bleaching

Trouble for clownfishes

October 27, 2025 By EarthWise Leave a Comment

Clownfishes or anemonefishes are colorful saltwater fishes that mainly inhabit coral reefs in the warm and tropical waters of the Indo-Pacific. Clownfishes have a symbiotic and mutually beneficial relationship with sea anemones, which they rely on for shelter and protection from predators. In turn, clownfishes will protect the anemone from anemone-eating fish, as well as clean and fan them. The popular film Finding Nemo is about a clownfish who lives in a secluded sea anemone.

The Red Sea, circled by Middle Eastern deserts, is home to marine life that is accustomed to very warm water – often 85 to 90 degrees during the summer. However, in the past three years marine heat waves have made the Red Sea even hotter. The rising sea temperatures have caused a breakdown in the symbiotic relationship between clownfish and anemones.

Anemones have a symbiotic relationship of their own with the same microscopic algae that pair with coral. Just as is the case with coral, anemones expel the algae from their tissues during periods of high heat, causing them to bleach. Prolonged bleaching can result in the death of the anemone and, in turn, exposes the clownfish to danger.

Researchers from Boston University monitoring three Red Sea reefs over a three-year period found that the marine heatwave in 2023 resulted in the death of 94 to 100% of the clownfish and 66-94% of the anemones. Rising ocean temperatures can be devastating for many sea creatures.

Anemones are not as well-studied as coral, so it is not clear whether their populations can recover, particularly once the clownfish are gone, making them much more vulnerable to their own predators.

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Clownfish and Anemones Are Disappearing Because of Climate Change

Photo, posted March 9, 2016, courtesy of John Voo via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

Marine heatwaves are spreading

July 21, 2025 By EarthWise Leave a Comment

Sea surface temperatures broke records in 2024 and a quarter of the world’s oceans are experiencing temperatures that qualify as a marine heatwave. A marine heatwave is a prolonged period during which ocean temperatures are significantly warmer than average for that specific location and time of year.

Unusual heatwaves have occurred in all the major ocean basins around the planet in recent years and some have become so intense that they are being called super marine heatwaves.

The seas off the coasts of the UK and Ireland experienced an unusually intense and long-lasting marine heatwave starting in April. Australia was recently struck by heatwaves on two coasts.

Hotter oceans are causing drastic changes to marine life, sea levels, and weather patterns. Some of the most apparent casualties of ocean warming have been coral reefs. About 84% of reefs worldwide experienced bleaching-level heat stress at some point between January 2023 and March 2025.

Excess heat in the oceans can affect weather patterns, making hurricanes more likely to rapidly intensify and become more destructive.

A recent study published in Proceedings of the National Academy of Sciences concluded that climate change has been responsible for the overwhelming majority of marine heatwaves in recent decades.

People are learning to forecast these events. Eventually, parts of the ocean might enter a constant state of marine heatwave, at least by how it is defined today. Studying what is going on in the oceans today may provide insights into the future of the world’s oceans and provide guidance on how to try to achieve different outcomes.

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See How Marine Heat Waves Are Spreading Across the Globe

Photo, posted December 5, 2015, courtesy of Susanne Nilsson via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

Corals and climate change

December 24, 2024 By EarthWise Leave a Comment

Climate change is a major threat to coral reefs around the world. Ocean warming triggers coral bleaching – a stress response where corals expel the symbiotic algae essential for their survival. If coral bleaching is severe, it can lead to coral death.

A new study led by scientists from Newcastle University in England suggests that corals are unlikely to adapt to ocean warming quickly enough to keep pace with global warming, unless there are rapid reductions in global greenhouse gas emissions.

The study, which was recently published in the journal Science, found that coral heat tolerance adaptation via natural selection could keep pace with ocean warming, but only if the climate goals of the Paris Agreement are realized. In the Paris Agreement, countries agreed to limit global warming by the end of the century to two degrees Celsius above pre-industrial levels.

However, current climate policies around the world have the globe on track to warm by three degrees Celsius. According to the research team, this could lead to significant reductions in reef health, elevated risks of local coral extinctions, and considerable uncertainty in the so-called “evolvability” of corals.

Coral reefs are among the most biologically diverse ecosystems on Earth. They are often referred to as the “rainforests of the sea” because they support an incredible variety of marine life. They provide essential ecosystem services, such as protecting coastlines from erosion and storm surges, supporting fisheries, and serving as a source of income through tourism. Coral reef health is vital for the health of the planet.

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Coral adaptation unlikely to keep pace with global warming

Photo, posted June 9, 2012, courtesy of Bokissa Private Island Resort via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

Mixed news for the Great Barrier Reef

August 27, 2024 By EarthWise Leave a Comment

A prolonged and widespread coral bleaching event in Australia’s Great Barrier Reef has taken place this year. It is the fifth such event over the past eight years and appears to be one of the worst ever. According to preliminary analysis, 97% of corals in some areas of the northern part of the reef died as a result of the bleaching. Over the entire length of the reef – which is more than 1,200 miles long – bleaching was observed on 74% of the more than 1,000 individual reefs that make up the Great Barrier Reef. Half of those observed recorded high or very high levels of bleaching, although less than 10% had extreme levels of bleaching.

Prior to this mass bleaching event, an extensive survey of the reef was conducted, and it provided some good news. Coral cover had increased in all three regions on the Great Barrier Reef and was actually at regional highs in two of the three regions. The surveys were completed before the passage of Tropic Cyclone Jasper in December 2023.

Bleached corals are very stressed, but they still remain alive for at least some period of time. Some types of corals can remain bleached for months, hanging on like a hospital patient in critical condition, but then recover. Depending upon water conditions going forward, it remains to be seen how much of the reef will survive the latest bleaching event. The next survey season by the Australian Institute of Marine Science will commence in September.

In many ways, the reef has had some lucky escapes in recent years. As marine heatwaves become increasingly common, its luck may eventually run out.

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New report on Great Barrier Reef shows coral cover increases before onset of serious bleaching, cyclones

Photo, posted 8, 2023, courtesy of Chris Hoare via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

Global coral bleaching

May 22, 2024 By EarthWise Leave a Comment

The world’s coral reefs are in the midst of a global bleaching event being driven by extraordinarily high ocean temperatures. This is the fourth such global event on record and is predicted to be the largest one ever. Coral bleaching occurs when corals are stressed by heat and eject the symbiotic algae within them that they need to survive. Bleached corals can recover if water temperatures cool soon enough. Otherwise, they die.

Each of the three previous coral bleaching events has been worse than the last. The first, in 1998, affected 20% of the world’s reefs. The second, in 2010, affected 35%. The third, from 2014 to 2017, affected 56% of reefs.

The current bleaching event was confirmed by satellite observations early in April and was already seen to be affecting more than half of the world’s coral areas across the Pacific, Indian, and Atlantic Oceans. The ongoing event is expected to be the worst bleaching ever experienced by Australia’s Great Barrier Reef. A small saving grace is that the current bleaching event is not expected to be of extremely long duration because the El Niño in the Pacific has abated.

Coral bleaching events are becoming more severe and frequent due to increased marine heat waves driven by climate change. Last year was particularly difficult for corals as global sea temperatures reached record high levels for several months.

Widespread coral bleaching impacts economies, livelihoods, food security, and more. Coral reefs provide ecosystem services essential to marine life and human populations as well. Global action will be needed for coral interventions and restorations.

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Satellites watch as 4th global coral bleaching event unfolds

Photo, posted March 23, 2012, courtesy of Oregon State University via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

Artificial reefs

May 8, 2024 By EarthWise Leave a Comment

The coral reefs that surround tropical islands are a refuge for a wide variety of marine life and also form a natural buffer against stormy seas. The changing climate is bleaching coral reefs and breaking them down. Extreme weather events are becoming more common and are threatening coastal communities with flooding and erosion.

Researchers at MIT are designing architected reefs – sustainable offshore structures that mimic the wave-buffering effects of natural reefs and can also provide habitats for fish and other marine life.

There are already artificial reefs in a number of places used to protect coastlines. These are typically made from sunken ships, retired oil and gas platforms, and even assemblies of concrete, metal, car tires, and stones. Generally, it takes quite a lot of material to form an effective barrier to waves.

The MIT group has developed a cylindrical structure surrounded by four rudder-like slats. Their experiments have shown that when this structure stands in the way of a wave, it efficiently breaks the wave and creates turbulent jets that dissipate the energy in the wave. The engineers calculated that the new design could reduce as much wave energy as existing artificial reefs but use 10 times less material.

Based on the initial experiments with lab-scale prototypes, these artificial reefs would reduce the energy of incoming waves by more than 95%.

Coral reefs are only found in tropical waters, whereas these artificial reefs don’t depend on temperature and could be placed along any coastline for protection. In a time of rising seas and increasingly frequent storms, these artificial reefs may be just what coastlines need.

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Artificial reef designed by MIT engineers could protect marine life, reduce storm damage

Photo, posted December 9, 2010, courtesy of Phoenix Wolf-Ray via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

Deeper corals bleaching

December 7, 2023 By EarthWise Leave a Comment

When ocean waters get too warm, corals – which are actually tiny animals – eject the colorful algae that inhabit their tissues. The symbiotic relationship between coral polyps and algae is essential to coral survival When the algae is ejected, previously colorful coral turns white, and the coral can ultimately die. If waters cool off, the algae can reestablish themselves and the coral can regain its color and health.

The world’s oceans have been warming at an unprecedented rate, making coral bleaching and die-off a global phenomenon. It is estimated that half of the planet’s reefs have already disappeared. Some places are worse off than others. For example, almost 95% of coral reefs in Southeast Asia are threatened. Florida’s reefs are especially threatened, particularly since there have been unprecedented marine heatwaves off its coast.

It has long been assumed that deeper reefs, where water is cooler, would remain safe from the effects of warming, but a few years ago researchers recorded coral bleaching some 300 feet underwater along the Egmont Atoll in the western Indian Ocean. At one point, bleaching affected 80% of corals in some areas. This discovery came as a huge surprise to oceanographers. It was probably associated with an El Niño-like phenomenon in the waters and those reefs have mostly recovered in the intervening years.

Fairly recently, researchers have found pristine coral reefs deep down in the waters off the Galapagos Islands, where shallow reefs have largely disappeared. There are likely to be similar reefs in the ocean depths around the world, but scientists are expressing concern that even coral reefs lying deep beneath the ocean surface may not ultimately be protected from the warming seas.

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As Oceans Warm, Coral Bleaching Seen at Greater Depths

Photo, posted June 5, 2023, courtesy of Ryan Hagerty / USFWS via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

Saving Florida’s Corals | Earth Wise

September 6, 2023 By EarthWise Leave a Comment

When corals are exposed to extended periods of excess heat, they are subject to bleaching, which occurs when they expel the algae that live within their structure. Bleaching can lead to coral death.

This summer, temperatures in the Florida Keys crossed the bleaching threshold in mid-June and remained above it for extended periods of time. This cumulative heat exposure leads to widespread bleaching and significant die-offs. The last major mass bleaching event in the Florida Keys occurred in 2014 and 2015.

The Coral Restoration Foundation has been receiving reports ranging from partial bleaching to mass coral mortality throughout the keys. Several coral restoration sites in the lower Keys have been totally lost already.

The National Oceanic and Atmospheric Administration and its state agency, university, and non-profit partners have initiated actions to try to save Florida’s corals.

They have halted all restoration-related planting and are evacuating some of their nursery-grown stock to climate-controlled labs. They are considering interventions such as shading coral nurseries or even high-value reef sites. They are also considering feeding nursery and wild corals until the waters cool off enough for algae to return.

Modeling indicates that there is a 70-100% chance that the extreme heat in the North Atlantic will persist through September-October. NOAA and its partners will continue to do what they can to save Florida’s Coral Reef for the marine and human communities that depend on them.

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NOAA and partners race to rescue remaining Florida corals from historic ocean heat wave

Photo, posted April 19, 2012, courtesy of U.S. Fish and Wildlife Service Southeast Region via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

Some Good News For The Great Barrier Reef | Earth Wise

September 5, 2022 By EarthWise Leave a Comment

It seems like there has been nothing but dire news from Australia’s Great Barrier Reef. Earlier this year, there was yet another mass bleaching event – the fourth in seven years and the first ever to strike during a cooler La Niña phase in the Pacific. But this bleaching event was less severe than other recent ones, which makes it possible for parts of the reef to bounce back.

In particular, in the northern and central stretches of the reef, scientists have recorded the most extensive coral cover seen in 36 years of study. In areas where coral cover has expanded, it is mostly fast-growing Acropora corals driving the growth. That isn’t the best outcome, given that Acropora are particularly vulnerable to strong waves, highly susceptible to bleaching, and are the preferred target of crown-of-thorns starfish.

Those creatures are a major problem for the Great Barrier Reef. In contrast to the upper stretches of the reef, the southern third actually saw coral cover drop from 38 to 34 percent over the course of the past year. Scientists blame the decline on an outbreak of crown-of-thorns starfish, which prey on corals. The starfish grow faster and eat more in warmer, more acidic waters. Carbon emissions are both raising ocean temperatures and turning waters more acidic.

The large increases in hard coral cover in the reef are certainly good news, but it is important to understand that they can be quickly negated by disturbance on reefs where Acropora corals predominate. Warming temperatures and mass bleaching events continue to pose a critical threat to all reefs, especially when there are crown-of-thorns starfish outbreaks and increasing frequency of tropical cyclones.

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Parts of Great Barrier Reef See Most Extensive Coral Cover In 36 Years

Photo, posted July 15, 2019, courtesy of Kenneth Lu via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

More Bleaching In The Great Barrier Reef | Earth Wise

April 27, 2022 By EarthWise Leave a Comment

Australia’s Great Barrier Reef is an ecosystem that can be seen from space. It has now suffered its 6^th mass coral bleaching event since 1998. Previous events happened in 1998, 2002, 2006, 2016, and 2017. This latest bleaching has occurred even though this is a La Niña year, when more rain and cooler temperatures are supposed to help protect delicate corals.

An aerial survey of 750 separate reefs across much of the 1500 mile-long Great Barrier Reef system found severe bleaching among 60% of the corals. The bleaching covers an area even wider than the back-to-back outbreaks in 2016 and 2017.

The bleaching is a product of a summer in Australia that started early. December temperatures were already warmer than the historical February summer maximums. Globally, 2021 was the hottest year on record for the world’s oceans for the sixth year in a row.

Bleached coral can recover if temperatures cool down for a long enough period, but this is becoming increasingly rare. Between 2009 and 2019, 14% of the world’s coral reefs were lost for good.

In Australia, the plight of the Great Barrier Reef has become politicized. The current government is not supportive of efforts to reduce the country’s fossil fuel dependence and has worked to keep the reef from being placed on the list of endangered world heritage sites. Instead of pushing for emissions cuts, Australia has focused on a variety of long-shot projects aimed at helping the reef.

The fact is that coral reefs cannot cope with the current rate of warming and unless that slows down soon, they will simply not survive for long.

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‘Can’t Cope’: Australia’s Great Barrier Reef Suffers 6th Mass Bleaching Event

Photo, posted September 28, 2009, courtesy of Matt Kieffer via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

Training Corals To Tolerate Heat | Earth Wise

April 19, 2022 By EarthWise Leave a Comment

When ocean water is too warm, corals expel the algae that lives in their tissues, which causes the coral to turn completely white. This is called coral bleaching. When this happens, the coral is not dead. However, corals are dependent upon the symbiotic relationship with algae and if conditions don’t improve, they don’t let the algae back in and the corals will die.

According to the National Oceanic and Atmospheric Administration, between 2014 and 2017, around 75% of the world’s tropical coral reefs experienced heat stress severe enough to trigger bleaching. For 30% of the world’s reefs, the heat stress was enough to kill the coral.

According to new research by the University of Miami published in the journal Coral Reefs, corals subjected to a stressful regimen of very warm water in the laboratory came to be more tolerant of high temperatures, offering a potential tool for preserving ailing coral reefs.

In the study, some corals were kept in water at a constant temperature of 82 degrees while others saw water temperatures fluctuating between 82 degrees and 88 degrees. After 90 days of this treatment, the corals exposed to variable temperatures were able to tolerate high heat for longer periods before bleaching. This training regime is akin to an athlete preparing for a race.

The findings suggest a possible approach for restoring coral reefs. Nursery-raised corals that are “trained” to tolerate heat could be planted onto reefs endangered by warming waters. Reefs populated by corals with boosted stamina to heat stress could have a greater chance of surviving the warming waters of the oceans.

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Some Corals Can Be Conditioned to Tolerate Heat, Study Finds

Photo, posted December 16, 2015, courtesy of Big Cypress National Preserve via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

Coral Reef Status Report | Earth Wise

December 23, 2021 By EarthWise Leave a Comment

In October, the Global Coral Reef Monitoring Network released the first-ever report collecting global statistics on the world’s corals. It documents the status of reefs across 12,000 sites in 73 countries over 40 years. Overall, the news is not good, but there were some bright spots.

From 2009 to 2018, the world has lost 14% of its corals, corresponding to about 4,500 square miles of coral. Global warming has led to prolonged marine heatwaves that trigger coral bleaching. Local pollution has also damaged reefs. The International Panel on Climate Change has reported that 2 degrees Celsius of global warming would wipe out 99% of the world’s corals.

The report does show that corals can recover globally if given a decade of cooler waters. Some places in the world – particularly the Coral Triangle in Asia, which contains nearly a third of the world’s coral – have actually seen coral growth over the past decade.

The Global Coral Reef Monitoring network started collecting data in 1978. Coral health was fairly steady until 1998 when the first mass bleaching event occurred, triggered by a powerful El Niño event. For the next 12 years, corals recovered nicely, but then bleaching events in 2010 and 2015-17 took their toll.

The Pacific, Australia, and the Caribbean have all seen major decreases in coral. The Coral Triangle is a major exception which is thought to be a result of genetic diversity among the region’s corals.

Coral conservationists globally are working to protect corals and to actively restore them. The situation is fairly dire, but there continue to be reasons for hope.

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Finding Bright Spots in the Global Coral Reef Catastrophe

Photo, posted October 13, 2015, courtesy of Albert Straub via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

Offsetting Reef Acidification | Earth Wise

August 13, 2021 By EarthWise Leave a Comment

The Great Barrier Reef is the world’s largest coral reef system. It is composed of nearly 3,000 individual reefs and 900 islands covering an area of more than 130,000 square miles. In recent times, it has been under unprecedented stress from ocean warming, tropical cyclones, sediment and nutrient runoff, marine pests, and ocean acidification.

Among these stressors, ocean acidification is one of the most significant threats to the long-term viability of the reef because acidification affects the ability of corals to rebuild and repair their structures and recover from bleaching events.

New research from CSIRO, Australia’s national science agency, studied the impact of artificial ocean alkalinization on the acidity of the waters in the Great Barrier Reef. The idea is to inject a source of alkalinity into the ocean, an accelerated version of a natural process that occurs from the chemical weathering of minerals under the sea.

The results of the study, published in the journal Environmental Research Letters, are that injecting an alkalinizing agent into the ocean along the length of the Reef would make it possible to offset ten years’ worth of ocean acidification based on the present rate of human-generated carbon emissions. Such an effort could use an abundant mineral resource like olivine, which is already mined near the Great Barrier Reef. Releasing 30,000 tons a day of the alkalinizing agent from an existing shipping line from a bulk carrier would reach almost the whole of the Great Barrier Reef.

In response to the declining health of coral reef ecosystems, many different intervention concepts and technologies are under consideration. The goal of these would be to minimize environmental pressures and enhance the resilience of the ecosystems.

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Projected acidification of the Great Barrier Reef could be offset by ten years

Photo, posted August 4, 2019, courtesy of Larry Koester via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

Hardier Corals For Endangered Reefs | Earth Wise

July 26, 2021 By EarthWise Leave a Comment

Mass coral bleaching events are getting increasingly frequent as the oceans continue to warm, endangering coral reefs all over the world. The damage to Australia’s Great Barrier Reef has been enormous and in 2015, nearly half of Hawaii’s coral reefs were affected by a severe bleaching event.

Not all coral bleaching is permanent. Corals can sometimes recover. Some corals even seem to resist bleaching altogether. Researchers from the University of Pennsylvania studied these resilient corals to see just how effective they are in resisting the effects of climate change.

Their experiments sought to determine whether corals that seem to resist bleaching can be moved to other locations and used as the seed stock to repopulate degraded reefs.

The researchers identified coral colonies that resisted bleaching during the 2015 Hawaiian bleaching event and collected samples from them. They transplanted some of them to a second reef as well as putting other samples in laboratory tanks and simulating a bleaching event by raising the water temperature over a period of several days.

Careful tracking of the corals’ health showed that the bleaching-resistant corals stayed that way even in a new environment and under additional stress. They also studied how well the corals reproduced and found that the corals that spent time in a favorable new site before being subjected to stress demonstrated greater fitness and improved reproduction.

The study indicates that coral transplantation using colonies known to be resistant to bleaching may be an effective way to buy some time in preserving the world’s coral reefs. But global action on climate change is essential because even bleaching-resistant corals aren’t going to survive forever if ocean warming keeps increasing.

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Climate change-resistant corals could provide lifeline to battered reefs

Photo, posted November 29, 2012, courtesy of Robert Linsdell via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

Climate Change And Dolphins

May 27, 2019 By EarthWise Leave a Comment

We don’t think of heatwaves as something that affects the ocean, but increasingly, as the planet warms, there have been instances where ocean water temperatures become much higher than normal for extended periods of time. There has been much discussion of this phenomenon with regard to coral reefs where the catastrophic rise in coral bleaching events has been the result.

Recently, a study at the University of Zurich looked at the effects of ocean heatwaves on marine life higher in the food chain. They studied the well-known dolphin population in Shark Bay, Western Australia.

In early 2011, a heatwave caused water temperatures in Shark Bay to rise more than 4 degrees above the annual average for an extended period. This led to a substantial loss of seagrass, which is a driving factor in the Shark Bay ecosystem.

The researchers investigated how this environmental damage affected survival and reproduction of dolphins, using long-term data on hundreds of animals collected over a ten-year period from 2007 to 2017.

Their analysis showed that dolphins’ survival rate dropped by 12% and female dolphins were giving birth to fewer calves. That phenomenon that began in 2011 lasted at least until 2017.

The researchers were surprised by the extent and the duration of the influence of the heatwave, especially the fact that the reproductive rate of dolphins had not returned to normal even after 6 years.

This study shows for the first time that marine heatwaves not only affect organisms at the lower levels of the food chain, but also might have considerable long-term consequences for the animals at the top, such as dolphins.

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Climate change is a threat to dolphins’ survival

Photo, posted December 14, 2014, courtesy of Ed Dunens via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

Another Problem For Coral Reefs

April 5, 2019 By EarthWise Leave a Comment

Coral reefs around the world have been suffering in recent years from warming ocean temperatures as well as from increasing ocean acidification. Corals are very sensitive organisms that can only tolerate relatively slight changes in their environment. Thus, the majority of reef-building corals are found in tropical and subtropical waters with favorable conditions.

New research has confirmed that drastic changes in ocean salinity from, for example, severe freshwater flooding, provoke similar stress responses in corals as the heating that has resulted in freshwater bleaching and, eventually, coral death.

The coast of northeast Queensland in Australia has experienced abnormal monsoon-related freshwater flooding that caused extreme and sudden changes in the ocean salt concentration. In places, nearshore reefs were exposed to water with only half the normal ocean salinity. The result has been a shock response in corals that prevents normal cell function. Unlike their response to heat stress, corals exposed to reduced salinity experience a complete collapse of their internal cellular protein balance.

The central Great Barrier Reef has actually been relatively free from mass thermal bleaching events this Australian summer, but many coastal reefs instead have been battling dramatic changes in water conditions as a result of massive plumes of floodwater.

The wild weather in Australia is undoubtedly associated with the changing climate and this new research shows that it is leading to yet another threat to the world’s coral reefs. With the frequency and severity of heavy rainfall and runoff events predicted to continue to increase over the next few decades, proactive measures to increase the resiliency of coral reefs are needed more than ever.

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Reduced salinity of seawater wreaks havoc on coral chemistry

Photo, posted December 12, 2010, courtesy of Gareth Williams via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

Disease On Coral Reefs

February 19, 2019 By EarthWise Leave a Comment

The warming oceans have led to bleaching events in coral reefs around the world, but bleaching is not the only problem corals face. Disease outbreaks are also becoming more frequent, severe, and widespread.

Many factors are contributing to the problem, including pollution and nitrogen runoff from fertilizers and coastal sewer and septic systems. However, the key culprit is likely the steadily increasing ocean temperatures, which are the cause of coral bleaching. Elevated water temperatures can cause coral polyps to expel the algae that sustains them and gives them color.

According to scientists, bleaching makes corals more susceptible to illness. In the Caribbean, a coral disease hotspot, about 80% of coral cover has disappeared, largely from outbreaks of “white band disease”, so called because of a white band of dead tissue that forms in affected corals. Two crucial reef-building species, elkhorn and staghorn coral, are now nearing extinction in the regions. The reef extending along the Florida coastline is the third largest reef ecosystem in the world and nearly 35% of it has been lost to disease.

Estimates are that disease outbreaks have wiped out at least 6% of the corals on the Great Barrier Reef in Australia. In that region, diseases are more prevalent in areas where corals were damaged by fishing and other human activity because wounded coral provides an entry point for pathogens and bacteria.

In the face of climate change and mounting disease outbreaks, scientists are scrambling for solutions to stave off catastrophe. Assisting the migration of hardier coral species and breeding so-called “super corals” are among the strategies being pursued. It is unknown whether these and other forms of intervention can be used on a wide enough scale to really make a difference.

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As Disease Ravages Coral Reefs, Scientists Scramble for Solutions

Photo, posted November 29, 2012, courtesy of Robert Linsdell via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

Is There Hope For Coral Reefs?

January 16, 2019 By EarthWise Leave a Comment

News about the world’s coral reefs has been relentlessly bad for a number of years. Warming, acidifying oceans have wreaked havoc with coral reefs leading to enormous losses. Nowhere have things been more dire than in Australia’s Great Barrier Reef. Coral bleaching events have been increasingly common and severe over the past two decades. In fact, only 7% of the Great Barrier Reef has escaped bleaching entirely since 1998.

While the future of the world’s coral reefs is very much uncertain as global heating continues, there is a recent bit of hopeful news. According to a study published in Nature Climate Change, the response of the Great Barrier Reef to the extreme temperatures in 2017 was quite different from that of the previous year in the aftermath of back-to-back bouts of coral bleaching.

Surprisingly, corals that bleached in 2016 but managed to survive were more resistant to the recurrence of hot conditions in 2017.

Many corals don’t survive bleaching events at all and, of course,those corals don’t bleach for a second time. But the surviving corals from the 2016 bleaching event were tougher species. As a result of bleaching, the mix of coral species on the reef is changing very rapidly. The net result was that there was less bleaching in 2017 even though the temperatures that year were even more extreme than in 2016.

There have now been four mass bleaching events on the Great Barrier Reef over the past 20 years and it is only a matter of time before another one occurs triggered by the next marine heatwave. Almost half of the corals on the northern two-thirds of the reef have been killed. But at least some of the reef is showing impressive survival skills.

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