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The foraminiferal record of the northern Adriatic: Brijuni Islands and Piran bay (same depths, different geologic background)

The northern Adriatic is a coastal marine ecosystem characterized by rapid Holocene transgression, regional climate fluctuations and strong anthropogenic pressure. Two 1.6-m-long sediment cores were taken from the eastern coast of the northern Adriatic at water depth of 44 m by UWITEC piston corer with hammer action in summer 2013. Cores were retrieved offshore from Brijuni Islands where due to the Cretaceous limestones in the hinterland terrigenous input is limited and in Piran bay with greater input due to weathering of the Paleogene clastic deposits exposed in the surrounding area. The cores cover approximately the last 10, 000 years and therefore document shifts in marine habitats and foraminiferal assemblages related to Holocene sea level changes and recent anthropogenic activities. The uppermost 20 cm of each core were sliced into 2 cm intervals whereas the core was sliced into 5 cm intervals and sedimentological, geochemical and micropaleontological analysis were performed. Altogether 245 foraminiferal species from Brijuni- and 210 species from Piran-core were identified based on their morphological characteristics, with species richness varying between 43 and 70 and 16 to 47 species in individual samples. Diversity is relatively stable throughout the cores and increases only in the uppermost 40 cm. The lowermost sediments of both cores consist of foraminiferal assemblages, dominated by epiphytes. Infaunal species attain low abundances in the lowermost cores (125-160 cm) and increase in abundance towards the top. Among epiphytic species, the permanently motile, grazing morphotype is dominant in the lower part and decreases in abundance towards the upper core. Temporarily attached epiphytic species show the opposite trend, reaching maximal values in the uppermost sediments (0-20 cm) the anthropogenic impact over the last century is reflected in a sharp increase in the concentrations of nutrients, persistent organic pollutants and heavy metals. Foraminiferal communities respond to these disturbances by increasing abundances of stress tolerant species, although Foram Stress Index retrained relatively high values (between 5 and 8).

Northern Adriatic, Benthic Foraminifera, Stress tolerant species

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