Sinking rates of fecal pellets from gelatinous zooplankton (Salps,Pteropods, Doliolids)

Sinking rates were determined for fecal pellets produced by gelatinous zooplankton (salps, Salpa fusiformis and Pegea socia; pteropods, Corolla spectabilis; and doliolids, Dolioletta gegenbaurii) feeding in surface waters of the California Current. Pellets from the salps and pteropods sank at rates up to 2 700 and 1 800 m d^-1, respectively; such speeds exceed any yet recorded for zooplankton fecal pellets. Fecal pellets of salps were rich in organic material, with C:N ratios from 5.4 to 6.2, close to values for living plankton. The relation between volume and sinking rate indicates that salp and pteropod pellets are slightly less dense than those of pelagic Crustacea; moreover, pellet density varied between different collection dates, probably because of differences in composition. In contrast, doliolid pellets sank at rates up to 208 m d^-1, a rate much lower than would be expected from pellet size. Thus, density and sinking rates of pellets are much more variable in zooplankton than would be expected from studies of crustaceans alone. Moreover, the extraordinarily high sinking rates of fecal pellets of salps indicates that these tunicates may be disproportionately important in the flux of biogenic materials during periods when they form dense population blooms.