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Marine Ecology Progress Series

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MEPS 239:251-261 (2002)  -  doi:10.3354/meps239251

Grazing during early spring in the Gulf of Aqaba and the northern Red Sea

Ulrich Sommer1,*, Ulrike G. Berninger1,2, Ruth Böttger-Schnack3, Astrid Cornils2, Wilhelm Hagen3, Thomas Hansen1, Tariq Al-Najjar4, Anton F. Post5, Sigrid B. Schnack-Schiel2, Herwig Stibor6, Dorothea Stübing3, Stephen Wickham5,7

1Institut für Meereskunde an der Universität Kiel, Düsternbrooker Weg 20, 24105 Kiel, Germany
2Alfred-Wegener-Institut für Polar- und Meeresforschung, 27515 Bremerhaven, Germany
3Marine Zoologie, Universität Bremen (NW2), Postfach 33040, 28334 Bremen, Germany
4Marine Science Station, PO Box 195, Aqaba, Jordan
5Interuniversity Institute, PO Box 469, 88103 Eilat, Israel
6Zoologisches Institut, Ludwig-Maximilians-Universität, Karlsstraße 23-25, 80333 München, Germany
7Zoologisches Institut, Universität Köln, Weyertal 119, 50923 Köln, Germany

ABSTRACT: Zooplankton grazing on bacterio- and phytoplankton was studied in the Gulf of Aqaba and the Northern Red Sea during Meteor Cruise Me 44-2 in February-March 1999. Protozoan grazing on bacterioplankton and autotrophic ultraplankton was studied by the Landry dilution method. Microzooplankton grazing on phytoplankton >6 µm was studied by incubation experiments in the presence and absence of microzooplankton. Mesozooplankton grazing was studied by measuring per capita clearance rates of individual zooplankton with radioactively labelled food organisms and estimating in situ rates from abundance values. Protozoan grazing rates on heterotrophic bacteria and on algae <6 µm were high (bacteria: 0.7 to 1.1 d-1, ultraphytoplankton: 0.7 to 1.3 d-1), while grazing rates on Synechococcus spp. were surprisingly low and undetectable in some experiments. Mesozooplankton grazing was weak, cumulative grazing rates being ca. 2 orders of magnitude smaller than the grazing rates by protozoans. Among mesozooplankton, appendicularians specialised on smaller food items and calanoid copepods on larger ones.

KEY WORDS: Phytoplankton · Protozoa · Bacteria · Zooplankton · Grazing · Red Sea · Gulf of Aqaba

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