COLONIZATION AND DISAPPEARANCE OF MYTILUS-GALLOPROVINCIALIS LAM ON ANARTIFICIAL HABITAT IN THE MEDITERRANEAN-SEA

A Mytilus galloprovincialis population, settled on a new artificial ha bitat at 12 m depth in the Central Tyrrhenian Sea, was investigated fo r 10 years. The new substratum, located at a depth lower than the pref erential range of the species, was colonized temporarily by mussels wh ich reached very high densities and dominated the benthic community fr om their colonization until the third year. The length-frequency distr ibution analysis showed a progressively complex population structure w ith up to three cohorts. The yearly recruitments were observed once a year in spring. The growth curve provided a maximum length higher than that reported for shallow waters. Nevertheless, the gregarious habits of mussels and the reduced water movement caused edaphic modification s of the substratum, which was covered progressively by sediments and biodeposits (pseudofaeces). Consequently, the population structure was affected by a reduction of the newly recruited cohorts, and mussels d isappeared after 5 years of colonization. This may be explained by the reduction in the substratum available for the first settlement (hydro id covering), as well as by the modification of the surface required f or final settlement. (C) 1996 Academic Press Limited