The extension and intensity of the upwelling season in the NW Iberian Peninsula (42º-43ºN) have decreased by 30% and 45% over the last 40 years, respectively. Accordingly, the renewal time (τ) of the Rías Baixas, four large coastal inlets where 15% of the World extraction of blue mussels occurs, has increased by 240%. We indirectly demonstrate here that the growing τ has caused the increasing occurrence of harmful microalgae in these embayments, dramatically affecting mussel raft cultivation. The equation            ) c exp(1 365 D 1 τ explains 80% of the variability of the number of days per year that mussels cannot be extracted from the hanging ropes because of the occurrence of harmful microalgae (D). The coefficient c 1 = 37± 2 days indicates that an average τ over the upwelling season of > 25±1 or 50± 3 days reduce mussel extraction to only 50% or 25% of the year, respectively.

[1] Sixteen hydrographic surveys were carried out in the middle segment of the Ría de Vigo (northwest Spain) at 3-to 4-day intervals during February, April, July, and September 2002 (four surveys per period). Simultaneously, an acoustic Doppler current profiler (ADCP) mooring recorded the velocity profile. Combination of direct current measurements with the output of an inverse model based on the time course of the distributions of salinity and temperature allowed an objective analysis of the effect of the meteorological forces on the hydrodynamics of the Ría. Remote shelf winds explained more than 65% of the variability of the subtidal circulation, which responded immediately to this forcing (lag time, <2 days). Shelf winds created a simple two-layered circulation pattern, with a surface outgoing current under northerly winds and a surface ingoing current under southerly winds. A three-layered circulation developed during the transitions from northerly to southerly winds and vice versa. At the same time, an empirical orthogonal function (EOF) analysis demonstrated the lack of contribution of local winds to the subtidal dynamics of the ría. Continental runoff and heat exchange with the atmosphere explained less than 5% and 25% of the variability observed in the subtidal circulation of the Ría de Vigo.Citation: Piedracoba, S., X. A. Á lvarez-Salgado, G. Rosón, and J. L. Herrera (2005), Short-timescale thermohaline variability and residual circulation in the central segment of the coastal upwelling system of the Ría de Vigo (northwest Spain) during four contrasting periods,

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Bays/estuaries forced by local wind show bidirectional exchange flow. When forced by remote wind, they exhibit unidirectional flow adjustment to coastal sea level. Acoustic Doppler Current Profiler observations over 1 year show that the Ria de Vigo (Iberian Upwelling) responds to coastal wind events with bidirectional exchange flow. The duration of the upwelling and downwelling events, estimated from the current variability, was ~3.3 days and ~2.6 days, respectively. Vectorial correlations reveal a rapid response to upwelling/downwelling, in which currents lag local wind by <6 h and remote wind by <14 h, less than the Ekman spinup (17.8 h). This rapidity arises from the ria's narrowness (nonrotational local response), equatorward orientation (additive remote and local wind responses), depth greater than the Ekman depth (penetration of shelf circulation into the interior), and vertical stratification (shear reinforcing shelf circulation). Similar rapid responses are expected in other narrow bays where local and remote winds act together and stratification enhances bidirectional flow.

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The dilution technique, combined with identification and enumeration of pico-, nanoand microplankton by microscopy, was used to estimate microzooplankton impact on the microbial community in surface waters of a coastal embayment on the NW Iberian upwelling system. Microzooplankton were important consumers of autotrophic and heterotrophic plankton in this system, feeding up to 93% of standing stock and more than 100% of production of several groups. Heterotrophic bacteria and heterotrophic picoflagellates experienced the highest and constant impact, with 75-84% of their standing stocks and 85-102% of their production being channelled through the microbial food web. Pico-and nanophytoplankton were also consumed, although maximum grazing occurred on diatoms during upwelling events, coinciding with highest primary production. Predation on pico-nanoheterotrophs was especially relevant under downwelling conditions, when consumption of total carbon and particularly autotrophic carbon was considerably lower than during upwelling. The results suggest that the existence of a multivorous food web, extending from the microbial loop to the herbivorous food web, could be a major feature in this coastal upwelling system. The microbial loop, which occurs as a permanent background in the system, would contribute to sustain the microbial food web during downwelling, whereas the herbivorous food web could coexist with a microbial food web based on large diatoms during upwelling. The multivorous food web would partially divert diatoms from sinking and hence favour the retention of organic matter in the water column. This could enhance the energy transfer to higher pelagic trophic levels in coastal upwelling systems.