Sinking rates of fecal pellets from the marine copepod Pontella meadii

Sinking rates of fecal pellets produced by the marine copepod Pontella meadii, grazing on 4 different phytoplankton diets, ranged from 15 to 153 m/day, with a mean of 66 m/day. Sinking rates, in general, were directly related to fecal pellet volumes, but unrelated to the diets used to produce the fecal pellets. There were two-to-threefold variations in sinking rates between fecal pellets of the same volumes, often produced on the same diets. Twenty repetitions of timed sinking of a single fecal pellet revealed sinking rates varying from 33 to 79 m/day, as well as variations in sinking rates within the course of individual descents. It is suggested that copepod fecal pellets are of such small volumes and densities that their sinking rates are subject to microstructural variations in the most carefully controlled water columns. Scanning electron microscope observations revealed lack of structural damage to some of the diatom frustules in the fecal pellets, suggesting that superfluous feeding may have occurred. Thus, the accelerated sinking rates of copepod fecal pellets may provide a mechanism for nutritional enrichment of the deep-sea ecosystem with organic parcels containing incompletely-assimilated plant material.