Corals, like canaries in coalmines, are early predictors of stress, climatic changes and the presence of chemicals within their environment. Like an army of silent sentinals, corals may prove to be more than reef architects - they may be saviours of the world's most biologically diverse area of marine life, the Great Barrier Reef.
The Great Barrier Reef, off the coast of Queensland, extends over 2,000 kilometres in a broken coral chain of reefs and cays from Fraser Island in the south to Cape York in the north. Billions of marine and coastal creatures live on and around the reef's protective islands and lagoons. The different corals that form the chain of reefs provide shelter for more fish species than any other marine habitat.
Coalmines, the major source of coal as fuel during the 1800s, contributed to the environmental, economic and social evolution of humans. However, carbon monoxide, a colourless, odourless gas formed in the mines when carbon oxidised in a limited supply of air. Starved of oxygen, the miners, deep in the coalmines, collapsed and died. The toxic fumes prevented haemoglobin from transporting oxygen to vital organs and tissues in their bodies.
More devastating than carbon monoxide is methane gas, also colourless and odourless. Methane burns with a bluish flame and explodes when mixed with air or oxygen. Known as firedamp, the deadly mixture of methane, nitrogen, carbon dioxide and hydrogen is the coalminers' worst fear. Canaries, introduced into the coalmines as early detectors of toxic gases and chemicals, saved the lives of many miners.
Corals, like canaries, are early predictors of climatic changes and the presence of pollutants and chemicals, and can serve a similar function to save the reef ecosystem and its commercial, scientific and environmental viability. Corals can provide scientists with crucial information on the changing climatic conditions and the effects of these conditions on the flora and fauna of coastal and inland areas of the reef.
Corals are sedentary animals related to sea anemones and other polyps. A coral polyp is a hollow "fleshy" cylinder of tissue, typically about a centimetre in diameter, with an open mouth at one end. Opposite the mouth, the polyp tube secretes limestone that forms the skeletal framework by which new coral polyps can become attached, secreting more limestone around it. Colonies of coral polyps grow rapidly with each polyp having the ability to reproduce, asexually and sexually, as much as 25,000 new polyps in one year. The limestone deposited from this growing community builds into a reef of hard, pockmarked and angular-shaped skeletons of coral. Marine populations can be markedly different within short distances due to different sea temperatures, wave actions, ocean depths and food sources. In these marine neighbourhoods, there are over 300 coral varieties of differing shapes and colours with names such as staghorn, brain, mushroom and red organ pipe. However, it the corals' symbiotic lifestyle that exposes a more fascinating and important existence.
The mouth with its flailing tentacles entraps plankton. But plankton and other minute drifting animals comprise only ten per cent of the coral polyp's diet. Paradoxically, though the reef supports a rich diversity of marine life, the intense blueness of the reef is caused by a lack of plankton due to low levels of nutrients in the sea water. As the oceanic surface waters are depleted of nutrients in the northward currents, the reef's plants and animals counteract the shortage by recycling nutrients within the reef.
Living in shallow tropical waters, corals have the ability to photosynthesize due to symbiotic single-celled algae, or zooxanthellae, growing in their tissue, harnessing sunlight to feed their coral hosts. It is, therefore, algae that determines the growth of the corals and provides a crucially important factor in the development and function of coral reefs.
When affected by stress and pollutants, such as oil and chemical spills, corals secrete copious amounts of mucous to purge the pollutants from their system. In doing so, they may expel the symbiotic algae that are crucial to the corals' growth and existence. Continual secretion eventually eliminates the algae from their system to the corals' detriment. Corals, stressed by temperature, climatic and chemical changes, exhibit a change of colour. Prolonged loss of colour, called "bleaching", can result in death.
Water motion may also play an essential role in sustaining the biological production that controls the algal growth on which the corals depend. There is the belief amongst scientists that corals can sustain a level of turbulent activity. However, they are often damaged or killed by changes in water temperature, strong currents, flooding and cyclonic winds along the sometimes turbulent Queensland coast. Tourists may also contribute to coral damage by snorkelling, diving and walking on the reefs. The annual bands of skeletal limestone, similar to that of tree "rings", can provide scientists with detailed information of the climatic history of the Great Barrier Reef.
Coral damage may also be caused by siltation due to the downstream effects of land clearing, dredging and mining, or from over-fishing and natural predators such as the crown-of-thorns starfish. Hence, the pursuit of land development, the tourist market, and commercial fishing within the Great Barrier Reef needs to be balanced with the protection of this ecosystem.
Scientists are therefore keen to study many aspects of corals and their role in the ecosystem of the Great Barrier Reef. Areas of research include the effects of water movements, water temperatures and cyclonic activity on the corals' growth and existence. Other areas of work include the effects of coastal land degradation, fishing pressure and tourist activity. It is also important to monitor and determine the effects of pollutants and chemicals, and the rate at which algae are eliminated from the coral's system under extremes of environmental stress. Innovative technology can play a vital role in determining the degree of natural and induced coral stress caused by pollutants, temperature and climatic changes without removing coral from the Reef. Devices, used since the late 1950s, are fitted to sea vessels to research and record salinity, temperatures and ocean depths. Tracking and data recording devices also include moored buoys and submersible data loggers.
Satellites are used to track ocean currents and determine water temperatures, density and turbidity. Satellite-based remote sensing, from above the ocean, can provide scientists with information to develop and conserve the natural resources and environment of the Great Barrier Reef while reducing the amount of vessel and manual activity. It offers many opportunities to improve our knowledge of the ocean with minimum disturbance.
The future of the Great Barrier Reef can be greatly advanced through the scientific study of ocean dynamics and informed knowledge to protect the world's greatest natural resource, the 'coral'-mines of the sea.
by Martina Nicolls
First published by the CRC Reef Research Centre, Queensland, Australia http://www.reef.crc.org.au/publications/explore/feat26.html
MARTINA NICOLLS is an international
aid and development consultant, and the author of:- The Shortness of
Life: A Mongolian Lament (2015), Liberia’s Deadest Ends (2012), Bardot’s Comet
(2011), Kashmir on a Knife-Edge (2010) and The Sudan Curse (2009).
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