Studio della popolazione di Pinna nobilis (L., 1758) (Mollusca, Bivalvia) nel Golfo di Oristano: analisi dei pattern di distribuzione spaziale in relazione all’habitat.

SUMMARY - Study of Pinna nobilis (L., 1758) (Mollusca, Bivalvia) population in the Gulf of Oristano: analysis of distributional patterns in relation to the habitat - Pinna nobilis is an endemic bivalve of the Mediterranean Sea. In the last decades it has declined drastically due to increasing anthropogenic pressure. Despite the need for conservation, knowledge of its ecology as well as monitoring of the main populations are limited. Object of this paper is the study of P. nobilis within a Posidonia oceanica meadow (Gulf of Oristano, Sardinia) in order to increase the knowledge of the population ecology of this species, and to support its conservation. This activity was conducted in the summer of 2007 and repeated in 2009. The study area, subdivided in 3 sub-areas, is partially included within the Sinis Marine Protected Area and the Site of Community Importance of Mistras. Density, percentage of dead individuals and orientation were considered according to sub-areas and habitat type (P. oceanica, dead matte and sand). Density, although variable in sub-areas and habitats, was consistent during all the study period (1 ind. 100 m-2) and comparable with the most common value found in Mediterranean populations. The spatial distribution of individuals was patchy with a marked concentration at the edge of the meadow. The population structure was bimodal and common shell orientations were detected in two sub-areas.