When Hurricane Walaka passed through the French Frigate Shoals as a category three hurricane last October, it left massive destruction of the coral reef, researchers recently found. Scientists also discovered an invasive algae overgrowing native corals and native algae at Pearl and Hermes Atoll.

Researchers with the National Oceanic and Atmospheric Administration and the University of Hawaii returned Tuesday to Honolulu after three weeks visiting the Papahānaumokuākea Marine National Monument for the first time since the hurricane hit the region.

Corals of the French Frigate Shoals, known for its abundant wildlife and considered one of the most significant reef systems in the national mounment, were pummeled and the fish colonies are gone, the reseachers said.

"The damage itself, it turned corals that were like six feet wide into tiny little pieces the size of your hand essentially," said Kaylie Pascoe, a team leader on the expedition.

"And obviously, we are now seeing like a very bare coral reeef made of rubble and there are no corals living and there are no more fish," she said.

Pascoe said corals need light to grow and feed but the hurricane left the reef covered in sediment.

Researchers are not sure whether the corals will grow back – or if they do – how long it will take.

The scientists are also investigating an invasive algae that is blanketing shallow reefs off the Pearl and Hermes Atoll, located more than 1,200 miles from Honolulu.

Researchers found the outbreak of the algae in the west and northwest areas of the atoll. Officials are not quite sure what type of algae it is – but they have theories.

"Just based on how it looks and it grows, it belongs to a family of algae that are used extensively for aquaculture," said Heather Spalding, an algae expert, who took part in the expedition. "And so these are farmed in many countries in the tropical Pacific and in other areas around the world by communities to produce carrageenan, which is a prdouct derived from the algae." Carrageenan is found in toothpaste and food as a binder.

Spalding said samples of the algae are being analyzed for more nformation before next steps are taken.

There was some good news from the expedition. Researchers said the deep coral reefs of Papahānaumokuākea appear to be healthy and supporting such species as sharks and ulua.

The board that manages the national monument plan more research to understand the impacts from the hurricane and growth of the invasive algae before they decide how to respond.