Publication Date:
2004-12-29
Description:
Microzooplankton grazing rate estimates by the dilution approach have recently been criticized as systematically biased in the direction of being overestimates of actual rates in nature, and particularly in the open oceans. This argument is based on observed mortality responses of ciliated protozoa to reduced food in several coastal experiments and a global extrapolation which assumes that all grazing in all ocean systems scales to the abundance of ciliates. We suggest that these conclusions are unrealistic on several counts: they do not account for community differences in open ocean and coastal systems; they ignore experimental direct evidence supporting dilution rate estimates in the open oceans, and they discount dilution effects on mortality as well as growth in multi-layered, open-ocean food webs. High microzooplankton grazing rates in open-ocean systems are consistent with current views on export fluxes and trophic transfers. More importantly, significantly lower rates would fail to account for the efficient nutrient recycling requirements of these resource-limited and rapid-turnover communities.
Print ISSN:
1812-0806
Electronic ISSN:
1812-0822
Topics:
Geosciences
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