A habitat suitability model for aquaculture site selection: Ria de Aveiro and Rias Baixas.

Aquaculture is one of the fastest-growing activities worldwide. This strong and rapid development of the sector tends to be reflected in significant environmental impacts and new challenges in the management of the coastal areas. In this context, this work intends to contribute to the sustainability of the sector, by proposing an innovative method to identify preferred locations to ensure sustainable expansion of fish and mussels aquaculture, under optimal hydrodynamic and water quality conditions in Ria de Aveiro (Portugal) and Rias Baixas (Spain). A habitat model was developed, integrating hydrodynamic and water quality modelling results into a suitability index based on the definition of variable suitability functions. The results show that 22% of Ria de Aveiro is very good for fish production. In contrast, the production of pelagic fish in Rias Baixas is not recommended due to vertical gradients of water temperature and seasonal events of hypoxia. Concerning to mussels, the habitat model classifies 31% of Ria de Aveiro area as very good for production, while most of the Rias Baixas area presents this highest classification, confirming the high exploitation of the region. The definition of appropriate areas for aquaculture exploitation is highly related with the different geomorphological, hydrological and biogeochemical processes of Ria de Aveiro and Rias Baixas. Results for Ria de Aveiro indicate that the upstream areas are the most vulnerable from the water quality point of view, highlighting the importance of the advective processes in the lagoon's water quality, in opposition to Rias Baixas dynamics, where stratification is more relevant. In Rias Baixas, the strong vertical gradient of water temperature and dissolved oxygen prevents fish from having sustainable growth rates. Therefore, this work demonstrated the potential of the proposed method based on hydrodynamic and biogeochemical modelling to support the decision-making process in planning aquaculture expansion.