Historical ecology and species diversity of Mediterranean marine apex predators

The Mediterranean Sea has played a crucial role for the development and socio-economic progress of the civilizations that have inhabited it for millennia and exploited its marine resources, determining a strong competition for habitat and food between humans and apex predators such as large epipelagic fish (e.g. sharks) and marine mammals (seals, whales, dolphins). To date, the undeniable decline of most of them has led conservationists to consider the knowledge of natural/anthropogenic drivers of this decrease as a key-target for protection. We multidisciplinary analyzed the historical biodiversity of three dolphin species and five species of elasmobranchs, the great white shark and four locally extinct sawfish species, using more than 500 historical osteological specimens (i.e. skulls, rostra, jaws, vertebra and teeth from 19th-21st centuries) provided by a network of more than 30 museums and private collections in the Mediterranean region. We combined traditional and geometric morphometry species identification with ancient DNA and multi-element stable isotope analyses to assess biocomplexity spatio-temporal shifts, identify the drivers of such changes and whenever possible assess historical baselines of biodiversity. Main goals we achieved are 1) a full representation of the pre-extinction species diversity of the Mediterranean sawfish apparently greater than that expected from sightings and anecdotal/documental records; 2) relative species frequency shifts of dolphins in the Italian seas with the identification of putative historical interspecific hybrids and 3) ecological shifts for habitat preferences and for feeding and reproductive behavior in the historical and contemporary Mediterranean white sharks. Knowledge of the pristine baseline of large predator populations is useful for the comparison with the current levels of biocomplexity and related human impacts, assuming crucial relevance both in scientific knowledge of nature and in conservation management.