Hurricane Walaka’s legacy: Decimated reefs and invasive algae

Published: Aug. 15, 2019 at 5:26 PM HST
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HONOLULU, Hawaii (HawaiiNewsNow) - Scientists who just completed underwater surveys in the Northwestern Hawaiian Islands found significant reef damage caused by Hurricane Walaka last October that could adversely affect Papahanaumokukea Marine National Monument for decades.

"I wouldn't say they're damaged, they're gone. They are completely unrecognizable. It was actually very shocking," NOAA lead scientist Rady Kosaki said.

The brunt of the destruction is at French Frigate Shoals. But it isn’t just storm damage.

College of Charleston biology professor Heather Spalding found a non-native algae near Pearl and Hermes Atoll.

"This invasive mat was as far as the eye could see," she said. "This thick mat had covered all of the reef and killed all of the corals and native algae growing underneath of it."

Spalding said the algae was 3 to 6 inches thick.

"One of the traits of a highly successful invasive species is that it fragments and forms new individuals," she said.

[Read more: Hurricane Walaka practically wiped an island off the map]

Kosaki said virtually all of the native fish have disappeared.

"They rely on the corals and coral reef structure itself for habitat. You destroy that habitat and the fish are gone," he said.

The expedition lasted 22 days, ample time for scientists to examine reefs both shallow and deep.

University of Hawaii Hilo researcher Kailey Pascoe said some reefs are reduced to rubble and larger corals are knocked over.

“That was definitely a wake-up call for hurricanes and climate change. If that wasn’t, this should be because reefs at 80 feet of water are being trampled,” she said.

Most of the damage occurred at depths of 10 to 100 feet.

"What we did see at depth was large volumes of sand was moved around and potentially buried some of the reefs that we used to dive on," Kosaki said.

Hurricane Walaka barreled over the the French Frigate Shoals as a major tropical cyclone, and wiped out an entire island in its path.

Another NOAA expedition to the national monument could take place next year.

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