THE ORIGIN OF SEDIMENTING DETRITAL MATTER IN A COASTAL SYSTEM

Total sedimentation and the fraction due to copepod fecal pellets were measured during the growth season (March-October 1989) in the souther n Kattegat, Denmark. In this period the sedimentation of detritus made up 52 g C m(-2), equal to 82% of the sedimenting matter from the euph otic zone, but fecal pellets (11 g C m(-2)) constituted only a minor f raction. The remaining detrital matter was produced by other heterotro phs than copepods. Published data on heterotrophic biomass and grazing obtained during the investigation in the Kattegat are reviewed in ord er to relate the sedimentation to processes in the pelagic system. Cop epod defecation nearly equaled the sedimentation of fecal pellets, ind icating that retention of this matter in the pelagic system was insign ificant. A considerable fraction (10-24%) of the carbon flow processed by heterotrophic pico-, nano-, and microplankton was converted to det ritus that was lost from the mixed system by sedimentation. The microb ial food web is thus not an exclusively regenerating system.