Coexistence of urban uses and shellfish production in an upwelling-driven, highly productive marine environment: The case of the Ría de Vigo (Galicia, Spain)

The Ría de Vigo, located at the northern border of the Iberia-NW Africa eastern boundary upwelling ecosystem, is an incised deep (45 m maxim depth) valley originated by the combined action of tectonic and erosive processes. Upwelling events promote a quick renewal (3-4 days) of the volume of water in the Ría, which is replaced by cold, oxygenated and nutrient-rich subsurface oceanic water, giving rise to nutrient fertilization of the embayment that translates into high primary production rates (ca. 3 g C m−2  d−1). This high productivity allows the development of an important shellfish exploitation activity. The Ría de Vigo has 529 rafts where 37 000 tons of mussels are produced annually. This territory has been subjected to an increasing human pressure since the early XX century deriving in an intense landscape transformation. The city of Vigo showed a six-fold increase in the number of inhabitants from 1900 to 2001 and more than 21% of the land in the study area is currently artificial. Therefore, urban and industrial activities coexist with local fisheries and shellfish mariculture that accounts for ca. 7% of the income and employment in this urban region. Incomplete depuration of wastewater in treatment plants, explain the relatively high contribution (22%) of sewage-derived nutrients to the total allochthonous fertilization in the Ría. Furthermore, and given the importance of shellfish production, microbial pollution originated from urban wastewater is considered as the main environmental threat of the Ría de Vigo. The dependence of the local economy on marine renewable resources together with the limitation of the natural productivity of the Rías imposed by anthropogenic pressure lies behind a significant fraction of the conflicts occurring in the region during the past two decades. The characteristics of Ría de Vigo, described in this review, confer this coastal ecosystem unique, conditions as a natural laboratory where the interaction between human activity and marine ecological processes can be studied within the framework of the World Harbour Project.