PROPAGULE DISPERSAL IN BENTHIC FORAMINIFERA: BIOGEOGRAPHY AND THE OCCURRENCE OF “EXOTIC” TAXA

The many studies on benthic foraminiferal distribution patterns and biogeography have demonstrated a rich array of correlations between environmental conditions and regional occurrences. Such studies emphasize assemblages of “adult” populations. As shown in previous studies, dispersal in Foraminifera occurs largely as tiny juveniles or “propagules” that are generated largely through sexual reproduction, but also via asexual reproduction. Further, dispersal may transport foraminiferal propagules well beyond the natural distribution of conspecific adults. Such propagules can grow and reproduce if returned to appropriate environmental conditions. This raises several questions. How far do foraminiferal propagules disperse? Does foraminiferal dispersal by propagules fit the Bass Becking adage pertaining to small organisms, that “everything is everywhere,” or rather, is dispersal considerably more limited? To begin to address such questions, fine-grained sediments that included banks of foraminiferal propagules were collected from onshore and offshore sites near Cape Cod, MA (USA) from water depths of 80, 340, 750, and 2000m. The <53-micron sediment fraction was isolated by sieving, distributed into a series of small containers, and Foraminifera were grown under a variety of temperature, salinity, light, and dietary conditions. The resulting assemblages that grew were assessed and compared with naturally occurring assemblages from each of the collection sites. Several taxa typical of shallow-water settings, particularly Rosalina, grew at room temperature from sediments collected at all sampling depths. The propagules of these shallow-water taxa clearly disperse well beyond the distributional patterns of conspecifics adults. They have the potential of being effective colonizers and opportunists in the event of changing environments. Supported by NSF OCE-0850505 to STG and OCE-0850494 to JMB.