Environmental Drivers and Social Structure Features behind the Low Reproductive Success of Dusky Groupers Epinephelus marginatus (Lowe, 1834) in a Mediterranean Marine Protected Area

Abstract

Marine protected areas (MPAs) are considered key tools for achieving the sustainability of coastal fisheries by allowing habitat and species conservation by means of use regulations and active management. The effects of protection are more visible in slow-growing, high site fidelity and late-maturing species such as dusky grouper, a flagship species for all the fishermen and divers in the Mediterranean Sea. We studied the reproductive behavior of dusky grouper at Tabarca Island Marine Protected Area (TIMPA) in order to: (a) describe its temporal pattern; (b) evaluate the relationships among reproductive behavior and environmental factors and (c) verify the effects of social structure on reproductive activity. We observed all the behavior patterns previously reported in other studies besides the final spawn event. Our results evidenced that the monthly average density of dusky groupers tended to increase when temperature rose close to the seabed and without defined temporal limits for reproductive behavior. Among the environmental factors considered, visibility exhibited a very strong effect on the reproductive behavior of dusky grouper, interacting significantly with seabed temperature and thermocline. Regarding the effects of social structure, reproductive activity was positively correlated with the presence of large-sized individuals. We have discussed the differential facts of the reproductive activity of dusky groupers observed at TIMPA relating the results to the biogeographical location, the patterns of the environmental drivers (such as the seabed temperature per day, the thermocline, the visibility, the stream force, the photoperiod and the divers per day) and the structure of the habitat. These negative results contrast with the existing knowledge and generate new working hypotheses useful to improve the efficiency of MPAs and the sustainability of coastal fisheries.