Ask NASA Climate | June 22, 2023, 10:44 PDT

Vanishing Corals: NASA Data Helps Track Coral Reefs

By Angela Colbert, Ph.D.,
NASA's Jet Propulsion Laboratory

A healthy coral reef. Credit: Jeremy Cohen, Penn State University

A healthy coral reef. Credit: Jeremy Cohen, Penn State University

In Brief:

Coral reefs, one of the most important ecosystems in the world, are in a global decline due to climate change. Data from airborne and satellite missions can fill in the gaps in underwater surveys and help create a global perspective on the state of ocean reefs.

Coral reefs, nicknamed the rainforests of the sea, are colorful, majestic underwater worlds teeming with life. However, their future is in jeopardy due to climate change, water pollution, and other human activities. Let’s explore why corals are important to us, how they are changing, and NASA’s role in monitoring their health.

Coral reefs are one of the most important ecosystems on the planet. While they cover less than 1% of the ocean floor, healthy coral reefs provide homes to approximately a quarter of all known marine species. Currently, scientists have identified almost 800 species of reef-building corals around the world.

An infographic from NOAA titled "What Makes a Coral Reef?" that shows the anatomy of a coral reef and three facts: one coral is made of many polyps, corals build coral reefs, and coral reefs provide food and shelter. There is an illustration of a coral reef with different kinds of corals and animals on the left and bottom. There is a zoomed-in diagram showing the anatomy of a coral polyp that looks like a tub with tentacles.
An infographic about the anatomy of a coral and how they form reefs. Credit: NOAA

Coral reefs also help protect human life and property. First, they act as a natural barrier for coastlines by dampening rough waves during storms. Second, they are the source of several cutting-edge medicines. And third, they generate billions of dollars for local economies through ecotourism and fisheries, while also serving as a critical food source in many island nations.

However, coral reefs are disappearing worldwide. We know this through extensive surveys conducted every decade. “Since 2009, the United Nations-supported Global Coral Reef Monitoring Network found that 14% of the corals have disappeared, and things are speeding up,” stated Dr. Ove Hoegh-Guldberg, professor of marine studies at the University of Queensland in Australia.

A special report in 2018 from the Intergovernmental Panel on Climate Change (IPCC) projected that coral reefs would decline by 70-90% if average global air temperatures warm by 1.5°C (2.7°F) above pre-industrial values. That number jumps to a 99% decline at 2°C (3.6°F) of warming. With the planet already warming approximately 1.1°C (2.0°F) due to human activities since the end of the 19th century, these declines in corals could be reached by 2050 or sooner.

It’s not feasible for scientists to monitor the state of every coral reef each year. While divers can provide detailed information about the health of individual corals, the work is labor- and time-intensive, often taking weeks to survey one reef. That’s where airborne and satellite data from NASA and other agencies play a vital role.

Sea surface temperature anomalies off the coast of eastern Australia in March 2022 compared to the average from 2003 to 2014. There is mainly yellows and red colors in all of the water locations shown, meaning warmer than normal sea temperatures. There are patches of bright red and dark red off the coast of Cairns where the Great Barrier Reef is located in part. The Great Barrier Reef is labeled near the top, Cairns is labeled toward the bottom of the tip of the continent, which is labeled Queensland. The Coral Sea is labeled to the left of the image.
The map shows sea surface temperatures in March 2022 near the northern Great Barrier Reef, Australia, compared to the average of water temperatures from 2003 to 2014. Red colors mean waters are warmer than normal. Credit: NASA/Landsat

According to Juan Torres-Pérez, research scientist with NASA’s Ames Research Center and a representative on the U.S. Coral Reef Task Force (USCRTF), several NASA satellites have proven very useful in monitoring sea surface temperature and water quality changes over time, both of which are associated with changes in coral reef health. “NASA’s publicly available data provides scientists with valuable information to identify these changes as they happen,” he said.

“To study a global problem, like the decline of coral reefs, you have to have a global perspective,” added Ved Chirayath, professor of Earth sciences at the University of Miami. Using NASA satellites and other remote sensing instruments, scientists can monitor coral reefs and their surroundings more frequently and more widely to help determine if they are changing. “Some challenging places to survey in the water are some of the most important to measure," he added, "as that’s where the changes are happening.”

One region that has been particularly challenging to measure from above is the tropics. According to Liane Guild, a scientist with NASA Ames and the USCRTF, prevalent cloud cover in the tropics can hinder the measurement of tropical regions from aircraft and satellites. “Innovative field tools, like using drones with cameras, can help acquire images below clouds, if present,” she said. “They can also collect fine-detailed images locally on corals to help understand coral health condition and decline.”

Once the causes of coral reef changes can be measured, tracked, and predicted, scientists can take action to protect them.