Tag Archives: Corals

Corals in the Mediterranean are becoming ‘functionally extinct’ due to climate change

Climate change is affecting corals everywhere — including in the Mediterranean, according to a new study.

Paramuricea clavata. Image via Wikimedia.

Coral populations in the Mediterranean are experiencing immense damage due to climate-change-induced heatwaves. Two emblematic species, the red gorgonian (Paramuricea clavata) and the red coral (Corallium rubrum), have lost 80 to 90% of their total biomass since 2003, according to new research.

The findings are very concerning. Coral populations are a linchpin of the marine ecosystems they belong to, providing food and shelter for a multitude of other species. The incredible decline seen in this paper is likely indicative of the broader coral communities in the Mediterranean. If so, wildlife in the sea could be in a much more dire situation than anyone believed.

A sea of troubles

“We observed an average biomass loss regarding the initial biomass of 80% in populations of red gorgonian, and up to a 93% regarding the studied population of red coral,” notes Daniel Gómez, a researcher at the Institute of Marine Sciences of Barcelona (ICM-CSIC) and lead author of the study.

“These data are worrying for the conservation of these emblematic species, and it indicates that the effects of the climate crisis are speeding up with obvious consequences for the submarine landscapes, where the loss of coral equals the loss of trees in forests,” notes Joaquim Garrabou, also member of ICM-CSIC.

The authors explain that populations of the two studied coral species could be unable to recover under current conditions. Their plight comes down to rising temperatures, but especially to significant heatwaves that have impacted the region repeatedly, with the first one occurring in 2003.

Water temperatures are reaching levels that are completely unbearable for these corals and maintaining those temperatures for days, even weeks at a time, the authors explain. While corals all over the world are affected, this is the first study to quantify the effects of climate change and heatwaves on Mediterranean corals in particular. Here, as in other areas, climate change is causing mass mortality in the sea’s coastal ecosystems.

Both species are emblematic of the Mediterranean, underpinning the area’s complex ecosystems. They also have a large role to play in shaping the sea’s distinctive landscapes and look.

Researchers currently have information on the short-term response of corals to marine heatwaves. That being said, corals are long-lived creatures with very slow population dynamics — they are slow to grow and slow to spawn new generations) — so accurately understanding their response to climate change required decades of study. And that’s what the team did.

They used data from a long-term project by the MedRecover research group, which monitored different populations of coral in the protected marine area of Scandola (in Corsega, France) which saw mass mortality after the 2003 heatwave. Of particular interest were population density, size structure, and total biomass, which were used as proxies to estimate the overall health of these coral communities. Data was collected for fifteen years following the heatwave (up to 2018).

The data showed that all populations monitored in the study hadn’t recovered following the heatwave. In fact, they tended to collapse. Today, they are functionally extinct, the team explains.

“We believe one of the main reasons why we observed these collapse trajectories is the potential recurrent exposure to heatwaves [in 2009, 2016, 2017, 2018], incompatible with the slow populational dynamics of these species,” says Cristina Linares, professor at the Department of Evolutionary Biology, Ecology and Environmental Sciences of the Faculty of Biology and member of IRBio, co-author of the paper.

“During these heatwaves, the temperature conditions in the studied area reached extreme levels which are incompatible with the life of these corals, which probably caused new mortality events to the decimated populations and made the recovery impossible.”

These populations are at serious risk of actual extinction, especially since the number and intensity of marine heatwaves is set to increase in the future as the climate crisis deepens. However, the team adds that there are likely some areas in the Mediterranean where the impacts of climate change may be lower due to local factors. These should act as ‘climate refuges’ to help preserve the corals, they conclude.

The team “Population collapse of habitat-forming species in the Mediterranean: a long-term study of gorgonian populations affected by recurrent marine heatwaves” has been published in the journal Proceedings of the Royal Society B: Biological Sciences.

Researchers sequence DNA of coral and their associated organisms

Research from The University of Queensland and James Cook University is looking into which genes allow corals to make friends with algae and bacteria.

Image via Pixabay.

Corals work together with microscopic organisms, establishing symbiotic relationships that benefit both parties. While we’ve been aware of this for some time now, we didn’t understand the biochemical mechanisms that underpin this collaborative predisposition. A new study is shedding light on the subject.

Coral secrets

“Symbiotic relationships are incredibly important for thriving corals,” says Dr. Steven Robbins, the paper’s lead author. “The most striking example of this is coral bleaching, where corals expel their algal symbiotic partners at higher-than-normal water temperatures.”

Corals partner up with algae and bacteria to make ends meet. The coral fishes raw material out of the water and provides housing, and, in return, the algae keeps everyone well fed and plump. Certain stressors, however — especially sustained, excessive heat — can cause a falling out between the two partners, i.e. bleaching. Judging by how well they work together, such a ‘breakup’ is undeniably bad for both, and we know for a fact that coral reefs suffer extensive damage as a result of bleaching episodes.

Dr. Robbins says that the findings further our understanding of these collaborations, and can aid in conserving or perhaps even healing the world’s coral reefs.

“As algae make up the bulk of the coral’s food through photosynthesis, the coral will die if temperatures don’t cool enough to allow symbiosis to re-establish,” he explains. “It’s possible that equally important interactions are happening between corals and their bacteria and single-cell microorganisms (archaea), but we just don’t know.”

The team worked with Porites lutea coral samples retrieved from a reef near Orpheus Island, north of Townsville, Australia. In the lab, they separated the coral itself from its algal symbiotes and associated microbes — then they did genetic sequencing for all the organisms.

After they had a complete picture of the genetic material involved, they used an algorithm to see which genes each actor in the collaboration could draw from.

“This allows us to answer questions like, ‘What nutrients does the coral need, but not make itself?’,” says Dr. Robbins.

Credit: University of Queensland
Associate Professor David Bourne from JCU and the Australian Institute of Marine Science said having high-quality genomes for a coral and its microbial partners was hugely important.

The study’s findings are important as it is the first overall look at the genetic material of corals, their associated organisms, and of the genes that keep them functioning. Associate Professor David Bourne from James Cook University and the Australian Institute of Marine Science calls the findings “truly ground-breaking”, as, in effect, they represent the “blueprint for coral and their symbiotic communities.”

The team hopes that their findings will be put to good use in safeguarding the world’s coral reefs. These beautiful communities have been created by corals over millions of years, but virtually all have experienced bleaching events in recent years as a consequence of man-made climate warming.

“Our coral reefs support incredible diversity and when we lose reefs, we lose far more than corals. There are many threats to coral, but climate change is the most existential [one] for our reefs,” Dr. Robbins said.

“In 2016 and 2017, nearly 50 percent of all corals on the Great Barrier Reef died, and we don’t see this trajectory reversing if carbon emissions remain at current levels.”

On the one hand, research such as this will enable us to better understand corals and to figure out ways of making them more resilient. On the other hand, however, we shouldn’t rest on our laurels. The most straightforward way to safeguard corals and all other life on Earth is to limit our environmental impact by slashing pollution, emissions, and habitat destruction — even kids know this.

The paper “A genomic view of the reef-building coral Porites lutea and its microbial symbionts” has been published in the journal Nature Microbiology.

Researchers look into reviving bleached corals using ‘non-preferred’ algal symbiotes

New research is looking into what makes algae ‘move in’ with their coral hosts — and why the partnership can turn sour, both under normal conditions and when temperatures increase.

Coral polyp.

Coral polyps extending to feed.
Image credits Егор Камелев.

What we know as corals aren’t really alive. They are large exoskeletons built by tiny animals called polyps. Tiny but industrious, these polyps work tirelessly to create the world’s wonderfully colorful coral reefs. A polyp has a sac-like body that ends in a mouth crowned with stinging tentacles called nematocysts (or cnidae). These animals filter calcium and carbonate ions from seawater that they combine to form the limestone (calcium carbonate) they use to build corals that protect their soft, defenseless bodies. If you ever get a chance to visit a coral reef at night, you’ll see these polyps extend their tentacles out to feed.

However, none of this would be possible without the help of various species of single-celled algae we call zooxanthellae, a type of dinoflagellate. These algae live in symbiosis with the polyps, taking up residence inside their cells in a mutually-beneficial relationship: the algae produce nutrients via photosynthesis, while polyps supply the raw materials. The algae are also what gives coral their dazzling colors, which brings us neatly to the subject of:


Warmer mean ocean temperatures (due to anthropic climate change) can apply so much thermal stress on the polyps that they ‘evict’ their symbiotic bacteria in a phenomenon called bleaching. We refer to it this way because, as the algae get expelled, the coral skeletons revert to their natural color: bone-white. If the bleached coral is not recolonized with new algae soon, however, it can die.

“We’re interested in understanding the cellular processes that maintain those preferential relationships,” says Arthur Grossman from the Carnegie Institution for Science, one of the paper’s co-authors.

“We also want to know if it’s possible that more heat tolerant, non-preferred algae could revive bleached coral communities even if the relationship is less efficient.”

The team focused on sea anemones, which are actually closely related to coral (they’re both part of the phylumCnidaria). Sea anemones also host algae, but are easier to work with than corals. The researchers looked at the differences in cellular function that occur when Exaiptasia pallida, a type of anemone, is colonized by two different types of algae — one native strain that is susceptible to thermal bleaching (Breviolum minutum), the other non-native but more resistant to heat (Durusdinium trenchii).

“In this study we hoped to elucidate proteins that function to improve nutrient exchange between the anemone and its native algae and why the anemone’s success is compromised when it hosts the non-native heat resistant algae,” Grossman said.

The anemones colonized by the native algae strain expressed heightened levels of proteins associated with the metabolism of organic nitrogen and lipids. Both are nutrients that get synthesized through the algae’s photosynthetic activity. These anemones also synthesized a protein called NPC2-d, which is believed to underpin the cnidarians’ ability to take in algae and recognize them as a symbiotic partner.

Anemones colonized by non-native algae species expressed proteins associated with stress, the team explains. This is likely indicative of a less-than-ideal integration between the metabolisms of the two organisms, they add.

“Our findings open doors to future studies to identify key proteins and cellular mechanisms involved in maintaining a robust relationship between the alga and its cnidarian host and the ways in which the metabolism of the organisms are integrated,” Grossman concluded.

The results can be used to further our understanding of the biochemical mechanisms that facilitate successful interactions between algae species and the corals that house them. Researchers can explore the metabolic pathways identified in this study to potentially find ways to merge corals with more heat-resistant species — all in a bid to help them both survive in the warmer world we’re creating on Earth.

The paper “Proteomics quantifies protein expression changes in a model cnidarian colonised by a thermally tolerant but suboptimal symbiont” has been published in the journal Nature.

Australia allows 1 million tons of sludge to be spilled into Great Coral Reef

Remember how a few days ago we wrote about the massive mud plume that hit the Great Coral Reef in Australia? Well, there’s another one headed for it — except this one will come directly from the port.

A plume of sediment off the coast of Queensland after recent flooding. Image credits: NASA.

Despite strict regulation against dumping things in and around the reef, port authorities have found a loophole: the law doesn’t apply to dredging spoils. The Great Barrier Reef Marine Park Authority (GBRMPA) has already given the go-ahead to the Port of Hay Point, home to one of the world’s largest coal loading facilities, to spill up to one million tons of sediment around the reef.

The North Queensland Bulk Ports Corporation, which operates the port at Hay Point, argued in a statement that all the spillage would occur at 100 km away from the reef waters, and will cause minimal damage. However, they agree that the home is area to “coral communities [..] and coastal habitats including mangroves”, as well as “a number of protected fauna species [..] including marine turtles, whales, dolphins, dugong, migratory shorebirds and the Water Mouse,” but argue that the area “does not provide critical habitat for any protected marine species.”

“Importantly, our assessment reports have found the risks to protected areas including the Great Barrier Reef Marine Park Authority and Great Barrier Reef Marine Park and sensitive habitats are predominantly low with some temporary, short-term impacts to benthic habitat possible.”

“Risks to sensitive habitats such coral communities are predicted to be low to negligible as they lie outside of area expected to have altered turbidity and sedimentation.”

However, environmentalists and researchers say this only adds insult to injury, and places the already struggling reef at even more risk.

“The last thing the reef needs is more sludge dumped on it, after being slammed by the floods recently,” Australia Green Party senator Larissa Waters, who hopes to get the permit revoked, tells Smee. “One million tonnes of dumping dredged sludge into world heritage waters treats our reef like a rubbish tip.”

Dr. Simon Boxall from the National Oceanography Centre Southampton echoed similar concerns, saying that it will be difficult to carry out the operation in a way that does little damage to corals. If the material gets too close to the reef, it can smother the corals, and even at large distances, trace metals and other chemicals can still have a damaging effect on the corals.

“If it’s put into shallow water it will smother sea life,” he told the BBC. “It’s important they get it right. It’ll cost more money but that’s not the environment’s problem – that’s the port authorities’ problem.”

Corals, and the Great Barrier Reef, in particular, are under massive threat from rising temperatures and bleaching effects. Studies have also shown that human activity is one of the main reasons why the reef is in decline..

Some corals seem to love the taste of plastic — and we’re not sure why

Image credits: Laurent Mekul.

When your grandparents went to the bathroom, they probably weren’t leaving deposits of plastic in the toilet bowl — not like we do, anyway. Recent results of a pilot study in Austria show that human feces contains microplastic. How it gets there is hardly a mystery: plastic is all around us, even in our food. Trophic transfer of toxins and metals has been
known for a long time: for example, it’s the reason we shouldn’t eat too much fish.

Now we see it happening with plastic. This raises the question: how is plastic entering the food chain?

A new study from Duke University has found one surprising entry point. They discovered that some coral species simply love the taste of plastic and will readily eat it. This is counterintuitive, as it’s hard to fathom what evolutionary advantage might be conferred on a coral for liking plastic.

In fact, previous studies have shown that many animals will ingest plastic accidentally, or because the size and shape are similar to a natural food source. However, now we see that some corals will also ingest plastic because of chemicals leaching from the microplastic particles.

The research team housed natural corals in their lab and started feeding them different types of plastic as well as sand. Surprisingly, the corals preferred plastic by a long shot. To address the hypothesis that the corals would accidentally ingest plastic, the researchers fouled pieces of plastic with microorganisms that you might expect to find in the coral’s habitat. You might assume that by adding this layer of biological material to the plastic, it appears more like food to the coral. However, this was not the case.

The study discovered that the corals were much more likely to refuse this microbe-infested meal and stick to the clean microplastic particles. This unexpected result is thought to be because the microbes are masking the plastic’s chemical signals that trick the coral into ingesting them.

Worryingly, the study found that 8% of these ingested plastics are retained in the coral for 24 hours or more — a proportion of which appeared to be permanently stuck. This is bad news for the corals which become full of plastic while gaining no growth benefit from their meal. it’s also bad news for us because, at this point, microplastics can start working their way up the food chain.

The study adds an extra layer of complexity to an already confusing conservation landscape. Now it seems that plastic doesn’t just need to be coated in biological material or look like food to be ingested — it can also taste really good to some animals. The only sure way to prevent the build-up of plastics in our environment and food is to reduce our dependence on it altogether.

This is a guest contribution by Ben Libberton, science communicator and microbiologist. Find out more about Ben by checking out his website.


Hawaii moves to ban common sunscreen mixes in a bid to safeguard its corals

Sunbathers beware — Hawaii plans to become the first US state to ban sunscreen mixes that are toxic to marine life.


Satellite view of the Hawaii archipelago. Image credits Jacques Descloitres, MODIS Land Rapid Response Team at NASA GSFC / Wikimedia.

Two chemicals that are often used in sunscreen mixes (oxybenzone and octinoxate) are also sadly quite very deadly — if you happen to be a coral, a fish, or some other kind of marine resident. While that may not often concern us, landlubbers, especially as we’re basking in the sun on those oh-so-sweet vacation days, it’s a real problem for beach-totting tourist hotspots such as Hawaii.

That’s why the state is moving to ban the sale of sunscreen mixes containing these two compounds, becoming the first US state to do so. The bill was passed by the Hawaii state legislature on Tuesday and is now awaiting the governor’s signature. If this comes to pass, the ban would enter into force in 2021.

More coral protection factor, please

One past study (published in Archives of Environmental Contamination and Toxicology, 2015) has shown that both oxybenzone and octinoxate break down coral reefs by leeching its vital nutrients. The same compounds also disrupt the normal development of simple marine organisms (like algae or sea urchins) as well as more complex creatures (like fish). According to the same paper, these compounds can be found in especially high-concentrations in beaches frequented by tourists.

NOAA has also warned about the dangers such sunscreen compositions pose.

They affect corrals in three different ways: by leeching them of nutrients, by altering their DNA, making coral more susceptible to bleachings, and finally, by inhibiting their endocrine system (i.e. glands), deforming and ultimately killing baby coral. These effects started at extremely low concentrations — only 62 parts per trillion (ppt). Oxybenzone can also turn adult male fish into female fish, cause sexually immature fish to adopt characteristics common to mature, pregnant female fish, is toxic to shrimp, sea urchins, bivalves (e.g., scallops, mussels), and is especially toxic to marine algae (according to the Haereticus Environmental Laboratory in Hawaii).

The reefs of Hawaii and the U.S Virgin Islands showed some of the highest concentrations of oxybenzone out of all coral reefs that attract tourists, the 2015 paper reported. Sunscreen enters the ocean both from direct contact with people wearing such compounds and from wastewater streams that drain into the sea. Both oxybenzone and octinoxate are widely employed in sunscreens, as well as some other types of lotions.

“More and more people realize, as you go home and shower the water is getting treated and put out into the ocean,” Hawaii state Sen. Laura Thielen told KHON2.

“So really it’s damaging our corals no matter whether you’re wearing it on land or at the beach.”

So the only realistic option that Hawaii had at its disposal was a carpet ban on all products containing these compounds. If the governor puts his signature on the bill, vacationers will have to use alternative sunscreen options. Luckily, these options are readily available, with mixes most often substituting ingredients such as titanium oxide or zinc oxide in lieu of the dangerous chemicals.