Coral Reef

The tropical coral reefs are the most beautiful ecosystem in the world.

There, I said it.

Porifera: Sponges

Sponges have what is often considered the most basic body plan of all the multi-cellular animals. They are sedentary as adults, and resemble plants in their simplicity and adherence to the substrate. Because of their simplicity and stillness, they were originally classified as a plant, and were only recognized as an animal in 1765 when their internal water currents were noticed.

Sponges are covered in tiny holes that draw water in. This is accomplished by small beating hairs that bring the water in. As the water is pumped throughout the inside of the animal, it is filtered for food particles. The water is the pumped out, exiting much larger holes.

This simple body plan and feeding technique of sponges has been very successful for a long time, for they have been around for half a billion years. During the Devonian period, well before the Dinosaurs, sponges were one of the most dominant forms of life on Earth. In modern times, they are more obvious in ar-eas of some water flow and nutrient load. Because of the generally clearer and nutrient poor waters of the tropical seas, they are not always as noticeable in the northern Australian waters as they are along the cooler southern coastlines. However, smaller and very attractively coloured species are present around coral reefs.

They vary in form, with some species growing distinctly shaped structures that look like balls, large cups or funnels, or they may simply grow as encrusting layers. Many of the tropical sponges, especially on coral reefs, can be quite colourful.

Phylum Cnidaria: Sea Jellies, Corals, Anemones

Class Scyphozoa: 'True Sea-jellies'

Order Rhizostomae

These are Jellyfish that have eight divided arms hanging from the bell, rather than tentacles.

Family Cassiopeidae: 'Upside down Jellies'

(Kakaban, Indonesia)

Cassiopeia ornata, 'Upside-down Jellyfish'.

Class Anthozoa: includes Stony Corals, Soft Corals, Anemones

Order Scleractinia: Hard/Stony Corals

Acropora spp.

The largest and usually most obvious genus of coral. Even the same species can grow in many forms, thus they have many common names such as 'Staghorn', 'Table' and 'Plate' Coral. 

Staghorn Coral Garden, Lizard Island (image by Damon Ramsey)(Lizard Island, Great Barrier Reef, Australia)

Sub-class Ceriantharia: Tube-dwelling 'Anemones'

(Kakaban Indonesia)

'Tube-dwelling Anemone'.

Phylum Platyhelminthes: 'Flatworms'

The flatworms on coral reefs can be confused with the nudibranch sea slugs, however the latter have obvious fluffy appendages (the Spanish Dancer is an example).

Order Polycladida

(Arnarvon Islands, Solomon Islands)

Thysanozoon flavomaculatum, 'Yellow spot Flatworm', 'Gold-flecked Flatworm'.

Phylum Annelida: Worms

This group includes the 'true' worms of the soil and sea.

Class Polychaeta

Family Serpulidae, 'Calcareous Tubeworms'

Like the 'Feather Duster Worms' of the Family Sabellidae, these worms also have two fans extending from the tube, however they differ in that the tube is hard and made from calcium carbonate. When disturbed they withdraw quickly and seal their tube off with the operculum.

(Rajah Ampat, Indonesia)

Protula bispiralis, 'Magnificent Tube Worm'. Two relatively large spires, with several beautifully delicate whorls. Orange and cream in colour. Tube often extending obviously from reef.

(Rajah Ampat, Indonesia)

Spirobranchus, 'Christmas Tree Worms'. Small and very common 'fluffy' feeding tentacles that usually grow out of the top of Boulder Coral in groups, and appear in many different colours. The tentacles suck back in quickly when the snorkeller gets too close.

Phylum Mollusca

Hapalochlaena spp., 'Blue-ringed Octopus'

There are at least three species in this genus. Blue-ringed Octopuses infamous for being one of the most venomous animals in the world. It is thought that the toxins from one small individual animal could kill over 25 people in one dose. The list of chemicals in the venom include: 5-hydroxytripamine, hyaluronidase, tyramine, histamine, tryptamine, taurine, acetylcholine, dopamine and tetrodotoxin; it is the latter that is most dangerous. Tetrodotoxin is found in pufferfish, and is reported to be some 100 times more toxic than cyanide. When the victim is bitten, they are partly paralysed, including the diaphragm, and thus unable to breath, and can die within minutes if not treated. There is no antidote. 

Hapalochlaena lunulata, 'Greater Blue-Ring Octopus'. Despite the common name, like all Blue-ring Octopuses, this animal is quite small, with short arms, and could fit in the palm of your hand - but don't pick it up! They are found around rubbly coral reefs across northern Australia, New Guinea and tropical Asian waters.

Phylum Echinodermata

Class Crinoidea: 'Feather Stars'

(Mangalonga, Solomon Islands)

Featherstars usually attach to coral on the edge of drop-offs and/or near areas with some flow of water. They are capable of 'swimming' freely.  There is a huge range of colours and combinations of colours.

(Lizard Island, Great Barrier Reef, Australia)

Class Echinoidea: 'Sea Urchins'


'Sea Urchin'.

Class Holothuroidea: 'Sea Cucumbers'

(Lizard Island, Australia)

Stichopus, 'Spiny Black'.

Phylum Chordata

Class Ascidiacea

Order Stolidobranchia

Family Styelidae

(Rajah Ampat, Indonesia)

Cnemidocarpa spp.

(Tangalooma Wrecks, Moreton Island, Queensland)

Cnemidocarpa stolonifera. Small and white, red 'veins'. Endemic to Australia, where it is found around coral reefs in tropics and subtropics, mostly along east coast.

Polycarpa spp.

(Mangalonga, Solomon Islands)

Polycarpa aurata. 'Gilded/Oxheart/Goldmouth/Ink Spot/ Yellow & Purple Ascidian/Sea Squirt'. One of the most obvious and commonly seen sea squirts on coral reefs.

Order/Sub-order Aplousobranchia

Family Didemnidae

(Pink Beach, Indonesia)

Didemnum molle, 'Green Sea Squirt'. A commonly seen sea squirt on coral reefs throughout the Indo-Pacific. It appears soft and squishy and swishes around in reaction to water movements. Another common sea squirt thay look similar is called Atriolum robustum. Or maybe I have these the wrong way around?

Class Thaliacea, 'Salps'

Family Salpidae

(Panagsama, Philippines)

A salp chain.

Class Chondrichthyes

Family Myliobatidae: Eagle Rays


Aetobatus narinari, 'Spotted Eagle Ray'.

For the page on the bony fish of the Indo-Pacific tropical coral reefs

(Miyako, Japan)

For the page on damselfish (including anemonefish) of coral reefs

(Miyako, Japan)

For the page on butterflyfish of the Indo-Pacific tropical coral reefs

Superfamily Chelonioidea: Marine Turtles

(Green Turtle, Fitzroy Island, Queensland, Australia)

There are half a dozen turtle species that can be seen around the tropical Indo-Pacific coral reefs. While they look superficially similar, if you can get a photograph or a good look, you should be able to identify them. 

The first step is to look at the lateral scutes (large scales in a line along either side) of the back of the carapace (shell). If the carapace has no scales, and the carapace is ridged, then that's easy - it is a Leatherback! (although these turtles are more commonly seen out to sea rather than around coral reefs).

If the there are four lateral scutes, then it is either a Green Turtle, Hawksbill or a Flatback Turtle. Also, the first lateral scute does not touch the nuchal (the small thin scute on the very front leading edge of the carapace, just behind the head). If the carapace is slightly upturned along the edge, then it is Flatback. The next step is to look at the head. The Green Turtle (and the Flatback) both have one large prefrontal scale along the front of the eye, while the Hawksbill clearly has two (as well as a more parrot-like beak). 

If there are five or more scutes along the outer edge of the carapace, then it is either a Loggerhead or an Olive Ridley. Also, the first lateral scute does touch the nuchal. The Loggerhead has either five or six lateral scutes, the shell itself is elongated in shape, and the turtle has a large head. The Olive Ridley has a more rounded shell with six or more thin lateral scutes.

(Fitzroy Island, Queensland, Australia)

Chelonia mydas, 'Green Turtle'. The most widespread and commonly seen of the marine turtles.

(Pink Beach, Indonesia)

Eretmochelys imbricata, 'Hawksbill Turtle'. Similar looking to Green Turtle, but with longer head and distinct 'parrot beak'. Note the two prefrontal scutes in front of the eye (split by a lighter edge) and the first lateral scute of the shell not touching the nuchal. 

Subfamily Hydrophiinae: Sea Snakes including Sea Kraits

'Sea Krait'.

now, there was a sea krait around here somewhere...

Family Haematopodidae: Oystercatchers

Family Scolopacidae: 'Sandpipers'

Tringa, 'Tattler'.

Family Burhinidae

(Montgomery Reef, Western Australia)

Esacus magnirostris, 'Beach Thick-knee/Stone-Curlew'.

Family Laridae: Terns and Gulls
Family Phalacrocoracidae: Cormorants

Family Ardeidae: Herons, Egrets, Bitterns

Egretta sacra, 'Eastern Reef Egret' grey morph.

(Montgomery Reef, Australia)

Egretta sacra, 'Eastern Reef Egret' white morph.

Family Pandionidae: Osprey

(Montgomery Reef, Australia)

Pandion cristatus, 'Eastern Osprey'.

Family Accipitridae: Hawks, Kites, Eagles

(Montgomery Reef, Australia)

Haliaeetus leucogaster, 'White-bellied Sea-Eagle'.

Places to see Indo-Pacific tropical coral reefs

The biggest reef in the world is of course the Great Barrier Reef, off eastern Australia. One of the best islands for reef is Lizard Island. Along the edge of this reef are the beautiful Ribbon Reefs. South of the Great Barrier Reef is some great coral and fish on the Tangalooma Wrecks. On the west coast of Australia there are other reefs, including Montgomery Reef in the north east, and further south is Ningaloo Reef.

The south west Pacific includes the Solomon Islands, my favourite country for snorkelling. One of the best sites in this area is at Maravagi Resort, on Mangalonga Island. Other areas in the Solomon Islands include: Uepi Resort, Marovo Lagoon and Arnavon (Arnarvon) Islands.

At a similar latitude is the relatively unspoilt island of New Guinea. This includes the most diverse coral reefs in the world, at Rajah Ampat.

Dominating the Indo-Pacific coral reefs is the huge country of Indonesia, including Kakaban Island. Indonesia also includes:  Menjangan Island, Bali Barat and Pink Beach Komodo.

Heading north there are the remote islands of Micronesia, including the stunning Palau. Then there is the diverse and many islands of the Philippines, including Panagsama. Even further north is the extent of tropical coral reefs, Japan. Here, snorkelling is easy at Miyako Island.

More remote areas across the vast Pacific include Aitutaki in the Cook Islands, Niue and further east Bora Bora, in French Polynesia. 

On the other side of the Indian Ocean, off the coast of Africa, are the Seychelles. Included in this island group is Farquhar Atoll.

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