The ocean off the Pacific Coast is simmering, threatening coral reefs and livelihoods around Hawaii and causing many to worry of worse to come.

“The ocean is very important to us,” said Ka’imi Kaupiko, who lives in Milolii, a community often called the last Hawaiian fishing village, on Hawaii Island. The way of life there depends on the fish provided by the reefs, reefs which are now becoming sick in the warming waters.

“It affects a lot of how we are going to survive,” Kaupiko said.

Researchers said the heat wave was reminiscent of 2014, when a hot spot that became known as the blob began forming in the Pacific. It expanded and lingered over much of the Pacific Coast from Mexico to Alaska for years.

At First, Healthy Coral

Both marine heat waves are “super unusual,” according to Andrew Leising, a research oceanographer with the National Oceanic and Atmospheric Administration. Nearly every other marine heat wave NOAA has recorded in 40 years of satellite monitoring shrinks in comparison.

“The event in ‘14-15 was maybe eight to 10 times the size of Alaska. And the current event we’re having is nearly that big,” Leising said. “And then, everything else is sort of an even further distant third or fourth.”

Researchers say they think that climate change strongly influenced the original blob’s creation.

The blob also led to the first known mass bleaching event in Hawaii, in which coral reefs stressed by the extreme temperatures shed the symbiotic plant that both gives them their flamboyant coloration and provides them with oxygen.

“Parts of Hawaii saw about 50% coral loss for the 2015 event,” Jamison Gove, a research oceanographer with NOAA, said by email. “It was particularly devastating in areas off Hawaii Island and Maui.” Reef watchers said they were worried about a repeat.

After Bleaching, a Dire Outlook

Last time, researchers were unprepared for the marine heat wave, said Greg Asner, director of the Center for Global Discovery and Conservation Science at Arizona State University, who is based in Hawaii part of the year.

This time, in addition to satellite observation and a network of sensors they deployed in July, researchers are using a community science project in which members of the public use a web platform to document any bleached coral that they see. It helps guide researchers’ decisions about where to survey, given how sprawling the Hawaiian Islands are.

Green on the platform’s maps means no bleaching, yellow and orange mean some bleaching, and red means a lot of bleaching. “And if you asked me if you looked at that a month ago, it was just a few yellow dots,” Asner said. “And then the orange dots started popping up. And now we have red dots.”

Then, the Algae

Entire fisheries collapsed along the Pacific during the previous heat wave as high water temperatures upended the aquatic food web. According to some estimates, 100 million cod disappeared off the coast of southern Alaska.

Warming waters can trigger the release of a neurotoxin called domoic acid from algae. Shellfish eat the algae, and when animals eat the shellfish they get sick and can die. Tens of thousands of dead seabirds washed up on beaches during the blob, as did sick and dying sea lions, most likely a result of domoic acid poisoning. In 2016, domoic acid also prompted officials to close the California Dungeness crab fishery.