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BULLETIN OF MARINE SCIENCE.
31(3): 801-808, 1981
COMPARATIVE STUDIES OF TROPICAL
AND TEMPERATE ZONE COASTAL SYSTEMS
F. John Vernberg
ABSTRACT
Although estuarine ecological systems are of proven importance to human society, estuarine studies tend to be site specific and restricted in scope. A vital need is research on the
comparative dynamics of estuarine systems from different climatic regions to provide a better
basis for developing a scientific understanding of their similarities and dissimilarities which
is essential to developing a rational management program.
One fundamental question is do the functional responses of coastal ecosystems differ
between temperate and tropical zones in the same way that the physiological responses of
organisms differ between these zones.
Since the beginning of human civilization, the human species has turned to the
sea for food and as a means of transportation. Thus it is not surprising that most
of the great centers of population are located in estuarine regions. For centuries
the resources of these coastal areas appeared limitless, and only recently have
their limits been recognized. Today competition for these resources from industry, urban centers, commercial and sports fisheries, and shipping is becoming
ever keener, and it is obvious that effective and rational resource utilization
depends upon a broad environmental data base and a knowledge of how estuarine
systems function. Estuaries of the world not only are of interest to society, but
also they are of immediate interest both to environmental scientists and to policy
decision-makers responsible for management of our natural resources. The scientist is concerned with understanding the nature of the various complex, interrelated processes governing the functioning of this ecological system. It is, of
course, necessary to understand the functioning of relatively undisturbed systems
for the development of ecological theory, but a knowledge of how environmental
perturbations influence undisturbed and disturbed estuaries is vital if we are to
devise a rational basis on which governmental decision-makers and citizens can
act to use estuaries wisely and to restore polluted areas.
In recent years more attention has been given:to the investigation of complex
estuarine processes using an interdisciplinary systems approach (Vernberg, 1977;
Dame, 1979). Along the east coast of the United States, studies have been concentrated in the following areas: Narragansett Bay, Rhode Island (Nixon and
Oviatt, 1973; Kremer, 1979); Chesapeake Bay; Newport River, North Carolina
(Wolfe, 1975); North Inlet Estuary, South Carolina; and Sapelo Island, Georgia
(Wiegert and Wetzel, 1979). In the Gulf of Mexico similar studies have been
centered in Apalachicola, Florida (Livingston, personal communication), and
Barataria Bay, Louisiana (Day et aI., 1973). Although these studies have reached
various levels of complexity, no significant attempt at a detailed inter-estuarine
comparison is possible because of significant data voids and methodological differences. Estuarine systems from tropical and subtropical regions have received
even less attention. The effects of thermal pollution of Biscayne Bay, Florida has
been reviewed by Zieman and Ferguson Wood (1975), and Chesher (1975) described the biological impact of a large-scale desalination plant at Key West,
Florida. An ecological study of the Terminos Lagoon, Mexico is currently in
progress (Yanex-Arancibia, personal communication). Basic questions exist as
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1981
to the reliability of transfer and application of ecological principles from one
temperate zone estuary to another, and it is obviously impossible to extrapolate
from a temperate zone estuary to one in the tropics. Farvar and Milton (1972)
have drawn attention to problems of applying terrestrial resource practices to the
tropics when patterned after temperate zone regions.
The present general paper has the following principal objectives: (1) to compare
tropical and temperate zone estuaries; (2) to present an overview of some current
research on an undisturbed temperate zone estuary, the North Inlet Estuary, in
South Carolina; and (3) to suggest some comparative studies of dynamic functional responses of tropical and temperate zone estuaries which would help answer the question do functional differences between temperate and tropical zone
estuaries vary in the same way that the physiological responses of organisms
differ between these zones.
COMPARISON
OF TROPICAL
AND
TEMPERATE
ZONE
ESTUARIES
Little work has been published on a systems analysis of tropical estuaries,
although ecological studies on isolated species, population dynamics, and various
physico-chemo-geologic processes are to be found. Therefore, critical comparisons of temperate zone estuaries with those in the tropics will have to await the
results of future investigations. However, some obvious differences between
these regions exist in the expression of various environmental factors which in
turn must differentially influence functional responses of these ecosystems. The
difference in one factor, annual thermal regimes, is well documented. The high
temperatures of the tropics are experienced in transitional regions of the temperate (semi-tropical) zone, but in the tropics there is relatively little annual
thermal variation, which is in sharp contrast to conditions in the temperate zone.
For example, in Bahia, Brazil (latitude l3°S) the annual seawater temperatures
range from 25° to 33.7°C, in Jamaica (latitude 18°N) the range is 2SOto 30°C, while
in North Inlet, South Carolina (latitude 33°N) the range is approximately 5° to
32°C. At sites at higher latitudes the range is reduced and displaced toward lower
temperatures. Other factors, such as light, considered independently, also vary.
Considering the potential impact of multiple factor interaction on biological systems, it is expected that profound functional differences have evolved in widely
separated estuarine systems. As intriguing as it is to discover and describe the
different homeostatic mechanisms which permit system survival under different
conditions, the need to understand the basic similarities between separated estuaries is essential to developing a more comprehensive basis for the theory of
estuarine systems. The general concepts of ecological systems have been known
at least since the work on oyster communities by Moebius in 1877 (Rice, 1883).
Now we need quantitative data on how systems operate. For example, temperature has a profound effect on metabolism. Based on studies of closely related
species from different climatic regions, a generalized metabolic response for heterothermal organisms has emerged. Tropical, temperate, and polar organisms
have similar metabolic rates (measured as oxygen consumption) when determined
at their respective habitat temperatures (Vernberg, 1962; Vernberg and Vernberg,
1972). However, tropical and polar organisms, which live in a relatively constant
thermal region, have limited ability to alter their metabolic response to different
temperatures in an adaptive or compensatory manner. In contrast, many temperate zone organisms do acclimate and, rather than passively responding to
thermal changes, have evolved homeostatic mechanisms which allow them to be
partially insensitive to temperature fluctuation. Figure 1 graphically depicts this
VERNBERG: STUDIES OF COASTAL SYSTEMS
803
metabolic temperature response. If the metabolism of individual species which
are part of an estuarine system, can be influenced by temperature, what is the
metabolic response of the entire system? Do entire systems show adaptive phenomena as do the separate parts of the system? Do tropical and temperate zone
systems have similar response patterns? Are metabolic rates of all estuaries similar? Johannes et al. (1972) reported that one metabolic parameter, primary production, is higher in tropical benthic communities than in those in the temperate
zone. However, Koblentz-Mishke et al. (1970) found that primary production of
tropical phytoplankton was lower than in populations from higher latitudes.
Similar questions can be raised in reference to other functional attributes of
estuarine systems: what is the differential effect of temperature on reproduction
in estuaries; since the mortality rates (lethal limits) of organisms are different in
the tropical and temperate zones, what influence would man-made thermal perturbation have on system stability? Johannes and Betzer (1975) have published
a more detailed listing of differences between tropical and temperate shallow
water communities which furnishes a valuable background for the present presentation. They commented on the paucity of data and a significant increase in
our knowledge has not taken place since their review was published.
SYSTEMS
ANALYSIS
OF
NORTH
INLET
ESTUARY
Since 1970 a multidisciplinary team of marine scientists has been studying the
structure and function of a relatively undisturbed estuarine system, the North
Inlet Estuary. The long-term goals of this research program are: (1) to understand
in detail the nature of the complex interaction and interdependence of various
estuarine processes in a system relatively free of man's impact, and (2) to compare
the response characteristics of this system to other estuarine systems throughout
the world in order to understand the similarities and dissimilarities between estuaries. Comparative system studies have importance to the development of both
ecological theory and management procedures.
Study Site
North Inlet is a 30 km high-salinity estuary-marsh system 110 km NE of Charleston, South Carolina, with only minor freshwater runoff. Cord grass, Spartina altemifiora, covers a major portion
of the marsh, which is interlaced with numerous tidal creeks. Water and nutrient exchange between
the Atlantic Ocean and this estuary is through North Inlet, which is between Debidue and North
Islands. Additional exchanges take place between the North Inlet Estuary and Winyah Bay to the
south.
North Inlet is an ideal location for an intensive study of long-term estuarine dynamic processes for
the following reasons: (I) The boundaries of the estuary are well-defined. (2) The estuary and marsh
lands are relatively undisturbed. Its waters are classified as "highest quality" by the South Carolina
Pollution Control Authority. The estuary is sufficiently small to be studied, but large enough to have
distinctive estuarine characteristics. The inlet is approximately 0.55 mile wide. The total estuarine
and tideland areas cover an area of approximately 10.8 square miles. The distance from the inlet to
the pier at Clambank is approximately 1.9 miles by boat. (3) The marsh lands and estuary are sufficiently large to permit experimental manipulation and control of experimental areas, and extensive
land holdings provide space for construction of experimental ponds. Extensive oyster beds, as well
as large populations of other commercially important species, such as blue crab, shrimp and mullet,
are found in this region. (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. Tide elevation, wind speed and direction,
atmospheric pressure, and rainfall have been recorded continuously for more than 3 years. (5) The
flow exchange between the estuary and the Atlantic Ocean and Win yah Bay takes place in a few welldefined creeks which are being monitored. It is possible to determine inputs of water and nutrients
from groundwater, terrestrial run off and rainfall. (6) Most of adjacent wooded highlands and the
marshes are owned and protected by the Belle W. Baruch Foundation. The University of South
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1981
b
c
a
h
I
T
Figure I.
The generalized matabolic (M) response to temperature (T) of animals from different
climatic regions: a = polar regions; b = temperate zone; and c = tropics. I = low and h = high.
Carolina has a 25-year contract with the Foundation to manage the marine area. This arrangement
insures protection for long-term studies. (7) A staff of 45 associates has demonstrated not only its
ability in studying separate problems associated with coastal environments, but also its ability to work
on complex problems in a coordinated manner.
The North Inlet estuary is a dynamic environment from a physical as well as a biological point of
view. The semi-diurnal tide has a mean range of 1.6 m, however, during spring tides the tidal range
has exceeded 2.2 m with associated maximum currents of 1.4 m S-l The estuarine waters usually
have salinities in the range from 30 to 34%0, due to the low fresh water run off into the system.
However, after frontal passages or summer rain-thunder storms, the salinity has been measured as
low as 4%0 in the upper reaches of some creeks.
North Inlet is vertically homogeneous, with a weak horizontal salinity/sigma-t gradient from the
inlet to Winyah Bay. The major variation in the above physical parameters is explained by fluctuations
due to the tidal wave, thus North Inlet is a tidally-dominated estuary. North Inlet is classified as a
type I-a estuary in the Hansen-Rattray (1967) circulation-stratification diagram. Many southeastern
estuaries apparently fit this type (Kjerfve, 1972; 1974), which is an advantage in mathematical modeling of estuaries, as variations with respect to depth may be of minor importance, allowing for the
use of vertically integrated hydrodynamic equations in any flow-simulation effort.
There are a number of distinctive habitat types within the North Inlet Estuary. There are approximately 6,500 acres of marshland, chiefly dominated by Spartjrra altemiflora.
Creek bottoms show,
in addition to the sands merrtioned above, sandy mud and firm shell substrates. Oyster beds and reefs
are extensive; other intertidal zone habitats include open sandy beaches, protected sandy beaches,
mud flats showing varying admixtures of different-sized sand-mud particles, dunes, and forest-marsh
edge habitats.
NIMES
A conceptual model of the North Inlet Marsh Estuarine System (NIMES) has been developed (Fig.
2) which consists of three major subsystems: water column, benthic, and intertidal components. Each
subsystem has been further subdivided. For example, an oyster reef subsystem model has been
developed. Recently, Summers and McKellar (1979) have published a detailed model of NIMES.
For the past 3 years, a comprehensive study, funded by the National Science Foundation, has been
underway to study the exchange of substances (biological and non-biological entities) across the
boundary between NIMES and adjacent systems. Basically we wanted to know whether specific
substances are exported or imported from the estuary. Haines (1975) presented data which suggested
VERN BERG: STUDIES OF COASTAL SYSTEMS
805
NORTH INLET
ESTUARY
Water Column
Subsystem
Subtidal
Benthic
Subsystem
....
.. .. ........
..
'
'
·Sediment···
.; ••••• : :.: •••
. ,'
,"
-,'.
Nutlients
Figure 2.
tions.
Conceptual model of the North Inlet Marsh-Estuarine
Ecosystem and the forcing func-
that export from estuarine systems had little impact on offshore waters and that nutrient regeneration
on the continental shelf had a greater impact on primary production than nutrients originating from
terrestrial runoff to rivers and estuaries. Others have stressed the importance of export from estuaries
to oceanic food webs (Nixon, 1980).
Our study involved a synoptic sampling program which was done four times per year for 2 years.
Each quarterly sampling effort consisted of two 50-h periods during which samples were simultaneously collected every 60 min at three transects. The number of sampling sites at each transect varied
from two to three. One 50-h period covered the neap tidal cycle, the other the spring tidal cycle. The
principal materials synoptically sampled were: nutrients, sediments, micro- and macrodetritus, microbial ATP, phytoplankton and zooplankton. In addition, physical measurements were made to
determine water movement, which is vital to making flux determinations. Although all of the numerous
samples collected have been analyzed, the resultant data are still undergoing statistical evaluation and
definitive conclusions cannot be published at present. However, some preliminary findings follow.
Fluxes are computed as a cross correlation between material concentration and instantaneous
discharge. The concentrations are obtained from daily water samples. A simultaneous estimate of the
tidal discharge was simulated from a multiple-regression model based on the tide record. An II-month
time series of daily fluxes of organic carbon, total nitrogen, total phosphorus, chlorophyll-a, and
phaeophytin resulted. By averaging these fluxes over 30 days the tidal variability was eliminated,
yielding monthly mean values. Over the II months, there was a highly significant export of organic
carbon, total nitrogen, and a significant export of total phosphorus. Chlorophyll-a and phaeophytin
were simultaneously imported. The organic carbon flux plus the organics accumulated in the sediment
indicate a minimum of 960 g carbon fixed per square meter per year within the North Inlet marsh.
Other results indicate that although North Inlet is a well mixed system, large cross-sectioned variations exist in many parameters, particularly in the distribution of net velocity. Also, the temporal flux
variability between tidal cycles may, for many parameters, approximate or exceed the long-term (e.g.
annual) cycle.
Concentrations of chlorophyll-a vary directly with the stage of the tide. An average of 151% more
chlorophyll came in on flood tides than went out on ebb tides, resulting in a net import of 34%.
Microscopic data on the same samples showed an import of the total volume of the dominant species
of 36%, indicating a net loss of cells from the water column. We suggest that the loss of cells can be
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BULLETIN OF MARINE SCIENCE. VOL. 31. NO.3.
Table
I.
Net flux of organic
carbon
from North
Inlet Estuary
(Town
1981
Creek;
spring tides)
Net nux (kgcJtidal cycle)
Constituent
February
May
Dissolved Organic C
Particulate
Organic C
Microbial biomass
Suspended
Detritus*
Zooplankton
Macrodetritus
(S)
(B)
41,600
3,700
1,500
2,200
33.12
-2.89
-43.81
19,400
6,260
1,950
4,307
-9.06
NA
-3.18
Total organic
48,986.42
31,904.76
flux
• Susp. Detritus = POC ~ ATP-C'.
best explained by grazing processes,
rather than by settling. Similarly, a net import of ATP into North
Inlet Estuary of 3.58 kg occurred during a 25-h period in November
1977. This represents
an import
of approximately
11 x 103 kg of living microbial biomass or 367 kglkm2 of marsh, of which a large
proportion
was phytoplankton.
An enrichment
of the water column by sediment bacteria during an
ebbing tide has been shown. Bacteria account for about 10% of the total microbial ATP in flood tide
waters and about 80% of the total microbial biomass suspended
in the water during low tide periods.
To date there is overwhelming
support for the estuarine detrital-export
hypothesis.
The magnitude
of macro-detrital
export from North Inlet seems to be a function of tidal height and season of the
year. When compared,
there is a larger floating macro-detrital
flux than submerged
macro-detrital
flux. On a concentration
basis, macro-detritus
is only a small portion of the total detritus concentration. The direction of flux for macro-detritus
is distinct while that of smaller particles is less certain.
A preliminary
summary of carbon flux for two periods of the year and spring sampling regime is
presented
in Table I. This work provides a basis for comparative
studies on other estuarine systems.
Is our data site-specific
or does it reflect the behavior of other estuarine systems?
COMPARATIVE
STUDIES
ON TEMPERATE
AND TROPICAL
ZONE
ESTUARIES
Comparative systems studies from different climatic zone is a necessary research goal to further our basic scientific knowledge of estuarine dynamics and
to provide a better base for resource management. Since much development is
taking place in tropical countries, the need for cooperative estuarine studies involving temperate and tropical areas is becoming even more vital. I propose that
cooperative studies be undertaken to determine the validity of the following hypotheses: (1) Estuaries having similar areas, hydrographies, and tidal regimes,
share numerous dynamic physical properties, regardless of where they are located
in the world. (2) Although they share many dynamic characteristics, tropical
estuaries have some fundamental functional differences from those of temperate
estuaries. (3) Given adequate, comparable data bases, it is possible to develop a
general ecosystem model that would encompass more than a single estuarine
system. (4) The dynamic responses of polluted estuaries are peculiar to the specific natures of the pollutants rather than the result of geographical location. (5)
The relative amounts of materials imported or exported between estuaries and
coastal waters is more a function of climatic regime than hydrography. (6) The
physiological adaptations of organisms to different environmental conditions is
a good corollary of the functional adaptations of ecosystems to different environmental conditions.
In summary, various scientific disciplines have benefitted by using a comparative interdisciplinary approach. To achieve a broader understanding of dynamics
of ecological systems, the time is here to analyze the comparative responses of
tropical and temperate zone estuaries on a multidisciplinary basis. Since the physiological response of estuarine organisms to environmental parameters can be
VERN BERG: STUDIES OF COASTAL SYSTEMS
807
measured and their ecological importance to the ecosystem estimated, the integration of physiological and ecological viewpoints will enhance further our ability
to manage natural systems.
ACKNOWLEDGMENTS
The North Inlet Flux study is supported by Grant DEB8004275 from the National Science Foundation to the University of South Carolina. This is Contribution Number 365 from the Belle w.
Baruch Institute for Marine Biology and Coastal Research.
LITERATURE
CITED
Chesher, R. H. 1975. Biological impact ofa large-scale desalination plant at Key West, Florida. Pages
99-]53 in E. 1. Ferguson Wood and R. E. 10hannes eds. Tropical marine pollution. Elsevier
Scientific Publishing Co. Amsterdam.
Dame, R. F. (ed.). ]979. Marsh-estuarine systems simulation. Belle W. Baruch Library in Marine
Science, University of South Carolina Press, Columbia, S.C. 8: 260 pp.
Day, 1. W., W. Smith, P. Wagner, and W. Stowe, 1973. Community structure and carbon budget of
a salt marsh and shallow bay estuarine system in Louisiana. Center for Wetlands Resources.
Louisiana State University. Baton Rouge. 79 pp.
Farvar, M. T., and 1. P. Milton. ]972. The careless technology: ecology and international development. Natural History Press. Garden City, N.Y. ]030 pp.
Haines, E. B. 1975. Nutrient inputs to the coastal zone: The Georgia and South Carolina shelf. Pages
303-325 in L. E. Cronin ed. Estuarine research. Academic Press, Inc., New York. Vol. I.
Hansen, D. V., and 1. Rattray, 1r. ]966. New dimensions in estuary classification. Limn. Oceanogr.
II: 319-326.
10hannes, R. E., 1. Alberts, C. D'Elia, R. A. Kinzie, L. R. Pomeroy, W. Sottile, W. Wiebe,
1. A. Marsh, 1r., P. Helfrich, 1. Maragos, J. Meyer, S. Smith, D. Crabtree, A. Roty,
L. R. McCloskey, S. Betzer, N. Marshall, M. E. Q. Pilson, G. Telek, R. 1. Clutter, W. D. DuPaul,
K. L. Webb, and 1. M. Wells, 1r. 1972. The metabolism of some coral reef communities:
a team study of nutrient and energy flux at Eniwetok. Bioscience, 22: 541-543.
---,
and S. B. Betzer. 1975. Introduction: Marine communities respond differently to pollution
in the tropics than at higher latitudes. Pages 1-12 in E. J. Ferguson Wood and R. E. 10hannes eds.
Tropical marine pollution. Elsevier Scientific Publishing Co. Amsterdam.
Kjerfve, B. 1972. Circulation and salinity distribution in a marsh-lake system in coastal Louisiana.
Center for Wetland Resources, Baton Rouge, La. Tech. Report SG-72-06. 53 pp.
---.
1974. Reversal of the new flow in a Georgia estuary. Abstract. Trans. Amer. Geophys. Union
55: ] 136.
Koblentz-Mishke, O. J., V. V. Volkouinsky, and J. G. Kabanova. 1970. Plankton primary production
of the world ocean. Pages ]83-193 in W. Wooster ed. Scientific exploration of the South Pacific.
Natl. Acad. Sci., Wash.
Kremer, 1. N. 1979. An analysis of the stability characteristics of an estuarine ecosystem model.
Pages 189-206 in R. F. Dame ed. Marsh-estuarine systems simulation. Univ. South Carolina
Press, Columbia. S.C.
Nixon, S. 1980. Between coastal marshes and coastal waters-a review of twenty years of speculation
and research on the role of salt marshes in estuarine productivity and water chemistry. Pages
43-526 in P. Hamilton and K. B. Macdonald eds. Estuarine and wetland processes. Plenum
Press. New York and London.
Nixon, S. W. and C. A. Oviatt. 1973. Ecology of a New England salt marsh. Ecol. Monographs 43:
463-498.
Rice, H. 1. 1883. Translation of "The oyster and oyster culture" by K. Moebius, 1877. Report U.S.
Comm. Fish. 8: 683-752.
Summers, J. K., and H. N. McKellar, 1r. 1979. A simulation model of estuarine subsystem coupling
and carbon exchange with the sea: I. Model Structure. Pages 323-366 in S. W. Jorgensen ed.
State-of-the art in ecological modeling. International Society of Ecological Modeling. Copenhagen.
Vernberg, F. J. 1%2. Latitudinal effects on physiological properties of animal population. Ann. Rev.
Physiol. 24: 517-546.
---.
1977. Characterization of the natural estuary in terms of energy flow and pollution impact.
Pages 29-39 in Estuarine pollution control and assessment. Proc. of a Conf. Vol. I. U.S. Environmental Protection Agency. EPA-600/3-77-016.
808
BULLETIN OF MARINE SCIENCE, YOLo 31, NO.3.
1981
Vernberg, W. B., and F. J. Vernberg. 1972. Environmental physiology of marine animals. SpringerVerlag. New York. 346 pp.
Wiegert, R. G., and R. L. Wetzel. ]979. Simulation experiments with a fourteen-compartment model
of a Spartina salt marsh. Pages 7-40 in R. F. Dame ed. Marsh-estuarine system simulation.
Univ. South Carolina Press, Columbia, S.C.
Wolff, W. J. 1975. Mechanisms causing benthic secondary productivity in estuaries. Pages 267-280
in B. C. Coull ed. Ecology of marine benthos. Univ. South Carolina Press, Columbia, S.C.
Zieman, J. C., and E. J. Ferguson Wood. 1975. Effects of thermal pollution on tropical-type estuaries,
with emphasis on Biscayne Bay, Florida. Pages 75-98 in E. J. Ferguson Wood and R. E. Johannes
eds. Tropical marine pollution. Elsevier Scientific Publishing Co. Amsterdam.
DATE
ACCEPTED:
March 16, 1981.
ADDRESS:
Belle W. Baruch Institute for Marine Biology and Coastal Research. University of South
Carolina. Columbia. South Carolina 29208.