IN A narrow back room at the Horniman Museum in south London, Jamie Craggs is counting down the minutes surrounded by gurgling tanks brimming with tan-coloured corals and tropical fish. Banks of LEDs cast an eerie blue light over the scene. It is 11.20 pm, and nothing much seems to be happening.
Twelve hours earlier and halfway around the world, relatives of Craggs’s corals bathe in the clear blue light of a full moon hanging above Fiji’s shallow seas. Silently, one of the ocean’s most magical moments begins. Pores open in the coral, releasing perfectly round millimetre-sized bundles, each containing millions of sperm or eggs. They float to the moonlit surface in their millions like gravity-defying snowdrops, transforming the shallow seas into an eddying soup of sex cells.
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Back in London, Craggs has spent the past year setting up his tanks to mimic those same conditions. Just a handful of white pearls inside the tank would be enough to tell him that his corals, like those off Fiji, are in the mood for love.
Coral spawning is not only one of the most entrancing events the oceans have to offer, but also one of the most mysterious. Each species may spawn for just one or two nights a year. After months of maturing their eggs and sperm, a sunset followed by a full moon seems to be the trigger for the mass-spawn. By syncing their cycles, sometimes down to the very minute, corals keep predators satiated and still have good odds of mating.
The events are rare, making them a pain for ecologists who study them. Bad weather, a miscalculation or a technical glitch during the dive means waiting months for the next opportunity, says Kristen Marhaver, who researches Caribbean corals at the CARMABI Foundation on Curaçao.
[youtube]https://www.youtube.com/watch?v=oUnY5m58PNc[/youtube]
Yet understanding what makes corals tick isĚývital if we want to halt their alarming worldwide decline. Since 1950, as a result ofĚýbleaching and human factors like pollutionĚý and dynamite fishing. We are still working out how climate change will affect them (żěè¶ĚĘÓƵ, 20 June 2015, p 36). The ocean’s loss is ours too. Coral reefs support a quarter of the fish we eat and the livelihoods of millions, act as natural flood defences against tsunamis, and are worth an estimated $29 billion per year to the global economy.
All of which explains why Craggs, who studies and takes care of the marine animals atĚýthe Horniman Museum, set up Project CoralĚýin 2012. Acropora, his coral genus of choice, are the architect of many reefs, and one of the world’s most threatened animals. “To understand what’s going to happen to reefs inĚýthe future, you have to understand reproduction,” he says. “It’s the only way a system continues.” He reasoned that if he could mimic natural reef conditions inside a tank in London, then maybe he could convince his corals to spawn.
Doing this is no small feat. “Corals are the hardest animals to grow and maintain in captivity,” says Mary Hagedorn, who studies Hawaiian corals at the Smithsonian Conservation Biology Institute. “It’s the pinnacle of what people do in zoos and aquariums.” Other breeding programmes invariably use real environmental cues to trigger spawning. Aquaria are set up near the coral’s natural home; skylights let the sun and moonlight through; and water can circulate through the tanks directly from the ocean.
LED moonlight
Such an approach is not an option for Craggs. Instead, species lifted from Fiji, Singapore and Australia cosy up together in adjoining tanks. Each is made toĚýfeel right at home. A computer program controls LED lights and water heaters for each tank to precisely simulate the sunrise, sunset, lunar cycles and temperature back home. Native fish dart around picking off parasitic sea anemones and suffocating algae.
If it works, this level of control would allow scientists to tinker with each environmental cue separately and see how the corals respond. “There’s just a myriad of experiments that can be done in lab conditions,” says Craggs. You could mimic the effects of varying degrees of climate change and ocean acidification, or compare larvae. Are some hardier than others? If so, can these be crossed and reintroduced into the wild?
Three times since 2012, Craggs has steadily warmed up the water over several months to mature eggs and sperm at the same time of year as in their native reefs. Then a “sunset”, followed by a “full moon”, have fired the starting gun for synchronous spawning.
Amazingly, he struck lucky first time. At 11.23 pm on 6 October 2013, thousands of egg-sperm bundles turned his Fiji tank into a giant snow globe. “They really chuck them out,” Craggs says. It was a world first.
But the next attempt, in 2014, failed. Initially, it appeared to be going well. The eggs matured, changing from a hoary colour to hues of purple. Then the simulated sunset andĚýfull moon cameĚý– and went. Nothing happened. “They reabsorbed their eggs,” Craggs says. He thinks a problem with the filtration system was to blame. The water was cycling through the tank more slowly than in 2013, and Craggs believes food and waste built up, ruining the romantic mood. Not ones to beĚýseduced by anything other than perfect conditions, the corals saved their resources forĚýanother time. “It’s a steep learning curve,” Craggs says.
With only three tanks and three fellow aquarists at the Horniman Museum, the scope of Craggs’s experiments is limited. His goal is to get captive breeding working smoothly and draw up a husbandry manual to assist other teams that have more resources. At the minute, those teams have to collect egg and sperm-carrying corals or scoop up their gametes during wild spawns, and then carefully take these back to the lab. “That’s one of the reasons the field moves forward so slowly,” says Marhaver. Madeleine van Oppen, a coral ecologist from the Australian Institute of Marine Sciences (AIMS), agrees. “It’s really quite limiting to have one or two spawnings a year. If you could have several a year it would be absolutely amazing.”
In 2014, AIMS opened the National Sea Simulator – a multimillion-dollar complex of hundreds of aquaria near the Great Barrier Reef that will try to scale up Craggs’s pioneering work in south London. “What Jamie does, no one in the world can do right now,” says Hagedorn.
After his setback in 2014, Craggs again played matchmaker in 2015. On 9 December, Cupid made another appearance at the Horniman. Not only did the Australian corals spawn in unison at 11.18 pm, but Craggs and his team were able to cross-fertilise the eggs and sperm in test tubes (see picture, left), produce larvae and rear them into adulthood. The feat shows that his captive populations are fertile, and opens the possibility of being in complete control of their cycles. After millennia of being guided by the seasons, the sun and the moon, corals now have a new helping hand.
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Article amended on 18 February 2016
Correction:ĚýA picture caption in this article has been changed to reflect the fact that many people have bred corals in captivity Ěý
