DETERMINING THE CAUSES OF BENTHIC CONDITION

A benthic index for northern Gulf of Mexico estuaries has been develop ed and successfully validated by the Environmental Monitoring and Asse ssment Program for Estuaries (EMAP-E) in the Louisianian Province. The benthic index is a useful and valid indicator of estuarine condition that is intended to provide environmental managers with a simple tool for assessing the ecological condition of benthic macroinvertebrate co mmunities. Associations between the benthic index and indicators of hy poxia, sediment contamination, and sediment toxicity were investigated to determine the most probable cause(s) of degraded benthic condition . The results showed that, on a local scale, the associations between the benthic index and potential environmental causes differed among es tuaries. In Pensacola Bay, FL, for example, there was a significant as sociation between the levels of toxic chemicals (e.g. DDT, silver, and TBT) in the sediment and the benthic index, especially in the bayous which have known sediment contamination problems. In Mobile Bay, howev er, degraded benthic communities were more closely associated with eut rophication and hypoxia. Nevertheless, a benthic index is a valuable t ool for identifying areas that could be already degraded and tracking the status of environmental condition in large geographical regions.