Living on the sea walls beneath the US city of Miami is a coral that could hold the key to saving its kind the world over – a hybrid of two closely related species. This hybrid coral, Acropora prolifera, is showing an ability to thrive in its urban environment much better than its parents.

The coral, which is formed by sexual reproduction between the critically endangered staghorn (A. cervicornis) and elkhorn (A. palmata) corals, has been seen living, and growing, in the city's busy shipping channel. Meanwhile further out to sea, the natural reefs where its parent species are found are said to be struggling.

It is thought that A. prolifera is sterile, meaning it may not be able to sexually reproduce, but because corals can also reproduce asexually – when fragments of the coral break off and re-establish – this hardy hybrid could prove to be very valuable in reef restoration projects.

Colin Foord, the marine biologist who first discovered Miami's A. prolifera, is so impressed with its resilience to disturbance that he is trying to gain both the permission and funding to establish a coral nursery off Miami Beach. This would allow the hybrid coral to be properly studied, as well as making it viewable to the public. 

Faced with the challenge of building sympathy for these seemingly motionless organisms that look their best underwater, Mr Foord has devised a way of filming them that showcases their unseen beauty which features in a new BBC / National Geographic coproduction series, a clip from which can be seen below.

Corals have been shown to fluoresce, or glow, as they defend themselves from the searing sun, producing beautiful displays of colour and light, but these are almost invisible to the naked eye and incapable of being filmed in daylight.

Mr Foord and musician Jared McKay set up Coral Morphologic to demonstrate the full splendour of corals in artworks and public installations, as a way of increasing public engagement with the important ecosystems. 

They were allowed to relocate some of the natural coral lying in the path of the dredgers and took some specimens into the studio to film, cultivate and study. They use blue light and lenses with special filters to allow the coral's fluorescent colours to be seen, as well as speeding up their natural movement with time lapse photography.

"Miami is a city that’s not only built on a coral reef, the construction materials that were used – the cement, the limestone, part of the architecture – were fossilised coral and marine life living on itself," Mr Foord says.

"It is the appropriate place to get people to see corals as something futuristic, colourful, sexy even. There’s something very fluid and elegant about the coral which you don’t really encounter in a dry environment, so I think all of these factors together enable us to tell a story that’s a little bit more creative."

Mr Foord is particularly motivated by ongoing dredging work in the area, which he says is adding to the pressures the corals on the natural reefs are facing. While some corals have been relocated, he is concerned at the large amounts of sediment or silt that is being whipped up by the operation, shown in his film below.

"In some respects the corals living inside Miami are the silver lining of Florida's environmental upheaval because 100 years ago they could never live here as it was a brackish water estuary, there was no salt water. The shipping channel brought in the salt water," Mr Foord says.

"But these are corals inside the city, they’re living on sea walls, they’re living on steep surfaces, they’re living on rocks, so the silt is not a problem.

"The problem is the natural reefs off Miami are, for the most part, very horizontal and the last year has basically been a snow storm of silt. I was out there two weeks ago doing a survey and saw corals buried under a centimetre or two of silt, it looked like a grey landscape on the bottom.”

Cloudy water conditions are dangerous for corals who need sunlight to reach them to keep alive the symbiotic algae that live inside their cells and on which they rely to survive.

Corals have been around for half a billion years

Corals can reproduce in different ways. In asexual reproduction or fragmentation, a branch falls off and reattaches to the reef in order to grow again. This technique is used in coral nurseries and subsequent restoration attempts.

They can also reproduce sexually, through synchronised spawning events which maintain genetic diversity. Mr Foord says it is this ability that has allowed corals to continously evolve and why he is so keen to be granted permission to take specimens out of the water, something not currently allowed under Florida law.

"Corals have been around for half a billion years, a lot longer than humans have, so maybe we should be paying attention to them," Mr Foord says.

"Obviously they’ve gone through tremendous extinction events in the past where they’ve bottlenecked down to very few and then they’ve come back, so if we learn how to control this technique of reproduction in the laboratory then we can create hybrids that may be more resilient."

Atlantic: The Wildest Ocean on Earth continues in the UK on BBC Two, Thursday August 6 at 21:00 BST.

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