Measurements of biomass and grazing for three size classes of mesozooplankton were carried out at two drifting stations: at 59°N, 20°W during a tracer release experiment, and at 37°N, 19°W at a conventional drifting station. Mesozooplankton biomass at 59°N did not vary between day and night (6.7 and 6.4 mg C m–3 for night and day samples, respectively). At 37°N, carbon biomass was much lower an...