Abstract
Large fecal pellets produced by macrocrustaceans, probably euphausiids, were observed frequently in the upper 20 m of the Santa Barbara and Santa Cruz basins off southern California at abundances ranging from 500 to 98,000 pellets m −3. Although sinking rates of these pellets, ranging from 18 to 170 m day −1, were rapid enough to remove the pellets from surface waters within hours, up to 40% of the pellets in the field had peritrophic membranes which were partially or totally decayed. Laboratory aging studies indicate that these decomposing pellets were from 4 to 10 days old. Moreover, the daily calculated flux of pellets from surface water, based on sinking rate measurements, was many times the photosynthetic carbon production of the euphotic zone, suggesting that sustained daily production of pellets at the abundances we observed would not be possible. We hypothesize that a proportion of fecal pellets produced by vertically migrating macrocrustaceans at night do not sink immediately, but accumulate in surface waters. Turbulent mixing processes, which increase the residence time of fecal pellets in the mixed layer, partially explain the observed accumulation.
Published Version
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