Do transparent exopolymer particles (TEP) inhibit grazing by the euphausiid Euphausia pacifica?

The hypothesis that ubiquitous, sticky transparent exopolymerparticles (TEP) formed from phytoplankton exudates will adhereto and coat the feeding structures of marine zooplankton grazers,and thus depress feeding on phytoplankton, was tested usingthe euphausiid, Euphausia pacifica, as a model organism. Duringtwo feeding experiments, E.pacifica were offered cells of thediatom Thalassiosira weissflogii, TEP, or both TEP and T.weissflogiicells. Ingestion rates on cells were lower in the presence ofTEP. However, contrary to the hypothesis, grazing on cells wasnot inhibited by TEP. Rather, TEP-clusters, aggregates whichformed from TEP and nano-sized particles normally too smallfor the filtering apparatus of E.pacifica to retain, servedas an alternative food source for E.pacifica, reducing theiringestion of cells. These clusters were very similar in formto the TEP actually available to marine grazers in nature. TEP-clusterswere similar to cells in size and food quality, and were grazedat similar rates. When feeding on TEP-clusters, euphausiidsshort circuit the food web by feeding on nano- and picoplanktondirectly, bypassing the microbial loop. Thus, the presence ofTEP appears to enhance, rather than depress, macrozooplanktongrazing.