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The North West Cape is surrounded by the Ningaloo Reef which is one of the world’s largest fringing reefs. This intricate reef system stretches over 260 km and, at some points, is only metres from the beach. The Ningaloo Reef is home to a myriad of marine life, including one of the rarest, and the largest fish in the world – the Whale Shark. These leviathans, of up to 18 metres in length, are regular visitors to the Ningaloo Reef from March to June, when the plankton rich waters draw them close to the reef in search of food.
Add the bio-diversity of 250 species of corals and over 450 different species of fish to the previously mentioned attractions and it makes Exmouth an impressive diving destination all year round.
The reefs of Ningaloo are very healthy compared with many of the reefs around the world. It is estimated that about 10% of the reefs have suffered so much damage that they will never recover.
Although our reefs are relatively healthy, it is important that we all try to protect these incredible wonders. As visitors to the reef, there are things YOU CAN DO to prevent damaging the reefs and help in protecting them:
Ningaloo Reef is a fringing, rather than a barrier reef, because it is closer to the shore with shallow water separating the land and reef.
No doubt most of you have come to North West Cape to dive or at least snorkel the reef to see coral and other marine life, so we hope this will provide you with some fascinating information about coral reefs.
Corals are little animals which are basically a stomach with a mouth surrounded by tentacles! These animals are called polyps. Lots of these polyps live together in colonies and build the hard coral skeletons which form the basis of coral reefs. These are important structures, which provide food, shelter and protection for a myriad of fish and other marine life.
Corals have fascinating ways of getting their food. In their tentacles they have little harpoon like structures called stinging cells or nematocysts. The polyps “fire” these harpoons which contain toxins into microscopic prey, which are then ingested.
Another way corals obtain their nutrition is by being able to absorb nutrients directly through their “skin” or epidermal tissue. Imagine if we could just lie in a bath of soup!
The last way that a lot of corals obtain their food is a very lazy way – they let another organism make their food for them! Guess it’s not much different from us dining out except their “chefs” live permanently with them.
Hermatypic (or reef building corals) have in their outer layer of tissue, single celled blue-green algae known as zooxanthellae (pronounced zo-zan-thell-ee). It is these little microscopic plants that act as the corals’ “chefs”. Like other plants the zoanthellae photosynthesise – that is they use the sun’s energy in the form of light along with nutrients to produce energy-containing compounds the corals can use to make their calcium carbonate skeletons. But these little algae are multi-talented, and unlike most cooks, they clean up after themselves by removing any waste products!
This funny arrangement between the coral polyps and the blue-green algae is known as a symbiotic relationship. So far it seems that the corals have all the benefit of the relationship , but that is not the case. The coral provides a comfortable place for the zooxanthellae to live and the rent is so cheap – all they want is some food in return!
However, sometimes the corals turf the poor little blue green algae out of their homes! If you have ever dived or snorkelled over reef, you may have sometimes seen patches of extremely white (bleached) coral. This is often caused when the coral polyps are under “stress”. Such things as pollutants in the water, or water temperatures over 300C, can cause the coral polyps to expel their useful little boarders. The problem is that the coral polyps then cannot survive without their little blue-green mates, hence the presence of dead bleached corals.
It is because the blue-green algae require light to photosynthesise, that coral reefs are restricted to warm, clear, sunlit, shallow waters.
No, this is not the x-rated section! – but all animals have to reproduce and quite often the way they do makes fascinating reading.
Although corals do reproduce sexually, they don’t do it in a very intimate way! At certain times of the year, usually over a few nights the coral polyps spawn – that is they release eggs and sperm into the water at the same time. The eggs and sperm fertilise to form a larva known as a planula. These little guys are planktonic – that is they float around in the ocean until they find somewhere suitable to settle – or they get eaten by something else!
On Ningaloo Reef, coral spawning usually occurs in the period 7 – 10 days after the full moon in March. It is an amazing sight which is a big draw card for many tourists. It’s a bit like diving in a big bowl of sex soup!!!
The other way corals reproduce is by “budding”. The polyps literally grow a little clone of themselves on their sides.
Not all corals produce a hard skeleton. Those that do are known, surprisingly enough, as “hard” corals. The most common hard corals you will see at places such as the Bundegi Sanctuary are staghorn, cabbage and plate corals – so called because of their appearance.
However, the “soft” corals, as the term suggests, do not have a hard skeleton, but instead have fleshy tissue containing calcareous particles, or sclerites. The shape and form of the sclerites are a means of scientists being able to identify the different species. A bit like fingerprints in humans.
An incredible fact about soft corals is that they have chemical secretions which act like “anti-fouling” paint – keeping other organisms from growing on their surface. Largely because of this, these corals have been targeted for medical research in the hope of finding substances that could help retard cancers and other diseases.
Corals are often referred to as being hard or soft corals. Hard coral refers to those that produce a hard limestone skeleton. Corals can be classified as hermatypic(reef building) or ahermatypic(non reef building). Hermatypic corals are for the most part hard corals. All hermatypic corals are zooxanthellate . This refers to the presence in their outer tissue layer (epidermis) of single celled blue green algae. This is known as a symbiotic relationship, where 2 types of organisms live together and both derive some benefit from the relationship.This symbiotic relationship allows for the production of enough calcium carbonate for coral reefs to originate and grow. Zooxanthellate corals often have golden brown colouration and are not brightly coloured. The coral provides a protected habitat for the algal cells and at the same time utilises products of algal photosynthesis to produce more calcium carbonate than it could without the algae. This excess production of calcium carbonate is what builds coral reefs. The building of reefs is actually a bipartisan effort between the coral host and the algal tenant and this close working relationship explains why coral reefs are restricted to the warm, clear, sunlit waters of the shallow water tropics.
Coral reefs are biogenic(produced by living organisms) limestone reefs. The reef is built of coral fragments, corals sands and solid limestone. As little as 50% of the material in a reef maybe coral, with other organisms such as coralline algae acting as a cement to bind the various components together. There are a substantial number of other organisms that live as part of the reef environment and which contribute small amounts of material to the reef framework. These organisms include Halimeda ( a green alga), molluscs (snails and clams), bryozoans, foramanifera, echinoderms (sea urchins, starfish, sea cucumbers) and others.
Reef building corals have very specific environmental requirements, which affects their growth: temperature, water depth, salinity and wave action.
For optimum coral growth the environmental conditions must meet the following criteria:
Temp: 23 degrees C – 27 degrees C
Water depth: shallow water to allow for penetration of light for photosynthesis (most reefs grow in depths of less than 25 metres)
Salinity: 30 to 40 parts per thousand
Wave action: corals thrive in areas of strong wave action which aerates the water
Coral reefs are extremely sensitive to the environmental conditions and changes outside those stated above cause the destruction of reefs. For instance heavy rainfall during monsoons and cyclones increase the run off into the ocean decreasing the salinity of inshore reefs. Run-off from river systems also increases the sediment in the water which can have devastating effects on reef systems.
Water temperatures above 30 degrees C cause coral to shed their symbiotic algae and bleach or lose their colour (this has occurred in the Bundegi Sanctuary, the Reef on the east side of the Gulf near Exmouth). Some researchers feel that global warming will lead to widespread bleaching of corals and could have a serious negative impact on marine biodiversity. Reef growth ceases with a widespread breakdown in the algal coral symbiotic relationship.
Natural threats to coral reefs and coral reef organisms include cyclones and hurricanes, periodic population explosions of echinoderms such as the Crown of Thorns starfish (Acanthaster plancii), periodic ocean warming events (such El Nino) and actions of earthquakes and volcanoes. Man made threats include chemical and nutrient pollution, sedimentation from land clearing and coastal development, overfishing and collecting for the aquariums ( especially with the use of dynamite and cyanide), jewellery and sea shell trades and recreational use(boat anchor damage and tourism impact).
A coral reef constitutes a varied and complex structure that serves as a habitat for many other marine animals, including echinoderms(starfish, sea urchins and sea cucumbers), molluscs (shells, Nudibranchs), crustaceans (crayfish and crabs) and especially fish.
Superficially coral reefs seem to lack plant life. The reef building colonial corals, however supply much of the photosynthese for these rich communities.
Among the organisms living in coral reefs the echinoderms play an important role. The crown of thorns starfish is a major coral predator (in the Indo-pacific region only) which is able to destroy large reas of living coral. Parts of the Great Barrier Reef have been significantly affected by these starfish. At one stage scientist were gravely concerned that the plagues were a result of some upset in the balance of the reefs (perhaps man made) and a great endeavour was made to control the starfish populations, by enlisting navy and volunteer divers to inject formalin into the starfish to kill them. However, research has indicated that the population buildup is natural part of the fluctuating buildup and breakdown of portions of coral reefs.
Ningaloo Reef does house the Crown of Thorns, but it appears to be in minimal numbers that have never seemed to build up the plague proportions seen on the Barrier Reef.
Feather stars are the most visible members of reef community, and are often found in areas where there is a relatively strong current as these animals are planktonic filter feeders. Other echnoderms that are part of the reef community are the sea cucumbers (also known as beche de mer). Some of these are “edible” and the Chines regard them as an aphrodisiac.
Other echinoderms include the sea urchins and sea stars.
Spectacular molluscs that are found in reef communities are many shells and the shells molluscs such as Nudibranchs. Nudibranchs have spectacular colours and are so named because most of them have exposed gills. The Reefs of Ningaloo have a spectacular array of Nudibranchs and I believe many which have yet to be identified. The Curator of Molluscs with the West Australian Museum, who is a Nudibranch specialist is coming to Ningaloo to look at the diversity of Nudibranch in this region.
Perhaps some of the most spectacular animals associated with coral reefs are the varied and often brightly coloured fish. According to Allen and Steene “Fishes are the coral reef’s most conspicuous inhabitants. In essence they are its personality”.
The majority of fish on a typical coral reef like Ningaloo belong to relatively few families. At a particular locality, about 60-70% of all fishes will belong to about ten families of fish. After a few dives or snorkelling sessions it is easy to recognise fish of the different families mainly on the basis of shape, general colour pattern themes and behaviour.
Very conspicuous small fish, which can form large plankton-eating schools. Often hide in coral. Some damsel fish cultivate a patch of algae, which they guard zealously. Divers are often “attacked” by these little fish.
Very colourful and conspicuous group of fish. Easily recognised by shape and bird like way of swimming. Most wrasses are capable of female to male sex change.
Exquisite colour patterns and graceful appearance. Perhaps the best known of reef fish. Most species feed partly or exclusively on live corals. Often seen in pairs, which are permanent life time bonds.
Close relative of the butterfly fish and equally as beautiful. Feed on sponges and small invertebrates. Large angel species produce loud drumming noise when agitated.
The nocturnal counterpart of the damselfish in terms of sheer abundance. At night actively feed on small shrimps and crabs. Males incubate the female’s egg masses in their mouth, every so often spitting them out to aerate them and then slurping them back in again.
Groupers and Basslets(Serrnidae). Includes some of the reefs largest fishes. Fro instances under the navy Pier, Potato cod and Qld gropers. The Qld gropers can grow to 2.7m and 400 kgs. Sex change from female to male is found in most species.
Close relative of the wrasses and one the dominant algae feeding families Juveniles and females are generally drab in colour compare with the gaudily coloured terminal phase males. Again sex change occurs from female to male. These fish consume considerable amounts of coral rock while feeding. It is ground to a fine powder by special teeth in the back of its throat and voided in the faeces.