Pigment dynamics associated with the grazing of a ciliate and a flagellate feeding on a cyanobacterium

International audienceThe egestion of particulate material as well as pigment degradation during microzooplankton grazing on phytoplankton are poorly known processes. In an attempt to evaluate these processes, changes in pigment concentrations within various size fractions were monitored in batch cultures of an assemblage of a pelagic ciliate (Strombidium sulcatum) and a heterotrophic flagellate (Paraphysomonas sp.) feeding on a cyanobacterium (Synechococcus sp.) over a 10-day period. Chlorophyll a, carotenoids and phaeopigments were not found in the 0.1-0.7 mu m fraction while the pigments originally in the 0.7-3.0 mu m fraction (prey) were transferred into the > 3.0 mu m size fraction (predator). During this transfer, the carotenoids (zeaxanthin and B-carotene) were not degraded significantly. In contrast, chlorophyll a was degraded into phaeophytin-like compounds which accounted for almost 100 % of the recorded phaeopigments. The destruction of chlorophyll a varied with time ranging from 4 % (day 3) to almost 100 % tend of the experiment) and this destruction was inversely related to micro-grazer ingestion rates. Microscopic examinations of samples did not reveal any large egested particles > 3.0 mu m, suggesting that phaeopigments and carotenoids measured in this size fraction were accumulated inside the protozoa. Zeaxanthin was very stable even when it was within the mice-grazer. (C) Elsevier, Paris