Assessing biotic response to anthropogenic forcing using mollusc assemblages from the Po-Adriatic System (Italy)

Preserving the adaptive capacities of coastal ecosystems in the Anthropocene requires an understanding of their natural variability prior to modern times. We quantified responses of nearshore molluscs assemblages to past environmental changes using 101 samples (c. 57300 specimens) retrieved from the subsurface Holocene succession and present-day seabed of the Po-Adriatic System (Italy). Present-day assemblages shifted in their faunal composition with respect to their mid-late Holocene counterparts. Major differences are observed in lower nearshore settings, where present-day samples show higher heterogeneity, reduced standardized richness, reduced relative abundance of Lentidium mediterraneum, and increased relative abundance of Varicorbula gibba, scavengers (genus Tritia), and deposit feeders (nuculid bivalves). A dominance of infaunal opportunistic species and shifts towards detritus-feeding and scavenging are often associated with disturbed benthic habitats. Our results suggest that the ongoing anthropogenic stressors (mainly bottom trawling and non-native species) are currently shifting benthic communities into novel states outside the range of natural variability archived in the fossil record.