Suspension-feeding activity of a dense Ophiothrix fragilis (Abildgaard) population at the water-sediment interface: Time coupling of food availability and feeding behaviour of the species

Ophiothrix fragilis is a suspension-feeder which forms dense aggregations (up to 2000 individuals m−2) in the Dover Strait. Its optimal suspension-feeding activity is expressed when currents are less than 20 cm s−1. Thus, the duration of this behaviour over a tidal cycle depends on the tidal velocity, and can be very short during spring tides. During neap tides, suspension-feeding is almost continuous but the flux of nutrients (phytoplankton, organic carbon and nitrogen) remains low because current increases slowly after slack water, and resuspension phenomena do not occur. In contrast, during spring tides, the current speed rapidly increases and induces an important resuspension of particles. Thus, the flux of nutrients is very important during the short duration of suspension-feeding of the O. fragilis population. Minimum gut contents were observed 3 h before slack current and maximum gut contents were observed about 1 h after slack water.