Coral Reefs - Algae Increases as Coral Declines
The Art
The Science
According to the report – Status of Coral Reefs of the World: 2020 (Executive Summary) issued by the Global Coral Reef Monitoring Network and International Coral Reef Initiative:
“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. The value of goods and services provided by coral reefs is estimated at US$2.7 trillion per year, including US$36 billion in coral reef tourism. However, coral reefs are among the most vulnerable ecosystems on the planet to anthropogenic pressures, including global threats from climate change and ocean acidification, and local impacts from land-based pollution such as input of nutrients and sediments from agriculture, marine pollution, and overfishing and destructive fishing practices…”
“..Large scale coral bleaching events are the greatest disturbance to the world’s coral reefs. The 1998 event alone killed 8% of the world’s coral. Subsequent disturbance events, occurring between 2009 and 20118, killed 14% of the world’s coral.”..
“…Prior to 2011, the estimated global average cover of algae was low (~16%) and stable for 30 years (Fig.4). Since 2011, the amount of algae on the world’s coral reefs has increased by about 20%, mirroring the decrease in hard coral cover…A progressive transition from coral to algae dominance in a reef community reduces the complex three-dimensional habitat that is essential to support high biodiversity and provide valuable goods and services for reef-dependent human communities…”
“…The most intense global coral bleaching event on record is still ongoing, according to scientists. One year on from the official declaration of the fourth global coral bleaching event by the International Coral Reef Initiative (ICRI), bleaching alerts continue to develop across the world.
From 1 January 2023 to 30 March 2025, bleaching-level heat stress impacted 84% of the world’s reefs, with 82 countries, territories and economies suffering damage. During the first global coral bleaching event in 1998, 21% of reefs experienced bleaching-level heat stress, rising to 37% in the second event in 2010 and 68% during the third event (2014-2017)1. Scientists called the fourth global coral bleaching event “unprecedented” as early as May 2024, and a widely-used bleaching prediction platform had to add three new levels (Levels 3-5) to their Bleaching Alert Scale to indicate the heightened risk of mass coral mortality. The previous highest level, Level 2, indicates risk of mortality to heat sensitive corals; Level 5 indicates the risk of over 80% of all corals on a reef dying due to prolonged bleaching…”
“There are many reasons for the demise of coral reefs; but let’s not beat around the bush. Corals are bleaching and dying primarily because the Ocean is warming at an alarming rate, as evidenced by the sheer scale of this Fourth Global Bleaching Event. The Ocean is warming primarily because of accumulating greenhouse gases emitted by humankind’s ongoing burning of fossil fuels. In short, if we want coral reefs to survive, we must drastically reduce our emissions and keep global warming to below 1.5 degrees Celsius.”
Ambassador Peter Thomson, United Nations Secretary-General’s Special Envoy for the Ocean
APRIL 23, 2025 84% of the world’s coral reefs impacted in the most intense global coral bleaching event ever ICRI
