Vertical flux and degradation rates of copepod fecal pellets in a zooplankton community dominated by small copepods

Sediment trap studies have revealed that copepod fecal pellets can be degraded at high rates in the sea, and copepods, particularly of the order Cyclopoida, have been implicated as the main degraders of these fecal pellets. A field budget of copepod fecal pellet production, degradation and sedimentation was constructed from water column and sediment trap samples as well as from shipboard incubations during a 7 d late-summer period in the North Sea.

In addition, fecal pellet degradation due to the activity of copepods and other zooplankton organisms >200 μm was estimated from shipboard experiments. The copepod community was dominated by the cyclopoid copepodOithona similis. Only 3 to 39% of the fecal pellets produced in the upper 50 m of the water column were collected by sediment traps at 50 m, corresponding to specific degradation rates of fecal pellets of 1 to 3 d–1.

Accordingly, the fraction of suspended fecal pellets lost through sinking (sinking losses) and estimated pellet sinking velocities were low, and residence times short. Small fecal pellets were degraded at higher rates than larger fecal pellets. However, copepods and other zooplankton organisms >200 μm did not play an important role in the degradation of fecal pellets, since the estimated degradation due to zooplankton was 3 orders of magnitude lower than the total degradation rates of fecal pellets in the water column.

This generally challenges the anticipated role of copepods in retarding the vertical flux of their own fecal pellets, and indicates that smaller plankton organisms (<200 μm) have an important role in degrading fecal pellets in the sea.