Experiments involving three species of copepods(Acartia clausi Giesbrecht 1889, Pseudocalanus elongatus Boeck 1872 and Calanusfinmarchicus Gunnerus 1765) incubated with freshly produced copepod faecal material were conducted and analyzed using automatic image analysis. For two species (A. clausi and C. finmarchicus) the bulk of faecal material was not ingested but was fragmented. This process, coprorhexy, was accompanied by a shift toward smaller particles in the particle size-spectrum. Increases in total volume of the faecal particles after incubation with these copepods led us to propose a process which we refer to as 'coprochaly', derived from the Greek xot/Vaoio,(a loosening, as of bandages). Coprochaly was promoted by manipulation of the faecal material by the copepods. For the third species (P.elongatus) coprorhexy and coprochaly were coupled with coprophagy (ingestion of faecal material). Calculations indicated that the combined effect of coprorhexy and coprochaly reduced sinking velocities of the faecal particles by up to 50%. These processes increase pelagic residency time of particles, increase substrate area for aerobic microbes and presumably enhance remineralization of particulate organic matter.

Confl~chng data have been previously presented on the ablllty of copepods to prey upon the prymneslophyte Phaeocystls pouchetu Whde some have suggested that gelatinous colonies of thls species c o n t a n blochemlcal substances that prevent t h e~r consumption others have shown that both slngle cells and colon~es of P pouchetu can serve as an excellent food source The present study presents data from feedlng expenments uslng 4 specles of copepods and natural samples of phytoplankton prey from a south-north transect dunng May 1989 in the Barents Sea Natural phytoplankton contalned P pouchefn colonies m assoclatlon w t h varylng amounts of diatoms Along the transect these colonies vaned from h~g h l y fluorescent and healthy In the north to weakly fluorescent In the south Results of expenments uslng both image analysis and radiotracer techniques indicate that diatoms were actlvely preyed upon In all expenments w t h long-chain-formlng species as the preferred food Predahon upon P pouchefn colon~es was dependent upon the physiological condition of the colonies Healthy colonies were not consumed, while suscephble colon~es were consumed at rates 2 to 10 tlmes those for chain-forrmng dlatoms The selective predalon descnbed here has important impl~cations for specles composition in Archc waters

Open ocean chloroplast‐containing chrysomonads have been observed to prey on bacteria. Predominant among these forms are new species of Ochromonas and Chrysamoeba. These algae coexist with nearly identical apochlorotic forms, are abundant in oceanic nanoplankton (averaging 100 cells ml−1), will not grow axenically, can be maintained for extended periods with endogenous bacteria enriched by rice grain culture in the light, and contain bacteria within their food vacuoles. The results demonstrate that protists with and without chloroplasts can occupy overlapping trophic roles and should therefore be studied together. They also challenge recent estimates of nanoflagellate predation on bacteria, as these estimates have assumed that only apochlorotic forms are predatory. If other groups of pelagic nanoflagellates with chloroplasts also prey on bacteria, the transfer of material from bacteria to protists in the open ocean could approach twice previous estimates.

No abstract

Nuclepore filters of 0.6-1.0μm pore size have been used to prepare "protist-free" water for a number of studies in microbial ecology. This procedure has been called into question by a recent study claiming that a significant portion of bacterial loss in filtrates could be due to uncharacterized predators passing through 0.6μm filters. We were unable to directly observe protists in 0.6μm filtrates using phase contrast, epifluorescence, or transmission electron microscopy. Using the culture techniques of rice grain enrichment and most probable number, however, we were able to observe and quantify several species of bacterivorous nanoflagellates that developed not only in 0.6μm, but also in 0.4μm seawater filtrates. The ability of predacious nanoflagellates to squeeze through bacteria-sized pores questions studies of bacterial production and chemical cycling that have assumed protist-free filtrates.