Biodiversity of benthic invertebrate communities in the Mobile-Tensaw Delta region of Alabama

The benthic invertebrate macrofauna and larger meiofauna in the Mobile-Tensaw Delta was sampled from December 2010 to June of 2011 along a salinity gradient from the brackish waters of Mobile Bay up into the fresh waters of the Tensaw River. Community composition varied, in both composition and abundance, along the salinity gradient. The brackish regions were dominated by polychaetes and crustaceans. These benthic communities transitioned to oligochaete and chironomid larvae dominance as the salinity decreased. There was high abundance in the number of individuals and the number of higher taxa in the spring and summer months, while the winter had very few benthic invertebrates. The high level of variability at the study sites, over short time scales, suggested that the strength and frequency of biotic interactions is reduced and abiotic factors drive ecosystem dynamics. The realized niche overlap among benthic invertebrates varied through time, from periods of moderate of overlap, to very little overlap. As abiotic factors take precedence in shaping these benthic communities, species distributions and abundances may become relatively independent of one another. Abiotic effects have implications for how the food web in this tidal freshwater marsh is structured. If what is shaping benthic invertebrates niches in this area, biotic or abiotic variables, could be distinguished, it could indicate that this delta ecosystem may operate more as a mosaic of independent patches, as opposed to an interconnected ecosystem. Many estuaries are believed to be highly interconnected habitats, not only in terms of food web dynamics and nutrient cycling, but in their ecosystem services to surrounding coastal areas and to humans. It is important to establish the role that abiotic and biotic factors play in shaping the distribution and abundances of the benthic invertebrate communities in this tidal freshwater marsh. Better knowledge about what shapes these freshwater systems can lead to better protection and more informed management choices.