DISPERSAL AND PROPAGULE BANKS OF BENTHIC FORAMINIFERA: SHELF TO BATHYAL SETTINGS, WESTERN NORTH ATLANTIC

Recent dispersal studies on benthic foraminifera from soft-sediment substrates show that many species disperse as small juveniles or propagules. Propagules undergo passive transport in the water column and subsequently settle onto marine sediments. Further, not all species present in sediments as propagules are represented in the in situ assemblages, indicating that propagules can disperse from allochthonous sources. The propagules present at any given site constitute a “propagule bank”. Here we compare in situ foraminiferal assemblages from 4 sites south of Cape Cod (from water depths of 80, 340, 750, and 2200 m) to assemblages grown experimentally at different temperatures from the corresponding propagule banks present in the fine sediment fraction from each site. The objectives are to determine the effects of temperature and offshore distance on these experimentally grown assemblages, and to identify species that disperse beyond the distribution of conspecific adults. The experimental assemblages were grown at 4, 7, 22, and 25°C. The 4°C and 7°C treatments were kept in the dark and fed a combination of Dunaliella and Isochrysis while the 22°C and 25°C treatments were grown with exposure to light, which allowed for algal growth. Preliminary results show that the propagule banks include foraminifera not present in situ and that species composition varied with temperature. Leptohalysis scottii was abundant in assemblages grown from all sites at 4°C and also appeared at 7°C. Bathysphon sp. was abundant in assemblages grown from all sites at 7°C. Rosalina sp. was abundant in the 22°C and 25°C experimental assemblages grown from all sites. The Rosalina sp. however did not occur in any of the in situ assemblages. Other notable taxa found widely in the experimental assemblages include Textularia sp. and multiple Bolivina sp. These results suggest that: 1. Propagules, particularly those of Rosalina sp., disperse from allochthonous sources. 2. Different species of foraminifera grew at different temperatures. 3. The most common species in the in situ assemblages were generally absent from the experimentally grown assemblages. 4. Several species display opportunistic behavior. Funded by NSF grants OCE 0850505 to STG and OCE 0850494 to JMB.