Seasonal variation in zooplankton and suspended faecal pellets in the subarctic Norwegian Balsfjorden, in 1996

Zooplankton and the vertical distribution of suspended faecal pellets at a central station in Balstjorden were investigated during 25 cruises between March and October 1996. Calanus finmarchicus followed by Metridia sp. domin ated the biomass of large (> 500 mum) zooplankton. as is typical for subarc tic fjords in northern Norway. However, small zooplankton (< 500 <mu>m), in particular nauplii, Oithona spp.. Microsetella sp., and protozooplankton, also contributed significantly to zooplankton biomass. The biomass of small zooplankton varied similarly to that of large zooplankton during the study period ranging from about 0.2 to 3.5 g C m(2), except For increased biomas s of large zooplankton during an advective episode in May/June. The grazing impact of the small forms must be at least equal to that of the large zoop lankton. Among the faecal pellets, cylindrical pellets of copepod origin pr evailed. Filiform pellets were most probably underestimated due to the samp ling procedure. Small pellets less than 80 mum in length and probably of na uplii and protozoan origin, contributed considerably to the total suspended faecal pellet biomass. They accumulated in parallel with their potential p roducers in the surface layers, in particular, during summer, and contribut ed to the typical summertime retention of nutrients and particulate biogeni c matter. The fate of phytoplankton-derived matter in north Norwegian coast al waters is influenced by grazing, resulting in either rapidly or slowly s inking Faecal matter, depending on the size spectrum and the prevailing fee ding modes of the grazer community. The importance of an adequate sampling of the entire zooplankton community to determine the impact of grazing on t he fate of phytoplankton-derived biomass is stressed.