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Marine Ecology Progress Series

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MEPS 223:261-276 (2001)  -  doi:10.3354/meps223261

Amphipod-based food web: Themisto gaudichaudii caught in nets and by seabirds in Kerguelen waters, southern Indian Ocean

Pierrick Bocher1,2, Yves Cherel1,*, Jean-Philippe Labat3, Patrick Mayzaud3, Suzanne Razouls4, Pierre Jouventin1,5

1Centre d¹Etudes Biologiques de Chizé, UPR-CNRS 1934, 79360 Villiers-en-Bois, France
2Laboratoire de Biologie et Environnement Marins, EA 1220 de l'Université de La Rochelle, 17026 La Rochelle Cedex, France
3Laboratoire d'Océanographie Biochimique et d¹Ecologie, ESA 7076-CNRS/UPMC LOBEPM, Observatoire Océanologique, BP 28, 06230 Villefranche-sur-Mer, France
4Observatoire Océanologique, UMR-CNRS/UPMC 7621, Laboratoire Arago, 66650 Banyuls-sur-Mer, France
5Centre d¹Ecologie Fonctionnelle et Evolutive, UPR-CNRS 9056, 1919 Route de Mende, 34293 Montpellier Cedex 5, France
*Corresponding author. E-mail:

ABSTRACT: Comparing food samples from diving and surface-feeding seabirds breeding in the Golfe du Morbihan at Kerguelen Islands to concurrent net samples caught within the predator foraging range, we evaluated the functional importance of the hyperiid amphipod Themisto gaudichaudii in the subantarctic pelagic ecosystem during the summer months. T. gaudichaudii occurred in high densities (up to 61 individuals m-3) in the water column, being more abundant within islands in the western part of the gulf than at open gulf and shelf stations. The amphipod was a major prey of all seabird species investigated except the South Georgian diving petrel, accounting for 39, 80, 68, 59 and 46% of the total number of prey of blue petrels, thin-billed prions, Antarctic prions, common diving petrels and southern rockhopper penguins, respectively. The length-frequency distribution of T. gaudichaudii was similar between the 2 diving species, which fed on 1 large size class of adult individuals, whereas the 3 surface-feeding seabirds preyed upon 2 size classes but in different proportions. Juveniles and adults T. gaudichaudii were equally important in the diet of blue petrels, whereas juveniles and adults predominated in the food of thin-billed and Antarctic prions, respectively. Comparison of T. gaudichaudii found in nets and food samples together with observations at sea indicated that common diving petrels and southern rockhopper penguins fed in the close vicinity of the colonies in the Golfe du Morbihan, whereas blue petrels, and thin-billed and Antarctic prions mainly preyed upon amphipods outside the sampled area. Our study shows that T. gaudichaudii is an important local component of the macrozooplankton community and the main prey for planktivorous seabirds inhabiting the Kerguelen archipelago. In certain areas of the subantarctic zone, it therefore has a trophic role similar to that of Antarctic krill Euphausia superba further south, in Antarctic waters.

KEY WORDS: Antarctica · Euphausia superba · Pelagic ecosystem · Penguins · Petrels · Prions · Top predators · Trophic web

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