Experimental shellfish culture on an artificial reef in the Adriatic Sea

Experiments were carried out on an artificial reef located in the central Adriatic Sea (Conero Promontory) to show the feasibility of using the submerged structures to culture mussels (Mytilus galloprovincialis Lamk) and oysters (Ostrea edulis L. and Crassostrea gigas Thunberg) in open sea areas not suitable for traditional Italian shellfish farming. Nylon ropes were found to be best to collect mussel seed and these collectors showed that mussel settlement extended from early winter until late summer. Highest settlement intensity was observed in late spring-early summer and from the first 5 m under the sea surface. Growth, survival and production of mussels were investigated from three experimental sets. A seasonal Von Bertalanffy length-growth equation was computed for this species under farming conditions. The minimum commercial size (TL = 50 mm) was attained by 50% of mussels after 5 months of growth. After 12 months the total production was about 7 kg of mussels per 1 kg of seed. Special plastic collectors were used to study settlement and to obtain oyster seed for subsequent farming. Oysters showed a short period of settlement, extending from late summer until early autumn. The collectors recovered in September contained the highest density of seed. Growth, survival and production of O. edulis and C. gigas were estimated for 1 year. For each oyster species, a seasonal Von Bertalanffy growth curve was fitted on size-class data. O. edulis showed slower growth than C. gigas, in fact they were marketable (TL > 60 mm) after 10 and 8 months of farming respectively, with a production of about 4 kg and 7 kg per collector after 11 months. During the experiment periods a reduction of growth rate, more pronounced for oysters than for mussels, was observed in the winter months.