Production, oxygen respiration rates, and sinking velocity of copepod fecal pellets: Direct measurements of ballasting by opal and calcite

Production, oxygen uptake, and sinking velocity of copepod fecal pellets egested by Temora longicornis were measured using a nanoflagellate (Rhodomonas sp.), a diatom (Thalassiosira weissflogii), or a coccolithophorid (Emiliania huxleyi) as food sources. Fecal pellet production varied between 0.8 pellets ind21 h21 and 3.8 pellets ind21 h21 and was significantly higher with T. weissflogii than with the other food sources. Average pellet size varied between 2.2 3105 mm3 and 10.0 3105 mm3. Using an oxygen microsensor, small-scale oxygen fluxes and microbial respiration rates were measured directly with a spatial resolution of 2 mm at the interface of copepod fecal pellets and the surrounding water. Averaged volume-specific respiration rates were 4.12 fmol O2 mm23 d21, 2.86 fmol O2 mm23 d21, and 0.73 fmol O2 mm23 d21 in pellets produced on Rhodomonas sp., T. weissflogii, and E. huxleyi, respectively. The average carbon-specific respiration rate was 0.15 d21 independent on diet (range: 0.08– 0.21 d21). Because of ballasting of opal and calcite, sinking velocities were significantly higher for pellets produced on T. weissflogii (322 6 169 m d21) and E. huxleyi (200 6 93 m d21) than on Rhodomonas sp. (35 6 29 m d21). Preservation of carbon was estimated to be approximately 10-fold higher in fecal pellets produced when T. longicornis was fed E. huxleyi or T. weissflogii rather than Rhodomonas sp. Our study directly demonstrates that ballast increases the sinking rate of freshly-produced copepod fecal pellets but does not protect them from decomposition.