Modelling the recruitment effect in a small marine protected area: the example of saltwater lakes on the Island of Mljet (Adriatic Sea)

This paper analyzes potential recruitment effect of endangered bivalve Pinna nobilis in a small marine protected area-Little Lake (Adriatic Sea). A box model has been applied for the estimation of residence time of the lake, forced by tides only at the open end of the lake system. The residence time of Little Lake was estimated to be 54 days. In our approach we assumed that P. nobilis larvae may be found in the surface waters only during the night, thus restricting their outgoing from the lake to about 7-8 hours per day in the June-August period, as the larvae need some time to reach surface waters. Therefore, the equivalent residence time of the larvae in Little Lake is estimated to be about 160-185 days. Knowing that the bivalve larva phase lasts between 3 and 5 weeks, one may estimate that only 11 to 22% of the larvae, respectively, leave Little Lake. From a conservation standpoint these low values imply a special level of protection within Mljet National Park. In addition, future climatic changes will affect the recruitment of P. nobilis, not only due to sea level rise but also with temperature and other changes which may influence its reproduction phase and larvae transport.