A modeling study on the hydrodynamics of a coastal embayment occupied by mussel farms (Ria de Ares-Betanzos, NW Iberian Peninsula)

• Published in: Estuarine, coastal and shelf science coastal and shelf science, 2014-06, Vol.147, p.42-55
• Main Authors: Duarte, Pedro, Alvarez-Salgado, Xosé Antón, Fernández-Reiriz, Maria José, Piedracoba, Silvia, Labarta, Uxío
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal aquaculture; Animal productions; Animal, plant and microbial ecology; aquaculture rafts; Biological and medical sciences; Brackish water ecosystems; Circulation; Coastal; Computational fluid dynamics; Farms; Fundamental and applied biological sciences. Psychology; Galician rias; General aspects; General aspects. Techniques; hydrodynamic modeling; Invertebrates; Marine; Mathematical models; Methods and techniques (sampling, tagging, trapping, modelling...); Mollusca; mussel cultivation; Mussels; Mytilus edulis; residual circulation; Ria de Ares-Betanzos; Synecology; Upwelling; Water circulation
• ISSN: 0272-7714; 1096-0015
• DOI: 10.1016/j.ecss.2014.05.021

The present study suggests that both under upwelling and downwelling winds, the residual circulation of Ria de Ares-Betanzos remains positive with a strong influence from river discharge and a positive feedback from wind, unlike what is generally accepted for Galician rias. Furthermore, mussel cultivation areas may reduce residual velocities by almost 40%, suggesting their potential feedbacks on food replenishment for cultivated mussels. The Ria de Ares-Betanzos is a partially stratified estuary in the NW Iberian upwelling system where blue mussels are extensively cultured on hanging ropes. This type of culture depends to a large extent on water circulation and residence times, since mussels feed on suspended particles. Therefore, understanding the role of tides, continental runoff, and winds on the circulation of this embayment has important practical applications. Furthermore, previous works have emphasized the potential importance of aquaculture leases on water circulation within coastal ecosystems, with potential negative feedbacks on production carrying capacity. Here we implemented and validated a 3D hydrodynamic numerical model for the Ria de Ares-Betanzos to (i) evaluate the relative importance of the forcing agents on the circulation within the ria and (ii) estimate the importance of culture leases on circulation patterns at the scale of the mussel farms from model simulations. The model was successfully validated with empirical current velocity data collected during July and October 2007 using an assortment of efficiency criteria. Model simulations were carried out to isolate the effects of wind and river flows on circulation patterns. Model simulations and empirical results show the presence of a cyclonic gyre in the central part of the ria that results from the combined effect of the Eume and the Mandeo river flows. Results suggest that the residual circulation is positive independently of the local wind regime and strongly depressed in the areas where mussel cultivation rafts are concentrated (up to 15%) as a result of their drag effects. [Display omitted] •A 3D hydrodynamic model was implemented to a Galician ria used for mussel culture.•The model included the drag effects due to the presence of mussel cultivation rafts.•After validation, simulations were performed under variable wind and river forcing.•Obtained results show that residual velocities are largely depressed by the rafts.•Residual circulation is positive under all tested forcing