Ria Formosa Hydrodynamics and the Best Location for Shellfish Beds

Abstract

Ria Formosa lagoon is a coastal system located in the South of Portugal. Represents a valuable socio-economic resource for the country, due to tourism, fisheries, salt extraction and aquaculture, namely shellfish production. Ria Formosa produces 80% of consumed shellfish in Portugal, mainly grooved carpet shell Ruditapes decussatus. The physical environment to bivalve’s production includes not only the sea water in which the stock is grown, but also the substrate on they are placed, and phytoplankton and nutrients availability. Growth of bivalves is also correlated with the current velocity. The food depletion at the benthic boundary layer can be alleviated, and growth rates increase, with the breakdown of vertical velocities gradients through turbulent mixing by waves and currents. The main objective of this work was to define the best location to shellfish beds in this coastal lagoon, considering growth requirements, physical conditions and 3 hydrodynamic indicators: average current velocity, maximum flood current velocity and residence time, which were calculated using time series of water level and longitudinal component of velocity variations time series, which covered complete tidal cycles. For this purpose we defined 12 stations in the main channels of Ria Formosa using scientific diving methodologies. The combination of the considered variables, suggested that Nave Pegos, Culatra, Cacoes, and Bela Romao stations and surrounding areas are the most suitable for shellfish beds. This study was based in an ecohydrological approach, integrating physical and hydrodynamics variables with biota requirements, to define the best locations to shellfish beds.