Evidence for food-resource partitioning by kelp-bed filter feeders

Abstract

Particle-size selection was studied in 3 species of suspension feeding bivalves, a n ascidian and a sponge, using a direct and an indirect technique. All 3 bivalve species retained particles > 4 p m with 100 % efficiency, while the retention of 0.6 pm cells dropped to approximately 20 %. In contrast, sponges showed the highest retention for the smallest particles and a declining efficiency for larger particles, suggesting an effective food resource partitioning on the basis of particle size between these 2 groups of animals. The ascidians, however, retalned all particles > 0.6 pm with approximately 100 % efficiency. The sponges, were able to meet thelr entire carbon requirements by utilization of particles < 1 vm in diameter. This size fraction could only meet 5 to 21 % of the bivalves', and l? % of ascidian carbon requirements, while free-living bacteria at a concentration of 0.5 X 106 ml-', provided 1 to 4 % of the bivalves' carbon requirements, 17 % of the sponges' and approximately 3 % of the ascidians' carbon requirements.