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Correcting for underestimation of microzooplankton grazing in bottle incubation experiments with mesozooplankton

Nejstgaard, Jens Christian; Naustvoll, Lars-Johan; Sazhin, Andrey
Journal article, Peer reviewed
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URI
http://hdl.handle.net/11250/108346
Date
2001-10-18
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Original version
http://dx.doi.org/10.3354/meps221059
Abstract
Bottle incubation experiments are widely used in mesozooplankton grazing studies.

However, we have shown here that traditional particle removal experiments with Calanus finmarchicus

and C. helgolandicus as grazers on natural plankton may yield low or even statistically significant

(p < 0.05) negative grazing estimates, even though negative grazing rates are impossible.

Low grazing rates are often reported, especially on smaller prey types, despite abundant food and

significant egg production. Microzooplankton, such as ciliates, show higher biomass-specific grazing

rates on algae than do copepods and other mesozooplankton. Instead, copepods often selectively

feed on the microzooplankton. Thus, apparent negative rates would be expected when the release of

microzooplankton grazing pressure outweighs the copepod grazing rates on the same food items in

the incubation bottle. We show that this potentially large bias increases with microzooplankton

community grazing pressure in the control. A simplified general method to correct for this bias is

presented and compared with the original method (Nejstgaard et al. 1997, Mar Ecol Prog Ser

147:197–217). Although complexity and the need for taxonomic accuracy are reduced in the general

method, the results are not significantly different between the 2 methods. Both methods also show a

good fit with ingestion rates estimated from faecal pellet production. We suggest that the general

method be combined with automated sample treatment in future studies. In addition, we argue that

carefully estimated faecal volume production provides a simple and quick overall feeding estimate

with important advantages over the common gut pigment technique, and it may be used as an independent

method in bottle incubation experiments.
Journal
Marine Ecology Progress Series

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