The Great Barrier Reef a Queensland Museum Discovery Guide the Great B Arrier Reef

© QUEENSLAND MUSEUM THE GREAT BARRIER REEF BARRIER THE GREAT The Great Barrier Reef is one of the world’s last GUIDE A QUEENSLAND MUSEUM DISCOVERY great wilderness areas. Stretching more than 2000 km along the coast of north-eastern Australia, the Reef is also the largest coral ecosystem on Earth. Its unique environment supports an astonishing and almost unequalled biodiversity, THE GREAT from microscopic plankton to whales, with many more species still to be discovered. The human history of the Reef is no less intriguing. Indigenous Australians have known the Reef for millennia and their Dreaming stories offer BARRIER REEF tantalising glimpses of a truly ancient world. A QUEENSLAND MUSEUM DISCOVERY GUIDE Europeans first encountered the Reef some 500 years ago on perilous voyages into unknown waters, but have only recently begun to understand its almost unimaginable complexity. This book weaves these equally vibrant strands of natural and cultural heritage into a single narrative that leads the reader on their own voyage of discovery through one of the most beautiful places on Earth. Published by the Queensland Museum with the generous support of BHP Billiton Cannington © QUEENSLAND MUSEUM 10 THE GREAT BARRIER REEF | DISCOVERY GUIDE FOUNDATIONS OF THE REEF The Great Barrier Reef is the largest reef system on Earth. However, Waier Island, Torres Strait. Located at the perhaps surprisingly, it is also one of the youngest reefs with its far northern end of the Great Barrier Reef, history of construction taking place within the past million years. this small volcanic island erupted through During this time, there have been several periods of reef growth, but the oldest foundations of the Great Barrier the modern Reef as we know it is only about 8000-years-old. Reef during the Pleistocene Epoch. The volcanic rocks of the island contain fragments Nonetheless, the Great Barrier Reef has a complex history linked to of limestone from these ancient reefs. The sea level and climatic change and the structural evolution of the Coral limestone shattered when the volcano Sea Basin.The Great Barrier Reef formed in the warm, shallow seas erupted through the reefs. The likelihood of of what is now the north-eastern part of Australia’s vast continental a volcano coming up through a reef is not shelf. Its beginnings are related to the plate tectonics of the Earth’s high and this event indicates the very specific early geological history and the break-up of the ancient super- geological evolution of the Great Barrier Reef. continent of Gondwanaland © QUEENSLAND MUSEUM GEOLOGY & GEOMORPHOLOGY 11 The Great Barrier Reef begins in the Gulf of Papua to Australia’s north, where its ancient foundations are overlaid by sediments from the Fly River in New Guinea. International oil drilling projects in the Gulf have revealed buried barrier reefs dating back 6–7 million years at about 100 m depth. However, long-term growth of these reefs was not possible because of continuing geological change, including temperature and sea level fluctuations, heavy sediment loads from the Fly River and the rising Eastern Highlands, as well as some volcanic activity. Even on the continental shelf, volcanic activity erupted through some early established reefs. A satellite view of the Great Barrier Reef. The Reef stretches 2300 km from the tip of Cape York, along the Queensland coast, to just off the southern city of Bundaberg, although its oldest foundations lie in Gulf of Papua to Australia’s north. © QUEENSLAND MUSEUM 40 THE GREAT BARRIER REEF | DISCOVERY GUIDE A coral-covered reef front, or reef slope, faces the open ocean. The reef front rises from the mesophotic zone (see p. 31) into coral covered buttresses and it consists of two distinctive ‘sub-zones’: the upper reef front and the outer reef. The upper reef front lies in well-lit waters of between 0–20 m depth and supports the greatest diversity of hard corals and fish of any part of a coral reef system. It tends to be dominated by resilient, massive or encrusting corals that face into the prevailing wind and wave direction and act as breakwaters. The corals often take a ‘spur and groove’ formation and some scientists believe that these buttresses act as passageways for sediments leaving the reef flat.Alternatively, they may have originated as karst landforms created by limestone erosion when the sea level was low (see p. 20). The outer reef below 20–30 m depth is typically steep and cliff-like, with overhangs, caves, rubble-covered terraces and sand or rubble-floored channels. Background: Osprey Reef, North Horn, Western Wall. Above left: Upper reef front. Lady Elliot Island. Below left: Aerial view of reef crest. Bramble Reef. © QUEENSLAND MUSEUM GEOLOGY & GEOMORPHOLOGY 41 The highest and shallowest part of the reef is the reef crest comprised of an intertidal algal pavement and a coral shingle zone. The crest is the narrowest of the main reef zones, ranging from a few metres to more than 100 metres in width. It separates the reef’s protected inner reef and lagoon from the ocean beyond and often looks like a dark, irregular band of seawater, or a line of white breakers when it is windy or stormy. The composition and structure of the reef crest is influenced by the prevailing wind direction, wave action, type of reef and geographic location. It incorporates channels, side pools, sand patches, crevices, structures that resemble miniature atolls and rubble fields. In contrast, on the protected sides of islands where there is little wave action.the crest is usually poorly developed, or may even be absent. Above: Lady Elliot Island Left: Osprey Reef, Admiralty Anchor, western side. © QUEENSLAND MUSEUM 62 DISCOVERY GUIDE TO THE GREAT BARRIER REEF HIGH ISLANDS The high, rocky (continental) islands close to the coast are parts of the mainland that have remained exposed since the last rise in sea levels. Not surprisingly, these islands support plants and animals also found on the adjacent mainland. Early naturalists often invoked divine intervention to explain the presence of terrestrial plants and animals on remote islands. However, such colonisation results from a mix of remarkable adaptations and chance. For example, some (insects, birds and bats) fly to these destinations, others are blown on air currents (insects and spiderlings), hitch a ride on floating debris (reptiles and mammals), or disperse by hardy eggs or seeds. Rocks and forests of Fitzroy Island. © QUEENSLAND MUSEUM REEF HABITATS 63 Travelling PLANTS Cay communities Plants grow on even the most isolated islands and cays. The first plants to colonise sand cays are the salt and Octopus Bush (Heliotropium foetherianum), above, which is drought-resistant species found on any beachfront and common on the Great Barrier Reef islands, has reached foredune, such as the the grass Thuarea involuta, Beach the world’s most remote atoll, Ducie Island, part of the Morning Glory (Ipomoea pes-caprae) and Beach Pea (Canavalia Pitcairn Islands group south-east of Tahiti. Floating, salt- rosea). On more stable and exposed cays, rings of shrubs tolerant seeds that can remain viable for many months can form. These are likely to contain Octopus Bush, Silver be carried vast distances by ocean currents. Seeds or fruit Bush (Sophora tomentosa), Fan-Flower (Scaevola taccada) that attach to birds and other animals on contact can also be and Beach Sheoak (Casuarina equisetifolia). Herb flats and deposited far from their point of origin. For example, Chaff succulent mats are also common on sand cays. Typical plants Flower fruit (Achyranthes aspera) attach with a long, recurved include grasses, (such as Lepturus repens and Stenotaphrum spine and Tarvine (Boerhavia albiflora) fruit is covered in small, micranthum), Tarvine, Caltrop (Tribulus cistodes), Lantern sticky projections. Flower (Abutilon albescens), the daisy (Wallastoni abiflora) and the succulents Sea Purslane (Sesuvium portulacastrum) and Pigweed (Portulaca oleracea). With time, increasing Below: Orb-weaving spider (Poltys sp.). complexity and increased nutrients, coral cays will develop forests of Pisonia, Beach Sheoak and Sea Trumpet (Cordia subcordata), or a community known as ‘coastal parkland’, with Octopus Bush, fan-flowers, Pisonias, screw palms (Pandanus spp.), above, figs such as Ficus opposite and Beach Sheoak. Where sediments collect along the shoreline, or in lagoons, stands of mangroves may be present. Left: Jumping spider (Cosmophasis sp.); Right: Bolboceratid beetle. © QUEENSLAND MUSEUM 74 THE GREAT BARRIER REEF | DISCOVERY GUIDE CORAL GROWTH FORMS The bewildering variety of shape and texture is made more The shape of hard corals varies enormously. Some colonies confusing by the fact that it is common for colonies of the resemble plates, others look like shrubs and they may also same species to grow into different shapes. Physical factors, be tongue, brain or vase-shaped. To help make sense of this such as the level of water turbulence and exposure, the profusion of shapes, marine biologists have recognized the impact of competitors or predators and storms and tidal following growth forms: surges, can all influence how a coral colony develops. MassIVE COLUMNAR rounded, domed or bulky masses of coral cylindrical, column or trunk-like BRANCHING FOLIACEOUS branched or antler-like leaf-like or lettuce-like © QUEENSLAND MUSEUM CORALS 75 LAMINAR VASE-SHAPED plates or tables arranged in a tier ENCRUSTING FREE-LIVING surface layer growths unattached to reefs Mushroom corals (Family Fungiidae) are so-named because they resemble the gilled underside of a mushroom (without its stem). Some mushroom corals house a single, large polyp that is not cemented to the reef but is instead free-living and mobile. The mouth of these polyps is located within a central depression from which the fine ribs or struts (septa) radiate. When the polyp is extended, its tentacles cover the upper surface. Mushroom corals are likely to be found in calm pools, lagoons and deep water.

Load more