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

Abstract

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 37000 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 allochtonous 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.

Complementary Methods to Improve the Depuration of Bivalves: A Review

“…Via this process, they accumulate pathogenic bacteria, viruses, toxins, and chemical pollutants in their tissues that can pose a risk to public health [4,5]. These can then be transmitted to future consumers, with a high risk for public health [6,7].…”

“…The ideal procedure to obtain mollusks safely would be cultivation and harvesting in areas that are not subject to any type of contamination. However, this is unfeasible from a productive point of view because of the scarcity of these areas [7]. Consequently, depuration is a legal requirement in large countries for the marketing of fresh mollusks in order to protect consumers' health.…”

Surface water subduction during a downwelling event in a semienclosed bay

“…Its situation in a productive upwelling region enables the port of Vigo, and its ria, to host one of the most economically important mariculture industries in Europe [ Blanton et al ., ; Figueiras et al ., ], an activity that coexists with roles as a major ship‐building center, Europe's principal landing point for fish, an area of ecological interest, and a major focus of tourism [ Huntington et al ., ; Fernández et al ., ]. At the end of summer, blooms of toxic alga (Harmful Algal Blooms or HAB) have frequently been observed to have a negative impact on this mariculture of mussels [ Álvarez‐Salgado et al ., ; González Vilas et al ., ].…”

The role of mixing in controlling resource availability and phytoplankton community composition

“…The hydrographic and circulation patterns consist of a succession of upwelling and downwelling events driven by the dominant shelf winds (Álvarez-Salgado et al, 2003(Álvarez-Salgado et al, , 2002. Thus, nutrient input into the Rías occurs mainly by coastal upwelling, while continental runoff and precipitation represent minor inputs (Fernández et al, 2016). New nitrogen supply in the Galician Rias was therefore computed as the sum of nitrate diffusive flux and nitrate supply through vertical advection due to upwelling.…”