Settlement and recruitment:: the first stages in the life cycle of two epibenthic suspension feeders (Corallium rubrum and Anomia ephippium)

Studies on the population dynamics of the Mediterranean octocoral Corallium rubrum may prove extremely important for the conservation and management of this overexploited species. This study provides a detailed analysis of the settlement and recruitment processes in a red coral coastal population of the Eastern Ligurian Sea. Marble tiles, placed at two different depths (25 m and 35 m) were sampled photographically each month over two years, and the resulting densities of settlers were compared with those measured on the natural substrate. Red coral planulae successfully colonized tiles from August to September, showing a time-limited recruitment. Contrary to red coral, Anomia ephippium, a bivalve that frequently colonizes tiles, exhibited a 'Pulsing' recruitment throughout the year. Red coral settler density varied significantly between the different depths and times, while no statistical difference was found between artificial and natural substrates. As the tiles were permanent, they enabled us to follow the history of individuals and cohorts from settlement to their second year of life. Several mortality events affected settlers at both depths contemporaneously. In November 1999, the mass mortality that occurred in Ligurian shores also affected red coral settlers. These findings provide basic knowledge on the early phases of the red coral life cycle.