A COMPARISON OF IN SITU AND EXPERIMENTALLY GROWN FORAMINIFERAL ASSEMBLAGES FROM THE “MUD PATCH” CONTINENTAL SHELF SITE (CAPE COD, USA): THE ROLE OF TEMPERATURE

Tiny juvenile foraminiferans that measure just 10s of microns are abundant in fine-grained sediments of many marine depositional systems, as shown by previous studies. These tiny juveniles collectively comprise a “propagule bank” that includes offspring derived from local populations as well as those that dispersed from other regions. Here we compare a naturally occurring, in situ assemblage of benthic foraminifera with a series of assemblages grown experimentally from the corresponding propagule bank from the same site under different temperatures that range from 4 – 25 ºC. Sediments were collected from the “Mud Patch”, a site located at 80 m water depth on the continental shelf south of Cape Cod (Massachusetts, USA) with a Soutar box corer in September, 2009. Sediments were sieved immediately after collection using bottom water from this site. The sediments finer than 53 microns were retained and used to experimentally grow assemblages from the propagule bank. Sediments coarser than 53 microns were fixed / preserved in either paraformaldehyde or ethanol and used to assess the in situ assemblage at this site. Whereas the in situ assemblage is dominated largely by Globobulimina turgida, Bulimina aculeata, Bathysiphon sp., and Elphidium cf. E. excavatum, the experimentally grown assemblages are dominated primarily by taxa that are either rare or absent from the in situ assemblage. These include Textularia earlandi, Bolivina cf. B. simplex, and, in some assemblages by Chitinosaccus sp. or Rosalina sp. Bathysiphon sp. is the only foraminiferan abundant in both the in situ and experimentally grown assemblages.