Scientists track weeks-long underwater blackouts affecting kelp and seagrass using seafloor light data
Offshore turbines, storms, and algae blooms are blacking out kelp forests — and scientists can now track it
Above the water, reading darkness is easy. Clouds roll in, smoke drifts across the sky, sunlight disappears. But beneath the ocean surface, a different kind of darkness has been spreading through coastal waters around the world — and for decades, scientists had no consistent way to even detect it.
In some areas, light reaching the seafloor can nearly vanish for days, weeks, or more than two months at a stretch. The ecosystems living there — kelp forests, seagrass meadows, corals — depend on that light to survive. Until very recently, these blackouts had no name, no shared measurement, and no global framework to track them.
By measuring these events consistently, the framework makes it possible — for the first time — to compare darkwave intensity and duration across different regions.
When the ocean goes dark
The forces behind underwater darkness look nothing like those above the surface. Instead of clouds or smoke, it’s sediment flushed in by storms, algae blooms spreading across coastal waters, and organic debris that can strip light from the seafloor almost entirely. What was once a bright, productive underwater environment can be reduced to near-night conditions — sometimes for weeks at a time.
Researchers are now calling these events marine darkwaves. An international team coined the term to describe short-lived but intense episodes of underwater darkness, with durations that vary wildly — some lasting only a few days, others persisting for more than two months. What they share is an abrupt, dramatic reduction in the light that coastal ecosystems depend on.
Why light is the ocean’s lifeline
Light isn’t just a backdrop in the ocean — it’s the engine. Kelp, seagrass, corals, and algae all rely on photosynthesis to grow and sustain the food webs built around them. When light drops sharply, that process stalls.
“Even short periods of reduced light can impair photosynthesis in kelp forests, seagrass and corals,” said lead author François Thoral, a postdoctoral fellow at the University of Waikato and Earth Sciences New Zealand. The consequences don’t stop at plants. Darkwave events can also alter the behavior of fish, sharks, and marine mammals that navigate and feed by light. “When darkness persists,” Thoral added, “the ecological effects can be significant.”
Decades of data, one new framework
The research team built their framework using long-term datasets from multiple coastal regions — 16 years of measurements from the Santa Barbara Coastal Long Term Ecological Research Site, 10 years of observations from New Zealand’s Hauraki Gulf, and 21 years of satellite-derived seafloor light estimates along New Zealand’s East Cape. That East Cape record is among the most comprehensive of its kind anywhere in the world.
The East Cape dataset alone revealed between 25 and 80 darkwave events since 2002. Many were tied to powerful storms and large weather systems, including Cyclone Gabrielle. By measuring these events consistently, the framework makes it possible — for the first time — to compare darkwave intensity and duration across different regions.
A threat hiding in plain sight
For years, ocean scientists focused primarily on gradual, long-term declines in water clarity — the slow dimming of coastal waters due to chronic pollution or sedimentation. Marine darkwaves are something else entirely: sudden, acute episodes that may cause damage just as serious, but compressed into a much shorter timeframe.
“We have long known that light levels are critical for photosynthetic organisms — like algae, seagrasses and corals — and that factors that reduce light to the seafloor can impact them,” said co-author Bob Miller, a research biologist at UC Santa Barbara’s Marine Science Institute. “This study creates a framework for comparing such events, which we call darkwaves.”
The framework is designed to complement existing monitoring tools, not replace them. Scientists already track marine heatwaves, ocean acidification, and oxygen depletion. Darkwave monitoring adds another layer — one that captures a form of acute stress that had previously gone unnamed and unmeasured — giving coastal managers and conservation groups a clearer picture of when ecosystems are under serious, immediate pressure.
What comes next for ocean monitoring
The research opens a practical path forward. At UC Santa Barbara, Miller and his colleagues plan to expand their work by investigating how fires and mudslides drive sedimentation and turbidity along the California coast, and what that means for the state’s kelp forests. It’s a timely focus given how frequently those events now occur.
The Santa Barbara Coastal LTER is one of only a handful of programs worldwide that collects long-term measurements of light directly on the seafloor — a rare asset, and a model for what broader monitoring could look like.
The longer ambition is global. The darkwave framework is designed to be scalable, giving researchers the tools to identify and compare these events in coastal regions far beyond California and New Zealand. As offshore development expands and climate-driven storms intensify, tracking sudden underwater light loss will only grow more important. The oceans have been going dark in ways we couldn’t measure. Now, at least, we’re starting to watch.
Learn more here: François Thoral, Matthew H. Pinkerton, Shinae Montie, Mads S. Thomsen, Christopher N. Battershill, Karen Filbee-Dexter, Mark Gall, Robert J. Miller, Shane Orchard, Daniel C. Reed, Leigh W. Tait, Spencer D. S. Virgin, Thomas Wernberg, John Zeldis, David R. Schiel. Marine darkwave as an event-based framework to assess unusual periods of reduced underwater light availability. Communications Earth, 2026; 7 (1) DOI: 10.1038/s43247-025-03023-4
Daniel García is an Editor-in-Chief with strong expertise in structural work and engineering principles. He combines this technical foundation with deep knowledge of energy, spatial design, and emerging technologies, bringing a forward-thinking and analytical approach to editorial leadership.
