Tag Archives: #corals

Coral Cells Seen Engulfing Algae For First Time (Marine Biology)


  • For the first time, scientists have seen stony coral cells engulf dinoflagellates – single-celled, photosynthetic algae that are crucial for keeping coral alive
  • The researchers used a cell line called IVB5, which contains endoderm-like cells cultured from the stony coral, Acropora tenuis
  • Around 40% of coral cells incorporated the algae in around 30 minutes and remained healthy for one month
  • The research is a step towards understanding the partnership between coral and dinoflagellates and could shed light on how coral bleaching occurs

Press Release

In a world-first, scientists in Japan have observed individual stony coral cells engulfing single-celled, photosynthetic algae.

The microscopic algae, known as dinoflagellates, were engulfed by cells cultured from the stony coral, Acropora tenuis, the scientists reported in the journal Frontiers in Marine Science.

“Dinoflagellates are crucial for keeping coral healthy and alive,” said Professor Noriyuki Satoh, senior author of the study and head of the Marine Genomics Unit at the Okinawa Institute of Science and Technology Graduate University. “Coral cells take up the algae and provide them with shelter and the building blocks for photosynthesis. In return, the algae provide the corals with nutrients that they synthesize.”

However, in recent decades, this essential relationship has been placed under strain. Driven by pollution, acidification and rising ocean temperatures, stressed coral cells are expelling the microscopic and colorful algae in mass bleaching events, resulting in huge swathes of dead, white reefs.

Stony coral from the Acroporidae family – the most common type of coral found within tropical and subtropical reefs – are particularly susceptible to these bleaching events. These fast-growing corals lay down calcium carbonate skeletons and therefore play a key role in building coral reefs.

“For coral reef conservation, it’s vital for us to fully understand the partnership between stony coral and the algae that live inside these animals, at the level of a single cell,” explained co-first Professor Kaz Kawamura from Kochi University. “But until recently, this was very hard to achieve.”

Coral cells are notoriously difficult to culture, so previously scientists had to rely on experimental systems of other closely related marine creatures, like sea anemones, to study the mechanism of how the dinoflagellates enter and leave cells.

It wasn’t until April 2021 that the research team made a major leap forward, reporting in Marine Biotechnologythat they had successfully cultured different cell lines from larvae of the stony coral, Acropora tenuis, in petri dishes.

For this study, the scientists focused on one coral cell line called IVB5. Many of the cells in this line have similar properties to endodermal cells, in terms of their form, behavior and gene activity. Importantly, in whole coral organisms, it is the endodermal cells that engulf the algae.

The scientists added the dinoflagellate, Breviolum minutum, to a petri dish containing the IVB5 coral cells.

Around 40% of the coral cells in the culture quickly formed long, finger-like projections that reached out to contact the dinoflagellates. The algae were then “swallowed” up, in a process taking around 30 minutes.

Caption: Dinoflagellates are single-celled algae that are essential for keeping corals healthy and alive. When dinoflagellates are added to coral cell in a petri dish, the coral cells quickly engulf the algae. Credit: Dr. Kaz Kawamura and Dr. Satoko Sekida, Kochi University

“It was amazing to see – it was almost a dream!” said Prof. Satoh.

Over the following couple of days, the algae inside the cell were either broken down into fragments or were successfully enclosed into membrane-bound sacs, called vacuoles, within the cells. For the researchers, this hints at how the relationship possibly started millennia ago.

“It may be that originally, the ancestors of coral engulfed these algae and broke them down for food. But then over time, they evolved to use the algae for photosynthesis instead,” co-first author, Dr. Satoko Sekida from Kochi University suggested.

The researchers are now using electron microscopes to gain more detailed images of how the coral cells engulf the dinoflagellates. They are also working on genetic experiments to pinpoint which coral genes are involved.

At this stage, the coral cells containing the algae live for around a month before dying. In the near future, the team hope to achieve a stable culture where both the coral cells and dinoflagellates can reproduce together.

“This would be very exciting as then we can ask new questions, like how the corals react when placed under stress,” said Prof. Satoh. “This could give us a more complete understanding of how bleaching occurs, and how we can mitigate it.”

Featured image: Caption: As marine heatwaves become more commonplace, coral reefs are expelling their microscopic and colorful algae and bleaching white. Scott Reef, Australia, April 2016.Credit: Australian Institute of Marine Science. This image has been cropped.

Article Information

  • Title: In vitro symbiosis of reef-building coralcells with photosynthetic dinoflagellates
  • Journal: Frontiers in Marine Science
  • DOI: 10.3389/fmars.2021.706308
  • Authors: Noriyuki Satoh, Kaz Kawamura,Satoko Sekida, Koki Nishitsuji, Eiichi Shoguchi,KanakoHisata, Shigeki Fujiwara
  • Date: 14th July 2021

Provided by OIST

Coral on the Red List of Endangered Species (Botany)

Data from extinct species helps to improve the assessment of extinction risk

The traits of coral species that have become extinct during the last few million years do not match those of coral species deemed at risk of extinction today. In a recently published article in the journal ‘Global Ecology and Biogeography’, a research team at FAU is therefore proposing that the International Union for Conservation of Nature (IUCN) revises its Red List of Threatened Species for coral.

The list categorises around a third of all 845 coral species that build reefs as endangered. The Red Lists published by the IUCN are considered extremely reliable as they are compiled by leading experts who regularly investigate how species populations have developed over the course of the last few years and decades. In conjunction with other factors such as conservation efforts or foreseeable influences such as climate change, these figures reliably predict the risk posed to a species in the future. ‘Unfortunately, it is extremely difficult to identify such trends for coral populations using the data currently available,’ explains Prof. Dr. Wolfgang Kießling,

Nussaïbah Raja Schoob at the Chair of Palaeoenvironmental Research (Prof. Kießling) at FAU therefore used an alternative method to investigate the extinction risk in reef coral in a collaborative project involving teams from the University of Queensland, Australia, and the University of Iowa in the USA. Schoob, who is a geoscientist, first investigated which traits the coral species on the Red List have in common. Climate change plays a significant role in the risk to this group. A similar phenomenon occurred during the last five million years when a land bridge formed between North and South America, which permanently shut down a strong ocean current from the Pacific into the Caribbean. This caused considerable changes to extremely important characteristics in the seawater such as temperature and salt content. At this time,18 species of coral disappeared from the Caribbean, and six of these species even became extinct. ‘We wanted to know which traits make coral species particularly sensitive to such significant changes and which traits improve their resilience,’ explains Nussaïbah Raja Schoob.

Schoob investigated a series of parameters such as the greatest water depth at which coral is found, the temperatures their larvae tolerate, how fast coral grows and which types of algae coral form symbiotic relationships with. Using machine learning, computer programmes identified similarities in the species that disappeared from the Caribbean in the past as well as in those which survived. Artificial intelligence was then used to identify the shared traits of the coral species categorised as endangered by the IUCN. Only 18 percent of the species on the Red List matched the results of the machine learning study based on palaeoenvironmental data.

‘These results contradicted all our expectations and we were therefore very puzzled by them,’ remembers Wolfgang Kießling. The researchers reviewed their findings to identify what had caused this discrepancy. It was unlikely that data from the coral populations of the past millions of years in the Caribbean had caused the unexpected findings. ‘This data is based on facts that we can observe and measure,’ explains Wolfgang Kießling. The scientists began to wonder if the problem was related to the Red Lists data.

This is where Nussaïbah Raja Schoob made a significant finding. The established and very successful system used by the IUCN to predict the risk to future populations of a species based on its population dynamics quickly reached its limits when examining reef-building coral. ‘There is hardly any data about population dynamics,’ explains Nussaïbah Raja Schoob. The IUCN had to adjust its methods and assessed the risk of extinction according to the changes in the surface area covered by coral reefs. ‘Even though this data is very important for the protection of coral reefs, which play an extremely important role for marine life they simply do not provide enough information about the risk to individual species for a very simple reason: Coral can also grow outside a reef directly on the sea floor, and this is quite common,’ explains Wolfgang Kießling. This means that there are usually still a few billion individuals of the species categorised as endangered, growing scattered on the ocean floor, which cannot simply just die off there simultaneously.

‘Our results show how important data from species that became extinct a long time ago is for assessing the risk for species that are alive today,’ explains Nussaïbah Raja Schoob. These palaeontological findings are a valuable source of data for developing the IUCN methods. Even if this means that the risk status of some coral species could be reduced, the study gives anything but the all-clear. ‘Coral reefs still continue to disappear, and with them a fantastic habitat that is very important for our oceans,’ says Wolfgang Kießling.

Original article: DOI: 10.1111/geb.13321

Featured image: How high is the extinction risk of coral in our oceans? FAU researcher Nussaïbah Raja Schoob used artificial intelligence to examine data from species that became extinct millions of years ago to assess this risk. (Image: Wolfgang Kießling)

Reference: Raja, NB, Lauchstedt, A, Pandolfi, JM, Kim, SW, Budd, AF, Kiessling, W. Morphological traits of reef corals predict extinction risk but not conservation status. Global Ecol Biogeogr. 2021; 00: 1– 12. https://doi.org/10.1111/geb.13321

Provided by FAU

How Reef-building Corals Got Their Bones? (Biology)

Coral ancestors had the genetic toolkit to make skeletal structures and only took simple evolutionary steps to begin building reefs.

Coral reefs provide shelter, sustenance and stability to a range of organisms, but these vital ecosystems would not exist if not for the skeletal structure created by stony corals. Now, KAUST scientists together with an international team have revealed the underlying genetic story of how corals evolved from soft-bodied organisms to build the myriad calcified structures we see today.

“While the processes involved in coral calcification are well understood, it is less clear how corals’ ability to grow calcium carbonate skeletons actually evolved,” says Xin Wang, a former KAUST Ph.D. student who worked on the project under the supervision of Manual Aranda.

“How did a squishy anemone-like organism begin to build reefs?” asks Aranda. “Did the ‘tools’ already exist in their genetic code?”

There is a debate surrounding when calcified corals first began to emerge; the earliest fossils found to date are around 265 million years old, but their evolution began far earlier.

The complex genomic analysis took two years to complete on KAUST's Shaheen-II Supercomputer.
The complex genomic analysis took two years to complete on KAUST’s Shaheen-II Supercomputer. © 2021 Morgan Bennett Smith

“We conducted a genomic search for conserved genes that might be involved in calcification,” says Wang. “Our findings suggest that corals evolved to calcify somewhere between 308 and 265 million years ago.”

The team compared the genomes of six different related species — two evolutionary divergent reef-building corals, two of their closest noncalcifying relatives and two sea anemones. The complex analysis took two years using the KAUST supercomputer.

“We found that the necessary proteins to make coral skeletons were already present in the soft-bodied ancestor and that various existing proteins were recruited to boost the calcifying process. Essentially, we believe we’ve found the genetic toolkit for coral skeleton creation,” says Wang.

To calcify, corals must draw in positively charged calcium ions from seawater. To make this process as efficient as possible, the coral proteins that help the calcium precipitate should be negatively charged and the pH balance of the calcifying fluid must be just right.

The team pinpointed the genes responsible for transporting calcium and removing protons in the soft-bodied organisms, and they showed that two of the three gene copies found in corals have been recruited to the calcifying tissue. The researchers then identified a gene encoding an acid-rich protein that was duplicated in corals twice and then recruited to precipitate and stabilize calcium carbonate in the initial stage of skeleton building. They also highlighted transmembrane proteins involved in bone matrix adhesion.

“This is a great example of how latent traits can evolve to become dominant given certain environmental pressures,” says Aranda. “Next we hope to verify which of these components is critical to calcification and investigate how coral reefs might be influenced by the changing pH of future oceans.”

Featured image: The genetic toolkit to produce skeletal structures that corals developed from their soft-bodied ancestors has been identified by KAUST researchers. © 2021 Morgan Bennett Smith


  1. Wang, X., Zoccola, D., Liew, Y.J., Tambutte, E., Cui, G., Allemand, D., Tambutte, S. & Aranda, M. The evolution of calcification in reef-building corals. Molecular Biology and Evolution advance online publication, 19 April2021.| article

Provided by KAUST

Could Corals Use Sound to Communicate? (Biology)

New evidence suggests corals may have genes involved in receiving or emitting sound

Corals are part of a highly complex ecosystem, but it remains a mystery if and how they might communicate within their biological community. In a new study, researchers found evidence of sound-related genes in corals, suggesting that the marine invertebrates could use sound to interact with their surroundings.

Coral reefs make up less than 1% of the ocean floor yet support more than 25% of all marine life. Around the world, coral reefs are being threatened by climate change, ocean acidification, diseases, overfishing and pollution. A better understanding of coral communication could help inform policies that aim to protect this critical ecosystem.

“A growing number of studies have shown that trees can communicate, and that this communication is important for ecosystems such as rain forests,” said Camila Rimoldi Ibanez, a high school student in the dual enrollment program at South Florida State College. “Coral reefs are often referred to as the rainforests of the sea because of the habitat they provide for a wide variety of plants and animals. Thus, we wanted to find out how coral communicates.”

Ibanez will present the new findings at the American Society for Biochemistry and Molecular Biology annual meeting during the virtual Experimental Biology (EB) 2021 meeting, to be held April 27-30. Her mentor is James Hawker, PhD, dean of arts and sciences at South Florida State College.

Camila Rimoldi Ibanez works with extracted coral DNA in the lab. © Camila Rimoldi Ibanez and James Hawker, South Florida State College

Many organisms that live in coral reefs perceive sound and use it to find their way to the reefs. Based on this information, the researchers decided to look for the presence of genes related to the reception and/or emission of sound in the coral Cyphastrea. Using PCR amplification, the researchers found probable evidence that two of the four genes they examined may be present in coral DNA. The genes they found — TRPV and FOLH-1 — are used for sound emission or reception in sea anemones and freshwater polyps, respectively.

In addition to performing more testing, the researchers want to sequence the TRPV and FOLH-1 genes they found to add additional evidence that these genes, or genes related to them, are present in coral.

“As we learn more about the negative impacts of sound in different kinds of ecosystems, it is vital that we set policies to protect and manage human noises in natural environments,” said Ibanez. “The more we know about how corals communicate, the better we can develop restoration and conservation projects to help corals as they face bleaching epidemics and other threats.”

Camila Rimoldi Ibanez will present the findings in poster R4543 (abstract). Contact the media team for more information or to obtain a free press pass to access the meeting.

Featured image: Researchers performed PCR amplification on extracted coral DNA mixed with primers for four genes related to sound emission or reception. If a gene is present, it will be amplified by PCR and can be detected by agarose gel electrophoresis as DNA bands of a specific size. The DNA bands showed probable presence of TRPV and FOLH-1 genes in coral DNA. © Camila Rimoldi Ibanez and James Hawker, South Florida State College

Provided by Experimental Biology

Scientists Have Cultured the First Stable Coral Cell Lines (Biology)


  • Researchers have successfully grown cells from the stony coral, Acropora tenuis, in petri dishes
  • The cell lines were created by separating out of cells from coral larvae, which then developed into eight distinct cell types
  • Seven out of eight cell types were stable and could grow indefinitely, remaining viable even after freezing
  • Some of the cell types represented endoderm-like cells, and could therefore shed light on how coral interacts with photosynthesizing algae and how bleaching occurs
  • The cell lines could be used in many avenues of coral cell research, including coral development, coral farming and the impact of climate change and pollution

Press release

Researchers in Japan have established sustainable cell lines in a coral, according to a study published today in Marine Biotechnology.

Seven out of eight cell cultures, seeded from the stony coral, Acropora tenuis, have continuously proliferated for over 10 months, the scientists reported.

“Establishing stable cells lines for marine organisms, especially coral, has proven very difficult in the past,” said Professor Satoh, senior author of the study and head of the Marine Genomics Unit at the Okinawa Institute of Science and Technology Graduate University (OIST). “This success could prove to be a pivotal moment for gaining a deeper understanding of the biology of these vitally important animals.”

Acropora tenuis belongs to the Acroporidae family, the most common type of coral found within tropical and subtropical reefs. These stony corals are fast growers and therefore play a crucial role in the structural formation of coral reefs.

A colony of Acropora tenuis grown in a natural sea environment and transferred to an aquarium to induce spawning. This image was reproduced from “Establishing sustainable cell lines of a coral, Acropora tenuis” by Kawamura et al, Marine Biotechnology.

However, Acroporidae corals are particularly susceptible to changes in ocean conditions, often undergoing bleaching events when temperatures soar or when oceans acidify. Establishing knowledge about the basic biology of these corals through cell lines could one day help protect them against climate change, explained Professor Satoh.

Creating the cultures

In the study, Professor Satoh worked closely with Professor Kaz Kawamura from Kochi University – an expert in developing and maintaining cell cultures of marine organisms.

Since adult coral host a wide variety of microscopic marine organisms, the group chose to try creating the cell lines from coral larvae to reduce the chances of cross-contamination. Another benefit of using larval cells was that they divide more easily than adult cells, potentially making them easier to culture.

Planula larva of Acropora tenuis. This image was reproduced from “Establishing sustainable cell lines of a coral, Acropora tenuis” by Kawamura et al, Marine Biotechnology.

The researchers used coral specimens in the lab to isolate both eggs and sperm and fertilize the eggs. Once the coral larvae developed, they separated the larvae into individual cells and grew them in petri dishes.

Initially, the culture attempts ended in failure. “Small bubble bodies appeared and then occupied most of the petri dish,” said Professor Kaz Kawamura. “We later found that these were the fragments of dying stony coral cells.”

In the second year, the group discovered that by adding a protease called plasmin to the cell culture medium, right at the beginning of the culture, they could stop the stony coral cells from dying and keep them growing.

Two to three weeks later, the larval cells developed into eight different cell types, which varied in color, form and gene activity. Seven out of the eight continued to divide indefinitely to form new coral cells.

The microscope image shows three of the cell lines established in the study, ranging in color and form. This image was reproduced from “Establishing sustainable cell lines of a coral, Acropora tenuis” by Kawamura et al, Marine Biotechnology.

Exploring the symbiosis integral to coral survival

One of the most exciting advancements of this study was that some of the cell lines were similar in form and gene activity to endodermal cells. The endoderm is the inner layer of cells formed about a day after the coral eggs are fertilized.

Corals are the one of the simplest animals, with only two layers of cells (called germ layers) forming in early embryonic development – an inner layer, the endoderm, and an outer layer, the ectoderm. Each germ cell layer ultimately develops into different types of cells, including digestive cells, muscle-like cells, nerve-like cells and stinging cells (cnidocytes) but how each cell type forms during development still requires investigation.

Importantly, it is the cells in the endoderm that incorporate the symbiotic algae, which photosynthesize and provide nutrients to sustain the coral.

“At this point in time, the most urgent need in coral biology is to understand the interaction between the coral animal and its photosynthetic symbiont at the cellular level, and how this relationship collapses under stress, leading to coral bleaching and death,” said Professor David Miller, a leading coral biologist from James Cook University, Australia, who was not involved in the study.

He continued: “Subject to confirmation that these cells in culture represent coral endoderm, detailed molecular analyses of the coral/photosymbiont interaction would then be possible – and from this, real advances in understanding and perhaps preventing coral bleaching could be expected to flow.”

For Professor Satoh, his interest is in how the photosymbiotic algae cells, which are almost as big as the larval cells, initially enter the coral.

“The algae are incorporated into the coral cells around a week after the larvae first develop,” said Prof. Satoh. “But no one has yet observed this endosymbiotic event on a single-cell level before.”

A new era for coral cell research

The scientists also found that the coral cell lines were still viable after being frozen with liquid nitrogen and then thawed. “This is crucial for being able to successfully supply the coral cell lines to research laboratories across the globe,” said Professor Satoh.

The implications for future research using these cell lines are far-reaching, ranging from research on how single coral cells respond to pollution or higher temperatures, to studying how corals produce the calcium carbonate that builds their skeleton.

Research could also provide further insight into how corals develop, which could improve our ability to farm coral.

In future research, the team hopes to establish cells lines that are clonal, meaning every cell in the culture is genetically identical.

“This will give us a much clearer idea of exactly which coral cell types we are growing, for example gut-like cells or nerve-like cells, by looking at which genes are switched on and off in the cells,” said Professor Satoh.

Header image credited to Chuya Shinzato

Article Information

Journal: Marine Biotechnology
Paper: Establishing Sustainable Cell Lines of a Coral, Acropora tenuis
DOI: 10.1007/s10126-021-10031-w
Authors: Kaz Kawamura · Koki Nishitsuji · Eiichi Shoguchi · Shigeki Fujiwara · Noriyuki Satoh

Provided by OIST

Corals Carefully Organize Proteins to Form Rock-Hard Skeletons (Botany)

Scientists’ findings suggest corals will withstand climate change

Charles Darwin, the British naturalist who championed the theory of evolution, noted that corals form far-reaching structures, largely made of limestone, that surround tropical islands. He didn’t know how they performed this feat.

Now, Rutgers scientists have shown that coral structures consist of a biomineral containing a highly organized organic mix of proteins that resembles what is in our bones. Their study, published in the Journal of the Royal Society Interface, shows for the first time that several proteins are organized spatially – a process that’s critical to forming a rock-hard coral skeleton.

“Our research revealed an intricate network of skeletal proteins that interact spatially, which likely applies to all stony corals,” said Manjula P. Mummadisetti, who led the research while she was a postdoctoral associate in the Rutgers Environmental Biophysics and Molecular Ecology Laboratory led by senior author Paul G. Falkowski. She is now a senior scientist at AVMBioMed in Pottstown, Pennsylvania. “It’s important to understand the mechanisms of coral biomineralization and how these invaluable animals persist during the era of anthropogenic climate change.”

“Our findings suggest that corals will withstand climate change caused by human activities, based on the precision, robustness and resilience of their impressive process for forming rock-hard skeletons,” said Falkowski, a Distinguished Professor in the School of Arts and Sciences and School of Environmental and Biological Sciences at Rutgers University–New Brunswick.

Coral reefs protect shorelines threatened by erosion and storms, and provide fish habitat, nursery and spawning grounds. Indeed, coral reefs provide food for about a half-billion people, who also depend on them to make a living. However, warming ocean waters from climate change put corals at risk from deadly bleaching and disease. More acidic ocean waters, sea-level rise, unsustainable fishing, vessels that damage reefs, invasive species, marine debris and tropical cyclones pose additional threats, according to the National Oceanic and Atmospheric Administration.

Rutgers scientists studied the spatial interactions of the proteins embedded within the skeleton of Stylophora pistillata, a common stony coral in the Indo-Pacific. Stony corals have evolved over more than 400 million years, forming enormous reefs in shallow subtropical and tropical seas. They’ve been called the “rainforests of the sea.”

Predicting the survival of corals based on how they adapted to global climate change over millions of years requires understanding, among other things, how they build reefs by secreting calcium carbonate. That process is called biomineralization.

The scientists showed that several proteins work together to create optimal conditions for biomineralization. These proteins are not located randomly but are well-organized spatially, which the scientists detailed for the first time. The scientists revealed the spatial patterns as new mineral is formed between the living tissue of the animal and its base or an older skeleton.

Jeana Drake, who earned a doctorate at Rutgers and coauthored the study, is now at the University of California, Los Angeles, and the University of Haifa.

Featured image: Stylophora pistillata, a common stony coral in the Indo-Pacific. Photo: Kevin Wyman/Rutgers University

Reference: Manjula P. Mummadisetti, Jeana L. Drake and Paul G. Falkowski, “The spatial network of skeletal proteins in a stony coral”, Journal of Royal Society Interface, Published:24 February 2021. https://doi.org/10.1098/rsif.2020.0859

Provided by Rutgers University

Scientists Discover Slimy Microbes That May Help Keep Coral Reefs Healthy (Biology)

The bacteria scrub out nitrogen, potentially defending against certain nutrient overloads.

Corals have evolved over millennia to live, and even thrive, in waters with few nutrients. In healthy reefs, the water is often exceptionally clear, mainly because corals have found ways to make optimal use of the few resources around them. Any change to these conditions can throw a coral’s health off balance.

Coral reefs, such as Los Jardines de la Reina, pictured, have microbes that may help protect the coral against certain nutrient imbalances. Credits: Image: Robert Walker

Now, researchers at MIT and the Woods Hole Oceanographic Institution (WHOI), in collaboration with oceanographers and marine biologists in Cuba, have identified microbes living within the slimy biofilms of some coral species that may help protect the coral against certain nutrient imbalances.

The team found these microbes can take up and “scrub out” nitrogen from a coral’s surroundings. At low concentrations, nitrogen can be an essential nutrient for corals, providing energy for them to grow. But an overabundance of nitrogen, for instance from the leaching of nitrogen-rich fertilizers into the ocean, can trigger mats of algae to bloom. The algae can outcompete coral for resources, leaving the reefs stressed and bleached of color.

By taking up excess nitrogen, the newly identified microbes may prevent algal competition, thereby serving as tiny protectors of the coral they inhabit. While corals around the world are experiencing widespread stress and bleaching from global warming, it seems that some species have found ways to protect themselves from other, nitrogen-related sources of stress.

“One of the aspects of finding these organisms in association with corals is, there’s a natural way that corals are able to combat anthropogenic influence, at least in terms of nitrogen availability, and that’s a very good thing,” says Andrew Babbin, the Doherty Assistant Professor in Ocean Utilization in MIT’s Department of Earth, Atmospheric and Planetary Sciences. “This could be a very natural way that reefs can protect themselves, at least to some extent.”

Babbin and his colleagues have reported their findings in the the ISME Journal.

Dead zone analogues

Babbin’s group studies how marine communities in the ocean cycle nitrogen, a key element for life. Nitrogen in the ocean can take various forms, such as ammonia, nitrite, and nitrate. Babbin has been especially interested in studying how nitrogen cycles, or is taken up, in anoxic environments — low-oxygen regions of the ocean, also known as “dead zones,” where fish are rarely found and microbial life can thrive.

“Locations without enough oxygen for fish are where bacteria start doing something different, which is exciting to us,” Babbin says. “For instance, they can start to consume nitrate, which has then an impact on how productive a specific part of the water can be.”

Researchers incubated coral fragments in contained chambers to measure the rates of microbial activity, as seen on the left. MIT professor Andrew Babbin sets up an incubation on the right. Credits: Courtesy of Andrew Babbin

Dead zones are not the only anoxic regions of the ocean where bacteria exhibit nitrogen-feasting behavior. Low-oxygen environments can be found at smaller scales, such as within biofilms, the microbe-rich slime that covers marine surfaces from shipwrecked hulls to coral reefs.

“We have biofilms inside us that allow different anaerobic processes to happen,” Babbin notes. “The same is true of corals, which can generate a ton of mucus, which acts as this retardation barrier for oxygen.”

Despite the fact that corals are close to the surface and within reach of oxygen, Babbin wondered whether coral slime would serve to promote “anoxic pockets,” or concentrated regions of low oxygen, where nitrate-consuming bacteria might thrive.

He broached the idea to WHOI marine microbiologist Amy Apprill, and in 2017, the researchers set off with a science team on a cruise to Cuba, where Apprill had planned a study of corals in the protected national park, Jardines de la Reina, or Gardens of the Queen.

“This protected area is one of the last refuges for healthy Caribbean corals,” Babbin says. “Our hope was to study one of these less impacted areas to get a baseline for what kind of nitrogen cycle dynamics are associated with the corals themselves, which would allow us to understand what an anthropogenic perturbation would do to that system.”

Swabbing for scrubbers

In exploring the reefs, the scientists took small samples from coral species that were abundant in the area. Onboard the ship, they incubated each coral specimen in its own seawater, along with a tracer of nitrogen — a slightly heavier version of the molecules found naturally in seawater.

They brought the samples back to Cambridge and analyzed them with a mass spectrometer to measure how the balance of nitrogen molecules changed over time. Depending on the type of molecule that was consumed or produced in the sample, the researchers could estimate the rate at which nitrogen was reduced and essentially denitrified, or increased through other metabolic processes.

In almost every coral sample, they observed rates of denitrification were higher than most other processes; something on the coral itself was likely taking up the molecule.

The researchers swabbed the surface of each coral and grew the slimy specimens on Petri dishes, which they examined for specific bacteria that are known to metabolize nitrogen. This analysis revealed multiple nitrogen-scrubbing bacteria, which lived in most coral samples.

“Our results would imply that these organisms, living in association with the corals, have a way to clean up the very local environment,” Babbin says. “There are some coral species, like this brain coral Diploria, that exhibit extremely rapid nitrogen cycling and happen to be quite hardy, even through an anthropogenic change, whereas Acropora, which is in rough shape throughout the Caribbean, exhibits very little nitrogen cycling. “

Whether nitrogen-scrubbing microbes directly contribute to a coral’s health is still unclear. The team’s results are the first evidence of such a connection. Going forward, Babbin plans to explore other parts of the ocean, such as the tropical Pacific, to see whether similar microbes exist on other corals, and to what extent the bacteria help to preserve their hosts. His guess is that their role is similar to the microbes in our own systems.

“The more we look at the human microbiome, the more we realize the organisms that are living in association with us do drive our health,” Babbin says. “The exact same thing is true of coral reefs. It’s the coral microbiome that defines the health of the coral system. And what we’re trying to do is reveal just what metabolisms are part of this microbial network within the coral system.”

Reference: Babbin, A.R., Tamasi, T., Dumit, D. et al. Discovery and quantification of anaerobic nitrogen metabolisms among oxygenated tropical Cuban stony corals. ISME J (2020). https://www.nature.com/articles/s41396-020-00845-2 https://doi.org/10.1038/s41396-020-00845-2

Provided by MIT

Coral Larvae Movement Is Paused In Reaction To Darkness (Biology)

Coral larvae movement is paused in reaction to darkness. Researchers find a new light responding behavior that may affect where corals live.

Light is essential for the growth of reef-building corals. This is because corals grow by using the photosynthetic products of the algae living inside their cells as a source of nutrients. Therefore, the light environment of coral habitats are important for their survival.

A type of reef-building coral, Acropora tenuis. ©NIBB

A new study published in Scientific Reports shows that coral larvae swimming in seawater behave in such a manner so as to temporarily stop swimming due to reduced light, especially blue light. Researchers think that this behavior may play a role in determining where corals settle.

Corals can only move freely during the larval stage of their lives. Larvae that hatch from eggs are able to swim by moving the cilia on the surface of their bodies. After that, when the larva settles on the seabed and transforms into a sedentary form (called a “polyp”), it becomes immobile.

How the corals, whose growth requires light, select a suitable light environment for survival is a mystery. To solve it, a research team led by Dr. Yusuke Sakai, Professor Naoto Ueno of the National Institute for Basic Biology in Japan thoroughly observed the response of coral larvae to light. They found that coral larvae temporarily stop swimming in response to a decrease in light intensity and then subsequently resumed swimming at their initial speed.

Upon light attenuation (at the 0 sec mark in the movie), the larvae temporarily stopped swimming (from around 20 sec mark). After a certain period of time from the light attenuation, the larvae resume swimming (from around 120 sec mark).

Corals mostly lay eggs once a year. “In collaboration with Andrew Negri, principal investigator at the Australian Institute of Marine Science, and Professor Andrew Baird and his colleagues at James Cook University, we have not only tested corals in Japan, but also in Australia’s Great Barrier Reef, where coral spawning occurs at a different time than here. This was performed in order to repeat the experiment and thus validate our findings ” said Dr. Sakai.

A larvae of Acropora tenuis. ©NIBB

The research team then conducted a detailed analysis of the wavelengths of light that coral larvae react to. The Okazaki Large Spectrograph, the world’s largest spectroscopic irradiator at the National Institute for Basic Biology, was used for this experiment. Experiments with coral larvae exposed to various light wavelengths revealed that coral larvae respond strongly to purple to blue light.

How does pausing behavior in response to light decay affect the destination of coral larvae? To answer this question, researchers conducted mathematical simulations; the results of which show that the pause caused by the attenuation of light and the subsequent resumption of swimming have the effect of resetting the swimming direction of the larva once when it moves into a dark region and turning it in a random direction. As a result, it was suggested that it would lead to the gathering of larvae in a bright space.

Dr. Sakai said “In cnidarians, including corals, the mechanism of light reception is largely unknown. We would like to clarify the molecular mechanism of light reception in coral larvae, which do not have an eye structure”.

“In the future, it will be important to elucidate not only this phenomenon but also the mysterious ecology of coral at the molecular and cellular levels, such as the mechanism for controlling the spawning time” Professor Naoto Ueno commented.

References: “A step-down photophobic response in coral larvae: implications for the light-dependent distribution of the common reef coral, Acropora tenuis” by Yusuke Sakai, Kagayaki Kato, Hiroshi Koyama, Alyson Kuba, Hiroki Takahashi, Toshihiko Fujimori, Masayuki Hatta, Andrew Negri, Andrew Baird, Naoto Ueno, Science Reports, 2020. DOI: https://doi.org/10.1038/s41598-020-74649-x

Provided by National Institute Of Natural Sciences

Coral Researchers Find Link Between Bacterial Genus And Disease Susceptibility (Biology)

Corals that appear healthy are more prone to getting sick when they’re home to too many parasitic bacteria, new research at Oregon State University shows.

Supported by the National Science Foundation, the study, published in Environmental Microbiology, adds fresh insight to the fight to save the Earth’s embattled coral reefs, particularly those in the Caribbean.

Healthy and diseased Acropora cervicornis (OSU College of Science) ©(OSU College of Science)

“The clear relationship we’ve discovered between this kind of bacteria and disease resistance in Caribbean staghorn coral is a crucial piece of the puzzle for coral restoration efforts in that region,” said study co-author Becca Maher, a Ph.D. candidate at Oregon State.

Found in less than 1% of the ocean but home to nearly one-quarter of all known marine species, coral reefs help regulate the sea’s carbon dioxide levels and are a crucial hunting ground that scientists use in the search for new medicines.

Between 2014 and 2017, more than 75% of the world’s reefs experienced bleaching-level heat stress, and 30% suffered mortality-level stress. Bleaching refers to the breakdown of the symbiotic relationship between corals and the algae they rely on for energy.

A complex composition of dinoflagellates, viruses, fungi, bacteria and archaea make up the coral microbiome, and shifts in microbiome composition are connected to changes in coral health.

In 2019, scientists in the lab of OSU microbiologist Rebecca Vega Thurber identified a new genus of parasitic bacteria that flourishes when reefs become polluted with nutrients, siphoning energy from the corals and making them more susceptible to disease.

The bacteria are in the order Rickettsiales, and the new genus is associated primarily with aquatic organisms. Scientists named the genus Candidatus Aquarickettsia and the coral-associated species in the 2019 study, Candidatus A. rohweri, was the first in the new genus to have its genome completely sequenced.

Acropora cervicornis under light microscopy, exhibiting signs of rapid tissue loss (OSU College of Science). ©(OSU College of Science).

Since their first appearance 425 million years ago, corals have branched into more than 1,500 species, including the one at the center of this research: the critically endangered Acropora cervicornis, commonly known as the Caribbean staghorn coral.

“The bacterial genus we’ve identified is found around the world and in multiple types of corals, but is most notably found in high abundance in the microbiomes of Caribbean staghorn coral,” said study co-author Grace Klinges, also a Ph.D. candidate in the Vega Thurber lab. “Now we’ve uncovered significant evidence that a high abundance of Ca. Aquarickettsia is a marker of disease susceptibility in corals that otherwise seem healthy.”

Disease-resistant corals were found to host a much more even mix of many types of bacteria, she said. Additionally, as corals experienced heat stress from a warming ocean, the microbiome dominance of Ca. Aquarickettsia eroded.

“That’s apparently because the bacteria rely on host nutritional resources that become scarce during periods of stress,” Vega Thurber said. “And then the sudden loss of a dominant community member frees up niche space and creates openings for opportunistic pathogens to proliferate and sicken the coral.”

Erinn Muller of the Mote Marine Laboratory in Sarasota, Florida, led the study.

References: Klinges, G., Maher, R.L., Vega Thurber, R.L. and Muller, E.M. (2020), Parasitic ‘Candidatus Aquarickettsia rohweri’ is a marker of disease susceptibility in Acropora cervicornis but is lost during thermal stress. Environ Microbiol. doi:10.1111/1462-2920.15245 link: https://sfamjournals.onlinelibrary.wiley.com/doi/10.1111/1462-2920.15245

Provided by Oregan State University