Application of the biogeochemical flux model (BFM) to a shallow water lagoon and possible links with SGCBNS activities.

At the CNR-IAMC of Oristano (Sardinia, Italy), in addition to the experimental part (e.g. sedimentology, benthic ecology, and fish ecophysiology), we developed a shal-low water hydrodynamic model based on finite elements, fully coupled with ecosys-tem model (biogeochemical flux model, BFM), and applied it to a microtidal Mediterranean lagoon system. One of the major applications of our model is the en-ergetics of grey mullets (Mugil cephalus). M. cephalus is a detrivore benthopelagic spe-cies which feeds on benthic organisms and swims in the water column in large aggregations, and therefore it represents a fundamental trophic link between the ben-thic and pelagic environments. The coupled hydrodynamic-ecological model was calibrated for reproducing the en-vironmental variability (water temperature, salinity, dissolved oxygen, ammonia, nitrate, orthophosphates and chlorophyll-a) in two adjacent Mediterranean shallow water environments: the Cabras lagoon and the Gulf of Oristano (Italy). This type of environments is particularly interesting as the physico-chemical characteristics of the water are widely fluctuating. The model was used to reproduce the temporal and spatial variation in the Metabolic Scope (MS) of a M. cephalus fish population in order to investigate the relationship between changes in MS and the observed seasonal mi-gration pattern between the gulf and lagoon. Results from numerical simulations show that during the spring and beginning of summer period, the Cabras lagoon provides a higher MS for M. cephalus than the gulf of Oristano. During the rest of the year, apart from some transitional phases, the Gulf provides more suitable conditions (i.e. higher MS) for M. cephalus. Results were compared to fisheries data, showing that M. cephalus catches are highest during the end-July to August period, coinciding with the period of MS drop in the lagoon, when fish are caught migrating from the lagoon into the gulf. By modelling their metabolic scope (i.e. scope for activity), we devel-oped a tool that allows to potentially forecast the distribution of grey mullets in Mediterranean coastal areas. This is a first step towards a more comprehensive coupling between ecosystem mod-elling and benthic processes. A further step will be to include in the model the ben-thic components, such nutrient flux from sediments and benthic macroinvertebrates. Therefore, we could support the activities of SGCBNS by testing the "new" functional groups modules in a different environment from the North Sea, e.g. a Mediterranean coastal lagoon, which differs with respect to the North Sea both from latitude and geomorphology stand point.