Diving deeper into our oceans: Underwater drones open new doors for global coral reef research

At the Okinawa Institute of Science and Technology (OIST), scientists at the Marine Genomics Unit, in collaboration with the Japanese telecommunications company NTT Communications, have identified the genera of mesophotic corals using eDNA collected by underwater drones for the first time. Their groundbreaking research has been published in the journal Royal Society Open Science. Now, with the help of submersible robots, large-scale eDNA monitoring of corals can be conducted without relying on direct observations during scientific scuba diving or snorkeling.

Mesophotic ('middle-light') coral ecosystems are light dependent tropical or subtropical habitats found at depths of 30 to 150 meters.

They are unique because they host more native species compared to shallow-water coral ecosystems.

Despite this, they are largely unexplored, and more research is needed to understand their basic biology.

Researchers studying corals access these invertebrate reef builders by snorkeling and scuba diving, but these methods have limitations, especially when identifying corals at deeper depths.

Using genetic material that organisms shed from their bodies into their environment -- environmental DNA or eDNA -- scientists can identify types of corals and other organisms living in a particular habitat, providing a powerful tool for biodiversity assessment.

Importantly, studying the eDNA of corals offers unique advantages.

First, unlike fish, corals are stationary, eliminating uncertainties about their location.

Second, they constantly secrete mucus into the sea, providing plenty of coral eDNA for sampling.

For this study, the researchers analyzed mitochondrial DNA, which is more abundant and of higher quality compared to nuclear DNA, improving the accuracy of their findings.

To learn more about the coral eDNA metabarcording analysis methods used in this study, see here.

Faster and easier monitoring of coral reefs

Mesophotic coral ecosystems (MCEs) in Japan have some of the highest diversity of stony corals (Scleractinia) in the world, making them particularly important for researchers, but difficult to monitor because they are often located at deeper depths.

Additionally, to accurately monitor corals, scientists require both scuba diving and taxonomy skills, which can be challenging.

Existing methods for monitoring MCEs therefore impose limitations on conducting thorough surveys, and new methods are needed.

In October 2022, Prof. Noriyuki Satoh, leader of the Marine Genomics Unit, was approached by Mr. Shinichiro Nagahama of NTT Communications who had read about his research on coral eDNA methods.

Mr. Nagahama suggested using their underwater drones to collect samples from deeper coral reefs for eDNA analysis.

Prof. Satoh then put forward the idea of using the drones to conduct extensive surveys of mesophotic corals at greater depths.

Kerama National Park in Japan, about 30 km west of Okinawa Island, boasts some of the most transparent water in the Okinawa Archipelago.

Often referred to as 'Kerama blue', these waters provided an excellent opportunity for the researchers to test this new sampling technique.

They collected seawater samples -- each measuring 0.5 liters -- from 1 to 2 meters above the coral reefs (between 20 and 80 meters deep). The sampling sites were chosen across 24 locations within 6 different areas around the picturesque Zamami Island.

The next step involved subjecting these samples to coral metabarcoding analyses, which uses Scleractinian-specific genetic markers to identify the different genera of corals present in each sample.

From the eDNA analysis results, the researchers successfully identified corals at the genus level.

The presence and absence of certain genera of stony corals shown by this method indicated that reefs around the Kerama Islands exhibited different compositions of stony corals depending on location and depth.

For example, the genus Acropora had the highest ratios at 11 sites, indicating that these corals are common at Zamami Island reefs.

The researchers also found that the proportion of Acropora eDNA was higher at shallow reefs and upper ridges of slopes, while the proportion of the genus Porites increased at mesophotic sites.

Regarding depth, Acropora was readily detected at shallow reefs (≤15 meters), while other genera were more frequently found at deeper reefs (>20 meters).

To study corals using eDNA metabarcoding methods, further sequencing of mitochondrial genomes of stony corals is needed, and this study suggests that it may be possible to more efficiently monitor mesophotic corals at the generic level using eDNA collected by underwater drones.

Collaborative innovation ahead

NTT Communications has developed a new version of the original drone used for this study.

In response to a request from Prof. Satoh, an additional sampler was added so that two samples can be collected during a single dive.

Additionally, the cable length between the controller and drone was extended from 150 meters to 300 meters and the battery is now changeable, so researchers can continue their survey work for an entire day.

Read more at Science Daily

Protecting coral 'nurseries' as important as safeguarding established coral reefs

When imagining corals, the picture that comes to mind is usually a stationary one: a garden of rock-like structures covering sections of the ocean floor.

Reef conservation efforts typically focus on preserving established coral and protecting them from known stressors such as pollution, overfishing and runoff from coastline populations.

However, new research near Miloliʻi in the southwestern part of the island of Hawaii, shows that identifying and protecting marine ecosystems both down-current and up-current of coral reefs, specifically areas where coral larvae are more likely to survive and thrive, is crucial to future coral conservation and restoration efforts -- especially as reefs face increasing pressure from the devastating effects of climate change.

The research, completed by Arizona State University scientists and their collaborators, appears in the current issue of Proceedings of the National Academy of Sciences.

Rachel Carlson, an ASU affiliate scientist and the study's first author, along with Greg Asner, director of ASU's Center for Global Discovery and Conservation Science, Larry Crowder, professor of oceans at Stanford University, and Robin Martin, associate professor with the ASU School of Ocean Futures in the Julie Ann Wrigley Global Futures Laboratory, collaborated on the project.

Additionally, the ʻĀkoʻakoʻa Reef Restoration Program, a regional effort that fuses cultural leadership, multi-modal education, advanced science and government engagement, backed the research.

Carlson says this type of collaborative work -- partnerships combining local, Indigenous knowledge and Western science -- is crucial to mapping out a future that ensures the survival of coral populations.

"There's a lot of Indigenous knowledge about coral spawning and fish populations in West Hawaii. In this study, we addressed an open question: How connected are coral populations between embayments along this coastline?" Carlson said. "What we essentially found is that the major factors in helping the coral keiki, known as larvae, settle down and survive are the nearshore current and the structure of the reef."

The study shows that the larvae more often settle in and inhabit areas with large boulders and uneven surfaces, or "chunky features," said Carlson, who is also a Chancellor's Postdoctoral Fellow at the UC Davis Bodega Marine Lab. Adult coral will spawn millions of larvae into the water column and those larvae prefer to settle in places with large knolls and boulders.

This discovery is good news: These kinds of seafloor features have been mapped via ASU's Global Airborne Observatory, a highly specialized aircraft that uses several types of remote sensing technologies to track both underwater and land-based habitats. This means that the researchers have the capability to help find and map priority reefs for conservation and restoration.

"This is foundational research in several important ways," said Asner, the study's senior author. "First, it gives us an understanding of the connectivity of different parts of reefs along our coastline and tells us the level of connectivity in the context of the birth, settlement and growth of corals miles apart. Second, our unique remote sensing capabilities can identify reef sites where coral restoration could be most viable in the future. Finally, these findings provide a critical building block for future restoration efforts by our ʻĀkoʻakoʻa team and collaborators."

The group's goal is to preserve and restore vitality to Hawaii's coral reefs and coastline health.

"We as lineal descendants of the Miloliʻi area have always relied on the reef for our ʻOhana (families). Our reef is our sustenance and is of enormous cultural value to us," said Kaʻimi Kaupiko, president of the nonprofit organization Kalanihale, which manages the Miloliʻi Community-Based Subsistence Fishing Area where the study took place.

Asner said the intertwined nature of reefs along Hawaii's coastlines is crucial to consider in reef protection strategies. Narrowing in on one area without consideration for the reproductive corridors of corals, he said, would be akin to worrying about planting trees in a certain place and not thinking about the forest as a whole. This sentiment is echoed by Martin, who said reef connectivity is an underutilized tool in reef restoration efforts globally.

"In Hawaii and worldwide, we're trying to figure out where we should place protections and restore areas to help reefs," Martin said. "This study is highly technical, but it needs to be part of that conversation and part of that work, because if you aren't protecting the upcurrent reefs, you are cutting off important reproductive areas."

Martin said reef restoration could, for example, expand a protected area of reefs beyond just the spots that have more dense coral coverage on the ocean floor; protection efforts would also be needed in the upcurrent path that the coral larvae traveled through before they settled in a new location.

Asner adds that this research could very well help conservation efforts expand to much greater distances than have been achieved previously.

"These kinds of studies of connectivity, flow and movement are needed because the west Hawaii island coastline is longer than the whole circumference of any other island," Asner said. "We have a lot of degraded reefs along our coastline, so knowing where and how to help baby corals thrive is fundamental to the ʻĀkoʻakoʻa restoration effort."

Read more at Science Daily

Coral reefs in peril from record-breaking ocean heat

Record breaking marine heatwaves will cause devastating mass coral bleaching worldwide in the next few years, according to a University of Queensland coral reef scientist.

The alarming finding is the result of an international study led by UQ's Professor Ove Hoegh-Guldberg of UQ's School of the Environment, who is currently attending the COP28 climate change meetings in Dubai.

"We were shocked to find heat stress conditions started as much as 12 weeks ahead of previously recorded peaks and were sustained for much longer in the eastern tropical Pacific and wider Caribbean," Professor Hoegh-Guldberg said.

"Historical data suggests the current marine heatwaves will likely be the precursor to a global mass coral bleaching and mortality event over the next 12 to 24 months, as the El Niño phase of El Niño-Southern Oscillation or ENSO continues.

"Across July 2023, Earth experienced its warmest days on record since 1910, as well as the warmest month ever recorded for sea surface temperatures.

"This puts immense pressure on vital but fragile tropical ecosystems, such as coral reefs, mangrove forests, and seagrass meadows.

"For example, a coral reef in the Florida Keys called Newfound Harbor Key accumulated heat stress almost 3 times the previous record and it occurred 6 weeks ahead of previous peaks."

Professor Hoegh-Guldberg said the findings come at a critical point in protecting global biodiversity, with commitment to climate change mitigation slipping in many nations.

"The latest environmental information indicates that we're well off-track when it comes to keeping global surface temperatures from reaching a very dangerous condition by mid to late this century," he said.

"Frankly, we're hurtling in the opposite direction.

"Compounding this is the fact these devastating impacts appear to be rolling into a vast record-breaking global event."

Professor Hoegh-Guldberg said that without serious and swift action, the persistence of coral reefs beyond the next few decades is in serious jeopardy.

"Our study shows that ENSO is a major determinant of the fate of the world's coral reefs," he said.

"Rising sea temperatures, coupled with other stressors such as ocean acidification and pollution, have severely weakened their resilience.

"This puts coral reefs and a quarter of the ocean's biodiversity at serious risk of annihilation."

Professor Hoegh-Guldberg said efforts to introduce of heat-tolerance genes into the natural coral population have shown promise, but the reality of scaling these efforts remains logistically challenging.

"Given the complex and interconnected nature of marine ecosystems such as coral reefs, a comprehensive approach is necessary for mitigating the impacts of changing oceanic conditions," he said.

"The importance of reducing our emissions is underscored in our findings, where massive changes to oceanic warming are set to destroy coral reefs and many other ecosystems.

Read more at Science Daily

Coral reefs in the Eastern Pacific could survive into the 2060s

Scientists at the University of Miami Rosenstiel School of Marine, Atmospheric, and Earth Science found that some reefs in the tropical Pacific Ocean could maintain high coral cover into the second half of this century by shuffling the symbiotic algae they host. The findings offer a ray of hope in an often-dire picture of the future of coral reefs worldwide.

While global warming is causing the loss of coral reefs globally, scientists believe that some corals are increasing their tolerance to heat by changing the symbiotic algae communities they host, which through photosynthesis provide them with the energy they need to live.

"Our results suggest that some reefs in the eastern tropical Pacific, which includes the Pacific coasts of Panama, Costa Rica, Mexico, and Colombia, might be able to maintain high coral cover through the 2060s," said coral biologist Ana Palacio-Castro, lead author of the study, alumna of the Rosenstiel School, and a postdoctoral associate at the school's Cooperative Institute for Marine and Atmospheric Studies. "However, while this may be seen as good news for these reefs, their survival may not continue past that date unless we reduce global greenhouse gas emissions and curtail global warming on a larger scale."

Shallow coral reefs in the eastern tropical Pacific Ocean are predominantly built by branching corals in the genus Pocillopora, which are extremely important for the reefs in the region. The microscopic algae they host in their tissue harvest light to help the coral produce energy to grow. The loss of these symbiotic algae causes the coral to turn white, or bleach, and the coral struggles to meet their energy needs, which can often prove fatal.

To better understand how corals improved their tolerance to heat stress, the researchers examined over 40 years' worth of coral reef-monitoring data from Panama, one of the longest datasets of its kind in the world. They analyzed temperature, coral cover, bleaching and mortality data spanning three ocean heatwaves -- in 1982-1983, 1997-1998, and 2015-2016 -- along with data on algal symbiont community data during the last two.

The analysis showed that the 1982-83 heatwave significantly reduced coral cover on the reef, but the effects of the 1997-98 and 2015-16 El Niño were milder, especially for corals in the genus Pocillopora -- sometimes known as cauliflower coral -- the predominant reef-building coral in the eastern tropical Pacific. They also confirmed that during strong ocean heatwaves, the heat-tolerant alga Durusdinium glynnii becomes increasingly common in this particular lineage of corals, allowing them to better withstand periods of elevated temperatures. When combined with climate projections of future heat stress, the reefs that were predominantly composed of Pocillopora corals and that hosted this heat-tolerant alga were found to be better equipped to survive and maintain high levels of coral cover well into the second half of the current century, indicating that some reef systems may be more resilient to warming than previously thought.

"This study shows that there are some unusual reefs that may be able to survive for several decades as a result of their ability to shuffle symbionts," said Andrew Baker, professor of marine biology and ecology at the Rosenstiel School, and senior author of the study. "While we don't think that most reefs will be able to survive in this way, it does suggest that vestiges of our current reefs may persist for longer than we previously thought, although potentially with many fewer species. Coral reefs are incredibly valuable natural assets, providing coastal protection and fisheries benefits, and supporting many local communities. We can still make a difference by protecting them."

Read more at Science Daily

Palau's Rock Islands harbor heat-resistant corals

Ocean warming is driving an increase in the frequency and severity of marine heatwaves, causing untold damage to coral reefs. Tropical corals, which live in symbiosis with tiny single celled algae, are sensitive to high temperatures, and exhibit a stress response called bleaching when the ocean gets too hot. In the last 4 decades, marine heatwaves have caused widespread bleaching, and killed millions of corals. Because of this, a global search is underway for reefs that can withstand the heat stress, survive future warming, and act as sources of heat-tolerant coral larvae to replenish affected areas both naturally and through restoration.

Now, scientists studying reefs in Palau, an archipelago in the western tropical Pacific, have identified genetic subgroups of a common coral species that exhibit remarkable tolerance to the extreme heat associated with marine heatwaves. Further, the scientists found evidence that larvae from these corals are traveling from their birthing grounds deep in Palau's lagoons, to the outer reef, where they survive and grow, and maintain their heat tolerance.

Understanding both the underlying mechanisms that facilitate heat tolerance of these corals, as well as the dispersal capabilities of their larvae will go a long way toward enhancing coral reef conservation and restoration efforts in the 21st century ocean, according to scientists at the Woods Hole Oceanographic Institution (WHOI) who led the research.

In Palau's main lagoon, a network of very ancient, fossilized reefs has been uplifted to form a series of mountains known as the Rock Islands. These formations slow water flow in and around them, creating localized environments in which the water temperatures are consistently higher than other areas of Palau's reefs.

Scientists sampled the keystone coral species Porites lobata (lobe coral) across Palau, including the Rock Islands. They took skeletal biopsies and examined the cores for stress bands, which are telltale signs of bleaching, a stress response corals have to high temperatures. They found corals from the Rock Islands bleached less during the intense 1998 heatwave than corals from other areas of the reef, indicating enhanced thermal tolerance.

Scientists then investigated the genetics of the corals and discovered four distinct lineages within the same species. Within the warmer Rock Islands, certain lineages, designated as "LB" and "RD" lineages, were much more common. The scientists were able to match the genetics of each coral with its own bleaching history and found that fewer individuals from the "LB" and "RD" lineages bleached during 1998, indicating enhanced thermal tolerance.

Remarkably, the scientists found the LB lineage was not restricted to the Rock Islands. They found some LB colonies also living on the cooler outer reefs. An examination of the bleaching histories of these colonies again revealed fewer stress bands, indicating that they maintained the thermal tolerance characteristic of their relatives in the Rock Islands.

"This suggests that the Rock Islands provide naturally tolerant larvae to neighboring areas," the scientists write in the paper titled "Palau's warmest reefs harbor thermally tolerant corals that thrive across different habitats," published in Communications Biology, a journal published by Nature. "Finding and protecting such sources of thermally-tolerant corals is key to reef survival under 21st century climate change."

"As oceans worldwide continue to warm, corals derived from extreme habitats will be at a competitive advantage and may enable the survival of otherwise vulnerable reefs," the authors continue. "Identifying and safeguarding natural breeding grounds of environmentally tolerant corals that can thrive under future climate conditions will be fundamental to the persistence of coral reef ecosystems worldwide in the coming decades."

"We found that some of Palau's reefs with the highest temperatures have corals that are more tolerant than one would expect," said the paper's lead author Hanny Rivera, a graduate of the MIT-WHOI Joint Program. Rivera, who conducted this work as part of her Ph.D. and postdoctoral research, is currently an associate director of business development at Ginko Bioworks. "In addition, they are genetically distinct from the same corals found in other parts of Palau, which suggests that there has been natural selection for hardier corals in these regions.."

Paper co-author Michael Fox added that the study is particularly exciting because it combines coral genetics with historical records of bleaching preserved in their skeletons to shed light on how corals from extreme habitats with high temperature tolerance can be dispersed across a reefscape. "This integrated perspective is essential for improving projections of coral communities in a warming ocean," said Fox, who was a postdoctoral scholar at WHOI during the research for this paper. He currently is an assistant research professor in the Red Sea Research Center at King Abdullah University of Science and Technology in Thuwal, Saudi Arabia.

The Palau research is directly related to the Super Reefs initiative WHOI launched with The Nature Conservancy and Stanford University to locate coral communities that can withstand marine heat waves, and work with local communities and governments to protect them.

"This work is the scientific basis for the Super Reefs initiative," said paper co-author Anne Cohen, a scientist at WHOI and Rivera's advisor on the study. "The Palau research demonstrates that Super Reefs exist and also provides actionable science knowledge that can be used to support their protection."

Cohen noted that there are other coral reefs, not just in Palau, where coral communities have not bleached as severely as scientists predicted based on the levels of thermal stress. "When we find the coral communities that are heat-tolerant or bleaching-resistant, and we protect them from other stresses that can kill them -- like dynamiting, overfishing, or coastal development -- they will produce millions of larvae that will travel on the currents, outside of their places of origin as we see on Palau, and they will repopulate reefs that have been devastated by heatwaves," she said. "Nature is amazing. Our job with the Super Reefs initiative is to protect these thermally resilient reefs and let nature do the rest."

Rivera added she is in awe of the immense appreciation, respect, and stewardship that the Palauan people have for their environment.

"They have been one of the pioneering countries in promoting marine conservation and ecological protection. It is wonderful to know that these special reefs are in such good hands," Rivera said. "It is my greatest hope that our research will further support the Palauan people in their efforts to maintain a healthy marine ecosystem."

Read more at Science Daily

Impact of coral chemical compounds on reef composition and health

Stumbling upon a new source of underwater caffeine was just an added bonus of a new study examining the impact of chemical compounds that corals release into the seawater.

The study found that the organic chemical compounds produced through metabolism -- known as metabolites or exudates -- vary significantly by coral species and that the compounds impact the abundances and compositions of reef microorganisms differently.

This differential release of metabolites from benthic reef organisms is particularly significant in the Caribbean where coral dominance is shifting from hard stony corals to soft octocorals in response to human-caused stressors such as eutrophication, overfishing, and global climate change.

The study "demonstrates the importance of benthic exudates for structuring microbial communities on oligotrophic reefs by focusing on the exudates released from abundant stony corals, octocorals, and an invasive alga," according to the paper led by authors from the Woods Hole Oceanographic Institution (WHOI), "Benthic exometabolites and their ecological significance on threatened Caribbean coral reefs," published in ISME Communications.

"We wanted to know what are the molecules that coral organisms release into the environment, and how do those molecules impact the reef microbes in the seawater surrounding the corals," said lead author Laura Weber, a former postdoc and current information systems associate in WHOI's Marine Chemistry & Geochemistry Department.

"As the species composition of these reefs shifts, it is likely changing the chemicals that are released on the reef that then will have impacts on the microbial community," Weber said. "We need to pay more attention to how changes in reef structure and species composition might influence the microbes that live on the reef, leading to more feedbacks in terms of reef health." She said that understanding microbes on reefs, how they are functioning, and how they might be contributing to the health of corals and of reefs themselves is "pretty much an untapped area to explore."

Here's the caffeine connection.

For the study, researchers collected exudates from six species of Caribbean benthic organisms in a lab setting, using organisms obtained from within the Virgin Islands National Park, including stony corals, octocorals, and an invasive encrusting alga called Ramicrusta textilis. The researchers surprisingly found that R. textilis released caffeine in high quantities.

Their results further "demonstrate that exudates from benthic organisms contribute to the complex pool of extracellular metabolites in reef seawater and that exudate composition varies significantly by species," according to the study

As to why R. textilis produces caffeine, the study notes that caffeine production has not been widely investigated for marine organisms, but that it is a common metabolite produced by land plants generally to deter herbivores and pathogenic microbes. These characteristics "could contribute to the ability of R. textilis to invade and flourish on Caribbean reefs," according to the report. "Given the growing prevalence of Ramicrusta on diverse Caribbean reefs, follow-up research examining the ecological significance of its metabolites on microbes and other reef organisms is needed."

This study "is an important step forward in identifying chemical signals that can help scientists assess reef health," said Elizabeth Kujawinski, co-author of the paper. "Similar to human health diagnostics, the chemical signals within a reef ecosystem are intimately linked to the functions of the symbiotic relationships within reefs." Kujawinski is a senior scientist in WHOI's Marine Chemistry & Geochemistry Department and director of the Center for Chemical Currencies of a Microbial Planet (C-CoMP), a National Science Foundation Science and Technology Center that is based at WHOI.

Co-author Amy Apprill, associate scientist in WHOI's Marine Chemistry & Geochemistry Department, said an important implication of the research is that a diverse benthic community helps to contribute to a more varied metabolite pool and likely supports a more diverse microbial community.

"We are trying to build kind of a library of what microbes and metabolites are present on reefs. My dream is to be able to go out to a reef, take a bucket of reef water, screen it for microbes and metabolites, and be able to tell something about the health of that ecosystem," Apprill said. "This is so important to do because the current methods to monitor reefs are highly visual-based, and it can take months or years to determine if coral is sick or growing. Metabolites and microbes have the potential to be really sensitive sensors for reef health."

This research was conducted with support from the National Oceanic and Atmospheric Administration and the National Science Foundation.

Key Takeaways

Chemical compounds produced through metabolism and then released -- known as metabolites or exudates -- vary significantly by coral species and impact the abundances and compositions of reef microorganisms differently.

The differential release of metabolites from benthic reef organisms is particularly significant in the Caribbean where coral dominance is shifting from hard stony corals to soft octocorals in response to human-caused stressors such as eutrophication, overfishing, and global climate change.

"As the species composition of these reefs shifts, it is likely changing the chemicals that are released on the reef that then will have impacts on the microbial community. We need to pay more attention to how changes in reef structure and species composition might influence the microbes that live on the reef, leading to more feedbacks in terms of reef health."

Stumbling on a new source of underwater caffeine was just an added bonus of a new study examining the impact of chemical compounds that corals release into the seawater.

This study "is an important step forward in identifying chemical signals that can help scientists assess reef health. Similar to human health diagnostics, the chemical signals within a reef ecosystem are intimately linked to the functions of the symbiotic relationships within reefs."

Read more at Science Daily

Scientists find link between fast-melting Arctic ice and ocean acidification

An international team of researchers have sounded new alarm bells about the changing chemistry of the western region of the Arctic Ocean after discovering acidity levels increasing three to four times faster than ocean waters elsewhere.

The team, which includes University of Delaware marine chemistry expert Wei-Jun Cai, also identified a strong correlation between the accelerated rate of melting ice in the region and the rate of ocean acidification, a perilous combination that threatens the survival of plants, shellfish, coral reefs and other marine life and biological processes throughout the planet's ecosystem.

The new study, published on Thursday, Sept. 30 in Science, the flagship journal of the American Association for the Advancement of Science, is the first analysis of Arctic acidification that includes data from more than two decades, spanning the period from 1994 to 2020.

Scientists have predicted that by 2050 -- if not sooner -- Arctic sea ice in this region will no longer survive the increasingly warm summer seasons. As a result of this sea-ice retreat each summer, the ocean's chemistry will grow more acidic, with no persistent ice cover to slow or otherwise mitigate the advance.

That creates life-threatening problems for the enormously diverse population of sea creatures, plants and other living things that depend on a healthy ocean for survival. Crabs, for example, live in a crusty shell built from the calcium carbonate prevalent in ocean water. Polar bears rely on healthy fish populations for food, fish and sea birds rely on plankton and plants, and seafood is a key element of many humans' diets.

That makes acidification of these distant waters a big deal for many of the planet's inhabitants.

First, a quick refresher course on pH levels, which indicate how acidic or alkaline a given liquid is. Any liquid that contains water can be characterized by its pH level, which ranges from 0 to 14, with pure water considered neutral with a pH of 7. All levels lower than 7 are acidic, all levels greater than 7 are basic or alkaline, with each full step representing a tenfold difference in the hydrogen ion concentration. Examples on the acidic side include battery acid, which checks in at 0 pH, gastric acid (1), black coffee (5) and milk (6.5). Tilting toward basic are blood (7.4), baking soda (9.5), ammonia (11) and drain cleaner (14). Seawater is normally alkaline, with a pH value of around 8.1.

Cai, the Mary A.S. Lighthipe Professor in the School of Marine Science and Policy in UD's College of Earth, Ocean and Environment, has published significant research on the changing chemistry of the planet's oceans and this month completed a cruise from Nova Scotia to Florida, serving as chief scientist among 27 aboard the research vessel. The work, supported by the National Oceanic and Atmospheric Administration (NOAA), includes four areas of study: The East Coast, the Gulf of Mexico, the Pacific Coast and the Alaska/Arctic region.

The new study in Science included UD postdoctoral researcher Zhangxian Ouyang, who participated in a recent voyage to collect data in the Chukchi Sea and Canada Basin in the Arctic Ocean.

The first author on the publication was Di Qi, who works with Chinese research institutes in Xiamen and Qingdao. Also collaborating on this publication were scientists from Seattle, Sweden, Russia and six other Chinese research sites.

"You can't just go by yourself," Cai said. "This international collaboration is very important for collecting long-term data over a large area in the remote ocean. In recent years, we have also collaborated with Japanese scientists as accessing the Arctic water was even harder in the past three years due to COVID-19. And we always have European scientists participating."

Cai said he and Qi both were baffled when they first reviewed the Arctic data together during a conference in Shanghai. The acidity of the water was increasing three to four times faster than ocean waters elsewhere.

That was stunning indeed. But why was it happening?

Cai soon identified a prime suspect: the increased melt of sea ice during the Arctic's summer season.

Historically, the Arctic's sea ice has melted in shallow marginal regions during the summer seasons. That started to change in the 1980s, Cai said, but waxed and waned periodically. In the past 15 years, the ice melt has accelerated, advancing into the deep basin in the north.

For a while, scientists thought the melting ice could provide a promising "carbon sink," where carbon dioxide from the atmosphere would be sucked into the cold, carbon-hungry waters that had been hidden under the ice. That cold water would hold more carbon dioxide than warmer waters could and might help to offset the effects of increased carbon dioxide elsewhere in the atmosphere.

When Cai first studied the Arctic Ocean in 2008, he saw that the ice had melted beyond the Chukchi Sea in the northwest corner of the region, all the way to the Canada Basin -- far beyond its typical range. He and his collaborators found that the fresh meltwater did not mix into deeper waters, which would have diluted the carbon dioxide. Instead, the surface water soaked up the carbon dioxide until it reached about the same levels as in the atmosphere and then stopped collecting it. They reported this result in a paper in Science in 2010.

That would also change the pH level of the Arctic waters, they knew, reducing the alkaline levels of the seawater and reducing its ability to resist acidification. But how much? And how soon? It took them another decade to collect enough data to derive a sound conclusion on the long-term acidification trend.

Analyzing data gathered from 1994 to 2020 -- the first time such a long-term perspective was possible -- Cai, Qi and their collaborators found an extraordinary increase in acidification and a strong correlation with the increasing rate of melting ice.

They point to sea-ice melt as the key mechanism to explain this rapid pH decrease, because it changes the physics and chemistry of the surface water in three primary ways:
 

• The water under the sea ice, which had a deficit of carbon dioxide, now is exposed to the atmospheric carbon dioxide and can take up carbon dioxide freely.
   
• The seawater mixed with meltwater is light and cannot mix easily into deeper waters, which means the carbon dioxide taken from the atmosphere is concentrated at the surface.
   
• The meltwater dilutes the carbonate ion concentration in the seawater, weakening its ability to neutralize the carbon dioxide into bicarbonate and rapidly decreasing ocean pH.

Cai said more research is required to further refine the above mechanism and better predict future changes, but the data so far show again the far-reaching ripple effects of climate change.

"If all of the multiple-year ice is replaced by first-year ice, then there will be lower alkalinity and lower buffer capacity and acidification continues," he said. "By 2050, we think all of the ice will be gone in the summer. Some papers predict that will happen by 2030. And if we follow the current trend for 20 more years, the summer acidification will be really, really strong."

Read more at Science Daily

Computer modelling aims to inform restoration, conservation of coral reefs

A UBC Okanagan research team has created a computer modelling program to help scientists predict the effect of climate damage and eventual restoration plans on coral reefs around the globe.

This is a critical objective, says Dr. Bruno Carturan, because climate change is killing many coral species and can lead to the collapse of entire coral reef ecosystems. But, because they are so complex, it's logistically challenging to study the impact of devastation and regeneration of coral reefs.

Real-world experiments are impractical, as researchers would need to manipulate and disrupt large areas of reefs, along with coral colonies and herbivore populations, and then monitor the changes in structure and diversity over many years.

"Needless to say, conducting experiments that will disturb natural coral reefs is unethical and should be avoided, while using big aquariums is simply unfeasible," says Dr. Carturan, who recently completed his doctoral studies with the Irving K. Barber Faculty of Science. "For these reasons, no such experiments have ever been conducted, which has hindered our capacity to predict coral diversity and the associated resilience of the reefs."

For his latest research, published recently in Frontiers in Ecology and Evolution, Dr. Carturan used models to create 245 coral communities, each with a unique set of nine species and each occupying a surface of 25 square metres. The model represents coral colonies and different species of algae that grow, compete and reproduce together while also being impacted by climate.

Crucially, he notes, all the key components of the model, including species' traits such as competitive abilities and growth rates, are informed by pre-existing, real-world data from 800 species.

The research team simulated various scenarios -- including strong waves, a cyclone or intense heat -- and then measured each model reef's resilience taking note of damage, recovery time and the quality of the habitat 10 years after the disturbance.

By running so many scenarios with computer modelling, the team found that more diverse communities -- those with species having highly dissimilar traits -- were most resilient. They were better at recovering from damage and had greater habitat quality 10 years after the disturbances.

"More diverse communities are more likely to have certain species that are very important for resilience," Dr. Carturan explains. "These species have particular traits -- they are morphologically complex, competitive and with a good capacity to recover. When present in a community, these species maintained or even increased the quality of the habitat after the disturbance. Contrastingly, communities without these species were often dominated by harmful algae at the end."

Coral diversity determines the strength and future health of coral reefs, he adds. Coral species are the foundation of coral reef ecosystems because their colonies form the physical habitat where thousands of fish and crustaceans live. Among those are herbivores, such as parrotfish and surgeonfish, which maintain the coral habitat by eating the algae. Without herbivores, the algae would kill many coral colonies, causing the coral habitat to collapse, destroying its many populations.

"What is unique with our study is that our results apply to most coral communities in the world. By measuring the effect of diversity on resilience in more than 245 different coral communities, the span of diversity likely overlaps the actual coral diversity found in most reefs."

At the same time, the study provides a framework to successfully manage these ecosystems and help with coral reef restoration by revealing how the resilience of coral communities can be managed by establishing colonies of species with complementary traits.

Looking forward, there are other questions the model can help answer. For instance, the coral species vital for resilience are also the most affected by climate change and might not be able to recover if strong climatic heatwaves become too frequent.

Read more at Science Daily

Pioneering study shows climate played crucial role in changing location of ancient coral reefs

The study, published in Nature Communications, demonstrates how changes in temperature and plate tectonics, where the positions of Earth's continents were in very different positions than today, have determined the distribution of corals through the ages.

Although climate has often been regarded as the main driver of the location of coral reefs, this had yet to be proven due to limited fossil records. Now, for the first time, a team of international scientists used habitat modelling and reconstructions of past climates to predict the distribution of suitable environments for coral reefs over the last 250 million years.

The researchers, from the University of Vigo, in Spain, the University of Bristol and University College London in the UK, then checked their predictions using fossil evidence of warm-water coral reefs. They showed that corals in the past, from 250 to about 35 million years ago, existed much further from the equator than today, due to warmer climatic conditions, and a more even distribution of shallow ocean floor.

"Our work demonstrates that warm-water coral reefs track tropical-to-subtropical climatic conditions over geological timescales. In warmer intervals, coral reefs expanded poleward. However, in colder intervals, they became constrained to tropical and subtropical latitudes," said first author Dr Lewis Jones, a computational palaeobiologist research fellow at the University of Vigo.

Suitable coral habitats became restricted to the tropical regions from about 35 million years ago, driven by global cooling and increases in shallow oceans resulting from tectonic changes of the Indo-Australian Archipelago which is recognised as a marine biodiversity hotspot.

Although this suggests warm temperatures permitted long-term poleward expansions of corals in the past, the researchers say coral reef ecosystems are unlikely to match the rapid rate of human-induced climate change.

"Current anthropogenic climate change will result in the poleward expansion of suitable habitat for coral reefs. In fact, we are already witnessing the expansion of some tropical reef corals. However, whether coral reef ecosystems -- and all the biodiversity they support -- can keep pace with the current rapid rate of anthropogenic climate change is another question," Jones said.

"Limiting global warming is fundamental to saving coral reefs, as well as the biodiversity they house. Yet, perhaps even more important is reducing the rate of global warming."

Warm-water coral reefs, also known as 'rainforests of the sea', support the greatest biodiversity of marine organisms on Earth. In today's oceans, these biologically rich ecosystems, including reef fishes, are limited to the tropics and subtropics, where temperatures of the ocean surface typically do not fall below 18ºC. A substantial proportion of this modern biodiversity is found in the Indo-Australian Archipelago. However, in the geological past, coral reef ecosystems also existed outside of the tropics and subtropics, with their fossil remains found much further from the equator.

Co-author Dr Alex Farnsworth, Senior Research Associate in meteorology and climate modelling from the University of Bristol Cabot Institute for the Environment, said: "Climate has changed significantly throughout geological time, however understanding how it has impacted coral reef ecosystems has been difficult due to a lack of quantifiable data which has significant gaps.

"Using this new combined data-model approach we can start to better understand reef ecosystems evolution and behaviour."

Previous work has failed to find a strong relationship between temperature and the distribution of coral reefs because the fossil record is incomplete and biased. For example, not all the remains of organisms or ecosystems that existed in the past are recorded in the fossil record, and it has been shown the single most important factor explaining the sampled distribution of ancient reefs is Gross Domestic Product, with the majority of known fossil reef data stemming from wealthy countries, purely because these are the regions where we have looked hardest.

Read more at Science Daily

Delicate balance of coral reef processes creates management challenges

An international team of researchers, including several from the University of Hawai'i (UH) at M?noa, has quantified five critical ecological processes on more than 500 coral reefs worldwide to understand how these processes relate to each other, what may distinguish the most functional reefs, and what that means for our management of reef functioning.

Their work, published today in Nature Ecology and Evolution, demonstrates that five key functions performed by fish communities-the removal of algae, predation, biomass production, and the cycling of nitrogen and phosphorus- are inherently interconnected. As such, while the performance of these processes is influenced by the community structure of reef fishes on any given reef, no reef can maximize each of the five processes simultaneously.

Coral reefs are often described as the rainforests of the ocean. They host a high diversity of species and are very productive. Climate change and local threats, such as overfishing, have caused a stark decline in coral reefs worldwide, leaving scientists questioning whether future generations will still encounter healthy, 'functional' coral reefs. But what exactly makes a coral reef 'functional'?

"Imagine a coral reef fish community swirling with small fishes that feed on algae," explained Nina Schiettekatte, the lead author, former doctoral student at the Center for Island Research and Environmental Observatory and postdoctoral fellow at UH M?noa's Hawai'i Institute of Marine Biology (HIMB). "This community will be characterized by high algal consumption and high biomass production, but it will have low phosphorus cycling because these species excrete very little phosphorus."

This means that ecological processes on coral reefs worldwide are in a delicate balance, where it is impossible to maximize all processes. The researchers gained this knowledge by collecting data from individual fishes and combining it with a large dataset on fish communities worldwide.

A detailed look reveals local super heroes

"Throughout this project, we collected thousands of fishes across more than 100 species to gain detailed biological information on how they acquire and use energy and nutrients," explained Jordan Casey, an Assistant Professor at the University of Texas at Austin.

This information can then be projected onto communities to understand how fish communities collectively move biomass and nutrients through the foodweb.

"Our work is novel because it quantifies multiple functions for the first time," Valeriano Parravicini, Professor at EPHE in Perpignan, France stated. "Previously, most researchers have used the biomass of a fish community as a proxy for coral reef functioning but we show that it is critical to look beyond biomass and really disentangle the different components of functioning to understand how reefs work."

Knowing that no reef can excel in all functions, the researchers asked whether there is a certain set of species that is more important than others. Surprisingly, they found that no single species was consistently important across its range, but half of all species were important in at least one location.

"This means that there are no global super-hero fish species for ecosystem functioning," said Sébastien Villéger, researcher at the CNRS in Montpellier, France. "But there are many local super heroes."

A more nuanced management approach

"This work really changes the way we need to think about coral reef conservation," Simon Brandl, an Assistant Professor at the University of Texas at Austin concluded. "Since we cannot maximize all aspects of functioning, we clearly need to develop a more nuanced approach to conserving coral reefs that considers local species, ecosystem dynamics, and stakeholder needs."

Read more at Science Daily

Some coral reefs are keeping pace with ocean warming

Some coral communities are becoming more heat tolerant as ocean temperatures rise, offering hope for corals in a changing climate.

After a series of marine heatwaves hit the Phoenix Islands Protected Area (PIPA) in the central Pacific Ocean, a new study finds the impact of heat stress on the coral communities lessened over time.

While a 2002-2003 heatwave devastated coral communities in PIPA, the reefs recovered and experienced minimal losses during a similar event in 2009-2010. Then, in 2015-2016, a massive heatwave put twice as much heat stress on the corals, yet the die-off was much less severe than expected, according to new research published in Geophysical Research Letters, AGU's journal for high-impact reports with immediate implications spanning all Earth and space sciences.

The authors of the new study suspect heat-tolerant offspring from the surviving corals are repopulating the reefs, allowing the community to keep pace with warming seas, at least for the time being.

The new study could help coral reef managers identify coral communities most likely to survive in the warming ocean, improving conservation and restoration outcomes.

"It's easy to lose faith in coral reefs," said first author Michael Fox, a postdoctoral scientist and coral reef ecologist at the Woods Hole Oceanographic Institution (WHOI). "But in PIPA, which is protected from local stressors, and where reefs have enough time to recover between heatwaves, the coral populations are doing better than expected."

UNDERWATER HEATWAVES

Just like on land, heatwaves underwater are becoming more frequent and intense as the world warms, putting stress on ocean ecosystems. High temperatures hit coral reefs especially hard by causing widespread bleaching events, where corals eject the symbiotic algae in their tissues, further weakening the animals. With continued ocean warming, coral reefs face a dim future.

In the new study, researchers monitored coral communities at four islands within PIPA, an area encompassing over 400,000-square-kilometers of coral reef and deep-sea habitat. The Republic of Kiribati established the reserve in 2008, and the United Nations Educational, Scientific and Cultural Organization (UNESCO) designated PIPA as a World Heritage Site in 2010. "The protected area gives us a rare opportunity to study pristine and isolated coral reef ecosystems, a privilege for which we thank the people of Kiribati," said co-author Anne Cohen, a marine scientist at WHOI.

The team used daily satellite data and temperature loggers to examine how each heatwave impacted the corals. They ruled out 11 environmental factors that might explain the higher-than-expected survival following the 2009-2010 and 2015-2016 heatwaves, such as greater cloud cover or more gradual warming.

After the 2002-2003 heatwave, the surveyed sites lost more than three-quarters of their coral cover. The reef was beginning to recover when the 2009-2010 heatwave hit, sparking fears of widespread bleaching, but two years later, coral cover had increased by more than 5%. Following the "Super El Niño" in 2015-2016, which raised ocean temperatures by 3 degrees Celsius (5.4 degrees Fahrenheit), the loss of coral cover was 40% -- about half of the 2002 losses, despite causing twice the level of thermal stress.

A SOURCE OF HOPE FOR CORAL REEFS

Many of the reef-building species survived the heatwaves. "We're seeing areas that were devoid of corals after 2002-2003 that are now flourishing with most of the original species," Fox said.

At other reefs worldwide, sometimes only a handful of especially hardy or fast-growing species recover after a bleaching event. Coral larvae can float long distances on ocean currents, but due to PIPA's isolation, the researchers hypothesize that local heat-tolerant individuals are repopulating the reefs.

Now that the researchers have shown that some coral communities have the potential to keep up with ocean warming, their next step is to figure out how they are doing it.

The findings are "important for giving us hope for the future of coral reefs, and also for helping to maintain support for protecting reefs, including efforts to reduce local threats, like pollution, sedimentation and overfishing that undermine the reefs' ability to adapt," said Lizzie McLeod, the Global Reef Systems Lead at the Nature Conservancy, who was not involved in the study.

She recommends reef conservationists prioritize the conservation of heat-tolerant reefs, because they can act as climate refuges that repopulate other sites decimated by heatwaves.

The study's authors caution that even these remarkable corals have their limits and reversing climate change remains paramount. As heatwaves become more frequent or intense, even heat-tolerant communities could die out.

Read more at Science Daily

Uncovering how some corals resist bleaching

 Coral reefs are beautiful and diverse ecosystems that power the economies of many coastal communities. They're also facing threats that are driving their decline, including the planet's warming waters.

This threat hit extreme levels in 2015, when high temperatures were turning corals white around the globe. Kaneohe Bay in Hawaii was hit hard; nearly half of its corals bleached.

Hidden in the aftermath of this extreme event, however, were biochemical clues as to why some corals bleached while others were resistant, information that could help reefs better weather warming waters in the future. These clues have now been uncovered by researchers at Michigan State University and the University of Hawaii at Manoa.

"It was kind of horrifying," said coral biologist Crawford Drury, who witnessed 2015's bleaching event from Florida before joining UH Manoa's Hawaii Institute for Marine Biology, or HIMB. "It's disheartening to watch, but I try to think of it as an opportunity."

How this disturbing event became an opportunity is now clear thanks to a Feb. 8 report in Nature Ecology & Evolution that showcases HIMB's stewardship and MSU's biochemical expertise.

The researchers discovered chemical signatures in the corals' biology, or biomarkers, that are present in organisms that were most resistant to the bleaching. This previously hidden insight could help researchers and conservationists better restore and protect reefs around the world.

"Usually, we think of biomarkers as signatures of disease, but this could be a signature of health," said MSU's Robert Quinn, an assistant professor in the Department of Biochemistry and Molecular Biology. "This could help us restore reefs with the most resistant stock."

Corals are symbiotic communities where coral animal cells build homes for algae that provide them energy and create their colors. When corals bleach, however, the algae are lost and leave behind skeletons that are susceptible to disease and death.

This symbiosis also plays a role in a coral's resistance and resilience to bleaching, which HIMB was in a unique position to investigate -- literally. The institute sits right next to the reef, enabling experiments in real time.

"The reef is about 100 feet away," Drury said. "I could be there in 30 seconds."

During the 2015 bleaching event, researchers in the Gates Coral Lab at HIMB had tagged individual corals to keep tabs on them. Because most of the corals recovered, the team could follow them over time.

"We think about it as a biological library," said Drury, the principal investigator with the Gates Coral Lab. "It was set up by researchers in our lab who knew it would be very valuable."

Following the bleaching, the team compared and contrasted coral samples in the wild, noting how the organisms responded and recovered, making some surprising observations along the way. For example, neighboring corals could behave completely differently in response to high temperatures. One coral could bleach completely while its neighbor maintained a healthy golden hue.

To understand why, Drury and HIMB postdoctoral researcher Ty Roach, the lead author of the study, sent samples to Quinn at MSU. Here, Quinn and his team could thoroughly analyze the biochemicals of corals collected from this biological library using a method called metabolomics.

"I'm known more for my medical work," said Quinn, who studies the biochemistry of health and disease in humans. "But I've always loved ocean science. My background is in marine microbiology."

If the coral samples are the books in the library, Quinn's lab used sophisticated equipment to reveal the biochemical language within. In particular, his team used tools known as mass spectrometers to understand what set resistant corals apart from susceptible ones.

"The corals are completely different in their chemistry, but you can't tell until you run the mass spec," Quinn said. "These mass specs are some of the most advanced technology on the planet."

Quinn's team found that corals that were resistant to bleaching and those that were susceptible hosted two different communities of algae. The distinguishing feature between these algal populations was found in their cells, in compounds known as lipids.

The researchers' metabolomic analysis detected two different lipid formulations. Bleaching-resistant corals featured algae that have what are known as saturated lipids. Susceptible corals had more unsaturated lipids.

"This is not unlike the difference between oil and margarine, the latter having more saturated fat, making it solid at room temperature," Quinn said.

This discovery poses all sorts of new questions for researchers: How do the corals get these different algae? Is this difference unique to Hawaiian corals or can it be found elsewhere? How can researchers promote the growth and proliferation of resilient corals in a warming world?

"Mass specs are such incredible machines and reveal intricate details of the chemistry involved. The biology is really the hard part." Quinn said. "We're working on new grants. There are so many avenues to explore."

This initial project was funded by the Paul G. Allen Family Foundation.

"This collaboration has been a great opportunity to ask and answer questions," Drury said. "Hopefully, we're just getting started."

In the meantime, having this chemical information is promising for coral conservation. When conservationists reseed corals to help restore reefs, they can potentially select more resilient specimens.

"We can use natural resilience to better understand, support and manage coral reefs under climate change," Drury said.

Read more at Science Daily

The cement for coral reefs

 Coral reefs are hotspots of biodiversity. As they can withstand heavy storms, they offer many species a safe home, and at the same time, they protect densely populated coastal regions as they level out storm-driven waves. However, how can these reefs that are made up of often very fragile coral be so stable? A team of researchers from Friedrich-Alexander Universität Erlangen-Nürnberg (FAU) and the University of Bayreuth have now discovered that a very specific type of 'cement' is responsible for this -- by forming a hard calcareous skeleton, coralline red algae stabilise the reefs, and have been doing so for at least 150 million years.

The wide variety of life they support is immediately apparent on images of tropical coral reefs. Their three-dimensional scaffolding provides a habitat for a large number of species. However, the skeletons of the coral are often so fragile that they would not be able to withstand heavy storms by themselves. Even if scientists have long suspected that coralline red algae provide support to reefs with their calcareous skeletons, this is the first time that this link has been proven.

Coralline red algae have been supporting coral reefs for at least 150 million years

The researchers from FAU and the University of Bayreuth were able to prove this supporting function by analysing more than 700 fossilised reefs from 150 million years of the Earth's history. 'The coralline red algae form a calcareous skeleton and cement the coral reefs together,' explains Dr. Sebastian Teichert from the Chair of Palaeoenvironmental Research at FAU. 'However, several crises over the course of millions of years have limited their capacity to do so.'

Successful adaptive strategies against plant grazers

These crises include the evolution of plant grazing marine animals such as sea urchins and parrot fishes who have repeatedly decimated populations of coralline red algae over the course of time. The algae, however, developed defence mechanisms such as special growth forms in order to defend themselves against their attackers. 'The algae have adapted so well that they now even benefit from these plant grazers,' says Teichert. 'They rid the coralline red algae of damaging growth such as green algae, allowing it to grow unhindered.' This means coralline red algae are more successful at supporting coral reefs today than ever before in the Earth's history.

Read more at Science Daily

Scientists shed new light on viruses' role in coral bleaching

 Scientists at Oregon State University have shown that viral infection is involved in coral bleaching -- the breakdown of the symbiotic relationship between corals and the algae they rely on for energy.

Funded by the National Science Foundation, the research is important because understanding the factors behind coral health is crucial to efforts to save the Earth's embattled reefs -- between 2014 and 2017 alone, more than 75% experienced bleaching-level heat stress, and 30% suffered mortality-level stress.

The planet's largest and most significant structures of biological origin, coral reefs are found in less than 1% of the ocean but are home to nearly one-quarter of all known marine species. Reefs also help regulate the sea's carbon dioxide levels and are a vital hunting ground that scientists use in the search for new medicines.

Since their first appearance 425 million years ago, corals have branched into more than 1,500 species. A complex composition of dinoflagellates -- including the algae symbiont -- fungi, bacteria, archaea and viruses make up the coral microbiome, and shifts in microbiome composition are connected to changes in coral health.

The algae the corals need can be stressed by warming oceans to the point of dysbiosis -- a collapse of the host-symbiont partnership.

To better understand how viruses contribute to making corals healthy or unhealthy, Oregon State Ph.D. candidate Adriana Messyasz and microbiology researcher Rebecca Vega Thurber of the OSU College of Science led a project that compared the viral metagenomes of coral colony pairs during a minor 2016 bleaching event in Mo'orea, French Polynesia.

Also known as environmental genomics, metagenomics refers to studying genetic material recovered directly from environmental samples, in this case samples taken from a coral reef.

For this study, scientists collected bleached and non-bleached pairs of corals to determine if the mixes of viruses on them were similar or different. The bleached and non-bleached corals shared nearly identical environmental conditions.

"After analyzing the viral metagenomes of each pair, we found that bleached corals had a higher abundance of eukaryotic viral sequences, and non-bleached corals had a higher abundance of bacteriophage sequences," Messyasz said. "This gave us the first quantitative evidence of a shift in viral assemblages between coral bleaching states."

Bacteriophage viruses infect and replicate within bacteria. Eukaryotic viruses infect non-bacterial organisms like animals.

In addition to having a greater presence of eukaryotic viruses in general, bleached corals displayed an abundance of what are called giant viruses. Known scientifically as nucleocytoplasmic large DNA viruses, or NCLDV, they are complex, double-stranded DNA viruses that can be parasitic to organisms ranging from the single-celled to large animals, including humans.

"Giant viruses have been implicated in coral bleaching," Messyasz said. "We were able to generate the first draft genome of a giant virus that might be a factor in bleaching."

The researchers used an electron microscope to identify multiple viral particle types, all reminiscent of medium- to large-sized NCLDV, she said.

"Based on what we saw under the microscope and our taxonomic annotations of viral metagenome sequences, we think the draft genome represents a novel, phylogenetically distinct member of the NCLDVs," Messyasz said. "Its closest sequenced relative is a marine flagellate-associated virus."

Read more at Science Daily

Mysterious glowing coral reefs are fighting to recover

A new study by the University of Southampton has revealed why some corals exhibit a dazzling colourful display, instead of turning white, when they suffer 'coral bleaching' -- a condition which can devastate reefs and is caused by ocean warming. The scientists behind the research think this phenomenon is a sign that corals are fighting to survive.

Many coral animals live in a fragile, mutually beneficial relationship, a 'symbiosis' with tiny algae embedded in their cells. The algae gain shelter, carbon dioxide and nutrients, while the corals receive photosynthetic products to fulfil their energy needs. If temperatures rise just 1?C above the usual summer maximum, this symbiosis breaks down; the algae are lost, the coral's white limestone skeleton shines through its transparent tissue and a damaging process known as 'coral bleaching' occurs.

This condition can be fatal to the coral. Once its live tissue is gone, the skeleton is exposed to the eroding forces of the environment. Within a few years, an entire coral reef can break down and much of the biodiversity that depends on its complex structure is lost -- a scenario which currently threatens the future of reefs around the world.

However, some bleaching corals undergo an, until now, mysterious transformation -- emitting a range of different bright neon colours. Why this happens has now been explained by a team of scientists from the University of Southampton's Coral Reef Laboratory, who have published their detailed insights in the journal Current Biology.

The researchers conducted a series of controlled laboratory experiments at the coral aquarium facility of the University of Southampton. They found that during colourful bleaching events, corals produce what is effectively a sunscreen layer of their own, showing itself as a colourful display. Furthermore, it's thought this process encourages the coral symbionts to return.

Professor Jörg Wiedenmann, head of the University of Southampton's Coral Reef Laboratory explains: "Our research shows colourful bleaching involves a self-regulating mechanism, a so-called optical feedback loop, which involves both partners of the symbiosis. In healthy corals, much of the sunlight is taken up by the photosynthetic pigments of the algal symbionts. When corals lose their symbionts, the excess light travels back and forth inside the animal tissue -reflected by the white coral skeleton. This increased internal light level is very stressful for the symbionts and may delay or even prevent their return after conditions return to normal.

"However, if the coral cells can still carry out at least some of their normal functions, despite the environmental stress that caused bleaching, the increased internal light levels will boost the production of colourful, photoprotective pigments. The resulting sunscreen layer will subsequently promote the return of the symbionts. As the recovering algal population starts taking up the light for their photosynthesis again, the light levels inside the coral will drop and the coral cells will lower the production of the colourful pigments to their normal level."

The researchers believe corals which undergo this process are likely to have experienced episodes of mild or brief ocean-warming or disturbances in their nutrient environment -- rather than extreme events.

Dr. Cecilia D'Angelo, Lecturer of Molecular Coral Biology at Southampton, comments: "Bleaching is not always a death sentence for corals, the coral animal can still be alive. If the stress event is mild enough, corals can re-establish the symbiosis with their algal partner. Unfortunately, recent episodes of global bleaching caused by unusually warm water have resulted in high coral mortality, leaving the world's coral reefs struggling for survival."

Dr. Elena Bollati, Researcher at the National University Singapore, who studied this subject during her PhD training at the University of Southampton, adds: "We reconstructed the temperature history of known colourful bleaching events around the globe using satellite imagery. These data are in excellent agreement with the conclusions of our controlled laboratory experiments, suggesting that colourful bleaching occurs in association with brief or mild episodes of heat stress."

Read more at Science Daily

Climate change triggers Great Barrier Reef bleaching

Australia's iconic Great Barrier Reef is experiencing its third coral bleaching event in just five years. The 2020 bleaching is severe, and more widespread than earlier events.

"We surveyed 1,036 reefs from the air during the last two weeks in March, to measure the extent and severity of coral bleaching throughout the Barrier Reef region," said Professor Terry Hughes, Director of the ARC Centre of Excellence for Coral Reef Studies at James Cook University.

"For the first time, severe bleaching has struck all three regions of the Great Barrier Reef -- the northern, central and now large parts of the southern sectors," Prof Hughes said.

Coral bleaching at regional scales is caused by thermal stress due to spikes in sea temperatures during unusually hot summers. The first recorded mass bleaching event along the Great Barrier Reef occurred in 1998, then the hottest year on record. Four more mass bleaching events have occurred since -- as more temperature records were broken -- in 2002, 2016, 2017, and now in 2020.

This year, February had the highest monthly temperatures ever recorded on the Great Barrier Reef since the Bureau of Meteorology's sea surface temperature records began in 1900.

"Bleaching isn't necessarily fatal, and it affects some species more than others," said Professor Morgan Pratchett, also from Coral CoE at JCU, who led underwater surveys to assess the bleaching.

"A pale or lightly bleached coral typically regains its colour within a few weeks or months and survives," he said.

However, many corals die when bleaching is severe. In 2016, more than half of the shallow-water corals died on the northern region of the Great Barrier Reef.

"We will go back underwater later this year to assess the losses of corals from this most recent event," Prof Pratchett said.

"The north was the worst affected region in 2016, followed by the central region in 2017. In 2020, the cumulative footprint of bleaching has expanded further to include the south."

The distinctive footprint of each bleaching event closely matches the location of hotter and cooler conditions in different years.

"As summers grow hotter and hotter, we no longer need an El Niño event to trigger mass bleaching at the scale of the Great Barrier Reef," Prof Hughes said.

"Of the five events we have seen so far, only 1998 and 2016 occurred during El Niño conditions."

The gap between recurrent bleaching events is shrinking, hindering a full recovery.

"We have already seen the first example of back-to-back bleaching -- in the consecutive summers of 2016 and 2017," Prof Hughes said.

Read more at Science Daily

Warming, acidic oceans may nearly eliminate coral reef habitats by 2100

Coral bleaching.

Rising sea surface temperatures and acidic waters could eliminate nearly all existing coral reef habitats by 2100, suggesting restoration projects in these areas will likely meet serious challenges, according to new research presented in San Diego at the Ocean Sciences Meeting 2020.

Scientists project 70 to 90 percent of coral reefs will disappear over the next 20 years as a result of climate change and pollution. Some groups are attempting to curb this decline by transplanting live corals grown in a lab to dying reefs. They propose new, young corals will boost the reef's recovery and bring it back to a healthy state.

But new research mapping where such restoration efforts would be most successful over the coming decades finds that by 2100, few to zero suitable coral habitats will remain. The preliminary findings suggest sea surface temperature and acidity are the most important factors in determining if a site is suitable for restoration.

"By 2100, it's looking quite grim," said Renee Setter, a biogeographer at the University of Hawaii Manoa who will present the new findings.

The results highlight some of the devastating impacts Earth's warming climate will have on marine life, according to the researchers. Although pollution poses numerous threats to ocean creatures, the new research suggests corals are most at risk from emission-driven changes in their environment.

"Trying to clean up the beaches is great and trying to combat pollution is fantastic. We need to continue those efforts," Setter said. "But at the end of the day, fighting climate change is really what we need to be advocating for in order to protect corals and avoid compounded stressors."

Projecting the future of coral reefs

Coral reefs around the globe face uncertain futures as ocean temperatures continue to climb. Warmer waters stress corals, causing them to release symbiotic algae living inside them. This turns typically vibrant-colored communities of corals white, a process called bleaching. Bleached corals are not dead, but they are at higher risk of dying, and these bleaching events are becoming more common under climate change.

In the new study, Setter and her colleagues mapped what areas of the ocean would be suitable for coral restoration efforts over the coming decades. The researchers simulated ocean environment conditions like sea surface temperature, wave energy, acidity of the water, pollution, and overfishing in areas where corals now exist. To factor in pollution and overfishing, the researchers considered human population density and land cover use to project how much waste would be released into the surrounding waters.

The researchers found most of parts of the ocean where coral reefs exist today won't be suitable habitats for corals by 2045, and the situation worsened as the simulation extended to 2100.

"Honestly, most sites are out," Setter said. The few sites that are viable by 2100 included only small portions of Baja California and the Red Sea, which are not ideal locations for coral reefs because of their proximity to rivers.

Read more at Science Daily

3-D printed coral could help endangered reefs

Natural disasters such as hurricanes often leave devastation in their wake. Residents living in affected areas are sometimes displaced or require temporary shelter while their homes -- or even neighborhoods -- are repaired or rebuilt.

But what if you are a fish and your home is a coral reef?

Researchers across the globe are searching for ways to help endangered reefs, and the animals that live there, withstand or recover from weather events, including bleaching and storms that can occur with increasingly warmer water temperatures.

One idea is to use 3D-printed coral models to replace or supplement coral reef systems that have been affected.

New research by the University of Delaware's Danielle Dixson and UD alumnus Emily Ruhl has shown that 3D-printed objects do not impact the behavior of coral-associated damselfish or the survival of a settling stony coral.

Further, the study demonstrated that fish showed no preference between materials used to 3D-print artificial corals, opening the door to using environmentally friendly materials, such as biodegradable cornstarch instead of plastic.

With mounting concerns about plastic pollution in the marine environment, it is timely evidence that can support environmentally conscious decisions about what is put in the ocean.

The researchers reported their results in PLOS One, a peer-reviewed open source journal.

Testing 3D-printed materials

Like others studying this problem, Dixson and Ruhl are looking for ways to keep the right animals on a reef after an emergency to fuel recovery. One important consideration is knowing that any 3D-printed material used won't harm coral or negatively affect fish behavior.

"If the fish on a reef won't use the 3D-printed coral models as a habitat in the wild, it could place them at greater risk for predation by other larger species," said Dixson, an associate professor in UD's College of Earth, Ocean and Environment's School of Marine Science and Policy. "If coral larvae won't settle on 3D-printed materials, they can't help to rebuild the reef."

In laboratory experiments, the researchers studied the behavior of damselfish and mustard hill coral larvae in the presence of a coral skeleton and four 3D-printed coral models made from different filaments. Blue-green damselfish (Chromis viridis) are a common coral-associated fish found in the Indian and Pacific Oceans, while mustard hill corals (Porites astreoides) are a stony coral found in the Caribbean Sea.

The 3D coral models were made by replicating a coral skeleton using 50 iPhone images of the coral taken from all angles and a 3D printer. The researchers 3D-printed four different artificial coral models from low-cost, widely available filaments, including polyester and two biodegradable materials, one made from cornstarch and another made from cornstarch combined with stainless steel powder.

The researchers placed the damselfish into a fish tank loaded with the coral skeleton and the four artificial habitat options, in what is known as a cafeteria-style choice experiment, and studied whether the fish preferred one habitat over another.

Behavior analysis showed the damselfish did not display a preference between the native coral skeleton and the 3D-printed coral materials. The fish's activity level, such as frequency of movement and distance the fish traveled in the tank, also remained unchanged regardless of what coral habitat they were provided.

Ruhl said she was surprised that the fish behaved the same near artificial coral even with a natural coral skeleton present.

"I thought the natural skeleton would elicit more docile (that is, accepting) behavior compared to 3D-printed objects," said Ruhl, who earned her master's degree in marine biosciences at UD in 2018. "But then we realized the small reef fish didn't care if the habitat was artificial or calcium carbonate, they just wanted protection."

The researchers' lab experiments also revealed that mustard hill coral larvae settled at much higher rates on 3D-printed surfaces compared to having no settlement surface at all, which could occur if a reef were flattened in a storm.

This is promising news since both reef-associated fish and coral are vulnerable animal species, making them a good proxy for understanding how other reef organisms will respond to 3D-printed materials in the open ocean.

As coral reefs degrade, they often lose structural complexity, which is a problem for reef-associated fish that rarely move more than 15 feet from home in their entire lives. Without proper habitat, coral reef associated juvenile fish don't grow up to be bigger fish, and without bigger fish that feed on competitive algae, the algae can overgrow live corals, causing destruction and placing the whole ecosystem at risk.

In ongoing work, the researchers are analyzing field data from Fiji where they deployed 3D-printed coral and tiles made from biodegradable cornstarch filaments after determining they were safe to use. They are analyzing what settled on the artificial tiles, with an eye toward methods that would support conservation efforts.

"Offering 3D-printed habitats is a way to provide reef organisms a structural starter kit that can become part of the landscape as fish and coral build their homes around the artificial coral," Dixson said. "And since the materials we selected are biodegradable, the artificial coral would naturally degrade over time as the live coral overgrows it."

In addition, 3D-printed coral models can be useful as a control for fish-related laboratory studies, enabling researchers to provide each fish an identical habitat, something that is currently not possible with the use of coral skeletons, Dixson said.

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Hope for coral recovery may depend on good parenting

The fate of the world's coral reefs could depend on how well the sea creatures equip their offspring to cope with global warming.

About half the world's coral has been lost due to warming seas that make their world hostile. Instead of vivid and floral, coral bleach pale as temperatures rise. This happens because the peculiar animal cohabitates with algae, which expel under stress. When that happens, coral lose their color and a life partner that sustains them, so they starve.

Yet, hope occurs in aquariums at the USC campus near downtown Los Angeles and at the Australian Institute of Marine Science. There, biologists study coral's unusual ability to shuffle their so-called symbionts -- the algae colonies inside their cells -- as a coping mechanism to potentially gain an advantage in a changing environment. For the first time, the researchers have shown that adult coral can pass along this ability to shuffle their symbionts to their offspring. It's a process that occurs in addition to traditional DNA transfer, and it's never been seen before until scientists began captive breeding research in labs on both sides of the Pacific Ocean.

"What we're finding is that corals can pass their shuffled complement of algal partners, or symbionts, to their offspring to bestow a potential survival advantage, and that's a new discovery," said Carly Kenkel, an assistant professor of biology at the USC Dornsife College of Letters, Arts and Sciences. "We care about this because coral reefs do so much for us. A reef provides breakwater for storms, fish protein people need and biodiversity we love and find beautiful."

The findings appear in a research paper published today in Scientific Reports.

Scientists have known for a long time that coral and algae live in mutual harmony. The two creatures live as one: a soft-bodied polyp animal similar to a sea anemone or jellyfish and an algae living within its cells. The animal provides algae safety and substances for photosynthesis; the algae produce oxygen, help remove wastes and supply the coral with energy. Corals use the energy to make calcium carbonate, the rigid architecture that builds reefs, while the algae contribute to the creatures' jewel-tone hues that make coral spectacular.

They live amicably together until environmental stress disrupts the partnership. When this happens, some coral succumb whereas others are capable of shuffling their symbionts, favoring some algae over others depending on water conditions, competition or available nutrients. "It's a messy divorce," Kenkel said.

Yet in this breakup, the kids could benefit. Kenkel wanted to understand if parent coral could pass along the reshuffled symbionts to its offspring. It's a tricky proposition because the algae exist independent of the cell nucleus and therefore are not part of the nuclear DNA transfer, parent to offspring, during reproduction.

Her curiosity took her to the Great Barrier Reef and Orpheus Island, off northeast Australia, where she joined scientists from James Cook University and the Australian Institute of Marine Science. The research team focused on a particular coral, Montipora digitata, which is common to the western Pacific Ocean and large swaths of the Great Barrier Reef.

The scientists focused on two consecutive spawning seasons: one under normal conditions during 2015 and the other during the global mass coral bleaching event of 2016. Using DNA sequencing, the scientists screened which corals showed potential to shuffle their symbionts and if the change was reflected in gametes. They found that the numbers and types of algal cells differed considerably from one year to the next, as measured in cell densities and photosynthesis output. It's a finding consistent with other research.

Montipora digitata coral can package algae in their eggs when they reproduce. In looking at the eggs between the two years, they discovered that rearrangements of the algae communities in the adults were also reflected in the coral's eggs, indicating that they could be passed down to offspring from the parents.

"To our knowledge, this is the first evidence that shuffled Symbiodiniaceae (symbiont) communities ... can be inherited by offspring and supports the hypothesis that shuffling in microbial communities may serve as a mechanism of rapid coral acclimation to changing environmental conditions," the study said.

The process is perhaps similar to how mitochondrial DNA works in humans. In that analog, the mitochondria -- an energy-producing unit inside the cell but outside the nucleus -- shares genetic material with offspring via the mother's egg. However, the researchers have not identified the mechanism for transfer in coral; they plan to answer that mystery in the next study.

The findings show coral may be more adaptable than thought, but is it enough?

Corals face an enormous challenge as ocean warming is increasing. According to a United Nations report, the world's coral reefs are at the epicenter for climate change impacts and species loss. If the world warms another 0.9 degrees Fahrenheit, which is likely, coral reefs will probably dwindle by 70% to 90%. A gain of 1.8 degrees, the report says, means 99% of the world's coral will be in trouble.

In some regions, the threat to coral is already severe. For example, as much as 80% of Caribbean Sea coral has been lost in the past three decades, according to the Smithsonian Institution.

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Strange coral spawning improving Great Barrier Reef's resilience

Great Barrier Reef

A phenomenon that makes coral spawn more than once a year is improving the resilience of the Great Barrier Reef.

The discovery was made by University of Queensland and CSIRO researchers investigating whether corals that split their spawning over multiple months are more successful at spreading their offspring across different reefs.

Dr Karlo Hock, from UQ's School of Biological Sciences, said coral mass spawning events are one of the most spectacular events in the oceans.

"They're incredibly beautiful," Dr Hock said.

"On Australia's Great Barrier Reef, all coral colonies typically spawn only once per year, over several nights after the full moon, as the water warms up in late spring."

Study co-author Dr Christopher Doropoulos from the CSIRO Oceans & Atmosphere said sometimes however, coral split their spawning over two successive months.

"This helps them synchronise their reproduction to the best environmental conditions and moon phases," he said.

"While reproductive success during split spawning may be lower than usual because it can lead to reduced fertilisation, we found that the release of eggs in two separate smaller events gives the corals a second and improved chance of finding a new home reef."

The research team brought together multi-disciplinary skills in modelling, coral biology, ecology, and oceanography, simulating the dispersal of coral larvae during these split spawning events, among the more than 3800 reefs that make up the Great Barrier Reef.

They looked at whether the split spawning events more reliably supply larvae to the reefs, as well as whether the ability to exchange larvae among the reefs is enhanced by them.

UQ's Professor Peter J. Mumby said split spawning events can increase the reliability of larval supply as the reefs tend to be better connected and have more numerous, as well as more frequent, larval exchanges.

"This means that split spawning can increase the recovery potential for reefs in the region.

"A more reliable supply of coral larvae could particularly benefit reefs that have recently suffered disturbances, when coral populations need new coral recruits the most.

"This will become more important as coral reefs face increasingly unpredictable environmental conditions and disturbances."

Dr Hock said the research also revealed that the natural processes of recovery can sometimes be more resilient than originally thought.

"However, even with such mechanisms in place, coral populations can only withstand so much pressure," he said.

"It all ends up being the matter of scale: any potential benefits from split spawning might be irrelevant if we don't have enough coral on these reefs to reproduce successfully.

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