Spawning grounds of the soles, Solea solea and Solea senegalensis, are distant from the estuarine nurseries where juveniles concentrate. Recruitment of these species is highly dependent on the success of the larval migration towards the inshore nursery grounds. Unfavourable climate and hydrodynamic circulation may lead to high mortality rates at this stage. The relation between river drainage, NAO index and the North-South wind component intensity over the three months prior to the end of the estuarine colonization and the densities of S. solea and S. senegalensis in the nursery grounds were investigated for both species based on a discontinuous historical dataset (from 1988 to 2006) for the Tagus estuary. Multiple linear regression models were developed for sole density and environmental data (separately for each species). Results showed that river drainage is positively correlated with juveniles’ densities of both species, possibly due to the existence of chemical cues used by larvae for movement orientation. NAO index and the North-South wind component intensity relations with soles densities were non-significant. It was concluded that the high complexity of the Portuguese upwelling system makes it hard to detect causal relations of the environmental variables tested. The importance of river flow for coastal ecosystems was stressed. Since climate change scenarios predict a strong decrease in rain fall over the Portuguese river basins, as well as a concentrated period of heavy rain in winter, it was hypothesised that future river drainage decrease over much of the year may lead to lower recruitment success for soles, especially for S. senegalensis.

Impact of climate and hydrodynamics on sole larval immigration towards the Tagus estuary, Portugal

Spatio-temporal trends in upwelling patterns were studied along the Canary Upwelling System for the period 1967-2006. The northwestern coast of African from lat 20 degrees N to 32 degrees N is observed to be under a permanent upwelling regime characterized by coastal sea surface temperatures (SST) colder than the oceanic ones at the same latitude. The temperature difference is termed the temperature upwelling index (UI(SST)). This regime is consistent with the wind-derived Ekman transport (UI(W)), which is observed near the coast and is directed offshore. This index shows the existence of upwelling-favorable conditions all year but has an annual cycle characterized by more upwelling-favorable conditions from April to September, with a maximum in July, and less upwelling-favorable conditions from October to March, with a minimum in December to January. Although both indices can be used to characterize the phenomenon, only UI(W) values were used to quantify upwelling change during the four decades under review because this index is less sensitive to external factors compared to UI(SST). A strong decrease in upwelling intensity has been observed in all seasons. In particular, the summer (winter) decrease is on the order of 45% (20%) of the mean amplitude of the upwelling cycle.

Spatio-temporal Upwelling Trends along the Canary Upwelling System (1967–2006)

An overview of the main oceanographic features of the eastern North Atlantic boundary, with emphasis toward the upper layers, is presented. The principal features discussed are: water mass boundaries; forcing by wind, density and tides; topographic features and effects; fronts; upwelling and downwelling; poleward flows; coastal currents; eddies. The occurrence and spatial and seasonal
variability of these features is described in five regional sections: Celtic Sea and western English Channel; Bay of Biscay; western Iberia; Gulf of Cadiz; northwest Africa. This paper is intended to provide a base of physical oceanographic knowledge in support of research in fisheries, biological and chemical oceanography, and marine biology.

An overview of the literature concerning the oceanography of the eastern North Atlantic region

The continental shelf of NW Iberia is of particular interest due to the complex North Atlantic rifting tectonics and modern oceanographic processes that led to its current geomorphological configuration and sediment dynamics. The shelf forms a narrow slow-dipping north-bearing geomorphological structure with a well-defined shelf break located at water depths of 160–180 m. It is a continental margin with sedimentation rates of about 1.5±2.0 mm a −1 (the highest values in recent bottom sediments of the ria) subjected to a highly energetic seasonal regime of waves and tides, seasonal upwelling and coast-parallel currents, significantly modulated by the North Atlantic Oscillation. Sediment provenance is dominated by inputs of continental sediments via runoff and riverine discharges and, to a lesser extent, by an upwelling-enhanced bioclastic input. Present-day sedimentation in the area occurs closely associated with two geomorphologically distinct sedimentary environments: the rias inner shelf sedimentary systems and the open continental shelf, and their subsequent evolution since the last glacial.

Chapter 8 The NW Iberian continental shelf

Tese de doutoramento em Biologia (Biologia Marinha), apresentada a Universidade de Lisboa atraves da Faculdade de Ciencias, 2007

L. Fariña-Busto

Papers

Physical and biogeochemical fluxes in shelf waters of the NW Iberian upwelling system. Hydrography and dynamics