Date Awarded


Document Type


Degree Name

Doctor of Philosophy (Ph.D.)


Virginia Institute of Marine Science


John A. Musick


The first two chapters of this study examine faunal composition and latitudinal patterns in diversity of fishes in warm-temperate and tropical estuarine waters of the western Atlantic from La Plata River (35&\sp\circ&S), Argentina, to Chesapeake Bay (37&\sp\circ&N), USA (33 faunal reports). Species distributions generally corresponded with previously recognized marine zoogeographic regions, and cluster analyses also showed that faunal similarity among estuarine sampling sites was related to the type of sampling gear used and to the type of habitat that was sampled in each estuary. The total number of fish species reported is positively related to the size of the area sampled and number of individuals collected, although latitude (or temperature related phenomena) played a critical role in determining richness and equitability among species. The results of this study show that interaction between disturbance frequency or magnitude (e.g. temperature and salinity variations) and the rate at which dominance is achieved can result in a predictable pattern of fish species diversity in estuaries. In the last chapter the structure of estuarine fish assemblages in Patos Lagoon (32&\sp\circ&S), Brazil, and York River (37&\sp\circ&N), USA is described using historical bottom trawl data, to examine similarities between geographically isolated fish assemblages. Within broad limits structural assemblage patterns were correlated with temperature changes, although the intensity of seasonal changes differed between them. The lowest winter temperatures in the York River were correlated with a pronounced seasonal species emigration from the estuary, a pattern which was not observed in the more thermally moderate Patos Lagoon. Patos Lagoon was more diverse in terms of equitability and species richness than the York River at any particular point in time, but the seasonal pattern of use of the estuary (i.e. nursery and feeding grounds) was similar between localities, and did not differ from other temperate or tropical estuaries. Comparing fish assemblages using a nondimensional diversity index (i.e, H&\sp\prime&) masks interesting differences in species richness and relative abundance, and measurements of species richness and equitability (rarefaction and relative species rank techniques) independent of sample size should be used in order to determine richness and equitability differences among systems.



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