Global Coral Coverage Down by Half Since the 1950s

By Jerri-Lynn Scofield, who has worked as a securities lawyer and a derivatives trader. She is currently writing a book about textile artisans.

A study published in the journal OneEarth on Friday describes the drastic decline in the health of the world’s coral reefs since the 1950s, Global decline in capacity of coral reefs to provide ecosystem services.

From the summary:

Coral reefs worldwide are facing impacts from climate change, overfishing, habitat destruction, and pollution. The cumulative effect of these impacts on global capacity of coral reefs to provide ecosystem services is unknown. Here, we evaluate global changes in extent of coral reef habitat, coral reef fishery catches and effort, Indigenous consumption of coral reef fishes, and coral-reef-associated biodiversity. Global coverage of living coral has declined by half since the 1950s. Catches of coral-reef-associated fishes peaked in 2002 and are in decline despite increasing fishing effort, and catch-per-unit effort has decreased by 60% since 1950. At least 63% of coral-reef-associated biodiversity has declined with loss of coral extent. With projected continued degradation of coral reefs and associated loss of biodiversity and fisheries catches, the well-being and sustainable coastal development of human communities that depend on coral reef ecosystem services are threatened.

What I found most disturbing about the study is that while it surveyed data from 3,582 reefs, it only covers the period up to 2007, since which date, there have been numerous serious bleaching events at various coral reefs throughout the world, including widely reported bleaching events at the Great Barrier Reef, the world’s largest. The report therefore understates the current health of reef systems.

Global Decline in Capacity of Coral Reefs to Provide Ecosystem Services

Figure 1: Global Coral Reef Cover Trends

From the study:

Our study has aggregated regional trends of coral reefs to provide ecosystem services and demonstrated that the continuing decline of healthy coral reefs and the quality of habitat that they provide is contributing to a global decrease in provision of ecosystem services for the millions of people who rely on them. Particularly, our results highlight the erosion of biodiversity and food provision. The species-area relationship suggests a high sensitivity of species richness as a function of coral habitat. The estimated historical loss in coral habitat directly translates into loss in capacity of the remaining coral reefs to support biodiversity. The decline in global CPUE, an index of relative abundance of coral-reef-associated fisheries resources, suggests a loss in the production potential of many fish stocks that are important sources of food, culture, and livelihoods for coastal dependent communities….

Our results highlight the sensitivity of coral reef ecosystems, because of their biology, as well as the high dependence on them by human communities. Our study has also highlighted important data gaps that exist for many nations—improved monitoring and reporting for healthy coral reef coverage, associated biodiversity abundance, fisheries’ catches and effort, and seafood consumption could reduce uncertainty in future coral reef ecosystem service analyses [Jerri-Lynn here: citations omitted].

Some human activities that have led to decline of reefs – overfishing, coastal development – can perhaps be reversed or at least mitigated. But precious little progress has been made in addressing the overriding threat global warming poses to the world’s coral reefs. Oceans have absorbed more than 90% of the heat trapped by rising greenhouse gases, according to the Guardian in Global coral cover has fallen by half since 1950s, analysis finds, thus increasing sea temperatures. Hotter waters have in turn had a profound effect on the health of coral reefs, withe many reefs – such as the Great Barrier Reef, the world’s largest – experiencing more frequent bleaching episodes. From the study:

Essential measures that are defined and agreed targets of the [Sustainable Development Goals (SDGs)], such as reducing overexploitation through effective fisheries management(SDG 14.4, 14.7), encouraging ecosystem protection and restoration (SDG 14.2), and reducing export of silt and nutrient pollution to coastal waters (SDG 14.1) can help countries mitigate some of the local impacts (within their EEZs) to coral reefs and can simultaneously benefit other social concerns and development objectives. However, climate change and ocean warming are the greatest threats to coral reef capacity, outweighing local stressors. Coral reefs such as the Great Barrier Reef have been experiencing bleaching events at unprecedented frequency, threatening their persistence, and recent research suggests that the most vulnerable species of coral are increasingly rare, and the species that persist are more tolerant of warming conditions. These observations fit with the global trend of decline in coral cover during the 1950s to 1970s, followed by a reduced decline since the 1980s. There have been efforts to restore coral reefs by transplanting them, cooling them with underwater pumps, manipulating genome, and employing robots to spread coral larvae; however, nothing yet has shown promise to be effective at the landscape scale that would be required to make a meaningful impact. Protecting coral reefs and their ecosystem services will require strong cooperation across scales to reduce emissions and frequency of heat waves and a deeper understanding of anthropogenic drivers and their effects.

The effects of degraded and declining coral reefs are already evident through impacts on subsistence and commercial fisheries and tourism in Indonesia, the Caribbean, and South Pacific, even when marine-protected areas are present, because they do not provide protection from climate change and could suffer from lack of enforcement and marine-protected-area staff capacity. Fish and fisheries provide essential micronutrients in coastal developing regions with few alternative sources of nutrition. Coral reef biodiversity and fisheries take on added importance for Indigenous communities, SIDSs, and coastal populations where they could be essential to traditions and cultural practices.The reduced capacity of coral reefs to provide ecosystem services undermines the well-being of millions of people with historical and continuing relationships with coral reef ecosystems [Jerri-Lynn here: my emphasis; citations omitted].

What Must Be Done

When the study drilled down on what needs to be done to address this ongoing ecological catastrophe, I became even more concerned. It’s well past the time for real action on global warming issues. From the study:

Developing pathways and targets for recovery and climate adaptation requires a globally coordinated effort while also addressing needs and management at local scales. Climate mitigation and adaptation actions as highlighted in the Paris Agreement are progressing but need to accompany other efforts to address direct and indirect drivers that are diminishing coral reef capacity. Such an approach is highlighted by recent collaborations between international institutions, exemplified by the joint report of the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) and the Intergovernmental Panel on Climate Change (IPCC) that calls for the need to address biodiversity, climate, and social challenges in an integrated manner [Jerri-Lynn here: citations omitted].

The Guardian article quoted some study authors, one of whom seemed genuinely surprised by the scale of decline in reef health:

Tyler Eddy, a research scientist at the Memorial University of Newfoundland who led the study, said even though the decline of coral reef ecosystems had long been recorded at a national level, he was surprised by the extent of the scale of the global decline.

“Coral reefs are among the most sensitive ecosystems on the planet so they’re the first ones that are really experiencing these effects of climate change. There’s quite dramatic declines in the 60s and 70s. Then, in the 80s, there’s still a slight decline in the coverage through time but it’s not as steep,” he said.

“If you look at the country-level trends of the coral reef cover, we see some of the biggest declines occurring in Papua New Guinea, Jamaica and Belize.”

While reviewing the surveys, Eddy said researchers noticed that the composition of species on the reef was changing in some areas, with temperature-sensitive fish declining and more resilient species becoming dominant.

Another study co-author, University of North Carolina marine ecologist John Bruno, emphasized that despite regional differences, global coral reef health had only worsened since the period covered by the study. Per The Guardian

“Unfortunately, we’ve continued to lose coral from most of the world’s reefs since the data for this study ends. Marine heatwaves are rapidly intensifying, leading to more frequent and severe bleaching events, including on some of the world’s most isolated and pristine coral reefs,” he said.

In the Caribbean, a recent study found reefs had been declining by about 0.25% a year, with only about 10% of the seabed occupied by living corals by 2017.

“Over the last few years, Caribbean reefs have been clobbered by hurricanes and new diseases, both linked to ocean warming. Frankly, the global picture for coral reefs is pretty grim,” Bruno added.

As we’ve seen especially during the last year, these climate-related trends seem only to be accelerating.