The effect of quality of food on feeding and digestion in<i>Paracentrotus lividus</i>(Lamarck) (Echinodermata: Echinoidea)

Abstract

Adults (40 to 50 mm horizontal diameter) were fed prepared foods containing a formulated meal and agar. The gut‐residence time ranged from 8 to 50 h indicating that the gut functions as a continuous‐flow, stirred tank reactor. The average gut‐clearance time was ca. 5 days with the rate of fecal production quickly decreasing, indicating that food is not retained in the gut with starvation to increase the efficiency of digestion. The rate of feeding of individuals ranged from an average (±SD) of 1.0 + 0.3 to 2.7 ± 1.1 g day‐1. The rate of feeding did not vary with time indicating continuous feeding and lack of satiation. The rate of feeding and fecal production and the total absorption efficiency did not vary with food quality, even when a high level of non‐digestible material was present. The absorption efficiency of digestible material must increase for the total absorption efficiency to remain the same with an increase in non‐digestible material. Modulation of the absorption efficiency rather than of feeding rate or gut‐clearance time may be the mechanism of responding to difference in food quality in a way predicted by optimization theory.