WARMING OCEANS AND POTENTIAL RANGE EXPANSION OF "SMALLER" BENTHIC FORAMINIFERA: INSIGHTS FROM PROPAGULE EXPERIMENTS

Shifts in the biogeographic ranges of species are among the many consequences of anthropogenic climate change, and most documented shifts have been in a pole-ward direction, consistent with temperature rise in the oceans. Range shifts of all organisms hinge on effective mechanisms of dispersal and subsequent recruitment in changing environments. Benthic foraminifera disperse largely via propagules, tiny juveniles generated primarily by sexual reproduction in a manner analogous to spawning in marine invertebrates. Following dispersal, propagules settle to the seafloor and collective form a “propagule bank” which includes both autochthonous and allochthonous species. Mature assemblages of foraminifera can be grown from propagule banks in the lab under controlled experimental conditions, and the application of non-ambient temperatures can promote the growth of allochothonous taxa. Here, we grew assemblages of benthic foraminifera from propagule banks collected from 4 sites ranging from 70 – 2200 m south of Cape Cod, MA (USA) at temperatures ranging from 4 - 25°C. Several species grew commonly at elevated temperatures, particularly Rosalina cf. R. floridana and Brizalina lowmani which grew from all sites. In addition, Bolivina variabilis grew from 2 of the sites (340- and 740-m). All three of these species are absent from the in situ assemblages examined for this study, and in general, are known from tropical to warm temperate regions (e.g., the Gulf of Mexico and warmer parts of the Atlantic). These species in particular all have the ability to reside in the water column as adults. Some species of Rosalina are known to calcify a float chamber prior to gametogenesis. B. lowmani has been reported in large abundances in plankton tows in the GOM, and B. variabilis (= Streptochilus globigerus) has a well-documented tychopelagic (coupled benthic – pelagic) mode of life. Because the individuals examined in this study were grown from propagules, it is highly likely that all of these species are capable of reproducing in the water column. These species disperse very effectively well beyond their documented biogeographic ranges and may be among the first “smaller” foraminiferal species to effectively expand their ranges. Supported by NSF OCE-0850505 to STG and OCE-0850494 to JMB.