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

Viitasalo, Markku, Mirja Rosenberg, Anna-Stiina Heiskanen, Marja Koski

Limnol. Oceanogr., 44(6), 1999, 1388-1399 | DOI: 10.4319/lo.1999.44.6.1388

ABSTRACT: We investigated the sedimentation of copepod fecal pellets in three different sea areas representing a sheltered bay, an archipelago area, and the open sea on the southwestern coast of Finland in the northern Baltic Sea. Fecal carbon sedimentation was always <0.05% of the total sedimentation of particulate 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 layer (0-20 m). However, in the area and season dominated by the large calanoid copepod Limnocalanus macrurus (bay station in spring), fecal carbon sedimentation was an order of magnitude higher than at the other two stations. From June onwards, when the bay station was dominated by cyclopoids, the situation changed: the fecal carbon sedimentation remained 30% lower in the bay than in the archipelago, although the fecal carbon production was estimated to be 2 times higher in the bay. Furthermore, pellet fragmentation (percentage of broken pellets of total fecal carbon sedimentation) was highest in spring and autumn at all areas and increased towards the open sea, being 27%, 45%, and 61% at the bay, archipelago, and open sea stations, respectively. This gradation was probably due to more intense turbulence and water column mixing in the open sea, resulting in more efficient loosening and breakup of pellets. The overall contribution of copepod feces to vertical carbon 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.

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