Observations on some reproductive features of the threatened limpet Patella ferruginea Gmelin, 1791 in north-western Mediterranean Italian waters

Information about the reproductive biology of the threatened limpet Patella ferruginea has been historically restricted to some of the few enclaves where healthy and conspicuous populations still persist, all located on the African coasts of the Alboran Sea, at the extreme south west of the species' distribution range, in the western basin of the Mediterranean. This paper provides data on sex ratio by size and sex change of the species from specimens in the northernmost extreme of its distribution, between the north east of Sardinia (Italy) and the Gulf of Genoa (Liguria, Italy), where much more restricted and small populations are found. In the study area, the population parameters were found to be quite similar to those known from the Alboran Sea: The ratio between males and females tends to decrease with size and the prevalence of females versus males (i.e. >50% females) from the 60-65 mm size class upwards. Notwithstanding the small sample size (n = 13), several sex changes were observed in 38.5% of specimens. Noteworthy is that this change not only occurred in the male to female direction (considered 'normal' for limpet species) but was also recorded in the female to male direction, confirming the complexity of the reproductive mode of P. ferruginea. The evidence of regular gonadal maturation of specimens and the occurrence of sex changes in the area investigated supports the potential viability of the species at its northernmost limit of distribution, where the species has only recently been reported. Such evidence provides important information for the implementation of management and conservation actions, such as restocking initiatives.