NATURAL WONDERS

With over 1500 species of fish on the reef the answer to this question is not an easy one. The use of identification books and underwater cards can be useful in identifying commonly encountered species. Body and mouth shape are often the best key features in identifying the type of fish. The reef fish section of the marine biology manual will outline the features of the most commonly encountered families of fish. Aim to learn the name of just one fish every time you visit the reef, and you will quickly recognise the most commonly encountered species.

If you see a shark while visiting the reef, consider yourself very lucky as sharks are not frequently encountered by visitors. Of those which are seen the most commonly encountered are the White Tip Reef and Black Tip Reef sharks. Easily identified by the white markings on the tips of the dorsal fins, they are often found resting upon the sea floor. Like most sharks White Tip's are extremely timid and won't stay long around divers. Most sharks found on the reef are fish eaters and therefore pose no threat to visitors. Do not harass or block off a shark's exit as they may attack out of fear.

The box jellyfish is found in the coastal waters of North Queensland during summer months (October to March). Visitors wishing to swim during this period should only do so in protective swimming enclosures or wear protective clothing. The Box Jellyfish is a coastal species and is not found out on the reef, but they can sometimes be found around the islands close to the mainland. Other stingers that are sometimes encountered on the reef include the Irukandji and Blue Bottle. Both can cause a nasty sting. Vinegar can be used on both Box Jellyfish and Irukandji stings but not on Blue Bottle stings. For Blue Bottles use cold water and ice.

Most visitors to the reef comment that the coral isn't very colourful as they are used to seeing brightly coloured images in books and on television. Natural white light is made up of all the colours of the rainbow. Underwater, these colours are filtered at different depths with red and yellow disappearing first. This gives the reef a predominantly blue/green appearance. Photographs and video are taken using lights to show the true colours of the reef. So the colours are there, it's just that you need white light to see them. This is why night diving on the reef is so spectacular.

Coral are made up of a thin layer of living animals called Polyps, which secrete a chalky, limestone skeleton as they grow. Coral colonies grow as the polyps divide and multiply in a process known as budding. In addition to catching planktonic prey with their tentacles, corals also derive nourishment from simple single-celled algae called Zooxanthellae (pronounced zoo-zan-thelly), living within their tissues. Like all plants, Zooxanthellae photosynthesize, producing nutrients from the suns' energy which are used by the polyp for its own nutrition. Corals with Zooxanthellae are able to lay down limestone skeletons up to three times faster than those corals without.

Trying to identify particular species of coral is very difficult. What makes it so difficult is that one type of coral may appear as a branching form in calm water and look like a plate coral in another area. In many cases it is the environmental conditions, such as wave action, light levels and the amount of sediment in the water, that influence coral colony shape. The easiest way to identify corals is by their appearance.

Every year over one-third of the reef's 350 species of coral reproduce sexually during a mass spawning event. The majority of inner reefs spawn around November with the outer reefs spawning later in December. Spawning always takes place at night, and follows any time up to six days after the full moon. Eggs and sperm are released into the water where they eventually combine to form a free swimming planktonic larval stage.

Most of the Great Barrier Reef is located off the mainland of Queensland. Corals need clear water which are low in nutrients. They cannot tolerate freshwater or nutrients carried in the water run-off from the mainland. That is why the most diverse and abundant corals grow offshore where the environmental conditions are more suitable.

The clarity of water on the reef is determined by a combination of the amount of sediment and the amount of phytoplankton in the water. Sediment becomes suspended due to increased water motion caused by tide changes, high winds and storms. Phytoplankton are the microscopic plants that drift around in the water. They are more numerous in areas where the nutrient levels of the water are higher, particularly around coastal reefs which receive nutrient rich runoff from the land.

Whales are normally encountered during the winter months when they migrate up to the reef from Antarctic waters to mate and give birth. One of the most spectacular visitors during this period is the Humpback Whale. They are seen in the shallow coastal waters of the Great Barrier Reef ranging from Hervey Bay to Port Douglas. Whale watching is conducted by a number of tourist operators through these areas. The Minke is another species of whale seen during winter, particularly around the Ribbon Reef area. The smallest whales, the dolphins can be seen all year round in most parts of the reef.

The cause of Crown of Thorn Starfish outbreaks is still the focus of a lot of research and debate. Increased nutrients from the mainland and effects due to El Nino are all being investigated as is the possibility that it is a naturally occurring event. Crown of Thorns starfish may actually serve to maintain coral diversity on the reef by feeding on the fast growing species, that if left unchecked, could dominate the reef.

Fishing is not allowed in green national park zones or pink preservation and orange scientific zones. In other zones fishing is allowed subject to Queensland Fisheries restrictions. Legal sizes, closed seasons and catch quotas also apply to a variety of fish and shellfish. The following animals are totally protected: whales, porpoises, dolphins, dugong and turtles, clam, trumpet and helmet shells, female crabs all grouper and cod over 1.2 metres.

In general the average passenger is not so much concerned with the weather as they are with how it will influence their day at the reef. Therefore an answer should be given in reference to their concerns e.g. seasickness, water clarity, and the colour of the reef.

When good growth conditions exist, blooms of a simple floating algae called Trichodesmium are often confused with oil and coral spawn slicks. Blooms can be easily identified by their rusty brown colour as they occur in wind rows along the surface of the water. Slicks of coral spawn generally do not last more than two days after coral spawning. Any oil spill should be immediately reported to the local maritime authority.