Dynamics of copepod faecal pellets in relation to a Phaeocystis dominated phytoplankton bloom: characteristics, production and flux

Copepod faecal pellet characteristics and production were measured in sprin g 1995, 1996 and 1997 in the North Sea Southern Bight in order to define ch anges due to the development of the phytoplankton bloom. Changes were relat ed to the succession from diatoms to a Phaeocystis sp. bloom. Mean monthly pellet production decreased during the Phaeocystis bloom development to 0.2 7 pellets ind.(-1) h(-1), approximately 80% lower than before and after the bloom. Although phytoplanktonic pigments showed significant differences be tween inshore and offshore stations, there mar no such significant differen ce for faecal pellet production. Faecal pellet sinking-rate decreased from 100 to 70 m day(-1) during the transition from a diatom- to a Phaeocystis-d ominated bloom. This was due to a decrease in pellet density and/or a decre ase of the pellet volume. These results supported the idea of lower feeding of copepods under Phaeocystis bloom conditions. As mean seasonal density o f copepod faecal pellets war higher (1.37 g cm(-3)) than in other seas, acc idental ingestion of sedimentary material as the cause of this high density is discussed.