NOAA Satellites Pinpoint Coral Bleaching Before It Happens 

Healthy coral reef in St. Croix, US Virgin Islands.

Healthy coral reef in St. Croix, US Virgin Islands.

High resolution (Credit: NOAA)

People know NOAA satellites as tools for weather forecasting and monitoring the Earth’s environment.  But did you know that these same satellites enable NOAA to be a global leader in assessing coral bleaching around the world?

Coral reefs are among the most diverse ecosystems on Earth, and people depend on reefs for fishing, coastal protection, and recreation.  However, rising ocean temperatures have put reefs at risk. 

Corals house algae inside their tissues and the algae provide corals with food and oxygen.  When ocean temperatures are too high, corals become stressed and expel their algae partners. This is called coral bleaching, because without their colorful algae, the corals turn pale white.  Prolonged bleaching can cause corals to starve and die.

Bleached brain coral.

Bleached brain coral.

High resolution (Credit: NOAA)

NOAA’s Satellite Monitoring System
NOAA satellites orbiting over 500 miles above the Earth are a crucial tool in monitoring for coral bleaching.  NOAA’s Coral Reef Watch uses satellite sea surface temperature data to pinpoint areas currently at risk for coral bleaching.  Data highlight areas where the ocean gets hot and stays hot, showing how heat stress builds up over time.  Areas where the colors are yellow to red and purple are at risk for bleaching. 

Recently, NOAA has expanded its Satellite Bleaching Alerts – e-mails that provide advance warning that a bleaching event is about to occur.  NOAA provides these alerts for free to researchers and managers around the world, with coverage at 60 coral reef sites from Aruba to Zanzibar.  This advance notice allows local officials to act to reduce human activity, such as diving, boating, and recreational fishing, that can add to the stress from high temperatures.

Satellite data showing accumulated heat stress that leads to coral bleaching.

Satellite data showing accumulated heat stress that leads to coral bleaching.

High resolution (Credit: NOAA)

Expanding this observing system internationally is a key outcome of NOAA’s partnership with the World Bank/GEF Coral Reef Targeted Research Program.

Corals and Climate Change
Coral bleaching is already a reality for many reefs around the world.  Massive warming in the Caribbean in 2005 caused major bleaching, killing half of the corals in some areas.  A recent report from the Global Coral Reef Monitoring Network, co-sponsored by NOAA, highlights the devastation and shows the value of the broad-scale monitoring that NOAA’s satellites provide.

River runoff can carry pollution from the land into the ocean.

River runoff can carry pollution from the land into the ocean.

High resolution (Credit: NOAA)

Many climate predictions indicate that ocean temperatures may warm more than 3°C (5°F) by 2100.  This temperature rise could make bleaching a regular event for the corals that survive that long.

Pollution, overfishing, and diseases add to the stress that corals are already experiencing.  The best hope for coral reefs to survive climate change is to reduce these other threats, giving corals a chance to bounce back from bleaching. 

How You Can Help
So what can you do?  A lot!  Even if you live far from the coast, your actions affect the future of coral reefs.  Everything flows into the ocean, so reduce your use of fertilizers and pesticides. Reduce your greenhouse gas emissions and eat fish that are harvested sustainably.  For more tips on what you can do to protect corals, visit NOAA's Coral Reef Conservation Program Web site. NOAA logo.