Food type and concentration affect chlorophyll and carotenoid destruction during copepod feeding

To evaluate the use of pigments as tracers for determining copepod grazing rates and selectivity, we examined the stability of several biomarker pigme nts during copepod feeding incubations. During these incubations, we measur ed changes in phytoplankton-derived chlorophylls and carotenoids in the par ticulate and dissolved pools. Budgets were calculated to determine changes in pigment concentrations in the food, copepod fecal pellets, copepod guts, and dissolved/colloidal fraction. For each of six algal diets, adult femal e Acartia tonsa copepods were fed limiting and saturating food concentratio ns, approximately 100 and 500 mu g CL-1 respectively. Thalassiosira weissfl ogii, Rhodomonas lens, Chroomonas salina, Dunaliella tertiolecta, and two T etraselmis strains were used in the feeding experiments to investigate the fate of fucoxanthin, alloxanthin, lutein, chlorophyll (Chl) b, and Chi a. I n all experiments using saturating food concentrations, the dissolved/collo idal pool contained no more than 3% (usually less than 1%) of any pigment, whereas in experiments using limiting food conditions, pigments were undete ctable in the dissolved/colloidal pool. Pheopigments were present in fecal pellets and copepod guts in most of the experiments. Chi a destruction (con version to colorless products) was variable among the different experiments , depending on algal species and food concentration and, in most cases, Chl a was destroyed to a greater extent than the carotenoids. In all cases, pi gment destruction was higher when copepods were fed Limiting rather than sa turating food concentrations. These data attribute the variability in pigme nt destruction to algal species and concentration, and suggest caution when pigments are used as tracers of herbivory. In such studies, assumptions ab out conservative behavior, even for the carotenoids, would need to be verif ied for each set of experimental conditions and grazers.