Use of isotopic signatures to assess the food web in a tropical shallow marine ecosystem of Southeastern Brazil

摘要

A dual isotope approach was used to assess the relative importance of terrestrial vegetation detritus and other primary producers in the trophic web of Flamengo Sound (Ubatuba, SP), SE Brazil, surrounded by the Atlantic Rain Forest. Primary producersshowed distinct gamma~13C signatures and the observed values suggest that little terrestrial (-29.4 +-0.3%e) or bulk sediment organic matter (-21.1 +- 1.3%o) enter the food web of the sound. Suspended particulate organic matter (POM, -18.6 +- 0.5%e) supports the bulk of the consumers, with some contribution by macroalgae (-15.6 +- 1.8%o). Consumers gamma~13C values ranged from -17.4 to — 12.7%o. At least three trophic levels were detectable in the food web. The gamma~15N value of POM was 7.5 +- 1.0%c,while that of sediment and detritus was 6.4 +- 0.7%o. The gamma~15N values of suspension feeding benthic invertebrates were 8.2-8.6%e, deposit feeders 8.3-10.2%0, and carnivores 10.7-13.2%o. Values for fishes were 9.4%o for detritivore, 11.4-13.3%e for benthic feeders, 12.4-13.3%o for zooplankti-vores, and 13.2%e for piscivores/benthic invertebrate feeders. Squid mean value was 12.8 +- 0.5%o. There is a reasonable agreement between feeding habits information from the literature and gamma~15N values fromthis study. In the sound, the first and second trophic steps seem to be about l-3%o higher than those of similar organisms studied in temperate waters and this may reflect an input of allochtonous anthropogenic nitrogen enriched in 15~N from human activities.