To what extent the size fraction affects an interpretation of planktonic foraminiferal assemblages - case study from Southern Adriatic

Abstract

Study of planktonic foraminifera, sampled from two levels of a 26 cm thick core, recovered at 1,200 m water depth, sheds some lights on the composition of foraminiferal assemblages that occur in the Southern Adriatic. Altogether 15 planktonic species (including one referred as undeterminable and two species recorded for the first time in the eastern Adriatic Sea) identified from 0-2 cm and 24-26 cm sediment intervals, were grouped into two assemblages: >63 μm fraction Turborotalita quinqueloba and >125 μm fraction as Globigerina bulloides-Globigerinoides ruber. The differences in core-top and core-bottom assemblages lie in: a) change in the relative proportion of some species; and b) slight differences in diversity indices. The relative proportions of species are strongly controlled by sieve mesh size, whereas the slight increase in diversity follows the increase in sieve mesh size. The benthic foraminifera, although constituting a negligible quantitative factor, show a slight increase in abundance and diversity of species with age.