Foraminiferal assemblages in Biscayne Bay, Florida, USA: responses to urban and agricultural influence in a subtropical estuary.

This study assessed foraminiferal assemblages in Biscayne Bay, Florida, a heavily utilized estuary, interpreting changes over the past 65 years and providing a baseline for future comparisons. Analyses of foraminiferal data at the genus level revealed three distinct biotopes. The assemblage from the northern bay was characterized by stress-tolerant taxa, especially Ammonia, present in low abundances ( approximately 2.0 x 10(3) foraminifers/gram) though relatively high diversity ( approximately 19 genera/sample). The southwestern margin of the bay was dominated by Ammonia and Quinqueloculina, an assemblage characterized by the lowest diversities ( approximately 12 genera/sample) and highest abundances ( approximately 1.1 x 10(4) foraminifers/gram), influenced by both reduced salinity and elevated organic-carbon concentrations. A diverse assemblage of smaller miliolids and rotaliids ( approximately 26 genera/sample) characterized the open-bay assemblage, which also had a significant component ( approximately 10%) of taxa that host algal endosymbionts. In the past 65 years, populations of symbiont-bearing taxa, which are indicators of normal-marine conditions, have decreased while stress-tolerant taxa, especially Ammonia spp., have increased in predominance.