Title

Ecological and physiological factors affecting the assembly of littoral fish communities along an environmental gradient

Date of Award

1987

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biological Sciences

First Advisor

Stephen T. Ross

Advisor Department

Biological Sciences

Abstract

To examine community responses of fishes and macrocrustaceans to a variety of physicochemical factors, I documented spatial and temporal patterns of habitat use along a natural environmental gradient in Old Fort Bayou, Mississippi. The tidal freshwater and oligohaline habitats fluctuated more in terms of the physicochemical environment than the mesohaline habitat. The former two habitats have higher diversity and evenness than the latter site, probably because of the interfacing of the dominant secondary freshwater and estuarine faunas. I demonstrated that the responses of fishes and macrocrustaceans to spatial and seasonal abiotic patterns can be explained by the species' ecophysiology and energetics. These responses suggested that patterns of distribution and relative abundance might be largely controlled by abiotic processes. Second, I documented species-specific osmoregulatory and metabolic responses to various naturally occurring salinities among members of the Centrarchidae, a numerically dominant family in low salinity habitats. Experimental evidence suggested that the confamilial differences in time course of acclimation, osmoregulation and metabolic responses across salinities quantify underlying physiological processes that explain in part centrarchid distribution, abundance and differential use of saline environments. Finally, I documented significant differences in length/weight characteristics among the centrarchids using tidal freshwater and oligohaline sections of this natural gradient. For the sunfishes, changes in abiotic conditions and subsequent longitudinal shifts in potential prey type increased the cost of using low salinity habitats and reduced the abundance and presence of selected species. Basses were also impacted by both the changing abiotic environment and one major source of prey, young sunfishes. The obvious reduction or disappearance of Lepomis spp. brought about by increasing salinity and pH coupled with the high osmoregulatory load may in part explain the seasonal use of saline habitats by basses. Thus, I was able to explain community responses to abiotic patterns from an individual level approach. This approach allows investigators to test specific hypotheses which in turn aid in understanding general patterns of community structure.