MICROHABITAT SELECTION BY BENTHIC FORAMINIFERA IN THE NORTHERN ADRIATIC SEA

A single station in the northern Adriatic Sea has been sampled seven times between December 1988 and November 1989. Quantitative data on Rose Bengal stained benthic foraminifera reveal that the majority live in the topmost centimeter of the sediment. However, most taxa occur throughout the top seven centimeters of the sediment column; taxa living exclusively on the sediment surface, or exclusively within the sediment, were not found. These results suggest that a simple bipartition between epifaunal and infaunal taxa is inadequate to describe foraminiferal microhabitat preferences. Three categories of benthic foraminifera are distinguished on the basis of their vertical distribution patterns. Taxa predominantly found in the top centimeter are termed epifaunal. Taxa which in all samples occur in the top 7 centimeters in about equal numbers are called predominantly infaunal. A third group, termed potentially infaunal, is largely restricted to the sediment top layer during part of the year, whereas it is predominantly found within the sediment in the remaining months. It is suggested that the latter taxa, most of which are generally considered as highly characteristic of dysoxic environments, track some critical oxygen level. Relations between test morphology and microhabitat are not as clear as often is suggested. In the northern Adriatic Sea the tests of most infaunal taxa are very small, and nearly all predominantly infaunal taxa are non-fossilizing agglutinated forms. In case these observations are representative for other shelf environments as well, the relative importance of the infaunal nicbe in fossil environments will often be under-estimated.