An international team of scientists has developed ways to measure and compare the impact of “darkwaves” – when extreme weather events or human activities reduce underwater light for extended periods, affecting the stability of marine ecosystems.
Published in Communications Earth & Environment, the study introduced the concept of marine darkwaves – periods when underwater light is drastically reduced by sediment, algal blooms, organic matter, excess nutrients and other factors, that starves marine life of the light essential for survival.
Using long-term data from California and New Zealand, researchers documented darkwaves up to two months in duration, with light levels dropping close to 100 per cent compared to normal conditions.
Dr Shinae Montie, from The University of Western Australia’s Oceans Institute and School of Biological Sciences, said the loss of underwater light had cascading effects throughout marine ecosystems.
“Light reduction affects everything from the productivity of kelp forests and seagrass meadows to the behaviour, reproduction and survival of fish and other animals,” Dr Montie said.
Researchers developed the first framework for quantitative analysis and comparison of marine darkwave events from local to continental scales, helping predict the marine ecosystems most at risk as extreme weather becomes more frequent.
Lead author Dr Francois Thoral, from The University of Waikato in New Zealand, said scientists had long considered gradual, long-term declines in water clarity as one of the most pressing concerns for coastal ecosystems.
“There is concern climate change is increasing precipitation and extreme weather events, while human activities like land use change are increasing sedimentation in coastal waters,” Dr Thoral said.
“This framework gives us a way to measure and compare these intense, episodic low-light events for the first time.
“By linking river catchment processes to coastal waters and combining field monitoring with satellite analysis, we can better understand how darkwaves affect marine communities and develop strategies to protect them.”
While the study focused on international sites, WA’s coastal waters face similar threats during cyclones and extreme flood events.
Satellite imagery from ex-Cyclone Joyce in 2018 and Cyclone Seroja in 2021 shows large sediment plumes spreading from the Gascoyne River mouth, turning normally clear waters dark brown.
“These events could have significant impacts on light-dependent organisms and entire ecosystems along the coast,” Dr Montie said.
Image above: The Gascoyne River following extreme cyclone events in 2018 and 2021.