ASTAXANTHIN IN CALANUS-PACIFICUS - ASSESSMENT OF PIGMENT-BASED MEASURES OF OMNIVORY

We investigated the suitability of the pigments astaxanthin and cantha xanthin as biomarkers for measuring the contribution of microzooplankt on prey to copepod diets. Identification and quantification of pigment s of the marine planktonic copepod Calanus pacificus and heterotrophic protists were made using reverse-phase HPLC with a photodiode array d etector. Astaxanthin content in the body tissues of C. pacificus decli ned significantly within 2 h after the onset of starvation. The esteri fied 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 la rge 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 proti st extracts, no single pigment was common to all heterotrophic protist s.