NOAA Expects ‘Extreme Bleaching Event’

Coral bleaching in West Hawai‘i waters. PC: The Nature Conservancy of Hawai‘i

Hawai‘i is only weeks away from experiencing what is currently tracking as the worst coral bleaching event in the state’s history, surpassing the 2015 bleaching episode that killed roughly 50% of all corals in West Hawai‘i.

The month of July 2019 was hotter across the state than any July before it since scientists began keeping records 140 years ago. Hawaiian waters this year were also the warmest in July’s history over that period of time.

Dr. Jameson Gove, research oceanographer with the National Oceanic and Atmospheric Administration (NOAA) Pacific Islands Fisheries Science Center, said ocean temperatures are currently hovering around 83.5°F, roughly three degrees higher than generally expected at this time of year.

“We’ve been tracking above what we experienced in 2015 for the last six to eight weeks,” Dr. Gove said. “If that trend continues, it’s likely we will see severe coral bleaching that is similar or worse than we experienced in 2015.”

“We are expecting an extreme bleaching event,” he continued.

Data indicates the bleaching will begin inside of two months, and possibly sooner, according to a Department of Land and Natural Resources (DLNR) press release.

Ocean temperatures aren’t expected to hold strong over that time—they’re expected to rise. Mid-September tends to represent the highest ocean temperatures of the year, Dr. Gove said.

What this means for the future of coral health in Hawai‘i is harder to say. The 2015 event killed half of all the corals in West Hawai‘i. It was particularly hard on cauliflower corals, Dr. Gove said. Without significant repopulation efforts, those corals are essentially without hope of resurrection. Another catastrophic bleaching event isn’t likely to make a difference either way.

Some areas of coral, on the other hand, have bounced back over the last four years, while others continued to thrive throughout bleaching events. And those that were damaged in 2015 won’t necessarily be any more susceptible to another bleaching episode just because they remain in recovery mode.

“It’s more complicated than just to say those that were bleached last time are more vulnerable this time because of what happened in 2015,” Dr. Gove explained. “If anything, we’d suggest the opposite. Those that survived are likely the ones that will survive here.”

Water temperatures are far and away the most significant factor as it pertains to coral health. But it’s not just how warm the water is, it’s how long the water stays warm.

There’s little the community can do to impact ocean temperatures in the short-term. Human activity, though, can improve water quality in susceptible areas throughout Hawai‘i, which will better equip coral to deal with its primary stressor. Limiting water pollution of any kind will only increase coral capability to defend itself, Dr. Gove said.

DLNR and NOAA will hold a joint news conference on the matter 11 a.m. Friday, Aug. 23, 2019, at Magic Island on O‘ahu, the Waikiki side. Featured will be Dr. Gove and Brian Neilson, administrator of the DLNR Division of Aquatic Resources.

The state will release a list of actions the public can take to help mitigate the bleaching event likely to come.