Comparing Aquatic Communities across Spatial and Environmental Scales in the Mobile Bay Estuary

Abstract

Abstract

Estuaries are important ecosystems that sit at the interface of marine and freshwater environments. Mobile Bay is a large, river-influenced estuary in the northern Gulf of Mexico. The mechanisms that govern the variability in aquatic communities of this system are not well understood. In Chapter 1, I quantified the fish and macroinvertebrate communities at 9 sites across a physical-chemical gradient. Species that could be used as indicators of the aquatic communities in the Mobile Bay were identified using multivariate methods. Salinity was found to be the most important environmental variable for structuring the aquatic communities, with dissolved oxygen and water temperature playing a secondary role. Seasonally, I found that aquatic communities showed the greatest differences across-sites during winter, probably due to migratory species spending part of their life history outside of the Mobile Bay. In Chapter 2, I investigated how Largemouth Bass used the variable forage base in the Mobile Bay estuary. Multivariate methods were used to identify important prey types to 467 adult Largemouth Bass along a spatial and seasonal gradient. I found that macroinvertebrates were important to Largemouth Bass diets at all 3 study sites. The greatest variation occurred during the spring, when Gulf Menhaden and other migratory species became available to predation, particularly at sites downstream in the estuary.