Differential routing of "new" nitrogen towards higher trophic levels within the marine food web of the Gulf of Aqaba, northern Red Sea

Aberle, Nicole, Hansen, Thomas, Böttger-Schnack, Ruth, Burmeister, Angela and Sommer, Ulrich (2010) Differential routing of "new" nitrogen towards higher trophic levels within the marine food web of the Gulf of Aqaba, northern Red Sea Marine Biology, 157 . pp. 157-169. DOI 10.1007/s00227-009-1306-y.

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Abstract

Mesozooplankton communities in the mesooligotrophic Gulf of Aqaba, Northern Red Sea, were investigated over a 2 years period (2005-2007) with emphasis on the trophodynamic relations among different taxonomic groups ranging from primary consumers to carnivorous predators. Based on stable isotope analyses, we present evidence for a strong contribution of 'new' nitrogen mainly derived from the utilization of aerosol nitrate by unicellular cyanobacteria especially during summer stratification and the propagation of exceptionally low δ15N onto higher trophic levels. In contrast, N2-fixation by diazotrophs seemed to play a minor role, while the utilization of deep water nitrate by cyanobacteria and eukaryotic algae might be of importance during winter mixing. Based on 15N enrichment of consumers, clear differences between exclusively herbivorous organisms (doliolids, appendicularians, pteropods) and those with omnivorous feeding modes were detected. The category of omnivores comprised a large variety of taxons ranging from small meroplanktonic larvae to non-calanoid copepods (harpacticoids, cyclopoids and poecilostomatoids) that together form a diverse and complex community with overlapping feeding modes. In addition, distinct seasonality patterns in δ15N of copepods were found showing elevated trophic positions during periods of winter mixing, which were most pronounced for non-calanoid copepods. In general, feeding modes of omnivores appeared rather unselective, and relative contributions of heterotrophic protists and degraded material to the diets of non-calanoid copepods are discussed. At elevated trophic positions, four groups of carnivore predators were identified, while calanoid copepods and meroplanktonic predators showing lowest 15N enrichment within the carnivores. The direct link between 'new' nitrogen utilization by primary producers and the 15N enrichment of consumers in the planktonic food web of the Gulf of Aqaba emphasizes the significant contribution of 'new' nitrogen to the nitrogen budget and ecosystem functions in subtropical and tropical oligotrophic oceans.

Document Type: Article
Keywords: Ecology; Marine Biology; Red Sea; Gulf of Aqaba; Food web; Marine environment; Trophic level; Nitrogen
Research affiliation: OceanRep > GEOMAR > FB3 Marine Ecology > FB3-EOE-N Experimental Ecology - Food Webs
OceanRep > The Future Ocean - Cluster of Excellence
OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-BI Biological Oceanography
Refereed: Yes
DOI etc.: 10.1007/s00227-009-1306-y
ISSN: 0025-3162
Projects: Future Ocean
Date Deposited: 17 Dec 2009 15:07
Last Modified: 06 Jul 2012 15:10
URI: http://eprints.uni-kiel.de/id/eprint/2609

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