Ar. Juhl et al., ASTAXANTHIN IN CALANUS-PACIFICUS - ASSESSMENT OF PIGMENT-BASED MEASURES OF OMNIVORY, Limnology and oceanography, 41(6), 1996, pp. 1198-1207
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.