A study from the University of Hawaii at Mānoa, published in Coral Reefs, revealed that the Hawaiian green sea turtles (Chelonia mydas) are playing a key role in reducing the biomass of Chondria tumulosa, an invasive algae that threatens the reefs of the northwestern archipelago.
The research documented that these reptiles actively feed on the algae, which could help mitigate its spread. However, scientists warn that during their migrations, the turtles could also disperse viable fragments, creating an ecological dilemma.
The expansion of Chondria tumulosa
- Identified in 2016 on the Manawai Atoll (Pearl and Hermes).
- In less than a decade, it spread to Kuaihelani (Midway) in 2021 and to Hōlanikū (Kure) in 2022.
- Currently covers more than 101 km² of coral ecosystems.
- Forms dense mats up to 6 cm thick, capable of smothering live corals and displacing native species.
This accelerated growth positions it as one of the most serious threats to the regional marine biodiversity, already affected by climate change and human activity.
Behavior of the green turtles
Observations made in the Papahānaumokuākea Marine National Monument recorded three specimens feeding on the algae for about 50 minutes. A female made 18 bites in 95 seconds, removing fragments between 5 and 15 cm.
The necropsy of a turtle found in the area showed that 25% of its digestive content corresponded to fragments of Chondria tumulosa. No local fish or urchin demonstrated similar efficiency in removing the invasive biomass.
Opportunity and risk
According to biologist Tammy Summers, green turtles act as native megaherbivores with the potential to suppress invasive biomass. However, the dispersal of fragments during their migrations could accelerate the spread of the algae to new areas.
96% of Hawaii’s green turtles nest in Lalo (French Frigate Shoals) and migrate to other areas of the archipelago, increasing the risk of transporting viable fragments.
Conservation strategies
Professor Celia Smith, the lead author of the study, emphasized the need to:
- Increase the populations of green sea turtles, an endangered species.
- Strengthen environmental monitoring using environmental DNA (eDNA) techniques.
- Identify critical migratory routes to anticipate new expansions of the algae.
These measures aim to balance the benefits of natural control exerted by the turtles with the risks of unintentional dispersal.
The behavior of green sea turtles towards Chondria tumulosa presents a complex scenario: they are allies in defending the reefs but also potential vectors for the expansion of the invasive species.
The rapid spread of the algae demands conservation strategies that integrate advanced monitoring, strengthening of native populations, and international cooperation to protect Hawaii’s coral biodiversity.
