Coral Bleaching | Reef Teach Select Page Coral Bleaching There are roughly 400 species of corals on the Great Barrier Reef, and most of them have a symbiotic relationship with zooxanthellae algae – a microscopic plant that lives inside the tissue of the coral in exchange for providing the coral with up to 90% of its energy requirements. Like most plants, zooxanthellae photosynthesize – using sunlight to turn water and carbon dioxide into carbohydrates (sugars) to feed themselves and the corals. This allows corals to grow much more quickly than they could if they relied on plankton for food. The skeletons of most corals are white – it’s the zooxanthellae living inside the tissue of the coral polyps that gives corals the browns, greens, purples and other colours we see out on the reef. Zooxanthellae (“sounds like jelly”!) are fussy about their living conditions.

They can’t survive in cold deep water, which is why corals reefs are found mainly in the tropics (although some corals that can survive in cold deep waters – for example off Scotland and Norway – they don’t have a relationship with zooxanthellae and grow too slowly to build the kind of reef systems we have along the Great Barrier Reef). Unfortunately zooxanthellae don’t like hot water either. If the sea temperature becomes too warm, the algae develops heat-stress, and stops producing carbohydrates. However, it begins to produce toxic waste products which poison the coral until it rejects the zooxanthellae – expelling it into the open water. When this happens, the coral turns white, and this is known as ”coral bleaching“. Bleached coral isn’t necessarily dead. If the sea temperature drops relatively quickly, the coral will survive and within a few months will have fully recovered its zooxanthellae.

However, if that sea temperature stays too high for too long (it’s impossible to generalise about how high and for how long because it depends on many variables, such as the particular strain of zooxanthellae, the species of coral and it’s geographic location, etc) the coral may not be able to feed itself effectively and the polyps will eventually die, leaving the dead, white, calcium-carbonate skeleton behind. The dead coral will eventually become covered with other types of algae, leading to changes in the species of fish and other animals living on the reef. The number of algae-eating species (e.g. surgeonfish, sea urchins) on the reef may increase, while coral dependent species (like butterflyfish) may decline, alongside an overall decline in species and even local extinctions. Bleaching can also occur (mainly on inshore reefs) after particularly heavy rainfall (for example during a cyclone), when a sharp drop in salinity causes stress in the algae. And other animals, like anemones and clams, nudibranchs and jellyfish, some of which also have a symbiotic relationship with zooxanthellae, can also bleach.

In 1998 and 2006 severe bleaching occurred around the world, caused by warmer than average sea temperatures linked to El Niño events. These widescale events are known as “mass bleaching“. Until 1979 only 3 mass bleaching events ahd been recorded around the world. In 2002 alone, 400 events mass bleaching events were recorded (UNEP) and by 2008 mass bleaching had occured in every coral reef region of the world. In 1998 and 2002 the worst bleaching ever experienced along the Great Barrier Reef (GBR) was recorded. In 2002 55% of corals on the GBR were affected (GBRMPA). Between 1871-2005, water temperature along the GBR rose 0.4°C , and is predicted to rise 1.1-1.2°C by 2050. Scientists are concerned that the reef will experience more frequent and severe episodes of mass bleaching.

There are many factors that affect resistance and recovery from coral bleaching, and while some reefs may recover within a decade or two, others may never recover. The more stresses a reef is exposed to – for example, storm damage, pollutants, destructive fishing methods, the effects of ocean acidification – the less resistance and resilience it is likely to have to bleaching. The Great Barrier Reef Marine Park Authority predicts a low risk of bleaching along the GBR for the summer of 2009-2010, however conditions are consistent with a weak El Niño event, and this has been associated with a higher likelihood of bleaching in the past. Enhance your Great Barrier Reef experience! Coral Bleaching - Maui Ocean Center Coral Bleaching Maui Ocean Center dives in on Efforts to Examine Coral Bleaching Around the Island of Maui If you were ever in search of a cool dip in the ocean to relieve you from the heat this summer, you may have been disappointed to find that the waters felt more like a luke warm bath rather than the comforting oasis you imagined it would be. Record-high summer temperatures have been felt across the entire Hawaiian island chain and coral experts have noticed the warm water temperatures too!

The warmer weather has increased the water temperatures significantly, which resulted in large amounts of coral bleaching along the coasts of Maui. Corals are tiny living animals that eat, grow and reproduce. They have a symbiotic relationship with an algae called zooxanthellae, but when water temperatures spike, the corals become stressed to this sudden change in their environment, causing them to expel the algae. This is called ‘coral bleaching’ and when it occurs, the corals will lose their color and turn bright white. Without zooxanthellae, corals are starved of their nutrients and energy, and may eventually die. Our head curator, John Gorman, explained that coral bleaching is a natural process that happens from time to time. Although reefs typically recover, the part that is alarming is the intensity of the bleaching. The last major bleaching occurred in 1997, but does not compare to the bleaching that has been seen this year so far. Adding to that, Maui Ocean Center’s head aquarist, Larissa Treese, also mentioned that in 2014 higher than average bleaching also occurred, so the intensity of this happening two years in a row is also concerning.

Eyes of the Reef Hawaii Network and DLNR’s Department of Aquatic Resources encourages all ocean users around the islands to monitor and report the condition of the coral reefs, which will help to determine the severity and scope of the bleaching. We are also participating in this statewide effort to monitor coral bleaching. In September, we began monitoring a section of the reef just off the Pali coastline (near the tunnel on Hwy. 30). Photos were taken to have a baseline for comparison. Then, on October 3rd, “Bleachapalooza” (a call-to-action encouraging coral monitoring and reporting) was held and we returned to the exact location of our previous dive. We noticed an increase in the amount of bright white corals present. Here are some photos and underwater footage of what we observed. Dive site off the Highway 30. Maui Ocean Center divers making their way toward the the reef Numerous bright-white bleached corals are seen in the foreground and background of this photo of the reef. Comparison photos show a slight increase in coral bleaching for this particular area. Overall, we noticed a visual increase in the amount of coral heads that were bleached as compared to the previous dive in September.

John explains that most of the corals that are being affected by the temperature change are branching corals, which includes lace and cauliflower corals (Pocillopora sp.). However, other species have been affected as well, like the rice coral (Montipora sp.). In the case of the Pali coastline reef, the corals along the shore show more coral bleaching and gradually decrease as you get into deeper waters. This may be due to the fact that those corals are closer to the highway where sediment and runoff are abundant. Scientists believe that the warm water temperatures will last through November and December, so the coral bleaching trend may continue through the winter. If you’d like to get your feet wet and do your part to help examine the reef you can; no training is necessary, just look for bright white corals. Report your findings, even if the coral is not bleaching, to Eyes on the Reef Hawaii at eorhawaii.org. At this point, it is hard to tell if the reefs will be able to recover. Some factors that determine the corals’ ability to recover are its health prior to the bleaching and the impacts we as humans have on the ocean.

The best way we can help the corals is by doing our part on land to minimize the stress that the reefs are facing right now. Here are six simple tips to help save our coral reefs: Take a stand on the sand – Coral is alive! When enjoying the ocean stay horizontal and float over the reef. If you need to take a break, find a sandy area to stand. Standing on or touching coral can kill it and you could get hurt by the corals sharp edges. Grow and buy organic – What happens on land affects the sea. Reduce chemical runoff from synthetic fertilizers and pesticides by choosing organically grown foods. Build a rain or shower garden – Rain gardens help coral reefs by filtering stormwater after heavy rainfall. Shower gardens collect greywater from beach showers and break down any pollutants before they enter the ocean. Skip the shampoo – Do not use personal care products such as shampoo at beach showers. Instead, take a quick rinse so the chemicals don’t enter the watershed leading to the ocean. Apply reef-safe sunscreen or better yet, wear a UV protective clothing and a hat instead – Protecting your skin from the sun is important, but some sunscreens can damage coral reefs.

Go to to view a current list of “reef-safe” sunscreens or opt out of wearing sunscreen and use a UV protective shirt or rash guard and hat. Dispose of your trash properly – Garbage, especially plastics, have a devastating effect on marine life and can even suffocate coral! For more info visit: UCSB Science Line UCSB Science Line Is coral bleached by higher temperatures? Answer 1: What we see as one thing, coral, is actually a partnership between an animal and a single-celled critter (more formally known as a protist, or more specifically, zooxanthella). The animal part is like a tiny sea anemone that builds the hard part of the coral. They look a bit like plants, but they eat, so they are animals. The protist does photosynthesis. Plants do this too, but plants are made of more than one cell (theyre multicellular). Corals get their bright colors from the protists. Protists have brightly-colored pigments to absorb light for their photosynthesis. When the partnership works well, the protist gets a valuable nutrients from the coral. The urine of the coral contains nitrogen, which the protist needs.

The coral also releases CO2 (carbon dioxide), which the protist uses to do photosynthesis. It takes the CO2 and water and uses the energy from the sun to make sugar. The coral use this sugar. Both partners benefit, so we call this mutualism. When conditions get bad, like when it gets too hot or cold, or when the tiny animals that the coral eat are scarce, the partnership can break down. The protists reproduce quickly and keep the sugar for themselves. The coral then uses chemicals to make them leave. This leaves them without the bright colors, so we say they are bleached. Can you think of other partnerships in the natural world? Thanks for asking. Answer 2: Yes, increased temperatures can lead to coral bleaching. Many corals (and some other sea animals) have single-celled algae that live in their bodies. These algae are a kind of dinoflagellate; otherspecies of dinoflagellate live freely and cause the phosphorescence or"glow" that you can sometimes see in the ocean at night as the water moves around, and some times large populations of dinoflagellates can cause "red tides" that kill a lot of fish.

The dinoflagellates that live in corals help the tiny coral animals, however--because they arephotosynthetic, they make extra food to give to their coral hosts, and they may help the coral make its mineral skeleton. When corals become stressed, however, the dinoflagellates can die or be expelled, and this is what is called "bleaching." Corals can become bleached for many different reasons, but one of the most important is higher temperatures (as you said). Although bleached corals can sometimes survive and regain their dinoflagellates, bleached corals grow and reproduce more slowly and are more likely to die. Coral bleaching has become much more common beginning in the 1980s, and with human-induced global warming represents a major threat to one of the Earth's grandest ecosystems. Answer 3: Yes, coral is definitely bleached by higher temperatures! I actually wrote an article all about coral bleaching for The Santa Barbara Independent last September, and talked about temperature affecting coral health in it -- this is the relevant part to your question: "The foundation of coral reefs is an ancient symbiotic relationship between coral and microscopic algae.

The single-celled, golden-brown algae, called zooxanthellae (genus Symbiodinium), are less than 0.01 millimeters in diameter, yet they are a fundamental part of most coral reef systems. The relationship between the coral and the zooxanthellae is mutualistic: Both gain something from it. This relationship works so well that, based on fossils, its been around for over 240 million years (since the Triassic period). While this relationship has endured the test of time, it is possibly being challenged more now than ever before, and, with it, the whole structure of coral reefs worldwide. Over the last 20 to 30 years, there has been a significant increase in coral bleaching. Bleaching occurs when the water temperatures increase only two to three degrees Fahrenheit above the normal temperatures. For reasons not fully understood, this causes the zooxanthellae, which are normally bound in the corals endodermis cells, to be expelled from the coral. If the coral does not get the zooxanthellae back within a month, the coral dies. The remaining coral skeleton is white, or bleached.

In 1998, an El Nino year, around 16 percent of the coral reefs worldwide were destroyed by bleaching. In the August 27, 2010, issue of the magazine Science, Clive Wilkinson, a reef expert at Australias Reef and Rainforest Research Center in Townsville, predicted that this year may be worse than 1998, which would be especially disastrous for the many reefs that have not yet recovered from 1998. If temperatures continue to increase, as some experts predict they will, in about 25 to 60 years most reefs will be damaged too greatly to ever recover. However, there is some evidence to suggest that there may be zooxanthellae that are temperature tolerant, and more resistant to bleaching; this has been especially seen in the fast-growing coral Acropora." Corals prefer to live in water temperatures that average around 82 degrees Fahrenheit and have minor fluctuations (highs of 85F and lows of 75F).

To see the article in its entirety, you can go to this website: coral-reefs Answer 4: Coral bleaching consists of the corals expelling the algae that live in their tissues that give the corals their color. Corals do this when stressed and high temperature is certainly one way this can happen, but not the only way. Not all corals respond the same way, either, and some coral die-offs are due to other effects such as infections (e.g. white band disease). Click Here to return to the search form. Copyright © 2015 The Regents of the University of California, All Rights Reserved. Coral bleaching - GBRMPA Marine debris Coral bleaching As the climate changes, coral bleaching is predicted to become more frequent and severe. Sea temperature increases and coral stress from other impacts may increase corals' vulnerability to bleaching. As part of its Reef Health Incident Response System, the Great Barrier Reef Marine Park Authority has a Coral Bleaching Response Plan for detecting and responding to coral bleaching on the Great Barrier Reef.

What is coral bleaching Many types of coral have a special symbiotic relationship with a tiny marine algae (zooxanthellae) that live inside corals' tissue and are very efficient food producers that provide up to 90 per cent of the energy corals require to grow and reproduce. Coral bleaching occurs when the relationship between the coral host and zooxanthellae, which give coral much of their colour, breaks down. Without the zooxanthellae, the tissue of the coral animal appears transparent and the coral's bright white skeleton is revealed. Corals begin to starve once they bleach. While some corals are able to feed themselves, most corals struggle to survive without their zooxanthellae. If conditions return to normal, corals can regain their zooxanthellae, return to their normal colour and survive. However, this stress is likely to cause decreased coral growth and reproduction, and increased susceptibility to disease. Bleached corals often die if the stress persists. Coral reefs that have high rates of coral death following bleaching can take many years or decades to recover.

What causes coral bleaching The main cause of coral bleaching is heat stress resulting from high sea temperatures.Temperature increases of only one degree celsius for only four weeks can trigger bleaching events. If these temperatures persist for longer periods (eight weeks or more) corals begin to die. High water temperatures can affect reefs at regional and global scale. Other stressors can also cause bleaching, including freshwater inundation (low salinity) and poor water quality from sediment or pollutant run-off. Coral bleaching on the Great Barrier Reef The Great Barrier Reef has experienced mass coral bleaching events in the past. In 1998, there was a global mass bleaching event where 50 per cent of the reefs on the Great Barrier Reef suffered bleaching. During this time, sea temperatures on the Great Barrier Reef were the highest ever recorded. Mass bleaching also occurred in 2002, with 60 per cent of reefs were affected. This was the largest coral bleaching event on record. Two periods of hot weather resulted in sea surface temperatures a few degrees centigrade higher than long-term summer maxima. In both events, about five per cent of the Great Barrier Reef's coral reefs were severely damaged.

Coral Reefs and Climate Change - How does climate change affect coral reefs - Teach Ocean Science Coral Reefs and Climate Change How does climate change affect coral reefs? The warmer air and ocean surface temperatures brought on by climate change impact corals and alter coral reef communities by prompting coral bleaching events and altering ocean chemistry. These impacts affect corals and the many organisms that use coral reefs as habitat. Climate change leads to coral bleaching Warmer water temperatures brought on by climate change stress corals because they are very sensitive to changes in temperature. If water temperatures stay higher than usual for many weeks, the zooxanthellae they depend on for some of their food leave their tissue. Without zooxanthellae, corals turn white because zooxanthellae give corals their color. White, unhealthy corals are called bleached. Bleached corals are weak and less able to combat disease. Bleaching events on coral reefs around the globe were observed in 1998 (West and Salm 2003). In some Pacific islands, a little bit of bleaching is common in the summer; however, there have been times when bleaching is particularly bad in this region (Craig 2009).

For example, larger than normal bleaching events in the National Park of American Samoa occurred in 1994, 2002, and 2003 (Craig 2009). As climate change continues, bleaching will become more common, and the overall health of coral reefs will decline. Climate change alters ocean chemistry leading to ocean acidification Much of the carbon dioxide that enters the atmosphere dissolves into the ocean. In fact, the oceans have absorbed about 1/3 of the carbon dioxide produced from human activities since 1800 and about 1/2 of the carbon dioxide produced by burning fossil fuels (Sabine et al. 2004). As carbon dioxide in the ocean increases, ocean pH decreases or becomes more acidic. This is called ocean acidification. With ocean acidification, corals cannot absorb the calcium carbonate they need to maintain their skeletons and the stony skeletons that support corals and reefs will dissolve. Already, ocean acidification has lowered the pH of the ocean by about 0.11 units (SCOR 2009).

Moving the ocean's pH from 8.179 to a current pH of 8.069, which means the ocean is about 30% more acidic now than it was in 1751 (SCOR 2009). If nothing is done to reduce carbon dioxide emissions into the atmosphere, ocean acidification will increase and more and more corals will be damaged or destroyed. Ocean acidification affects more than just corals. Snails, clams, and urchins also make calcium carbonate shells and ocean acidification negatively impacts these organisms as well. Just like corals, ocean acidification makes it harder for these organisms to absorb the calcium carbonate they need to build their shells. If we continue to produce carbon dioxide at the current rate, future atmospheric carbon dioxide will be high enough to lower ocean surface pH to 7.8 by the year 2100 (Royal Society 2008). Scientists have done laboratory studies that suggest a pH about this low could dissolve coral skeletons and may cause reefs to fall apart (Fine and Tchernov 2006). If coral reefs are lost, vital habitat will be lost too.

The future health of coral reefs and many marine organisms depends on our ability to reduce our carbon dioxide emissions on a global scale. Future emissions depend on how many people there are on the planet, what energy sources we use, how much energy we use, what new technologies we create—just to name a few factors. So, how do scientists investigate what the world will look like in the future if it is not know what future greenhouse gas emissions will be? They try to make predictions about what the world will look like in the future by using different scenarios. For example, scientists from all over the world work together on the Intergovernmental Panel on Climate Change (IPCC) to generate models that reflect different rates of population growth, economic growth, technology application, and social change. These models help us understand what climate change means for our future and have predicted how the ocean pH may decrease as carbon dioxide emissions increase. Of course, climate change affects more than just coral reefs and has implications for national parks outside of the Pacific Island Network. Explore how other parks are anticipate the impacts of climate change on their ecosystems. ʻIno ka moana ke ahu mōkākī nei ka puna i uka.

The sea is rough, for the corals are strewn on the beach. (Here are all the indications that there is trouble yonder.) This Hawaiian proverb reminds us the sky and ocean are connected, with the conditions of the atmosphere influencing those of the ocean. Corals and Coral Reefs | Smithsonian Ocean Portal Corals and Coral Reefs by The Ocean Portal Team; Reviewed by Nancy Knowlton, Smithsonian NMNH Corals, sponges and seaweeds cover most of the surface of many coral reefs . Credit: Wolcott Henry Coral reefs are the most diverse of all marine ecosystems. They teem with life, with perhaps one quarter of all ocean species depending on reefs for food and shelter. This is a remarkable statistic when you consider that reefs cover just a tiny fraction (less than one percent) of the earth’s surface and less than two percent of the ocean bottom. Because they are so diverse, coral reefs are often called the rainforests of the sea. Coral reefs are also very important to people. The value of coral reefs has been estimated at 30 billion U.S. dollars and perhaps as much as 172 billion U.S.

dollars each year , providing food, protection of shorelines, jobs based on tourism, and even medicines. Unfortunately, people also pose the greatest threat to coral reefs. Overfishing and destructive fishing, pollution, warming, changing ocean chemistry, and invasive species are all taking a huge toll. In some places, reefs have been entirely destroyed, and in many places reefs today are a pale shadow of what they once were. What Are Corals? Animal, Vegetable & Mineral The brownish-green specks are the zooxanthellae that most shallow, warm-water corals depend on for much of their food. Credit: © osf.co.uk. All rights reserved. Corals are related to sea anemones, and they all share the same simple structure, the polyp. The polyp is like a tin can open at just one end: the open end has a mouth surrounded by a ring of tentacles. The tentacles have stinging cells, called nematocysts, that allow the coral polyp to capture small organisms that swim too close. Inside the body of the polyp are digestive and reproductive tissues. Corals differ from sea anemones in their production of a mineral skeleton.

Shallow water corals that live in warm water often have another source of food, the zooxanthellae (pronounced zo-o-zan-THELL-ee). These single-celled algae photosynthesize and pass some of the food they make from the sun’s energy to their hosts, and in exchange the coral animal gives nutrients to the algae. It is this relationship that allows shallow water corals to grow fast enough to build the enormous structures we call reefs. The zooxanthellae also provide much of the color that corals have. Coral Diversity Flower-like clusters of pink polyps make up this coral colony. Credit: Photo Collection of Dr. James P. McVey, NOAA Sea Grant Program In the so-called true stony corals, which compose most tropical reefs, each polyp sits in a cup made of calcium carbonate. Stony corals are the most important reef builders, but organpipe corals , precious red corals , and blue corals also have stony skeletons. There are also corals that use more flexible materials or tiny stiff rods to build their skeletons—the seafans and sea rods, the rubbery soft corals, and the black corals.

The family tree of the animals we call corals is complicated, and some groups are more closely related to each other than are others. All but the fire corals (named for their strong sting) are anthozoans , which are divided into two main groups. The hexacorals (including the true stony corals and black corals, as well as the sea anemones) have smooth tentacles, often in multiples of six, and the octocorals (soft corals, seafans, organpipe corals and blue corals) have eight tentacles, each of which has tiny branches running along the sides. All corals are in the phylum Cnidaria , the same as jellyfish. Reproduction A purple hard coral releases bundles of pink eggs glued together with sperm. Credit: Chuck Savall Corals have multiple reproductive strategies – they can be male or female or both, and can reproduce either asexually or sexually. Asexual reproduction is important for increasing the size of the colony, and sexual reproduction increases genetic diversity and starts new colonies that can be far from the parents.

ASEXUAL REPRODUCTION Asexual reproduction results in polyps or colonies that are clones of each other - this can occur through either budding or fragmentation. Budding is when a coral polyp reaches a certain size and divides, producing a genetically identical new polyp. Corals do this throughout their lifetime. Sometimes a part of a colony breaks off and forms a new colony. This is called fragmentation, which can occur as a result of a disturbance such as a storm or being hit by fishing equipment. SEXUAL REPRODUCTION In sexual reproduction, eggs are fertilized by sperm, usually from another colony, and develop into a free-swimming larva. There are two types of sexual reproduction in corals, external and internal. Depending on the species and type of fertilization, the larvae settle on a suitable substrate and become polyps after a few days or weeks, although some can settle within a few hours! Most stony corals are broadcast spawners and fertilization occurs outside the body (external fertilization). Colonies release huge numbers of eggs and sperm that are often glued into bundles (one bundle per polyp) that float towards the surface.

Spawning often occurs just once a year and in some places is synchronized for all individuals of the same species in an area. This type of mass spawning usually occurs at night and is quite a spectacle. Some corals brood their eggs in the body of the polyp and release sperm into the water. As the sperm sink, polyps containing eggs take them in and fertilization occurs inside the body (internal fertilization). Brooders often reproduce several times a year on a lunar cycle. Video of How Coral Reefs Spawn From Corals to Reefs Coral Growth Ultraviolet light illuminates growth rings in a cross-section of 44-year-old Primnoa resedaeformis coral found about 400 m (1,312 ft) deep off the coast of Newfoundland. Credit: Owen Sherwood Individual coral polyps within a reef are typically very small—usually less than half an inch (or ~1.5 cm) in diameter. The largest polyps are found in mushroom corals , which can be more than 5 inches across. But because corals are colonial, the size of a colony can be much larger: big mounds can be the size of a small car, and a single branching colony can cover an entire reef.

Reefs, which are usually made up of many colonies, are much bigger still. The largest coral reef is the Great Barrier Reef , which spans 1,600 miles (2,600 km) off the east coast of Australia. It is so large that it can be seen from space ! It takes a long time to grow a big coral colony or a coral reef, because each coral grows slowly. The fastest corals expand at more than 6 inches (15 cm) per year, but most grow less than an inch per year. Reefs themselves grow even more slowly because after the corals die, they break into smaller pieces and become compacted. Individual colonies can often live decades to centuries, and some deep-sea colonies have lived more than 4000 years . One way we know this is because corals lay down annual rings, just as trees do. These skeletons can tell us about what conditions were like hundreds or thousands of years ago. The Great Barrier Reef as it exists today began growing about 20,000 years ago. Where are Reefs Found? Shallow water coral reefs straddle the equator worldwide.

Credit: ©UNEP World Conservation Monitoring Centre/Global 1KM Version 7.0 Dataset Corals are found across the world’s ocean, in both shallow and deep water, but reef-building corals are only found in shallow tropical and subtropical waters. This is because the algae found in their tissues need light for photosynthesis and they prefer water temperatures between 70-85°F (22-29°C). There are also deep-sea corals that thrive in cold, dark water at depths of up to 20,000 feet (6,000 m). Both stony corals and soft corals can be found in the deep sea. Deep-sea corals do not have the same algae and do not need sunlight or warm water to survive, but they also grow very slowly. One place to find them is on underwater peaks called seamounts . Scientists have been studying why populations of crown-of-thorns sea stars ( Acanthaster planci ) have mushroomed in recent decades. Coral reefs can suffer when the sea star's numbers explode; the echinoderm has a healthy appetite and few predators. Credit: Klaus Jost, Reefs are the big cities of the sea.

They exist because the growth of corals matches or exceeds the death of corals – think of it as a race between the construction cranes (new coral skeleton) and the wrecking balls (the organisms that kill coral and chew their skeletons into sand). When corals are babies floating in the plankton, they can be eaten by many animals. They are less tasty once they settle down and secrete a skeleton, but some fish, worms , snails and sea stars prey on adult corals. Crown-of-thorns sea stars are particularly voracious predators in many parts of the Pacific Ocean. Population explosions of these predators can result in a reef being covered with tens of thousands of these starfish, with most of the coral killed in less than a year. Corals also have to worry about competitors. They use the same nematocysts that catch their food to sting other encroaching corals and keep them at bay. Seaweeds are a particularly dangerous competitor, as they typically grow much faster than corals and may contain nasty chemicals that injure the coral as well. Corals do not have to only rely on themselves for their defenses because mutualisms (beneficial relationships) abound on coral reefs.

The partnership between corals and their zooxanthellae is one of many examples of symbiosis, where different species live together and help each other. Some coral colonies have crabs and shrimps that live within their branches and defend their home against coral predators with their pincers. One kind of goby chews up a particularly nasty seaweed, and even benefits by becoming more poisonous itself. These bleached corals in the Gulf of Mexico are the result of increased water temperatures. Credit: Emma Hickerson/NOAA GLOBAL THREATS The greatest threats to reefs are rising water temperatures and ocean acidification linked to rising carbon dioxide levels. High water temperatures cause corals to lose the microscopic algae that produce the food corals need—a condition known as coral bleaching . Severe or prolonged bleaching can kill coral colonies or leave them vulnerable to other threats. Meanwhile, ocean acidification means more acidic seawater, which makes it more difficult for corals to build their calcium carbonate skeletons. And if acidification gets severe enough, it could even break apart the existing skeletons that already provide the structure for reefs. LOCAL THREATS Unfortunately, warming and more acid seas are not the only threats to coral reefs .

Overfishing and overharvesting of corals also disrupt reef ecosystems. If care is not taken, boat anchors and divers can scar reefs. Invasive species can also threaten coral reefs. The lionfish , native to Indo-Pacific waters, has a fast-growing population in waters of the Atlantic Ocean. With such large numbers the fish could greatly impact coral reef ecosystems through consumption of, and competition with, native coral reef animals. Even activities that take place far from reefs can have an impact. Runoff from lawns, sewage, cities, and farms feeds algae that can overwhelm reefs . Deforestation hastens soil erosion, which clouds water—smothering corals. Compare the healthy coral on the left with the bleached coral on the right. Credit: Wolcott Henry “Coral bleaching” occurs when coral polyps lose their symbiotic algae, the zooxanthellae. Without their zooxanthellae, the living tissues are nearly transparent, and you can see right through to the stony skeleton, which is white, hence the name coral bleaching.

Many different kinds of stressors can cause coral bleaching – water that is too cold or too hot, too much or too little light, or the dilution of seawater by lots of fresh water can all cause coral bleaching. The biggest cause of bleaching today has been rising temperatures caused by global warming. Temperatures more than 2 degrees F (or 1 degree C) above the normal seasonal maximimum can cause bleaching. Bleached corals do not die right away, but if temperatures are very hot or are too warm for a long time, corals either die from starvation or disease. In 1998, 80 percent of the corals in the Indian Ocean bleached and 20 percent died. Protecting Coral Reefs Losing Our Coral Reefs Losing Our Coral Reefs Comments New Guinea coral reef. Photo credit: Mbz1 at en.wikipedia Coral reefs, the “rainforests of the sea,” are some of the most biodiverse and productive ecosystems on earth.

They occupy only .2% of the ocean, yet are home to a quarter of all marine species: crustaceans, reptiles, seaweeds, bacteria, fungi, and over 4000 species of fish make their home in coral reefs. With an annual global economic value of $375 billion, coral reefs provide food and resources for over 500 million people in 94 countries and territories. But tragically, coral reefs are in crisis. Coral reefs are endangered by natural phenomena such as hurricanes, El Nino, and diseases; local threats including overfishing, destructive fishing techniques, coastal development, pollution, and careless tourism; and the global effects of climate change—warming seas and increasing levels of CO2 in the atmosphere. According to Reefs at Risk Revisited, a recent report by the World Resources Institute (WRI), 75% of the world’s coral reefs are at risk from local and global stresses. Ten percent of coral reefs have already been damaged beyond repair, and if we continue with business as usual, WRI projects that 90% of coral reefs will be in danger by 2030, and all of them by 2050.

Coral reefs are colonies of individual animals called polyps, which are related to sea anemones. The polyps, which have tentacles to feed on plankton at night, play host to zooxanthellae, symbiotic algae that live within their tissues and give the coral its color. The coral provides CO2 and waste products that the algae need for photosynthesis. In turn, the algae nourish the coral with oxygen and the organic products of photosynthesis. The coral uses these compounds to synthesize calcium carbonate (limestone) with which it constructs its skeleton—the coral reef. The symbiotic relationship between corals and zooxanthellae can only exist within the narrow band of environmental conditions found in tropical and subtropical waters. The water must be clear and shallow so that the light algae need for photosynthesis can penetrate, and water temperatures must ideally remain between 23˚ and 29˚ C (77˚ to 84˚ F). The number of coral species in each reef varies: the Great Barrier Reef off Australia has over 500 species of coral while a Caribbean reef has about 50. Today many reefs have 40%-50% less coral than they did just 30 years ago.

Coral reef locations Natural phenomena such as hurricanes or prolonged cold and rainy weather can harm coral reefs. The El Nino weather pattern, which can result in lower sea level, altered salinity due to too much rainfall, and elevated sea-surface temperatures, can also damage coral. When corals become overheated, they react to the stress by expelling their symbiotic zooxanthellae, which results in coral bleaching. Bleached staghorn coral. Photo credit: Matt Kieffer If the bleaching is mild or short-term, corals can recover as algae recolonize, but if the bleaching lasts too long, corals starve to death. Other natural phenomena that stress coral reefs include predators such as parrotfish, barnacles, crabs and crown-of-thorns starfish, and diseases. Of local threats to coral reefs, overfishing and damaging fishing techniques such as deep water trawling and the use of explosives and cyanide, are the most destructive. When herbivorous fish that eat seaweed are overfished, uncontrolled seaweed growth can smother corals. Coastal development results in erosion, and runoff containing the excess sediment can block the light zooxanthellae need.

Nutrient-rich fertilizer runoff and sewage effluent can boost algae growth, which starves the water of oxygen, causing eutrophication. Pollution from land, including hot water releases from power plants, pathogens, and trash, and from marine activities, such as fuel leaks and oil spills, also endangers coral reefs. Tourism, while relying on the appeal of coral reefs, can be damaging when careless divers trample on corals or break off pieces as souvenirs. In addition more and more coral and tropical fish are being harvested for the aquarium trade. The global effects of climate change are also having critical impacts on coral reefs, and “the evidence is overwhelming that the ability of corals and the reefs they build to keep pace with the current rate of climate change has been exceeded” according to a recent study . The average temperature of tropical oceans has increased by .7˚ C which, combined with natural fluctuations of warmer ocean temperatures, has resulted in extensive coral bleaching around the globe, involving thousands of square miles of reefs.

When El Nino occurred in 1997-1998, widespread and severe coral reef bleaching occurred in the Indo-Pacific region and the Caribbean, killing 16% of the world’s coral reefs in 12 months. Photo credit: World Resources Institute The 2010 El Nino has also resulted in massive bleaching around the world. Scientists don’t yet understand the long-term impacts of coral bleaching, but they do know that bleaching leaves corals vulnerable to disease, stunts their growth, and affects their reproduction, while severe bleaching kills them. The 30 million tons of carbon dioxide our oceans absorb every day is changing the chemistry of seawater and increasing acidification. Today, coral reefs are experiencing warmer ocean temperatures and more acidity than they have at any time in the last 400,000 years. Acidification reduces the water’s carrying capacity for calcium carbonate that corals need to build their skeletons. Even a small decrease in the coral’s ability to construct its skeleton can leave it vulnerable to erosion, and research suggests that coral reefs will begin to dissolve if atmospheric carbon dioxide levels double this century.

It’s estimated that by 2050, only 15% of coral reefs will have enough calcium carbonate for adequate growth. A new study also shows that ocean acidification profoundly alters coral reef ecosystems. As C02 levels rise and acidification increases, the biodiversity of coral reefs drops, resulting in the elimination of key species needed for healthy reef formation. “The decline of the structurally complex corals means the reef will be much simpler and there will be less habitat for the hundreds of thousands of species we associate with today’s coral reefs,” said Katherina Fabricius, a scientist at the Australian Institute of Marine Science. All of these factors act in concert on coral reefs, and complex interactions between the threats leave coral reefs even more vulnerable. Climate change will also bring sea level rise that may result in drowned coral reefs, and more intense storms that produce excessive nutrient or sediment runoff. The overfishing of herbivorous fish and excess nutrients decrease coral’s resilience in the face of increased CO2. Rising ocean acidity lowers the threshold at which corals bleach.

If we reach 450 parts per million of C02 in the atmosphere (as of 2010, we were at 388 ppm) ocean temperatures will rise 2˚ C, calcium carbonate levels in the oceans will decrease, and we will largely destroy all our coral reefs. Coral reefs provide us with food, construction materials (limestone) and new medicines—more than half of new cancer drug research is focused on marine organisms. They offer shoreline protection and maintain water quality. And they are a draw for tourists, sometimes providing up to 80% of a country’s total income. Losing the coral reefs would have profound social and economic impacts on many countries, especially small island nations like Haiti, Fiji, Indonesia, and the Philippines that depend on coral reefs for their livelihoods. What can be done to save these precious and beautiful ecosystems? Reefs at Risk Revisited calls for the expansion of Marine Protected Areas (MPAs) where fishing and fishing methods are regulated, curbing unsustainable fishing, better management of coastal development, and the reduction of both land and marine-based pollution.

It also recommends comprehensive ecosystem management that includes all stakeholders, and stresses the need to invest in scientific research and educate the public about the importance of coral reefs. It’s crucial, of course, for national and international bodies, and for all of us to address the threats of climate change by curbing carbon emissions. The Coral Restoration Foundation protects and restores coral reefs through creating coral nurseries and transplanting corals into degraded reef areas. Concerned individuals can adopt a coral through the Coral Restoration Foundation or a coral reef through the Nature Conservancy , which uses the funds to conduct research, promote marine conservation and support the creation of MPAs. MPAs, which are being created worldwide, protect biodiversity and help communities manage resources sustainably. Great Barrier Reef. Photo credit: Richard Ling The Great Barrier Reef is the largest and richest coral reef in the world because it has been protected since the early 1970s. The creation of an MPA off St. Lucia in the Caribbean has resulted in a tripling of the fish population. Everyone can help coral reefs by practicing sustainable fishing, and eating only sustainably caught fish. When vacationing near coral reefs, be careful not to touch them and don’t buy souvenirs of coral or other marine species.

CERC students who want to learn more about coral reefs can take CERC’s spring break Coral Reef Ecology course in Bermuda in March 2012. It deals with the biology and microbiology of corals, the ecology of coral communities, anthropogenic factors that impact coral reefs, and coral reef restoration and sustainability. Tags: 7 thoughts on “Losing Our Coral Reefs” Fly Shop What is coral bleaching? Home Ocean Facts What is coral bleaching? What is coral bleaching? When corals are stressed by changes in conditions such as temperature, light, or nutrients, they expel the symbiotic algae living in their tissues, causing them to turn completely white. Can coral survive a bleaching event? If the stress-caused bleaching is not severe, coral have been known to recover. If the algae loss is prolonged and the stress continues, coral eventually dies. Warmer water temperatures can result in coral bleaching. When water is too warm, corals will expel the algae (zooxanthellae) living in their tissues causing the coral to turn completely white. This is called coral bleaching. When a coral bleaches, it is not dead.

Corals can survive a bleaching event, but they are under more stress and are subject to mortality. In 2005, the U.S. lost half of its coral reefs in the Caribbean in one year due to a massive bleaching event. The warm waters centered around the northern Antilles near the Virgin Islands and Puerto Rico expanded southward. Comparison of satellite data from the previous 20 years confirmed that thermal stress from the 2005 event was greater than the previous 20 years combined. Not all bleaching events are due to warm water. In January 2010, cold water temperatures in the Florida Keys caused a coral bleaching event that resulted in some coral death. Water temperatures dropped 12.06 degrees Fahrenheit lower than the typical temperatures observed at this time of year. Researchers will evaluate if this cold-stress event will make corals more susceptible to disease in the same way that warmer waters impact corals. Search Our Facts

Question: What type of sea creature can become "bleached" if the water temperatures is too high?
Answer: Coral