October 28, 2021

Reef Check Contributes to Newly Released Status of Coral Reefs of the World Report

This month saw the release of the Status of Coral Reefs of the World Report: 2020, of which Reef Check and its tropical coral reef database was a contributor.

This report is the flagship product of the Global Coral Reef Monitoring Network (GCRMN) and describes the status and trends of coral reefs worldwide. This sixth edition of the report is the first since 2008, and the first based on the quantitative analysis of a global dataset compiled from monitoring data contributed by more than 300 members of the network. The global dataset spanned more than 40 years from 1978 to 2019, and consisted of almost 2 million observations from more than 12,000 sites in 73 coral reef countries around the world.

The report documents the loss of approximately 14 percent of the world’s coral since 2009, but also found that many of the world’s coral reefs remain resilient and can recover if conditions allow, providing hope for the long-term health of coral reefs if immediate steps are taken to reduce emissions to curb future warming.

The analysis which examined 10 coral reef regions around the world showed that coral bleaching events caused by elevated sea surface temperatures (SSTs) were the main driver of coral loss, including an acute event in 1998 that is estimated to have killed eight percent of the world’s corals, which, to put this in context, is more than all the coral that is currently living on reefs in the Caribbean. While coral cover recovered to pre-1998 levels by 2009, the long-term decline seen during the last decade coincided with persistent elevated SSTs.

The analysis investigates changes in the cover of both live hard coral and algae. Live hard coral cover is a scientifically based indicator of coral reef health, while increases in algae are a widely accepted signal of stress to reefs. Between 2010 and 2019, the amount of algae increased by 20 percent, corresponding with declines in hard coral cover. This progressive transition from coral to algae-dominated reef communities reduces the complex habitat that is essential to support high levels of biodiversity.

The report also highlights that although the interval between mass coral bleaching events over the last decade has been insufficient to allow coral reefs to fully recover, some recovery was observed in 2019 with coral reefs regaining 2% of coral cover. This indicates that coral reefs are still resilient and if pressures on these critical ecosystems ease, then they have the capacity to recover, potentially within a decade, to the healthy, flourishing reefs that were prevalent pre-1998.

Key findings:

– Large scale coral bleaching events are the greatest disturbance to the world’s coral reefs. The 1998 event alone killed eight percent of the world’s coral, which is the equivalent of about 6,500 square kilometers of coral. The greatest impacts of this mass bleaching event were seen in the Indian Ocean, Japan, and the Caribbean, with smaller impacts observed in the Red Sea, The Gulf, the northern Pacific in Hawaii and the Caroline Islands, and the southern Pacific in Samoa and New Caledonia.

– Between 2009 and 2018, the world lost about 14 percent of the coral on its coral reefs, which equates to around 11,700 square kilometers of coral, more than all the living coral in Australia.

– Reef algae, which grows during periods of stress, has increased by 20 percent over the past decade.

– Coral reefs in East Asia’s Coral Triangle, which is the center of coral reef biodiversity and accounts for more than 30 percent of the world’s reefs, have been less impacted by rising sea surface temperatures. Despite some declines in hard coral during the last decade, on average, these reefs have more coral today than in 1983 when the first data from this region were collected.

– Almost invariably, sharp declines in coral cover corresponded with rapid increases in sea surface temperatures, indicating their vulnerability to temperature spikes, which is a phenomenon that is likely to happen more frequently as the planet continues to warm.

The Executive Summary, Global Analysis and Regional Chapters are all available to download at https://gcrmn.net/2020-report/