The grazing impact of microzooplankton off south west Western Australia: as measured by the dilution technique

Harriet Paterson, B. Knott, T. Koslow, Anya Waite

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Grazing rates of microzooplankton feeding on picophytoplankton (Flow-cytometry) and total phytoplankton (Chlorophyll a) were measured in the eastern Indian Ocean off south west Western Australia from February 2003 to December 2004. Three sites representing different oceanographic habitats, the coastal lagoon, the outer shelf and the continental slope (1000 m) were sampled. The dilution method of Landry and Hassett (1982, Estimating the grazing impact of marine micro-zooplankton. Mar. Biol., 67, 283-288) was used and analysed by chlorophyll a analysis and flow-cytometry. During summer, the apparent growth rate of total phytoplankton exceeded loss due to microzooplankton grazing in the lagoon and at the outer shelf. On the slope, the phytoplankton assemblage was always dominated by small cells (< 5 mu m). Although their apparent growth rates were also higher in summer, these were matched by increasing microzooplankton grazing rates. Saturated feeding responses at the outer shelf and slope stations during summer were detected. In this low prey, low productivity environment, this response is either a new type of threshold feeding or an artefact of the dilution method which would result in an over-estimate of both phytoplankton growth and microzooplankton grazing.
Original languageEnglish
Pages (from-to)379-392
JournalJournal of Plankton Research
Issue number4
Publication statusPublished - 2008


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