Effects of planktonic copepods on transparent exopolymeric particles (TEP) abundance and size spectra

Abstract

Diatoms exude considerable quantities of polymers, mainly polysaccharides, that play an important role in the process of sestonic particle aggregation in the sea. We investigated the impact of copepods on transparent exopolymeric particles (TEP) generated by the diatom Thalassiosira weissflogii. Grazing experiments with 14C-labelled algae exudates demonstrated that copepods typical of the Baltic Sea were not actively filtering TEP. Control experiments showed that 'uptake' of radioactivity could be ascribed to passive uptake, such as adsorption of radioactively-labelled particles to the body surface. Furthermore, we tested the effect of copepods on TEP size spectra. The abundance and size distribution of TEP (from 1.4 to 180 μm of Equivalent Spherical Diameter) were analysed in a 4 h incubation experiment. In the presence of copepods, the proportion of larger TEP was higher. An increase in total volume of TEP in jars containing copepods (∼2 × 107 μm ml-1) compared with control jars without copepods (∼0.5 × 107 μm3 ml-1) was also observed. The process of aggregation of TEP demonstrated in this work, whereby copepods increase downward particle flux without consuming carbon, can have far-reaching consequences for carbon fluxes along the water column and for copepods feeding dynamics.