Christmas Island is surrounded by a narrow fringing reef which supports bountiful marine life, including 88 coral species and more than 650 species of fish. The island is located on the edge of the Java Trench, the deepest point in the Indian Ocean, creating spectacular steep drop-offs just beyond the fringing reefs.
The marine area of Christmas Island National Park extends 50 metres seaward of the low water mark from the national park boundary. The park’s marine area protects the shoreline, reef shelf and tidal pools and much of the island’s shallow and narrow fringing coral reefs that provide habitat for hundreds of tropical fish species.
Spinner and common dolphins inhabit the island’s waters and small numbers of green turtles nest on Dolly and Greta beaches. Watch the baby green sea turtle hatching
Magnificent migrating whale sharks regularly visit during the wet season. They generally first appear when the red crabs are spawning at the start of the wet season — they converge to supplement their plankton diet with crab larvae. Read more about ocean fish
Christmas Island’s seabirds and land crabs also rely on the marine environment for their survival. The endangered Abbott’s booby and the iconic golden bosun (Christmas Island’s wildlife emblem) are just two of the many species of seabirds that can be seen foraging for fish in the marine environment.
Read more about seabirds
Land crabs such as the red crab use the marine environment for breeding rather than feeding and put on a spectacular show each year when they move from the rainforest to the sea to spawn (release their eggs).
Read more about crabs
These linkages between the marine and terrestrial environments create the island’s diverse and spectacular ecosystem.
Christmas Island’s fish community is distinctive because the island is a meeting place for Indian and Pacific Ocean fish species – it’s one of the few locations in the world where Indian and Pacific Ocean fish swim side by side. Some of these species interbreed to produce hybrids. Christmas Island has more hybrid fish than anywhere else in the world, making it a marine hybridization zone of international significance.
Surgeonfish and unicornfish
Surgeonfish are an important herbivore on the reef and are commonly seen grazing in shallow waters, often in schools. They are named for the scalpel-like blades at the base of their tail. These blades can inflict a serious wound if the fish is handled carelessly. Unicornfish are generally found in smaller groups or pairs and many species feed midwater on plankton.
Toadfish and puffers
These slow moving fish are able to puff themselves up into a ball. This puffing ability, along with their highly toxic flesh and skin, make them unpalatable to predators. They vary in size from 5 to 90 cm, are generally uncommon, occurring singly or in pairs.
Damselfish are probably the most common shallow water fish found on coral reefs with over 300 species found worldwide. The group includes the most famous coral reef fish – the clownfish or anemonefish. There are three species of anemonefish at Christmas Island (among other damselfish species) and they can be seen living safely amongst the tentacles of their host anemone on the reef top and edge between five and 40 m. Damselfish range between 4 and 10cm in length.
At least 11 different hybrids have been recorded at Christmas Island. These hybrids are often a result of interbreeding between Indian and Pacific Ocean species. Usually one of the parent species is rare and unable to find a partner, forcing it to mate with the next closest species. On Christmas Island, species of surgeonfish, butterflyfish, angelfish, triggerfish, wrasse and toadfish have been know to produce hybrids. The hybrids are identified by their unique colour patterns, which are a mixture of the two parent species. Hybrids can be seen in the same locations as the parent species and often in the same social groups.
Cods and basslets
This broad group includes small colourful basslets (15 cm) and large predators (up to 2.7 m). The basslets may form harems of one male and many females, or large schools. These vibrantly coloured fish (usually purples, reds and yellows) are abundant on the drop-offs, where they hover above the reef feeding on plankton. The cods and groupers (20-270 cm) are ambush predators that camouflage with the reef and engulf prey such as fish and crabs with their large mouths. They are often spotted or barred.
These slender cigar-shaped fish are easily recognised by their two barbells (whiskers) situated under the chin. The sensitive barbels are used to sift through the sand and detect prey such as shrimps. Goatfish are commonly between 20 and 40 cm in size and they often have a distinct stripe or spot on the body.
These spectacularly coloured fish are highly prized by photographers. Ranging in size from five to 50 cm, they are among the most elaborately patterned fish in the world. Angelfish are distinguished from other fish by a noticeable spine on their lower cheek. The Cocos angelfish is found only at Christmas and Cocos Islands as is the endemic subspecies of the lemonpeel angelfish. Lemonpeel angelfish are common in the shallows at Christmas Island – identify the juveniles by the black spot with a blue margin which fades as they become adult
The Moorish idol is a picturesque fish that looks like a butterflyfish but is in a family of its own. It has black, yellow and white vertical stripes with a trailing dorsal filament and is found in the same shallow coral reef habitat as butterflyfish. You may see it on its own, in pairs or in small schools. Look for juveniles sheltering amongst branching corals.
These pelagic fish are long (up to1.8 m) and have large teeth. Silver in colour with a series of dark bars, they are regularly encountered on the drop-offs where they hunt fish. Larger barracudas are often alone but smaller barracudas will form schools.
Thirty-four species of moray eels have been recorded at Christmas Island all of which come in a variety of colours, shapes and sizes. They are generally found hiding in and around hard corals and can often be seen whilst snorkelling or scuba diving. Some species have blunt teeth which are used for crushing crabs and molluscs while others have sharp, needle-like fangs used more for feeding on prey items such as fish, shrimp and octopus. Moray eels are not normally aggressive however the masked moray eel can be territorial and bite intruders if they come too close.
This is a diverse group that exhibit a range of sizes (5-230 cm), colours and diets. The majestic humphead maori wrasse is the largest member and uses its powerful jaws to crush shellfish or feed on crown-of-thorns starfish. One of the smallest members of this group is the blue and white striped cleaner wrasse, which feeds by eating parasites from other fish that visit the wrasse’s ’cleaning station’. Most wrasses form harems where the largest member of the social group is a brightly coloured male surrounded by dull coloured females.
These are one of the most beautiful groups of fish in the sea. Their posterlike colours and unique patterns make them easy to identify. Typically 8-15 cm in length, butterflyfish can be seen on shallow coral reefs, swimming in pairs and picking at food on the substrate. Some species feed exclusively on corals, while others have a broad diet.
Triggerfish and leatherjackets
These two closely-related families are distinguished from other fish by the presence of a sturdy dorsal spine that they erect to help wedge themselves into holes when danger approaches. These fish have rough skins and some, such as the clown triggerfish, have vivid colour patterns.
Parrotfish are closely related to wrasses but can be distinguished by their fused teeth that look like a parrot’s beak. Usually 20 to 100 cm in length these fish are commonly seen in shallow water grazing on algae. Some species eat corals that they crush with their powerful jaws, returning sediment to the reef in the form of sand. Like wrasses, many parrotfish have a haremic social system with the largest fish being a brightly coloured male and the smaller fish are dull coloured females.
Christmas Island’s pelagic (open ocean) species include tunas, wahoo, barracuda, rainbow runners, mackerel scad, sailfishes, marlin, swordfishes and trevallies. Many are fast swimmers, escaping danger by bursts of speed. Many are schooling fish and find added safety by gathering together and swimming about in large numbers. Most pelagic fishes have protective colouration - blue or dark grey above and white or silvery underneath, making them less visible to predators from above or below them.
These huge rays cruise the open water in search of tiny plankton to feed on, using their wings to propel themselves through the water - they may have a wingspan over seven metres. Manta rays are usually black all over with white patches and two protruding flaps on either side of the mouth that are used to funnel plankton as they feed. Manta rays can occasionally be seen leaping from the water but are most commonly seen cruising just under the surface, or visiting ‘cleaner stations’ on the reef where cleaner fish remove parasites.
These are the largest fish in the sea, growing up to 18 m in length but are harmless. Every wet season (November to March) they congregate at Christmas Island, with juveniles (3-7 m) the most common. Whale sharks feed primarily on plankton and their arrival at Christmas Island coincides with the annual spawning of red crabs and corals, whose larvae they presumably feed on. Each whale shark has a unique arrangement of white spots that can be used as a visual fingerprint to identify individuals as they travel around the world.
Several other shark species inhabit Christmas Island’s waters but are relatively uncommon compared to other tropical areas. The most common species that can be seen whilst snorkelling or diving include white tip reef sharks (which grow up to around 2 m) and requiems (often referred to as whalers). Other sharks include the grey reef shark, scalloped hammerhead, silvertip shark and the oceanic whitetip. The tiger shark is the largest dangerous shark in Christmas Island’s waters, but is rarely seen.
Christmas Island’s dominant group of marine species are its corals, which are tiny animals called polyps that live in colonies. More than 100 species of coral are found in the island’s warm tropical waters, providing habitat for all coral reef species.
Hard (reef building) corals
Hard corals - also known as stony or true corals - grow by building a chalky limestone case with calcium taken from sea water. Large plate corals, branching corals and encrusting corals are common in Christmas Island’s waters.
It is difficult to identify particular species of coral as the shape of a coral colony depends on its environment. A species which grows in a rounded mass in areas with strong waves may produce slender branches in deeper, calmer water. Light level and the amount of sediment in the water also influences coral colony shapes.
Soft corals and sea fans have no hard external skeleton and can also be distinguished from hard corals by their swaying soft bodies. The soft body is defended by chemicals which make the coral toxic and bad tasting to predators. Sea fans (also called gorgonians) are supported by a flexible skeleton made of a substance similar to fingernails, called gorgonin. They generally inhabit vertical reef walls at the outer edge of of coral reef shelves.
Three major molluscs grow on the reefs:
Bivalves - The body of a bivalve shell is flattened and is attached to both its hinged shells. The largest of all bivalves and the easiest to find are the clams.
Gastropods - The most common mollusc, with most of the body typically hidden within its shell, which offers protection from predators.
Cephalopods - Octopi, cuttlefishes, squids and nautiluses are all cephalopods, and with the exception of nautiluses, can expel ink to confuse predators. They are the most highly advanced form of mollusc and the most intelligent invertebrate group. The nautilus is the only cephalopod with a true external shell. The inside of the shell is divided into many gas-filled chambers and buoyancy is controlled by taking in or pumping out water.
There are two kinds of marine plants - algaes (seaweeds) and seagrasses. Coral reefs are 'turfed' with fine hair-like algae which are grazed by many animals. Some red algae form hard pink crusts which cement sand and dead coral together.
Sponges stand out from the reef community with their bright colours and range of shapes. Sponges are filter feeders, taking in water and straining off tiny plants and animals, bacteria and oxygen.
Echinoderms include sea stars, brittle stars, feather stars, sea urchins and sea cucumbers. The skins of these creatures are hard plates or spines. Sea urchins are usually nocturnal, spending daylight hours wedged under rocks or in crevices. They are herbivorous and graze on algae on the reef and are in turn eaten by triggerfish and pufferfish.
Crabs, crayfish and shrimps belong to a group of ten-legged crustaceans called decapods. The banded coral shrimp is one of the best known cleaner shrimp species. They clean parasites and excess mucus off fish.
A sea anemone is a large polyp. Its mouth is surrounded by feeding tentacles and each one contains stinging cells. These are used to capture the plankton and small creatures the anemone feeds on. Some species have special symbiotic relationships with anemonefish. These fish hide amongst the tentacles of anemones to protect themselves and are not affected by the anemone's sting.