coral

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

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

Seabirds rescuing coral reefs

January 8, 2024 By EarthWise Leave a Comment

A new study by researchers at Lancaster University in the UK has found that the presence of seabirds on islands adjacent to tropical coral reefs can more than double the coral growth rates on those reefs.

The study found that when coral reefs grow faster, they can bounce back more quickly from bleaching events that occur when the seas become too warm. The focus of the study was a type of coral called Acropora, which provides complex structures supporting fish populations and reef growth.

The researchers found that Acropora around islands populated by seabirds recovered from bleaching events about 10 months faster than reefs located away from seabird colonies. Speeding up coral recovery times could prove the difference between continuing to bounce back from bleaching events and dying off.

The seabirds are helping the coral reefs with their droppings. The birds feed on fish in the open ocean far from islands and then return to the islands to roost. They deposit nitrogen- and phosphorus-rich nutrients in the form of guano, some of which is washed off of the islands by rain and into the surrounding seas. The nutrients fertilize corals and other marine species.

To determine whether the faster growth rates were really due to the bird-supplied nutrients, the researchers studied rat-infested islands that had no bird populations. The study confirmed that it was the presence of seabirds that provided enhanced nutrients for the coral reefs. In fact, a primary outcome of the study was to add further weight to the growing body of evidence of the ecological damage across ecosystems on land and sea from invasive rats on tropical islands.

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Feathered friends can become unlikely helpers for tropical coral reefs facing climate change threat

Photo, posted September 15, 2019, courtesy of Rickard Zerpe via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

Cryopreserving Corals | Earth Wise

October 3, 2023 By EarthWise Leave a Comment

Recent climate models estimate that if the effects of climate change are not mitigated soon enough, 95% of the world’s corals could die by the mid 2030s. Given the current rate of greenhouse gas emissions, this is an increasingly likely outcome. Coral reefs are estimated to have a $10 trillion economic value apart from their essential role in marine ecosystems.

Researchers at the University of Hawaii at Manoa have demonstrated a successful technique for cryopreserving entire coral fragments; in other words, preserving coral using cold temperatures and successfully reviving them.

Existing coral cryopreservation techniques rely on freezing sperm and larvae, which can only be collected during spawning events, which occur only a few days each year for coral species. This makes it logistically very challenging for researchers and conservationists.

The Hawaiian researchers focused on a process called isochoric vitrification, which is a method of freezing with liquid nitrogen that prevents the formation of ice crystals. They tested the technique with thumbnail-sized fragments of coral, freezing them in small aluminum chambers which restrict the growth of ice crystals that would otherwise damage delicate polyp tissues. Once the chambers were warmed, the fragments were transferred to seawater and allowed to recover. They found that the revived corals behaved the same as those that were never cooled.

The process holds great promise to conserve the biodiversity and genetic diversity of coral. If the process can be scaled up, it may be possible to preserve as many species of coral as possible by 2030, when it may no longer be viable for them to survive in the warming and acidifying oceans.

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Cryopreservation breakthrough could save coral reefs

Photo, posted June 2, 2023, courtesy of USFWS – Pacific Region via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

Climate Resilient Microalgae | Earth Wise

July 21, 2022 By EarthWise Leave a Comment

The plight of the world’s coral reefs has been a growing environmental crisis for many years. Coral reefs provide sustenance and income to half a billion people, are major tourist attractions, protect coastlines, and are important centers of biodiversity. And because of the warming climate as well as other effects of human activity, more than half of the world’s coral reefs are under stress.

The primary threat is coral bleaching, which is the disruption of the symbiotic relationship between coral polyps (which are tiny animals) and the heavily pigmented microalgae that live within the coral structures and provide most of the energy for the polyps. When corals are stressed, often because water temperatures are too high, they expel the microalgae within them. The structures then become transparent, leaving only the white skeletal corals. Bleached corals aren’t dead, but they are at great risk of starvation and disease until and unless new symbiont algae are acquired.

A new study by scientists at Uppsala University in Sweden investigated how different species of coral symbiont algae react to temperature stress. They discovered differences among symbiont cells that enable the prediction of how temperature stress tolerant the cells are. Such predictive ability could provide the means to identify and select more temperature-tolerant coral symbionts that could conceivably be introduced into coral host larvae in order to make corals more robust against climate change.

The research has a ways to go, but the new tools may help coral reef monitoring and increase the speed at which reef restoring efforts can create stocks of climate-resistant symbionts.

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Climate resilient microalgae could help restore coral reefs

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.

Rising Seas In The Maldives | Earth Wise

May 24, 2021 By EarthWise Leave a Comment

The Republic of Maldives is an archipelago in the Indian Ocean, southwest of Sri Lanka and India and about 400 miles from the Asian mainland. It is one of the world’s most geographically dispersed sovereign states, the smallest Asian country by land area, and, with a little over 500,000 inhabitants, the second least populous country in Asia. With its spectacular scenic beauty, it is also a premier tourist attraction.

With more than 80% of its 1,190 coral islands standing less than 1 meter above sea level, the Maldives has the lowest terrain of any country in the world. As a result, the Maldives is particularly vulnerable to the sea level rise associated with climate change.

Some studies predict a grim future for the Maldives as well as other low-lying islands. One study concluded that the islands could become uninhabitable by 2050 as wave-driven flooding becomes more common and freshwater becomes limited.

The Maldives government has explored plans to purchase land on higher ground in other countries. Planners are also working to enhance the resilience of the country’s current islands. An example is Hulhumalé, a newly constructed artificial island northeast of the country’s capital, Malé.

Construction of Hulhumalé began in 1997 and it now covers 1.5 square miles, making it the fourth largest island in the Maldives. Its population is now more than 50,000, with more than 200,000 expected to eventually move there. The new island, built by pumping sand from the seafloor onto a coral platform, rises about 2 meters above sea level. The extra height could make the new island a refuge for Maldivians driven off lower-lying islands by the rising seas.

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Preparing for Rising Seas in the Maldives

Photo, posted June 15, 2009, courtesy of Elena N via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

Assisting Evolution | Earth Wise

March 11, 2021 By EarthWise Leave a Comment

As plants and animals around the world grapple with climate change, invasive species, disease, and other threats, conservationists grapple with the issue of what it means to protect what is natural and how far to go to prevent extinctions.

Australia is where many of these issues have risen to the forefront. Imported mammals – particularly cats and foxes – have decimated many of Australia’s indigenous marsupials. Much of the focus for decades has been on killing off the invaders and cordoning off protected animals. In recent years, however, there have been efforts to expose prey animals to limited numbers of predators to develop prey populations that are better equipped to survive among predators. Getting rid of all the predators is not realistic. Saving species may require helping them to adapt.

On the Great Barrier Reef, where half its coral populations have perished because of rising water temperatures, scientists are breeding corals that are more heat tolerant. They are even considering the use of gene editing technology to “assist evolution” in developing corals that can survive in a changing world.

At SUNY College of Environmental Science and Forestry in Syracuse, New York, researchers have produced a genetically modified American chestnut tree that is resistant to chestnut blight, the fungal pathogen that killed off nearly every chestnut tree in North America in the early 20^th century.

The idea of conservation is to protect what is natural in our world. However, at a time when there are unprecedented threats to so many species, the distinction between what is natural and what is artificial may no longer provide a sound guide to what should be done to protect life on earth.

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Assisting Evolution: How Far Should We Go to Help Species Adapt?

Photo, posted November, 2000, courtesy of Bernard Dupont via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

Restoring Coastal Ecosystems | Earth Wise

February 1, 2021 By EarthWise Leave a Comment

Research published by CSIRO, Australia’s national science agency, examined the positive effects of restoration efforts for coastal ecosystems in terms of biodiversity, local economies, and human wellbeing.

Coastal ecosystems include saltmarshes, mangroves, seagrasses, oyster reefs, kelp beds, and coral reefs. All of these have suffered declines of up to 85% over recent decades. The research identified a number of successful coastal and marine restoration projects in recent years that indicate the likelihood that such efforts could be expanded by as much as a factor of ten to support human health and wellbeing, boost the adaptation response to climate change, and generate jobs.

Some of the successful efforts identified included projects in the Great Barrier Reef to harvest coral larvae to boost large-scale coral restoration efforts. Simple changes to how saltmarshes are planted have resulted in doubled survivorship and biomass. In the U.S., the propagation of seagrass seeds has resulted in seagrass meadows recovering in areas where they had been lost decades ago. In Indonesia, recovery of reefs impacted by blast fishing has been achieved by placing rocks or other hard structures underwater to help with coral colonization.

Investing in coral restoration creates jobs and can be used as a strategy to boost economic recovery and coastal marine health. Restoration of marine habitats like kelp forests and oyster reefs has improved commercial and recreational fishing.

The United Nations has recognized the importance of coastal restoration and has declared the Decade on Ecosystem Restoration to start from 2021.

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Scientists shine light on ‘bright spots’ to restore coastal ecosystems

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

Earth Wise is a production of WAMC Northeast Public Radio.

Caribbean Coral Reefs Under Siege | Earth Wise

January 4, 2021 By EarthWise Leave a Comment

Coral reefs around the world have been suffering from warming seas and increasing acidification, both a result of human activity. In the Caribbean, a new threat has emerged in the form of invasive algae.

New research published in Scientific Reports explains how an aggressive, crust-like alga is overgrowing shallow reefs and taking the place of coral that was damaged by powerful storms that exposed areas of the undersea rock where corals grew.

Researchers from Oxford University, the Carnegie Institution, and California State University Northridge have been studying these peyssonnelid algal crusts, or PACs, for several years in the U.S. Virgin Islands. The PAC has been out-competing coral larvae for surface space and then growing over the existing reef architecture, greatly damaging delicate reef ecosystems.

New corals actually prefer to settle on crusty surfaces created by a different type of algae called crustose algae, or CCA. CCA acts as guideposts for coral larvae by producing biochemical signals as part of a microbial community that entice baby coral to affix itself.

In contrast, the destructive PAC algae exclude coral settlement. The researchers determined that the microbial community associated with PAC algae is deployed to deter grazing from fish and other marine creatures. Unfortunately, it also deters coral.

Fragile coral ecosystems are already under assault by environmental pollution and global warming. Now, in the aftermath of powerful hurricanes like Irma and Maria, algal crusts are taking over reef communities and posing an existential threat to Caribbean corals.

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An unusual microbiome characterises a spatially-aggressive crustose alga rapidly overgrowing shallow Caribbean reefs

Photo, posted January 11, 2015, courtesy of Falco Ermert via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

Heat-Resistant Coral | Earth Wise

June 23, 2020 By EarthWise Leave a Comment

Coral reefs are in decline all over the world. Corals are under increasing pressure as water temperatures rise and the frequency and severity of coral bleaching events increase. Nowhere is this more evident than in Australia’s Great Barrier Reef system, where severe bleaching events have happened in three of the past five years. Long-term prospects for the survival of the world’s largest reef system are now considered to be poor.

A team of scientists at Australia’s national science agency – the Commonwealth Scientific and Industrial Research Organization – along with the Australian Institute of Marine Science and the University of Melbourne have successfully produced in a laboratory setting a coral that is more resistant to increased seawater temperatures.

The team made the coral more tolerant to temperature-induced bleaching by bolstering the heat tolerance of the microalgae symbionts that live inside the coral tissue. They isolated the microalgae from coral and cultured it in the laboratory using a technique called “directed evolution”. Over the course of four years, they exposed the microalgae to increasingly warmer temperatures. When the heat-adapted strain of algae was reintroduced into coral larvae, the newly established coral-algal symbiosis was more heat tolerant than the original one. The heat-tolerant microalgae are better at photosynthesis and improve the heat response of the coral animal.

The next step is to further test the algal strains in adult colonies across a range of coral species. This groundbreaking research provides a promising and novel tool to increase the heat tolerance of corals and might potentially lead to a way to save the Great Barrier Reef as the world continues to warm.

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Scientists successfully develop heat resistant coral to fight bleaching

Photo, posted September 22, 2010, courtesy of NOAA via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

A New Kind Of Coral Nursery

October 22, 2019 By EarthWise Leave a Comment

Coral reefs around the world are struggling from warming waters and increasing ocean acidification driven by excess carbon dioxide. Many of the world’s greatest reefs – such as Australia’s Great Barrier Reef – have seen steep declines over the past decade.

But apart from the global environmental threat, reefs also are often damaged by various marine accidents such as ships grounding on them. Such events can severely damage a reef and scatter countless small coral fragments onto the seafloor. These small pieces of coral are not actually dead; they can continue on with their lives if they are relocated to a suitable environment such as a coral nursery.

Coral nurseries are generally small installations that allow coral fragments – typically pieces about 4 inches in length – to recover from their reef breaking up and to grow until they are large enough for conservation managers to replant them into reefs that need them. This strategy works well in places where corals grow relatively quickly – such as Florida and the Caribbean – but not as well in places where coral grows more slowly, such as Hawaii.

Recently, coral experts at the National Oceanic and Atmospheric Administration working with mechanical engineering students at the University of Hawaii have developed a new type of coral nursery that can save fully formed coral colonies as opposed to small coral fragments.

The nurseries are large, carefully designed structures that can be loaded up with corals that have become detached from their reefs. Some of these new structures were installed in the waters of Oahu in the summer of 2018 and were populated with corals. The relocated corals, which would have otherwise died, are now recovering nicely in their new coral daycare centers and will soon be replanted back into the reef.

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NOAA Develops A New Type of Coral Nursery

Photo, posted July 29, 2010, courtesy of Kyle Taylor 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.

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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