Nuisance Alga Found in New Locations of Papahānaumokuākea Marine National Monument

By Sarah Marquis

September 2023

Scientists recently returned from a 23-day research expedition in Papahānaumokuākea Marine National Monument to study a mat-forming alga, Chondria tumulosa, that has invasive characteristics and is overgrowing some of the most pristine coral reefs in Hawai‘i. They found the first confirmed record of Chondria at Hōlanikū, or Kure Atoll ─ the furthest extent of the monument, about 1,350 miles from Honolulu.

Hawaiian monk seal
Hawaiian monk seals, like this one seen at Hōlanikū (Kure), depend on a healthy habitat. Photo: Kim Fuller/DLNR. Permit PMNM 2023-01.

When NOAA divers first detected the alga in 2016, it grew in lower abundances and was not yet widespread. By August 2019, the algae had grown into abundant mats of over 100,000 square feet each at Manawai (Pearl and Hermes Atoll), outcompeting the species typically living in these ecosystems. Chondria was also documented around Kuaihelani (Midway) in 2021 and 2022. With the recent confirmation at Hōlanikū, Chondria is now known to exist at all three northernmost atolls of the monument.

“Invasive and nuisance species are some of the most serious threats to our native ecosystems,” said Brian Hauk, NOAA sanctuary resource protection specialist and chief scientist for the expedition. “This alga has the potential to negatively impact entire island-scale coral reef ecosystems.”

Heather Spalding, Ph. D. of the College of Charleston collects water samples
                                from within <em>Chondria</em> mats for nutrient analysis.
Heather Spalding, Ph. D. of the College of Charleston collects water samples from within Chondria mats for nutrient analysis. Photo: Brian Hauk/NOAA

During this recent expedition, Chondria distribution at Manawai (Pearl and Hermes Atoll) appeared similar to observations from 2019 and 2021. Chondria was also observed on this expedition around Kuaihelani (Midway), with a few mat formations, with little apparent change from earlier expeditions

scientists researching alga species
Scientists collaborated to better understand the biology of this alga species, how it spreads so rapidly, and its impact on the reef ecosystem. The information gathered will help form a baseline for monitoring the alga, and will help inform future management practices. Photo: Brian Hauk/NOAA

Investigating the Mystery

Chondria can form large, thick mats, which smother native corals and virtually all other organisms under the mats. The origin of this alga is a mystery and very little is known about its ecology, physiology, or potential biological drivers. It was identified as a species new to science in 2020, and to date has only been observed in Papahānaumokuākea.

Managing for Protection

“Marine nuisance and alien species are notoriously difficult to get rid of once they become established,” said Kim Fuller, marine invasive species specialist with the Department of Land and Natural Resources.

Fuller led experiments to validate best management practices that have been used to help prevent the spread of Chondria to other islands or atolls. To ensure that no Chondria was inadvertently transported back to O‘ahu as a hitchhiker, everything the team used in the water, including their dive and research gear, was soaked in a strong bleach solution. The small dive boats and the deck of Kahana II were also sprayed with bleach prior to returning home.

“Prevention is the most time- and cost- effective solution for protecting our marine resources from invasive and nuisance species,” Fuller said.

NOAA’s Office of National Marine Sanctuaries leads and collaborates in research that is fundamental to understanding the natural and cultural resources in the monument. Conservation science allows sanctuary staff and partners to document the condition and trends of protected ecosystems and the significance of emerging threats.

Sunset at Hauk La Perouse
Researchers traveled past La Perouse Pinnacle at Lalo (French Frigate Shoals), Papahānaumokuākea. Photo: Brian Hauk/NOAA

Scientists aboard Kahana II included researchers from NOAA’s Office of National Marine Sanctuaries, Hawai'i Department of Land and Natural Resources/Division of Aquatic Resources, the University of Hawai'i Cooperative Institute for Marine and Atmospheric Research, University of Hawai'i at Mānoa, University of Hawai'i Maui College, the College of Charleston, and the University of Alabama at Birmingham.

Researchers part of the 23-day Chondria mission posing infront of the Kahana II
Researchers on the 23-day Chondria mission to Papahānaumokuākea. Photo: NOAA

Papahānaumokuākea Marine National Monument is cooperatively managed by NOAA (Office of National Marine Sanctuaries, NOAA Fisheries), U.S. Fish and Wildlife Service (Ecological Services, Refuges), the State of Hawai‘i (Division of Aquatic Resources, Division of Forestry and Wildlife), and the Office of Hawaiian Affairs.

Sarah Marquis is the West Coast/Pacific Islands media coordinator for NOAA’s Office of National Marine Sanctuaries

Chondria Fast Facts

  • Chondria is the genus name for a nuisance algae in Papahānaumokuākea Marine National Monument. A nuisance algae is defined as algae that might be native to the location, but has overgrown native species and negatively affected the habitat. Invasive species are non-native and cause harm.
  • Chondria tumulosa was identified as a species new to science in 2020, and to date has only been observed in Papahānaumokuākea Marine National Monument.
  • Chondria tumulosa can reproduce both sexually and asexually.
  • Researchers have been tracking the spread of this nuisance algae since it was first discovered in 2016.
  • To date, Chondria tumulosa has been documented growing as thick mats at Manawai, and has been deemed present in lower abundances at Hōlanikū and Kuaihelani.
  • More research is needed to determine how Chondria spreads, and what might help reduce Chondria growth.