The diet of the coral Millepora complanata mainly consists of copepods, while Alcyonium siderium shows a strong positive selectivity for ascidian larvae . Predation on their larvae by corals may even alleviate competition by decreasing the competitor's recruitment. Other meroplankton species would be larvae of crabs, lobsters or mussels. To support coral reefs with their enormously diverse and dense assemblages of organisms, input of nutrition from waters that overflow the reef is necessary. The open ocean is therefore a source of zooplankton that gets washed over the reef in currents and is stripped from the water by planktivorous fish and filter feeding organisms.
Cnidarians possess special cells called cnidocytes that are especially abundant in the tentacles.
The interior of a cnidocyte cell is filled with a capsule containing a coiled pleated tube. When water rushes into this capsule the pressure within rises, a lid opens and the tube gets everted, turning the whole cell inside out. The end of the tube is pointed and bores its way into the tissues of the prey like a miniature harpoon. A toxin is sometimes injected that paralyzes the prey. The tentacles then pulls the captured prey towards the coral's mouth.