Harbor estuary, will undoubtedly affect the suitability of the 

 estuary as a nurseryground. 



A reduction of freshwater inflow will eventually increase the 

 homeohalinity of this estuarine system. A displacement of the 

 current mesopolyhaline zone further upstream will affect the 

 distribution and abundance of larval and juvenile fishes and 

 shrimps. Upestuary marshes are critical areas for early devel- 

 opmental stages of fishes and shellfish (Weinstein 1979). The 

 inflow of freshwater, which currently inundates marshes and 

 abandoned rice fields in the Cooper River-Charleston Harbor 

 estuarine system is more important in maintaining upestuary 

 marsh habitat suitable for fishes and decapod crustaceans. After 

 rediversion, much of this habitat, currently subject to overflow, 

 will no longer be available as a nursery due to lowered water 

 levels and higher salinities (U.S. Army Corps of Engineers 

 footnote 2). A substantial reduction in nursery habitat could 

 affect the entire estuarine foodweb. Estuarine salt marshes are 

 highly productive, being dominated by cordgrass (Spartina) 

 which ultimately provides a source of food to organisms in the 

 estuarine system (Massmann 1971). Thus, the nursery functions 

 of estuaries are closely related to the viability of plant commu- 

 nities. Alteration of areas which supply much plant detritus 

 may lower the numbers of detritus-algae consumers which, in 

 turn, will eventually limit subsequent trophic levels. This may 

 be particularly troubling from an economic point of view be- 

 cause the abundance of commercially valuable penaeid shrimp 

 is directly related to the absolute area and type of estuarine- 

 intertidal vegetation (Turner 1977). 



The habitat of stenohaline marine species may not be af- 

 fected deleteriously by rediversion. In fact, these species will 

 probably penetrate even farther upriver than they currently 

 do. Because numbers of species and individuals of fishes and 

 decapod crustaceans are now higher in more saline reaches of 

 the river, species diversity of areas in the Cooper River- 

 Charleston Harbor which are currently lower in salinity could 

 be increased by rediversion. Increases in diversity probably will 

 be attributed to higher numbers of stenohaline marine species 

 rather than euryhaline or resident estuarine species; however, 

 many estuarine species, whether resident or transient, are liv- 

 ing near the limit of their physiological tolerance of tempera- 

 ture or salinity, so further alteration of the environment may 

 exclude some species permanently (Odum 1970). 



In addition to changes in diversity, the species assemblages 

 as we have defined them by station location will probably be 

 altered following rediversion. Whether this alteration will en- 

 tail a mere shifting of assemblages upriver or the introduction 

 of completely different groupings of species will depend on the 

 effects of rediversion on competition and predation. Food re- 

 sources can be limiting in estuaries (Lasker 1975; Houde 1978; 

 Laurence 1977). If habitat is lessened and the opportunity for 

 spatial segregation becomes minimal, then seasonality and 

 other forms of temporal segregation may be the only means of 

 reducing competition among species with similar food require- 

 ments (Weinstein 1979). Seasonality, which includes differ- 

 ences in spawning periods as well as density-independent fac- 

 tors such as temperature, dissolved oxygen, and nutrient 

 inputs, may mitigate any changes in competition or predation 

 (Enright 1976) precipitated by man-made perturbations. In 

 turn, the adverse effects of rediversion on the estuarine biota 

 may be neither drastic nor irreversible, although this remains 

 to be seen. 



ACKNOWLEDGMENTS 



We are grateful to all persons who assisted in collection of 

 specimens and data in the field, especially J. Miglarese, R. 

 Richter, and J. Bishop. We thank T. D. Mathews and K. H. 

 Austin for analysis of water samples; K. Swanson for prepara- 

 tion of figures; N. Kopacka for assistance with computer pro- 

 gramming; and B. J. Ashby and L. Hodges for typing and 

 retyping the manuscript. The field study and manuscript ben- 

 efited from comments by our colleagues: E. B. Joseph, V. G. 

 Burrell, Jr., G. R. Sedberry, and C. Bearden. 



The data were collected and automated by financial support 

 from the Coastal Plains Regional Commission (Contract 

 10340031) as part of the Estuarine Survey Program of the 

 South Carolina Marine Resources Center and were analyzed 

 and published through funding from NOAA Office of Sea 

 Grant (Grant 00140-93027). 



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