The Great Barrier Reef : How was it formed? Tyrone Ridgway Australia’s marine jurisdiction Under the United Nations Convention on the Law of the Sea, Australia has rights and responsibilities over some 16 million square kilometers of ocean. This is more than twice the area of the Australian continent. 1 Australia’s large marine ecosystems North Australian Shelf Northeast Australian Shelf/ Northwest Australian Shelf Great Barrier Reef West-Central Australian Shelf East-Central Australian Shelf Southwest Australian Shelf Southeast Australian Shelf Antarctica The Great Barrier Reef 2 Established in 1975 Great Barrier Reef Marine Park Act 345 000 km2 > 2 000 km long 2 800 separate reefs > 900 islands Importance to the Australian community The Great Barrier Reef contributes $5.8 billion annually to the Australian economy: $ 5.1 billion from the tourism industry $ 610 million from recreational fishing $ 149 million from commercial fishing Thus the GBR generates about 63,000 jobs, mostly in the tourism industry, which brings over 1.9 million visitors to the Reef each year. 3 It is not just about the fish and corals!! There are an estimated 1,500 species of fish and more than 300 species of hard, reef-building corals. More than 4,000 mollusc species and over 400 species of sponges have been identified. 4 Invertebrates Porifera Cnidaria Annelida Crustacea Mollusca Echinodermata Vertebrates Osteichthyes Chondrichthyes Reptilia Aves Mammalia bony fish cartilaginous fish reptiles birds mammals 5 The Great Barrier Reef The reef contains nesting grounds of world significance for the endangered green and loggerhead turtles. It is also a breeding area for humpback whales, which come from the Antarctic to give birth to their young in the warm waters. The islands and cays support several hundred bird species, many of which have breeding colonies there. How did it all begin? 6 ERA PERIOD EPOCH MYA Quaternary Holocene 0.01 Pleistocene 1.8 Pliocene 5 Cainozoic Miocene 25 Tertiary Oligocene 37 Eocene 54 Palaeocene 65 Scleractinian Cretaceous 140 corals are Mesozoic Jurassic 210 thought to Triassic 245 have turned Permian 290 Carboniferous 365 up around the Devonian 413 TRIASSIC. Palaeozoic Silurian 441 Ordivician 504 Cambrian 570 Precambrian Thought to have originated in the Tethys Sea Tethys Sea = 40 millon years ago = present day 7 WhatWhat isis aa coral?coral? Plant or animal? 8 Phylum CNIDARIA Class Hydrozoa Class Scyphozoa Class Cubozoa Class Anthozoa class Anthozoa sub class Alcyonaria Zoantharia Ceriantipatharia 8 tentacles 6 tentacles order Alcyonacea Scleractinia Antipatharia Gorgonacea Actinaria Pennatulacea Zoanthidea 9 Order Scleractinia (reef-building corals) ring of tentacles mouth stomach 10 Structure of the coral polyp Tentacle Oral disc Mouth Pharynx Gonads Mesenteries Gastrovascular cavity Calcifying ectodermis External skeleton ectodermis mesoglea endodermis 11 Structure of the corallite Costa(e) Septa(e) Paliform lobes Coenosteum Collumella Wall Solitary vs colonial? solitary / free-living Fungia sp. Heliofungia sp. 12 Solitary vs colonial? Majority of scleractinian corals are colonial Each coral is made up of many genetically identical polyps Courtesy Krupp 2001 Solitary vs colonial? colonial arrangement of corallites within a colony 13 Colony growth forms of corals Courtesy Veron 2000 How do corals get their food? Capture and ingestion of plankton and particulates from the seawater. Absorb nutrients directly from the seawater. Utilize the photosynthetic products of the zooxanthellae. 14 Hermatypic vs ahermatypic? Hermatypic corals have symbiotic dinoflagellates (zooxanthellae). Have the ability to build reefs. Ahermatypic corals do not have zooxanthellae. They are poor builders of calcium carbonate skeletons and therefore are poor reef builders. What are zooxanthellae? Single celled dinoflagellates from the genus Symbiodinium that are located in the endodermis of the coral. Ectodermis Mesoglea Zooxanthella Endodermis Gastrovascular cavity 15 Reef building corals live in an obligatory symbiosis. waste products from metabolism coral zooxanthellae products from photosynthesis coral zooxanthellae N and P Light energy (visible and UV) H2O Photosynthesis Organic energy O2 ZOOXANTHELLAE Respiration CO2 excess H2O Nitrogen poor food Respiration CO2 Ca + CO Zooplankton Nitrogen CORAL 3 or DON rich food Waste CaCO3 products Skeleton formation 16 WhereWhere dodo wewe findfind corals?corals? 17 Areas of major coral reef development Caribbean realm: Indo-Pacific realm: Up to 20 genera Up to 70 genera Areas of major coral reef development 18 Areas of major coral reef development Yellow and Red = 18oC isotherm of average winter sea temperature Factors important in formation of coral reefs Temperature - 18°C (64°F) rule of thumb 19 Reef building corals live in an obligatory symbiosis. waste products from metabolism coral zooxanthellae products from photosynthesis Factors important in formation of coral reefs Temperature - 18°C (64°F) rule of thumb Light - functioning of symbiosis 20 Nutrients high temperate 25°N sub-tropical 0° tropical low 25°S sub-tropical temperate high Nutrients Competition with macroalgae. Algae have faster growth rates than corals. 21 Factors important in formation of coral reefs Temperature - 18°C (64°F) rule of thumb Light - functioning of symbiosis Nutrients - low importance of zooxanthellae - competition with macroalgae Factors important in formation of coral reefs Temperature - 18°C (64°F) rule of thumb Light - functioning of symbiosis Nutrients - low - competition with macroalgae Sedimentation/turbidity - rivers - reduces light levels - smothers benthic organisms 22 northern (coral) 24 major central rivers entering (no coral) the ocean southern (coral) Temperature Nutrients Light cold high lower temperate sub-tropical low tropical warm higher sub-tropical temperate cold high lower 23 Temperature Nutrients Light Great Barrier Reef Coral species attenuation with latitude 350 300 250 200 150 100 No. of species 50 0 18 20 22 24 26 28 30 32 Latitude WAUS EAUS JAPAN 500 400 300 species of 200 No. 100 0 18 20 22 24 26 28 30 32 34 Latitude º 24 CURRENTS Global patterns of water movement are key to the explanation for the distribution of marine animals. Why are currents important? Differences between land and sea Animals in the sea tend to have external fertilization and blastulas that develop in the sea. land – internal fertilization. The larvae of marine animals tend to be highly dispersive. - currents play a major role 25 land sea restricted dispersal great potential (10-1000 kms) Pocillopora damicornis: Larval life can be as long as 40-60 days. Very broad distribution. Australomussa rowleyensis: Larval life may be only as long as a day. Highly restricted distribution. 26 Why are currents important? Currents help link reefs (connectivity) and hence offer larvae the ability to travel (often large distances) between reefs. SOURCE = sink reef CURRENT Factors important in formation of coral reefs Temperature Light Nutrients Sedimentation/turbidity Sea surface currents 27 Principle types of coral reef development Mainland Coastal Island Continental Barrier fringing fringing island Cay reef reef reef Lagoon Platform reef Continental Continental shelf slope Fringing reefs Well-developed reefs (with platform reefs) attached to mainland or continental islands. Lizard Island 28 Submerged reefs A large number of reefs occur in which there is no intertidal component. GBRMPA Patch reefs Young patches of coral growing up off bottom (common in lagoons). Often reach surface and spread outwards with a pool forming in the centre. GBRMPA 29 Platform or lagoonal reefs Akin to a large patch reef, these reefs begin by growing toward the surface of the ocean, eventually spreading out laterally. In many cases, wave action hollows the interior and a lagoon forms. One Tree Island Ribbon reefs This type of reef is that which makes up the reefs that line the continental shelf (the so-called “outer barrier”) It is riddled with narrow passages that drain the lagoon during tidal flux. Outer GBR 30 Atolls This is the classic type of coral reef structure. It was the type of reef development that Darwin focused on in his studies of the origin of coral reefs. Note: Atoll reefs are not typically found in Australia but are common in the central and western Pacific 31.