Improving pacific oyster (Crassostrea gigas, Thunberg, 1793) production in Mediterranean coastal lagoons: Validation of the growth model "ShellSIM" on traditional and novel farming methods

Bivalve farming is a major European aquaculture activity, representing 48.5% of total biomass produced. Italy is one of the largest consumers of oysters but local production does not meet the market demand. Italy has approximately 384,000 ha of shallow lagoons in its coastal area, already devoted to extensive aquaculture activities, which could also represent potential locations for Pacific oyster (Crassostrea gigas, Thunberg, 1793) farming. The aim of this study is to enhance Pacific oyster farming in shallow coastal lagoons by testing novel farming technologies and validating an existing bioenergetic growth model (ShellSIM). Commercial performance of Pacific oysters and associated environmental parameters were monitored in two Sardinian coastal lagoons (San Teodoro and Santa Gilla, Italy). Oyster growth and survival were compared during a production cycle for two rearing systems: traditional systems (floating bags or lanterns) and Ortac units. The latter has not been previously tested in coastal lagoons. Measured performances were compared with ShellSIM predictions to evaluate the model's ability to predict growth and the potential production in other coastal lagoons. Results showed that at the end of a six months cycle the oysters mean weight and Condition Index were significantly higher (p value < 0.05) in floating bags than in Ortac, (55.8 +/- 0.9 g and 50.1 +/- 1.3 g; 4.6 +/- 0.1 and 3.9 +/- 0.1 respectively). Also, the minimum commercial size (40 g) was reached by 98% and 68% of the oyster farmed in floating bags and Ortac units respectively. On the other hand, oysters reared in the Ortac showed a higher survival than in the floating bags (95.8 +/- 0.9% and 82.1 +/- 3.4%, respectively). ShellSIM growth predictions were highly correlated with the observed data in both lagoons. However, high values for root mean square deviation (RMSD) indicated that ShellSIM predictions were significantly validated for San Teodoro lagoon but not for Santa Gilla suggesting further tailoring to some environmental conditions to produce more realistic growth predictions. Results of this study indicate that both floating bags and Ortac system should be employed during the production cycle to maximise oysters' survival and growth performances. Furthermore, this study provides a new validated tool to farmers and stakeholders to monitor oysters' performances and estimate productivity in local waters.