The world's largest coral reef, the Great Barrier Reef off Australia's northeast coast, consists of more than 2,900 reefs, 600 mainland islands, 300 reefs and thousands of animal species. Below is a synopsis of native organisms that inhabit one of the world's most complex ecosystems, including fish, corals, molluscs, echinoderms, jellyfish, sea snakes, turtles, sponges, whales, dolphins, seabirds, and shorebirds.
Hard coral
The Great Barrier Reef is home to approximately 360 species of hard coral, including bottlebrush coral, bubble coral, brain coral, mushroom coral, staghorn coral, tabletop coral, and needle coral. Hard corals, also known as stony corals, congregate in shallow tropical waters to help build coral reefs that grow in a variety of aggregates, including mounds, plates, and branches. As coral communities die, new coral colonies grow on the limestone skeletons of their predecessors, creating the three-dimensional structure of the reef.
sponge
While they are not as obvious as other animals, the 5,000 or so species of sponges along the Great Barrier Reef perform basic ecological functions, paving the way for a new generation that maintains the overall health of the reef. In general, sponges are close to the bottom of the food chain and provide nutrients to more complex animals. Meanwhile, there are sponge species that can help recover calcium carbonate from dying corals. In turn, the released calcium carbonate is eventually incorporated into the mollusks and diatoms.
Starfish and sea cucumbers
The Great Barrier Reef's more than 600 species of echinoderms – including starfish, starfish and sea cucumbers – are mostly good citizens and form an important link in the food chain that helps sustain the reef's overall ecology. The only exception is the crown of thorns starfish, which feeds on coral's soft tissues and, if left unchecked, can cause a dramatic decline in coral populations. The only reliable remedy is to maintain the population of Crown of Thorns predators, including the giant Triton snail and the Star River fish.
mollusca
Molluss are a wide variety of animals, including clams, oysters, and cuttlefish. Marine biologists believe that the Great Barrier Reef is home to at least 5,000 species and possibly as many as 10,000 molluscs, most notably giant clams, weighing up to 500 pounds. The ecosystem is also known for sawtooth oysters, octopus, squid, shells (whose shells were once used as currency by Indigenous Australian tribes), bivalves and sea slugs.
fish
The more than 1,500 species of fish that inhabit the Great Barrier Reef range from tiny gobies and larger bony fish, such as ivory and potato cod, to large cartilaginous fish, such as manta rays, tiger sharks and whale sharks. Damselfish, wrasse and ivory are among the most abundant fish species on coral reefs. There are also sea bass, butterfly fish, trigger fish, cowfish, pufferfish, angelfish, anemone, coral trout, seahorse, sea bass, sea bass, scorpion fish, eagle fish and stickleback.
sea turtle
Seven species of sea turtles are regularly found in the Great Barrier Reef: green sea turtles, loggerhead sea turtles, hawksbill turtles, flatback turtles, Pacific ridley turtles and leatherback turtles. Green, red and hawksbill turtles nest on coral reefs, while flatback turtles prefer mainland islands, and green turtles and leatherback turtles live on the Australian mainland and only occasionally forage as far as the Great Barrier Reef. All of these turtles — like many animals in coral reefs — are currently classified as vulnerable or endangered.
sea snake
About 30 million years ago, a group of terrestrial Australian snakes ventured out to sea. Today, there are about 15 species of sea snakes endemic to the Great Barrier Reef, including the large olive sea snake and the banded sea snake. Like all reptiles, sea snakes are equipped with lungs, but they can absorb a small amount of oxygen from the water and have special glands that excrete excess salt. All sea snake species are venomous, but far less threatening to humans than terrestrial species such as cobras, oriental corals or copperheads.
birds
Where fish and mollusks are found, there are pelagic birds that nest on nearby islands or the Australian coastline and venture to the Great Barrier Reef for regular meals. On Heron Island alone, you can find a wide variety of birds such as spotted shouldered doves, black-faced cuckoos, Capricorn silvereyes, yellow belt railroad tracks, sacred kingfishers, silver gulls, East Reef egrets, and white-bellied sea eagles, all of which rely on nearby coral reefs for nutrients.
Dolphins and whales
The relatively warm waters of the Great Barrier Reef make it a top destination for about 30 species of dolphins and whales. Some of these marine mammals travel through the waters almost year-round, others swim to the area to give birth and raise their young, while others simply pass through during the annual migration. The most spectacular and interesting cetacean in the Great Barrier Reef is the humpback whale. Lucky visitors can catch a glimpse of five-ton pygmy minke whales and bottlenose dolphins, which love to travel in groups.
Dugong
These large, comical-looking mammals are strictly herbivorous and feed on numerous aquatic plants of the Great Barrier Reef. Sometimes considered the source of mermaid mythology, dugongs are often thought to be closely related to dolphins and whales. Although they share the "last common ancestor" with modern elephants, dugongs are cousins of manatees.
Their natural predators are sharks and saltwater crocodiles, which only occasionally venture into the area – but often with bloody consequences. Today, more than 50,000 dugongs are believed to be around Australia, an encouraging rise in numbers for this still-endangered Kraken.
jellyfish
Before dinosaurs, jellyfish were one of the oldest creatures on Earth. Of course, jellyfish are not fish at all, but a gelatinous form of invertebrate zooplankton (cnidarians), whose bodies consist of up to 98% water. Sea turtles prefer to feed on several species of native jellyfish of the Great Barrier Reef, while some smaller fish use them as protection, swimming with them and hiding in the tangles of tentacles to ward off predators.
More than 100 recorded species of jellyfish are found near the Great Barrier Reef, including the infamous spiny blue bottle and box jellyfish. But these aren't the only species to be wary of. Measuring just a cubic centimeter (about the same size as a green pea, pencil eraser tip or chocolate chip), the Iruconji jellyfish is one of the smallest and most poisonous jellyfish species in the world.
While jellyfish don't have brains or hearts, some jellyfish, including box jellyfish, can be seen. Box jellyfish has 24 "eyes" (vision sensors), two of which are able to interpret and distinguish colors. Marine biologists believe that this complex sensory array of organisms makes it one of the few species on Earth that can observe the world around it in a 360° angle.