SARSIA INTRODUCTION Zooplankton fecal pellets play an important role in oce- anic and coastal carbon cycles either through the sedi- mentation and removal of organic carbon or through the recycling and retention of carbon in the surface waters (Fowler & Small 1972; Angel 1984; Welschmeyer & Lorenzen 1985; Bathmann & al. 1987; Lampitt & al. 1990; Noji 1991; Marty & al. 1994). The contribution of fecal pellets to sediment traps has been found to range from < 1 % up to 100 % of the particulate organic carbon (POC) flux (Smetacek 1980; Urrère & Knauer 1981; von Bodungen & al. 1987; Fowler & al. 1991; Small & Ellis 1992; González & al. 1994; Lane & al. 1994). Many interacting biological and physical factors affect the export of particulate and dissolved organic carbon (DOC) by fecal pellets from the euphotic zone to deeper waters and the sediments. These factors include: fecal pellet production rates, the carbon con- tent and settling velocity, as well as the zooplankton community composition, microbial activity, current velocities and physical mixing of the water column (Hofmann & al. 1981; Alldredge & al. 1987; Noji 1991; Lane & al. 1994; Urban-Rich 1997, 1999). The quantity, quality and composition of the avail- able seston influence production rates of copepod fecal pellets (Dagg & Walser 1986; Ayukai 1990). Typically, high concentrations of food result in faster fecal pellet production rates and greater concentrations of organic carbon in the fecal pellets due to superfluous feeding and selective grazing (Knauer & al. 1979; Cowles & al. 1988). Houde & Roman (1987) found that copepod ingestion increased with a decrease in the protein con- tent of the food suggesting that the copepods try to maxi- mize their intake of protein. Changes in the amount in- gested could lead to variable defecation rates over the course of the year depending upon the quality and quan- tity of seston present. Changes in zooplankton grazing are also reflected in the C:N content of the fecal pel- lets. High C:N ratios are found in fecal pellets produced on a diet of phytoplankton in stationary growth with a high C:N ratio or on a diet of detritus (Checkley & Entzeroth 1985; Morales 1987; Butler & Dam 1994). Herbivory, carnivory and coprophagy can all result in fecal pellets with potentially different carbon concen- trations. The seasonal aspect of the Ocean Margin Ex- change (OMEX) study, prebloom conditions in spring to post-bloom conditions in the fall, allowed us to in- Contribution by mesozooplankton fecal pellets to the carbon flux on Nordvestbanken, north Norwegian shelf in 1994 Juanita Urban-Rich, Eirik Nordby, Inger J. Andreassen & Paul Wassmann Urban-Rich J, Nordby E, Andreassen IJ, Wassmann P. 1999. Contribution by mesozooplankton fecal pellets to the carbon flux on Nordvestbanken, north Norwegian shelf in 1994. Sarsia 84:253-264. Fecal pellet production rates for mesozooplankton (> 500 µm) were measured monthly at a shelf edge and inshore station in northern Norwegian coastal waters during March-September as part of the Ocean Margin Exchange (OMEX) study. The total potential fecal pellet carbon flux was higher at the inshore station except in May when Calanus finmarchicus (Gunnerus) was more abundant at the shelf edge. Mesozooplankton fecal pellets had the potential to contribute 2.5 % (April & September) to > 100 % (May-August) of the POC flux found in sediment traps. This compared with only 5-35 %, when fecal pellet carbon flux was measured from trap pellets suggests that a significant amount of fecal pellet remineralization or coprophagy was occurring in the surface waters. Calanus finmarchicus apparently plays a pivotal role in moderating pellet carbon flux on Nordvestbanken both through its potential fecal pellet production and possibly through coprophagy. Carbon ingestion by the large mesozooplankton at the shelf edge station was found to be 250 g C m –2 for the duration of the OMEX study (March-Septem- ber). This is significantly higher than that estimated for new production during the course of this study suggesting that the large copepods were also feeding on detritus and/or microzooplankton. The high estimated carbon ingestion also indicates that the mesozooplankton were able to apply sufficient pres- sure to maintain the low chlorophyll standing stocks observed during this study. Juanita Urban-Rich, Horn Point Environmental Laboratory, University of Maryland, PO Box 775, Cambridge MD 21613, USA. (present address: LUMCON, 8124 Highway 56, Chauvin LA 70344, USA.) – Eirik Nordby, Inger J. Andreassen & Paul Wassmann, Norwegian College of Fishery Science, University of Tromsø, N-9037 Tromsø, Norway. E-mail: jurban@lumcon.edu – eirikn@nfh.uit.no – i-andrea@online.no – paulw@nfh.uit.no Keywords: Fecal pellet production rates; carbon flux; OMEX; sedimentation.