• Coral reefs - "the rainforests of the ocean" are some of the most beautiful, biologically diverse and delicate ecosystems in the world.
  • The UN Environment Programme estimates that about 25 to 50% percent of the world's coral reefs have been destroyed and another 60% are under threat.
  • In addition to ocean acidification, coral bleaching, nutrient and sediment run-off, poor waste and sewage management along unsustainable fishing practices severely diminish the resilience and recovery of coral reefs.

A scientific research mission supported by UNESCO has discovered a pristine, 3km (1.8 mile) long reef of giant rose-shaped corals off the coast of Tahiti, in waters thought to be deep enough to protect it from the bleaching effects of the warming ocean. The reef, which lies at depths of more than 30 metres (100 feet), probably took around 25 years to grow. Some of the rose-shaped corals measure more than 2 meters in diameter. Most of the world's known coral reefs are in warmer waters at depths of up to 25 meters, UNESCO said. The reef off Tahiti lies in the "twilight zone", 30 to 120 meters below the surface where there is still enough light for coral to grow and reproduce.

Coral reefs symbolize the starkest visible imagery of climate change impacts. Even if drastic emission reductions ensured global heating was limited to 1.5C above pre-industrial levels – which would require almost halving global CO2 emissions by 2030 from 2010 levels – 70% to 90% of today’s corals would vanish. Coral reefs occur in more than 100 countries and territories and whilst they cover only 0.2% of the seafloor, they support at least 25% of marine species and underpin the safety, coastal protection, wellbeing, food and economic security of hundreds of millions of people, as per the UN Environment Programme. Coral reefs also contribute US$36 billion to the global tourism industry annually.

A Nobel prize-winning economy theory repurposed for coral conservation

A team of researchers led by Professor Ove Hoegh-Guldberg and Dr. Hawthorne Beyer at Australia’s University of Queensland used the Nobel prize-winning modern portfolio theory (MPT), a mathematical framework developed by the economist Harry Markowitz in the 1950s, to identify the 50 reefs or coral sanctuaries around the world that are most likely to survive the climate crisis. The study, as part of the "50 reefs"-initiative, recommends targeting investment in conservation projects that have the “strongest potential to succeed” by protecting priority reefs.

The strategy, which came out of a meeting of scientists at the Hawaiʻi Institute of Marine Biology in 2017, tapped into the theory to help scientists choose a “balanced” portfolio of coral reefs. The team used MPT to quantify threats and identify the reefs offering the best options for conservation, while allowing for the uncertainty over future risks from climate change. We dig deeper into how these coral sanctuaries could serve as models for resilience and lead to more targeted investments in coral conservation with Prof. Hoegh-Guldberg and Dr. Beyer. Here's what they said:

What led you to use modern portfolio theory (MPT) in your research to identify the 50 reefs and coral sanctuaries around the world which are most likely to survive the climate crisis?

Climate change has led to the severe degradation of many coral reefs globally. The adverse impacts are projected to increase dramatically over the coming decades. The transformation of coastal ecosystems, which once fostered biodiversity, and are now increasingly polluted and depleted in resources, has created a crisis for coral reef conservation and the millions of people that depend on them for their livelihood. Recognising this challenge, we must invest strategically into coral reefs that have the strongest potential for longest-term persistence.

The purpose of the "50 Reefs" project was to identify a set of reefs that have relatively low vulnerability to climate change and high connectivity to other reefs. These resilient reefs are more likely to survive till the end of the century and could serve as ecosystems that help in repopulating other reef systems that are damaged or lost. This lies at the heart of the "50 reefs" project.

There is, however, substantial uncertainty about projected climate conditions given current climate action commitments are not on track to meet the Paris Agreement goals. Consequently, long-term coral reef conservation planning becomes a potentially high-risk strategy. In this context, MPT is a simple but powerful approach to maximising expected future benefits while also reducing the expected variance in those benefits.

The challenge for us was to apply a model from finance to a problem in coral reef conservation where the objectives that we are trying to maximise are low climate vulnerability and high connectivity. The team of scientists that developed this work has done this using 30 measures relating to historical and future climate change, cyclone exposure, and connectivity among reefs.

Understanding coral sanctuaries and resilience

What are “well-connected coral reefs”?

Coral reef connectivity is determined by ocean currents that transport spawn (coral eggs, sperm, and larvae) from one area to another. After floating for several weeks, the coral spawn settles and grow into new reefs. Under ideal conditions, even severely degraded reefs can regrow into highly diverse reefs over a decade or two. The speed that this happens at is determined by the rate at which currents (and the number of corals) flow from a source reef to a sink reef. Reefs with large or multiple “upstream” sources of larvae and close proximity to the sources are considered to have high “connectivity”.

What is your most important takeaway from studying resilience in these coral sanctuaries?

We have limited ability over the short term to directly address climate change adversities such as ocean warming and acidification which deteriorate reefs. However, there are many other threats that are degenerating reefs - nutrient and sediment discharge from agricultural lands, poor waste water management, unsustainable fishing practices, plastic in the oceans, and invasive species. By selecting the reefs that have the lowest predicted vulnerability to climate change and intensively managing all the other factors impacting those reefs, we create the best conditions to ensure long-term reef persistence and resilience to climate change.

The main takeaway being - this is not a hopeless situation. If we are smart with investments, there is a great deal that we can achieve to promote coral reef conservation. The study recommends targeting investment in conservation projects that have the “strongest potential to succeed” in protecting reefs.

The model excluded several ecologically significant areas, such as Hawai'i and Central America’s Barrier Reef. How can we mobilise action to protect them?

We hope that this is the beginning of a global initiative that will prioritize conservation actions. There is nothing to say that identifying and strategically protecting the least exposed coral reefs in, say, the Americas isn’t an equally sensible strategy if the goal is to build a strategy to protect coral reefs in that region as well. It basically comes down to the mission involved objective.

In all of this, it is vitally important that the global community addresses the root of the problem: reducing greenhouse gas emissions and sequestering carbon as quickly as is possible. Achieving the goal of limiting global warming to less than 1.5oC set out by the Paris Agreement would improve the probability of long-term persistence of coral reefs globally. In the short term, reducing the impact of other threats that impact reefs are a key strategy for improving the resilience of reefs to climate change impacts.

Mobilizing action towards more effective ocean conservation

The recent underwater volcanic eruption in Tonga could deliver long-lasting damage to coral reefs, erode coastlines, and disrupt fisheries. Tonga’s reefs have already been threatened by disease outbreaks and coral bleaching, and falling ash is expected to damage coral reefs there. How would you recommend managing this?

Reefs are regularly exposed to various sorts of disturbance events (i.e. cyclones, which are more common than volcanos) and they are resilient enough to recover rapidly under the right conditions. Under suitable conditions, reefs have the ability to recover from natural disturbances like the volcanic eruption in Tonga within a few years, but the poor management of land, waste, and fisheries can severely erode the ability of reefs to recover and resist disease.

These are all factors that we can readily address in the short term, and in doing so we create the conditions in which reefs can recover from disturbance events. From a conservation perspective, our primary focus is on resolving these sorts of chronic problems because they are preventable. There are many other factors impacting reefs that we can reduce or eliminate using existing management methods and technologies. Improving conditions for coral reefs to recuperate is key to improving resilience, so that reefs can also better recover from the disturbances we cannot do anything about in the short term.

The other problem we have is that, unlike terrestrial ecosystems, coral reefs are very difficult to monitor because we have limited ability to use remote sensing technologies to track the condition of reefs. Furthermore, expeditions to some of these remote places are expensive, so they occur infrequently.

What has been the biggest impact of the “50 reefs” project?

The "50 reefs"-inspired approach had helped at least 26 organisations, and eight funders have now prioritised 60 coral reef ecosystems across more than 40 countries. Nearly $93m (£70m) has been invested in the project, funded by Bloomberg Philanthropies’ Vibrant Oceans initiative and others and the World Conservation Society (WCS) has $18m in funding for work in 11 countries, including Fiji, Indonesia, Kenya and Tanzania, on 21 of the 50 reefs, to help communities reduce pressure on the precious ecosystems.

The Coral Reef Rescue Initiative is a collaboration among major NGOs, led by WWF, and the University of Queensland to implement the "50 Reefs" program. We are currently developing activities in Fiji, the Solomon Islands, Tanzania and Madagascar, Indonesia, Philippines, and Cuba, which will be scaled up to other locations in the future. As part of a multi-national and multi-NGO initiative, we are implementing a large-scale project at some of the least exposed reef areas globally.