What happens if a coral reef gets too hot?

[MarkLaymon]

What happens if a coral reef gets too hot?​

But when the ocean environment changes, if it gets too hot, for instance, the coral stresses out and expels the algae. As the algae leaves, the coral fades until it looks like it's been bleached. If the temperature stays high, the coral won't let the algae back, and the coral will die.

 

[MarkLaymon]

What is coral bleaching?​

What is coral bleaching?

When corals are stressed by changes in conditions such as temperature, light, or nutrients, they expel the symbiotic algae living in their tissues, causing them to turn completely white.

oceanservice.noaa.gov

 

[MarkLaymon]

In January 2010, cold water temperatures in the Florida Keys caused a coral bleaching event that resulted in some coral death. Water temperatures dropped 12.06 degrees Fahrenheit lower than the typical temperatures observed at this time of year. Researchers will evaluate if this cold-stress event will make corals more susceptible to disease in the same way that warmer waters impact corals.

 

[MarkLaymon]

Warming Temperatures and Coral Bleaching​

Some scientists predict that 90% of global reefs will experience severe bleaching annually by 2055.

Global Threats to Coral Reefs - Coral Reef Alliance

Coral reefs are threatened by warming waters from climate change, ocean acidification and other stressors.

coral.org

Most corals have a narrow temperature tolerance. When temperatures become too warm, corals will expel the symbiotic algae (zooxanthellae) that live inside them causing them to turn white and lose an important food source. Although corals can survive a bleaching event, they are more vulnerable to disease and will eventually die if the marine heatwave lasts too long.

 

[MarkLaymon]

Ocean Acidification​

48% of fossil fuel emissions are absorbed by the ocean. As oceans absorb carbon dioxide (CO2), they become more acidic. This affects the ability of reef-building corals to grow their skeletons and form the foundation for coral reefs. Weaker skeletons also make corals more vulnerable to disease and destruction by storms. In fact, research shows that when exposed to high levels of CO2, corals stop being productive and their risk of bleaching increases by up to 50%.

 

[MarkLaymon]

• The world has lost 30% to 50% of its reefs in the last 40 years.
• Scientists have warned that remaining reefs could be gone within decades.
• Over the past century, sea surface temperatures have risen by an average of about 0.13 degrees Celsius per decade.
• Corals can become stressed when temperatures around them rise just 1 C.
• Minor heat waves can be devastating for reefs.

 

[MarkLaymon]

As the water temperature rose, the corals began to bleach. To the untrained eye, the scene would have looked fantastic. When the water heats up, corals become stressed and they expel the tiny algae called dinoflagellates that live in their tissue. Bleaching isn’t as simple as going from a living coral to a bleached white one, though. After they expel the algae, the corals turn fluorescent pinks and blues and yellows as they produce chemicals to protect themselves from the Sun’s harmful rays.

 

[MarkLaymon]

A warning for other ecosystems

The Chagos reefs could potentially recover – if they are spared from more heat waves. Even a 10% recovery would make the reefs stronger for when the next bleaching occurs. But recovery of a reef is measured in decades, not years.

So far, research missions that have returned to the Chagos reefs have found only meager recovery, if any at all.

We knew the reefs weren’t doing well under the insidious march of climate change in 2011, when the global reef expedition started. But it’s nothing like the intensity of worry we have now in 2021.

Coral reefs are the canary in the coal mine. Humans have collapsed other ecosystems before through overfishing, overhunting and development, but this is the first unequivocally tied to climate change. It’s a harbinger of what can happen to other ecosystems as they reach their survival thresholds.

What happens when a coral reef dies? An expert explains

Minor heat waves can be devastating for reefs, Miami University Professor Sam Purkis explains what it feels like to witness one die.

www.weforum.org