Benthic foraminifera in the Long Island Sound (LIS) urban estuary constitute marginally marine, low-diversity assemblages, dominated by Elphidium excavatum. Buccella frigida is common in fine-grained sediments at water depths greater than ~15 m. Assemblages in grab samples taken in the mid-1990s differ considerably from those in samples taken in the early 1960s: Eggerella advena has become much less common, and Ammonia beccarii has become more abundant in western LIS. In order to determine the timing of faunal changes in detail, we studied benthic foraminifera in 7, ~50cm-long, cores collected in the Narrows, Western Basin, Central Basin and Eastern Basin. Age models are based on ²¹⁰Pb, ¹³⁷Cs, and (in one core) a pollen profile. Analyses of metals (e.g., Hg) and of the bacterial spore Clostridium perfringens were performed on the same cores. The time period represented in each core ranges from several centuries to <150 years.

Assemblages vary by water depth and by sub-basin. A core taken to the east of the Connecticut River contains assemblages with open marine shelf species (e.g., Eponides repandus). The relative abundance of the herbivorous species E. excavatum is highest (>90%) in cores at water depths <10 m, and increased throughout LIS from ~1850 AD on, possibly in response to anthropogenic eutrophication. The increase in relative abundance of Ammonia beccarii is a post-1960s phenomenon, and is most pronounced at sites at water depths <10 m and in western LIS. A core collected near the mouth of the Connecticut River shows a high relative abundance of A. beccarii in post-1960 samples, despite its location in eastern LIS, possibly as a result of high nutrient influx from the river. In the Gulf of Mexico and Chesapeake Bay, recent increases in relative abundance of A. beccarii have been linked to increased hypoxia/anoxia, but our data, the species’ biogeography and laboratory behavior suggest that in LIS regional warming may also be important.