Scientists returning from a 22-day expedition to Papahanaumokuakea Marine National Monument aboard NOAA Ship Rainier on Thursday 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 assessed coral reef damage at the monument 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 underwater. What they found upon diving underwater on this expedition, however, was a shock.
They found that Rapture Reef on the south side of French Frigate Shoals, previously one of the most beautiful, diverse reefs in the isles, teeming with fish, is now just a wasteland of rubble.
“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.”
>> Photo Gallery: Scientists aboard NOAA Ship Rainier return
University of Hawaii-Hilo researcher Kailey Pascoe vividly remembers her first visit with a dive team to conduct photogrammetry surveys back in 2015. She described Rapture Reef as “one of the most beautiful” reefs she had ever seen, with broad table corals and clouds of fish. But on this expedition 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 out this beautiful reef.
“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 went ahead with her survey, and she said she did see a few, surviving corals of about 1 to 2 centimeters, offering some hope the reef eventually will 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, using rebreather diving technology.
While they did discover numerous new species of algae in the deep sea, researchers were alarmed by a new sight — thick mats of an 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 of the invasive alga was also hidden in cracks and crevices, and among native algae.
Heather Spalding, assistant professor of biology at College of Charleston, said she dived down and saw “this invasive algal mat as far as the eye could see.” She knew then that this was serious.
Spalding had originally gone on the expedition to document native limu. Instead, the team curtailed activities planned at other locations 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 underway at a lab to try to determine what the invasive alga is, which could help determine where it came from.
Athline Clark, superintendent of Papahanaumokuakea, said the team put additional biocontrol protocols in place to prevent spreading the invasive alga to other locations. The monument also has assembled a working group to respond to the invasive alga.
Damage from Hurricane Walaka likely was limited to the French Frigate Shoals, according to NOAA, since the storm did not approach other reefs with the same intensity.
