Eels are one of the reef's largest predators and feed on the small fishes, octopuses, shrimps, and crabs. Fringing reefs border shorelines of continents and islands in tropical seas. Barrier reefs occur farther offshore. The Great Barrier Reef off northern Australia in the Indo-Pacific is the largest barrier reef in the world. This reef stretches more than 2000 km.
Atolls are reefs that surround a central lagoon.
The result is several low coral islands around a lagoon. Atolls commonly occur in the Indo-Pacific region. Importance of corals and coral reefs Corals remove and recycle carbon dioxide. Excessive amounts of this gas contribute to global warming. Reefs shelter land from harsh ocean storms and floods by breaking the force of the waves, thereby allowing mangroves and seagrass to flourish.