Studies of fecal pellet fluxes and retention have revealed that most pellets are degraded within the surface waters. However, the key degraders are poorly known. The retention of carbon and nutrient is not matched by bacterial respiration and the major degradation process is believed to be coprophagy (ingestion of fecal pellets) by copepods, though field evidence lacks. We observed copepods rejecting pellets immediately after capture, often with pellet fragmentation as outcome. Pellet ingestion was rare and only of small pellet fragments unintentionally along with alternative food. Therefore, coprorhexy (fragmentation of pellets) seems the main impact by copepods, and they are not the key degraders. From size fractionation of the plankton community (Øresund, Denmark), we identified large heterotrophic dinoflagellates as major pellet degraders in the upper ocean. In deeper waters bacterial degradation dominates, only limited by pellet residence time, which is hypothesized to be dependent on ballast minerals. Bacterial degradation was independent on ballast material whereas sinking velocity increased with denser diet, leading to <10-fold higher carbon flux with coccolithophorid and diatom diets than with flagellate diet.