AME 46:1-13 (2007)  -  doi:10.3354/ame046001

Krill larvae, copepods and the microbial food web: interactions during the Antarctic fall

Stephen A. Wickham1,3,*, Ulrike-G. Berninger2,3

1Zoological Institute, University of Cologne, Weyertal 119, 50923 Cologne, Germany
2Biological Oceanography, Alfred Wegener Institute of Polar and Marine Research, Am Handelshafen 12, 27570 Bremerhaven, Germany
3Present address: Department of Organismal Biology, University of Salzburg, Hellbrunnerstr. 34, 5020 Salzburg, Austria

ABSTRACT: Experiments were run in the Antarctic Bellinghausen Sea during the austral fall to ascertain the interactive effects of krill larvae (furcilia) and copepods on the microbial food web. A cross-classified design with addition of the small cyclopoid copepod Oithona similis and either the furcilia larvae of Euphausia superba or the calanoid copepod Metridia gerlachei to the natural planktonic community was used, as well as a single experiment with varying densities of O. similis. The experiments showed furcilia to have much higher grazing rates on copepods and ciliates than on algae, with positive selection for ciliates that was not influenced by the presence or absence of O. similis. M. gerlachei had a grazing impact on ciliates that was much less than that of furcilia larvae, but due to a high taxonomic resolution of the ciliate community it could be shown that there were groups of grazing-vulnerable and -resistant forms. Contrary to expectations, O. similis had very low grazing rates on both ciliates and algae, but here too grazing-vulnerable and -resistant groups of ciliates could be distinguished. Neither the very strong impact of furcilia on ciliates, copepods and algae nor the more moderate impact of M. gerlachei cascaded down to heterotrophic and phototrophic nanoplankton or to bacteria. At least at the time of our experiments, ciliates were tightly bound to the ‘classic’ aquatic food web, but do not serve to transmit a trophic cascade from the classic and microbial food webs.

KEY WORDS: Ciliate · Grazing · Antarctica · Copepod · Krill · Furcilia · Trophic cascade

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