The abundance, taxonomic composition and biomass of plankton components were studied in the mostl... more The abundance, taxonomic composition and biomass of plankton components were studied in the mostly eutrophic waters of the Ria de Ferrol (Galicia, NW Spain) in contrasting seasons. Three stations arranged in a transect along the main ria axis were sampled during cruises in February, May, July and September 2000. Phytoplankton, bacteria, micro-(40-200 mm) and mesozooplankton (O200 mm) compartments were considered. Phytoplankton blooms (O10 3 cel ml ÿ1 ) and high total plankton biomass (up to 44 g C m ÿ2 ) was found at all seasons, except in winter when values were !1 g C m ÿ2 . Phytoplankton generally accounted for most of total plankton biomass, particularly in late summer, thus driving most of plankton dynamics. The blooming species were always diatoms, either fast-growing, chain-forming species, well adapted to relatively turbulent conditions (e.g. Chaetoceros socialis), or disturbancetolerant, estuarine adapted species (e.g. Skeletonema costatum). In addition, microflagellates (!10 mm) reached high abundances, particularly during summer. The influence of shelf waters, where coastal upwelling events are frequent for most of the spring and summer, prevents the establishment of a marked pycnocline and the dominance of dinoflagellates. Microheterotrophs (bacteria, protozoa and larval stages of metazoa) increased their abundance and biomass from winter to late summer, while mesozooplankton peaked in spring and summer. Zooplankton dynamics were characterised by the presence of large numbers of larvae of both planktonic copepods and benthic metazoans, the latter mainly cirripeds and bivalve molluscs. The absence of a definite succession pattern in the mesozooplankton species abundance data, in contrast with phytoplankton data, along with the dominance of estuarine species (e.g. Acartia margalefi), suggest that mesozooplankton communities inside the ria behave differently from communities in shelf waters. Despite its small size and reduced influence of upwelling compared with other Galician rias, the input of shelf waters in the Ria de Ferrol drives massive phytoplankton blooms supporting a rich heterotrophic community.
The abundance, taxonomic composition and biomass of plankton components were studied in the mostl... more The abundance, taxonomic composition and biomass of plankton components were studied in the mostly eutrophic waters of the Ria de Ferrol (Galicia, NW Spain) in contrasting seasons. Three stations arranged in a transect along the main ria axis were sampled during cruises in February, May, July and September 2000. Phytoplankton, bacteria, micro-(40-200 mm) and mesozooplankton (O200 mm) compartments were considered. Phytoplankton blooms (O10 3 cel ml ÿ1 ) and high total plankton biomass (up to 44 g C m ÿ2 ) was found at all seasons, except in winter when values were !1 g C m ÿ2 . Phytoplankton generally accounted for most of total plankton biomass, particularly in late summer, thus driving most of plankton dynamics. The blooming species were always diatoms, either fast-growing, chain-forming species, well adapted to relatively turbulent conditions (e.g. Chaetoceros socialis), or disturbancetolerant, estuarine adapted species (e.g. Skeletonema costatum). In addition, microflagellates (!10 mm) reached high abundances, particularly during summer. The influence of shelf waters, where coastal upwelling events are frequent for most of the spring and summer, prevents the establishment of a marked pycnocline and the dominance of dinoflagellates. Microheterotrophs (bacteria, protozoa and larval stages of metazoa) increased their abundance and biomass from winter to late summer, while mesozooplankton peaked in spring and summer. Zooplankton dynamics were characterised by the presence of large numbers of larvae of both planktonic copepods and benthic metazoans, the latter mainly cirripeds and bivalve molluscs. The absence of a definite succession pattern in the mesozooplankton species abundance data, in contrast with phytoplankton data, along with the dominance of estuarine species (e.g. Acartia margalefi), suggest that mesozooplankton communities inside the ria behave differently from communities in shelf waters. Despite its small size and reduced influence of upwelling compared with other Galician rias, the input of shelf waters in the Ria de Ferrol drives massive phytoplankton blooms supporting a rich heterotrophic community.
Chlorophyll-a and primary production on the euphotic zone of the N-NW Spanish shelf were studied ... more Chlorophyll-a and primary production on the euphotic zone of the N-NW Spanish shelf were studied at 125 stations between 1984 and 1992. Three geographic areas (Cantabrian Sea, Rías Altas and Was Baixas), three bathymetric ranges (20 to 60 m, 60 to 150 m and stations deeper than 200 m), and four oceanographic stages (spring and autumn blooms, summer upwelling, summer stratification and winter mixing) were considered. One of the major sources of variability of chlorophyll and production data was season. Bloom and summer upwelling stages have equivalent mean and maximum values. Average chlorophyll-a concentrations approximately doubled in every step of the increasing productivity sequence: winter mixing — summer stratification — high productivity (upwelling and bloom) stages. Average primary production rates increased only 60% in the described sequence. Mean (± sd) values of chlorophyll-a and primary production rates during the high productivity stages were 59.7 ± 39.5 mg Chl-a m−2 and 86.9 ± 44.0 mg C m−2 h−1, respectively. Significant differences in both chlorophyll and primary production resulted between geographic areas in most stages. Only 27 stations showed the effects of the summer upwelling that affected coastal areas in the Cantabrian Sea and Rías Baixas shelf, but also shelf-break stations in the Rías Altas area. The Rías Baixas area had lower chlorophyll than both the Rías Altas and the Cantabrian Sea areas during spring and autumn blooms, but higher during summer upwelling events. On the contrary, primary production rates were higher in the Rías Baixas area during blooms in spring and autumn. Mid-shelf areas showed the highest chlorophyll concentrations during high productivity stages, probably due to the existence of frontal zones in all geographic areas considered. The estimated phytoplankton growth rates were comparable to those of other coastal upwelling systems, with average values lower than the maximum potential growth rates. Doubling rates for upwelling and stratification stages in the northern and Rías Altas shelf areas were equivalent, despite larger biomass accumulations during upwelling events. Low turnover rates of the existing biomass in the Rías Baixas shelf in upwelling stages suggests that the accumulation of phytoplankton was due mainly to the export from the highly productive rías, while the contribution of in situ production to these accumulations was relatively lower.
Chlorophyll-a and primary production on the euphotic zone of the N-NW Spanish shelf were studied ... more Chlorophyll-a and primary production on the euphotic zone of the N-NW Spanish shelf were studied at 125 stations between 1984 and 1992. Three geographic areas (Cantabrian Sea, Rías Altas and Was Baixas), three bathymetric ranges (20 to 60 m, 60 to 150 m and stations deeper than 200 m), and four oceanographic stages (spring and autumn blooms, summer upwelling, summer stratification and winter mixing) were considered. One of the major sources of variability of chlorophyll and production data was season. Bloom and summer upwelling stages have equivalent mean and maximum values. Average chlorophyll-a concentrations approximately doubled in every step of the increasing productivity sequence: winter mixing — summer stratification — high productivity (upwelling and bloom) stages. Average primary production rates increased only 60% in the described sequence. Mean (± sd) values of chlorophyll-a and primary production rates during the high productivity stages were 59.7 ± 39.5 mg Chl-a m−2 and 86.9 ± 44.0 mg C m−2 h−1, respectively. Significant differences in both chlorophyll and primary production resulted between geographic areas in most stages. Only 27 stations showed the effects of the summer upwelling that affected coastal areas in the Cantabrian Sea and Rías Baixas shelf, but also shelf-break stations in the Rías Altas area. The Rías Baixas area had lower chlorophyll than both the Rías Altas and the Cantabrian Sea areas during spring and autumn blooms, but higher during summer upwelling events. On the contrary, primary production rates were higher in the Rías Baixas area during blooms in spring and autumn. Mid-shelf areas showed the highest chlorophyll concentrations during high productivity stages, probably due to the existence of frontal zones in all geographic areas considered. The estimated phytoplankton growth rates were comparable to those of other coastal upwelling systems, with average values lower than the maximum potential growth rates. Doubling rates for upwelling and stratification stages in the northern and Rías Altas shelf areas were equivalent, despite larger biomass accumulations during upwelling events. Low turnover rates of the existing biomass in the Rías Baixas shelf in upwelling stages suggests that the accumulation of phytoplankton was due mainly to the export from the highly productive rías, while the contribution of in situ production to these accumulations was relatively lower.
Current flow cytometry techniques allow the rapid estimation of the abundance of 2 distinct group... more Current flow cytometry techniques allow the rapid estimation of the abundance of 2 distinct groups of heterotrophic bacteria, characterized by their relative nucleic acid content. High nucleic acid (HNA) bacteria are, at least in coastal environments, usually regarded as more active than the low nucleic acid (LNA) group. We tested the effects of substrate supply and bacterial cell size on the relationship between bacterial activity and the abundance of HNA bacteria by simultaneous measurements of LNA and HNA cell distributions, chlorophyll a and 3 H-leucine uptake rates in temperate shelf waters of the northern Iberian Peninsula. We considered 3 zones based on hydrological properties. Significant correlations were found between bacterial activity (range 0.1 to 80 pmol Leu l -1 h -1 ) and both total and relative (range 28 to 84%) HNA cell abundance for pooled data, but the ready use of HNA bacterial abundance as a proxy for activity in natural systems was questioned by the low percentage of variance explained (16%). However, a detailed regional study of bottom-up effects revealed that the strength of this relationship increased significantly when bacteria were apparently controlled by phytoplankton substrate supply. Moreover, the relationship between mean biomass (overall range 12.4 to 21.2 fg C cell -1 ) and abundance-activity correlation coefficients in the 3 zones (r = 0.94, p = 0.005, n = 6) suggests that only at large cell sizes can we expect bacterial activity and production to be reasonably predicted by the abundance of HNA cells.
This study describes the main seasonal stages in oceanographic conditions and phytoplankton off L... more This study describes the main seasonal stages in oceanographic conditions and phytoplankton off La Coruñ a (Galicia, NW Spain), during 1991 and 1992, based mainly on monthly cruises near the coast. Upwelling conditions were studied using an upwelling index calculated from local winds. The Galician coast is affected by a long upwelling season for most of the year. The upwelling pulses interact with the thermal stratification-mixing cycle of surface waters, primarily affecting the dynamics of phytoplankton. In addition, the presence of water masses of different salinity in the subsurface layers changes the stratification of the water column. The less-saline North Atlantic Central Water (NACW) was normally associated with upwelling events during summer. However, on several occasions during the study, the presence of Eastern North Atlantic Water (ENAW) of subtropical origin was observed with salinities up to 36·22 and temperatures between 13 and 14 C.
Current flow cytometry techniques allow the rapid estimation of the abundance of 2 distinct group... more Current flow cytometry techniques allow the rapid estimation of the abundance of 2 distinct groups of heterotrophic bacteria, characterized by their relative nucleic acid content. High nucleic acid (HNA) bacteria are, at least in coastal environments, usually regarded as more active than the low nucleic acid (LNA) group. We tested the effects of substrate supply and bacterial cell size on the relationship between bacterial activity and the abundance of HNA bacteria by simultaneous measurements of LNA and HNA cell distributions, chlorophyll a and 3 H-leucine uptake rates in temperate shelf waters of the northern Iberian Peninsula. We considered 3 zones based on hydrological properties. Significant correlations were found between bacterial activity (range 0.1 to 80 pmol Leu l -1 h -1 ) and both total and relative (range 28 to 84%) HNA cell abundance for pooled data, but the ready use of HNA bacterial abundance as a proxy for activity in natural systems was questioned by the low percentage of variance explained (16%). However, a detailed regional study of bottom-up effects revealed that the strength of this relationship increased significantly when bacteria were apparently controlled by phytoplankton substrate supply. Moreover, the relationship between mean biomass (overall range 12.4 to 21.2 fg C cell -1 ) and abundance-activity correlation coefficients in the 3 zones (r = 0.94, p = 0.005, n = 6) suggests that only at large cell sizes can we expect bacterial activity and production to be reasonably predicted by the abundance of HNA cells.
The project ''Studies on time series of oceanographic data'' was established as a pilot project b... more The project ''Studies on time series of oceanographic data'' was established as a pilot project by the Instituto Españ ol de Oceanografía (I.E.O.) in 1991. After more than a decade, the project has grown to encompass a network of 19 sampling stations in five different transects along the North and Northwest coast of Spain: Vigo, Coruñ a, Cudillero, Gijó n and location a coastal-ocean gradient is sampled monthly for hydrography, nutrients and planktonic communities. We have used these data to set with statistical significance the range of variability of several environmental variables and biological communities and determined the rates and trends of warming due to climate change as well as to describe some direct and indirect effects of the increase in water temperature on the pelagic ecology. The project had substantially contributed to get a deeper knowledge on planktonic communities and species and to produce baselines, climatologies and reference levels for the North coast of Spain, which allow us to do accurate evaluations on the effects of environmental perturbations on the ecosystem and forecast the expected recovery time. These changes both in the physical structure of the water column and in the trophic level that drives ecosystem production and functioning are likely to also modify the structure, production and organization of higher trophic levels like zooplankton. Our analysis shows that only through sustained and repeated time series sampling it is feasible to detect these changes. Indeed, the annual cycle of zooplankton biomass seems to be restricted in time, with the annual decrease in zooplankton biomass matching the onset of stratification. The observed patterns in the seasonal occurrence of incoming species like Temora stylifera are related to those observed in the water column stratification, which is reinforced by the warming trend.
Journal of The Marine Biological Association of The United Kingdom, 2004
Slope Water anticyclonic Oceanic eDDIES (SWODDIES) are typical mesoscale features of open-ocean w... more Slope Water anticyclonic Oceanic eDDIES (SWODDIES) are typical mesoscale features of open-ocean waters of the southern Bay of Biscay which usually develop in winter by shedding from the seasonal poleward current £owing along the northern Spanish slope. These eddies have been intensively studied from the physical perspective. However, their e¡ect on the distribution of biological properties and on the functioning of the pelagic ecosystem has not been assessed so far. To this aim, a sea-truth, multidisciplinary and comprehensive study of a SWODDY was carried out in summer 1998. The eddy, radius of *50 km, was initially centred at 45.58N 6.08W, being characterized by a relatively homogeneous core of water in the centre of the eddy extending from 80 to about 200 dbar. In the central region of the core, temperature (12.55^12.758C) and salinity (*35.70) values were higher than outside the eddy. The optical properties of the eddy also di¡ered from those of the surrounding waters. A distinct biological signature was found associated with the eddy. Depth-integrated chlorophyll-a concentrations were 25% higher at the eddy centre where upward doming of the seasonal pycnocline (up to 30 dbar) occurred. Enhanced phytoplankton biomass was related to a higher contribution of 410 mm cells, mainly represented by diatoms and chrysophyceans. Phytoplankton and mesozooplankton species composition in and outside the eddy di¡ered signi¢cantly re£ecting the coastal origin of the water parcel trapped by the eddy. The sharp modi¢cation of the planktonic community composition, biomass and associated size-structure caused by slope water oceanic eddies are likely to exert a signi¢cant e¡ect upon the upper trophic levels of the pelagic ecosystem of the southern Bay of Biscay.
The project ''Studies on time series of oceanographic data'' was established as a pilot project b... more The project ''Studies on time series of oceanographic data'' was established as a pilot project by the Instituto Españ ol de Oceanografía (I.E.O.) in 1991. After more than a decade, the project has grown to encompass a network of 19 sampling stations in five different transects along the North and Northwest coast of Spain: Vigo, Coruñ a, Cudillero, Gijó n and location a coastal-ocean gradient is sampled monthly for hydrography, nutrients and planktonic communities. We have used these data to set with statistical significance the range of variability of several environmental variables and biological communities and determined the rates and trends of warming due to climate change as well as to describe some direct and indirect effects of the increase in water temperature on the pelagic ecology. The project had substantially contributed to get a deeper knowledge on planktonic communities and species and to produce baselines, climatologies and reference levels for the North coast of Spain, which allow us to do accurate evaluations on the effects of environmental perturbations on the ecosystem and forecast the expected recovery time. These changes both in the physical structure of the water column and in the trophic level that drives ecosystem production and functioning are likely to also modify the structure, production and organization of higher trophic levels like zooplankton. Our analysis shows that only through sustained and repeated time series sampling it is feasible to detect these changes. Indeed, the annual cycle of zooplankton biomass seems to be restricted in time, with the annual decrease in zooplankton biomass matching the onset of stratification. The observed patterns in the seasonal occurrence of incoming species like Temora stylifera are related to those observed in the water column stratification, which is reinforced by the warming trend.
Herbivory by copepods was studied from the coast towards the ocean, during a bloom in May 1994 of... more Herbivory by copepods was studied from the coast towards the ocean, during a bloom in May 1994 off NW Spain. Ingestion rates were estimated by the gut chlorophyll content method in three size fractions. The chlorophyll content displayed significant daily cycles. Three different water bodies were described: coastal, shelf break and oceanic; the latter two zones separated by a thermohaline frontal structure. Marked differences in plankton species composition, vertical distribution and biological rates were found between zones. Thehighest phytoplankton biomass, dominated by chainforming diatoms, occurred in the oceanic zone associated with low primary production rates. Copepod feeding had a low effect on oceanic phytoplankton; up to 0.2% of carbon stock and <3% of carbon production was consumed daily. In contrast, medium-sized and large copepods removed 3% of carbon stock and 12% of primary production daily near the coast, where phytoplankton were dominated by small flagellates in active growth. The highest variability in both plankton composition and ingestion rates was found in the shelf-break zone, probably due to displacements of the front. Copepods exerted a moderate predation pressure on phytoplankton in coastal waters. Meanwhile, the impact of copepods on the offshore bloom was negligible and the fate of the accumulated particulate carbon would be mostly determined by sedimentation and water dynamics.
Journal of The Marine Biological Association of The United Kingdom, 2004
Slope Water anticyclonic Oceanic eDDIES (SWODDIES) are typical mesoscale features of open-ocean w... more Slope Water anticyclonic Oceanic eDDIES (SWODDIES) are typical mesoscale features of open-ocean waters of the southern Bay of Biscay which usually develop in winter by shedding from the seasonal poleward current £owing along the northern Spanish slope. These eddies have been intensively studied from the physical perspective. However, their e¡ect on the distribution of biological properties and on the functioning of the pelagic ecosystem has not been assessed so far. To this aim, a sea-truth, multidisciplinary and comprehensive study of a SWODDY was carried out in summer 1998. The eddy, radius of *50 km, was initially centred at 45.58N 6.08W, being characterized by a relatively homogeneous core of water in the centre of the eddy extending from 80 to about 200 dbar. In the central region of the core, temperature (12.55^12.758C) and salinity (*35.70) values were higher than outside the eddy. The optical properties of the eddy also di¡ered from those of the surrounding waters. A distinct biological signature was found associated with the eddy. Depth-integrated chlorophyll-a concentrations were 25% higher at the eddy centre where upward doming of the seasonal pycnocline (up to 30 dbar) occurred. Enhanced phytoplankton biomass was related to a higher contribution of 410 mm cells, mainly represented by diatoms and chrysophyceans. Phytoplankton and mesozooplankton species composition in and outside the eddy di¡ered signi¢cantly re£ecting the coastal origin of the water parcel trapped by the eddy. The sharp modi¢cation of the planktonic community composition, biomass and associated size-structure caused by slope water oceanic eddies are likely to exert a signi¢cant e¡ect upon the upper trophic levels of the pelagic ecosystem of the southern Bay of Biscay.
The storage of nitrate by phytoplankton cells during the early phases of upwelling was studied in... more The storage of nitrate by phytoplankton cells during the early phases of upwelling was studied in coastal stations off northern Spain (southern Bay of Biscay) between 1990 and 1994. In this region, a persistent upwelling during summer is characterised by intermittent pulses of variable intensity, and increased nutrient concentrations in the surface layer. The main effect of an upwelling pulse on phytoplankton distribution is the shifting of the chlorophyll a and primary production maxima to near the surface. When the upwelling relaxes, thermal stratification of the water column occurs, and a distinct subsurface chlorophyll maximum develops below the production maximum. An accumulation of intracellular nitrate characterized the early phases of upwelling (mean = 2.73 μmol N m−3), maximum concentrations being attained at depths where biomass and production values were moderate. In contrast, phytoplankton cells from non-upwelling situations contained significantly lower concentrations of intracellular nitrate (mean = 0.17 μmol N m−3). The variations in the intracellular pool of nitrate may result from the differential allocation of resources within the cell as a result of variations in the energy available, since the uptake and assimilation of nitrate is a relatively expensive process involving several enzymatic systems. We hypothesize that nitrate storage by phytoplankton cells is characteristic of early phases of upwelling and is linked to patterns of carbon fixation. Average nitrogen budgets for upwelling and non-upwelling situations indicate that intracellular nitrate reserves are not responsible for maintaining high phytoplankton growth rates, since they only account for <2% of daily primary production during upwelling events.
The abundance, taxonomic composition and biomass of plankton components were studied in the mostl... more The abundance, taxonomic composition and biomass of plankton components were studied in the mostly eutrophic waters of the Ria de Ferrol (Galicia, NW Spain) in contrasting seasons. Three stations arranged in a transect along the main ria axis were sampled during cruises in February, May, July and September 2000. Phytoplankton, bacteria, micro-(40-200 mm) and mesozooplankton (O200 mm) compartments were considered. Phytoplankton blooms (O10 3 cel ml ÿ1 ) and high total plankton biomass (up to 44 g C m ÿ2 ) was found at all seasons, except in winter when values were !1 g C m ÿ2 . Phytoplankton generally accounted for most of total plankton biomass, particularly in late summer, thus driving most of plankton dynamics. The blooming species were always diatoms, either fast-growing, chain-forming species, well adapted to relatively turbulent conditions (e.g. Chaetoceros socialis), or disturbancetolerant, estuarine adapted species (e.g. Skeletonema costatum). In addition, microflagellates (!10 mm) reached high abundances, particularly during summer. The influence of shelf waters, where coastal upwelling events are frequent for most of the spring and summer, prevents the establishment of a marked pycnocline and the dominance of dinoflagellates. Microheterotrophs (bacteria, protozoa and larval stages of metazoa) increased their abundance and biomass from winter to late summer, while mesozooplankton peaked in spring and summer. Zooplankton dynamics were characterised by the presence of large numbers of larvae of both planktonic copepods and benthic metazoans, the latter mainly cirripeds and bivalve molluscs. The absence of a definite succession pattern in the mesozooplankton species abundance data, in contrast with phytoplankton data, along with the dominance of estuarine species (e.g. Acartia margalefi), suggest that mesozooplankton communities inside the ria behave differently from communities in shelf waters. Despite its small size and reduced influence of upwelling compared with other Galician rias, the input of shelf waters in the Ria de Ferrol drives massive phytoplankton blooms supporting a rich heterotrophic community.
The abundance, taxonomic composition and biomass of plankton components were studied in the mostl... more The abundance, taxonomic composition and biomass of plankton components were studied in the mostly eutrophic waters of the Ria de Ferrol (Galicia, NW Spain) in contrasting seasons. Three stations arranged in a transect along the main ria axis were sampled during cruises in February, May, July and September 2000. Phytoplankton, bacteria, micro-(40-200 mm) and mesozooplankton (O200 mm) compartments were considered. Phytoplankton blooms (O10 3 cel ml ÿ1 ) and high total plankton biomass (up to 44 g C m ÿ2 ) was found at all seasons, except in winter when values were !1 g C m ÿ2 . Phytoplankton generally accounted for most of total plankton biomass, particularly in late summer, thus driving most of plankton dynamics. The blooming species were always diatoms, either fast-growing, chain-forming species, well adapted to relatively turbulent conditions (e.g. Chaetoceros socialis), or disturbancetolerant, estuarine adapted species (e.g. Skeletonema costatum). In addition, microflagellates (!10 mm) reached high abundances, particularly during summer. The influence of shelf waters, where coastal upwelling events are frequent for most of the spring and summer, prevents the establishment of a marked pycnocline and the dominance of dinoflagellates. Microheterotrophs (bacteria, protozoa and larval stages of metazoa) increased their abundance and biomass from winter to late summer, while mesozooplankton peaked in spring and summer. Zooplankton dynamics were characterised by the presence of large numbers of larvae of both planktonic copepods and benthic metazoans, the latter mainly cirripeds and bivalve molluscs. The absence of a definite succession pattern in the mesozooplankton species abundance data, in contrast with phytoplankton data, along with the dominance of estuarine species (e.g. Acartia margalefi), suggest that mesozooplankton communities inside the ria behave differently from communities in shelf waters. Despite its small size and reduced influence of upwelling compared with other Galician rias, the input of shelf waters in the Ria de Ferrol drives massive phytoplankton blooms supporting a rich heterotrophic community.
Chlorophyll-a and primary production on the euphotic zone of the N-NW Spanish shelf were studied ... more Chlorophyll-a and primary production on the euphotic zone of the N-NW Spanish shelf were studied at 125 stations between 1984 and 1992. Three geographic areas (Cantabrian Sea, Rías Altas and Was Baixas), three bathymetric ranges (20 to 60 m, 60 to 150 m and stations deeper than 200 m), and four oceanographic stages (spring and autumn blooms, summer upwelling, summer stratification and winter mixing) were considered. One of the major sources of variability of chlorophyll and production data was season. Bloom and summer upwelling stages have equivalent mean and maximum values. Average chlorophyll-a concentrations approximately doubled in every step of the increasing productivity sequence: winter mixing — summer stratification — high productivity (upwelling and bloom) stages. Average primary production rates increased only 60% in the described sequence. Mean (± sd) values of chlorophyll-a and primary production rates during the high productivity stages were 59.7 ± 39.5 mg Chl-a m−2 and 86.9 ± 44.0 mg C m−2 h−1, respectively. Significant differences in both chlorophyll and primary production resulted between geographic areas in most stages. Only 27 stations showed the effects of the summer upwelling that affected coastal areas in the Cantabrian Sea and Rías Baixas shelf, but also shelf-break stations in the Rías Altas area. The Rías Baixas area had lower chlorophyll than both the Rías Altas and the Cantabrian Sea areas during spring and autumn blooms, but higher during summer upwelling events. On the contrary, primary production rates were higher in the Rías Baixas area during blooms in spring and autumn. Mid-shelf areas showed the highest chlorophyll concentrations during high productivity stages, probably due to the existence of frontal zones in all geographic areas considered. The estimated phytoplankton growth rates were comparable to those of other coastal upwelling systems, with average values lower than the maximum potential growth rates. Doubling rates for upwelling and stratification stages in the northern and Rías Altas shelf areas were equivalent, despite larger biomass accumulations during upwelling events. Low turnover rates of the existing biomass in the Rías Baixas shelf in upwelling stages suggests that the accumulation of phytoplankton was due mainly to the export from the highly productive rías, while the contribution of in situ production to these accumulations was relatively lower.
Chlorophyll-a and primary production on the euphotic zone of the N-NW Spanish shelf were studied ... more Chlorophyll-a and primary production on the euphotic zone of the N-NW Spanish shelf were studied at 125 stations between 1984 and 1992. Three geographic areas (Cantabrian Sea, Rías Altas and Was Baixas), three bathymetric ranges (20 to 60 m, 60 to 150 m and stations deeper than 200 m), and four oceanographic stages (spring and autumn blooms, summer upwelling, summer stratification and winter mixing) were considered. One of the major sources of variability of chlorophyll and production data was season. Bloom and summer upwelling stages have equivalent mean and maximum values. Average chlorophyll-a concentrations approximately doubled in every step of the increasing productivity sequence: winter mixing — summer stratification — high productivity (upwelling and bloom) stages. Average primary production rates increased only 60% in the described sequence. Mean (± sd) values of chlorophyll-a and primary production rates during the high productivity stages were 59.7 ± 39.5 mg Chl-a m−2 and 86.9 ± 44.0 mg C m−2 h−1, respectively. Significant differences in both chlorophyll and primary production resulted between geographic areas in most stages. Only 27 stations showed the effects of the summer upwelling that affected coastal areas in the Cantabrian Sea and Rías Baixas shelf, but also shelf-break stations in the Rías Altas area. The Rías Baixas area had lower chlorophyll than both the Rías Altas and the Cantabrian Sea areas during spring and autumn blooms, but higher during summer upwelling events. On the contrary, primary production rates were higher in the Rías Baixas area during blooms in spring and autumn. Mid-shelf areas showed the highest chlorophyll concentrations during high productivity stages, probably due to the existence of frontal zones in all geographic areas considered. The estimated phytoplankton growth rates were comparable to those of other coastal upwelling systems, with average values lower than the maximum potential growth rates. Doubling rates for upwelling and stratification stages in the northern and Rías Altas shelf areas were equivalent, despite larger biomass accumulations during upwelling events. Low turnover rates of the existing biomass in the Rías Baixas shelf in upwelling stages suggests that the accumulation of phytoplankton was due mainly to the export from the highly productive rías, while the contribution of in situ production to these accumulations was relatively lower.
Current flow cytometry techniques allow the rapid estimation of the abundance of 2 distinct group... more Current flow cytometry techniques allow the rapid estimation of the abundance of 2 distinct groups of heterotrophic bacteria, characterized by their relative nucleic acid content. High nucleic acid (HNA) bacteria are, at least in coastal environments, usually regarded as more active than the low nucleic acid (LNA) group. We tested the effects of substrate supply and bacterial cell size on the relationship between bacterial activity and the abundance of HNA bacteria by simultaneous measurements of LNA and HNA cell distributions, chlorophyll a and 3 H-leucine uptake rates in temperate shelf waters of the northern Iberian Peninsula. We considered 3 zones based on hydrological properties. Significant correlations were found between bacterial activity (range 0.1 to 80 pmol Leu l -1 h -1 ) and both total and relative (range 28 to 84%) HNA cell abundance for pooled data, but the ready use of HNA bacterial abundance as a proxy for activity in natural systems was questioned by the low percentage of variance explained (16%). However, a detailed regional study of bottom-up effects revealed that the strength of this relationship increased significantly when bacteria were apparently controlled by phytoplankton substrate supply. Moreover, the relationship between mean biomass (overall range 12.4 to 21.2 fg C cell -1 ) and abundance-activity correlation coefficients in the 3 zones (r = 0.94, p = 0.005, n = 6) suggests that only at large cell sizes can we expect bacterial activity and production to be reasonably predicted by the abundance of HNA cells.
This study describes the main seasonal stages in oceanographic conditions and phytoplankton off L... more This study describes the main seasonal stages in oceanographic conditions and phytoplankton off La Coruñ a (Galicia, NW Spain), during 1991 and 1992, based mainly on monthly cruises near the coast. Upwelling conditions were studied using an upwelling index calculated from local winds. The Galician coast is affected by a long upwelling season for most of the year. The upwelling pulses interact with the thermal stratification-mixing cycle of surface waters, primarily affecting the dynamics of phytoplankton. In addition, the presence of water masses of different salinity in the subsurface layers changes the stratification of the water column. The less-saline North Atlantic Central Water (NACW) was normally associated with upwelling events during summer. However, on several occasions during the study, the presence of Eastern North Atlantic Water (ENAW) of subtropical origin was observed with salinities up to 36·22 and temperatures between 13 and 14 C.
Current flow cytometry techniques allow the rapid estimation of the abundance of 2 distinct group... more Current flow cytometry techniques allow the rapid estimation of the abundance of 2 distinct groups of heterotrophic bacteria, characterized by their relative nucleic acid content. High nucleic acid (HNA) bacteria are, at least in coastal environments, usually regarded as more active than the low nucleic acid (LNA) group. We tested the effects of substrate supply and bacterial cell size on the relationship between bacterial activity and the abundance of HNA bacteria by simultaneous measurements of LNA and HNA cell distributions, chlorophyll a and 3 H-leucine uptake rates in temperate shelf waters of the northern Iberian Peninsula. We considered 3 zones based on hydrological properties. Significant correlations were found between bacterial activity (range 0.1 to 80 pmol Leu l -1 h -1 ) and both total and relative (range 28 to 84%) HNA cell abundance for pooled data, but the ready use of HNA bacterial abundance as a proxy for activity in natural systems was questioned by the low percentage of variance explained (16%). However, a detailed regional study of bottom-up effects revealed that the strength of this relationship increased significantly when bacteria were apparently controlled by phytoplankton substrate supply. Moreover, the relationship between mean biomass (overall range 12.4 to 21.2 fg C cell -1 ) and abundance-activity correlation coefficients in the 3 zones (r = 0.94, p = 0.005, n = 6) suggests that only at large cell sizes can we expect bacterial activity and production to be reasonably predicted by the abundance of HNA cells.
The project ''Studies on time series of oceanographic data'' was established as a pilot project b... more The project ''Studies on time series of oceanographic data'' was established as a pilot project by the Instituto Españ ol de Oceanografía (I.E.O.) in 1991. After more than a decade, the project has grown to encompass a network of 19 sampling stations in five different transects along the North and Northwest coast of Spain: Vigo, Coruñ a, Cudillero, Gijó n and location a coastal-ocean gradient is sampled monthly for hydrography, nutrients and planktonic communities. We have used these data to set with statistical significance the range of variability of several environmental variables and biological communities and determined the rates and trends of warming due to climate change as well as to describe some direct and indirect effects of the increase in water temperature on the pelagic ecology. The project had substantially contributed to get a deeper knowledge on planktonic communities and species and to produce baselines, climatologies and reference levels for the North coast of Spain, which allow us to do accurate evaluations on the effects of environmental perturbations on the ecosystem and forecast the expected recovery time. These changes both in the physical structure of the water column and in the trophic level that drives ecosystem production and functioning are likely to also modify the structure, production and organization of higher trophic levels like zooplankton. Our analysis shows that only through sustained and repeated time series sampling it is feasible to detect these changes. Indeed, the annual cycle of zooplankton biomass seems to be restricted in time, with the annual decrease in zooplankton biomass matching the onset of stratification. The observed patterns in the seasonal occurrence of incoming species like Temora stylifera are related to those observed in the water column stratification, which is reinforced by the warming trend.
Journal of The Marine Biological Association of The United Kingdom, 2004
Slope Water anticyclonic Oceanic eDDIES (SWODDIES) are typical mesoscale features of open-ocean w... more Slope Water anticyclonic Oceanic eDDIES (SWODDIES) are typical mesoscale features of open-ocean waters of the southern Bay of Biscay which usually develop in winter by shedding from the seasonal poleward current £owing along the northern Spanish slope. These eddies have been intensively studied from the physical perspective. However, their e¡ect on the distribution of biological properties and on the functioning of the pelagic ecosystem has not been assessed so far. To this aim, a sea-truth, multidisciplinary and comprehensive study of a SWODDY was carried out in summer 1998. The eddy, radius of *50 km, was initially centred at 45.58N 6.08W, being characterized by a relatively homogeneous core of water in the centre of the eddy extending from 80 to about 200 dbar. In the central region of the core, temperature (12.55^12.758C) and salinity (*35.70) values were higher than outside the eddy. The optical properties of the eddy also di¡ered from those of the surrounding waters. A distinct biological signature was found associated with the eddy. Depth-integrated chlorophyll-a concentrations were 25% higher at the eddy centre where upward doming of the seasonal pycnocline (up to 30 dbar) occurred. Enhanced phytoplankton biomass was related to a higher contribution of 410 mm cells, mainly represented by diatoms and chrysophyceans. Phytoplankton and mesozooplankton species composition in and outside the eddy di¡ered signi¢cantly re£ecting the coastal origin of the water parcel trapped by the eddy. The sharp modi¢cation of the planktonic community composition, biomass and associated size-structure caused by slope water oceanic eddies are likely to exert a signi¢cant e¡ect upon the upper trophic levels of the pelagic ecosystem of the southern Bay of Biscay.
The project ''Studies on time series of oceanographic data'' was established as a pilot project b... more The project ''Studies on time series of oceanographic data'' was established as a pilot project by the Instituto Españ ol de Oceanografía (I.E.O.) in 1991. After more than a decade, the project has grown to encompass a network of 19 sampling stations in five different transects along the North and Northwest coast of Spain: Vigo, Coruñ a, Cudillero, Gijó n and location a coastal-ocean gradient is sampled monthly for hydrography, nutrients and planktonic communities. We have used these data to set with statistical significance the range of variability of several environmental variables and biological communities and determined the rates and trends of warming due to climate change as well as to describe some direct and indirect effects of the increase in water temperature on the pelagic ecology. The project had substantially contributed to get a deeper knowledge on planktonic communities and species and to produce baselines, climatologies and reference levels for the North coast of Spain, which allow us to do accurate evaluations on the effects of environmental perturbations on the ecosystem and forecast the expected recovery time. These changes both in the physical structure of the water column and in the trophic level that drives ecosystem production and functioning are likely to also modify the structure, production and organization of higher trophic levels like zooplankton. Our analysis shows that only through sustained and repeated time series sampling it is feasible to detect these changes. Indeed, the annual cycle of zooplankton biomass seems to be restricted in time, with the annual decrease in zooplankton biomass matching the onset of stratification. The observed patterns in the seasonal occurrence of incoming species like Temora stylifera are related to those observed in the water column stratification, which is reinforced by the warming trend.
Herbivory by copepods was studied from the coast towards the ocean, during a bloom in May 1994 of... more Herbivory by copepods was studied from the coast towards the ocean, during a bloom in May 1994 off NW Spain. Ingestion rates were estimated by the gut chlorophyll content method in three size fractions. The chlorophyll content displayed significant daily cycles. Three different water bodies were described: coastal, shelf break and oceanic; the latter two zones separated by a thermohaline frontal structure. Marked differences in plankton species composition, vertical distribution and biological rates were found between zones. Thehighest phytoplankton biomass, dominated by chainforming diatoms, occurred in the oceanic zone associated with low primary production rates. Copepod feeding had a low effect on oceanic phytoplankton; up to 0.2% of carbon stock and <3% of carbon production was consumed daily. In contrast, medium-sized and large copepods removed 3% of carbon stock and 12% of primary production daily near the coast, where phytoplankton were dominated by small flagellates in active growth. The highest variability in both plankton composition and ingestion rates was found in the shelf-break zone, probably due to displacements of the front. Copepods exerted a moderate predation pressure on phytoplankton in coastal waters. Meanwhile, the impact of copepods on the offshore bloom was negligible and the fate of the accumulated particulate carbon would be mostly determined by sedimentation and water dynamics.
Journal of The Marine Biological Association of The United Kingdom, 2004
Slope Water anticyclonic Oceanic eDDIES (SWODDIES) are typical mesoscale features of open-ocean w... more Slope Water anticyclonic Oceanic eDDIES (SWODDIES) are typical mesoscale features of open-ocean waters of the southern Bay of Biscay which usually develop in winter by shedding from the seasonal poleward current £owing along the northern Spanish slope. These eddies have been intensively studied from the physical perspective. However, their e¡ect on the distribution of biological properties and on the functioning of the pelagic ecosystem has not been assessed so far. To this aim, a sea-truth, multidisciplinary and comprehensive study of a SWODDY was carried out in summer 1998. The eddy, radius of *50 km, was initially centred at 45.58N 6.08W, being characterized by a relatively homogeneous core of water in the centre of the eddy extending from 80 to about 200 dbar. In the central region of the core, temperature (12.55^12.758C) and salinity (*35.70) values were higher than outside the eddy. The optical properties of the eddy also di¡ered from those of the surrounding waters. A distinct biological signature was found associated with the eddy. Depth-integrated chlorophyll-a concentrations were 25% higher at the eddy centre where upward doming of the seasonal pycnocline (up to 30 dbar) occurred. Enhanced phytoplankton biomass was related to a higher contribution of 410 mm cells, mainly represented by diatoms and chrysophyceans. Phytoplankton and mesozooplankton species composition in and outside the eddy di¡ered signi¢cantly re£ecting the coastal origin of the water parcel trapped by the eddy. The sharp modi¢cation of the planktonic community composition, biomass and associated size-structure caused by slope water oceanic eddies are likely to exert a signi¢cant e¡ect upon the upper trophic levels of the pelagic ecosystem of the southern Bay of Biscay.
The storage of nitrate by phytoplankton cells during the early phases of upwelling was studied in... more The storage of nitrate by phytoplankton cells during the early phases of upwelling was studied in coastal stations off northern Spain (southern Bay of Biscay) between 1990 and 1994. In this region, a persistent upwelling during summer is characterised by intermittent pulses of variable intensity, and increased nutrient concentrations in the surface layer. The main effect of an upwelling pulse on phytoplankton distribution is the shifting of the chlorophyll a and primary production maxima to near the surface. When the upwelling relaxes, thermal stratification of the water column occurs, and a distinct subsurface chlorophyll maximum develops below the production maximum. An accumulation of intracellular nitrate characterized the early phases of upwelling (mean = 2.73 μmol N m−3), maximum concentrations being attained at depths where biomass and production values were moderate. In contrast, phytoplankton cells from non-upwelling situations contained significantly lower concentrations of intracellular nitrate (mean = 0.17 μmol N m−3). The variations in the intracellular pool of nitrate may result from the differential allocation of resources within the cell as a result of variations in the energy available, since the uptake and assimilation of nitrate is a relatively expensive process involving several enzymatic systems. We hypothesize that nitrate storage by phytoplankton cells is characteristic of early phases of upwelling and is linked to patterns of carbon fixation. Average nitrogen budgets for upwelling and non-upwelling situations indicate that intracellular nitrate reserves are not responsible for maintaining high phytoplankton growth rates, since they only account for <2% of daily primary production during upwelling events.
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