The 30-million-year-old 'cities of the sea'

Getty Images

Researchers are unlocking nan ancient secrets of nan world's astir divers marine habitat. Could their discoveries thief america prevention our oceans?

In an agency helping of nan Natural History Museum successful London, 2 researchers descent unfastened a plain retention cupboard doorway to uncover a hidden treasure: shelves of fossilised corals, up to 30 cardinal years old, from nan world's astir divers marine habitat. Some look for illustration petrified brains, others for illustration rocks pinch filigrane patterns.

"I for illustration to look astatine things successful nan past and spot if we tin study lessons from them," says Ken Johnson, pinch an oculus connected nan fossils. Johnson is simply a palaeontologist and main interrogator astatine nan museum's Earth Sciences department. Next to him stands Nadia Santodomingo, a marine biologist and geoscientist, and curator astatine nan museum. They and their squad collected nan fossils successful Indonesia much than a decade ago, moving pinch colleagues from nan Indonesian Geological Agency. The extremity was to effort and ace nan secrets of an expanse of water known arsenic nan "coral triangle" – and, they hoped, to usage those secrets to protect reefs today. 

"Understanding really corals person responded to erstwhile biology changes tin thief america spot really they mightiness respond to early changes," says Johnson. In fact, nan fossils not only led to a wholly caller position connected marine life, but drew attraction to important coral sanctuaries that had antecedently been overlooked – and which could go important refuges for type arsenic nan satellite warms, nan researchers say.

Sophie Hardach

Coral experts Ken Johnson and Nadia Santodomingo show up to 30-million-year-old coral fossils astatine nan Natural History Museum successful London (Credit: Sophie Hardach)

The 'Amazon of nan Seas' 

"The coral triangle successful South East Asia is nan astir divers spot connected Earth," successful position of marine habitats, says Johnson. "There are much marine type location than anyplace else. My colleagues and I wondered: why? What caused nan diversity?" 

Individual corals, known arsenic polyps, are spineless small marine animals measuring only a fewer millimetres, and are related to jellyfish and oversea anemones. They build difficult outer skeletons, and together pinch tens of thousands of different polyps, shape nan dazzling structures we cognize arsenic coral reefs. The skeleton remains aft nan polyp dies.

The fossils lined up successful nan furniture are successful a amazingly pristine state, pinch each delicate swirl and dent still intact. In nan coral triangle and different reefs, these analyzable structures support an abundance of life, says Santodomingo.

"[Corals] are for illustration mini buildings," she says. "One isolated building wouldn't do anything, but erstwhile they each turn together, for illustration large cities, they tin big a batch of different animals. Baby food tin hide there, truthful ample predators can't scope them." When corals die, they time off their skeletons behind, for illustration quiet houses, she explains. "And past different animals tin colonise nan reef – sponges, aliases snails, aliases clams – who usage these quiet 'buildings' and toggle shape it into their ain home." 

Johnson adds: "The metaphor we ever usage [for coral reefs] is 'cities of nan sea'."

Zarinah Waheed, University Malaysia Sabah

A diver collects coral fragments successful turbid reefs successful Darvel Bay, Malaysia (Credit: Zarinah Waheed, University Malaysia Sabah)

In nan early 2010s, nan squad and their Indonesian colleagues collected astir eight tonnes of fossil-rich stone from Indonesian Borneo, which yielded 70,000 coral specimens – complete 200 coral species, from up to 30 cardinal years ago. When they compared them to nan type surviving successful nan coral triangle today, they made a astonishing discovery: galore of them are still there.

Santodomingo cautiously lifts a immense fossilised coral retired of nan cabinet, a Porites coral, and holds it up: "This 1 present is astir 10 cardinal years old." Today, Porites corals, which build tremendous reefs, are still thriving successful nan coral triangle, she says.

She gives different example, nan antler-like staghorn coral, called Acropora monticulosa, which is among nan collected fossils from Indonesia. Acropora corals still live successful nan coral triangle today. These staghorn corals "have been location for 18 cardinal years aliases so", she says. Other acropora type recovered successful nan coral triangle are moreover older.

This bonzer resilience tin thief explicate why location are truthful galore type successful nan coral triangle today, says Johnson. "The logic it's nan astir divers spot connected Earth is that erstwhile [a coral] gets there, it doesn't spell extinct," he says. This is very different from really corals fared elsewhere, including successful places for illustration nan Caribbean that we mightiness deliberation of arsenic vibrant coral habitats, says Johnson. "In different parts of nan world wherever location are coral reefs, for illustration nan Caribbean, location were extinction events successful nan past," he says, caused by melodramatic changes successful nan situation and climate. "So, two cardinal years ago, half of nan coral type successful nan Caribbean went extinct. And truthful it's overmuch little diverseness there."

In immoderate places, corals were wiped retired altogether: "The Mediterranean utilized to person tons of corals," he continues. "But nan Mediterranean dried up, and corals went extinct."

In South East Asia, nan researchers say, nan fossil grounds suggests location wasn't specified an extinction event. But, it appears, nan corals besides had different advantage, 1 that mightiness moreover thief america protect marine habitats today: they lived successful murky water.

Getty Images

A immense assortment of marine life flourishes successful nan coral triangle (Credit: Getty Images)

The powerfulness of mud

When we deliberation of an perfect coral habitat, nan image that comes to mind is usually "clear water, thenar character connected nan beach", Johnson says – a cleanable vacation snapshot of those celebrated reefs successful sparkling colours.

But arsenic he and Santodomingo constituent out, that's partially conscionable a reflection of wherever we've traditionally looked for corals: successful clear waters, wherever it's easy to spot them. The fossils from Indonesia, however, told a different story. Research suggests that they lived successful cloudy, turbid water, amid swirling sediment and rainwater wash-off.

"We deliberation location were these murky environments that helped corals survive," says Santodomingo, possibly because nan comparatively dark, challenging situation encouraged an particularly reliable and resilient excavation of type to form, each pinch different traits that allowed them to header complete millions of years.

With world warming devastating coral reefs astir nan world, this penetration from nan fossils led to different question: if murky h2o had helped corals successful nan past, could it still do truthful today, successful an era of world warming and decimated reefs? Specifically, could nan muddiness protect reefs from nan melodramatic arena known arsenic coral bleaching – erstwhile full reefs move a ghostly achromatic arsenic a consequence of power stress? 

When relationships move toxic 

Bleaching happens erstwhile location is simply a breakdown successful a important relationship. Corals location mini colourful algae, a mutually beneficial narration that has been astir since agelong earlier dinosaurs became extinct – and which makes nan reefs truthful famously rainbow-like.

"Corals are fundamentally farmers, but their crops unrecorded wrong their bodies," says Johnson. "So nan coral gets nutrient from nan plants surviving wrong of it, and it fertilises nan plants pinch its animal waste. It's a circle betwixt nan works and nan animal."

When seawater warms to a level that stresses nan corals, for illustration during a marine heatwave, nan coral expels nan colourful plant, and turns white. "It becomes for illustration a toxic relationship," says Santodomingo, successful which nan coral decides it's amended to upwind nan situation connected its own. Scientists are still figuring retired why precisely this usually beneficial narration breaks down nether accent – 1 logic whitethorn beryllium that nan algae starts to behave more for illustration a parasite than an ally, taking up much power and nutrients for their ain growth. Another mentation is that nether higher temperatures, nan works produces substances that are harmful to nan coral. Reefs tin retrieve from bleaching – essentially, nan stressful arena passes, and nan works moves backmost successful – but if nan accent is too terrible aliases goes connected for excessively long, nan corals will die.

Murky h2o whitethorn buffer that impact, and make corals much resistant to bleaching, investigation suggests. In 2020, scientists from nan University of Malaysia Sabah investigated really reefs successful murky and clear h2o successful nan coral triangle responded to a heatwave. They surveyed 2 habitats successful Malaysia: the turbid reef of Sakar and nan clear-water reef of Blue Lagoon. In nan turbid reefs, little than 10% of colonies bleached. In nan clear-water reef, an mean of 37% of coral colonies bleached. The consequence supports "the presumption of turbid reefs hosting resilient coral communities successful nan look of ambiance change", nan study's authors concluded.

One imaginable mentation for this protective effect is that bleaching whitethorn beryllium caused not only by nan warming oversea water, but also, by intense sunlight, says Johnson. "When nan h2o is turbid, there's little light," he says, and this could protect nan corals.

A study of a 2016 marine heatwave that caused wide bleaching successful nan Great Barrier Reef besides recovered that corals successful turbid water, adjacent nan shore, were much resistant to bleaching than those successful clear water. The authors based on that this showed "the value of these resilient but often overlooked coral reef habitats arsenic imaginable refugia during climate-related disturbances".

Protecting murky coral havens from plastic

Separately, a 2020 study of information connected bleaching, somesthesia and turbidity from much than 3,600 coral sites worldwide recovered that turbidity reduced coral bleaching during power stress. "We propose that these turbid nearshore environments whitethorn supply immoderate refuge done ambiance change, but these reefs will request precocious conservation position to prolong them adjacent to dense quality populations," nan authors warned. Since murky waters thin to beryllium adjacent to nan shore, wherever rainfall washes ungraded into nan sea, they are much affected by quality pollution, specified arsenic plastic waste from single-use plastics for illustration dumped integrative bottles.

The findings person encouraged efforts to protect turbid reefs successful nan coral triangle, Santodomingo and Johnson say, pinch a scheme underway to grow a marine protected area successful Malaysia, for example. As clear-water reefs proceed to suffer, these turbid reefs could supply a refuge for coral species, nan researchers say.

As Johnson mildly shuts nan fossil furniture of wonders, he turns towards different cabinets, filled pinch corals collected by erstwhile generations of researchers and explorers, arsenic acold backmost arsenic nan 19th Century. Some of these aged collections are now being analysed utilizing modern technological methods, to study much astir reefs and their history, specified arsenic CT scans to analyse nan fossils' insides without cutting them open. One day, early researchers whitethorn do nan aforesaid pinch nan caller fossil collection, he says – utilizing methods we tin hardly fathom today.

"That's why depository collections are important," he says. "We can't ideate what will beryllium imaginable [in nan future]. Just for illustration erstwhile they collected these corals successful 1850s, they couldn't ideate what we tin do pinch them now."

 --

For basal ambiance news and hopeful developments to your inbox, motion up to the Future Earth newsletter, while The Essential List delivers a handpicked action of features and insights doubly a week.

For much science, exertion and wellness stories from nan BBC, travel america on Facebook and X.