Will wiping out COT starfish protect coral reefs?
2018 is the Third International Year of the Reef
Whether you live near the shore or thousands of miles away, any change in marine biosphere is likely to affect you. Hence it is necessary to understand what is ailing the ‘lives’ in seas and the oceans, and whether steps—and correct steps at that—are being initiated as cure. A submarine robotic gizmo is ready to spell a doom on the entire specie of crown-of-the-thorns starfish! However, both national and international scientists are of divided view, with many believing that it would make more sense to attack the fundamental trigger for the overpopulation of starfish- that is to control increased toxicity of coastal waters from agricultural practices. Read on to understand the whole issue…
A Corals on reefs are actually small animals. This living ecosystem is thus very fragile and susceptible to damage. The coral animals are not mobile. They live in colonies, and possess skeletons of hard calcium carbonate, which is what gives the coral reef its structure. Coral reefs are found in all three of the Earth’s oceans that have portions in the tropics - the Atlantic, Pacific and Indian. Some coral reefs are very large. The Great Barrier Reef, which stretches more than 1,400 miles off the coast of Australia, is the world’s largest reef. The Great Barrier Reef is in straitened circumstances after repeated bleaching events due to climate breakdown over the last few years. In a 2015 report, the World Wide Fund for Nature noted that in the previous three decades, the reef had lost half its coral cover and 40 percent of that loss was due to COTS. Though the crown-of-thorns starfish (Acanthaster planci), or COTS, in normal circumstances, is a useful part of reef ecosystems. It feeds on the fastest-growing corals, allowing the slower species time to establish themselves and form colonies. However, it is claimed that every few years, there is a COTS outbreak. Why? They are attracted by the nitrogen run-off from fertiliser used on farms nearby. The nitrogen leads to algal blooms, which the COTS larvae feed on before reaching their full size and moving on to their adult food source - the coral. And thanks to overfishing, their natural predators are scarce, so they have pretty much free reign. Thus, an underwater drone RangerBot is ready to reportedly protect the Great Barrier Reef from the crown-of-thorns starfish by poisoning and killing them.
Machine to massacre the COTS specie is ready
“RangerBot is the world’s first underwater robotic system designed specifically for coral reef environments, using only robot-vision for real-time navigation, obstacle avoidance and complex science missions,” roboticist Matthew Dunbabin of the Queensland University of Technology has claimed. “This multifunction ocean drone can monitor a wide range of issues facing coral reefs including coral bleaching, water quality, pest species, pollution and siltation. It can help to map expansive underwater areas at scales not previously possible, making it a valuable tool for reef research and management.” RangerBot has been in development to fight this threat for several years now. Its original iteration - dubbed ‘The Terminator’ - was called COTSbot. It was in development for 10 years before its first trial in 2015. RangerBot is the new and improved model, the result of a collaboration between the Queensland University of Technology, Google, and the Great Barrier Reef Foundation. It has an advanced vision system that allows it to see while patrolling the reef, and can patrol autonomously without COTSbot’s tether, or operated by a human with a tablet when the need calls for it. It can also monitor reef health, something COTSbot wasn’t equipped to handle. Back in 2005, Dunbabin developed a vision system that could identify a crown-of-thorns starfish with 65 percent accuracy. Today, RangerBot has a COTS identification accuracy rate of 99.4 percent accuracy.
When it identifies its quarry, the robot deploys an arm, which injects the starfish with bile salts. This triggers necrosis or apoptosis, killing the starfish within 48 hours, with 100 percent mortality rate, without— ‘reportedly’ again— harming anything else in the surrounding waters. In addition to its ability to enter spaces that may be dangerous for human divers, the RangerBot can stay in the water for up to eight hours on a single charge - nearly three times as long as a human - and operate during all times of the day, and in all conditions. RangerBot’s capabilities have been proven both in the lab and on the reef; the next step is to work with the Great Barrier Reef Marine Park Authority to get the approvals needed to put the robot to work. The team also plans to make the robot available for reef management teams around the globe.
Not all are in favour though
“I agree that COTS (crown-of –thorns starfish) species is particularly harmful to the great barrier reef, but just by killing the COTS, the coral reefs cannot be saved. COTS is not the only threat to corals. Climate change, due to which sea temperatures have risen, causes bleaching which is one major cause of damage to Great Barrier Reef. Another cause is agricultural runoff. These are three threats combined effect of which has caused and continues to cause damage to the reef. The scientists of Queensland University have claimed that the injection will be harmless to other species. But quite possible, other fish and other marine beings could eat poisoned fish and may die . There is no doubt that indiscriminate killing (or culling) will spell a doom for this species. All species have a role in maintaining an ecological balance. Should the Australian Government go ahead with this plan? A research publication by Dr Brian Lassing and Dr Peter Moran from Queensland university was submitted in September 1995 to The Great Barrier Reef Marine Park Authority. It went into this question. The conclusion is that the risks from adopting a policy of massive destruction of crown-of-thorns starfish are significant and that the only potential benefits may turn out to be costs in the long run. If, however, for instance, it appeared that 30 percent of all the reefs of the system were to be seriously affected, then I would be asking the Government for resources to undertake population control. This explains why so far the Authority has maintained the policy of not undertaking massive starfish killing. In my views, though there are economic benefits of protecting the reef areas, killing starfish on a large scale may have an unforeseen significant effect on the whole Reef ecosystem. Such a decision is not at all justified,” points out Vidyanand Garg, former chairperson, UP Forest Corporation; former principal secretary, Forest & Environment; former chairman, UP Pollution Control Board.
According to noted scientist and professor of geodynamics at the Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore, Dr CP Rajendran: “Here’s a case where over population of crown-of-thorns starfish feeding on coral polyps is thus destroying the young growing corals with great barrier reef of Australian waters. This is a double whammy in the sense that ocean warming has already become extremely detrimental to corals. Thus the rationale for developing a submarine robotic gizmo to kill the starfish! But I think it would make more biodiversity sense if we attack the fundamental trigger for the overpopulation of starfish- that is to control increased toxicity of coastal waters from agricultural practices. Rather than killing the entire population of starfish using artificial means, it makes more scientific sense if we approach this problem in a sustainable way.”
Charlie Veron, the world’s leading expert on coral reefs, says future of the Great Barrier Reef is dire. “The reef is in strife, and to say otherwise is bullshit. Half the place is dead already. It won’t be here in 15 years. Contrary to public opinion, COTS outbreak and runoff from nearby farms is not nearly as big a threat to the reef as climate change, embodied most recently in the proposed Carmichael coal mine, in north central Queensland. The mine’s proponent, the Indian multinational conglomerate Adani, projects there will be more than 4.7 billion tonnes of carbon dioxide emissions associated with the mine over its lifetime – nine times Australia’s total production of the greenhouse gas in 2015.” Vernon was the first to show that, contrary to received wisdom, the Indo-Philippines archipelago has the world’s greatest diversity of coral, not the Great Barrier Reef. He was instrumental in identifying the Coral Triangle – the so-called ‘Amazon of the seas’, a 5.7-million-square-kilometre area from the Solomon Islands in the east to Brunei in the west, which is now recognised as the world’s centre of marine biodiversity and a global priority for conservation.
Understanding Coral Reef Ecosystems
Coral reefs are one of the most diverse and beautiful natural environments on earth. The world’s first coral reefs occurred about 500 million years ago, and the first close relatives of modern corals developed in the southern Europe about 230 million years ago. Coral reefs are extraordinary living geological structures. They are highly diverse and productive, but grow best in oceanic waters with very low levels of nutrients. Coral reefs can form only in relatively clear, shallow and warm waters. Corals belong to the group of animals (Cnidarians) that also include anemones, jellyfish, bluebottles and hydroids. This group of animals is quite simple, with a nervous system but no brain. The basic structure shared by all corals is the coral polyp. This is the basic building block of a coral colony. The polyp is a small tube-like structure, with a central space opening via the mouth. The mouth of the polyp is surrounded by six (or a multiple of six) tentacles. A coral polyp resembles a small anemone. A coral colony is made up of thousands of tiny little animals. A coral reef is therefore made up of millions of these animals. Other types of animals and plants also contribute to the structure of the reef. Many types of algae, seaweed, sponge. Sediment and even molluscs like giant clams and oysters add to the corals’ growth at different rates, depending on water temperature, salinity, turbulence and the availability of food. The massive corals are the slowest growing species, adding between 5 to 25 millimetres (.2 to 1 inch) per year to their length. Branching and staghorn corals can grow much faster, adding as much as 20 centimetres (8 inches) to their branches each year. Most coral polyps have clear bodies and their skeletons are white, like human bones. Most corals get their colour from the zooxanthellae inside them. Several million zooxanthellae live in just one square inch of coral and produce pigments. These pigments are visible through the clear body of the polyp and give the coral its beautiful colour.
The corals can be hard or soft. In hard corals the polyp sits in a small limestone cup (corallite) that secretes and protects the soft polyp tissue. The limestone cup is in fact made by coral polyps extracting calcium from seawater. When the polyp grows upwards, it is divides into two. Each new polyp secretes a new corallite. Thus as the coral grows upward and outwards, the coral tissue lifts itself up and lays down new skeleton, forming something similar to tree rings. In most coral species, the new polyps remain joined together as they grow and food can be moved between the polyps through the coral colony. Inside a coral polyps clear outer tissues live microscopic algae called zooxanthellae. This is called a symbiotic relationship, where both parties benefit from their partnership. The algae transform sunlight and use polyp’s waste to make sugars through photosynthesis. The coral helps itself to some of the sugars enabling it to grow and the algae gain protection from predators inside the coral polyp’s tissues. The sugars can provide up to 98% of the polyps dietary requirements. This is why corals are found in shallow waters, as they require sunlight to survive. The zooxanthellae give the corals their brilliant colours of pinks, greens, yellows and browns.
How do corals reproduce?
Corals reproduce in two ways: asexually and sexually. Some corals divide to form individuals. This is known as asexual reproduction. Sexual reproduction takes place as a mass-spawning event, where polyps release millions of eggs and sperm, all at the same time and on the same night. This timing is linked to moon cycles. Polyps are either male or female or both male and female. After the eggs and sperm are released, they float to the surface. The fertilised eggs, that escape predation by other animals, hatch into larvae and drift with the plankton and currents. The tiny per cent that survives settles on the reef and begins new coral colonies. Although corals look like strong sturdy rocks, they are in fact very fragile creatures. The actual layer of ‘live tissue’ on a coral colony is very thin, therefore touching it or knocking it with fins can scratch this layer of tissue off and cause scarring. Most corals have a special mucus they cover themselves with. Studies say that this mucus helps the coral combat infections by containing antibacterial agents, protects the coral from harmful UV sun rays by containing agents similar to what we use as sunscreen. It stops them from drying out and keeps the coral moist when exposed at low tide, and can also help the coral shed sediment. The mucus can be wiped off through contact. Studies show that if a coral is injured, death is not instantaneous, however slowly infections can take hold and the coral generally dies within 3-5 months.
Types of Coral Reefs
Most reef scientists generally recognize three MAJOR types of coral reefs: Fringing Reefs, Barrier Reefs, and Atolls.
Fringing Reefs (Shore Reefs): Fringing reefs are reefs that grow directly from a shore, with no ‘true’ lagoon (i.e. deep water channel) between the reef and the nearby land. However, there often are areas of shallow intertidal or sub-tidal sand bottom lying between the beach and the inshore edge of coral growth. The fringing reef is by far the most common of the three major types of coral reefs, with numerous examples in all major regions of coral reef development. Without an intervening lagoon to effectively buffer freshwater runoff, pollution, and sedimentation, fringing reefs tend to particularly sensitive to these forms of human impact. Thus, it is no surprise then that increasing human populations in coastal areas - and the accompanying increases in coastal development and intensive agriculture - have resulted in the decimation of fringing reefs throughout the world in recent years.
Barrier Reefs: Barrier reefs are extensive linear reef complexes that parallel a shore, and are separated from it by lagoon. A lagoon - as used in the context of coral reef typology - refers to a comparatively wide band of water that lies between the shore and the main area of reef development, and contains at least some deep portions. Barrier reefs are far less common than fringing reefs or atolls, although examples can be found in the tropical Atlantic as well as the Pacific. The 1200-mile long Great Barrier Reef off the NE coast of Australia is the world’s largest example of this reef type. The GBR is not actually a single reef as the name implies, but rather a very large complex consisting of many reefs. The second largest Indo-Pacific barrier reef lies off New Caledonia's NE coast - it is some 400 miles long with a lagoon 1-8 miles wide. Another large barrier reef extends for nearly 170 miles to the north of Fiji and Vanua Levu. This reef type is even rarer in the Caribbean region, where only two true barrier reefs are found. The largest of these runs off the coast of Belize, and the other off the north coast of the island of Providencia (east of Nicaragua).
Atolls: An atoll is a roughly circular (annular) oceanic reef system surrounding a large (and often deep) central lagoon. In the South Pacific, most atolls occur in mid-ocean. Examples of this reef type are common in French Polynesia, the Caroline and Marshall Islands, Micronesia, and the Cook Islands. The Indian Ocean also contains numerous atoll formations. Examples are found in the Maldive and Chagos island groups, the Seychelles, and in the Cocos Island group. In contrast, atolls are relatively rare in the Caribbean. Published counts range from 10-27. The far greater number of atolls in the Indo-Pacific region of coral reef development - as opposed the Greater Caribbean region - can be mainly attributed to the far greater size of the former region along with its unique geomorphology, which is far more conducive to volcanic island formation and subsequent subsidence .
A Caveat on Reef Typology: Readers should be aware that identifying major reef types may not always be quite as simple as the above discussion may suggest. Some reefs seem to be intermediate versions that defy any simple ‘either or’ classification scheme. This is especially true in the Caribbean region, where some of the fringing reefs are separated from shore by open waters that may reach 6-8m in depth and extend a kilometer or more from shore. Are these fringing reefs, barrier reefs, or something else? The answers to such questions depend on who you ask, but don’t let that bother you. Such issues are common in science when our human classification schemes simply fail to account for the seemingly infinite variability found in nature.
Why must coral reefs be protected?
Coral reefs provide an important ecosystem for life underwater, protect coastal areas by reducing the power of waves hitting the coast, and provide a crucial source of income for millions of people. Coral reefs teem with diverse life. Thousands of species can be found living on one reef. The Great Barrier Reef contains over 400 coral species, 1,500 fish species, 4,000 mollusc species and six of the world’s seven sea turtle species. The Coral Triangle - a coral-rich marine region in Southeast Asia that encompasses the waters between Indonesia, Malaysia, the Philippines and Papua New Guinea - is the most biologically diverse marine ecosystem on Earth. Coral reefs have an estimated global value of ￡6 trillion each year, due in part to their contribution to fishing and tourism industries and the coastal protection they provide. More than 500 million people worldwide depend on reefs for food, jobs and coastal defence. The ridges in coral reefs act as barriers and can reduce wave energy by up to 97%, providing crucial protection from threats such as tsunamis. They help protect areas such as mangrove forests and seagrass beds that act as nurseries for marine animals, as well as human coastal populations. Extracts from animals and plants living on reefs have been used to develop treatments for asthma, arthritis, cancer and heart disease. Coral has a multitude of uses as a construction tool. It can be utilised for the production of lime kilns, house foundations and embankment of streets, canals and fish ponds. Huge businesses also thrive on collecting coral and selling it as souvenirs or exporting it for sale in the aquarium trade. Like any ecosystem, coral reefs can withstand and adapt to certain impacts. But the combination of multiple stresses of global changes in ocean temperature and acidification, with local pressures such as pollution, overfishing and declining water quality, has led to changes that could become irreversible within the next few decades. To sum up:
Coral reefs provide protection and shelter for many species of fish and sea life: From the smallest shrimp to the largest predator, sea creatures find both food and protection on coral reefs. Without these important habitats in which to thrive, fish and sea life will cease to exist. Coral reefs provide shelter to nearly one quarter of all known marine species. Over the last 350 million years, reefs have evolved into one of the largest and most complex ecosystems on the planet. The reefs are home to 4,000 species of fish, 700 species of corals and thousands other forms of plants and animal life. Scientists estimate that, in total, more than 1 million species of plants and animals are associated with the coral reef ecosystem.
Coral reefs protect coasts from strong currents and waves: Coral reefs slow down the flow of water and break the power of the waves during storms, hurricanes, typhoons, and even tsumanis. And interestingly coral reefs are most likely to have formed where an oceans’ currents and waves are the most powerful. Reefs in places such as the Florida Keys help prevent beach erosion. Without coral reefs many of the world’s most fragile, coastal ecosystems would be unable to thrive.
Coral reefs are nature’s water filtration system: Reefs cannot exist in murky or polluted waters. Many individual corals and sponges consume particles found in the ocean. In turn, this enhances the clarity and quality of the ocean’s waters. Clean and clear water makes our beaches more beautiful and also allows coral reefs to continue to thrive. Coral reef communities are extremely efficient at acquiring, retaining and recycling nutrients received from multiple sources. The key elements in the coral reef recycling process are (1) the symbiotic relationship between hard corals and their zooxanthellae, and (2) the rapid and effective exchange of nutrients and energy between different coral reef habitats. It is this highly efficient ‘recycling programme’ - along with the organic contributions from primary producers within the ecosystem as well as from the open sea - that allows for the sustenance and growth of coral reefs in the midst of waters so stripped of dissolved nutrients that they are often referred to as biological deserts.
Coral reefs control how much carbon dioxide is in the ocean water: Coral’s limestone shell is formed by the ocean’s processing of carbon dioxide. Without coral the amount of carbon dioxide in the ocean rises, which in turn, affects all living things on Earth.
Coral reefs are an important food source for humans: As long as there have been humans, fish have been consumed as a source of protein. The abundance of edible sea life in healthy coral reefs, therefore make them important to human nutrition. They form the nurseries for about a quarter of the ocean's fish, and thus provide revenue for local communities as well as national and international fishing fleets. An estimated one billion people have some dependence on coral reefs for food and income from fishing. If properly managed, reefs can yield around 15 tonnes of fish and other seafood per square kilometre each year.
Vital to tourism industry: Coral reefs are vital to the tourism industries, creating and protecting many of the world’s most beautiful beaches. Without clear waters and opportunities for recreational exploring through diving and snorkeling, tourist dependent economies collapse. Tourism revenues generated by coral reefs are also significant. For example, according to a report by the Key West chamber of commerce, tourists visiting the Florida Keys in the US generate at least US$3 billion dollars in annual income, while Australia’s Great Barrier Reef generates well over US$1 billion per year. Sustainably managed coral reef-based tourism can also provide significant alternative or additional sources of income to poorer coastal communities in developing countries.
Source of medical advances: We can also expect coral reef species to contribute to future medical advances. Already coral reef organisms are being used in treatments for diseases like cancer and HIV. Just as with tropical forests, we may continue to find the answers to medical problems in the coral reefs - so long as we can keep them healthy.
Intrinsic value: For many coastal societies around the world, coral reefs and their inhabitants are intricately woven into cultural traditions. For these people, a world without coral reefs would be an infinitely poorer place.
Threats to Coral Reefs
Coral Reefs are suffering from natural and anthropogenic threats. Anthropogenic means human influence or human impact. Many anthropogenic influences are resulting in the degradation and destruction of coral reefs causing loss of biodiversity, essential food supplies and economic revenue. Combined with threats from nature in the form of storms, typhoons and diseases, coral reefs are struggling to survive. Natural stressors are made worse by human disturbances. For instance, the presence of disease may be higher in corals stressed by human impacts such as mechanical damage and pollution.
Natural Impacts
Storms and Earthquakes: Disasters such as storms and earthquakes occur naturally and periodically and devastate large areas of reefs. These natural events are more severe if reef communities are already weakened by other impacts and recovery is inhibited by algal overgrowth due to the lack of grazing organisms, removed by fishing.
Water temperature rise and coral bleaching: Unusual climatic patterns can result in stress to coral reefs. The dramatic effects of El Nino have raised concern over the effect of climate change on corals. Climate change and heated water released from coastal developments can lead to warm waters and change local ecological conditions. An increase in the sea temperature can cause the phenomenon known as coral bleaching where the corals, stressed by the temperature change, expel their algal symbionts and turn bright white. Just one degree above the typical summer max is enough to bleach many corals. Other causes of bleaching are changes in nutrient levels and salinity, extreme low tides and increased UV radiation. Corals may recover but are generally presumed to be weakened by such an incident. Death, if it does occur, may be largely attributed to starvation, although it is thought that some autolysis (tissue destruction) occurs. The physiological mechanisms involved with bleaching are not fully understood and are currently a source of investigation. It has been hypothesised that the algae are expelled to make way for the potential repopulating of the coral by more stress resistant algae.
Crown-of-Thorns Starfish (COTS): Recent increases in the populations of the coral eating crown-of-thorns sea star have posted another natural threat to reefs. When present in huge numbers, these animals are able to devastate huge areas of reef. Recovery of the coral from these outbreaks may take as long as 20-40 years, where damage is not severe. However, recovery in some parts of the world may never happen as the coral is being taken over by algal cover and other coral species. COTS can have several million babies in a year. We have contributed to their increase through over harvesting their natural predator the Triton Trumpet (Davui) and through nutrients from sewage etc. By giving baby COTS more food (seaweed) when they are young, they are more likely to survive to become the destructive adults we know today.
Disease: Corals under stress often suffer from bacterial infections due to excess production of protective mucus. Excessive mucus production resulting from natural and man made influences (e.g. increased sedimentation, toxic chemicals) may also enhance the number of blue green algae thought to be responsible for black band disease, which is seen as dense band of filaments across the coral colony. Coral polyps are killed as the band advances leaving only white limestone behind. High temperatures allow corals to become sick more easily, and allow disease-causing organisms to grow faster. There is a huge array of different diseases in corals. Most of them are named after how they change a sick coral’s appearance, like black band, white band, white spot and purple blotch diseases.
Ocean Acidification: As more carbon dioxide (CO2) is released into the atmosphere, it also has adverse effects on the oceans. Recently, ocean acidification has emerged as another potentially serious threat to coral reefs. Seawater absorbs some of the excess CO2 from the atmosphere, causing the oceans to become more acidic. As a result, the oceans’ acidity has increased by 25 percent over the past 200 years. These acidic conditions dissolve coral skeletons, which make up the structure of the reef, and make it more difficult for corals to grow. If left unchecked, scientists estimate that the oceans could become 150 percent more acidic by the end of this century, making it very hard for corals to grow at all.
Human Impacts
Chemical Pollution: Agriculture and industry release a variety of chemicals into coastal waters. Pesticides and fertilisers used in agricultural development projects are carried in run off to sea and have been known to take part in coral reef destruction. Pesticides can destroy or damage zooplankton or reef communities. They cause further damage by accumulating in animal tissue and may affect physiological processes. Herbicides may interfere with the basic food chain by destroying or damaging zooxanthallae in coral, free living phytoplankton, algal or sea grass communities. Exposure to chemicals (namely hydrocarbons) released by spillage from oil tankers, harbours and pipelines has been known to affect reproduction, growth rate and feeding, defensive responses and cell structure in corals. Industrial practices such as mining, dredging and refining all release heavy metals into coastal waters. Some coral species are sensitive to these, although the extent is not yet known.
Nutrients Loading/Sewage: The discharge of fertilisers, waste feed and other materials from aquaculture and agriculture into coastal waters can result in nutrient loading. The introduction of organic compounds results in eutrophication and subsequent oxygen depletion. Europhication is where the nutrient load gets to an extent that the community becomes dominated by algal/seaweed, exceeding the capacity to control by grazing organisms. This leads to oxygen and light reduction and perhaps death of the communities living there. Coral reef ecosystems have been described as oases in the oceanic desert due to the lack of nutrients present in their environment. When faced with large quantities of nutrients, they are easily overcome by algae and severely damaged, if not killed. Sewage from coastal developments and local communities can supply these nutrients providing food for algae, which go on to overgrow the coral.
Overfishing: Over exploitation affects the vast majority of the world’s reefs. This leads to an average decrease in the size of the fish and a reduction in predatory target fish. Removal of key herbivores and predator species may result in large scale ecosystem change. If grazers are removed from reefs, algae are quick to take over and dominate, especially if the area is also suffering from organic pollution.
Destructive fishing and boating practices: Fishing methods in the tropics can be particularly destructive especially those of dynamite ‘blast’ fishing, cyanide or poison (duva) fishing and fish hunting with gum boots. Other adverse fishing practices include disintegration of the reef structure in order to weight traps and remove hiding places and beating coral surfaces to herd fish into nets. Anchor damage and accidental grounding of boats can be a serious threat to reefs. For example, one cruise ship destroyed 3150km2 anchoring on one occasion. These practices lead to habitat destruction and disintegration of the reef ecosystem.
Construction and Sedimentation: Sedimentation (losing soil from upland areas) is an extremely important cause of coral reef destruction. Coastal construction and shoreline development often result in heavy sediment loading. Further effects are caused by inadequate land management and deforestation where soil run off from farms and settlements delivers sediments to the reefs. Watersheds cleared of their forests and other vegetation cover is vulnerable to erosion and flooding, resulting in increased levels of sediments reaching the reefs. Chemicals applied to upland agriculture also make their way down to the reefs via run off from land and rivers. Dredging has many very serious implications for reefs. The most dramatic effects are caused by suspension of silt, sedimentation, turbidity, oxygen reduction and the release of bacteria and toxic matter. A large quantity of either coarse or fine particles will bury the corals, which are unable to withstand cover for more than one or two days. Sedimentation causes corals to secrete the protective mucus mentioned earlier, in a bid to rid themselves of the sediment. This process requires increased energy levels, which have to be diverted away from essential processes. If the problem is exacerbated by other external stresses e.g. temperature change, then the corals become over stressed and can die. The secretion of this sediment clearing mucus also makes the coral more susceptible to bacteria and therefore more likely to suffer from disease. Excessive sedimentation exceeds the clearing capacity of some filter feeders and smothers the substrate. It reduces light penetration and can alter the vertical distribution of plants and animals on reefs. Sediments can also absorb and transport other pollutants.
Mangrove cutting: The destruction of mangroves by clear cutting or pollution has resounding consequences on coral reef ecosystems. To remove mangroves, is to remove the main source of leaf litter, a food resource for the variety of coral reef animals. Mangroves also provide the nutrient rich feeding grounds for many marine species, which if removed would eliminate fishing grounds. Furthermore, mangroves protect the shoreline against cyclones and storms and stabilise it against erosion and land loss.
Rubbish/Litter: Rubbish and litter is one of the biggest problems. All these artificial products take a long time to decompose. Plastic bags breakdown in 50 years, plastic bottles in 150 years, and cigarette buts in 75 years, paper in one year and batteries in 200 years: These all take so much time to breakdown to the detriment of creatures that live around us. Batteries leak poisons as they breakdown and can contaminate the fish, as well as kill corals and other marine life. If rubbish is left lying around, it can easily get blown into the sea.
Tourists: Tourism is a great industry as it provides people with jobs and income. However, tourists are not always as educated as we hope. A lot of them come from large cities and towns and have spent very little time around natural environments. Tourists come to visit and experience an environment they do not have at home. We therefore need to take the responsibility to inform them how to respect and treat that environment.
Fish-feeding: The feeding behaviour of reef fishes, eels, sharks and even rays has come to a selling point through commercial fish feeding dive tours and ‘interactive diving’. However, many do not realise the harmful effects this activity has on these animals. Studies done around the world have indicated that fish feeding significantly alters behavioural patterns by ‘training’ these wild creatures with human food handouts. In addition, fish feeding causes health problems for the fed animals and disrupts the natural processes within the marine community. By feeding the algae eaters that control algae growth, they become handout feeders that soon neglect their important role of eating algae, which in turn can overgrow coral.
What the researchers say
A group of international scientists, including scientists from Australia, have issued advice that more research is urgently required to determine whether corals can acclimatise and adapt to the rapid pace of climate change. The team of coral experts, led by Dr Gergely Torda from the ARC Centre of Excellence for Coral Reef Studies (Coral CoE) at James Cook University and the Australian Institute of Marine Science (AIMS), have delivered recommendations for future research. As the Great Barrier Reef faces unprecedented coral mortality from back-to-back mass bleaching in 2016 & 2017, rising carbon dioxide and other natural and human-induced pressures, scientists advise more research is urgently needed into the poorly-understood mechanisms that corals might use to survive in a rapidly warming world. “There is still a lot to understand about corals,” says Dr Torda. “While our only real chance for their survival is to reverse climate change, a nugget of hope exists - that the corals may be able to adapt to their changing environment,” he says. “However, there are major knowledge gaps around how fast corals can adapt or acclimatise to changes in their environment, and by what mechanisms they might use to achieve this,” adds co-author Professor Philip Munday of Coral CoE. “For example,” explains Dr Jenni Donelson, co-author at Coral CoE, “recent studies show that fish can acclimatise to higher water temperatures when several generations are exposed to the same increased temperature, but whether corals can do the same, and how they might achieve this, is largely unknown.” The team agrees that further research identifying how corals respond to climate change is critical, as the Earth undergoes an unprecedented rate of environmental change.
Crown-of-thorns-starfish
Some interesting facts
Fossil evidence suggests COTS have been around for millions of years although outbreaks have only been observed in the last 50 or so years. COTS are a natural part of the ecosystem and an over-abundance only occurs when the reef is out of balance and unhealthy. In healthy reef conditions COTS can play a productive role by eating some of the faster-growing corals and giving the slower-growing corals a chance to catch up and regenerate.
The first recorded outbreak of COTS was in the Ryukyu Islands off Japan in the 1950s. The first COTS outbreak in Australia was recorded in 1962 at Green Island. There has now been between 3-4 recorded outbreaks in Australia. The Crown of Thorns has only a few predators, which include triton’s trumpet, the white spotted puffer fish, the lined worm, the harlequin shrimp and two species of triggerfish (yellowmargin triggerfish and titan triggerfish). The red emperor, spangled emperor and parrotfish are also known to eat juvenile COTS before the starfish grow their spikes.
COTS spawn on the Great Barrier Reef between October-March when water temperatures are at their highest. Female COTS release eggs into the water and nearby males release sperm, which then fertilise the eggs. Large female COTS can produce up to 65 million eggs per season. COTS start off as planktonic larval and drift along on top of the water for weeks before settling at the bottom of the ocean floor. They are most vulnerable to predators as juveniles before their spiky spines have grown. At about one year of age they develop spines and begin to feed on coral. Adult COTS can grow up to a metre in diameter and have up to 21 arms. If they shed an arm due to stress or injury they regrow within six months. COTS spines are long and sharp and covered with an epidermis containing the venom ‘plancitoxin’. They are toxic to both marine life and humans. COTS eat by everting their stomach through their mouth and then spreading it out over the surface of the coral using their tube feet. They then digest their food externally. Adult COTS almost exclusively eat scleractinian. They can survive without feeding for up to nine months.
COTS outbreaks are a threat to the future of the Great Barrier Reef because they are happening more regularly and there is not enough time between outbreaks for coral to regenerate. An average of 15 years between outbreaks is sustainable but with other environmental factors also causing damage such as cyclones and coral bleaching, it puts the Reef at great risk. Research suggests that the increasing COTS outbreaks are caused by several contributing factors. These include excessive nutrients in the water as a result of fertilisers and sewage running off the land and overfishing which reduces the number of their natural predators.
How you can help protect coral reefs
Boycott damaging fishing methods. If you consume fish caught in a way that damages coral reefs, you are part of the problem. Understand which fish are caught in a way that damages reefs, and spread the word. Don't eat fish caught with bottom trawling methods. Bottom trawling is so damaging that it can destroy reefs that could live for thousands more years and exist deep in the ocean.
Tell others about coral reefs. Many people touch or otherwise harm coral reefs without intending to do so. They may simply not understand that reefs are full of fragile living creatures or realize that the smallest contact can cause them harm. Helping educate as many people as possible about coral reefs can make a difference.
Pressurize politicians to support reefs. Legal mechanisms that protect coral reefs can be critical. Let your politicians know that you want them to support measures that will ensure coral reefs suffer less damage. Creating marine protected areas is a measure that can make a difference.
Oppose global warming. General worsening of the environment is an indirect way that people are causing harm to coral reefs. They are very sensitive to rising water temperatures, which cause them harm. Reducing your carbon footprint also helps stop global warming.
Use organic fertilizer to avoid chemicals running into the ecosystem. Don't assume that chemicals in your garden or on your farm won't find their way back into the ocean just because you don’t live near it.
Practice general conservation. Coral reefs are damaged when the general environment around them declines. So, you can help protect coral reefs simply by leading a more sustainable lifestyle.
Plant trees: Trees reduce runoff into oceans, and runoff can damage coral reefs.
Reduce your carbon footprint. This really matters. Increasing carbon dioxide in the air can lead to global warming, which can harm coral reefs. It's all interconnected. Ways to reduce your carbon footprint include biking to work and using a clothes line.
Use less water. This will help decrease runoff, which is a key way that coral reefs are harmed.
When travelling, choose a hotel that embraces environmentalism. Hotels can make a big impact on the environment. They are often close to shores, and a lot of people pass through them. Support hotels with policies designed to reduce pollution. Hotels that have programmes to treat sewage and offer recycling and other sustainability measures can help protect coral reefs by improving the overall environment around them.
Snorkel and scuba dive with care. Many people enjoy snorkeling near coral reefs because of their unique beauty. Snorkelers and divers can cause serious damage to coral reefs, especially in areas with heavy tourism. Don't ever pull a piece of coral reef off to take with you. They say you should leave only bubbles and take only pictures when you are in the ocean. Remember that you are destroying a living organism if you do take a piece of the reef. Practice snorkeling before you venture anywhere near a coral reef, so you don’t come into accidental contact with it. Stay horizontal in the water and avoid kicking sand or flailing around with your fins. Don't swim too fast or use your arms when swimming. If you touch a coral reef, it can cause you harm, too. People have been cut and stung by coral reefs. Don’t get too close to a coral reef while wearing a lot of sunscreen. The oils from the lotion cause coral reefs damage.
Don’t litter on the beach or in the ocean. Leaving behind things like fishing nets or general garbage on a beach can harm coral reefs. Throwing litter into the ocean itself can eventually cause the trash to come into contact with the coral reef. When trash ends up on a coral reef, it can actually smother the corals. Remember, they are living organisms. Sometimes people see corals as they see shells. However, corals are alive and, thus, they are very susceptible to harm. Littering can also cause harm or even kill the fish that populate coral reefs. The technical term for this kind of litter is ‘marine debris’. Marine debris also damages other organisms on coral reefs that are necessary for their survival. Don’t discharge wastewater from your boat into the ocean. Find an acceptable wastewater discharge facility in the area instead.
Avoid striking or touching a coral reef. Running your boat into a coral reef can cause it serious damage. Protecting coral reefs depends on what experts call proper ‘vessel management’. Understand where coral reefs are so your boat doesn't strike them, even incidentally. People can also damage coral reefs simply by touching them.
Don’t purchase coral souvenirs. You shouldn't take anything out of the ocean that's alive, or buy it in a store, either. In some countries, you will find jewelry and other souvenirs made out of coral. Don't buy them. It is illegal to sell coral in some countries. Coral can take a long time to grow, so taking it for your aquarium or jewelry box can have a lasting effect that will take years to undo. Red and pink coral is especially prized as jewelry because of its coloring. It comes from deeper waters. Don’t purchase coral reef fish, either. Inquire about marine fish before you buy them in pet stores.