Professor Peter Mumby, head of the Marine Spatial Ecology Lab (MSEL) at the University of Queensland (UQ), is working to move beyond charting the decline of coral reefs, to find practical ways to help them. Since 2017, he has been able to point to 112 reefs in the Great Barrier Reef (GBR) – comprising roughly 3% of its total size – that his team’s modelling shows are particularly resilient, and are also able to reseed 47% of the rest of the reef after a single spawning event.
UQ’s team has one of the world's most comprehensive models of coral reef ecosystems, integrating the results of hundreds of studies on everything from currents and spawning sites to climate modelling and bleaching histories. Its focus is notably on the GBR, although the lab works on reefs globally. “We know there is nothing we can do directly at this point to stop the water getting hot,” Mumby says. “So we use modelling to get a better idea of what the future might look like for reefs and to what extent different protection can take us on a better path."
Consider, says Mumby, the major bleaching events that have been affecting vast sections of the GBR in recent decades due to climate-change driven warming of marine waters. Because of the sheer size of the GBR – 2,300km long and made up of 3,000 separate reefs – for any given bleaching event there are some places that remain relatively healthy. This could be, for example, because they exist in areas where upwelling brings cooler waters to the surface.
“So, you have these little pockets that are generally going to do a bit better,” Mumby explains. These become particularly important when the GBR’s corals are spawning, which they do en masse in an annual synchronised event. After spawning, fertilised eggs drift about on currents for up to a month before settling out of the water column, presenting an opportunity for renewed coral growth on damaged reefs.
“We now have pretty good intel on which reefs are strongly connected to others,” Mumby says. “We can predict to the very evening when they are going to spawn and, by modelling the ocean currents at that time of year, we’ve got a good way of determining how connected the system is and identifying where hubs are.”
“If you can identify areas that are really well connected and still have a fair amount of living coral, which means they have plenty of eggs to deliver, and those eggs are going to be travelling to where reefs are trying to recover, then you can stop anything else threatening those reefs, like a crown-of-thorns starfish outbreak, or anchor damage.”
Connected to coral
Although coral is a fundamental element for reef survival, supporting coral is a complex endeavour. Throughout the year, Mumby and his team carry out a range of ecological studies to see how local stressors like pollution and overfishing affect reef resilience.
In 2019, in a case study of Bonaire in the Dutch Caribbean, Mumby was on an international team that looked at how limiting herbivore overfishing across 15 years controlled algal abundance and created conditions that facilitated survival and growth in coral. Reefs with more parrotfish were shown to bounce back better from hurricane damage. Another international study Mumby took part in that year used simulations to show that prioritizing habitat diversity protects heat-resistant flora and fauna populations, creating cooler refuges and better stepping stones between them.
In 2018, the Australian government provided AU$6 million to a consortium of major research institutions, including UQ, through the Reef Restoration Adaptation Program. The goal was to determine the feasibility of intervening at scale on the GBR to help it adapt to, and recover from, the effects of climate change. A recently released report found effective intervention strategies, combined with carbon emissions reduction and best-practice conventional management, could strongly increase the likelihood of sustaining the reef in good condition until 2050.
Possible interventions could include local and regional cooling and shading technologies, such as spraying nano-sized salt crystals into the air from a barge, brightening clouds to reflect sunlight and shade the reef, says Mumby, as well as assisting the natural evolution of corals to increase their resilience to the changing environment, and measures to support and enhance the natural recovery of damaged reefs.
Where crown-of-thorn starfish are of concern, such as on the GBR, key sites can be targeted by fleets of boats with dive teams that are dedicated to killing the coral-eating starfish. “We may need to prioritise more surveillance on some of these reefs to ensure that should they start to develop crown-of-thorns outbreaks, we can jump on them quickly,” Mumby adds.
However, obtaining extensive information on the state of GBR reefs is beyond most institutions' resources, so Mumby has co-developed a project called the Great Reef Census that’s being led by the not-for-profit Citizens of the GBR. It’s enlisting the help of citizen scientists on boats operating on the GBR to help provide the preliminary surveying needed to identify the most important sources (reefs) of recovery across the reef.
During a three-month period from October to December 2020, the citizen scientists took photographs of the GBR reefs they visited to be uploaded online where they can be reviewed and explored by people worldwide. “We have some first estimates of the state of reefs, but now we will have hundreds of additional locations that have been surveyed by citizens,” says Mumby.
“We’ll obviously do some quality control on that,” Mumby adds. “The data collected will be cleansed and analysed by UQ researchers, and the outcomes shared with project partner, the Great Barrier Reef Marine Park Authority. But because the GBR is an ecosystem the size of Italy, this is exactly the kind of cost-efficient, practical system needed to help target interventions where they can best help the reef recover.”