MOLLUSK ASSEMBLAGES AS PROXIES FOR INTERPRETING WATER QUALITY: THE IMPACT OF ANTHROPOGENIC MANIPULATION OF THE CALOOSAHATCHEE WATERSHED, SOUTHWEST FLORIDA

The Caloosahatchee Estuary, located in Southwest Florida, supports over 500 species of benthic macroinvertebrates. These organisms are an important part of the trophic web and play a significant role in the sedimentary regime of the estuary. The majority of these macroinvertebrates is sessile, and therefore especially vulnerable to environmental stressors and changes in water quality. The Caloosahatchee watershed drains from Lake Okeechobee to the Gulf of Mexico. Since the 1880s, the hydrology of this watershed has been significantly altered by land and canal development, resulting in an artificial connection to Lake Okeechobee. This connection is used to discharge excess freshwater into the Gulf of Mexico, resulting in decreased salinity throughout the estuary. Mollusks are an important part of the Caloosahatchee's macroinvertebrate fauna. As such, they are useful proxies for interpreting pre- and post-anthropogenic water quality within the river. This study compares life and death assemblages of mollusks along the present-day salinity gradient down the Caloosahatchee's estuarine axis. The results from this analysis will be used to determine what environmental parameters control their temporal and spatial variability. Although the comparison of death assemblages to their living counterparts is a standard approach for evaluating and interpreting paleoecological data, some uncertainty still reigns over the degree of fidelity afforded by such a comparison. This study seeks to address some of these uncertainties by determining whether life-death assemblage fidelity resolution is high enough to observe differences or similarities among communities over a relatively short (≈150 years) timespan. The study took place between June 2005 and January 2006. Four sites were sampled along the lower reaches of the Caloosahatchee River monthly during the wet and dry seasons. The in situ collection was compared to the South Florida Water Management District's invertebrate records database using multivariate statistical methods. Preliminary results show differences between the life and dead assemblages, and also between the life assemblages of each site. Clearly, salinity dictates the composition of the live communities, but it is not yet known whether this pattern is also present in the death assemblages.