Heron Island, Great Barrier Reef

In March this year I went on a diving trip to Heron Island on the Great Barrier Reef. It is not very big and is situated on the southern end of the reef. It is probably not much more than a 1km all the way around. I spend most of the time in the water when I'm there however each morning as the sun comes up and every afternoon after the last dive I wander around the island exploring the shore line. Heron Island is a Coral Cay, which means it is made of sand and coral and at its highest point it is only a few metres above sea level.

Pre-dawn on Heron Island

Some parts of the shore line are rock and provide a protective habitat for some creatures like this beautifully marked crab. Shore Crab (Grapsus albolineatus).

Juvenile Silver Gulls(Larus novaehollandiae).

Heron Island got its name from these birds, which were mistakenly called herons by early explorers. They are related to herons but they are actually Reef Egrets(Egretta sacra). There are many of them on the island and unlike other egrets in Australia they come in two colours, white and black.

White Reef egret,

and the dark coloured one.

There are a number of different birds on the island. Some are permanent residents like the Reef Egrets but birds like the one above, a Pacific Golden Plover (Pluvialis fulva)are migratory waders that spend only some of their lives here. There are no cats or foxes either so they are safer here than many places on the mainland.

Although coral and fish are the things most people dive the reef to see, many of the smaller things are really colourful and interesting to look at to. This is a nudibranch, a type of sea slug with visible external gills. There are many differnt types of these and they are some of the prettiest things living on the reef. They get their bright colours from the food they ingest, they graze on a variety of things depending on the species. Some eat sponges, while others coral or algae etc. They can often eat things that that contain toxins which they, instead of excreting, store in their bodies...often evident in the bright colourations that their diet causes. They really stand out but are left alone by most things...their markings acting as a warning, they may also give off scent to that tells other organisms that they are distasteful. It is because of what they eat that they are left alone by most predators and is the reson that they dont need a shell, like many other smaller molluscs.

Corals are a very diverse group. They come in all shapes and colours and many of them are not even hard. Corals generally, are a colonial animal, each individual is a polyp that looks a little bit like a small sea anemone (to which they are closely related - they are both Cnidarians, which also include seajellies and hydroids) The tentacles of these creatures contain stinging cells, some of which affect people while others can't pentrate our skin. Touching corals for this reason is not a good idea. (There other reasons to, like the fact that we can leave a residue from our skin or damage protective coatings that they may have).

Those classified as hard corals excrete calcium carbonate to make a skeleton which is shared by the surrounding polyps. Many of them have a microscopic organism living within them called zooxanthallae which photosynthesizes food for the coral. They (the zooxanthellae)are a type of plant so they need sunlight to do this...for this reason corals live mainly in shallow waters. (often the best diving is in about 12 mtres of water). The other type of coral..soft coral sometimes forms calcium carbonate to, but they are often in the forms of fibres that reinforce structure. When coral feeds ( on the plankton and micro-organisms suspended in the water) the polyps are extended making them look more like flowers than animals. When the polyps are withdrawn the calcified structure is all that is obvious.

This is a Moorish Idol.

Sea turtle resting on the bottom. They visit Heron Island to lay their eggs.

Sponge (Porifera - means pore bearer) comes in many shapes and colours. It is also an animal..very simple single colonial animal, that basically filters micro-organisms out of the water. They do best in areas with some current. They have openings where the water flows in, is flitered of food then flows out. They help keep water clean as they act like filters. There are fossils of sponges that are 1800 million years old....this makes them a life form that evolved very early on in the history of life on earth.

pair of nudibranchs. The feathery bits are their gills. The name, nudibranch means naked gill. above and below.

This is a Black Noddy Tern (Anous minutus). They breed on the island.

Manta Ray . We saw manta rays on most dives this trip. They are really big rays with a span that can be measured in metres. Both of these were at least 2 metres across. They are harmless to people and they are filter feeders feeding on tiny organisms suspended in the water. The extensions at the front helps funnel the water into their mouths.

The orange in this image is sponge. The feathery structures next to it are hydroids, relatives of the anemones. They have stinging cells to immobilise small prey (The stinging cells are a charactersitic of all the Cnidarians)

Sometimes when swimming through gaps or under overhangs you come across a school of fish. As they swim past every single eye looks at you and they all have they same expression, it is almost surrealistic and every time it happens it is as exciting as the first. These fish are Hussar.

During the summer months and a little before and after sea turtles come to Heron Island to lay their eggs. The hatchlings often emerge on mass from the nest (a hole in the sand where the eggs were buried) at night time. (it gives them protection from many birds) but some times odd ones emerge in daylight hours and make their way to the water. If they aren't eaten by birds first, they have to swim the guantlet....the sharks know that there are hatchlings at this time of year so they hang in the shallows and wait for them arrive, picking off most of them before they get to come up for their third breath of air. Turtles can lay roughly 60 - 160 eggs each year that they reproduce. They live along time, it is estimated that they may not reach sexual maturity till they are at least 25 years old. They may live around 80 years but figures are estimates because no one really knows. In their lifetime out of all the eggs they produce only 2 need to make it to adulthood and reproduce to keep the numbers up. (Thats the theory anyway...its one very good reason why these animals need protecting....from people) In the early days of Heron Island's history the island was used for making turtle soup. Now there is a turtle research station there.

This is a Gorgonia fan...a type of coral.

When we think of worms we generally dosn't envisage creatures that we would think of as attractive but marine flatworms can be really eye catching like this one pictured above. Some of these worms can swim by undulating their bodies and they look like a ribbon fluttering in the breeze. This one was about 6cm long.

This is a hard coral.

Hard coral. Corals are hard to identify to species level because colonies of the same species can take on very different forms according to where they are growing.

This a coral with all its polyps exposed for feeding. double click on this to have a closer look.

In this coral head there are other creatures living in holes, they are tiny hermit crabs...less than 1 cm across. Most hermit crabs live in shells that they claim, these little crabs spend their hole..oops, whole life living in the same coral head. I have not found these crabs very often, it is a shame that when you are doing a 'drift dive' you cant stop for too long at any one place to have a really good look.

Hard coral.

This is another type of colonial animal...not as simple as a sponge however. The mass above is actually a group of colonial sea-squirts...or ascidians. Their lives are fairly simple, another creature that just sucks water in, filters it of food and then squirts it out. each individual generally has an inlet syphon and an outlet syphon. Sometimes though in colonies they may share an outlet. When these organisms are in the early stages of their lives they are free swimming larvae for a number of hours before they settle in a suitable spot. The really intersting thing about these creatures is that they have a very rudimentry spinal chord..or notochord! This is the first of what we see of a backbone. All creatures with back bones, including us, evolved from this creatures ancient ancestor...the beginnings of the tree of chordates ..or back boned creatures.

This is one of my favourite fish..a Bat fish. They are the size of a dinner plate and fairly slow moving, which makes them a good candidate for photos with simple digital cameras that have delay after you press the shutter!

Cartilaginous Fishes (Sharks & Rays)

Sharks and their relatives differ from other types of fishes in that they don't have any true bone in their bodies. Their skeleton is made of cartilage. Their teeth are the hardest part of their body and they grow continually all their lives, always with a new one waiting to replace any that are wrenched out when they feed. Some sharks have very sharp teeth while other members of this family have teeth that are flattened plates more suited to crushing. The type of teeth they have depends on their diet. I find them really interesting because not only do they have teeth in their mouths, their whole body is covered with denticles (tiny teeth) which makes their skin really tough and abrasive. If just about any shark rubs against your skin it will take the skin off as though it was being rubbed with sandpaper, and can be used as such.
Although when most of us think about sharks we think of White pointers, Makos and Tiger sharks there are many more types of sharks and rays with diverse appearance, habitat and diets. Very few of them are considered to be dangerous to people if left alone. Many members of this family, especially those without the really sharp teeth, have a venomous barb/barbs which are used solely for defence.


These two photos were taken at an Australian territory - Christmas Island, in the Indian Ocean. The fish in these images is a whale shark, the biggest fish in the oceans. The can easily grow to 45 feet and they are totally harmless. This biggest fish in the world feeds on some of the smallest marine creatures- plankton, krill and other tiny creatures. It swims with its mouth open, filtering out everything edible. We were approached by two of these amazing fish while we were diving at Christmas Island. They swam between us and even though we were dwarfed by them they moved around us slowly and gracefully, close enough to touch but with out flicking us with their tails or huge fins.

This is a close up of a Port Jackson shark. The denticles on its skin are the little raised cross shaped light areas. Their teeth have evolved into flat plate like structures to accommodate their diet of crustaceans and bivalve molluscs (crabs and mussels) which they crush.

This is a white tipped reef shark taken at Heron Island. It is asleep in a gully. Some sharks need to keep moving so that the water is continuously washing over their gills supplying them with oxygen. This is not the case with reef sharks as well as many others.

The above photo and below are images of black tipped reef sharks. I took them at Heron Island during the season that turtles hatch on the beach and make their way to their ocean. These sharks are in about 300mm or 1 foot of water and they are waiting for any turtle hatchlings to arrive. If a lot of hatchlings all make it to the water at once some of them have a chance at getting through all the sharks to deeper water. It sounds harsh but each turtle lays many eggs each season that they mate. They have long lives and each female only really needs for two of her offspring to make it to adulthood to keep turtle numbers stable.

Black-tipped Reef shark, Qld.

Eastern Sawshark, Vic. These sharks are found in NSW and eastern part of Victoria. They are found in deep water from 100 m to over 600m so are not seen in their natural habitat by divers. They give birth to live young and the teeth are already present. Fortunately the teeth fold back during the birth process so that the mother is not injured.

Elephant Fish- Victoria. They are called this because of their nose. They are shark like in appearance but they have smooth skin over most of their body instead of the rough teeth like scales that other sharks and rays have. The markings on the top of the head are part of its sensory system.

These sharks are bottom dwellers and use their nose to find molluscs and other invertebrates in the sand.

Elephant Fish, Vic. It is part of a group of fish known as Ghost Sharks and this is the only species found in southern waters. It is found in sandy areas like estuaries and inshore areas and also in deeper water up to 200 meters.

Banjo Shark or Fiddler Ray - so named as their body shape resembles that of a banjo. Vic.

This is the underside of a Banjo shark. The gill slits and the mouth are easily visible. The small nostril like holes are part of their sensory system called spiracles and lead into the mouth and gills. Vic.

Blue-spotted Stingray, NSW. This is a tropical species that is sometimes found as far south as Sydney, NSW.

This is an Eagle Ray (above and below) Vic.

This is the underside of a large stingaree. The two nostril like holes are spiracles and lead into the mouth and gills. The mouth is the small slit behind them and the gills are obvious as well. This is a male - Only males have the modified fins at the base of their wing disc obvious in the lower left of the photo.

Manta Ray, Heron Island, Qld. The flaps at the side of the mouth are used to funnel the water (full of the tiny invertebrates that they eat) into their mouths when they are feeding. They are big, graceful and harmless to everything bigger than micro organisms. Sometimes they are in groups that swim in a spiraling manner upwards and then come back down and repeat it. As a diver it leaves you with a real feeling of being privileged to see such beautiful animals in their natural environment. It is easy to get so engrossed that you stop thinking about about how much air you have in your tank and some divers have been known to suck their tanks almost dry before they leave for the surface. They have a wing span of 2 - 3 meters and they seem to fly through the water rather than swim. They live in tropical waters in many parts of the world.

Leopard Shark, Heron Island, Qld.

These two photos of leopard sharks (above and below) were taken at the Melbourne Aquarium.

Some sharks give birth to live young while others lay eggs. These three images are from sharks found in Victorian waters. This egg case is from a Draughtboard shark.

Elephant shark egg case. Vic. These sharks take six - eight months to hatch.

This is an egg case from a Port Jackson Shark. They lay their eggs in rocky crevices and the screw shape keeps them wedged in place until they hatch about twelve months later. It takes ten years to reach maturity but even fully grown they are much less than a meter long.

Port Jackson Shark - above and below

Although these sharks are placid and not a threat to people, they have two sharp venomous barbs placed at the front of each dorsal fin that can inflict injury if the creature is handled incorrectly. They are visible in the above pictures.

Port Jackson Shark -close up.

Varied Catshark . These are a bottom dwelling shark that spends its days hidden in crevices, becoming active at night. The barbels hanging from the corner of its mouth help it find food on the sea floor. It belongs to a family known as the Collared Catsharks. It uses its barbels (the things hanging from the corner of its mouth) as sensory organs to help it find small bottom dwelling invertebrates on which it feeds.

This shark is found in NSW and further north in warmer water. It is a Blind shark.

This is a shark egg case. They are often washed up on the beach with seaweed, usually empty. The reason it looks so much like seaweed is for camouflage as these eggs are laid in amongst it.

This is a draughtboard shark. They are another species of egg laying sharks common in Victorian waters. They are also known as swell sharks because they can inflate their stomachs!