Jun 14, 2023 - Energy & Environment

The discovery that could help save coral reefs

Illustration of a sea turtle wearing aviator sunglasses and wearing a security earpiece wire.

Illustration: Aïda Amer/Axios

Scientists have uncovered an El Niño-induced phenomenon that could help conservationists better protect coral reefs against lethal marine heatwaves.

Why it matters: The early development of El Niño, which boosts the impacts of climate change, is raising concern over what the ocean and atmosphere cycle will mean for already-embattled marine ecosystems.

What they found: According to a study published Wednesday in Science Advances, regional ocean currents during the 2015-2016 El Niño provided food to coral reefs that allowed them to survive warmer ocean temperatures that triggered mass coral bleaching events.

  • The research focused on reefs off of the Central Pacific island of Palmyra, where several terrestrial and marine ecosystems function as a "living laboratory" for coral research, per USGS.

What they're saying: Under the right set of circumstances, certain ocean conditions can align to create more favorable outcomes for reefs during El Niño events, says KAUST coral reef ecologist and lead author Michael Fox.

  • He notes it was “surprising that something positive could come from El Niño," citing the historical impact of the climate cycle on coral reefs — where bleaching reports are "the broadest and most extreme" — as akin to a wildfire.
  • "Things move hotter and faster during El Niño, and they're more intense overall,” says Fox.

Zoom out: El Niños supercharge ocean surface temperatures, which have been seeing record-breaking spikes in recent months.

  • The 2015-2016 El Niño event spurned the longest, most widespread and "probably the most destructive" coral bleaching event in recorded history, prolonged in part by global warming, per NOAA.
  • Triggered by increasing marine temperatures, bleaching is what happens when corals get stressed, expel algae which they rely on for food, and if they remain stressed for too long, die.

Zoom in: The study authors found that the eastward-flowing North Equatorial Counter Current, which spans the tropical Pacific and hits Palmyra's western shores, was significantly strengthened during the 2015-16 El Niño.

  • This, coupled with the development of a warmer sea surface, drove a huge surge in upwelling, delivering food by way of cooler plankton-rich waters to the corals — enabling them to better handle heat stress.
  • Thanks to these ocean processes, the reefs studied at Palmyra suffered limited coral loss during that El Niño, a period when roughly 30% of the world's corals perished.

Of note: The North Equatorial Counter Current actually starts thousands of miles away in the Philippines, before accelerating due to large changes in ocean temperatures and wind patterns that are common during strong El Niños.

The intrigue: In theory, any other island that's influenced by this particular current, or any of the other currents in the ocean that change speed during El Niño, could benefit from the exact same set of conditions, according to Fox.

  • "By identifying one set of changes that benefited Palmyra, it gives us the opportunity to start looking more broadly and say 'Where else did this type of thing happen?'" says Fox.
  • "And we can start to put other places on the map that may benefit from the same set of conditions under future heat waves, and start working that into our reef models and management and conservation priorities."

Yes, but: The paper doesn’t address several questions, including whether the same food resource shows up regularly at the site studied, or which corals in particular benefit from this limited phenomenon.

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