A new species of seaweed covers dead a coral reef at Pearl and Hermes Atoll in the remote Northwestern Hawaiian Islands. Photos / AP
A new species of seaweed covers dead a coral reef at Pearl and Hermes Atoll in the remote Northwestern Hawaiian Islands. Photos / AP
Researchers say a recently discovered species of seaweed is killing large patches of coral on once-pristine reefs and is rapidly spreading across one of the most remote and protected ocean environments on earth.
A study from the University of Hawaii and others says the seaweed is spreading more rapidly thananything they've seen in the Northwestern Hawaiian Islands, a nature reserve that stretches north of the main Hawaiian Islands.
The study was published in the journal PLOS ONE.
The algae easily breaks off and rolls across the ocean floor like tumbleweed, scientists say, covering nearby reefs in thick vegetation that out-competes coral for space, sunlight and nutrients.
"This is a highly destructive seaweed with the potential to overgrow entire reefs," said biologist Heather Spalding, a study co-author and longtime Hawaii algae researcher. "We need to figure out where it's currently found, and what we can do to manage it."
In 2016, government researchers were on a routine survey of Pearl and Hermes Atoll when they found small clumps of seaweed they'd never seen before.
Last summer, they returned to find algae had taken over huge areas of the reef — in some areas covering "everything, as far as the eye could see" — with seaweed nearly 20cm thick, said Spalding, who was among the divers there.
The area was mostly devoid of large schools of tropical fish and other marine life that usually cruise the vibrant reef, and fish that typically eat algae were not grazing on the new seaweed, researchers said.
Dives along the outer reef of the 24km atoll revealed the seaweed in varying densities and depths.
Scientists say the actual coverage area is likely much larger than documented because they couldn't survey many sites during their brief visit.
Researchers say the recently discovered species of seaweed is killing large patches of coral on once-pristine reefs.
Close to Midway Atoll, site of a pivotal World War II air and sea battle, Pearl and Hermes Atoll is mid-Pacific about 3200km from Asia and North America.
The uninhabited atoll is in the 1.6 million sq km Papahanaumokuakea Marine National Monument, one of the world's largest protected marine environments.
Noting that individual mats of seaweed were as big as several soccer fields, researchers say the algae could dramatically alter Pearl and Herme's reef and threaten the entire Hawaiian archipelago if it spreads.
Hawaii's main islands have several established invasive seaweeds, but cases in the remote northwest are rare.
"We have, not until now, seen a major issue like this where we have a nuisance species that's come in and made such profound changes over a short period of time to the reefs," said University of Hawaii at Manoa Interim Associate Dean and Professor Alison Sherwood, chief scientist on the study.
Researchers studied the seaweed's DNA to try to determine its origin but concluded it's a new species of red algae they named Chondria tumulosa.
Scientists say seaweed blooms happen worldwide and can be seasonal, but this does not appear to be the case. The National Oceanic and Atmospheric Administration has been monitoring the site for over 20 years.
