In October, Hurricane Walaka literally wiped East Island off the map, and with it the primary nesting grounds of thousands of threatened green sea turtles in French Frigate Shoals.

But until now it wasn’t clear what happened to the surrounding reefs and sea life in this remote stretch of the Northwestern Hawaiian Islands, about 550 miles from Honolulu.

Researchers with the National Oceanic and Atmospheric Administration and their partner scientists returned this week from a 22-day expedition in Papahanaumokuakea Marine National Monument.

Divers discovered devastating damage to the coral at French Frigate Shoals, an atoll featuring a crescent-shaped reef. Photos show rubble not recognizable as the former coral reef, one of the most significant reef systems in the nearly 600,000-square-mile monument, NOAA officials revealed Thursday.

Once abundant wildlife, brimming with colorful corals and diverse fish communities, is now gone. Scientists are unsure if the corals will grow back, or how long it will take.

Lead scientist Randy Kosaki of NOAA said French Frigate Shoals has been hit by tropical storms in the past. After Hurricane Neki passed through in 2009, researchers documented the immediate damage and how the corals grew back over the next several years.

This time was different, after Walaka passed through as a powerful Category 3 hurricane.

“The reefs weren’t damaged, they were just gone,” Kosaki said. “We weren’t expecting complete devastation.”

The team repeatedly checked their GPS to ensure they were in the right spot, unable to believe the wasteland below the surface. They received extra confirmation from an underwater receiver that shark researcher Carl Meyer and his team from the University of Hawaii’s Institute of Marine Biology had anchored there last July to monitor the movement of tiger sharks.

Rapture Reef was one of the most beautiful dive sites that Kosaki said he had ever dived. But there wasn’t even a mound of rubble left.

Scientists have said the hurricane’s pathway wasn’t a function of climate change, but its strength and timing were consistent with the effects of a warming ocean and rising global temperatures that make storms more intense.

Researchers on this expedition did not get close enough to East Island to see how it’s doing firsthand, Kosaki said. But recent satellite images suggest sand is building up there, the first step in its road to recovery. Re-establishing the vegetation there, which helps hold the tiny island in place, is likely years away.

Good Algae, Bad Algae

The fate of the reefs around French Frigate wasn’t the biggest surprise though. That came farther up the archipelago at Pearl and Hermes Atoll, which has a huge fringing reef.

NOAA divers documented mats of an unidentified, likely invasive algae overgrowing native corals at the tiny cluster of islands about 1,200 miles northwest of Honolulu.

Scientists found most of the damage on the west and northwest sides of the atoll. Many of these red algae mats were the size of several football fields. Underneath, the native corals were dead.

NOAA scientists find invasive algae at Pearl and Hermes Atoll.

“Normally, you think of that as something from a human introduction, like at Kaneohe Bay,” Kosaki said. “It’s the last thing on your mind when you go to a slice of heaven like Pearl and Hermes. It was just a punch in the gut.”

Access inside the monument is tightly controlled. Humans can’t get within 200 miles of its islands and atolls without a special permit for scientific, educational or cultural purposes.

The scene at Pearl and Hermes was so bad that the researchers decided to forgo other plans so they could focus on the effects of this invasive algae. They were also concerned about transporting anything invasive back to the Main Hawaiian Islands.

Courtesy: NOAA

“It was the first time we have had to worry about bringing those back here,” Kosaki said. “There are no laws about this. We self-imposed a quarantine on the ship.”

The team disinfected the ship, NOAA’s Rainier, as well as their gear and all their scientific instruments before sailing back to Honolulu.

Researchers brought back samples of the algae to try to identify it and determine where it came from. They now have a baseline, too, so that in subsequent trips they can see if it is getting worse or better.

“We found places with a lot of it and got mad. We found places with none of it and got scared,” Kosaki said.

While the shallow reefs were faring poorly, the situation was better a few hundred feet deep.

The team found deep coral reefs to be quite healthy, supporting large numbers of sharks and giant trevally, or ulua.

NOAA divers discover new algae species.

Few have explored these depths within the monument. And on this trip, divers discovered new species of algae in addition to the invasive algae, NOAA officials said.

It was the first time that a coral reef habitat that’s common in tide pools and shallow habitats in Hawaii was found at such depths.

“These deep reefs continue to yield a wealth of new discoveries,” Kosaki said.

He said it offered a teachable moment. While the algae that was smothering the coral to death at Pearl and Hermes was obviously bad, the beds of algae that the researchers found at deeper depths was providing homes to fish — similar to corals.

“You can’t just say algae is bad or algae is good,” Kosaki said.

Papahanaumokuakea is jointly managed by NOAA, the U.S. Fish and Wildlife Service, the Hawaii Department of Land and Natural Resources and the state Office of Hawaiian Affairs.

The management board plans to use the findings from the expedition as a baseline of the hurricane’s impacts as they weigh how best to respond.

The team has assumed the damage from Walaka is likely limited to French Frigate Shoals, based on the intensity of the storm and its path.