Journal Article

The pelagic foodweb in the upwelling ecosystem of Galicia (NW Spain) during spring: natural abundance of stable carbon and nitrogen isotopes

Antonio Bode, Pablo Carrera and Santiago Lens

in ICES Journal of Marine Science

Volume 60, issue 1, pages 11-22
Published in print January 2003 | ISSN: 1054-3139
Published online January 2003 | e-ISSN: 1095-9289 | DOI: http://dx.doi.org/10.1006/jmsc.2002.1326
The pelagic foodweb in the upwelling ecosystem of Galicia (NW Spain) during spring: natural abundance of stable carbon and nitrogen isotopes

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The structure of the pelagic foodweb in the upwelling ecosystem of Galicia (NW Spain) was studied by means of the enrichment in 13C and 15N isotopes in plankton (four size classes from 20 to >1000 μm), sardine (primary consumer) and dolphin (top consumer). Samples were collected in March 1998, during the spawning period of sardines at the beginning of the upwelling season. Isotopic enrichment across plankton size classes was lower than either enrichment between plankton and sardine or enrichment between sardine and dolphin. This difference may be attributed to the presence of chain-forming phytoplankton in some plankton size classes but also to a large degree of omnivory among zooplankton. Also, there was a size-dependent effect on 15N enrichment of sardine. Sardines <18 cm had a variable isotopic enrichment but generally higher than those of larger sardines, revealing omnivorous but mostly zoophagous diets. In contrast, sardines ≥18 cm showed a linear decrease of 15N enrichment with length, as a consequence of the increase in the efficiency of filter-feeding and in the amount of phytoplankton ingested. According to 15N enrichment, we concluded that probably there are no more than four trophic levels in the studied ecosystem. Nevertheless, our results revealed that the pelagic food web in this upwelling area is more complex than expected due to the generalized omnivory in all organisms. Furthermore, the obtained relationships between δ15N and the size of organisms provide the basis for a quantitative analysis of changes in the trophic structure of this ecosystem.

Keywords: dolphin; foodweb; Galicia; NE Atlantic; plankton; sardine; stable isotopes; upwelling

Journal Article.  0 words. 

Subjects: Environmental Science ; Marine and Estuarine Biology

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