Hydrography of shellfish harvesting areas in the western Cantabrian coast (Rías Altas, NW Iberian Peninsula)

Intertidal shellfish banks in estuarine areas are influenced by a wide variety of environmental conditions, including the physical and chemical characteristic of the water that floods the grounds. In this study we carry out a cross-comparison of the hydrographic characteristics and nutrient fertilization patterns of the waters that laps the shellfish grounds of a group of five drowned valleys collectively known as “Rías Altas”, located in the western Cantabrian coast (NW Iberian Peninsula). This region is affected by coastal upwelling from June to August resulting in a water exchange between the embayments and the shelf varying between 31.5 and 220.5 m3s−1. The fresh water discharge followed a seasonal cycle too, with maxima in winter and minima in summer, and long-term average flow rates ranging from 5.9 m3s−1 to 22.2 m3 s−1. Significant differences were observed among the five embayments with regard to temperature and salinity and also with inorganic nutrients, chlorophyll a and particulate organic matter concentrations in the continental waters.