Changing structure of benthic foraminiferal communities: implications from experimentally grown assemblages from coastal Georgia and Florida, USA

Environmental changes such as ocean warming or sea-level rise have a profound impact on shallow-water coastal environments. Benthic foraminifera have long been successfully used as indicators for ecologic responses. The propagule method is a useful tool to evaluate the reactions of entire assemblages of foraminifera when exposed to different environmental conditions. Here we present results from growth experiments of foraminiferal assemblages from three sites in coastal Georgia and Florida (USA) under different temperatures (18, 24 and 30 degrees C) and salinities (15 and 35). Results show that assemblages grown at the higher temperatures had greater abundances of foraminifera, whereas salinity was the primary factor in shaping the composition of the experimentally grown assemblages from the three sites. We also show that experimentally grown assemblages contain high numbers of exotic' species that result from successful propagule recruitment from outside of the original environments (e.g. the open shelf). Overall, opportunistic and previously termed pioneer species' proved to be the most successful constituents of the experimental assemblages, showing that reactions of foraminiferal assemblages to environmental changes can appear remarkably quickly (e.g. in the course of several weeks). Our observations on the faunal reactions to different temperatures and salinities indicate that ongoing environmental alterations of coastal areas will likely result in significant changes in the shallow-water foraminiferal assemblages of the coasts of Georgia and Florida. As such, our study provides general insights into the ecologic effects of current climate change.