Recent studies highlight an increase in the frequency and intensity of marine mass mortalities of several species over the past 30–40 years, mainly in tropical and temperate areas. In the Mediterranean Sea these episodes particularly affect benthic suspension feeders, such as sponges and cnidarians. The main objective of this work was to document the loss of one of the main Mediterranean seascapes, Paramuricea clavata forests at the Marine Protected Area of Tavolara Punta Coda Cavallo, Sardinia (Italy), during the summer of 2008. Data regarding colony height, density, level of damage, and microbiological community were collected at two sites. Such parameters help us understand how mass mortality mechanisms act on this ecosystem engineer. We identified a change in size class distribution following a mass mortality that leaves mainly small colonies with a decrease in habitat complexity. Several tests on water chemistry demonstrate that the mortality event was not caused by local contamination. Moreover, microbiological tests on potential pathogenic agents suggest that bacteria belonging to the genus Vibrio are present as an opportunistic and not an etiological cause of P. clavata mortality events. Possible restoration approaches are discussed.
Portofino and Cap de Creus, respectively. Minimum harvestable size (7 mm basal diameter) was reached in 30-35 years, and the percentage of colonies above it was 6.7 % at Portofino and 2.1 % at Cap de Creus, where juvenile and adult colony densities were significantly lower and the percentage of commercial-sized colonies reduced by 25 % in just a few years. notwithstanding similar growth and fecundity, the two populations showed different densities and size/age structures suggesting local factors, together with different fishing pressures, have to be taken into account in the management plans for this species. Introduction Population dynamics depend largely on demographic histories (Dobson 1998; ebert 1999, particularly for slowgrowing, long-lived species, which have been subjected to dramatic reductions in survival, reproduction and/ or recruitment rates (e.g., Fujiwara and Caswell 2001;
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