Coral spawning. Image Credit: Gary Cranitch, Queensland Museum

Matchmaking scientists grow baby corals for Great Barrier Reef

  • BY Angela Heathcote |
  • November 28, 2017

Large-scale larval resettlement, a new technique developed by scientists to restore damaged patches of the reef, has shown early signs of success, however they say this isn't the solution to all the reefs problems.

SCIENTISTS ARE trying to regrow damaged coral populations on reefs by capturing coral eggs and sperm after spawning, nurturing it in the laboratory and then returning mature coral larvae to debilitated sites on the southern Great Barrier Reef.

The project, headed by coral biologist Peter Harrison, founding director of the Marine Ecology Research Centre at Southern Cross University, is different from other coral restoration techniques that have previously been heavily criticised by reef experts.

Rather than fragmenting coral and re-planting it, also known as ‘coral gardening’, or lab-growing entire coral colonies, Peter and his team have collected coral spawn and larvae from Heron Island and One Tree Island reefs, and once matured, resettled larvae on damaged patches of reef. 

Peter and his team collected the coral larvae during the annual spawning event on the Great Barrier Reef, a rare natural wonder first discovered by Peter back in the early 1980s.

“There are so many millions, probably billions of larvae that are produced during these amazing events that we should be able to take some samples of those larvae and retain them so that they’re able to grow effectively without being eaten by fish, then put them onto damaged reef systems,” he told Australian Geographic.

However, Peter says that although many coral larvae have so far successfully resettled just days after they were released onto the reef test sites, there’s no guarantee that the deposited larvae will grow into adult corals.

“We’ve succeeded in getting the larvae onto the reef and we’ve found evidence of some of them settling but we just don’t know how many are settled until they grow big enough for us to start monitoring them on the reef, which will be in about a year’s time.”

coral spawn

Coral spawning at night under a red light.

Larval resettlement

‘Larval resettlement’ involves collection of the egg and sperm of corals during the reef’s annual spawning events and then nurturing fertilised eggs and embryos in the laboratory. After the larvae develop and mature, they have been returned to test areas and enclosed by mesh curtains to prevent the larvae being swept away with the currents. 

“One of the interesting things about coral reproduction is that because they’re relying on external fertilisation they have to produce immense quantities of egg and sperm and they’re often dispersed due to currents and sometimes rough weather,” Peter says. “Naturally on some reef systems you get high rates of fertilisation when it’s calm and there isn’t much tidal movement.”

coral spawn

Scientists work on coral spawn collected in a tub.

Large scale

Peter says that smaller scale larval resettlement has been attempted in the past but not on this scale.

“We’re increasing the scale and we’re adding in larvae of multiple species. We’ve got branching coral and brain coral larvae and we’re putting those mixtures onto the reef for the first time,” he says. “That hasn’t been done before.”

The approach is also far less invasive than other attempts at coral restoration.

“We’re developing the restoration techniques that could be used to help maintain natural coral reefs over the next few years but can also be used in the future if we have to start thinking about selective breeding. “

Bad reputation

According to Peter, coral restoration has a bad reputation among researchers mainly because of the way it’s been carried out in the past.

“The primary way people around the world are still trying to do coral restoration is by fragmenting coral, which means breaking healthy coral colonies and then replanting fragments, either directly on the reef, in which case many of them end up dying or putting them into nurseries. You get better outcomes from nursery rearing, but it’s much more expensive and it requires a lot of diving and maintenance for those nurseries on the reef.

“Coral gardening may work for very small scale resort reefs but that type of restoration is never going to be effective at managing larger reef areas, it’s just too time consuming and too expensive.”

coral spawn

Researchers collecting genetic samples from parent-colonies.

Climate change the biggest threat to the reef

Peter acknowledges that larval resettlement isn’t the answer to saving the reef.

“This just gives us another opportunity and a different approach to try and adapt to some of the complex issues facing coral reefs. For example the northern and central parts of the Great Barrier Reef have been doubly impacted by successive mass coral bleaching resulting in a massive loss of corals.

“There’s no way we can go immediately from what we're doing now to repairing large areas of damaged coral reefs. We just don’t have the resources or the capacity to invest or even know how to do it on that larger scale.”

Peter says that a combination of natural and human solutions will be needed to help preserve the world’s coral reefs.

“We’re trialling different techniques now so we can scale up the larval restoration process over the next few years.

“Even if in the future managers and researchers decide that we do need to breed more tolerant corals in laboratory conditions, we’re still going to need to put large numbers of coral larvae back onto the reef and have them retained so most of them can settle and don't disappear. The new technique we are trialling now can be adapated to using new types of coral in the future. 

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