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1Fix the driver behind crashes, sound loss and screen glitches2Clear out junk files and repair common Windows errors3Scan for outdated or missing drivers - takes under a minuteCoral bleaching happens when heat stress breaks down the partnership between a coral animal and the algae living in its tissue. The coral loses or expels many of those algae, its tissue turns pale or white, and it loses an important source of food. A bleached coral is stressed, not automatically dead. The longer and more intense the heat, though, the greater the risk that it dies.
What happens inside a bleaching coral
Reef-building corals live in partnership with algae that sit inside their tissues. The algae supply much of the coral’s color and a major share of its food. NOAA/AOML’s “Threats to Coral” page describes prolonged extreme heat as disrupting this beneficial relationship.
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The whitening you see follows the loss of algae and their pigments. The coral’s tissue becomes see-through, so the pale skeleton underneath shows. The coral has not turned into a different substance. It has lost its tenants and a large part of its nutrition.
Bleached does not mean dead
Whiteness alone does not establish that a coral has died. A bleached colony can survive if conditions improve before it starves or succumbs to other problems. When heat is prolonged or severe, the odds shift toward mortality. When heat stress hits many colonies at once, the amount of living coral on a reef can fall, with consequences for the wider reef ecosystem. Outcomes still vary by species, colony and place, so not every bleached colony dies and not every reef responds the same way.
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What kind of heat triggers bleaching
NOAA/AOML’s explanation of bleaching in the Florida Keys describes two routes to thermal stress:
- Acute stress: water gets very hot for several days.
- Cumulative stress: temperatures stay moderately elevated for weeks.
There is no single temperature at which all corals bleach. Thresholds differ among coral communities, and long-term observations made on or near the reef help establish which local conditions are associated with bleaching. Species, depth and region all matter, so any universal number should be treated with suspicion.
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- 🐠 EVERYTHING YOU NEED - Feature a compact and customizable filtration chamber that is already built-in to the back of the aquarium – easy to setup and maintain
- 🐠 GREAT FEATURES – Includes quiet submersible pump, dual intakes and adjustable return nozzle. Compatible with all existing BioCube accessories. Fish, corals, substrate and décor are sold separately.
- 🐠 SLEEK & MODERN – Biocubes feature a rounded edge design and is the perfect innovative all-inclusive aquarium for all needs!
- 🐠 VIBRANT LED LIGHTING - Low-profile hood contains vibrant LED lighting that is capable of sustaining and growing healthy, vibrant corals and live plants.
- 🐠 MAXIMIZE BEAUTY - 24-hour timer which makes it easy to control the three independent light channels for maximum beauty: bright white, sparkling blue and color enhancing LEDs.
How scientists track heat stress: Degree Heating Weeks
NOAA Coral Reef Watch summarizes accumulated thermal stress with a measure called Degree Heating Weeks (DHW). According to its methodology pages, DHW adds up Coral Bleaching HotSpots greater than 1°C over a rolling 12-week window. The result is expressed in °C-weeks. Because it combines how hot the water got with how long it stayed that way, it captures both intensity and duration.
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DHW is a stress indicator derived from satellite sea-surface temperature. It is not a count of bleached colonies and not a direct observation of coral health.
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- Reminder : Before each use, please ensure that the long straw has been cleaned thoroughly; When feeding coral or other fish, turn off the circulation pump; When used in hot water, the temperature of the liquid should not exceed 176℉
NOAA’s DHW thresholds
| DHW value | What NOAA’s methodology associates with it |
|---|---|
| Above 4°C-weeks | Has been shown to cause significant coral bleaching |
| Above 8°C-weeks | Associated with severe, widespread bleaching and significant mortality; the 5-km methodology says reef-wide bleaching with mortality of heat-sensitive corals can be expected by this level |
These are monitoring thresholds and risk expectations that NOAA derived from past events. They are not a deterministic biological rule for every coral. NOAA Coral Reef Watch’s 50-km methodology puts the central point this way: “Mass coral bleaching has been shown to be caused by prolonged periods of thermal stress.”
Reading satellite data without over-reading it
Satellite products summarize conditions across mapped pixels. A pixel’s reading does not mean every coral inside it experiences identical temperatures or the same biological outcome. NOAA’s pages explain the satellite products and the variability of local thresholds, but they do not establish a depth-resolved product for general readers. If you are comparing risk between two sites, compare:
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- accumulated heat stress (DHW);
- the period over which it built up;
- local thresholds and long-term observations;
- the coral community at each site.
The latest global picture
NOAA Coral Reef Watch’s update of June 2, 2026 says the fourth global mass coral bleaching event likely ended in 2025. For January 1, 2023 through September 30, 2025, NOAA reports:
- Bleaching-level heat stress affected approximately 84.4% of the world’s coral reef area.
- Mass bleaching was documented in at least 83 countries and territories.
- For comparison, the 2014–2017 third global event affected 68.2% of reef area.
These figures describe that stated event period. They are not a live reading of current reef conditions.
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