MEPS 208:13-20 (2000)  -  doi:10.3354/meps208013

Trophic structure of the marine food web at the Prince Edward Islands (Southern Ocean) determined by δ13C and δ15N analysis

S. Kaehler1,*, E. A. Pakhomov2, C. D. McQuaid1,2

1Department of Zoology and Entomology and
2Southern Ocean Group, Rhodes University, PO Box 94, Grahamstown 6140, South Africa

ABSTRACT: The origins (autochthonous or allochthonous) and pathways of organic matter in various marine communities were investigated in the vicinity of the sub-Antarctic Prince Edward Islands using stable-isotope analysis. Four major assemblages, comprising zooplankton, kelp-associated species, inter-island and nearshore benthos, were considered. Despite consumers exhibiting a predictable enrichment in δ13C and δ15N with trophic position, only the zooplankton community displayed distinct trophic levels. The benthic and the kelp-associated communities showed trophic continua. Both pelagic (zooplankton) and benthic inter-island communities ultimately derived their diets from phytoplankton (associated with surface-water POM). However, planktonic grazers fed primarily on allochthonous nano- and pico-plankton, while inter-island benthos seemed to rely mostly on microphytoplankton derived from autochthonous blooms. In contrast, kelp-associated animals derived a high proportion of their diet from kelp. The nearshore benthic community had an intermediate position between kelp-associated and inter-island communities. While POM was of primary importance, kelp-derived organic matter accounted on average for >30% of the nearshore animals¹ diet. Findings of the present study indicate for the first time that autochthonous sources of organic matter (e.g. kelp-derived and microphytoplankton blooms), are important components of the diets of all but the zooplankton community at the sub-Antarctic Prince Edward Islands.

KEY WORDS: Marine food web · Stable isotopes · Sub-antarctic · Kelp · POM

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