The most abundant species of invasive macroalgae, commonly known as seaweed, in the main Hawaiian Islands has been found for the first time in the Papahānaumokuākea National Marine Sanctuary.
A November report, published in the journal BioInvasions Records, detailed the discovery of Acanthophora spicifera at Kuaihelani, or Midway Atoll, in 2022.
Also known as the prickly seaweed, the invasive algae was first reported in Hawaiʻi at Pearl Harbor in 1952, and can now be found on all eight of the main Hawaiian Islands.
Taylor Williams, a Dr. Nancy Foster Scholar with the National Oceanic and Atmospheric Administration’s Office of National Marine Sanctuaries, was one of the researchers at Midway who found the seaweed while doing other research.
“We were up there surveying for some other species of seaweed,” she said. “It sort of raised a bunch of red flags for the whole team, because it had never been reported in Papahānaumokuākea before."
The article suggested that the prickly seaweed reached the Northwestern Hawaiian Islands by hitching rides on boats and ships from the main Hawaiian Islands.
Biofouling, or the accumulation of organisms on the sides of manmade vessels, is a common way for marine invasive species to spread. It’s also how the species first reached Hawaiʻi 70 years ago.
After it arrived, Acanthophora spicifera was able to thrive likely because it can reproduce both sexually and asexually — through fragmentation — and can grow in a wide range of habitats.
Those characteristics have allowed it to successfully outcompete native species. Just a decade after reaching Oʻahu, it spread through the rest of the main Hawaiian Islands.
Immediately after Acanthophora spicifera was discovered at Midway, the federal government did respond to make sure it was contained.
“We implemented biosecurity plans for Midway immediately,” said NOAA resource protection specialist Brian Hauk.
“(The U.S. Fish and Wildlife Service) started different practices of biosecurity for their boats and vessels that are in the water, and what they do when they're moving them around and quarantining the area so that people weren't inadvertently spreading (the prickly seaweed).”
Since then, scientists have also been trying to learn more about how the seaweed reproduces, also in an effort to stop it from spreading.
There are ongoing efforts to better monitor its distribution in the area. Researchers have found that they can accurately determine where Acanthophora spicifera is by checking for its DNA in samples of ocean water — instead of just trying to find it visually.
That should make the work of tracking it easier and more accurate.
Both Williams and Hauk say preventing the prickly seaweed’s spread depends significantly on biosecurity protocols in the sanctuary.
“That’s part of why we emphasize so strongly the biosecurity that we have within the sanctuary — to try to prevent a 10-year spread to the rest of the Northwestern Hawaiian Islands, like what we saw in the main Hawaiian Islands,” Williams told HPR.
There are federal guidelines to reduce chances of spreading invasive species to Papahānaumokuākea.
“Any permitted vessel that wants to enter Papahānaumokuākea has to adhere to strict biosecurity protocols that include things like hull inspections prior to them entering the monument, to try our best to prevent this type of thing,” Hauk said.
But he noted that some cargo ships, and vessels used in military activities, can be exempt from those protocols.
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