Nutritional ecology of the ascidian Pyura stolonifera: influence of body size, food quantity and quality on filter-feeding, respiration, assimilation efficiency and energy balance

Abstract

Effects of body size, cell density and food type on filtration rate, respiration rate and assimilation efficiency in the ascidian Pyura stolonifera were determined using a continuous-flow circulating seawater system. Filtration and respiration rates were related to body size. Assimilation efficiency was independent of body size for the consumption of the alga Dunaliella primolecta but was correlated with size for natural food. Different types of food, such as phytoplankton species and kelp detritus, which occur in the natural environment, were filtered by the ascidian at equal efficiency and rate. Under controlled conditions, the organic fraction of kelp particles is assimilated at 42% efficiency while D. primolecta cells are assimilated at 75% efficiency. Net energy balance and the conversion efficiency for artificial and natural diets were estimated. The potential for utilization of natural food resources by P. stolonifera is compared with other members of the filter-feeding community