Potential effect of phytoplankton colony breakage on the calculation of zooplankton filtration rates

Substantial net production of short chains of the diatom Skeletonema costatum occurred in grazing experiments conducted with Acartia hudsonica (=A. clausi). A general model was then constructed to evaluate the influence of colony breakage during grazing on the calculation of zooplankton filtration and ingestion rates. Breakage can lead to either over-or underestimation of these rates. The magnitude of error is related to breakage probability, particle size distribution, size of the largest colonies, length of the experiment, copepod concentration and actual filtration rates. Size distributions similar to those described in the literature as manifestations of a complex selection for size and particle abundance can be generated by the grazing model under conditions of a uniform filtration rate accompanied by colony breakage. Unless the rate of breakage exceeds the rate of removal and causes net particle production, the occurrence of breakage may go undetected.