As ocean temperatures rise, turf algae are replacing kelp forests in the Gulf of Maine, triggering ecological and chemical changes that threaten marine biodiversity.
Kelp Forests Collapse as Turf Algae Take Over
The warming waters of the Gulf of Maine are accelerating a dramatic transformation beneath the surface. Once-dense forests of tall kelp are being replaced by low-lying, fast-growing turf algae, altering the entire marine ecosystem.
This shift is not just about space—turf algae are chemically attacking kelp, preventing their recovery and locking coastal reefs into a degraded state.
New Study Reveals “Chemical Warfare” Between Algae
A groundbreaking study published in Science by Bigelow Laboratory for Ocean Sciences, along with collaborators from the University of Maine, UC Riverside, and Harvard University, reveals that turf algae release harmful chemicals that kill young kelp. This phenomenon, known as allelopathy, creates a destructive feedback loop:
- More turf algae → More harmful chemicals → Less kelp recovery → Even more turf algae.
Senior author Dr. Doug Rasher describes this as a form of chemical warfare, reshaping Maine’s reef ecosystems in ways previously overlooked.
Why Is This Shift So Dangerous?
Kelp forests are known as the rainforests of the sea. They provide critical habitat, increase marine biodiversity, and support coastal economies. Replacing them with turf algae is like turning a forest into a weedy field.
Lead author Shane Farrell, a PhD candidate at the University of Maine, explains:
“This is comparable to a forest turning into a grassland. We lose biodiversity, productivity, and essential ecosystem services.”
Cutting-Edge Research Methods
To understand the underwater chemical warfare, the researchers conducted:
- Three years of reef surveys along the Gulf of Maine coast.
- Water and seaweed sampling for chemical analysis.
- Non-targeted metabolomics, a state-of-the-art method for identifying unknown chemical compounds.
Less than 2% of the molecules they found had been described in scientific literature. Advanced computational tools were used to predict and classify these compounds into new chemical families, offering rare insights into marine chemical ecology.
Lab Experiments Confirm: Turf Algae Chemicals Kill Kelp
In controlled lab experiments, researchers exposed kelp gametophytes (early life stages) to waterborne chemicals collected from turf-dominated reefs. The result:
- Kelp survival dropped by up to 500% when exposed to turf algae chemicals.
- The most harmful substances came from the five most abundant turf species.
This confirms that turf algae directly prevent kelp from recovering, even if temperatures stabilize.
Global Implications for Marine Ecosystem Recovery
Interestingly, similar chemicals have been linked to reef degradation in tropical ecosystems like coral reefs. This suggests that chemical feedback loops may be a global obstacle to marine ecosystem restoration, not just in cold-water environments.
“We’re just beginning to understand how chemicals shape marine recovery patterns worldwide,” says Rasher.
What Can Be Done?
Ocean warming remains the primary cause of kelp forest decline. But reversing climate change alone won’t bring kelp forests back in the Gulf of Maine.
“We need local interventions,” says Farrell. “Removing turf algae may be the only way to help kelp forests recover.”
Key Takeaways for Conservation
- Turf algae are chemically suppressing kelp growth through allelopathy.
- The loss of kelp forests threatens biodiversity and human coastal benefits.
- Local restoration efforts must target turf algae removal alongside global climate action.
Reference
Farrell, S., Rasher, D., et al. (2025). Turf algae redefine the chemical landscape of temperate reefs, limiting kelp forest recovery. Science. DOI: 10.1126/science.adt6788