PROPAGULES OF BENTHIC FORAMINIFERA AND THE OFFSHORE DISPERSAL OF MODERN SHALLOW-WATER TAXA

Small juvenile foraminifera function as propagules, undergo dispersal, and reside in the fine sediment fraction of many marine depositional systems, as shown in previous studies. These propagules can survive in unfavorable settings, and subsequently grow to maturity when exposed to appropriate environmental conditions. To examine the extent of offshore dispersal by shallow-water taxa, we collected propagule banks from fine-grained sediments at a series of offshore sites that include stations at 80, 340, 750, and 2000 m water depth south of Cape Cod (USA) in the western Atlantic in May, 2010. At each site, we first retrieved bottom water using CTD casts equipped with a rosette of 10-l Niskin bottles. We then collected sediments using a Soutar box corer, removed the top ~1-2 cm of sediment using a siphon, and used the local bottom water to process the samples. The fine sediment fraction [<53 microns] from each site was isolated by sieving, distributed to a series of small containers, and foraminifera were grown under a variety of temperature, salinity, and light/dark conditions. Here we focus on those foraminifera that grew from all sites with illumination at room temperature (~22° C) and/or 25° C, temperatures that are considerably elevated relative to the ambient temperatures of these sites (7° C or less). Two common shallow-water taxa, Bolivina sp. and Rosalina sp., grew abundantly from all sites under these conditions. Morphologically, individuals of these respective taxa are quite similar from all sites. However, a comparison of SSU rDNA sequences for Bolivina sp. shows that the population structure is more complicated and indicates gene flow between some populations, but not others. Most likely, this suggests multiple sources for the dispersal of the Bolivina propagules. Funded by NSF OCE-0850505 to STG and OCE-0850494 to JMB.