Network


Latest external collaboration on country level. Dive into details by clicking on the dots.

Hotspot


Dive into the research topics where C. Almeida is active.

Publication


Featured researches published by C. Almeida.


Progress in Oceanography | 1998

The Transition Zone of the Canary Current Upwelling Region.

Eric D. Barton; Javier Arístegui; Paul Tett; M. Cantón; J.A. García-Braun; Santiago Hernández-León; L. Nykjaer; C. Almeida; J. Almunia; S. Ballesteros; Gotzon Basterretxea; J. Escánez; L. Garcı́a-Weill; Alonso Hernández-Guerra; Federico López-Laatzen; R. Molina; María F. Montero; E. Navarro-Pérez; J.M. Rodríguez; K. van Lenning; H. Vélez; K. Wild

Abstract Like all the major upwelling regions, the Canary Current is characterised by intense mesoscale structure in the transition zone between the cool, nutrient-rich waters of the coastal upwelling regime and the warmer, oligotrophic waters of the open ocean. The Canary Island archipelago, which straddles the transition, introduces a second source of variability by perturbing the general southwestward flow of both ocean currents and Trade winds. The combined effects of the flow disturbance and the eddying and meandering of the boundary between upwelled and oceanic waters produce a complex pattern of regional variability. On the basis of historical data and a series of interdisciplinary field studies, the principal features of the region are described. These include a prominent upwelling filament originating near 28°N off the African coast, cyclonic and anti-cyclonic eddies downstream of the archipelago, and warm wake regions protected from the Trade winds by the high volcanic peaks of the islands. The filament is shown to be a recurrent feature, apparently arising from the interaction of a topographically trapped cyclonic eddy with the outer edge of the coastal upwelling zone. Its role in the transport and exchange of biogenic material, including fish larvae, is considered. Strong cyclonic eddies, observed throughout the year, drift slowly southwestward from Gran Canaria. One sampled in late summer was characterised by large vertical isopycnal displacements, apparent surface divergence and strong upwelling, producing a fourfold increase in chlorophyll concentrations over background values. Such intense eddies can be responsible for a major contribution to the vertical flux of nitrogen. The lee region of Gran Canaria is shown to be a location of strong pycnocline deformation resulting from Ekman pumping on the wind shear boundaries, which may contribute to the eddy formation process.


Journal of Marine Systems | 2001

Zooplankton biomass and indices of feeding and metabolism in island-generated eddies around Gran Canaria

Santiago Hernández-León; C. Almeida; May Gómez; Santiago Torres; I. Montero; A. Portillo-Hahnefeld

Abstract Zooplankton biomass and indices of grazing (gut fluorescence), respiration (electron transfer system, ETS), ammonia excretion (glutamate dehydrogenase, GDH) and growth (aspartate transcarbamylase, ATC) were studied around the island of Gran Canaria (Canary Islands) during the so-called “late winter bloom”. Four size classes (100–200, 200–500, 500–1000 and >1000 μm) were studied to assess the contribution of each size fraction to the mesoscale plankton distribution around the island. Cyclonic and anticyclonic eddies were observed downstream the island transporting and entraining water rich in chlorophyll. Zooplankton biomass showed a high variability around the island but it was dramatically lower in the core of the cyclonic eddy induced by the island, probably due to the divergent effect produced by the physical structure. A filament of relatively cold-water was also found reaching the island from the upwelling area off northwest Africa. High zooplankton biomass was observed in association with the filament water and in the vicinity of the anticyclonic eddy shed by the island. Specific gut content showed higher values in the boundaries of the cyclonic structures, while ETS and GDH activities where higher windward of the island, in both the cyclonic and anticyclonic eddies depending on the size fraction considered. With the restrictions of using those indices, control of primary production by grazing was 11–22% and up to 41% of the calculated ingestion from the indices of metabolism and growth could be supported by nonpigmented food. Calculated excretion rates could support about 8% of primary production. The low impact of zooplankton on autotrophic production, the low values of the index of growth and the distribution of biomass in relation to the presence of eddies downstream of Gran Canaria suggest that accumulation was the causative mechanism for the presence of high zooplankton biomass leeward of the island.


Journal of Marine Research | 2002

Zooplankton biomass and indices of feeding and metabolism in relation to an upwelling filament off northwest Africa

Santiago Hernández-León; C. Almeida; A. Portillo-Hahnefeld; May Gómez; J.M. Rodríguez; Javier Arístegui

Zooplankton biomass and indices of grazing (gut e uorescence), respiration (electron transfer system activity, ETS) and growth (aspartate transcarbamylase, ATC) were studied in relation to an upwelling e lament off northwest Africa during August 1993. The e lament extended 150 km offshore into the oligotrophic waters. It was generated by a trapped, quasi-permanent cyclonic eddy located between the Canary Islands and the African shelf. High biomass, specie c gut e uorescence and electron transfer system activity in zooplankton were observed along the e lament structure. In contrast, low values of biomass, gut e uorescence, ETS and ATC specie c activities were found in the center of the trapped cyclonic eddy. Assuming a 50% of pigment destruction, the calculated grazing impact of zooplankton on primary production varied between 16 and 97%, a high range compared to other oceanic systems. Ingestion, estimated from indices of metabolism and growth, accounted for 47- 296% of the primary production (assuming an herbivorous feeding). Mesozooplankton trans- ported offshore into the oligotrophic area fule lled their metabolic demands with nonpigmented food as observed from the increase of omnivory from the coastal waters to the open ocean. The progressive decay of grazing and metabolic indices along the e lament suggests that advection, rather than local enrichment processes, is mostly responsible for the high biomass values in this physical structure.


Polar Biology | 1999

Biomass and metabolism of zooplankton in the Bransfield Strait (Antarctic Peninsula) during austral spring

Santiago Hernández-León; Santiago Torres; May Gómez; I. Montero; C. Almeida

Abstract Zooplankton biomass (as dry weight), respiration and ammonia excretion were studied in three different size classes (200–500, 500–1000 and >1000 μm) in the Bransfield Strait during December 1991. Average mesozooplankton biomass was 86.45 ± 56.74 mg · dry weight · m−2, which is in the lower range of the values cited in the literature for polar waters. Higher biomass was observed in the Weddell water. The small size fraction accounted for about 50% of total biomass while the largest one represented 35%. Rather high metabolic rates were found, irrespective of whether the organisms were incubated in the presence of food. No significant differences were observed in mass specific respiration and ammonia excretion rates between different temperatures of incubation (0.2–2.3°C) and between the size classes studied. Because of the very low biomass values observed, the metabolic requirements of mesozooplankton during December represented a small fraction of the primary production.


Journal of Oceanography | 1999

Large-Scale and Mesoscale Distribution of Plankton Biomass and Metabolic Activity in the Northeastern Central Atlantic

Santiago Hernández-León; Lutz Postel; Javier Arístegui; May Gómez; María F. Montero; Santiago Torres; C. Almeida; Eugen Kühner; Ullrich Brenning; Eberhard Hagen

Plankton biomass and indices of metabolism and growth [electron transport system (ETS), glutamate dehydrogenase (GDH) and aspartate transcarbamylase (ATC) activities] were studied over a 2,800 km east-west section of the tropical North Atlantic Ocean (21°N) in <200, 200–500 and >;500 µm size classes. On the large-scale, zooplankton (>;200 µm) enzymatic activities increased westward in the study section, where large cyanobacteria chains (Trichodesmium spp.) were observed. Parallel to it, an increase in medium calanoids (1–2 mm length) was observed towards the western part of the transect, whereas small calanoids (<1 mm) were dominant throughout the boundary area of the subtropical gyre. Microplankton ETS and mesoplankton ETS and ATC activities seemed to match the wave length of low frequency waves. Our results suggest that such waves are related to the observed enhancement of metabolic activity of micro- and mesoplankton. The large-scale and mesoscale variability observed give evidence of the inadequacy of assuming a steady-state picture of the euphotic zone of tropical and subtropical waters.


Polar Biology | 2000

Biomass and potential feeding, respiration and growth of zooplankton in the Bransfield Strait (Antarctic Peninsula) during austral summer

Santiago Hernández-León; C. Almeida; A. Portillo-Hahnefeld; May Gómez; I. Montero

Abstract Biomass (as dry weight and protein content), gut fluorescence, electron transfer system (ETS) and aspartate transcarbamylase (ATC) activities were studied in different size fractions (200–500, 500–1000 μm and 1–14 mm) in the Bransfield Strait (Antarctic Peninsula) during January 1993. Very low values of zooplankton biomass were observed in all the size classes studied. About 56% of total biomass was due to the large size fraction (1–14 mm) while the smallest one (200–500 μm) accounted for about 26%. Gut fluorescence values increased in relation to the size class considered, as expected, being the differences from the smaller to the highest size fractions of orders of magnitude. Calculated ingestion rates showed that about 60–80% of total zooplankton ingestion (<14 mm) was due to the smaller organisms. Higher average values and higher variability of specific ETS activity was observed in the smaller size fraction while no differences between size classes were observed for the specific ATC activity. Biomass, gut fluorescence, ETS and ATC activities were not significantly different between the Bellingshausen and Weddell waters, although higher standard deviation was normally found at the former area. With the restrictions of using the above indices to estimate physiological rates, potential grazing of mesozooplankton (<14 mm) accounted for a rather low portion (<10%) of the primary production. The index of growth showed high values, suggesting no food limitation of mesozooplankton. Therefore, other processes such as predation should account for the very low biomass found and for the fate of a large portion of primary production.


Polar Research | 2009

Metabolism and biomass vertical distribution of zooplankton in the Bransfield Strait during the austral summer of 2000

Lidia Yebra; Santiago Hernández-León; C. Almeida; P. Bécognée

The vertical distribution (0–550 m) of zooplankton biomass, and indices of respiration (electron transfer system [ETS]) and structural growth (aminoacyltRNA synthetases activity [AARS]), were studied in waters off the Antarctic Peninsula during the austral summer of 2000. The dominant species were the copepod Metridia gerlachei and the euphausiid Euphausia superba. We observed a vertical krill/copepod substitution in the water column. The zooplankton biomass in the layer at a depth of 200–500 m was of the same magnitude as the biomass in the layer at a depth of 0–200 m, indicating that biomass in the mesopelagic zone is an important fraction of the total zooplankton in Antarctic waters. The metabolic rates of the zooplankton community were sustained by less than 0.5% of the primary production in the area, suggesting that microplankton or small copepods are the main food source. Neither food availability nor predation seemed to control mesozooplankton biomass. The wide time lag between the abundance peak of the dominant copepod (M. gerlachei) and the phytoplankton bloom is suggested to be the main explanation for the low summer zooplankton biomass observed in these waters.


Journal of Plankton Research | 2002

Lunar cycle of zooplankton biomass in subtropical waters: biogeochemical implications

Santiago Hernández-León; C. Almeida; Lidia Yebra; Javier Arístegui


Deep-sea Research Part I-oceanographic Research Papers | 2001

Vertical distribution of zooplankton in Canary Island waters: implications for export flux

Santiago Hernández-León; May Gómez; Marı́a Pagazaurtundua; A. Portillo-Hahnefeld; I. Montero; C. Almeida


Scientia Marina | 2001

Zooplankton abundance in subtropical waters: is there a lunar cycle?

Santiago Hernández-León; C. Almeida; Lidia Yebra; Javier Arístegui; M. L. Fernández de Puelles; J.A. García-Braun

Collaboration


Dive into the C. Almeida's collaboration.

Top Co-Authors

Avatar

Santiago Hernández-León

University of Las Palmas de Gran Canaria

View shared research outputs
Top Co-Authors

Avatar

Javier Arístegui

University of Las Palmas de Gran Canaria

View shared research outputs
Top Co-Authors

Avatar

Lidia Yebra

Spanish National Research Council

View shared research outputs
Top Co-Authors

Avatar

A. Portillo-Hahnefeld

University of Las Palmas de Gran Canaria

View shared research outputs
Top Co-Authors

Avatar

I. Montero

University of Las Palmas de Gran Canaria

View shared research outputs
Top Co-Authors

Avatar

May Gómez

University of Las Palmas de Gran Canaria

View shared research outputs
Top Co-Authors

Avatar

Alonso Hernández-Guerra

University of Las Palmas de Gran Canaria

View shared research outputs
Top Co-Authors

Avatar
Top Co-Authors

Avatar

María F. Montero

University of Las Palmas de Gran Canaria

View shared research outputs
Top Co-Authors

Avatar

Eric D. Barton

Spanish National Research Council

View shared research outputs
Researchain Logo
Decentralizing Knowledge