Aggressive seaweed hits one of the most remote reefs in the world

HONOLULU – Researchers say the seaweed species found recently killed a large patch of coral on a reef that was once pristine and quickly spread in one of the most remote and protected marine environments on earth.

A study from the University of Hawaii and others said seaweed spreads faster than anything they see in the Northwest Hawaiian Islands, a nature reserve that stretches more than 1,300 miles north of the main Hawaiian Islands.

That research published in the journal PLOS ONE on Tuesday.

Algae break easily and roll around at the bottom of the ocean like tumbleweed, scientists say, covering nearby reefs in thick vegetation that outperform coral to get space, sunlight and nutrients.

“This is very damaging seaweed with the potential to grow entire coral reefs,” said biologist Heather Spalding, study co-author and longtime Hawaii algae researcher. “We need to find out where it is currently found and what we can do to manage it.”

In 2016, government researchers conducted a routine survey of Pearl and Hermes Atoll when they discovered a small clump of seaweed they had never seen before.

Last summer, they returned and found that the algae had taken over a very large area of ​​coral reef – in some areas that included “everything, as far as the eye could see” – with seaweed about 8 inches (20 cm) thick, said Spalding, which belongs to among them. divers there.

“Everything underneath is dead,” he said.

The area largely lacks a large school of tropical fish and other marine life that normally cruises on vibrant reefs and fish that normally eat algae do not graze on new seaweed, the researchers said.

Diving along the reefs outside the atoll 15 miles (24 kilometers) reveals seaweed in various densities and depths.

Scientists say the actual coverage area is likely to be far greater than documented because they were unable to survey many sites during their brief visit.

Close to Midway Atoll, where air and sea battles were very important in World War II, Pearl and Hermes Atoll are located in the central Pacific about 2,000 miles (3,200 kilometers) from Asia and North America.

Uninhabited atolls are at the Papahanaumokuakea National Marine Monument, 600,000 square miles (1.6 million square kilometers), one of the largest protected marine environments in the world.

Noting that each seaweed mat is as large as several soccer fields, researchers say the algae can dramatically change the Pearl and Herme reefs and threaten the entire Hawaiian islands if they spread.

The main island of Hawaii has some invasive seaweed, but cases in the remote northwest are rare.

“We have not, until now, seen a big problem like this where we have disturbing species that come and make such big changes in a short time to the reef,” said University of Hawaii at Manoa Interim Associate Dean Dean Dean and Professor. Alison Sherwood, chief scientist in this study.

The researchers studied seaweed DNA to try to determine its origin but concluded that it was a new species of red algae that they named Chondria tumulosa.

Algae can spread in various ways, Sherwood said. This produces clumps similar to tumbleweed that move around the immediate area, but also produce spores that can travel much greater distances.

Among the unknowns is why algae grows so fast and how it reaches remote locations.

Scientists say seaweed blooms occur all over the world and can be seasonal, but this does not appear to be the case. The National Oceanic and Atmospheric Administration has monitored this site for more than 20 years.

“When you see something unusual in the last few years, you can be sure that this is something rather special compared to things that change from year to year,” said Queensland University Professor Peter Mumby, who is also chief scientist for the Great Barrier Reef Foundation Australia. “But it becomes a problem every time you see an ecosystem starting to show symptoms … like this.”

Mumby, who was not involved with Hawaii research, said more had to be done to understand what was driving the growth of seaweed.

But he noted that in other parts of the world algae bloom often because fish that eat plants have been harvested or forced to move due to environmental changes.

New seaweed could have been introduced by ships or sea debris. But no fishing is permitted at Pearl and Hermes and every boat that enters the area must be inspected and cleaned up. The species can also be native, after living in small gaps and gaps before changes in local conditions cause it to bloom, the researchers said.

The NOAA research crew will return soon to study the outbreak and find out if the current has spread it to the nearest Midway, home to the Battle of Midway National Memorial, the base of the US Fish and Wildlife Service and the region’s only airfield.

The first business order, officials say, is to make sure anyone who studies seaweed doesn’t accidentally pass it on.

“All of our diving equipment, all of our vessels, are all saturated with bleach,” said Randall Kosaki, NOAA’s research coordinator at sea monuments and expedition leader for the previous survey.

“If something like this goes back to Waikiki or anywhere in the main Hawaiian Islands it will be an ecological disaster, but also an economic disaster,” Kosaki said. “You can imagine what tourism would do to have algae like this that grow too high on coral reefs.”