stations. The
differences cannot be explained on the basis of light, as the average
Secchi disc readings at the shallow station were not significantly
different from those at other stations. The biomass, as measured by
functional chlorophyll, was significantly lower than at other stations.
In January, the bloom of Vaucheria sp. that occurred at the shallow station
was reflected by significantly higher productivity than at other stations.
Such blooms of Vaucheria have been reported from elsewhere (Taylor, 1969;
Simons, 1974).
Of some concern was the magnitude of the productivity of the benthic
microflora as compared to other studies. An annual rate of 685 g/m^/yr
(i.e. 1.90 g/nr/day) is over three times greater than any annual rate for
belithic algal productivity found in the literature (Table 8). There are
at least three possible explanations: 1) my values are correct and the
North Inlet is a unique, highly productive estuary; 2) my values are
incorrect because of some gross technical or computational error; or
3) my values are the correct order of magnitude, while the values in the
literature are underestimated. I can reasonably discuss explanations 1)
and 2) but, not 3). As I have checked and rechecked my computations and
have tested and calibrated the sampling, incubation, processing, and
enummerative techniques, I am confident that my values are correct.
Further, reports in the literature indicate that benthic productivity may
be up to about twice that of the phytoplankton (Marshall et al., 1971).
The rate of benthic productivity in this study was 2.5 times that of the
phytoplankton productivity. I am left with the possibility that North
Inlet is a unique estuary.
RELATIONSHIP BETWEEN PRODUCTION AND TEMPERATURE
Salinity, temperature, pH, and transparency in the North Inlet
estuary seemed to be suitable for growth of algae throughout the year.
There was a pronounced seasonal cycle in production of phytoplankton
36
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TABLE 8. ANNUAL RATES OF BENTHIC ALGAL PRODUCTIVITY AS REPORTED IN THE
LITERATURE.
Location
Georgia estuary
Puget Sound
Danish lake
Western Wadden Sea
Method of
Measurement
°2
°2
14C
14C
Rate of Production
g C • M~2 - yr-1
200
143-226
143
100 + 40
Reference
Pomeroy(1959)
Pamatmat(1968)
Hunding(1971)
Cad£e and
Danish Wadden Sea
Danish fjords
New England estuaries
Scottish estuary
Intertidal sandy beach
*C
*C
14,
14,
115-178
116
81
31
4-9
Hegeman(1974)
Grrfntved (1962)
Grrfntved (1960)
Marshall
et al
Leach (1970)
Steele and
Baird (1968)
and benthic microalgae, however, that was highly correlated with the
seasonal variation in water temperature. Such correlations with
temperature are characteristic of shallow, high salinity estuaries of
widely separated areas such as Massachusetts, Long Island, North Carolina,
Italy, and Denmark. Many of these studies attribute the correlation to a
dependency of the rate of nutrient regeneration on temperature (Riley,
1941; 1956; Steeman-Nielsen, 1958; Grtfntved, 1960; Vatova, 1961; Ryther,
1963; Williams, 1966; 1973; Williams and Murdoch, 1966; Thayer, 1971;
Sellner et al., 1976). Whether nutrient regeneration was regulated in
part or wholly by the temperature of North Inlet is not known, as
nutrients were not measured during this study. However, Thayer (1971)
reported evidence that seasonal changes in nitrate and phosphate concen-
trations in Beaufort, N. C. were influenced by temperature, microbial
immobilization and remineralization, and phytoplanktonic utilization.
The fact that changes in temperature cause changes in rates of metabolic
processes may also explain the data.
STANDING CROP OF THE PHYTOPLANKTON AND BENTHIC MICROALGAE
Concentrations of phytoplankton in North Inlet were reported to vary
annually between 1.04 and 3.40 x 106 cells/1 (Sellner et al., 1976) with
no indication of a seasonal cycle. In contrast, there was a pronounced
37
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seasonal cycle in functional chlorophyll a_ concentrations of both phyto-
plankton and benthic microalgae in the present study, which coincided with
annual temperature cycles. The similarity in concentrations of functional
phytoplanktonic pigments at all stations and at all depths indicates that
the standing crop of phytoplankton was unstratified and mixed. The
average concentration of chlorophyll a_ in North Inlet was 9.63 mg Chi a/m2
while that at Beaufort, N. C. was approximately 2.8-4.3 mg Chi a/m2
(Williams and Murdoch, 1966; Thayer, 1971). These are actually comparable
values on a m^ basis, when one realizes that the average depth of the
photic zone in North Inlet is about three times that of the Beaufort, N. C.
estuaries (Thayer, 1971). The annual mean Fo/Fa ratio (fluorescence before
and after addition of acid, a measure of living chlorophyll) of the
phytoplanktonic chlorophyll of 1.78 indicates that the phytoplankton of
North Inlet were reasonably productive (Yentsch, 1965).
Microbial biomass (including bacteria, algae, protozoa and fungi) in
estuarine sediments can be greater than that of the water column by several
orders of magnitude (Zobell, 1946; Ferguson and Murdoch, 1975). The
standing crop of benthic microalgae in the present study was greater than
that of phytoplankton by 193 to 374 times. The standing crop at the
shallow station averaged almost two times less functional chlorophyll than
at the others. Presence of a bloom of Vaucheria sp. in January was
evident in elevated concentrations of chlorophyll at the shallow station
and the biomass of the benthic maiofauna showed a marked increase
following the bloom of Vaucheria (B. C. Coull, personal communication).
The appearance of this bloom was not correlated with a rise in
temperature. It is not possible to compare my benthic chlorophyll data
with most other papers, as other investigators reported chlorophyll as
mg Chl/g/dry wt (Leach, 1970; Cadee and Hegeman, 1974). However, the
annual concentration of chlorophyll in North Inlet was similar to that
reported by Ferguson and Murdoch (1975) for Beaufort, N. C. and about 10
times as great as data reported by Marshall et al. (1971) for southern New
England. The annual mean Fo/Fa ratio of 1.36 at Station 1 was quite low,
indicating that a significant amount of non-functional chlorophyll as well
as phaeophytins, phaeophorbides and other degradation products of chloro-
phyll were present in the sediments. Such pigment products are commonly
found in aquatic sediments (Daley et al., 1973). The mean Fo/Fa ratio of
1.60 at the deeper stations indicated a healthier and potentially more
productive benthic microalgal community than at the shallow station. This
was confirmed by the productivity data.
CONCLUSIONS
The above-ground production of halophytes in North Inlet, mainly
Spartina alterniflora, has been estimated as about 900 g/m2/yr (J. M. Dean,
personal communication). Considering the productivity data reported here,
phytoplankton, together with benthic microflora, fix an amount of carbon
per year equivalent to the halophytes. Since the "aufwuchs" community,
the benthic macroalgae and the surface film community (Gallagher, 1975) is
not considered, it appears from the above data that in North Inlet, the
38
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algae are the most important primary producers. If this is true, then our
concepts regarding the relative ecological significances of the various
plant communities in salt marsh estuaries must be revised. At the very
least the algae must be considered as an important trophic compartment in
our model of the North Inlet Ecosystem.
39
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COMPOSITION AND SEASONALITY OF THE NORTH INLET
ZOOPLANKTON: ESTABLISHMENT OF THE BASELINE
Bruce C. Coull
ABSTRACT
Zooplankton of the North Inlet estuary near Georgetown, South Carolina
were collected bi-weekly from January 1974 to August 1975 at four stations.
Zooplankton numbers ranged from 377 to 84,414/nT (x = 9234/m3) and biomass
from 640 to 140,169 yg dry weight/m^). The major peak in density of
zooplankton occurred between April-July both years.
Copepods (including larval stages) were the most dominant taxon,
comprising 64-69% of total zooplankton numbers and biomass. The most
common species were Paracalanus crassirostris, Acartia tonsa, Oithona
colcarva, and Euterpina acutifrons. Cirripedia nauplii were the most
common meroplankter comprising 13% of the total for the entire sampling
period. Other important groups were bivalve and polychaete larvae and
Oikopleura sp. Comparison of the major species of copepods and their
reproductive periodicities with those reported in the literature suggests
that the North Inlet fauna is most closely allied to that of Florida waters.
INTRODUCTION
To date, composition of the South Carolina zooplankton is virtually
unknown. Along the Atlantic coast, studies have extended south to North
Carolina (Thayer et al., 1974) and from Florida to the Caribbean (Grice,
1960; Gonzalez and Bowman, 1965). South Carolina may represent a transition
zone between the north-temperate, mid-Atlantic coast and the tropical waters
of Florida and the Caribbean, and as part of an intensive ecosystems
analysis of the North Inlet estuary, it was imperative to obtain basic
information on the zooplankton in order to provide the information
requisite for a trophic model of the estuary.
Since the first phase of any community study must provide baseline
analyses of the component fauna as a reference for future studies, this
study dealt with specifying the zooplanktonic taxa (particularly the
copepods), their densities, and their standing crops. Further, the North
Inlet zooplankton was compared to those reported from other areas of the
40
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Atlantic coast using a similarity matrix to determine to what area the
North Inlet fauna was most closely allied.
DISCUSSION
Unlike many temperate regions where zooplankton exhibit spring and fall
blooms together with a summer ebb, the North Inlet zooplankton attained
maximum abundance in the summer. Greatest numbers were found from June
through mid-July; a pattern also reported for the phytoplankton in North
Inlet by Sellner (1973), who found that primary production increased with
temperature and was maximal in summer. Thus, the observed summer maximum of
zooplankton was concurrent with that of the phytoplankton.
Numbers and biomass indicate that Stations B and C, located in ebb
channels, had the highest "productivity" averaged over the year. Station A
was located off of a major creek in which Winyah Bay waters may flow into
North Inlet. The creek is 1-1.5 m deep and 4 m wide at low tide. Station B
was located in the main ebb channel of the North Inlet (700-800 m wide at
low tide) in 4-5 m of water. This locale is representative of a fairly
predictable environment in terms of temperature and salinity, having a
direct connection with the offshore, oceanic waters. Additionally, in this
area, offshore waters enter into the estuary on flood tide. Station C was
located in an ebb-oriented channel (200-500 m wide at low tide) off the main
arm of the oceanic channel in 3-3.5 m of water. Station D was located at
the upper reaches of a Spartina marsh.
The zooplankton at B and C were approximately two times more abundant
than at Stations A or D; differences that are statistically significant
(a = 0.05). Highest zooplankton densities were found at Station B in most
of the months and only on very few occasions did the densities at C exceed
those at B. In comparing the two upper tidal reach stations (A and B)
Station A, proximal to Winyah Bay, was consistently less populated than
Station D which was located well within the North Inlet system. Since there
was a net flow of water out of the inlet when averaged over time (Kjerfve
et al., 1975), the higher densities at Station B and/or C might be attributed
to recruitment of plankters from the upper reaches of the marsh. Since
there is a funneling effect, large amounts of the zooplankton would be
washed out of the marsh and into the inlet and perhaps into the outer
coastal waters. As stated before, Stations B and C were located in ebb
channels, B being located in the major one for the entire estuary. Hence,
Station B had recruitment from a larger area of the marsh than Station C.
This accounts, in part, for higher numbers and biomass there.
The average number of zooplankton in the North Inlet (9234/m3) is
comparable to figures reported for estuaries along the Atlantic coast,
8501/m3 and 4000-8000/m3 (Sage and Herman, 1972 and Thayer et al., 1974,
respectively). The mean dry weight in North Inlet, 16,009 pg/m3 is also
within the range of a North Carolina estuary, 14,000-21,000 yg/mj (Thayer
et al., 1974).
41
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Total number of organisms is often used as the main indicator of the
fraction of the total biomass contributed by one species. This index alone
can be misleading when considering the trophic importance of the various
components of the zooplankton (Reeve, 1970). For example, in our study, the
copepod Paracalanus crassirostris was significantly more dominant in terms
of numbers than Acartia tonsa, but there was no statistical (a = 0.05)
difference between the two species in total biomass. Although numbers of _A.
tonsa and Oithona colcarva were not statistically different, A^ tonsa
dominated in terms of biomass. Therefore, both numbers and biomass are
important components to consider in a discussion of zooplankton population
dynamics. Paracalanus crassirostris is one of the smallest calanoid
copepods (Davis, 1944) and we found it weighed three times less than .A.
tonsa. Since smaller animals characteristically have higher metabolic rates
per unit of body weight when compared to larger ones (Zeuthen, 1953), P_.
crassirostris was probably the most energetically important species in the
plankton.
Hutchinson (1967) believed that a body size factor difference of 1.35
is sufficient to allow separation of food resources in co-occurring
copepod species. Therefore, although P^ crassirostris and A. tonsa occur
concurrently, their difference in size may reduce competition for food
resources. On the other hand, £. colcarva and P_. crassirostris were similar
in size, thus other mechanisms must be important in fractionating the food
resources of these species (Maly and Maly, 1974). This abundance-size
relationship may reflect, to some extent, resource partioning in these
species of copepods.
The abundance of small copepods may also impart some competitive
advantage with respect to predation pressures for species which occur year-
round in the plankton. Larval fishes prey on zooplankton; Acartia,
Centropages, Temora and Euterpina are common prey for pinfish, spot and
menhaden (Thayer et al., 1974). Preliminary observations on the larval
fishes in North Inlet indicate a year-round production of these and/or
associated species (J. M. Dean, personal communication). Vertebrate
predation pressure is selectively greater on larger zooplankton (Deevey,
1964; Brooks and Dodson, 1965) and since the North Inlet zooplankton is
dominated by small species and fishes, grazing presumably takes place year-
round and the small species may be at a competitive advantage in such a
system.
Dominance of copepods in plankton is a common phenomenon. Herman et al.
(1968) found that copepods comprised 98.1% of the total zooplankton in a
Maryland estuary, Sage and Herman (1972) reported 84% in New Jersey, and
Thayer et al. (1974) found it to be 81% by numbers and 84% by dry weight in
North Carolina. In North Inlet, the copepods comprised only 68-69% of the
total zooplankton numbers and biomass, primarily because meroplanktonic
forms comprised a larger segment of the population here than elsewhere.
Cirripedia nauplii made up 13% of the North Inlet zooplankton and Herman
et al. (1968) reported a figure of less than 1%. Similarly, in North
Inlet, bivalve, gastropod and polychaete larvae comprised 12% of the fauna
while in the Herman et al. study this figure was less than 1%.
42
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North Inlet zooplankton did not exhibit the successional pattern
typical of mid-Atlantic and northern estuaries where Acartia clausii (a
winter-spring form) replaced A^. tonsa (a summer-fall form) and vice-versa
(Jeffries, 1962). Acartia clausii did not occur in the North Inlet plankton
but this was not unexpected since Sutcliffe (1948) noted its absence from
Beaufort, North Carolina plankton. Woodmansee (1958) described the replace-
ment of A. tonsa in the winter and spring by Paracalanus parvus in the
tropical waters of Florida. However, in North Inlet P. crassirostris and A.
tonsa did not exhibit this type of successional or replacement pattern; both
species were abundant throughout the year. Thus, even if P_. crassirostris
is considered the "niche equivalent" of £. parvus, there is no apparent
correlation with the results of Woodmansee (1958). Although P_. parvus is
reported both north and south of North Inlet (Sutcliffe, 1948; Reeve, 1970),
there was no evidence of this species being present. However, due to the
large numbers of Paracalanus encountered, not every individual was examined
under a compound microscope. If P_. parvus did, in fact, occur in North
Inlet, it must have been of minor importance.
Copepod species composition and seasonal distribution in the North Inlet
estuary were very similar to those reported by Grice (1960) from Florida.
He reported a year-round production of the six most common species,
including Acartia tonsa and Oithona colcarva, although there were fluctuations
in their densities. As in North Inlet, P_. crassirostris was the most
abundant species along the inshore Florida coast and showed a year-round
reproductive pattern. Grice (1960) also found that (). venusta was a year-
round reproducer with no particular pattern in reproduction and that
Centropages hamatus bred in the winter. Sutcliffe (1948) found this to be
true of C^. hamatus in North Carolina while Centropages typicus was observed
only in very low numbers in June. Another year-round producing copepod in
North Inlet, Euterpina acutifrons, is very cosmopolitan and has been
reported to have a world-wide distribution in tropical and subtropical
waters (Gonzalez and Bowman, 1965). Moreover, Weiss and Hopkins (1975)
reported Oithona brevicornis (colcarva) ,A., tonsa, and J?. crassirostris as the
dominant zooplankton species in a Florida estuary.
Other data which are in agreement with that of Grice (1960) were the
presence of Saphirella sp., and that Labidocera aestiva breeds in late
spring and summer. However, in North Inlet, this pattern was extended to the
early portion of the winter. Fleminger (1956) stated that L^. aestiva was
representative of a northern temperate coastal area while Labidocera scotti
was representative of a tropical or near-tropical coastal area. Lapidocera
scotti was not found in our study. Thus, the North Inlet zooplankton is
more closely allied than that from more northern regions to that of the
Florida region, since many of the species are tropical forms and most
exhibit reproductive patterns characteristic of this area.
In order to approach the study of community structure of the North
Inlet, we compared our data with other areas of the eastern Atlantic
coast. The comparison of diversity indices, H' and J, of the North Inlet
with these other zooplankton studies suggests that the different estuarine
43
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regimes are indistinguishable. Furthermore, it is noteworthy that the
indices obtained from the Patuxent River Estuary, Sandy Hook Bay area and
North Inlet are quite similar to that of an inshore station in Bermuda
despite the fact that the species compositions of these four stations are
very dissimilar.
Additionally, throughout the year, the diversity indices calculated on
North Inlet zooplankton remained virtually unchanged (+ one standard
deviation) while composition of the species of copepods changed to some
extent with the seasons (one exception to the diversity consistency). Thus,
within North Inlet and other areas, there appears to be a rather constant
"diversity" for estuarine, inshore coastal zooplankton assemblages. The
zooplankton community of North Inlet is very much like other systems of the
East Coast in terms of diversity, and these diversity values may represent
a standard range which any estuarine zooplankton community may be expected
to attain.
44
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VERTICAL MIGRATION OF LARVAL UCA IN NORTH INLET ESTUARY
P. DeCoursey
ABSTRACT
Stage I Uca zoeae in a main ebb channel of the North Inlet Estuary under-
go regular changes in numbers and vertical position. Maximum numbers are
found at the time of low and rising tides. Concentration in the lower quarter
of the water column occurs at this time.
INTRODUCTION
Vertical migration in the ocean water column has been shown to be a fea-
ture of many mid-water plankters (Gushing 1951, 1955; Bainbridge, 1961; Dietz,
1962; Woodmansee, 1966; Pearre, 1973; Rudjakov and Vororina, 1973). Since the
discovery in the early 1940's that the DSL (deep scattering layer) of open
ocean waters correlated closely with movements of small nocturnal animals
(Dietz, 1962), the study of vertical migration has made rapid strides (Boden,
1962; Barham, 1963, 1966; Kampa, 1971; Beamish, 1971; Donaldson and Pearcy,
1972; Issac et al., 1974). Consisting primarily of myctophid fishes and
euphasiid shrimp, the layers range from 200-800 m in depth during the day,
then move toward the surface at night (Dietz, 1962). A number of factors
appear to influence vertical migration patterns in open ocean waters, includ-
ing light intensity (Herman, 1963a, b; Bayne, 1964; Thorson, 1964; Boden and
Kampa, 1967; Miller, 1970; Kampa, 1976), hydrostatic pressure (Lincoln, 1970,
1971; Ennis, 1973), salinity (Grindley, 1964), and temperature (McLaren, 1963).
In addition, laboratory studies have considered the role of light and salinity
as well as endogenous timing mechanisms as controlling factors in vertical
migration (Lance, 1962; Bayne, 1964; Ringelberg, 1964; Enright and Hamner,
1967; Lincoln, 1970; Hughes, 1972; Crisp and Ritz, 1973; Ennis, 1973; Forward,
1974; Sulkin, 1975). The conclusion from studies using a wide array of tech-
niques is that many mid- and deep-water plankton undergo rapid, extensive
vertical movements on a daily basis.
The vital importance of planktonic components in ocean food chains has
long been recognized. Vertical migration is of special interest in the study
of energy flow in an ecosystem, since vertical displacement may markedly alter
the availability of a component in the food chain.
Vertical migration studies have concentrated on open ocean waters. Only
a few studies have considered estuarine waters where a relatively large number
45
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of environmental factors may significantly affect water column movements of
plankton (Carriker, 1951; Pinschmidt, 1963; Bosch and Taylor, 1973; Sandifer,
1973; Sameoto, 1975). Palmer (1974) studied vertical migration of benthic,
intertidal forms. Carrlker (1951) considered shallow water movement of bi-
valve larvae over two tidal cycles. As a consequence, only limited information
is available on vertical movement of crab larvae in coastal marsh waters where
they may be one of the dominant planktonic forms during the summer. Therefore,
these experiments were carried out in the North Inlet Estuary to determine
concentrations and patterns of distribution in relation to tides, light condi-
tions and other environmental factors.
DISCUSSION
The data processed thus far suggest that Uca Stage I zoeae are one of the
predominant brachyuran plankters of the estuary. Furthermore, they appear to
undergo a tide-related change in concentration as well as in distribution.
The cyclic change in numbers could represent peaks of hatching of the young,
and/or concentration of the zoeae at low tide in the main channel after being
carried down from the headwater creeks. The resolution of this issue lies in
careful studies of flushing rates and residence time in the estuarine waters
(currently being carried out by B. Kjerfve), and by concurrent studies of
larval concentrations at headwater, mid-channel, and outside the Inlet mouth
over several tidal cycles. The latter project has been too time-consuming to
prove feasible.
The period of vertical movement, based on the present state of data
analysis, appears to be tidal. Salinity changed very little in the water col-
umn during the sample period. Most other studies of vertical distribution in
estuarine waters (Carriker, 1951; Pinschmidt, 1963; Bosch and Taylor, 1973;
Sandifer, 1973) concerned low-salinity, and may play an important role in
upstream transport of larvae (Carriker, 1967). With the lack of a salinity
gradient in the North Inlet Estuary, this factor is clearly of little impor-
tance; similarly, temperature plays little part.
Changes in distribution at the sample site, Old Man Creek in the North
Inlet Estuary (Fig. 2), are not merely a function of laminar, differential
flow rates in the water column. In the ebb channel, ebb flow rate reached a
maximum during Tide Phase II, with relatively little difference in flow rate
except for a few centimeters above the substrate (See Fig. 9 for graphical
representation of the six phases of the tidal cycle). During Phase IV a
slightly greater ebb flow occurred in the lower half of the water column but
the rate overall was very low. Again, on the flood stages V and VI, the flow
rate was relatively uniform from top to bottom of the water column. A large
number of laboratory and field studies have suggested a role of light in the
vertical movement of larvae (Gushing, 1951; Bainbridge, 1961; Herman, 1963 a,
b; Bayne, 1964; Ringelberg, 1964; Thorson, 1964; Verwey, 1966; Boden andKampa,
1967; Rudjakov, 1970; Lincoln, 1971; Forward, 1974; Kampa, 1976; Sulkin, 1975).
Especially striking demonstrations of the effectiveness of light in depth reg-
ulation of zooplankton in the field have been studied during solar eclipses
(summary in Kampa, 1976). Nevertheless, much remains to be discovered con-
cerning phototactic responses at light intensities in estuarine and ocean
waters. For example, the phototactic process itself may undergo endogenous
rhythmic changes in Euglena (Bruce and Pittendrigh, 1958).
46
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T3
r£ O
4J O
P.r-4
O M-l
»O
i r
n)
0)
i-l
•8
0 24
6 8 10 12 hr.
Time
Figure 9. Sampling site for 1974 vertical migration study (tide phases)
47
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LIGHT, TIME OF DAY AND METABOLISM IN
LARVAE OF UCA PUGILATOR
W. B. Vernberg and D. D. Jorgensen
INTRODUCTION
It has been well documented that many aspects of behavior of zooplank-
tonic larvae of marine organisms are controlled by light (Thorson, 1964;
Herrnkind, 1968; Vernberg et al., 1973; Sulkin, 1975). Vertical migration
of both larval and adult zooplankton, for example, is thought to be largely
controlled by light (Boden and Kampa, 1967; Bainbridge, 1961; Thorson, 1964).
It also has been postulated (McLaren, 1963) that there is a link between
vertical migration of marine animals and their metabolism. McLaren (1963)
suggested that animals come to the surface waters to feed but, after feeding,
descend to lower depths to conserve energy by reducing their metabolism at
the lower temperatures found there. These studies indicate a possible link
between vertical migration, metabolism and response to light. The present
study was undertaken to measure the metabolic response of first-stage larvae
of the fiddler crab, Uca pugilator, throughout a 24-hr period under different
light regimes in an attempt to correlate metabolic response with light and
with the vertical distribution of first-stage U_. pugilator larvae observed in
the field.
RESULTS AND DISCUSSION
In an experiment conducted under light-dark (LD) conditions (14 hrs
light: 10 hrs dark), the slowest rate of respiration was observed when light
intensity was highest. This occurred at 1600 hrs when light intensity was
7.0 Joulesfur /sec. As light intensity dropped, oxygen consumption rates
decreased. Shortly after light intensity dropped to 0.5 J/m^/sec, the
metabolic rate increased, followed by a steady decline until the light intens-
ity increased again at 0800 hrs. At that point, the metabolic rates began
to increase again. The highest peak during the day occurred at 1000 hrs
when light intensity was 3.1 J/m^/sec.
Light intensities on the continuous light (LL) cycle remained high fol-
lowing 1600 hrs and oxygen consumption rates did not show the increase
observed in larvae in the LD cycle. At 2200 hrs, when larvae on the LD
cycle showed a sharp increase in respiration rate, the metabolic response of
those exposed to the LL cycle decreased markedly; the response was a mirror
48
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image of that observed for larvae in the LD cycle. After 2400 hrs, rates
paralleled those of larvae in the LD cycle.
Sulkin (1975) demonstrated that responses to both light and gravity are
used by crustacean larvae in depth regulation. He also noted that in one
species, Leptodius floridanus, the larvae swim less actively when light
intensity is high. Such a response would tend to position the larvae lower
in the water column during the day when light intensity was highest.
It has been demonstrated in the laboratory that first-stage zoea of _U.
pugilator are highly phototactic at least during a part of the day (Vernberg
et al., 1973). Data from the present study indicate that low light intensity
has a very stimulating effect on respiration rates when it occurs following
a period of exposure to bright light. Conversely, in the absence of darkness
following exposure to bright light, respiration decreases sharply.
-------
ENERGETICS OF ZOOPLANKTON
W. B. Vernberg
Respiratory rates have been determined for the most commonly found
species of adult zooplankton in the North Inlet Estuary and for three species
of larval zooplankton. These data are summarized in Table 9. Data for meio-
faunal species are given in Table 10.
Rates for both zooplankton and meiofauna were determined in Cartesian
diver respirometers. Total volume of the divers was approximately 10 yl.
Usually only one animal was used per diver, although with very small species
*-t was necessary to use 2-4 for each determination.
These data are to be used in development of the energy flow model.
CONCLUSIONS
There are obvious species differences in the respiratory rates of zoo-
plankton. Generally, oxygen uptake rates of larval zooplankton are lower
than those of adult zooplankton. Respiration rates of meiofaunal adults also
tend to be lower than those of the pelagic adult zooplankton. Since these
are marked species differences, it is necessary to construct an energy budget
for various species to understand their energetic role in the estuary.
50
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TABLE 9. RESPIRATORY RATES OF ZOOPLANKTON FROM THE NORTH INLET ESTUARY.
Temperature/Salinity yls 02/hr/mg dry wt
ADULT ZOOPLANKTON
Parvocalanus crassirostris 25° - 30 °/<>o
Acartia tonsal
Oithona brevicornis
o
Euterpina acutifrons
(non-gravid females)
LARVAL ZOOPLANKTON
0
Uca pugilatorj
Stage I
Stage III
Balanus balanoides
Stage I
Stage IV
Cyprid
Nassarius obsoletus
1 day - Veligers
7 day - Veligers
J-Anderson, Gary. 1975.
2Vernberg, W. B. 1972.
3Vernberg, W.B. et al.
25° - 25 °/«o
25° - 30 °/o»
Cold-acclimated (15°C)
15° - 30 °/°o
20° - 30 °/°°
25° - 30 °/oo
30° - 30 °/oo
Warm-acclimated (25°C)
15° - 30 °/o°
20° - 30 °/oo
25° - 30 °/oo
30° - 30 °/oo
20° - 30 °/oo
25° - 30 °/oo
30° - 30 °/oo
20° - 20 °/oo
30° - 20 °/oo
25° - 30 °/oo
20° - 30 °/oo
20° - 20 °/oo
25° - 30 °/oo
25° - 30 °/oo
25° - 30 °/»o
25° - 25 °/oo
15° - 25 °/°o
25° - 25 °/oo
1973.
12.9 + 1.0
24.3 + 1.3
7.5 + 0.8
8.3 + 0.9
14.1 + 1.3
19.7 + 2.0
22.3 + 2.3
2.7 + 0.2
8.8 + 0.5
11.4 + 0.7
9.8 + 0.3
4.0 + 0.5
6.6 + 0.5
3.9 + 0.4
5.2 + 0.5
4.6 + 0.3
4.9 + 0.2
4.8 + 0.3
2.8 + 0.2
12.5 + 1.0
21.7 + 2.2
12.7 + 0.8
6.4 + 0.9
5.1 ± 0.7
5.4 + 1.1
51
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TABLE 10. RESPIRATORY RATES OF MEIOFAUNAL SPECIES FROM THE NORTH INLET
ESTUARY.*
Species Temperature/Salinity yls 02/hr/mg dry wt
COPEPODS
Hastigerella leptoderma 25° - 30 °/°° 4.9 + 0.6
Leptastacus macronyx 25° - 30 °/00 7.5 + 1.5
Scottolana canadensis 25° - 30 °/°° 4.0 + 0.8
Nannopus palustris 25° - 30 °/oo 7.2 + 0.9
Thompsonula hyaena e 25° - 30 °/oo 21.2 + 1.7
KINORFYNCH
Echinoderes sp. 25° - 30 °/<>o 10.3 + 0.9
TURBELLARIAN
Pogaina sp. 25° - 30 °/<>o 3.4 + Q.2
CILIATE
Tracheloraphis sp.2 25° - 30 °/oo 4.5 + 0.5
, B. W. 1976. (in press)
2Vernberg, W. B, and B, C, Coull. 1974.
*These data were obtained during a study under Grant R802928-02-0 from
the National Science Foundation.
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THE MACROBENTHIC FAUNA OF NORTH INLET:
ABUNDANCE, DIVERSITY AND RESPIRATION
Richard Dame
INTRODUCTION
The benthic macrofauna are commonly members of the second and third
trophic levels of most estuarine ecosystems and many species are economically
important as food resources. Because of their trophic status, feeding
methods and generally sessile existence, some benthic macrofauna may concern-
trate environmental pollutants such as heavy metals and pesticides, thus
becoming pollutant indicators. In addition, some species of benthic macro-
fauna probably play important roles in cycles of nutrients and flow of energy.
North Inlet is typical of the small shallow, turbid estuaries in the
southeastern United States. Because North Inlet is undisturbed, it is an
ideal place to conduct base-line studies on an entire system. Benthic macro-
fauna undoubtably form an integral component in such a system. There are two
basic benthic environments common to North Inlet, intertidal and subtidal.
The intertidal environments can be divided into salt marsh, oyster bars,
mud flats and sand flats. The subtidal habitats are mainly sandy and muddy
bottoms.
Previous and current work on the benthic macrofauna in North Inlet has
been limited to the intertidal zone. Dame (1972, 1976) investigated energy
flow in the intertidal oyster population, while Holland (1972) studies the
population ecology of the clam Tagelus plebeius. Dame and Vernberg are
studying the distribution and abundance of the snail Littorina irrorata, the
fiddler crab Uca pugilator, and the crab Panopeus herbstii. In addition,
Holland studied the animal-sediment relationships on the intertidal sand
bars and mud flats.
Other studies of the macrobenthos of marsh-estuarine systems in the
southeastern United States are taking place at Sapelo Island, Georgia and
Beaufort, North Carolina. Early studies by the Georgia groups were directed
at energy flow (Odum and Smalley, 1959; Smalley, 1960; Kuenzler, 1961; Teal,
1962). The Georgia studies have centered on carbon flux and nutrient cycling
(Wiegert et al., 1975). The Beaufort studies have attacked a broad range of
problems including energy flow and nutrient cycling (Wolf, 1975). These
studies have recently concentrated on sea grass beds (Thayer, Wolf and
William, 1975; Thayer, Adams and LaCroix, 1975).
53
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The major objective of the project is investigation and modeling of the
functional and structural aspects of the system as a whole and not community
analysis. To achieve this objective, the macrobenthic faunal studies of
North Inlet have been and are being developed in three distinct phases.
Phase I determined the distribution, abundance, biomass and diversity of the
benthic macrofauna and is reported here. Phase II is currently in progress
and determines the influences of the natural environment on various popula-
tion and metabolic parameters. Phase III, not yet begun, will emphasize
influences of environmental stress on major groups within the benthic macro-
faunal component and how these stresses influence various components and the
entire system.
DISCUSSION
The chemical-biological concept of benthic communities, as proposed by
Petersen (1913), has been adapted by many workers to suit their projects.
Marine biologists have traditionally recognized discrete communities or
assemblages which existed in the North Inlet system and by sampling these
selected areas over a long, period.
The intertidal areas studied, Salicornia marsh, short Spartina marsh,
tall Spartina marsh and oyster beds, are along an environmental gradient of
decreasing elevation above mean low water or, in other words, decreasing
stress due to exposure. The complexity of the macrofaunal assemblages of
each of these areas showed the influence of exposure by decreasing the number
of species and individuals per m^. This agrees with many other investiga-
tions (Johnson, 1970; Holland and Dean, in press). The fiddler crab Uca
pugilater was the only organism common to the four intertidal habitats. While
seasonal fluctuations in the number of organisms per nr of certain species
were apparent (e.g., Nereis succinea and Crassostrea virginica), these fluc-
tuations appear to be related to reproductive events and the influence of
predators. Nereis succinea is common in the upper sediments and is known
to become very active near the surface immediately after inundation by the
tides. In the warmer months, North Inlet has a large resident population of
birds, some of which commonly feed on macrofauna along the rising tide line.
The number of young worms entering the populations was not studied during
summer and winter because they are smaller than the 1-mm mesh of the sieve
and thus pass through. It is not until winter that young worms have grown
large enough to be found in the samples. The seasonal fluctuations of oyster
numbers per m^ was directly related to the July and August spatfall and has
been discussed by Dame (1976).
Each of the five sobtidal macrobenthic stations had a distinct faunal
assemblage except at Horth Inlet mouth. The North Inlet mouth stations were
in the main channel that empties the inlet and were exposed to the extreme
stress of high flood and ebb currents. These currents are so strong that I
believe no stable benthic cooounity exists at this site and the organisms
there are washed in from other areas.
The Jones Creek station (Fig. 2) is a sandy habitat (81% sand) and is
numerically dominated by haustoriid amphipods. This compares well with
54
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investigations of intertidal sandy habitats along the eastern U.S. where
these animals also predominate (Holland and Dean, in press).
The Crab Haul Creek station (Fig. 2) was a muddy habitat dominated by
many species also found in the intertidal oyster beds (16 out of 32 species
found at Crab Haul station were also found in intertidal oyster beds). This
might be expected since the habitats are adjacent. The major faunal differ-
ence was due to the ability of the oysters to survive extremely well in the
nearby intertidal habitat thus increasing the developmental chances of the
organisms living in this muddy zone.
The Debidue Creek mouth station (Fig. 2) was dominated by haustoriid
amphipods also found at Jones Creek station, but an entirely different
assemblage of polychaete worms was in evidence as well as a common predatory
gastropod Terebra dislocata.
The last station was the Debidue Creek shelly site (Fig. 2) which had
the most diverse assemblage of organisms of any sample site. This high
diversity was mainly due to large,numbers of tube-dwelling and burrowing
polychaetes. The broken shells seemed to partition the environment and pro-
vide many habitats, allowing a highly diverse biological community.
Respiration studies that were begun are only a beginning in what seems
to be a virtually unexplored area in the biology of southeastern estuaries.
While many intertidal forms have been studied in detail (Teal, 1962;
Vernberg, 1969; Dame, 1972; Holland, 1972) little is known about the func-
tional aspects of most of the subtidal macrobenthic forms found.
The macrobenthic fauna are important in two components of the North
Inlet system: the intertidal and the benthic subtidal. In order to facili-
tate the systems modeling aspect of the study, the standing crops of the
yearly average biomass, respiration and production in kilocalories for the
components indicated was calculated as follows. The caloric content of all
organisms was assumed to be 5 kcal/g dry weight (Cummings, 1962). Yearly
respiration was calculated using specific oxygen consumption found in our
studies and data taken from the literature. Yearly respiration values for
a given species in kcal/m2/yr could be substituted into a relationship
developed by McNeil and Lawton (1970) to predict annual production. Our
values compare favorably with those estimates of Teal (1962) on a Georgia
salt marsh. I know of no comparable work on subtidal estuarine macrobenthic
fauna.
In conclusion, the macrobenthic fauna of the North Inlet system are
both productive and important to the functioning of the system. The data
gathered here is only a first step towards a more complete understanding of
North Inlet as an undisturbed estuarine system.
55
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DECOMPOSERS: MICROBIOLOGICAL STUDIES
L. Harold Stevenson and Carl W. Erkenbrecher
The microbiology group has been involved with measurement of two
primary parameters within the estuarine system: decomposers (as indicated
by ATP measurements of total microbial biomass) and water column detritus
(as indicated by particulate organic carbon). In addition, several secondary
factors, i.e., current, depth, suspended solids, heterotrophic bacteria,
dissolved oxygen, etc., have also been measured. The assay of these
parameters within the type of environment to be modeled presents several
unique problems. A salt marsh is not a homogenous environment. Individual
creeks differ one from another and their overlying water masses also differ.
The rise and fall of the tides present an additional complicating factor.
Tidal flux has been shown to influence the distribution and ecology of
many estuarine plants and animals. Yet, the effect of tides on estuarine
microorganisms in the water has received little attention. Some data on the
numbers of aerobic, heterotrophic bacteria in coastal waters are available
(ZoBell, 1946; Stevenson et al., 1974). Other studies have focused on such
topics as the tidal transport of detritus (Odum and de la Cruz, 1967), the
distribution of nutrients in estuarine (Leach, 1971), coastal (Alexander et
al., 1973), and swamp waters (Walsh, 1967), the activity of microorganisms
over a tidal cycle (Morita et al., 1973), and the enumeration of sediment
microflora and grain size distribution (Krumbein, 1971). A major portion of
the work, therefore, was initiated to measure the influence of tides on the
concentration of the microflora in the water column.
The investigation of the estuarine system has progressed through
several phases of increasing complexity. They include: 1) monitoring two
small tidal creeks over 12-hr tidal cycles, 2) statistical analysis of the
12-hr data, 3) survey data from several creek stations throughout the marsh,
4) monitoring marsh creeks of increasing size over 40-hr sampling periods,
and 5) analysis of sediments.
The first phase consisted of a comparison of two marsh creeks.
Station 1 was located at the entrance to a small, intertidal creek that
drained 4 hectares of Spartina marsh and had a soft, silty-clay bottom.
Salinity during the sampling periods ranged from 15 to 34 o/oo. The
maximum number of bacteria per ml of water was reached just prior to low
tide and appeared to be associated with the resuspension of sediment since
56
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increase in the turbidity of the water at Station 1 was frequently
encountered at low tide. The slightest wind disturbance of the shallow
water resulted in suspension of the soft sediment. The average number of
bacteria over the complete tidal cycle was 2.18 x 10^/ml. The concentrations
of particulate organic carbon (POC) and ATP likewise changed over the tidal
cycle with POC at low tide (6.10 g/m3). Although the increased turbidity of
the water near low tide did not result in a substantial discontinuity of the
POC data, the concentration of ATP did reflect this disturbance. Prior to
low tide, the concentration of ATP rose about 9-fold to a maximum of
3.52 mg/m3.
Station 2 (Fig. 2) monitored a creek that drained 13 ha of marsh and
about 170 ha of pine forest. The creek had a firm sandy bottom and measured
15 m across at the sampling site. Salinity ranged from 2 to 34 o/oo during
the sampling periods. The highest number of bacteria per ml of water
occurred just prior to low tide and then declined on a rising tide. The
average number of bacteria over the tidal cycle was 1.73 x 10^/ml and was
an order of magnitude lower than that reported for Station 1 over a similar
tidal cycle. Maximum POC was observed just prior to low tide; this
concentration was about three times greater than that at high tide. The
mean concentration of POC, 1.69 g/m3, was less than half that observed at
Station 1. The concentration of ATP in the water progressively increased
from a minimum value of 0.33 mg/m3 at high tide to a maximum value of
1.82 mg m3 at low tide. The mean concentration of ATO over the tidal cycle
(1.01 mg/m3) was not significantly different from the mean concentration
reported for Station 1. Additional tidal studies of both marsh creeks
confirmed these earlier observations. In all cases, maximum and minimum
values occurred at or near low tide and high tide, respectively. In
general, the concentrations of ATP and POC were greater at Station 1 for
the same sampling periods. Bacterial numbers, on the other hand, were
consistently higher at Station 2.
The second phase of the study consisted of an extensive statistical
analysis of the relationships between the physical-chemical parameters and
the biological components of the water column. Emphasis was placed on the
distinction between ebb and flood water masses. There was significant
(0.05 level) Pearson correlation coefficients between all of the biological
components (ATP, bacteria, and POC). Likewise, there were significant
correlations between salinity and water level and the biological parameters.
The flood tide data lacked most of the significant linear relationships
observed for ebb tide data. The interaction between the biological
components all but disappeared except for ATP with bacteria.
The third phase of the investigation involved sampling a total of
eight stations at points throughout the system from 1973 to 1975. More
complete data are available on four locations of increasing complexity:
Clambank, Oyster Landing, Old Man Creek, and North Inlet. Mean data for
detritus-carbon (POC) decreased with increasing size of the creek (1662 mg/
m3 at Clambank to 850 mg/m3 at North Inlet); while biomass carbon was more
abundant in the two larger creeks than the small systems (about 400 mg/nP
vers 300 mg/m3).
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Several long-duration studies of the amounts of microbial biomass and
detritus in the water column of Oyster Landing Creek comprised the fourth
section of the study. Each study period included bihourly sampling through
at least three high tides and three low tides. The previous observations,
that the biological parameters were minimal at high tide while highest values
were recorded at low tide, were confirmed. However, consecutive tidal cycles
demonstrated marked differences in the values recorded. Transport values
calculated in conjunction with these studies indicated that the marsh
environment studied was generally an exporting system which consistently
(but not always) lost more detritus and biomass on a falling tide than was
imported on a rising tide.
Limited data are available on the fifth segment of the work — biomass
measurements in sediments. Preliminary information indicates that the
interface zone in the high marsh between the forest and the Spartina-area
contains highest levels of detritus carbon (18 mg/g) and biomass carbon
(4 mg/g).
There are two significant points in addition to a direct interpretation
of the results. These relate to station location and sampling schedules.
The data indicate that marked differences were found among various stations.
The values obtained were directly influenced by location of station. The
selection of one or a few stations and considering them to be indicative of
the entire marsh cannot be done. Likewise, critical differences were
observed among data collected on the various sampling dates and, perhaps more
importantly, between consecutive tidal cycles. The selection of a single
cycle or a single sampling time as representative of a longer period, i.e.,
a month, is not valid.
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RADIATION BALANCE IN THE NORTH INLET MARSH
Sterling J. Crabtree and Bjorn Kjerfve
INTRODUCTION
Radiant energy received by the earth's surface is primarily composed of
short-wave (~0.5 ym) radiation from the sun and long-wave (~12 vim) radiation
from the atmosphere. This radiant energy is either absorbed by the earth or
reflected. The absorbed radiation heats the surface, which reradiates long-
wave energy. The difference between incoming radiation and outgoing
radiation is called net radiation and is a measure of the energy available at
the earth-atmosphere interface at a given site for heating of water, soil and
air, and for evaporation and photosynthesis.
The radiation balance has been studied by a number of investigators
over a wide variety of natural and agricultural surfaces (Monteith and
Szeicz, 1961, 1962; Ekern, 1965; Stanhill et al., 1966; Polavarapu, 1970).
Most investigators have used only data obtained on clear days in determining
relationships between net radiation and total incoming radiation. We show
that a linear relationship exists between net and incoming radiation for a
Spartina marsh site at North Inlet, not only on sunny days, but also on
partly cloudy days if the radiation data are numerically smoothed to remove
random short term variability.
Monteith and Szeicz (1961, 1962) showed that the radiative characteris-
tics of agricultural surfaces can be described by the linear regression
equation
Qn = Qs(l - ct)/(l + $) + LQ (1)
where O = net radiation integrated over all wavelengths
Qg = total short-wave radiation from the sun and sky
ct = albedo or reflection coefficient of the surface
Qs(l - o) = net short-wave radiation
B = heating coefficient
L = balance of long-wave radiation between the surface and atmosphere
Studies by Davies (1967) and Ekern (1965) have shown that the totals of
net radiation, Qn, for daytime conditions can be expressed as a function of
the total solar radiation, Qt where a is the axis intercept and b is the
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slope of the regression line, the regression coefficient, in a simpler
form
Qn - bQt - a (2)
with a correlation coefficient better than 0.9 (Davies, 1967).
From equations (1) and (2), it follows that the regression coefficient,
b, is given by b = (1 - a)/(I + g). Monteith and Szeicz (1962) found that
.a and & were equally important in determining 0. On the other hand,
'Stanhill et al. (1966) concluded that B and Lo varied only slightly for
different surfaces while a affected Qn the most (Davies, 1967).
RESULTS AND DISCUSSION
Instruments were placed on two adjoining sites in a 1-m high Spartina
alterniflora salt marsh at North Inlet between 4-9 July 1974. All data
were recorded as analog traces on strip charts and digitized with a 10-min
sampling rate on a Bendix Datagrid digitizer. In the following analyses we
used only data points measured during daylight.
Since the two sites were separated by 200 m, all data were filtered to
remove data noise generated by differential cloud passages and other high
frequency phenomena. We chose a second order, recursive, Butterworth low-
pass digital filter (Ackroyd, 1973) after considerable experimentation.
After filtering, we computed the daily means and standard deviations of
net, solar, and reflected radiation.
Linear regression of net radiation, 0~, on solar radiation, Qg, yielded
QN = 0.72 Qs - 9.5 (3)
with a correlation coefficient r = 0.98, where Q« and Qg are measured in
W m2. Equation (3) is in fair agreement with the relationship found by
Ekern (1965) for a sugar cane field in Hawaii. His regression coefficient
is 0.83 and LQ * -105 W m2.
Equation (3) applies to summer conditions for clear to moderately cloudy
days. Most afternoons, thunder showers passed over North Inlet, reducing
the total amount of incoming radiation. The daily average of total solar
radiation was 380 ly (15.9 x 106 J m2) as compared to 750 ly for total
solar radiation received on clear summer days on Hawaii (Ekern, 1965).
Ekern's regression fit included only data from clear days, which explains
his higher LQ value as compared to our analysis. In agreement with Davies
(1967), the strength, of Equation (3), however, is that it shows an excellent
fit to typical North Inlet July conditions with a considerable fair-weather
cumulus cloud cover and occasional thundershowers.
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Comparison of net radiation to incoming radiation for the 6-day period
indicates that QJJ on the average amounts to 69% of the incoming radiation.
Ekern (1965) listed the Qjj-percentages for a variety of surfaces between
latitudes 56°N and 19°N. The summer values ranged from a low of 41% above
grass sod in England to a high of 59% above sugar cane in Hawaii. Sugar
cane has a primary production rate greater than Spartina alterniflora.
The albedo, a, was computed as the ratio of total reflected radiation to
total solar radiation for each day and allowed the calculation of daily
heating coefficients, $. Whereas a is fairly constant coefficient of
variation (c.v. = 16%), 3 and LQ both vary considerably (c.v. = 61 and 76%,
respectively) and therefore control QN. This is in disagreement with
previous studies, but is probably due to day-to-day variations in cloud
cover, which greatly affects the long-wave radiation balance. Other studies
have usually only treated conditions on clear days.
Further, it is desirable to be able to estimate the reflected
irradiance from measurements of Qg to enable albedo computations. We
regressed QR on Qg and found
QR = 0.079 Qs + 3.4 (4)
with r = 0.94, using all 495 filtered data points. As Qs > QR it is obvious
that the relationship is not valid for very low values of solar radiation.
The analysis implies a mean summer albedo of 0.09 for the S^. alterniflora
marsh. It also shows a slowly decreasing albedo for higher values of Qg as
can be expected with a greater solar elevation. In comparison, Ekern (1965)
reported a range of albedos in Hawaii from 0.05 for lava to 0.15 for cane,
whereas Monteith and Szeicz (1961) computed a 0.26 albedo for grass in
England. Our low albedo may be explained, considering that the reflected
radiation is an area-composite value including Spartina plants and the
underlying, dark mud surface.
In summary, the empirical relationships, Equations (3) and (4), enable
direct computation of net and reflected radiation from a pyranometer record
for typical July conditions in a South Carolina Spartina marsh. Whereas
QN and QR seldom are measured directly in spite of their wide variations
with the underlying surface, Qs is measured routinely at most meteoro-
logical instrument sites.
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HYDROGRAPHY OF NORTH INLET, SOUTH CAROLINA
Bjorn Kjerfve, M. Susan Ivester, Linda L^ Vansant,
Mary L. Sloan, Richard L. Grout, and Jeffrey E. Greer
North Inlet belongs to a class of coastal plain estuaries which has
received only limited attention by physical oceanographers. An extensive
field investigation in 1974 resulted in 947 vertical profiles of velocity,
temperature, salinity, and 0T at 20 stations. During 1975 an additional
1,100 profiles were measured. Tidal elevation, atmospheric pressure, and
wind speed and direction were recorded continuously at one location. During
the perigee-syzygy tide in February 1974 the 300 km2 estuary-marsh system
experienced a maximum 2.4 m tidal range and 140 cm/sec currents. Neap tides
are characterized by a 1.0 m tidal range and maximum currents of 80 cm/sec.
Gravitational circulation is extremely weak as fresh water is primarily
derived from local rainfall. However, during periods of high discharge of
the Pee-Dee River into Winyah Bay, fresh water spills into North Inlet,
primarily through Jones Creek, increasing the gravitational circulation.
The net, depth-mean flow, averaged over the 20 stations, was 6.9 cm/sec in
the ebb-direction during high run-off conditions compared to 1.9 cm/sec ebb
flow during low run-off. Similarly, salinity was 33.1 o/oo and 34.4 o/oo,
respectively. Tidal pumping appears to be the dominant circulation mode with
net ebb currents in the main channels and net flood currents in the secondary
channels. Weather systems commonly cause mean sea level in the estuary to
oscillate as much as 80 cm with a typical period of 5-7 days. With respect
to density, North Inlet is vertically and horizontally homogenous, but time-
variations of OT are highly significant. North Inlet is a class la estuary
(Hansen and Rattray, 1966) during high and low run-off with a circulation
parameter on the order of 1 and a stratification parameter on the order of
10~3. Simultaneous tide measurements at the North Inlet stations over a 3-
week period indicated that the tide may be approximated by a frictional
progressive wave. Extensive bathymetric measurements indicated that net
circulation patterns in this kind of estuary may be induced from cross-
sectional channel shapes and the longitudinal orientation of sand waves.
FIELD MEASUREMENTS
Current speed and direction, conductivity, and temperature were
measured at 20 stations in the North Inlet estuary at one-meter intervals
from surface to bottom. Water elevation, wind speed and direction, and
atmospheric pressure were recorded continuously at one station. Bottom
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morphology was determined for a large number of cross sections and some
longitudinal sections throughout the system.
PRELIMINARY CIRCULATION RESULTS
During the perigee-syzygy February tide in 1974, tidal currents reached
a maximum of 140 cm/sec; the maximum tidal range was 221 cm; net currents in
places reached 26 cm/sec, directed toward the inlet. This field study
coincided with high run-off through Winyah Bay (Fig. 2) with some flow-
through into the North Inlet system.
During the October neap tide, tidal currents reached no greater speeds
than 94 cm/sec; the tidal range was as low as 110 cm; and the net velocities
were typically below 10 cm/sec. The run-off in Winyah Bay was low at this
time and no inflow from Winyah Bay was noticed.
North Inlet is a homogeneous estuary with respect to density, salinity,
and temperature. A three-way analysis of variance, replicating on station,
tidal stage, and depth, indicated that only the stage accounts for a highly
significant amount of variation and with a significant amount of variation
due to station location. Interaction terms and variations due to depth were
insignificant. Therefore, a one-dimensional numerical model could success-
fully be used to model the North Inlet circulation.
The gravitational circulation is weak but noticeable during high run-off
through Winyah Bay. The most important circulation mode seems to be a
pumping circulation: net velocities are directed oppositely in the same
cross section, pointing to a Class C estuarine type (Pritchard, 1955), where
lateral circulation is the main feature.
North Inlet may best be classified as a type la estuary (Hansen and
Rattray, 1966). It appears that this can be expected of most southeastern
marsh-estuary complexes (Kjerfve and Ivester, 1974). These estuaries are
characterized by low values of the circulation and stratification parameters
and have not previously been described with respect to the physical
oceanography.
BATHYMETRY AS AN INDICATION OF CIRCULATION
Net ebb-directed currents were found in the deep channels of Town
Creek, Old Man Creek, and North Inlet (Fig. 2), whereas net flood flow was
measured in the secondary channels in the same cross sections. Extensive
longitudinal fathometer traces were made during flood and ebb tides,
showing the existence of ebb-oriented sand waves (approximate height 0.6 m;
approximate wavelength 20 m) and flood-oriented sand waves in the secondary
channels.
The implication is that net circulation patterns possibly could be
determined from bathymetry measurements alone in shallow estuaries similar
to North Inlet (Kjerfve, 1975).
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DISCHARGE COMPUTATIONS
The tidal prism for North Inlet, as determined from velocity measure-
ments varied from 47 x 106/m3 for neap to 106 x 106/m3 for spring tides.
The intertidal volume fraction was then approximately equal to the mean
estuarine volume during spring tide but only 0.45 of that volume for neap
tide.
The maximum discharge through the North Inlet section consistently
occurred during the first half of the falling tide. The maximum ebbing
discharge then exceeded 2,200 m^/sec. Maximum flood discharge occurred
during the middle of the falling tide, with a maximum discharge below
1,500 m3/sec.
The time-averaged or net discharge through the same cross section was
typically on the order to 20 m3/sec but in extreme cases exceeded 100 m3/sec.
This happened during the February 1974 study.
The time-averaged exchange between North Inlet and Winyah Bay
primarily seemed to take place through Jones Creek. However, the direction
of exchange varied. An appreciable net discharge occurred during the
February 1974 study from Winyah Bay into North Inlet. The net discharge
was then estimated to be approximately 60 nr/sec. However, during the neap
tide study in October 1974, net flow, as measured at a cross section, was
7 m3/sec directed from North Inlet to Winyah Bay.
WATER LEVEL SPECTRA
Finite Fourier transforms were carried out on 3 simultaneous 20-day
water level records. The records were digitized with a sampling rate of
1 hr. The semi-diurnal tidal peak completely dominated each spectrum.
However, the diurnal peaks were also easily recognized. There also existed
a dominant peak in the ocean gauge record at a period of 2.2 days, which
probably is associated with passages of weather systems.
Cross-spectral analysis indicated a lag of 41 min for the semi-diurnal
tide wave at Clambank Creek (Fig. 2) relative to the ocean gauge. This
lag time was 4-5 times longer than what could be expected from a friction-
less shallow water wave. The phase relationship between currents and water
level fluctuations indicated that the North Inlet tide may have been of the
standing type. However, Hunt (1964) pointed out that a frictional,
progressive wave may exhibit the same current-tide phase relationship as a
standing wave. Therefore, in modeling the North Inlet tide, it will be
necessary to include friction in order to simulate the tidal behavior
succe ss fully.
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DATA RETRIEVAL SYSTEM
BjOrn Kjerfve, Linda L. Vansant,
Richard L. Grout, and Mary L. Sloan
A modeling oriented research project requires good field data for model
calibration. The present study has focused on collecting physical time
series data from the North Inlet Estuary. These data have been incorporated
into an easily accessible computer disk storage system.
The completed data set consists of four variables: 1) water elevation
at Clambank Creek (Fig. 2), relative to existing NOAA bench marks; 2) wind
speed at an elevation of 15 m at Clambank; 3) wind direction at Clambank;
and 4) atmospheric pressure at Clambank. The variables have been recorded by
means of a WeatherMeasure F551 water elevation gauge for the tide, a Climet ©
(Climet Instrument Co., Redlands, CA) CI-26 recording wind system with a
two-channel Easterline Angus recorder for the wind speed and direction, and
a WeatherMeasure B211 microbarograph for the atmospheric pressure.
Each instrument was installed in late April 1974, and has given a
continuous time series. This has required constant checking of instrument
operation and calibration. We have serviced the instruments on at least a
weekly basis since installation. With respect to the tide gauge, this
included a monthly relevelling of the baseline relative to existing bench
marks to insure against bias errors.
Each analog record trace was prepared in the office. Field time checks
were converted to Eastern Standard Time (EST) and coded according to Time-
Day-Month-Year: e.g., 2015-03-02-75 would mean 8:15 p.m. on 3 February 1975.
Each time series was digitized using an existing Bendix Datagrid Digiti-
zer ^. The analog records were converted to information on electromagnetic
tape. Through an elaborate FORTRAN program, the tape information was sampled
at 10-min intervals on the hour and each 10-min clock increment. Corrections
were made for non-linear instrument chart-paper feeding, curve-linear record-
ing pens, and sloppy digitizing procedures. The sampled data points were
punched on computer cards. These cards were hand-edited, insuring corres-
pondence between recorded signals and punched data points.
In the next step, these edited data points were stored on a direct-
access disk, available through the University of South Carolina Computer
Services Division IBM 370/168 system. The total data set presently consists
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of one complete year, beginning at 0000 1 June 1974 and ending at 2350
31 May 1975. The sample rate is 10 min and each one of the four series
consists of 52,560 data points. A variable pointer, IR, can be set to an
arbitrary hour value subsequent to the IR=1, the beginning of the series.
However, IR must be less than 8,760, the total number of data hours. Thus
it is possible to access the entire set or only a portion thereof, depending
on the particular application. The FORTRAN IV program, which runs in class
B in less than 2 min CPU time, may be used to access the data set.
The Eppley pyranometer located 100 m south of the Baruch coastal labora-
tory on a Salicornia marsh plot has yielded continuous records of total
incoming solar radiation for two years. Portions of this record have been
digitized and processed in a manner similar to the other four parameters.
However, extensive statistical calibration of these data compared to several
other similar instruments erected next to the pyranometer indicates exten-
sive data inconsistencies. The reason appears to be poor maintenance of the
pyranometer cell: paint flaked from the sensor unit and salt and dust spray
covered the hemispherical sensor dome for extended time periods. For these
reasons, we decided not to store the 1974-75 radiation data on the data disk
along with the tide, wind, and pressure records.
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SALT MARSH UNIT MICROECOSYSTEMS FOR
ASSESSMENT OF POLLUTANT ADDITION PERTURBATIONS
Wiley Kitchens
INTRODUCTION
Detailed studies of the coastal ecosystems (Odum and Smalley, 1959;
Smalley, 1959; Pomeroy, 1959) have led to a general awareness of the intrin-
sic value of the Spartina alterniflora salt marsh community to the coastal
systems through its various supportive roles, such as (1) an ultimate source
of carbon and other nutrients to the complex marine food webs, (2) a primary
nursery ground for the coastal fisheries, providing both food and harborage
to larval and juvenile stages of various species, and (3) a stabilizing
force retarding coastal erosional processes. Further studies have detailed
aspects of community structure, energy flow, and material fluxes through
the marsh system (Teal, 1962; Odum and de la Cruz, 1967; Day et al., 1973).
To date, however, the only substantive data available regarding environmental
alterations are the studies of Chapman (1968) and Schmidt (1966) detailing
the effects of dredging and filling operations and Valiela et al. (in press)
detailing the effects of sewage applications.
The microecosystem or "microcosm" approach is a logical way to experi-
mentally assess whole community responses in terms of sensitivity or sus-
ceptibility to additions of real or potential pollutants under controlled
conditions. This approach has been successfully employed to investigate
aspects of such fundamental ecosystem processes as nutrient cycling in
aquatic systems (Whittaker, 1961), patterns of community metabolism (Beyers,
1963, 1965), patterns of ecological succession under various environmental
regimes and stresses (Cooke, 1967; Wilhm and Long, 1969; Kitchens, unpub-
lished data), response to low freshwater flow regimes in estuaries (Cooper,
1970), and assorted community responses to environmental alterations in flow-
ing streams (Odum and Hoskin, 1957; Kevern and Ball, 1965; Lauff and Cummings,
1964; Mclntire et al. , 1964). Odum and Chestnut (1970) reported ecological
systems that developed when the treated waste from municipal sewage systems
flowed into estuarine waters.
One obvious advantage to the microecosystem approach is that the test
pollutants are not released into a natural ecosystem if a treatment system
is attached to it. This can be a critical factor in heavy metals and pesti-
cide studies. Other advantages are (Beyers, 1963): (1) some control of
boundary conditions so that variations can be attributed to the response
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under investigation, (2) ease of replication for statistical analyses and
modeling, (3) study of systems small enough to control, but large enough to
maintain complexity, (4) sacrifice of units at given intervals, so that ran-
dom errors will be independent of random error in other experiments, and
(5) the test pollutants are not directly released into the natural ecosystem;
they can be managed and/or controlled.
This study has and is currently being conducted in several phases. The
initial phase was the period during which the microecosystem marsh units
were being designed and constructed. The second phase was testing and
evaluation of the replicability of the units for various critical response.
The third phase will be the perturbation phase during which replicate micro-
ecosystem units will be manipulated by pollutant additions and compared with
unperturbated control units for assessment of effects of pollutant additions.
The community metabolism response was selected for several reasons:
(1) it has been shown to be a sensitive indicator of community imbalances in
various aquatic systems (Copeland and Dorris, 1962; Copeland, 1965, 1967),
(2) replicate laboratory aquatic systems do not differ significantly with
respect to rates of community metabolism (Abbott, 19*6), and (3) ease of
automation for measurement of response.
Other measurements of either community structure or physiology have been
used as time permitted to determine the validity of the community metabolism
response and calibrate the test against the natural marshes.
The specific aims of this work are: (1) to determine and demonstrate
the general utility and universal application of the microecosystem technique
for pollution studies at various marine laboratories, (2) to develop several
predictive and simulative models for various potential pollutants threatening
coastal marshes, and (3) to test the validity of the general ecosystem model
for the North Inlet area by direct measurements as well as contribute data
to that model.
DESCRIPTION OF EXPERIMENTAL TANKS
The units were designed essentially as combination "containerized"
short Spartina alterniflora salt marsh plots and metabolism chambers. The
following sections will outline and detail construction and sampling pro-
cedures .
Construction of the Combination Holding Tanks
and Metabolism Chambers
Tank Fabrication—
Four replicate square tanks (8' x 8' x 3.5') were fabricated from rigid
sheets of PVC. The tanks were constructed to serve dually as a holding tank
for minaturized salt-marsh plots (with attendant floral and faunal communi-
ties) and gas analysis chambers for measurement of community metabolism.
Each unit also is fitted with an airtight plexiglas lid for sealing tank
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atmospheres for gas analysis. During normal operation the tanks are left
open to the atmosphere and are flooded and drained twice daily in synchroni-
zation with the local tides.
Marsh Plots—
Each of the tanks was sodded with plots of Spartina alterniflora salt
marsh (1 ft2 in area) with substrate intact to a depth of 6 inches. These
plots were transplanted from the local marsh during the first two weeks of
January, 1975. It was hoped that the trauma of transplantation would be
minimized during this rather dormant period for both the Spartina and the
invertebrate benthic fauna within the substrate. The following photographs
depict layout of the units as well as some close-ups of the marsh plots. New
growth of the Spartina was observed along with increased activity among the
infaunal and epifaunal communities within the ponds in the eight months since
transplantation. Oysters have been placed upon racks within the screening
box at the effluent water drain end of each tank. Growth studies will be
initiated as a further test of system replicability.
Overview of tanks (with lids in
place) depicting the layout of some
of the plumbing and the marsh plots.
Tidal Sea Water System—
Within tank view of the trans-
planted marsh (note shoots).
Water from a creek adjacent to the transplant area in the marsh is
pumped into the units upon signal from a set of remote timers. The period
between successive high tides is 12.45 hours and is reset on occasion to
approximate tidal conditions in the local marsh. The system has been
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operating as a flowthrough system. However, it is adapted for the inclusion
of a 900 gallon capacity storage tank to operate on a closed system for units
exposed to pollutants. The pools are filled at a rate of 5.4 1/min and
drained at a rate of 2.4 1/min. The water attains a level of 6 inches over
the base of the marsh plants within the 2-hr filling period.
Gas Analysis System—
The gas sampling and analysis system for each of the tanks is now com-
plete. The system is composed of: 1) an interval timer, 2) flow meters, 3)
tubing (polyethylene), 4) pumps, 5) PVC needle valves, 6) infrared C02 analy-
zer, and 7) a digital data recorder. The system is designed to permit
either flowthrough or closed circulation analytical sampling techniques. We
have employed the integration of C02 concentration rates of change curves as
described in Odum and Hoskins (1958) for oxygen concentration (modified for
C0£ in our study). Prior to the analysis (C02 concentration determinations)
each of the tanks is sealed with a transparent plexiglas lid. The lid is
composed of two 4* x 8' sheets of 1/4" plexiglas and PVC supports. When
fitted in place the lid seals the tank to the atmosphere and forms a fixed
inside chamber volume. Samples of the atmospheres within the tanks are
pumped to the gas analysis equipment by remote signal timers, pumps, and
solenoid valves. C02 flux is monitored during a 24-hr period at hourly inter-
vals in each of the tanks. From these data, net photosynthesis and respira-
tion rates are determined.
Temperature Control System—
An air conditioning system for temperature regulation was installed in
each of the tank units to prevent heat buildup due to a greenhouse effect.
This system consists of an individual 7800 BTU air conditioner for each tank.
The units share a common control system designed to keep the temperature
within the tanks within 3°F of the ambient atmosphere. The control relay
regulating the temperature is activated,by differential internal refrigerant
pressures within the inside and outside temperature sensors.
Nutrient Flux Determinations
Nutrient flux rates into and out of each of the units were determined
utilizing concentration of the various constituents and discharge measure-
ments for the tidal waters into and out of each of the units. The following
determinations were made for a sampling period at 30 min intervals:
1) reactive phosphorous, 2) total phosphorous, 3) ammonia nitrogen, 4) nit-
rite nitrogen, 5) nitrate nitrogen, 6) total nitrogen.
Community Structure Analyses
The benthic communities in each of the units was subsampled by extract-
ing a 10 cm^ core the depth of the substratum. Ten replicates were taken
from each of the units and sacrificed and analyzed for macrobenthos by the
technique of Dame (see Macrobenthos section). A replacement core from the
natural marsh was substituted for the removed core sample.
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Microbial biomass determinations will be made on a quarterly basis
utilizing the technique of Stevenson (see Microbiology section).
RESULTS
In summary, we have found good agreement among the four replicates both
primary productivity and nutrient budget studies. Although the studies are
still in the preliminary stages, we have observed rather consistent trends
in the ratio of net photosynthesis to nighttime respiratory values. For our
first three preliminary sample runs, the values have been just slightly less
than 1 or unity. Our preliminary nutrient budget indicates importing of
total phosphorus and exporting total nitrogen. This pattern has been noted
for our first two sample runs with good agreement among replicates for each
run.
The benthic community faunal survey at this point is still incomplete.
Initial data indicate a lower species diversity in the tank units that at
the sample site for the natural marsh. We feel this may indicate a drainage
problem in the units and will follow the results of this study closely, pre-
paring to make some alterations to improve drainage if necessary.
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SECTION 8
SUMMARY OF REPORT
F. J. Vernberg
This report represents the results of the first two years of what was
designed as a five-year project. To understand the dynamics of a relatively
undisturbed marsh-estuarine ecosystem, the North Inlet Estuary, Georgetown,
S. C. both macroecosystem and microecosystem approaches were used. The two
principal objectives of this macroecosystem study were: 1) to establish
baseline data on an undisturbed estuary to provide a scientific basis for
comparative studies on the effects of various stresses of pollutants on
other estuarine environments; and 2) to develop models of an estuarine eco-
system which would predict the probable effects of environmental perturbation.
The principal objectives of the microecosystem were: 1) to develop and test
replicate experimental salt marsh units at the microecosystem level as
diagnostic tools for the assessment of both long- and short-term pollution
effects on the Spartina alterniflora salt marsh community; and 2) since this
study was conducted in conjunction with the ecosystem analysis of North
Inlet Estuary, these simulated marshes will be utilized to test, as well as
to provide some data relevant to the general overall ecosystem model being
constructed for the area.
During the initial phase of this five-year study, specific substudies
were started and the study of other key processes were to be investigated
in subsequent years. Therefore, in keeping with the experimental design of
the project, only these substudies are discussed and a comprehensive analysis
of the marsh-estuarine ecosystem cannot be presented at this time.
Field studies involving 10 faculty and postdoctoral investigators and
modeling procedures were initiated simultaneously.
A comprehensive conceptual energy flow model has been formulated which
consists of three distinct subsystems: water column, intertidal marsh zone,
and the benthic subtidal zone. A linear dynamics system with 22 states was
chosen as the mathematical model. A "first attempt" dynamic model for the
water column submodel has been formulated mathematically and a simulation
program constructed. Additional field work, which was proposed as part of
the original experimental design, is needed to evaluate various system para-
meters.
In addition, a linear systems model of the intertidal oyster community
was developed. Simulation of the mathematical model indicated that the
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original model was near stability. This result agrees with those of a five-
year field study of oysters. A 1% sensitivity analysis of the parameters in
the mathematical model affords some order in which these parameters should be
studied.
PRIMARY PRODUCERS
The aboveground production of halophytes in North Inlet, mainly Spartina
alterniflora, has been estimated as about 900 g/m^/hr. Considering the pro-
ductivity data reported here, the phytoplankton, together with the benthic
microflora, produced about the equivalent amounts of carbon per year as the
halophytes. Since the "aufwuchs" community, the benthic macroalgae and the
surface film community are not considered, it appears that in North Inlet,
the algae are the more important primary producers. If this is true, then
our concepts regarding the relative ecological significances of the various
plant communities in salt marsh estuaries must be revised. At the very
least, algae must be considered as an important trophic compartment in our
model of the North Inlet Ecosystem.
ZOOPLANKTON
The zooplankton of the North Inlet Estuary were collected bi-weekly from
January 1974 to August 1975 at four stations. Zooplankton numbers ranged
from 377 to 84,414/m3 (X=9234/m3) and biomass from 640 to 140,169 pg dry
weight/m3 (X=16,009 yg dry weight/m3). The major peak in the density of zoo-
plankton occurred between April-July both years.
Copepods (including larval stages) were the most dominant taxon compris-
ing 64-69% of total zooplankton numbers and biomass. The most common spe-
cies were Paracalanus crassirostris Dahl, Acartia tonsa Dana, Oithona
colcarva Bowman and Euterpina acutifrons (Dana). Cirripedia nauplii were the
most common meroplankters, comprising 13% of the total zooplankton for the
entire sampling period. Other important groups were bivalve and polychaete
larvae and Oikopleura sp. Comparisons of the major species of copepods and
their reproductive periodicities with those reported in the literature sug-
gests that the North Inlet Fauna is most closely allied to that of Florida
waters.
The analysis of zooplankton vertical migration was undertaken to estab-
lish both a basis for estimating standing crop and an understanding of the
role of environment fluctuation on species disposal. Uca zoeae, predominant
brachyuran plankters, were found to undergo regular changes in numbers and
vertical position in the water column. Maximum numbers were found at the
time of low and rising tides and a concentration in the lower quarter of the
water column occurred at these times.
Laboratory estimates of the energetics of various zooplankton species
were determined under combinations of temperature and salinity. These data
will be used in the development of the energy flow model.
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MACROBENTHIC FAUNA
Data on the macrobenthic fauna for model development in the following
subject areas were analyzed: abundance, diversity, and respiration. These
data were collected on a phasic experimental design. The first phase dealt
with distribution, abundance, biomass and diversity of the benthic macro-
fauna. The second, which was initiated the second year, involved a study of
the influence of natural environmental factors on populations and metabolic
responses. The next phase, not yet begun, will emphasize the influence of
environmental stress, including pollutants, on the benthic macrofauna.
DECOMPOSERS
The role of decomposers was studied in phases. Numbers of decomposers
and amount of water column detritus were determined. Initially, the smaller
tidal creeks were monitored over a 12-hr tidal cycle. This was followed by
statistical analysis of the relationship among the physical-chemical para-
meters and biological components of the water column using an IBM-370 com-
puter and the SPSS and SAS statistical packages. The monitoring program was
expanded to include larger creeks over a 40-hr sampling period. These data
were needed for estimation of energy flow dynamics.
SOLAR RADIATION BALANCE
The radiation balance in the Spartina marsh was studied in order to
have an estimation of solar energy imput to at least one phase of the marsh-
estuarine ecosystem.
PHYSICAL CHARACTERISTICS
To understand the dynamics of a marsh-estuarine ecosystem, the physical
characteristic of the study area needs to be evaluated. The hydrography of
North Inlet Estuary was described after extensive field studies. In addition,
an easily accessible computer disk storage system was developed to store
physical time series data for later model calibration.
SALT MARSH MICROECOSYSTEMS
The last portion of this study deals with the salt marsh microecosystems
program. The initial phase was concerned with design and construction of
the microecosystem marsh units. In the current phase, these units have been
tested to evaluate the replicability of the several units and to compare
these units with the salt marsh. The primary response studied was community
metabolism. The next phase is study of the influence of specific perturba-
tions on these experimental units.
74
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/3-77-016
2.
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
The Dynamics of an Estuary as a Natural Ecosystem
5. REPORT DATE
Januarv 1977 (Issue)
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
F. J. Vernberg, R. Bonnell, B. Coull, R. Dame, Jr.,
P. BeCoursey,W. Kitchens, Jr., B. Kjerfve, H. Stevensoti
tJ. Vprnnprp- R- 7incrmark 1
8. PERFORMING ORGANIZATION REPORT NO.
,ERL/GB 324
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Belle W. Baruch Institute for Marine Biology and
Coastal Research
University of South Carolina
Columbia, South Carolina 29208
10. PROGRAM ELEMENT NO.
nrCT3WniACT/GRANT NO.
R 802928
12. SPONSORING AGENCY NAME AND ADDRESS
Environmental Research Laboratory
U. S. Environmental Protection Laboratory
Office of Research and Development
Gulf Breeze, Florida 32561
13. TYPE OF REPORT AND PERIOD COVERED
Final. 1/14/74 - 1/13/76
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
A research program was initiated to understand the dynamics of a relatively
undisturbed estuary-marshland ecosystem, the North Inlet Estuary near Georgetown,
South Carolina. Because of the relative complexity of this type of study, a five
year study was proposed; this report summarizes results of the first two years.
This study consisted of two substudies: a macroecosystem substudy and a micro-
ecosystem substudy. The objectives of the macroecosystem study were: 1) to
establish baseline data on an undisturbed estuary to provide a scientific basis for
comparative studies on effects of various stresses of pollutants on other estuarine
environments; and 2) to develop models of an estuarine ecosystem which would predict
probable effects of environmental perturbation. The principal objective of the micro-
ecosystem study was to develop and test replicate experimental salt marsh units at the
microecosystem level as diagnostic tools for the assessment of both long- and short-
term pollution effects on the Spartina alterniflora salt marsh community.
A conceptual model of energy flow for the entire marsh-estuarine ecosystem was
developed which consisted of three sub-models. A simulation of the water column sub-
model and a simulation by a linear systems model of an intertidal oyster community was
completed. Much baseline data needed for model development is available on primary
producers, zooplankton, meiofauna, benthic macrofauna, decomposers, and relevant
physical parameters. .
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS C. COS AT I Field/Group
Animal ecology, plant ecology, barnacles,
mussels, phytoplankton, primary biological
production, tides.
North Inlet Estuary, Sout
Carolina, Spartina altini
salt marsh, energy flow,
fauna, modelling, ecosyst
flora,
flora,
em.
18. DISTRIBUTION STATEMENT
Release unlimited
19. SECURITY CLASS (ThisReport)
Unclassified
21. NO. OF PAGES
86
20. SECURITY CLASS (Thispage)
22. PRICE
EPA Form 2220-1 (9-73)
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