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Response of small grazers to iron-induced phytoplankton blooms in the Antarctic Polar Frontal Zone
J. Henjes, P. Assmy, C. Klaas & V. Smetacek
Fig. 1:The complex phytoplankton-based food web (Fig. modified from a graphic by Z. Johnson)
Fig. 2: Temporal development of A) microproto- zooplankton, B) acantharia and C) copepod nauplii abundance during EIFEX. Data from 20 m depth.
Alfred-Wegener-Institute for Polar and Marine Research, Am Handelshafen 12, 27570 Bremerhaven, Germany
Conclusions
• Microprotozooplankton show only a small increase in abundance
→Tight coupling between prey and predators regulates population dynamics
• For the first time it could be shown that Acantharia respond to enhanced primary production with population growth within short time scales
→Indication for their role as possible paleoproxy for high productivity regimes
•Small pelagic copepods show significant increase in abundance
→Significant portion of the fertilised phytoplankton biomass was channelled to higher trophic levels
Mesoscalein situiron fertilisation experiments have resulted in the build-up of phytoplankton biomass and established beyond doubt that iron availability is the key factor limiting growth rates of oceanic phytoplankton in “high-nutrient, low-chlorophyll” (HNLC) regimes (see poster Assmyet al.). The response of important groups (microproto-, mesoproto- and small metazooplankton) of the pelagic community and the processes within the food web (Fig. 1) were studied in detail and compared with processes in the surrounding water during two iron fertilisation experiments in austral spring (EisenEx) and summer (EIFEX).
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Microprotozooplankton l-1
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Fig. 4:Temporal development of A) microprotozooplankton B) acantharia and C) small copepods (<1.5 mm) abundance during EisenEx. Integrated over 80 and 150 m depth, respectively.
Fig. 3: Light micrographs of some dominant genera or groups of microproto- (A, B), mesoproto- (C) and small metazoo- plankton (D, E). A)Thecate dinoflagellate (Protoperidinium spp.), B) tintinnid ciliate (Codonellopsis pusilla), C) acantharia, D) copepod nauplii and E) adult of Oithona similis.
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