UC San Diego

We investigated the suitability of the pigments astaxanthin and canthaxanthin as biomarkers for measuring the contribution of microzooplankton prey to copepod diets. Identification and quantification of pigments of the marine planktonic copepod Calanus pacificus and heterotrophic protists were made using reverse-phase HPLC with a photodiode array detector. Astaxanthin content in the body tissues of C. pacificus declined significantly within 2 h after the onset of starvation. The esterified and unesterified pigment fractions behaved differently, with the unesterified fraction initially increasing in starved animals. Tissue astaxanthin content of C. pacificus increased by 50% in 24 h when fed the cryptomonad alga Rhodomonas sp. Such rapid changes in copepod body tissue pigments in response to starvation or feeding would lead to large errors in pigment-based measures of omnivory. Furthermore, neither astaxanthin nor canthaxanthin could be detected in any extract of six species of cultured and one species of field- collected heterotrophic marine protists. Although a variety of carotenoids were found in protist extracts, no single pigment was common to all heterotrophic protists.