Évaluation des nurseries de sars (Diplodus spp.) du massif des calanques (Marseille)

Nursery grounds of Diplodus spp. count for 9 % of the calanques’ shoreline. This amount is small in comparison with areas such as Marseille’s Bay. Such nurseries are found in sheltered areas, with shallow waters, gently sloping substrates of gravel, pebbles, or boulders. These areas are found in the inner zone of each calanque. Within the same calanque, settlement rates of juveniles are highly variable in space. The mean growth rate for D. puntazzo is 0.272 mm/d (±0.094), and the highest rates occurs at Callelongue, with 0.388 mm/d (±0.097). D. vulgaris displays a mean growth rate of 0.318 mm/d (±0.036), with no significant difference between calanques. At the regional scale, nurseries exhibit lower settlement rates for the shore between Mounine and Podestat (“ Centre ”
zone) and also for the Riou zone. Nurseries’ surface area may be an important quality factor. Most probably, adult populations in the calanques area depend not only on local nursery grounds, but also rely on the migration of adults or sub-adults from outer areas, such as Marseille shores.