In an office wing of the Natural History Museum in London, two researchers open the door of a simple cupboard and discover a hidden treasure: shelves of fossilized corals, up to 30 million years old, from the most diverse marine habitat in the world. .
Some look like petrified brains, others rocks with filigree patterns.
“I like to look at things from the past and see if we can learn lessons from them,” says Ken Johnson, with one eye on fossils. Johnson is a paleontologist and senior researcher in the museum’s Earth Sciences department.
At his side is Nadia Santodomingo, marine biologist, geoscientist, and museum curator. They and their team collected the fossils in Indonesia more than a decade ago, working jointly with colleagues from the Indonesian Geological Agency.
The objective was to try to decipher the secrets of an area of ocean known as the “coral triangle”and they hoped to use those secrets to protect the reefs today.
“Understanding how corals have responded to past environmental changes can help us see how they might respond to future changes,” Johnson says.
In fact, the fossils not only provided a completely new perspective on marine life, they drew attention to important, previously overlooked coral sanctuaries that could become crucial refuges for species as the ocean evolves. Planet is warming, researchers say.
Sometimes called “the Amazon of the seas,” the coral triangle is as species-rich and teeming with life as a lush rainforest.
Covers Malaysia, the Philippines, Indonesia, Papua New Guinea, East Timor and the Solomon Islands.
About 75% of all known coral species live there – more than 700 different species – as well as 3,000 species of reef fish and six of the world’s seven species of sea turtles.
“The coral triangle of Southeast Asia is the most diverse place on Earth” in terms of marine habitats, says Johnson. “There are more marine species there than anywhere else. My colleagues and I asked ourselves: why? “What is the reason for this diversity?”
Individual corals, known as polyps, are small, spineless marine animals measuring just a few millimeters and are related to jellyfish and sea anemones.
They build tough external skeletons and, along with tens of thousands of other polyps, form the dazzling structures we know as coral reefs. The skeleton remains after the death of the polyp.
The fossils lined up in the display case are in surprisingly pristine condition. In the coral triangle and other reefs, these complex structures support abundant life, Santodomingo says.
The corals “They are like small buildings”he states. “A single building wouldn’t do anything, but when they grow together, like big cities, they can house many other animals. “Baby fish can hide there, so large predators can’t get to them.”
When corals die, they leave their skeletons behind, like empty houses, he explains. “And then other animals can colonize the reef – sponges, snails or clams – that use these empty ‘buildings’ and transform them into their own home.”
Johnson adds: “The metaphor we always use (for coral reefs) is ‘cities of the sea.’”
The conditions that enable its diversity
In the early 2010s, the team and their Indonesian colleagues collected about eight tons of fossil-rich rock from Borneo, Indonesia, containing 70,000 specimens: more than 200 species of coral, up to 30 million years old.
When they compared them to the species currently living in the coral triangle, they made a surprising discovery: many of them are still there.
Santodomingo carefully lifts a huge fossilized coral from the cabinet, a Porites coral, and holds it up: “This one here is about 10 million years old.” Today, Porites corals, which build huge reefs, continue to develop in the coral triangle, he adds.
The researcher gives another example: the staghorn coral called Acropora Monticulosa, which is among the fossils collected from Indonesia. Acropora corals still live in the coral triangle. These staghorn corals “have been there for about 18 million years“he says. Other Acropora species found in the coral triangle are even older.
This extraordinary resilience may help explain why there are so many species in the coral triangle today, Johnson says.
“The reason this is the most diverse place on Earth is that once (a coral) gets here, it doesn’t go extinct.”he maintains.
This is very different from how corals fared elsewhere, even in areas like the Caribbean that we might consider vibrant coral habitats, Johnson says.
“In other parts of the world where there are coral reefs, such as the Caribbean, extinctions have occurred in the past,” he explains, which were caused by drastic changes in the environment and climate. “Thus, two million years ago, half of the coral species in the Caribbean became extinct. And that’s why the diversity is much less there.”
In some places, corals disappeared completely: “The Mediterranean used to have a lot of corals,” he continues. “But the Mediterranean dried up and the corals became extinct.”
In Southeast Asia, researchers say, the fossil record suggests there was no such extinction event. But corals also apparently had another advantage, which could even help us protect marine habitats today: They lived in murky waters.
The power of mud
When we think of an ideal coral habitat, the image that comes to mind is usually “clear water, palm tree on the beach,” says Johnson, a perfect vacation photo with those famous vibrantly colored reefs.
But, as he and Santodomingo point out, that’s partly just a reflection of where we’ve traditionally looked for corals: in clear waters, where they’re easy to see.
Fossils from Indonesia, however, tell a different story. Research suggests that they lived in hazy, murky waters, among swirling sediments and rainwater.
“We believe that these murky environments helped the corals survive,” says Santodomingo, perhaps because the relatively dark and challenging environment favored the formation of a group of especially tough and resistant species, all of them with different traits that allowed them to resist for millions of years. years.
With global warming devastating coral reefs around the world, this view of fossils led to another question: If murky water had helped corals in the past, could it continue to do so today, in an era of global warming and decimated reefs?
Specifically, could turbidity protect reefs from dramatic phenomena such as coral bleaching, in which entire reefs turn ghostly white as a result of thermal stress?
When relationships become toxic
Discoloration occurs when a crucial relationship breaks down. Corals are home to tiny, colorful algae, a mutually beneficial relationship that existed long before the dinosaurs became extinct and gives reefs their famous rainbow appearance.
“Corals are basically farmers, but their crops live inside their bodies,” Johnson explains. “The coral feeds on the plants that live inside it and fertilizes them with its animal waste. It is a circle between the plant and the animal.”
When sea water warms to a level that stresses corals, for example during a marine heat wave, the coral expels the colorful plant and turns white.
“It becomes a toxic relationship”explains Santodomingo, in which the choir decides that it is better to face the crisis on its own. Scientists have not yet been able to discover why this normally beneficial relationship breaks down in stressful situations.
One reason could be that the algae begin to behave more like a parasite than an ally, consuming more energy and nutrients for their own growth.
Another explanation is that, under higher temperatures, the plant produces substances harmful to the coral.
Reefs can recover from bleaching—essentially, the stressful event passes and the plant settles back in—but if the stress is too severe or lasts too long, the corals will die.
Cloudy water could lessen that impact and make corals more resistant to bleaching, research has suggested. In 2020, scientists at University Sabah Malaysia investigated how reefs in the triangle’s murky, clear waters responded to a heat wave.
They focused on two habitats in Malaysia: the murky reef of Sakar and the clear-water reef of Blue Lagoon. On turbid reefs, less than 10% of colonies suffered bleaching, while on clear-water reefs, an average of 37% of coral colonies bleached.
The results support “the hypothesis that turbid reefs host coral communities that are resilient to climate change,” concludes the author of the study.
A possible explanation for this protective effect is that this bleaching may be caused not only by warming seawater, but also by intense sunlight, says Johnson. “When the water is cloudy, there is less light,” he adds, and that could protect the corals.
A study of a 2016 marine heatwave that caused widespread bleaching on the Great Barrier Reef also found that corals in murky waters, close to shore, were more resistant to bleaching than those in clear waters. The authors argued that this demonstrated “the importance of these resilient but often overlooked coral reef habitats as potential refuges during climate-related disturbances.”
The threat of plastic
Separately, a 2020 analysis of bleaching, temperature and turbidity data from more than 3,600 coral sites around the world found that turbidity reduced coral bleaching during thermal stress.
“We suggest that these turbid coastal environments may provide some refuge from climate change, but these reefs will need high conservation status to remain close to dense human populations.”the authors warned.
Because murky waters tend to be near the coast, where rain washes soil into the sea, they are more affected by human pollution, such as single-use plastic waste, including plastic bottles.
The findings have spurred efforts to protect turbid reefs in the coral triangle, Santodomingo and Johnson say. For example, with a plan in motion for ex pandir a marine protected area in Malaysia.
As clear-water reefs continue to suffer, these murky reefs could provide a refuge for coral species, the researchers explain.
As Johnson gently closes the cabinet of wonder-filled fossils, he heads toward other cabinets, filled with corals collected by previous generations of researchers and explorers, dating back to the 19th century.
Some of these ancient collections are now being analyzed with modern scientific methods, to learn more about the reefs and their history, such as CT scans to examine the inside of the fossils without cutting them up.
One day, researchers of the future could do the same with the recent collection of fossils using methods that we can barely imagine today, the paleontologist says.
“This is why museum collections are important”he adds. “We cannot imagine what will be possible (in the future). Just like when they collected these corals in the 1850s; “They couldn’t imagine what we could do with them now.”
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