EXPERIMENTALLY GROWN FORAMINIFERAL ASSEMBLAGES FROM THE "MUD PATCH" CONTINENTAL SHELF SITE (CAPE COD, USA): THE ROLES OF TEMPERATURE AND DIET

Fine-grained sediments of many marine depositional systems contain a bank of foraminiferal propagules, tiny juveniles that originated either from local or distant populations. As shown previously, these propagules can grow to maturity when exposed to appropriate environmental conditions. Further, propagule banks from the same site can be grown under different conditions thus producing distinct assemblages of mature foraminifera. Here we examine the influence of temperature and diet on assemblages grown from propagule banks collected at a site known as the “Mud Patch” located south of Cape Cod (USA) at 80 m water depth in the western Atlantic. We grew assemblages at 4, 7, 12, 18, ~22, and 25° C. Those grown from 12 to 25° C were provided with light which allowed algal cells present in the sediments, particularly diatoms, to grow. Those grown at 4 and 7° C were grown in the dark and fed a mixture of two food organisms, Dunaliella and Isochrysis approximately every 10 days. Assemblages were harvested after growth by sieving with a 63-µm, stainless-steel sieve and preserved in either ethanol or buffered paraformaldehyde. Assemblages were compared with each other as well as with the naturally occurring, in situ assemblage from the Mud Patch at the time of collection. The in situ assemblage is dominated largely by Globobulimina turgida, Bulimina aculeata, Bathysiphon sp., Saccammina atlantica, and Elphidium cf. E. excavatum. Of these, only Bathysiphon sp. grew abundantly in any of the experimental assemblages. Rather, experimentally grown assemblages were dominated by species that were either rare or absent in the in situ assemblages, including Textularia earlandi, Eggerella advena, and Bolivina sp. which grew from 12 - 25° C with exposure to light, and Leptohalysis scottii and Saccmmina sp. 2 which grew abundantly at 4 or 7° C in the dark with supplemental food provided. The in situ assemblage was distinct from all experimentally grown assemblages, but statistically was more similar to those grown at the coldest temperature. Results suggest that both temperature and food availability are important in structuring foraminiferal assemblages. Funded by NSF OCE-0850505 to STG and OCE-0850494 to JMB.