Algae viability within copepod faecal pellets: evidence from microscopic examinations

The viability of different phytoplankton species within copepod faecal pellets was tested. Monocultures of the dinoflagellate Scrippsiella trochoidea and the diatoms Fragilariopsis kerguelensis, Proboscia alata and Chaetoceros dichaeta were fed to Calanus helgolandicus, Temora longicornis and Centropages typicus. Microscopic observations of faecal pellet content, chlorophyll auto-fluorescence and the fluorescence of cells stained with the viability stain fluorescein diacetate (FDA) revealed that some S. trochoidea cells survived the gut passage of T longicornis and C. typicus. Viable cells of F kerguelensis were observed in faecal pellets of all copepod species investigated. The 2 diatom species P. alata and C. dichaeta were reduced to small fragments within all faecal pellets, and hence did not survive grazing by any of the 3 copepod species.