Climate change and biological traits: interglacial stability and higher glacial functional diversity in Late Quaternary molluscan assemblages of the Adriatic Sea (Italy)

Abstract Studies on the effects of long-term climate change on marine communities are crucial to our understanding of ecosystem resilience. The Late Quaternary fossil record, dominated by extant taxa, provides a valuable archive of past biotic responses to major climate fluctuations. While most studies on faunal turnover so far have focused on taxonomic identity, trait-based approaches are becoming increasingly common as they provide a stronger link to ecosystem functioning. We applied biological traits analysis based on a set of ecologically relevant traits to study functional turnover in nearshore molluscan assemblages from the Late Quaternary of the Po-Adriatic system (Italy). We found that the functional composition of fossil assemblages from the last two interglacials was statistically indistinguishable. In contrast, the assemblage from the last glacial was characterized by higher functional diversity, as indicated by dispersion, richness, and evenness metrics. Lower diversity in interglacial assemblages is related to the high dominance of the bivalve Lentidium mediterraneum , which strongly impacts the distribution of functional profiles. Functionally distinct species are more evenly distributed in the glacial assemblage, probably because of greater habitat variation coupled with individualistic responses of species to temperature changes. While functional similarity between the assemblages from the last interglacial and the Holocene indicates resilient response to natural climatic shifts, more extreme scenarios of future global warming will likely induce elevated rates of species turnover. Furthermore, additional anthropogenic pressures, including bottom trawling, eutrophication, and invasive species can also affect functional diversity to a higher degree. Thus, biotic responses to Late Quaternary climate change documented herein provide a valuable baseline of natural functional variability against which modern and future shifts in nearshore ecosystems of the Adriatic Sea driven by higher rates of warming and other human pressures can be assessed.