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Scientists have discovered sudden underwater blackouts that can plunge the seafloor into darkness and threaten marine life.
Clouds, smoke, and fog can dim the sky above, but underwater, a different set of forces can block sunlight entirely. Sediment runoff, algae blooms, and organic material can sharply reduce the amount of light reaching the ocean floor, sometimes creating near total darkness. To better understand and compare these events, an international team of scientists has developed the first framework for identifying marine blackouts.
The research, published in Communications Earth & Environment, defines a new phenomenon known as a marine darkwave. These events are brief but severe periods of underwater darkness that can disrupt kelp forests, seagrass beds, and other marine ecosystems that rely on light.
Why Underwater Light Is Essential
“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 goal of the project was to establish a shared system that allows scientists to compare extreme light loss events across different coastal regions. Until now, researchers lacked a consistent way to evaluate how severe or widespread these underwater blackouts could be.
“Light is a fundamental driver of marine productivity, yet until now we have not had a consistent way to measure extreme reductions in underwater light,” said lead author François Thoral, a postdoctoral fellow at the University of Waikato and Earth Sciences New Zealand.
Decades of Coastal and Satellite Data
To build the new framework, the team analyzed long-term observations from multiple locations. This included 16 years of data collected at the Santa Barbara Coastal Long Term Ecological Research Site (LTER) and 10 years of measurements from New Zealand coastal sites in Hauraki Gulf/Tīkapa Moana, in the Firth of Thames. Researchers also examined 21 years of seafloor light estimates derived from satellite imagery along New Zealand’s East Cape.
Across these regions, marine darkwaves varied widely in duration. Some lasted only a few days, while others continued for more than two months. In the most extreme cases, sunlight reaching the seabed was almost entirely blocked.
The analysis identified between 25 and 80 darkwave events along the East Cape since 2002. Many of these episodes coincided with powerful storms and large weather systems, including Cyclone Gabrielle.
Short Events With Major Ecological Effects
For many years, scientists have focused on slow, long-term declines in water clarity as a major threat to coastal ecosystems. The new findings suggest that sudden darkwave events can be equally damaging.
“Even short periods of reduced light can impair photosynthesis in kelp forests, seagrass, and corals,” Thoral said. “These events can also influence the behavior of fish, sharks ,and marine mammals. When darkness persists, the ecological effects can be significant.”
A New Tool for Monitoring Ocean Stress
The marine darkwave framework adds a new dimension to existing systems used to track marine heatwaves, ocean acidification, and deoxygenation. Together, these tools give coastal communities, resource managers, and conservation groups a clearer way to identify when marine ecosystems are experiencing intense short-term stress.
Because the Santa Barbara Coastal LTER is one of the few programs worldwide that collect long-term measurements of light on the seafloor, Miller and his colleagues at UCSB plan to expand their research. They aim to further study how sedimentation and turbidity — which are influenced by fires and mudslides — affect California’s kelp forests.
Reference: “Marine darkwave as an event-based framework to assess unusual periods of reduced underwater light availability” by 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 and David R. Schiel, 12 January 2026, Communications Earth & Environment.
DOI: 10.1038/s43247-025-03023-4
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