Foraminiferal patterns in two trophically different regions: the northern Adriatic Sea and the southern Levantine Basin.

Abstract

In spite of the fact that the northern Adriatic Sea and southern Levantine Basin are trophically quite different, the benthic foraminiferal standing stocks through the seasons were found to be in the same range. This suggests that the amount offood (organic matter) available at the sediment-water interface was not the major factor that determined the foraminiferal abundances. Our data suggest that not simply the amount of food, but the delicate balance between organic matter supply and oxygenation was the important ecological factor. The assemblages of the two areas have a lot of taxa in common but they differ significantly with respect to diversity. The Levantine assemblages contain a high amount of species occurring in low frequencies. In the more eutrophic Adriatic Sea the simple diversity is considerably lower, as can be expected in such a seasonally highly variable setting. These assemblages contain more opportunistic taxa than those of the oligotrophic Levantine basin. In the latter, an increase of infaunal taxa with water depth can be observed. A comparison of the in-sediment distributions of five representative taxa demonstrate a large resemblance for the different stations. Considering the substantial differences in oxygenation as well as organic matter concentration, this implies that the general microhabitat partitioning is inherent to these taxa themselves and not dependent on environmental variation. For most of these taxa, no correlation was found between the average living depth, or the in-sedilTlent distribution, versus oxygenation. An exception formed the miliolids, their in-sediment distribution appeared to be rather strongly dependent on sediment oxygenation.