THE INFLUENCE OF FOOD QUALITY ON THE NUTRITIONAL ACCLIMATION OF THE COPEPOD ACARTIA-CLAUSI

The influence of food quality on the nutritional metabolism of Acartia clausi was studied experimentally using four different diets: (1) dia tom cells of Thalassiosira weissflogii, (2) detritus prepared from the same culture, (3) 50:50 mix on a protein basis of the two previous di ets, and 4) dinoflagellate cells of Prorocentrum micans. For each trop hic, ingestion, gut transit time, trypsin activity and K-m (half satur ation constant) were measured at limiting and saturating concentration . Assimilation rates were also estimated for both pure diatoms and mix ed live-detrital cell diets. Ingestion followed a Holling type 2 respo nse for diets 1 and 4, a linear one for detritus and an intermediate r esponse for diet 3. Gut transit time displayed different adaptive chan ges with food regime depending on protein concentration. Trypsin activ ity was lower for detrital food and trypsin K-m significantly decrease d with increasing concentration of live diatoms. Assimilation rates we re higher for live food than for mixed live-detrital food. Results ill ustrated that Acartia-type copepods optimize nitrogen or protein uptak e. They suggest that besides chemoreception-mediated selectivity, inte rnal controls by digestion and assimilation also regulate ingestion (f eed-back). (C) 1998 Elsevier Science B.V. All rights reserved.