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The dynamics of individual phytoplankton species are often more variable than predicted for their functional groups. This observation is poorly understood in highly perturbed coastal systems. Trends in the abundance of 54 phytoplankton species spanning a volumetric size range from ~102 to ~105 µm3 in shelf waters of the NW Iberian upwelling system since the late 1980s were modelled as a function of environmental variables. Functional traits were assessed for their ability to explain the across-species changes in occurrence and abundance due to the environmental drivers. Species-specific responses to the environment were heterogeneous, precluding any generalisation by taxonomic groups, although these responses were partially related to cell size. Smaller species showed a high probability of occurrence and higher abundance under high nitrate concentration in the euphotic layer, pointing to a major role of the upwelling of Eastern North Atlantic Central Water but also to inputs of nutrients mineralised over the shelf. However, cell size explained only a small amount of the variability in the individual species’ responses to the environment. Growth rate and maximum rate of nitrogen uptake normalised to cell size provided additional explanation for the individual species’ responses to the environmental drivers. Fast-growing species, though less efficient in taking up upwelled nutrients, thrived in favourable upwelling conditions. These results support the dominance of species of intermediate size during blooms in this upwelling region, and suggest that variability in functional traits among species rather than cell size alone affects the response of phytoplankton to environmental changes in upwelling ecosystems.

Phytoplankton species assemblages in estuaries are connected to those in rivers and marine environments by local hydrodynamics leading to a continuous flow of taxa. This study revealed differential effects of upwelling and river flow on phytoplankton communities observed in 2011 along a salinity gradient from a river reservoir connected to the sea through a ria-marine bay system in A Coruña (NW Spain, 43° 16-21’ N, 8° 16-22’ W). With 130 phytoplankton taxa identified, the assemblages were dominated in general by diatoms, particularly abundant in the bay and in the estuary, but also by chlorophycea and cyanobacteria in the reservoir. Considering the entire seasonal cycle, the local assemblages were mainly characterized by changes in cryptophytes and diatoms, small dinoflagellates and some freshwater chlorophycea. Salinity, nitrate, and organic matter variables, were the main environmental factors related to the changes in the phytoplankton communities through the system, while phosphate and nitrite were also important for local communities in the estuary and the bay, respectively. The corresponding local phytoplankton assemblages showed moderate levels of connectivity. The estuarine community shared a variable number of taxa with the adjacent zones, depending on the relative strength of upwelling (major influence from the bay) and river flow (major influence of the reservoir) but had on average 35% of unique taxa. Consequently, local and zonal diversity patterns varied seasonally and were not simply related to the salinity gradient driven by the river flow.

Phytoplankton is a sentinel of marine ecosystem change. Composed by many species with different life-history strategies, it rapidly responds to environment changes. An analysis of the abundance of 54 phytoplankton species in Galicia (NW Spain) between 1989 and 2008 to determine the main components of temporal variability in relation to climate and upwelling showed that most of this variability was stochastic, as seasonality and long term trends contributed to relatively small fractions of the series. In general, trends appeared as non linear, and species clustered in 4 groups according to the trend pattern but there was no defined pattern for diatoms, dinoflagellates or other groups. While, in general, total abundance increased, no clear trend was found for 23 species, 14 species decreased, 4 species increased during the early 1990s, and only 13 species showed a general increase through the series. In contrast, series of local environmental conditions (temperature, stratification, nutrients) and climate-related variables (atmospheric pressure indices, upwelling winds) showed a high fraction of their variability in deterministic seasonality and trends. As a result, each species responded independently to environmental and climate variability, measured by generalized additive models. Most species showed a positive relationship with nutrient concentrations but only a few showed a direct relationship with stratification and upwelling. Climate variables had only measurable effects on some species but no common response emerged. Because its adaptation to frequent disturbances, phytoplankton communities in upwelling ecosystems appear less sensitive to changes in regional climate than other communities characterized by short and well defined productive periods.

Time series records are crucial to understand the dynamical processes that occur within phytoplankton communities. This is even more important in the context of the current global change that is already forcing alterations of unprecedented nature and might have unknown consequences for multiple ecosystem processes. Here we present time series analyses of the biogeochemical trends that occurred in the shelf of the Galician coast (station 2 off A Coruña, NE Atlantic) since late 1980s. Upwelling strength and sea temperature in the area have not changed substantially during the last decades. However, while nitrate fertilization from upwelled waters has remained relatively stable, phosphate concentration has increased leading to a negative trend in the N:P ratio. Those trends have impacted the phytoplankton resource use efficiency jointly with the evenness of the community. Phytoplankton used resources more efficiently at higher values of upwelling strength and at lower values of nutrient concentration and evenness. Phytoplankton communities that were more even had higher dinoflagellate diversity contrasting to dominance of diatoms that used resources more efficiently. Moreover, variability in resource use efficiency increased with evenness.

From September 2000 to September 2001 the concentration of chlorophyll a, and the abundance and composition of the phytoplanktonic community was studied in a neritic station of the Mallorca Channel (Western Mediterranean). Sampling was performed approximately every 12 days. Chlorophyll a concentration and phytoplankton abundance reached maxima of 1.79 mg L2l and 352 cells mL21, respectively. It was a relatively productive period, as a result of the high convective mixing in winter and the prevalence of northern waters during most of the cycle. Phytoplankton proliferations (chlorophyll-a concentration .1 mg L21) were detected in January, February, March and June. Those blooms mainly happened under the influence of northern waters, with the exception of the February proliferation, when mixing conditions were found. During bloom conditions it highlights the presence of coccolithophores as proliferation precursors. During no-bloom situations the phytoplankton community was mainly constituted by nanoplanktonic flagellated forms. The Winter Mixing period was dominated by different groups of nanoflagellates, including coccolithophores, undetermined flagellates and dinoflagellates. However, in the most oligotrophic conditions (from April until November) dinoflagellates were clearly dominant, except in the DCM in summer where diatoms prevailed.

Planktonic communities play pivotal roles within marine ecosystems, affecting their structure, functioning and services. Although they have been extensively studied in the epipelagic ocean, the knowledge about these communities in the dark ocean is rather short. In this study, we explored patterns of abundance and biomass of a wide variety of taxonomic groups from the prokaryotes to mesozooplankton in the epi-, meso- and bathypelagic waters off the Galician coast. As expected, ciliate and zooplankton abundances are depleted in the bathypelagic waters relative to abundances of prokaryotes and nanoflagellates. The rate of decrease of zooplankton biomass with depth is twice as that of prokaryotes and nanoflagellates, indicating that relative contribution of mesozooplancton to the total plankton biomass decreases with depth. Overall, the diversity of prokaryotes in the dark ocean is almost as high as in the epipelagic layer, although the phylotypes are different. The major fraction of epipelagic ciliates belongs to alloricate genera, whereas tintinnids dominate the deep ciliate populations. Small copepods were dominant in the epi- and meso-pelagic zone. By contrast, foraminiferans, big copepods and myctophic fishes were more abundant in the deep ocean.

Phytoplankton is a sentinel of ecosystem change in marine ecosystems. Composed by many species with different life-history strategies, it rapidly responds to environment changes. An analysis of time-series of the abundance of 54 phytoplankton taxa in Galicia (NW Spain) between 1989 and 2008 to determine the main trends in relation to climate and upwelling showed that most of their variability was stochastic, as seasonality and long term trends accounted for a minor fraction of the series. All trends were non linear, and taxa clustered in 4 groups according to the trend pattern but there was no defined pattern for diatoms, dinoflagellates or flagellates. No clear trend was shown by 23 taxa, 14 taxa decreased and 4 taxa increased during the early 1990s, while only 13 taxa showed a general increase through the series. In contrast, series of local environmental conditions (temperature, stratification, nutrients) and climate-related variables (atmospheric pressure indices, upwelling winds) showed a high fraction of their variability in deterministic seasonality and trends. As a result, each taxa showed independent responses to environmental and climate variablity, measured by generalized additive models. Most taxa showed a positive relationship with nutrient concentrations but only a few showed a direct relationship with stratification and upwelling. Climate variables only had measurable effects on some taxa but no common response emerged. Because its adaptation to frequent disturbances, phytoplankton communities in upwelling ecosystems appear less sensitive to changes in regional climate than communities characterised by short and well defined productive periods.

We have determined planktonic community N2 fixation, Trichodesmium abundance, the concentration and vertical diffusive flux of phosphate, and satellite-derived estimates of atmospheric concentration of dust along two longitudinal transects in the eastern subtropical North Atlantic during November 2007 and from April–May 2008. Trichodesmium abundance was particularly low (<3 trichome l−1) during the spring 2008 cruise, when low sea surface temperatures were recorded and vertical stratification was less marked. However, community N2 fixation was always measurable, albeit low compared with other regions of the tropical Atlantic. The average, vertically-integrated N2 fixation rate was 1.20 ± 0.48 µmol N m−2 d−1 in autumn 2007 and 8.31 ± 3.31 µmol N m−2 d−1 in spring 2008. The comparison of these rates of diazotrophy with the observed Trichodesmium abundances suggests that other, presumably unicellular, diazotrophs must have contributed significantly to community N2 fixation, at least during the spring 2008 cruise. Satellite data of atmospheric dust concentration suggested similar rates of atmospheric deposition during the two surveys. In contrast, vertical diffusive fluxes of phosphate were 5-fold higher in spring than in autumn (14.2 ± 12.1 µmol P m−2 d−1 and 2.8 ± 2.6 µmol P m−2 d−1, respectively), which may have stimulated N2 fixation. These findings agree with the growing view that N2 fixation is a more widespread process than the distribution of Trichodesmium alone may suggest. Our data also suggest a role for phosphorus supply in controlling the local variability of diazotrophic activity in a region subject to relatively high atmospheric inputs of iron.

[Resumen] Entre septiembre de 2000 y septiembre de 2001 se estudió la concentración de clorofila-a, junto con la abundancia y composición de la comunidad fitoplanctónica de una estación nerítica en el Canal de Mallorca (Mediterráneo Occidental). El muestreo se realizaba aproximadamente cada 12 días. La concentración de clorofila-a varió entre 0.04 µg l-1 y 1.79 µg l-1; mientras que la abundancia de fitoplancton osciló entre 15 céls ml-1 y 352 céls ml-1. Fue un año relativamente productivo, consecuencia de la importante mezcla convectiva ocurrida ese invierno y al predominio de aguas del norte. El nitrógeno fue el principal elemento limitante del fitoplancton. El grupo taxonómico dominante fue el de los dinoflagelados nanoplanctónicos, seguidos por los cocolitoforados y los nanoflagelados. Se detectaron proliferaciones de fitoplancton (concentración de clorofila-a > 1 µg l-1) en enero, febrero, marzo y junio. El patrón de las floraciones encontradas fue el siguiente: cocolitoforados y nanoflagelados (con presencia desigual de diatomeas) > diatomeas ruderales > dinoflagelados. La estructura trófica dominante fue la red trófica microbiana, sin embargo la red trófica multívora pudo ser importante en las proliferaciones de enero y marzo y, en menor medida, en el DCM (Máximo Profundo de Clorofila) durante la época de estratificación estival., [Resumo] Entre setembro de 2000 e setembro de 2001 estudiouse a concentración de clorofila-a, xunto coa abundancia e composición da comunidade fitoplanctónica dunha estación nerítica na Canle de Mallorca (Mediterráneo Occidental). A mostraxe realizábase aproximadamente cada 12 días. A concentración de clorofila-a variou entre 0.04 µg l-1 e 1.79 µg l-1; mentres que a abundancia de fitoplancto oscilou entre 15 céls ml-1 e 352 céls ml-1. Foi un ano relativamente productivo, consecuencia da importante mixtura convectiva acontecida ese inverno e ó predominio de augas do norte. O nitróxeno foi o principal elemento limitante do fitoplancto. O grupo taxonómico dominante foi o dos dinoflaxelados nanoplanctónicos seguidos polos cocolitoforados e os nanoflaxelados. Detectáronse proliferacións de fitoplancto (concentracións de clorofila-a > 1 µg l-1) en xaneiro, febreiro, marzo e xuño. O patrón das floracións atopadas foi o seguinte: cocolitoforados e nanoflaxelados (con presencia desigual de diatomeas) > diatomeas ruderais > dinoflaxelados. A estructura trófica dominante foi a rede trófica microbiana nembargantes a rede trófica multívora puido ser importante nas proliferacións de xaneiro e marzo e, en menor medida, no DCM (Máximo Profundo de Clorofila) durante a estratificación estival., [Abstract] Between September 2000 and September 2001 the concentration of chlorophyll-a, along with the abundance and composition of the phytoplanktonic community was studied in a neritic station in the Mallorca Channel (Western Mediterranean). Sampling was performed every 12 days approximately. The chlorophyll-a concentration ranged from 0.04 mg l-1 to 1.79 mg l-l, while the abundance of phytoplankton varied between 15 cells ml-1 and 352 cells ml-1. It was a relatively productive year, as a result of the important convective mixing occurred that winter and the prevalence of northern waters. Nitrogen was the main limiting element for the phytoplankton. The dominant taxonomic group was the nanoplanktonic dinoflagellates, followed by coccolithophores and by nanoflagellates. Phytoplankton blooms (chlorophyll-a concentration > 1 mg l-1) were detected in January, February, March and June. The bloom sequence was: coccolithophores and nanoflagellates (with unequal presence of diatoms) > ruderal diatoms > dinoflagellates. The dominant trophic structure was the microbial food web, however the multivorous food web could had been important in the January and March blooms and, to a lesser extent, in the DCM (Deep Chlorophyll Maximum) during the summer stratification period.

Esta obra ofrece una síntesis de la información recogida en las series temporales de observaciones oceánicas del IEO en la región atlántica del norte de España iniciadas en 1943 con el registro mareográfico; muestra evidencias de cambios interanuales en la física, la química y la biología del océano en relación con los factores climáticos, y estima los impactos más probables del clima en el océano futuro. Este volumen continúa la serie de estudios de la influencia del cambio climático en el mar iniciada con el Cambio climático en el Mediterráneo español (Vargas Yánez et al., 2010). En este caso, el enfoque es multidisciplinar, empleando, por primera vez, series de observaciones recogidas de forma coordinada y simultánea. A lo largo de sus ochos capítulos, se analiza la variabilidad climática atmosférica reciente y su influencia sobre las condiciones oceanográficas de la región, especialmente en relación con la intensidad y frecuencia del afloramiento de aguas profundas que determina, en gran medida, el aporte estacional de nutrientes a la superficie y, por tanto, la producción biológica. Se describen las tendencias en el nivel del mar a partir de las medidas de los mareógrafos de la zona con una estimación de los niveles extremos esperados a largo plazo. Se realiza un análisis comparativo –entre Galicia y el Cantábrico– de la variabilidad en los nutrientes inorgánicos y se determinan los elementos limitantes de la producción primaria en cada zona. Finalmente, se analizan las variaciones en las comunidades de fitoplancton, picoplancton y zooplancton como indicadoras de cambios en el ecosistema pelágico, destacando las fluctuaciones en la biomasa y producción primaria, base de la red trófica pelágica de la región, y la presencia de medusas y salpas y su relación con el clima., This book presents a synthesis of the oceanic time-series observations of IEO in the Atlantic region of northern Spain. These series, starting in 1943 with tide-gauges, reveal evidence of interanual changes in physical, chemical and biological properties of the ocean that were related to climatic factors, allowing to estimate future impacts of climate on the ocean. The volume continues the series started with “Climate Change in the Spanish Mediterranean” (Vargas Yánez et al., 2010). In this case the study is multidisciplinary, including for the first time series obtained in coordinated and simultaneous observational programs. The eight chapters first analyse recent climatic variability and its influence on the regional oceanography, particularly in relation to the intensity and frequency of the deep-water upwelling that largely determines the seasonal inputs of nutrients and primary production in this region. Next, the main trends in sea level revealed by tidal gauges along with the estimates of expected extreme levels are described. The variability in inorganic nutrients and the identification of limiting elements for primary production were presented as a comparative analysis between Galicia (in the West) and the Mar Cantábrico (in the east). Finally, the variability in the composition of the plankton communities, including phytoplankton, picoplankton and zooplankton, is analysed as indicative of changes in the pelagic ecosystem. Particular attention is given to the fluctuations in primary biomass and production and to the presence of salps and jellyfish in relation to climate.

The available information on phytoplankton biomass and species composition in Galician waters was studied to find out their spatial variability as well as the annual trends. The areas covered included the oceanic zone, the shelf and the inner part of the Rías. In general a significant drop in diatoms was observed. The series also indicated an increase in dinoflagellates, although it was not statistically significant. The diatom species related to blooms in the area declined, whereas those indicative of weak upwelling or stratificacion showed an increase. Even though not all trends were significant, the available data are consistent with the decrease in upwelling intensity over the last 40 years. The results also suggest that effects of climate changes on phytoplankton may be delayed for several years. In any case, the large oceanographic variability of the region, along with the lack of continuity of some of the series, makes it difficult to find clear relationships between environmental changes and phytoplankton.

Long-term variability of phytoplankton biomass (chlorophyll a) and primary production (carbon fixation) in relation to changes in climatic and oceanographic factors was analysed for oceanic and shelf waters of the north and northwest Iberian Peninsula. Changes related to stratification in the water column and upwelling intensity were specifically addressed. The time series include measurements of primary production and biomass over 19 yr. Seasonally, the main mode of temporal variability of the series is the occurrence of phytoplankton blooms during the winter-spring and summer- autumn transition periods. On the northwestern coast (Galicia), the blooms are more frequent and attain higher biomass and production values than on the northern coast (Mar Cantábrico) due to the longer duration and higher intensity of upwelling in the former region. Even for the longest series there is no significant long-term trend in biomass, but primary production increased in Galicia and decreased in the Mar Cantábrico at nearly equivalent rates when considering monthly series. The lagged relationships between external factors and phytoplankton biomass and production suggest non-linear interactions between phytoplankton and climate. Neither the increase in surface stratification nor the decrease in upwelling intensity has negatively affected primary production in this region following consistent and systematic patterns. Changes in the amount and proportions of nutrients during winter water-mass formation, and an increased use of nutrients remineralised in situ, are proposed as the main causes of decadal variability in primary production in this region.

We present ocean, basin-scale simultaneous measurements of N2-fixation, nitrate diffusion, and primary production along a south–north transect in the Atlantic Ocean crossing three biogeographic provinces: the south subtropical Atlantic (SSA; , 31uS–12uS), the equatorial Atlantic (EA; , 12uS–16uN), and the north subtropical Atlantic (NSA, , 16uN–9uN) in April–May 2008. N2-fixation and primary production were measured as 15N2 and 14C uptake, respectively. Dissipation rates of turbulent kinetic energy (e) were measured with a microstructure profiler. The vertical input of nitrate through eddy diffusion was calculated from the product of diffusivity, derived from e, and the gradient of nanomolar nitrate concentration across the base of the euphotic zone. The mean N2-fixation rate in EA was 56 6 49 mmol N m22 d21, whereas SSA and NSA had much lower values (, 10 mmol N m22 d21). Because of the large spatial variability in nitrate diffusion (34 6 50, 405 6 888, and 844 6 1258 mmol N m22 d21 in SSA, EA, and NSA, respectively), the contribution of N2-fixation to new production in the SSA, EA, and NSA was 44% 6 30%, 22% 6 19%, and 2% 6 2%, respectively. The differences between SSA and NSA in the contribution of N2 fixation were partly due to the contrasting seasonal forcing in each hemisphere, which likely affected both N2 fixation rates and vertical nitrate diffusion. The variability in the nitrogen budget of the Atlantic subtropical gyres was unexpectedly high and largely uncoupled from relatively constant phytoplankton standing stocks and primary production rates.

Summer upwelling and downwelling processes were characterized in the Northern Galician Rias during July and August 2008 by means of sampling carried out onboard R/V Mytilus (CSIC) and R/V Lura (IEO). Thermohaline variables, dissolved oxygen, nutrients, chlorophyll, phytoplankton, ciliates and zooplankton abundances were measured at sections located in the Rias of Viveiro, Barqueiro and Ortigueira and their adjacent shelves. Ekman transport was calculated from QuikSCAT satellite, upwelling intensity estimated with upwelling index from the average daily geostrophic winds, and SST maps obtained from NASA GHRSST satellite. Ekman transport and SST behaviour showed two different patterns: (i) offshore and upwelling favourable conditions on 13–22nd of July; (ii) onshore and downwelling favourable conditions from 23rd July to 19th August. During upwelling, TS diagram showed an intrusion of Eastern North Atlantic Central Water affecting the continental shelf but not the rias. Nutrient salt concentrations increased with depth, reaching their maximum values near the mouth of Ortigueira Ria. During downwelling, coastal water increased its temperature (18.5–19.8 °C) and was retained inside rias; nutrients were nearly depleted, except for the innermost ria (estuarine zone) due to fluvial nutrient inputs. In this inner area, the maximum of chlorophyll-a (Barqueiro Ria) was observed. Low phytoplankton abundances were measured in both cases, even though a short increase in the plankton biomass was observed inside rias during upwelling, while under downwelling a small red tide of Lingulodinium polyedrum was detected. During the upwelling period Northern Rias tend to be mesotrophic systems as revealed by nutrient concentrations, chlorophyll levels and plankton abundances. On the contrary, in similar situations, the Western Rias behaves as eutrophics. In the Northern Galician shelf, the average of upwelling (downwelling) was 1.9±0.8 (2.1±1.0) events yr−1 from May to September (1990–200

To ascertain the general patterns in phytoplankton size structure of a temperate, coastal ecosystem, we determined the scaling relationship between total abundance and cell size (size spectrum) for nano- and micro-phytoplankton in a shelf station off NW Iberian Peninsula on a monthly basis during the period 1993–2002. The inverse linear relationship between log abundance and log cell size was persistent throughout the water column and across seasonal and inter-annual time scales. In addition, and despite the high productivity and marked temporal variability in water column structure at our study site, departures from linearity in the size spectra were rare. The slope (−0.96) of the overall size spectrum for the entire time series indicated that roughly equal amounts of biomass were present over different logarithmic size classes in the size range considered. The phytoplankton size spectra had similar average slopes during winter mixing, early upwelling, summer stratification and autumn downwelling, suggesting that, under these oceanographic conditions, both nano- and micro-phytoplankton respond similarly to environmental variability. In contrast, significantly less negative slopes were observed during upwelling relaxation, indicating an increased importance of larger cells. Our results illustrate the utility of individual size distributions to provide a synthetic description of phytoplankton community structure in dynamic, non steady-state marine ecosystems.

Seasonal variability of diatom abundances was measured in the water column, sediment traps and in the underlying sediment from the Pontevedra ría. Seasonal variations of the diatom species in the water column were indicative of ocean influence, river influx and water column stratification. Additionally, analysis of diatom distribution and other biosiliceous components was studied in 27 surface sediment samples. The marine planktonic assemblage in the surface sediments is located in the outer area of the ría. It is mainly composed by Chaetoceros resting spores (R.S.) together with Thalassionema nitzschioides, Leptocylindrus danicus R.S. and Paralia sulcata. Higher abundances of freshwater assemblages are limited to the inner ría, as well as crysophycean cysts and phytoliths, where the Lérez River has its strongest influence. The benthic group is also restricted to the innermost and shallow areas where shallow water depths allow for growth. Factor analysis distinguished between estuarine-freshwater and ocean-dominated upwelling areas in the Pontevedra ría. A mixed area where both processes take place was also discriminated. A good agreement between the biocoenotic and the thanatocoenotic diatom community was found. Despite the fact that the low preservation of some species obscures the interpretation of the sedimentary record of biogenic silica flux and accumulation, the results are useful in the reconstruction of hydrodynamics and production in the marine paleo-records in the ría and estuarine domains. This is even though the low preservation of some species results in difficulties interpreting the sedimentary record. Biological response, production patterns and diatom succession related with ecological preferences in this ría can also be applied to other rías and temperate coastal environments.

The evolution of a warm water mass related to the Iberian Poleward Current (IPC) was characterized along the northern Galician shelf in November 2008 by means of Sea Surface Temperature and wind data. It was observed that under upwelling favorable conditions water temperature decreased along the northern coast and a temperature break appeared between Cape Vilano and Cape Ortegal showing a relaxation of the poleward intrusion. The effect of the IPC was also analyzed inside the Northern Galician Rias taking into account the hydrographical and biogeochemical properties measured on November 18. Water driven by the IPC was observed close to the mouth of the rias, around Cape Estaca de Bares, causing a nutrient salts decrease. Inside the rias a slight biological activity was found near surface resulting from fluvial contributions.

To study the biogeochemical response and the coupling plankton–benthos to an unusual winter upwelling event a cruise was carried out in February 2005 in the Sound of Corcubión, near Cape Finisterre (NW Iberian Peninsula), the Galician upwelling core. This area represents the northern boundary of the Eastern North Atlantic Upwelling System (ENAUS). The spatial distribution of plankton assemblages (phytoplankton and zooplankton), chlorophyll, physical and chemical parameters as well as diatom distribution in surface sediments, were studied in a total of 17 stations in the Sound. The upwelling processes caused an important accumulation of water in the inner Sound and near the Cape. This accumulation zone must be persistent through the upwelling events in the area, including those of summer, as indicated by the diatoms' distribution in the sediment. Unlike the summer upwelling events, the main effect of winter upwelling in the area is the increase in solar radiation due to the persistent clear skies. In this season nutrient supply is not critical due to water column mixing. The meteorological conditions were equivalent to those of early spring. As a result, both phyto- and zooplankton species assemblages were typical of spring blooms in Galician coasts. The bloom lasted for up to 6 days, as estimated from the availability and uptake of nitrogen forms. Winter blooms represented ca. 20% of total annual phytoplankton biomass, and 30% of the average biomass during summer upwelling, in the period 1997–2007, as estimated from the analysis of both, in situ and satellite derived chlorophyll.

The mean intensity of the NE Atlantic upwelling system at its northern limit (Galicia, NW Spain) decreased during the last 40 years. At the same time, warming of surface waters was detected. Plankton biomass and composition are expected to reflect such changes when integrated over large time and space scales. In this study, biomass, abundance and species composition of phyto- and zooplankton were analysed to search for significant patterns of annual change and relations with upwelling intensity. Regionally integrated, mostly offshore, data were obtained from the Continuous Plankton Recorder (since 1958) whereas coastal data from Vigo and A Coruña came from the Radiales program (since 1987). No significant trends were found in phytoplankton biomass at either regional or local scales. However, there was a significant decrease in diatom abundance at regional scales and also of large species at local scales. Zooplankton abundance (mainly copepods) significantly decreased offshore but increased near the coast. Biomass of zooplankton also increased near the coast, with the fastest rates in the south. Warm-water species, like Temora stylifera, were increasingly abundant at both regional and local scales. Significant correlations between upwelling intensity and plankton suggest that climatic effects were delayed for several years. Our results indicate that the effects of large scale climatic trends on plankton communities are being effectively modulated within the pelagic ecosystem in this upwelling region.

A winter shelf-water upwelling evidence (February 2008) is described by first time in the Northern Galician Rias (NW Iberian Peninsula). On February 20, after 9 consecutive days of upwelling favorable conditions, inside the O Barqueiro Ria was observed the presence of seawater below 10 m depth which replaced the less saline water previously observed in January. This situation was in agreement with the analyzed Ekman transport close to the northern Galician coast. Salinity and temperature distribution revealed that the upwelled water inside the rias corresponds to shelf bottom seawater which is not associated with Eastern North Atlantic Central Water or the Iberian Poleward Current. In addition, TS diagram indicated a higher influence of upwelling eastward (Viveiro–Barqueiro–Ortigueira). Nutrient salts' concentrations also suggested the presence of seawater from subsurface origin with a small variation with regard to the winter mixing in this marine area. Plankton showed the existence of spring conditions related to solar radiation increase associated to upwelling favorable winds. Some species also corroborated the intrusion of shelf-water inside the ria. Results from the analysis of Ekman transport data from 1967 to 2007 revealed that this event cannot be considered an isolated episode. In fact, the number of days per month under upwelling favorable conditions in winter (January–March) was not negligible (8–10 days) showing that upwelling events along the northern Galician coast are also possible during winter.

The spatial distribution of phytoplankton assemblages, chlorophyll, primary production and physical and chemical parameters were studied in the Pontevedra Ria in Galicia (NW Iberian Peninsula) from October 1997 to October 1998. In addition to the usual oceanographic periods described for the Galician Coast, two other periods were observed: a Prebloom or winter bloom, occurring during calm, sunny days in winter and a Continental period, related to the allochthonous intrusion of low salinity water from the Miño River in late spring. The phytoplankton biomass and production in both periods reached values of up to 145 mgChl-a m−2 and 3.6 gC m−2 day−1, respectively, which were similar to those found in summer upwelling blooms. Throughout the year, the phytoplankton biomass and primary production gradients along the ria’s axis were highly dependent on the balance between upwelling and runoff. When the latter prevailed, increased values were measured toward the inner ria, while the opposite pattern was observed during summer upwelling blooms. According to projections derived from climate models and the analysis of wind patterns, temperature and precipitation trends in the area, a drop in the productivity of the ria would be expected as a result of reduced upwelling intensity in summer and decreasing rainfall in spring. In any case the estuarine part of the ria would be the most seriously affected.