Ocean Science www.ocean-sci.net 1812-0784 1812-0792 1 1 2005 10.5194/os-1-39-2005 http://www.ocean-sci.net/1/39/2005/ http://www.ocean-sci.net/1/39/2005/os-1-39-2005.html http://www.ocean-sci.net/1/39/2005/os-1-39-2005.pdf 39 44 2005-08-02 Reality checks on microbial food web interactions in dilution experiments: responses to the comments of Dolan and McKeon M. R. Landry A. Calbet Integrative Oceanography Division, Scripps Institution of Oceanography, University of California at San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0227, USA Institut de Ciències del Mar, CMIMA (CSIC), P. Marítim de la Barceloneta 37–49, 08003 Barcelona, Spain Dolan and McKeon (2005) have recently criticized microzooplankton grazing rate estimates by the dilution approach as being systematically biased and significantly overestimated. Their 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 between open ocean and coastal systems; they ignore direct experimental evidence supporting dilution rate estimates in the open oceans, and they discount dilution effects on mortality rate 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.