LANDWARD-DIRECTED DISPERSAL OF BENTHIC FORAMINIFERAL PROPAGULES AT TWO SHALLOW-WATER SITES IN THE DOBOY SOUND AREA (GEORGIA, USA)

Transport of foraminiferal propagules is an important mode of dispersal in benthic foraminifera. Known to occur from tidal marshes and estuaries to deep-water environments, the former are particularly vulnerable to ongoing climate change. Because rising sea levels can have profound implications on local salinity and associated faunal compositions, transport of foraminiferal propagules within these environments can be crucial for local assemblages to respond to changing conditions. Here we focus on a shallow-water environment in southeastern Georgia to evaluate whether propagule transport occurs evenly or whether it shows a predominant direction, such as land- or seaward. Two sites were sampled in the Doboy Sound area: the southern tip of Sapelo Island and a site on the North River located approximately 10 km inland. We applied the propagule method using the fine fraction of the sediments that contains the propagule bank. Experimental conditions in the laboratory included three temperatures (18, 24 and 30 degrees C) and three salinities (15, 25 and 35) to simulate a range of environments that might trigger the growth of various foraminiferal species. While adult in situ assemblages of both sites were at least partly influenced by the adjacent salt marshes, experimentally grown assemblages were dominated by mudflat, estuarine or more open marine species. Thus, propagule transport from the more terrestrial side of the assemblage gradient is limited, while propagules of more marine species can be transported far into the extensive estuarine system of the study area, where they can remain viable within the local propagule banks. Results provide important insights into possible changes in foraminiferal assemblages with rising sea-level on the Georgia coast.