Biodiversity and feeding ecology of pelagic decapods in the south-east Atlantic Ocean
Carballo, R. (2010). Biodiversity and feeding ecology of pelagic decapods in the south-east Atlantic Ocean. MSc Thesis. University of Bremen, Department of Biology and Chemistry: Bremen. 34 pp.
Pelagic decapods play an important role in the food web of marine ecosystems, as predators for zooplankton and as prey for fishes. Due to their diel vertical migration, they also contribute to the vertical flux of organic matter, by transferring carbon from the surface to the deep ocean. In the Benguela upwelling system their distribution, abundance and community structure has been registered in previous studies, but no data exist on their ecology. Therefore, in this study the biodiversity of pelagic decapods has been determined and their feeding ecology has been elucidated by the use of trophic biomarker analysis. Decapods were sampled in the northern Benguela upwelling system (17-23S and 10°-12°E) during the cruise of the FRS Africana in December 2009. Fatty acids and stable isotopes were applied as trophic biomarkers to elucidate dietary composition and trophic level. Sergestes sp. showed to be the most common species and they all distributed along the continental rise and in oceanic waters. Total lipid content remained stable with 7-20 % of dry mass, across all species up to a body mass of 130 mg,individuals above this weight accumulated higher amounts of lipids (15-40% of DM). Eleven fatty acids contributed more than 1% of total fatty acids in almost all species, but four stood out in percentage: 16:0, 18:1(n-9), 20:5(n-3) and 22:6(n-3). Stylopandalus cf. richardi, Gennadas sp., unidentified caridean sp3 and sp4 did not contained any fatty alcohol, while Acanthephyra. cf. pelagica and Sergia cf. splendens presented the higher percentages of wax ester in total lipid content. All species presented values higher than 1 for both fatty acid biomarker ratios, for the ratio 18:1(n-9)/18:1(n-7) Gennadas sp. showed the highest value and for PUFA/SFA unidentified sp4. Values for stable carbon isotope ratios ranged from -18.2 to -15.2 and for stable nitrogen isotope ratios ranged from 6.1 to 8.8. All decapods in the Benguela upwelling system presented a carnivory trophic level, according to the fatty acid carnivory indices and delta 15N values, with differences in the degree of carnivory. They showed a difference in the dietary composition, hence their fatty acid and alcohol composition was different between species. Some species utilized wax ester as lipid storage, which may be an adaptation to successfully cope with long periods of food shortage or highly unpredictable food supply. Ontogenetic changes were identified with regard to lipid accumulation. Decapods showed an increase in lipid content in relation to a higher body mass and an increase in their trophic level according to fatty acid ratio indices.
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