The merging of long underwater linear transects with multiple spot dives to find Pinna nobilis (Linnaeus, 1758) survivors

Since 2016, the bivalve mollusc Pinna nobilis, endemic to the Mediterranean Sea, has been suffering a mass mortality in the whole basin caused by multiple pathogens. This situation has now led the species close to the extinction. In this scenario, the looking for safe zones and/or individuals resistant to the infection is of paramount importance. To achieve this goal, due to the low probability of finding living specimens, is important to develop and apply a monitoring strategy that maximizes the chance of success vs the survey effort. We adopted an integrated approach between long underwater linear transects at different depths and spot dives in habitats preferred by P. nobilis, i.e., the Posidonia oceanica meadows, along the Ionian coast of Apulia (Southern Italy). Despite this, we did not find survivors but only empty shells, a clear sign of the vanishing of the species from Apulian seabeds.