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

• 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 F 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.

Ämnesord

NATURVETENSKAP  -- Biologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences (hsv//eng)

Nyckelord

food web structure

coastal lagoon

estuaries

benthic-pelagic coupling

isotopic mixing models

nitrogen stable-isotope

organic-matter

fresh-water

marine intrusions

perca-flavescens

yellow perch

south-africa

salt-marsh

carbon

estuary

Publikations- och innehållstyp

ref (ämneskategori)

art (ämneskategori)