Sedimentation of copepod fecal material in the coastal northern Baltic Sea: Where did all the pellets go?

We investigated the sedimentation of copepod fecal pellets in three differe nt sea areas representing a sheltered bay, an archipelago area, and the ope n sea on the southwestern coast of Finland in the northern Baltic Sea, Feca l carbon sedimentation was always <0.05% of the total sedimentation of part iculate organic carbon, whereas the fecal carbon production (estimated from copepod abundance, assuming production rate of 10 pellets copepod(1) d(-1) ) contributed to 4-17% of particulate organic carbon sedimentation. Thus, > 99% of copepod fecal material was remineralized within the mixed water laye r (0-20 m). However, in the area and season dominated by the large calanoid copepod Limnocalanus macrurus (bay station in spring), fecal carbon sedime ntation was an order of magnitude higher than at the other two stations. Fr om June onwards, when the bay station was dominated by cyclopoids, the situ ation changed: the fecal carbon sedimentation remained 30% lower in the bay than in the archipelago, although the fecal carbon production was estimate d to be 2 times higher in the bay. Furthermore, pellet fragmentation (perce ntage of broken pellets of total fecal carbon sedimentation) was highest in spring and autumn at all areas and increased towards the open sea, being 2 7%, 45%, and 61%: at the bay, archipelago, and open sea stations, respectiv ely. This gradation was probably due to more intense turbulence and water c olumn mixing in the open sea, resulting in more efficient loosening and bre akup of pellets. The overall contribution of copepod feces to vertical carb on export in the northern Baltic Sea appears to be small, but, seasonal and spatial variations in hydrography and mesozooplankton community structure significantly affect the fecal pellet sedimentation rates.