Animals of Australia's Great Barrier Reef

Meet the corals, kraits, and dugongs that live in this unique ecosystem

The largest coral reef in the world, the Great Barrier Reef off the northeastern coast of Australia, consists of more than 2,900 coral reefs, 600 continental islands, 300 coral cays, and thousands of animal species. Here's a rundown of indigenous creatures—including fish, corals, mollusks, echinoderms, jellyfish, sea snakes, marine turtlesspongeswhales, dolphins, seabirds, and shorebirds—that inhabit one of the world's most complex ecosystems.

Hard Coral

Heron Island Underwater Collection
Colin Baker / Getty Images

The Great Barrier Reef is home to about 360 species of hard coral, including bottlebrush coral, bubble coral, brain coral, mushroom coral, staghorn coral, tabletop coral, and needle coral. Also known as stony corals, hard corals congregate in shallow tropical waters and help build coral reefs, growing in various aggregations including mounds, plates, and branches. As coral colonies die, new ones grow atop the limestone skeletons of their predecessors, creating the reef's three-dimensional architecture.

Sponges

Heron Island Underwater Collection
Colin Baker / Getty Images

Although they're not as visible as other animals, the 5,000 or so species of sponges along the Great Barrier Reef perform essential ecological functions that pave the way for new generations and maintaining the reef's overall health. In general, sponges are near the bottom of the food chain, providing nutrients for more complex animals. Meanwhile, there are some sponge species that help recycle calcium carbonate from dying corals. The freed calcium carbonate, in turn, ends up being incorporated into the bodies of mollusks and diatoms.

Starfish and Sea Cucumbers

Lodestone Reef, Great Barrier Reef, Australia
Joao Inacio / Getty Images

The Great Barrier Reef's 600 or so species of echinoderms—the order that includes starfish, sea stars, and sea cucumbers—are mostly good citizens, constituting an essential link in the food chain and helping maintain the reef's overall ecology. The exception is the crown-of-thorns starfish, which feeds on the soft tissues of corals and can cause drastic declines in coral populations if left unchecked. The only reliable remedy is maintaining populations of the crown-of-thorn's natural predators, including the giant triton snail and the starry puffer fish.

Mollusks

Maxima clam (Tridacna maxima), Great Barrier Reef, Queensland
Michael Szonyi / Getty Images

Mollusks are a widely divergent order of animals, including species clams, oysters, and cuttlefish. Marine biologists believe there are at least 5,000 and possibly as many as 10,000 species of mollusks inhabiting the Great Barrier Reef, the most visible being the giant clam, which can weigh up to 500 pounds. This ecosystem is also notable for zig-zag oysters, octopuses, squid, cowries (the shells of which were once used as money by Australia's indigenous tribes), bivalves, and sea slugs.

Fish

Clownfish in anemone on the Great Barrier Reef
Kevin Boutwell / Getty Images

The more than 1,500 species of fish inhabiting the Great Barrier Reef range from tiny gobies and larger bony fishes, such as tusk fish and potato cods, up to massive cartilaginous fish such as manta rays, tiger sharks, and whale sharks. Damselfish, wrasses, and tusk fish are among the most abundant fish on the reef. There are also blennies, butterflyfish, triggerfish, cowfish, pufferfish, angelfish, anemone fish, coral trout, seahorses, sea perch, sole, scorpionfish, hawkfish, and surgeonfish.

Sea Turtles

Green Turtle Swimming Over Coral
Vicki Smith / Getty Images

Seven species of sea turtles frequent the Great Barrier Reef: the green turtle, loggerhead turtle, hawksbill turtle, flatback turtle, Pacific ridley turtle, and leatherback turtle. Green, loggerhead, and hawksbill turtles nest on coral cays, while flatback turtles prefer continental islands, and the green and leatherback turtles reside on mainland Australia, only occasionally foraging as far out as the Great Barrier Reef. All of these turtles—like many animals of the reef—are currently classified as either vulnerable or endangered species.

Sea Snakes

Olive Sea Snake
Brandi Mueller / Getty Images

About 30 million years ago, a population of terrestrial Australian snakes ventured toward the sea. Today, about 15 sea snakes are endemic to the Great Barrier Reef, including the large olive sea snake and the banded sea krait. Like all reptiles, sea snakes are equipped with lungs, but they can absorb a small amount of oxygen from water and have specialized glands that excrete excess salt. All sea snake species are venomous but are much less of a threat to humans than terrestrial species such as cobras, Eastern corals, or copperheads.

Birds

Roseate Tern with baby under its wing Lady Elliot
Darrell Gulin / Getty Images

Wherever there are fish and mollusks, there will be pelagic birds, which nest on nearby islands or the Australian coastline and venture out to the Great Barrier Reef for frequent meals. On Heron Island alone, you can find birds as diverse as the bar-shouldered dove, black-faced cuckoo shrike, Capricorn silver eye, buff-banded rail, sacred kingfisher, silver gull, eastern reef egret, and white-bellied sea eagle, all of which rely on the nearby reef for their nutrition.

Dolphins and Whales

Curious adult dwarf minke whale (Balaenoptera acutorostrata), underwater near Ribbon 10 Reef, Great Barrier Reef, Queensland, Australia, Pacific
Michael Nolan / Getty Images

The relatively warm waters of the Great Barrier Reef make it a favored destination for about 30 species of dolphins and whales. Some of these marine mammals ply the waters virtually year-round, others swim to the region to give birth and raise young, while others simply pass through during their annual migrations. The most spectacular and entertaining cetacean of the Great Barrier Reef is the humpbacked whale. Lucky visitors can catch glimpses of the five-ton dwarf minke whale and the bottlenose dolphin, which like to travel in groups.

Dugongs

Dugong
Brandi Mueller / Getty Images

These large, vaguely comical-looking mammals are strictly herbivorous, feeding on the numerous aquatic plants of the Great Barrier Reef. Sometimes reputed to be the source of the mermaid myth, Dugongs are often thought to be closely related to dolphins and whales. While they share a "last common ancestor" with modern elephants, dugongs are cousins to the manatee.

Their natural predators are sharks and also saltwater crocodiles that venture into the region only occasionally—but often with bloody consequences. Today, upwards of 50,000 dugongs are believed to be in the vicinity of Australia, an encouraging upturn in numbers for this still-endangered sirenian.

Jellyfish

Predating dinosaurs, Jellyfish are some of the Earth’s oldest creatures. Of course, jellyfish aren’t fish at all, but rather a gelatinous form of invertebrate zooplankton (Cnidaria), whose bodies are comprised of as much as 98% water. Marine turtles are partial to feeding on several of the Great Barrier Reef's indigenous jellyfish species, while some smaller fish use them as protection, swimming in tandem with them and hiding in the tangle of their tentacles to ward off predators.

There are more than 100 recorded species of jellyfish in the vicinity of the Great Barrier Reef, including the infamous stinging blue bottles and box jellyfish. But those aren’t the only species to be wary of. Measuring a mere cubic centimeter (about the same size as a green pea, pencil eraser tip, or a chocolate chip), the Irukandji jellyfish, is one of the world’s tiniest—and most venomous jellyfish species.

While jellyfish lack brains or hearts, some, including the box jellyfish, can see. The box jellyfish has 24 “eyes” (visual sensors) two of which are capable of interpreting and differentiating color. Marine biologists believe this creature’s complex sensory array makes it one of only a handful of species on the planet to have a full 360° view of the world around it.