MEPS 362:69-83 (2008)  -  DOI:

Food web of a SW Atlantic shallow coastal lagoon: spatial environmental variability does not impose substantial changes in the trophic structure

Laura Rodríguez-Graña1,6,*, Danilo Calliari2,6, Daniel Conde1, Javier Sellanes3,4, Roberto Urrutia5

1Sección Limnología, and 2Sección Oceanología, Facultad de Ciencias, Universidad de la República, Iguá 4225, CP 11400 Montevideo, Uruguay
3Departamento de Biología Marina, Universidad Católica del Norte, Larrondo 1281, Coquimbo, Chile
4Centro de Investigación Oceanográfica en el Pacífico Sur-Oriental (COPAS),  and 5Centro EULA, Universidad de Concepción, Casilla 160-C, Concepción, Chile
6Present address: Department of Marine Ecology, Göteborgs University, Kristineberg 566, 450 34 Fiskebäckskil, Sweden

ABSTRACT: We performed a detailed analysis of the food web structure of Laguna de Rocha, a temporally open coastal lagoon in the Southwest Atlantic, characterised by spatial gradients in salinity, nutrient levels and trophic status. Carbon and nitrogen stable isotopes of main producers, invertebrate and vertebrate consumers, and stomach contents of ichthyofauna were analysed seasonally at freshwater (north) and marine-influenced (south) sites to determine whether environmental differences induced changes in food web structure. Contribution of primary and secondary food sources and trophic linkages were assessed with the multisource-partitioning model IsoSource and an index that quantifies the contribution of each organism as food for the ecosystem. Isotopic analyses were performed for 10 primary organic matter sources (OM), 13 invertebrates and 9 fish species. Suspended and sediment OM constituted the most important primary sources, while direct consumption of macrophytes and macroalgae was marginal. The small invertebrates Neomysis americana, Nephtys fluviatilis, Pseudodiaptomus richardii and an amphipod were the most important intermediate consumers at both sites (except P. richardii, which was present only in the north). Top predators were the fish species Micropogonias furnieri, Paralichthys orbygnianus and Hoplias malabaricus, and the maximum estimated trophic level (between 3.4 and 4.8) varied seasonally, but not between sites. Fish stomach content analyses largely confirmed results from the IsoSource mixing model. Overall results indicated that, despite environmental differences between sites, the structure of the biological assemblages and general trophic patterns were similar at both sites.

KEY WORDS: Food web structure · Coastal lagoon · Estuaries · Benthic–pelagic coupling · Isotopic mixing models

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Cite this article as: Rodríguez-Graña L, Calliari D, Conde D, Sellanes J, Urrutia R (2008) Food web of a SW Atlantic shallow coastal lagoon: spatial environmental variability does not impose substantial changes in the trophic structure. Mar Ecol Prog Ser 362:69-83.

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