Influence of algal diet on growth and ingestion of Calanus helgolandicus nauplii

Nauplii of Calanus helgolandicus were raised from eggs, laid within a 12 h period, to Copepodite Stage I (CI) on 5 different species of algae at high concentrations at 15 degreesC. The diets used were Isochrysis galbana (5 mu m spherical diameter), Rhodomonas baltica (7 mum), the coccolithophorid Ple urochrysis carterae (12 mum), the diatom Thalassiosira weissflogii (14 mum) and the dinoflagellate Prorocentrum micans (30 mum). Each day a sample was taken and preserved for later cohort analysis. Growth was estimated from C HN samples collected almost daily, from which naupliar stages were also dis tinguished. Ingestion was measured for each naupliar feeding stage. The fas test development was obtained with I. galbana and P. micans. We found the h ighest value of carbon and nitrogen content of Naupliar Stages NV to Cl for individuals reared on the smallest algae, I. galbana and R. baltica. Howev er, ingestion rate in terms of carbon or nitrogen was lowest with these sam e (smallest) algae. Therefore, the gross growth efficiency was highest for the smallest algae. These results suggest the following: Firstly, that fact ors influencing development time and weight in stage are different; weight in stage is negatively related to algal size, whereas development time is i ndependent of it, The quality of the algal biochemical components could be the factor influencing development. Secondly, that small algae are fully as similated in the gut whereas larger cells, i.e. those with indigestible com ponents around the cell (theca, frustule, calcium layer) are only partly as similated.