Experimental assembly of foraminiferal communities from coastal propagule banks

Benthic foraminifera (protists) have long been recognized as sensitive indicators in studies on natural and human-induced environmental, paleo-environmental, and climate change. These wide-ranging applications are founded on more than a century of field-based investigations in which environmental data were related to species distributions, and have subsequently been refined by the development of chemical proxies and a variety of culture-based studies. The recent discovery of foraminiferal propagule banks that occur in the fine-sediment fraction of marine depositional settings provides a novel experimental tool for examining the ecology of benthic foraminifera, their processes of dispersal, and the responses of multi-species assemblages to changing environmental conditions. In the 'propagule method' presented here, we use experimental arrays in which foraminifera are grown from propagule banks under different controlled abiotic conditions. We examined the roles of temperature, salinity, and site (exposed vs. protected) in structuring coastal assemblages and show that, because individual species respond differently, distinct assemblages grew from the same propagule bank under different environmental regimes. Temperature was the most important factor distinguishing experimental assemblages, whereas exposure of the collection site (e.g. to waves and currents, that promote or limit species dispersal to and from each site) was most important in determining species richness. The diversity of the propagule bank therefore imparts resilience to foraminiferal associations and provides a rapid-response mechanism for changing environments. This method further provides a tool for documenting changes in coastal assemblages that potentially result from warming or cooling climates.