Water Flow Affects Zooplankton Feeding by the Scleractinian CoralGalaxea fascicularison a Polyp and Colony Level

Several factors may affect heterotrophic feeding of benthic marine invertebrates, including water flow rate and polyp context (i.e., the presence of neighbouring polyps). We tested the interactive effects of water flow rate and polyp context on zooplankton feeding by the scleractinian coralGalaxea fascicularis. Single polyps and colonies were incubated in a flow cell for 30 minutes with an ambientArtemianauplii concentration of 10,000 L−1and water flow rates ranging from 1.25 to 40 cm s−1. Water flow rate and polyp context showed significant main and interactive effects on feeding rates ofG. fascicularispolyps. More specifically, feeding rates were optimal at flow rates of 1.25 cm s−1for single polyps and 5 to 10 cm s−1for polyps inhabiting colonies. The presence of epizoic acoelomorph flatworms may have negatively affected the observed feeding rates, especially at high flow. Our results demonstrate that water flow affects coral feeding and thus heterotrophic nutrient input at both a polyp and colony level. These findings are of relevance to our understanding of how biotic and abiotic factors interact on coral heterotrophy and may serve to optimise coral aquaculture.