Historical exploitation of the Mediterranean Sea and the absence of rigorous baselines makes it difficult to evaluate the current health of the marine ecosystems and the efficacy of conservation actions at the ecosystem level. Here we establish the first current baseline and gradient of ecosystem structure of nearshore rocky reefs at the Mediterranean scale. We conducted underwater surveys in 14 marine protected areas and 18 open access sites across the Mediterranean, and across a 31-fold range of fish biomass (from 3.8 to 118 g m−2). Our data showed remarkable variation in the structure of rocky reef ecosystems. Multivariate analysis showed three alternative community states: (1) large fish biomass and reefs dominated by non-canopy algae, (2) lower fish biomass but abundant native algal canopies and suspension feeders, and (3) low fish biomass and extensive barrens, with areas covered by turf algae. Our results suggest that the healthiest shallow rocky reef ecosystems in the Mediterranean have both large fish and algal biomass. Protection level and primary production were the only variables significantly correlated to community biomass structure. Fish biomass was significantly larger in well-enforced no-take marine reserves, but there were no significant differences between multi-use marine protected areas (which allow some fishing) and open access areas at the regional scale. The gradients reported here represent a trajectory of degradation that can be used to assess the health of any similar habitat in the Mediterranean, and to evaluate the efficacy of marine protected areas.

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Mediterranean monk seals Monachus monachus attacked fish on 11 marine fish farms in the Turkish Aegean between 1992 and 2000. There were 40 attacks on fish farms where gilthead sea bream Sparus auratus and European sea bass Dicentrarchus labrax were raised in holding cages. Single seals usually attacked cages at night, regardless of the size of fish in the cages. The seals damaged both holding nets of the cages and fish and, on most occasions, fish escaped as a result of the attacks. With the exception of only one facility, all fish farms attacked by monk seals were concentrated on the large peninsulas including Karaburun and Bodrum Peninsulas, and the number of seal attacks was higher during the winter months. A direct intervention to deter seals such as the use of lights, feeding with pesticide‐injected fish, noise generation, warning and direct shots with rifles and physical exclusion of seals from holding cages by installing antipredator nets were applied to prevent or reduce seal attacks. Our study shows that deterrents such as lights and warning shots were not effective in preventing monk seal attacks. However, both curtain‐ and bag‐type antipredator nets were found to be effective.

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