Coral reefs are home to many diverse creatures, plants and other forms of life. They all combine to create a habitat that is like no other environment on Earth.
The coral reef ecosystem is a diverse collection of species that interact with each other and the physical environment. The sun is the initial source of energy for this ecosystem. Through photosynthesis, phytoplankton, algae, and other plants convert light energy into chemical energy. As animals eat plants or other animals, a portion of this energy is passed on.
Sponges have been a part of the coral reef ecosystem from early on. Several species of these porous animals inhabit reefs. Sponges provide shelter for fishes, shrimps, crabs, and other small animals. They appear in a variety of shapes and colors.
Sea anemones are close relatives of corals. Indo- Pacific reef anemones are known for their symbiotic relationships with clownfish and anemonefishes. An anemone's tentacles provide refuge for these fishes and their eggs. In return, anemonefishes may protect the anemone from predators such as butterflyfishes. Anemonefishes may even remove parasites from their host anemones.
Bryozoans encrust the reef. These microscopic invertebrates from branching colonies over coral skeletons and reef debris, cementing the reef structure.
The reef is also home to a variety of worms, including both flatworms and polychaetes. Flatworms live in crevices in the reef. Some polychaetes such as Christmas tree worms and feather duster worms bore into coral skeletons. Other familiar species include bristleworms.
Sea stars, sea cucumbers, and sea urchins live on the reef. The crown-of-thorns sea star is a well- known predator of coral polyps. Large numbers of these sea stars can devastate reefs, leaving behind only the calcium carbonate skeletons. In dead reefs, recently killed by the crown-of-thorns sea star, larger food and game fish are almost totally absent. Even deep-sea fish populations may be affected by this breakdown in the food chain.
Shrimps, crabs, lobsters, and other crustaceans find protection from predators in crevices or between coral branches. Crustaceans are also predators. The coral crab crushes sea urchins and clams with its strong claws. The banded coral shrimp is an example of a cleaner shrimp. It removes parasites and dead skin from reef fishes.
Octopuses, squids, clams, scallops, marine snails, and nudibranchs are all molluscs that live on or near the reef. Many feed by filtering food particles from the water. Carnivorous snails are capable of drilling holes into clams or other shelled animals and then eating them. One of the largest molluscs on the reef is the giant clam. This clam may reach a length of 4 ft. (1.2 m).
Both schooling and solitary fishes are essential residents of the reef ecosystem. Fishes play a vital role in the reef's food web, acting as both predators and prey. Their leftover food scraps and wastes provide food or nutrients for other reef inhabitants.
Some species of sharks, skates, and rays live on or near the reef. Others swim in to eat. Shark species include lemon, nurse, Pacific blacktip, white-tipped reef, and zebra sharks. These sharks as well as rays generally eat crabs, shrimps, squids, clams, and small fishes.
Parrotfish use chisel-like teeth to nibble on hard corals. These fish are herbivores and eat the algae within the coral. They grind the coral's exoskeleton to get the algae, and defecate sand. A single parrotfish can produce about five tons of sand per year.
Wrasses comprise a large group of colorful cigar-shaped fishes. Some species are known as cleaners, and set up cleaning stations along the reef. When a larger fish aligns itself at one of these cleaning stations, a cleaner wrasse removes parasites from the fish.
Eels are one of the reef's top predators. These fishes live in crevices in the reef and venture out at night to hunt and feed. They have sharp teeth set in a powerful jaw. Eels eat small fishes, octopuses, shrimps, and crabs.
Other fishes found on the reefs include angelfishes, butterflyfishes, damselfishes, triggerfishes, seahorses, snappers, squirrelfishes, grunts, pufferfishes, groupers, barracudas, and scorpionfishes.
Some sea turtles frequent reef areas. Green, loggerhead, and hawksbill sea turtles live in the warm waters of the Great Barrier Reef.
Sea snakes are rarely found on reefs but do inhabit the waters around reefs in the Indo-Pacific. They possess small fangs but inject a potent venom.