30-year ecological legacy of illegal harvesting of the date mussel Lithophaga lithophaga along the Apulian coastline (SE Italy)

Illegal harvesting of the date mussel Lithophaga lithophaga has long been recognized as one of the most destructive human pressures on Mediterranean rocky reefs, historically causing extensive habitat loss and the large-scale formation of barren grounds. This degradation has been particularly dramatic along the Salento coastline, where past large-scale surveys documented severe damage. In this context, the present study assessed the current impact of illegal date mussel L. lithophaga harvesting along the southern Apulian coastline, focusing on the spatial distribution of the damage, the persistence of barren grounds, and their relationship with the population densities of the sea urchins Paracentrotus lividus and Arbacia lixula . Between summer 2023 and winter 2024, 42 sites were surveyed along the rocky coast of southern Italy, covering a total area of 59.196 m 2 . Albeit much less widespread than in the past and mainly confined to small, isolated patches, date mussel harvesting still occurs despite strict legal protection and a ban enforced since 1988. Overall, recent harvesting impacts were low, with an average damage index of 0.07, demonstrating a sharp decline compared to the historical baseline of 0.34. However, a major persisting consequence of date mussel harvesting is the widespread occurrence of barren grounds, quantified here using the Rock Desertification Index (RDI). Sea urchin densities were positively associated with barren ground cover, with a significantly steeper response in A. lixula than in P. lividus . These findings highlight that, although illegal date mussel harvesting has strongly declined, its ecological legacy persists through barren-ground formation and sea urchin-mediated feedbacks.