Low concentrations of large inedible particles reduce feeding rates of echinoderm larvae

Abstract

The planktonic larvae of many marine invertebrates must feed to develop to metamorphosis. The rate at which feeding larvae accumulate energy affects the amount of time they must spend in the plankton, which affects larval dispersal and mortality; it may also affect the amount of energy gained before metamorphosis, and thus limit growth or survivorship of early juveniles. Rates of energy acquisition are partly determined by the quantity of edible particles in the plankton. However, the plankton also contains many particles that are too large to be ingested. Prior studies suggest that high concentrations of such large inedible particles reduce larval feeding rates. This study examines whether the feeding rates of larvae of southern California echinoderms are reduced by lower, more frequently encountered concentrations of large inedible particles. Larvae of a holothuroid, two asteroids, and three echinoids were fed 6-µm beads alone or with large inedible beads at 25–500 inedible beads mL⁻¹. Five of the six species showed reduced clearance rates on 6-µm beads when exposed to as few as 25 inedible beads mL⁻¹. In similar experiments on an asteroid and an echinoid using natural large inedible particles (centric diatoms), larval clearance rates were reduced at 25 cells mL⁻¹ and higher. Larval clearance rates were reduced by ~50% in treatments of 100 or 500 large inedible particles mL⁻¹. These results suggest that in nature, rates of food acquisition by larvae may depend not only on the abundance of food particles, but also on the abundance of potentially interfering non-food particles.