FEEDING RHYTHM OF THE POLYCHAETE NEREIS-D IVERSICOLOR (MULLER,O.F.) ACCORDING TO CHANGES IN TIDE

The feeding rhythm of the polychaete Nereis diversicolor (O.F. Muller) was studied during tidal cycles (spring and neap tide) at three sites in hale du Mont St-Michel and the Rance estuary in summer 1990. For m ost of the sites, the polychaetes were mainly feeding during spring ti des when immersion occurred. Dietary activity decreased at emersion si tes depending on low tide duration. During this period, the physical a nd chemical conditions in the mud flat sediments are not favourable to polychaetes' activities (high temperature, high desiccation, low oxyg en content) and can cause mortality or migration of the population. Re pletion indices from polychaetes of the Hirel sector (baie du Mont-St- Michel) showed a decrease of their dietary's activity during the neap tide period even if the site was permanently immersed.