Omnivores living on coral reefs include fishes, crabs and other crustaceans. Coral fishes feed on algae and animals, whereas crabs consume algae, bacteria, fungi, mollusks and worms. The diet of crabs also includes detritus and other crustaceans.

Animals called coral polyps dominate coral reef ecosystems and make up the structural base of coral reefs. Vertebrates, or animals that have backbones, and invertebrates, or animals that lack backbones, are the two primary animal groups that live on coral reefs.

Bigger coral reef crustaceans include crabs, lobsters and shrimps, whereas smaller ones include copepods, stomatopods and amphipods. Crustaceans are characterized by an exterior jointed skeleton and paired appendages that enable them to move and feed on prey. Some crustaceans are omnivores, but others are active predators or scavengers.

Crabs dwelling on reefs typically stay inside the reef structure during daytime. Some reef crabs contribute to coral reef health by cleaning hard coral colonies. They get rid of harmful organisms, such as infesting parasites, from the bodies of hosts.

Coral reef fishes prey on various crustaceans. Around 1,000 goby species devour small animals living at the bottom, including shrimps and worms. Damselfishes consume zooplankton suspended above the corals. Parrotfishes and surgeonfishes nibble the algae on the reefs, thus cleaning the surfaces and allowing various colonizing animals to live on the reefs.