THE RETENTION OF PARTICLES INTERCEPTED BY A DENSE AGGREGATION OF LAKE-OUTLET SUSPENSION FEEDERS

A thin film of water flowed vertically over the wooden planks impoundi ng a eutrophic lake in Kent, United Kingdom. Suspension-feeding larvae of the blackfly Simulium noelleri Friederichs formed a carpet-like, d ense aggregation over these planks and fed on the suspended particles (seston) carried from the lake. Yellow, fluorescent dye particles were used to model the abundant seston and to produce easily-identifiable bands across the gut contents of larvae. No bands were found in larvae that had been feeding for 3 h after the initial application, so egest ion of the bands will have been complete by this time. Nevertheless, d ye particles were found in the gut contents of larvae after 3 h and 6 h of feeding on natural seston, though quantities were small (approxim ately 8% of the initial concentration after 3 h and 2% after 6 h). Ret ention of particles at this site was thus surprisingly low.