RESILIENCE OF DELTA-ASSOCIATED BENTHIC COMMUNITIES DURING THE LATEST QUATERNARY GLACIAL-INTERGLACIAL CYCLES IN THE PO PLAIN-ADRIATIC SEA SYSTEM

Global environmental changes present increasing threats to transitional ecosystems and their biodiversity. The Quaternary fossil record provides a way to quantify the effects of natural climatic and sea-level oscillations on these ecosystems. Such historical perspective may help us to understand and predict long-term biotic responses to the ongoing anthropogenic changes. Here, we use sediment cores from deltaic deposits of the Po River sampled within three key time-intervals: (1) Pleistocene interglacial (~125–120 ka), (2) late glacial (18–14 ka), and (3) present interglacial (< 6 ka), to test if delta-associated benthic communities were characterized by a long-term persistence, resilient reassembly or continuous compositional change during the latest Quaternary glacial-interglacial cycles.

Quantitative analyses of mollusk fauna reveal striking similarity between the two interglacial assemblages. Strong overlap among samples in the non-metric multidimensional scaling (nMDS) ordination space and positive correlation of species rank abundances between the two time intervals suggest a reassembly of analogous deltaic communities during the successive interglacials. In contrast, late glacial samples form a distinct cluster in the nMDS ordination and are characterized by a higher share of species with a boreal affinity or cosmopolitan biogeographic distribution compared to the interglacial assemblages. This compositional shift is reflected by much weaker correlation of species rank abundances between the glacial assemblage and the two interglacial faunas.

Our results suggest that deltaic mollusk-dominated benthic ecosystems of the Adriatic Sea have shifted back and forth between two ecosystem states and responded with remarkable resilience to major, long-term shifts in climate and sea-level. The recognition of such high resilience in response to long-term natural changes provides an important baseline for assessing effects of recent anthropogenic changes in deltaic ecosystems.