CAROTENOID-PIGMENTS IN MICROZOOPLANKTON

The carotenoid pigments astaxanthin and canthaxanthin were measured in cultured and field-collected heterotrophic dinoflagellates (2 species), ciliates (3 species) and copepod eggs (1 species). The heterotrophic dinoflagellates contained either astaxanthin or canthaxanthin as a single dominant pigment. Conversely, the choreotrichous ciliates contained both carotenoids. A small amount of canthaxanthin was detected only at high concentrations in the oligotrich Strombidium sp. Copepod eggs contained astaxanthin and xanthophyll esters. The esters were not detected in the protozoans. Cellular pigment content varied both within and between taxonomic groups, but was low compared with phytoplankton. Microzooplankton which have low C:carotenoid ratios (e.g. some dinoflagellates), and large organisms, even when not heavily pigmented (e.g. Favella ehrenbergii) are readily detected by carotenoid analysis. Small, weakly pigmented ciliates, however, are more difficult to detect when they are present in low concentrations. The pigment content of a heterotrophic dinoflagellate (Gymnodinium sp.) cultured at 29-mu-E m-2 s-1 (low-light group) was approximately 42 % of the average pigment content of the same species cultured in the same food environment but at 290-mu-E m-2 s-1 (high-light group). Inadvertent starvation of the cultures in the low-light group for less-than-or-equal-to 3 d resulted in the loss of all measureable pigmentation.