REGIONAL RESPONSE OF MARINE BIODIVERSITY TO CLIMATE-DRIVEN SEA-LEVEL CHANGES: AN EXAMPLE FROM THE ADRIATIC SEA

Climate-driven changes in marine biodiversity during the latest Quaternary ice ages are poorly understood. This is largely because lowstand (glacial) records of marine communities are difficult to study due to their offshore location. Thanks to extensive sampling efforts in both proximal and distal parts of the Adriatic Sea, we now have an opportunity to quantitatively evaluate changes in marine biodiversity of benthic communities during latest Quaternary sea-level changes.

The Po Delta (situated nowadays in the northern Adriatic) resided in its current location during the previous interglacial (isotope stage 5.5, ~125ka). During the following glacial phase, the regional sea-level dropped by ~120 meters and the Po Delta shifted ~200km south-eastward to the edge of the Mid-Adriatic Deep. Subsequently, with the onset of the current interglacial phase, the Po Delta reverted to its present-day location. Here, we document biodiversity patterns across climate cycles by comparing proximal core samples from the Po Delta (the previous and current interglacial time intervals) and the distal core samples from the Mid-Adriatic Deep (the end of the last glacial interval).

Alpha diversity (mean sample-standardized diversity) of lowstand to early transgressive delta samples from the latest Pleistocene of the Mid Adriatic Deep (8.18) was elevated when comparing to highstand samples of the previous (7.50) and current (7.01) highstand deltas. In contrast, beta diversity (measured here as a mean pairwise Sorenson dissimilarity) is notably lower in lowstand samples (0.29) when comparing with highstand samples (Holocene=0.37, Pleistocene 5e=0.36).

The differences in alpha and beta diversity between lowstand and highstand deposits may represent taphonomic processes (a more extensive time-averaging in lowstand systems tracts) or ecological processes (ecosystem changes in response to long-term climate change). Whereas the preliminary results presented here are insufficient to distinguish between those two rival hypotheses, they indicate that the regional biodiversity pattern varies along the depositional profile of a sedimentary basin.