Division of Aquatic Resources

First identified in 2016 at Manawai (Pearl and Hermes Atoll) in the Papahānaumokuākea Marine National Monument, Chondria tumulosa quickly became a major concern for marine managers in Hawaiʻi. This fast-growing red algae forms dense mats that can smother coral reefs, overgrow native species, and disrupt delicate reef ecosystems. If you have ever laid on a bed of thick moss, you can imagine how little sunlight and space remain for anything trying to grow underneath it! Since its initial discovery, C. tumulosa has also been found at Hōlanikū (Kure Atoll) and Kuaihelani (Midway Atoll). Managers are concerned about preventing it from spreading to other areas in Papahānaumokuākea or even the Main Hawaiian Islands, where it has not yet been identified.

Biosecurity Efforts

Kate Gonzalez analyzing the viability of C. tumulosa using a PAM fluorometer

Biosecurity is the practice of preventing biological threats from spreading into new environments where they could cause ecological harm. The spread of Chondria tumulosa can be reduced through the development and implementation of biosecurity protocols that target potential pathways of introduction and spread. In 2023, the co-managing agencies of Papahānaumokuākea Marine National Monument developed a best management practices document (BMP20) outlining extensive measures to help prevent the spread of nuisance algae species. The guidance includes strict cleaning, inspection, and disinfection procedures for vessels, scientific equipment, dive gear, and marine debris entering or leaving affected areas. Co-managing agencies and partners continue to refine these practices by developing new biosecurity techniques that are safer, more effective, and more efficient to use.

Researching Solutions to Stop the Spread

One reason Chondria tumulosa is such a formidable pest is its remarkable ability to survive conditions that would normally kill most limu species. While many native algae die after a few days of drying in the sun, a short freshwater soak, or minutes in a mild bleach solution, C. tumulosa has been shown to survive for months while desiccated on the hot tarmac of Kuaihelani. It also appears resistant to freshwater treatment and requires extremely concentrated bleach solutions for decontamination, levels that can pose risks to human health and the environment.

Lizzy Monaghan collecting Chondria tumulosa in the field

Division of Aquatic Resources (DAR) Aquatic Biologists Lizzy Monaghan and Kate Gonzalez traveled to Kuaihelani in September 2025 for two weeks to research a potential solution. In collaboration with University of Hawaiʻi limu biologists Dr. Angela Donna-Richards and Dr. Celia Smith as well as a team of Kuaihelani-based US Fish & Wildlife Service resource managers, Lizzy and Kate tested hot water as a decontamination method.

The DAR biologists collected fresh samples from a nearby affected reef site and began testing how the algae responded to heated seawater and freshwater treatments. After several preliminary trials, Lizzy and Kate identified a range of temperatures and exposure times for a larger experiment designed to simulate real-world decontamination scenarios. They filled bins containing nets with either seawater or freshwater heated to different temperatures, then exposed C. tumulosa samples for varying lengths of time to determine which combinations were most effective at killing the algae. Following treatment, the samples were analyzed using a PAM fluorometer, which measures whether the algae can still photosynthesize, both immediately after the experiment and again after 72 hours of recovery in ideal conditions.

Early Findings and Next Steps

Through this experiment, the DAR biologists were able to identify a range of temperatures and times that could work for Chondria tumulosa decontamination using either seawater or freshwater. Having these options will be helpful for making management decisions and editing current Best Management Practices in the future. However, research is on-going to identify techniques that will work at larger scales, and work for all activities that happen on Chondria-affected reefs.

Old Woman Wrasse (Hinalea luahine), Convict Tangs (Manini), surgeon fish, and Spectacled Parrotfish (Uhu uli uli) on the reef

Biosecurity is critical to protecting the fragile coral reef ecosystems of Papahānaumokuākea Marine National Monument. By improving tools and decontamination methods, scientists and resource managers are helping preserve the monument’s vibrant reefs, native species, and cultural heritage for future generations.

Authors: Lizzy Monaghan & Kate Gonzalez