The coral whisperer
Duygu Sevilgen is enriching our understanding of life on the reef.
Corals are animals, not plants. They are the quirky, sedentary members of the Cnidaria family: unlike their jellyfish cousins, they build skeletons and don’t move.
Healthy coral reefs are the rainforests of the ocean, a nursery for young fish, and a shelter for countless other species. They are a massive natural barrier for coastlines, breaking up violent waves before they hit land.
But due to the impacts of human-caused climate change, these wonders of the natural world are at risk. As extreme weather increases in severity and the ocean warms, corals are suffering.
If their shallow water environment is unstable for long enough, corals will die. We see this in the massive coral bleaching events plaguing reefs around the world, reducing them to rubble.
If we don’t stop global temperatures from rising – both on land and at sea – the world's great reefs could become coral graveyards.
Duygu Sevilgen, Research Associate in Earth Sciences and Plant Sciences, wants to understand how corals build their skeletons. To do this, she uses homemade ’microsensors’ to measure the finest details and probe the corals’ symbiotic relationships. In doing so, Duygu is determining how much change corals can bear, and improving our chances of saving them.
Duygu reaching into one of her tanks.
Duygu reaching into one of her tanks.
Duygu’s life in marine biology started with a plunge into the Tyrrhenian Sea. She learned to dive off the coast of Elba, the island where Napoleon was first exiled (and shortly escaped from).
Moving south, Duygu caught her first sight of corals in the Red Sea. What she saw in those shallow waters took her breath away. Such a vibrant overflow of life felt illusory. HD television documentaries did not do the reefs justice.
“Coral reefs are beautiful and complex. They are astonishingly colourful. Observing them is surprisingly funny, with curious fish darting between their branches,” says Duygu. “They offer a biodiversity we rarely see in other ecosystems.”
“Corals offer a biodiversity we rarely see in other ecosystems.”
But when corals die, the entire ecosystem dies with them. When they become rubble, they can no longer offer sanctuary and protection. To offer them the best chances of survival, understanding the peculiar life of corals is vital.
Duygu's microsensors
Born and raised in Germany, Duygu studied biology in Cologne. From there she moved to Bremen, a renowned hub for marine research.
At the Max Planck Institute for Marine Microbiology, she was part of Dirk de Beer’s Microsensor Working Group, where she learned how to build microsensors capable of measuring an environment in meticulous detail.
Microsensors have their origin in neurobiology. Scientists started using them for environmental studies in the 1980s. People like Niels Peter Revsbech at Aarhus University were among the first to develop new sensors for uses in microbial ecology.
Microsensors are superfine needles, with a micrometre-diameter tip. For scale, a micrometre is one-thousandth of a millimetre: about the length of a single bacterium, or 4 times thinner than a spider’s silk. They allow us to measure chemical changes faster than the time it takes a housefly to flap its wings. They are one of a very few methods that lets scientists measure what’s happening inside a live coral.
Since her time in Bremen, Duygu has set up sensors both in the lab and the ocean, where diving allows her to gather data from the seabed, sometimes with the help of underwater robots.
Duygu and Oscar Branson in the lab.
Duygu and Oscar Branson in the lab.
After bringing her microsensor research to the Scientific Centre in Monaco, Duygu heard about the work of Oscar Branson at Cambridge. Oscar was setting up a coral lab to study biomineralisation (a fancy word for ‘how to make a skeleton’), and asked Duygu to join his group.
Cambridge presented Duygu with her current mission: to grow corals in captivity and uncover the secrets of their skeletons.
Growing corals in the lab
Plate 49 from Ernst Haeckel's 'Art Forms In Nature' (1904).
Plate 49 from Ernst Haeckel's 'Art Forms In Nature' (1904).
Plate 58 from Ernst Haeckel's 'Art Forms In Nature' (1904).
Plate 58 from Ernst Haeckel's 'Art Forms In Nature' (1904).
Plate 71 from Ernst Haeckel's 'Art Forms In Nature' (1904).
Plate 71 from Ernst Haeckel's 'Art Forms In Nature' (1904).
Oscar and Duygu in the lab.
Oscar and Duygu in the lab.
How do corals respond to temperature changes in the surrounding water? Or the acidity levels of the ocean? Where are their climatic limits and how do different coral species compare?
These are some of the questions Duygu and the rest of Oscar’s team hope to answer. Their work extends to other marine ‘biomineralisers' such as foraminifera – single-celled organisms that build shells.
To bring these skeletons out of the closet, the team has built a coral lab in the basement of an old Cambridge Zoology building.
The lab hosts two main coral tanks. Inside these lie multicoloured miniature forests, whose branches reach out to meet small crabs and fish. Conditions are tuned for optimum coral happiness, mimicking their ecosystem in the wild.
In the wider lab sit 10 experimental tanks, each representing a different environment.
“We can alter a lot of the environment in our experimental tanks, changing the temperature, light and the chemical makeup,” Duygu says. “We use the tanks to conduct our experiments. We want to see how the corals and other biomineralisers can keep up with environmental changes.”
In nature, all species on a reef interact and play a role in the health of the ecosystem. Duygu watches the captive corals closely as she tweaks their conditions, and logs how they respond.
“We can’t recreate everything. Many reef players are missing. We don’t recreate seasons, and we can’t recreate the soundscape of the reef – which, amazingly, has been shown to be very important for ecosystem health. However, our studies will illuminate the corals’ fundamental mechanisms.”
Other group members work on different aspects of coral biomineralisation. PhD student Alice Ball and postdoc Nishant Chauhan focus on physiology and how environmental changes affect coral respiration, photosynthesis, calcification, and gene expression. Madison East uses computer modelling techniques to understand how corals control their crystallisation processes.
Madison also takes incredible photos, both with the scanning electron microscope and her camera. She works with the photogenic foraminifera, single-celled organisms made famous by the psychedelic illustrations of Ernst Haeckel, whose grandson was a cruise leader on one of Duygu’s deep sea expeditions.
A tank full of coral in Duygu's aquarium.
A tank full of coral in Duygu's aquarium.
Exactly how corals construct their intricate skeletons is not fully understood. What we know so far suggests that bone-weaving requires tenacity and patience.
Skeleton quay
Corals combine ocean salts and carbon to make their skeletons. They use calcium and carbon from seawater, and craft these into an intricate skeleton that is integral to their survival.
Some species use their skeletons to branch out, forming massive 3D structures. The corals Duygu keeps are not a single animal – they are actually colonies of thousands of individual polyps.
Polyps of Duygu’s corals look a bit like a rubber glove, with 6 (or a multiple of 6) tentacles. Their skeleton is covered by tissue, like the skin covering our bones. Individual polyps are connected through this tissue, allowing them to communicate. If you touch one, the polyp will inform its fellow colony members of danger, and those nearby will retract.
In tissue pockets, the corals host a useful partner, their symbiotic algae. Named zooxanthellae, these algae bring the power of photosynthesis to the colony.
A closer look at the texture of the skeletal lattice for an A. cf. austera branch, using the Scanning Electron Microscope. You can see an almost shingle-like texture made up of bundles of crystals. For corals specifically, these are bundles of aragonite fibres (a type of calcium carbonate mineral). Image by Madison East.
A closer look at the texture of the skeletal lattice for an A. cf. austera branch, using the Scanning Electron Microscope. You can see an almost shingle-like texture made up of bundles of crystals. For corals specifically, these are bundles of aragonite fibres (a type of calcium carbonate mineral). Image by Madison East.
Zooxanthellae use the sunlight that penetrates shallow waters. Just like plants, they photosynthesise: transforming light and carbon dioxide into oxygen and food for the coral, paying rent for their tissue tenancy.
The zooxanthellae bring a brownish, greenish colour to the coral colony. But if the environmental conditions become too hot or acidic, they leave, taking the colour with them. This leads to bleached coral reefs, where white coral skeletons show through transparent tissue.
A certain future
The ocean has a natural variability, with 5-to-10-year cycles of fluctuating temperatures. However, the CO2 humans have released is causing the world to warm. Much of that extra heat goes into the ocean.
When natural climate oscillations coincide with a warming planet, corals experience never-before-seen conditions. This is driving increasingly severe coral bleaching and death. Six of the worst recorded global bleaching events have occurred in the last 20 years.
“What we see in the oceans now is the cumulative effect of what we did on land, since the industrial revolution,” says Duygu. “It’s a delayed fuse.”
The only certainty is that if we do nothing, the coral reefs and the biodiversity that comes with them will disappear with alarming speed. Scientists like Duygu are uncovering the hidden lives of corals, and the conditions they need to survive, before it's too late.
Published on 25 February 2025
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