The in situ sinking rates of herbivore fecal pellets

The vertical flux of pigmented fecal pellets was measured forperiods of 4 h or less with closely spaced sediment traps. Thesettling of the nighttime injection resulting from macrozooplanktongrazing activity could be monitored as the pellets settled throughthe water column. Sinking rates of fecal pellets showed a rangeof 31 – 122 m d^–1 with an average of 87 m d^–1.Longer term experiments show that the vertical phaeopigmentflux is conservative, and that there is no significant lossof pigments en route to the sea floor. In Dabob Bay, coprophagyin the water column is most likely a minor consideration. Theamount of chlorophyll sinking out of the euphotic zone usuallyrepresents <1% of the standing crop, and is usually only5% or less than the phaeopigment flux. This suggests that grazingis the predominant process accounting for the major loss ofchlorophyll from the water column. ¹Contribution no. 1332 from the School of Oceanography, Universityof Washington, Seattle, WA 98195, USA. ²Present address: The Biological Laboratories, Harvard University,Cambridge, MA 02138, USA.