Researchers Suspect Increase of Invasive Alga at Papahānaumokuākea Marine National Monument

The amount of invasive alga at Papahānaumokuākea Marine National Monument does not appear to have diminished and may have increased since the last observations in 2019.

A research expedition, led by NOAA’s Office of National Marine Sanctuaries, recently returned to O‘ahu after 20 days at sea collecting data on a nuisance seaweed at Manawai (Pearl and Hermes Atoll). Thick mats of the invasive-like alga, Chondria tumulosa, were first documented in 2019, overgrowing and smothering native corals and algae at Manawai. It was identified as a species new to science in 2020.

During this research cruise, divers documented Chondria at approximately 30% of the locations that were surveyed, in dense, attached mats that were up to nine inches thick and hundreds of square meters in extent, according to a press release from NOAA. Although the data collected will take six months to a year to analyze, researchers say, the amount of algae does not appear to have diminished and may have increased since the last observations in 2019.

The expedition included researchers from the College of Charleston, University of Hawaiʿi, NOAA Papahānaumokuākea Marine National Monument, and the University of Alabama. Research was supported by the National Fish and Wildlife Foundation, NOAA’s Office of National Marine Sanctuaries and NOAA’s Office of Marine and Aviation Operations.

To help prevent its spread, best management practices were developed by the monument co-trustee agencies for any vessels approved to travel near Manawai. All diving gear and boats are soaked in high concentrations of bleach solutions and examined for fragments of the alga prior to departure from Manawai.