Scientists returning from a 22-day expedition to Papahanaumokuakea Marine National Monument today announced their findings, including the destruction of a significant reef by Hurricane Walaka.

The National Oceanic and Atmospheric Administration researchers are the first team to have visited Papahanaumokuakea aboard NOAA Ship Rainier since Hurricane Walaka, a powerful category 3 hurricane, passed through the Northwestern Hawaiian Islands, in October.

Scientists knew via satellite images that the majority of East Island at French Frigate Shoals appeared to be under water. What they found upon diving underwater on this expedition, however, was a shock.

Rapture Reef at French Frigate Shoals, previously one of the most beautiful, diverse reefs in the isles, is now just a wasteland of coral rubble.

>> Click here to see more photos of the damage caused by Hurricane Walaka.

“After the hurricane, those reefs are gone,” said Randall Kosaki, Papahanaumokuakea’s deputy superintendent of research and field operations. “Not even damaged. They’re just gone. There’s barely rubble.”

There are no more colorful, table corals or schools of fish, according to University of Hawaii at Hilo researcher Kailey Pascoe, who vividly remembers her first visit with a dive team to conduct photogrammetry surveys back in 2015. Instead, it was a desert.

“When we got down there, it was quite shocking because it was essentially flat, no coral, and rubble,” she said.

At first, she thought she was in the wrong location. Then she found the pins used to mark the monitoring sites, and realized what had happened. Hurricane Walaka had wiped this beautiful reef out.

“There were tiny pieces of coral that were dead, covered in algae, about the size of your hand … lots of sand, some toppled-over corals,” she said. “It was kind of devastating.”

While there were still some Hawaiian monk seals and sharks swimming around the reef, which she described as about the size of a football field, there were no longer any clouds of fish or vibrant corals to be seen. Still, she saw a few live corals of about 1- to 2-centimeters, offering some hope the reef will eventually regrow.

NOAA researchers had gone on the expedition to survey and monitor coral reefs and associated reef fish communities, and to search for new species and habitat types on deep coral reefs.

While they did discover numerous new species of algae in the deep sea, researchers also found thick mats of invasive, red alga – yet to be identified — on the west and northwest sides of Pearl and Hermes Atoll.

Many of these mats were as large as multiple football fields, according to researchers. Beneath them, they discovered bare, dead native corals. Some growths of the alga were also found hidden in cracks or crevices, and among native alga.

Assistant professor of biology Heather Spalding said she dove down and saw “this invasive algal mat as far as the eye could see.” She knew then that this was serious. The team curtailed other planned activities to focus on studying the invasive alga.

“When you have an invasive species like this come in and basically destroy the existing reef and wipe out the corals and native limu, there’s nothing really there to document,” she said. “So it’s really disheartening, and important that we limit the spread of this invasive alga, and really try and find out where it occurs now so we don’t spread it further.”

A detailed DNA analysis is already under way at a lab to try to determine what the invasive alga is.