Imagine a world where the ocean's rich ecosystems face a grave threat from mysterious "underwater blackouts." Recent research reveals that increasing storm activity is putting marine life in jeopardy by blocking vital sunlight with what scientists have termed "darkwaves." This phenomenon occurs when natural light is obstructed from penetrating the ocean depths due to various factors, including sediment plumes, algal blooms, erosion, or even human activities.
International scientists have meticulously analyzed long-term data from California and New Zealand over a two-month stretch, identifying specific areas where light levels in the ocean had plummeted significantly. This reduction in light can devastate marine ecosystems, such as kelp forests and seagrass meadows, leading to a scarcity of nutrients essential for fish breeding grounds.
Lessons From History
Reflecting on past events, a similar ecological crisis unfolded 15 years ago in Western Australia’s Gascoyne region. Intense rainfall caused sediment from the river to spread across Shark Bay, located 840 kilometers north of Perth, resulting in detrimental effects on marine life.
In 2011, a combination of flooding and an extreme marine heatwave created conditions ripe for an algal bloom, which annihilated about 1,200 kilometers of seagrass meadows—critical habitats for species like dugongs. Liam Ridgley, the leader of the Shark Bay Seagrass Restoration project, noted that these meadows were unable to withstand rising ocean temperatures. "We experienced a significant warming event where the water temperature remained at 30 degrees Celsius for 90 consecutive days; sadly, the seagrass could not cope with it," Mr. Ridgley explained. He further elaborated on how heavy rainfall from inland floods led to sediment entering the bay, generating a low-light scenario that turned the water black for approximately four years due to a massive algal bloom.
More than a decade later, Mr. Ridgley continues his restoration efforts by planting seedlings anchored in sandbags on the bay floor, striving to revive the lost ecosystems.
Cyclone Brings Back Memories
As restoration initiatives progress, Mr. Ridgley is feeling a sense of déjà vu while monitoring the development of Cyclone Mitchell along Western Australia’s Pilbara coast. "It’s eerily reminiscent of the events in 2011, though currently, Shark Bay's water temperatures are somewhat more stable," he remarked. "If this cyclone tracks inland and triggers another significant flooding event in the Gascoyne River, introducing nutrient-rich plumes into the bay, it would be deeply concerning. Given that we do not experience large tides this time of year, flushing the bay will be quite challenging."
Researching the Impact
Shinae Montie, a research fellow at the University of Western Australia, emphasized the duration and extensive consequences of darkwaves, which can endure for weeks or even months. "When these events occur, fish lose access to their feeding grounds, and breeding habitats may vanish, leading to cascading effects that last far beyond the darkwave itself," Montie stated. "These changes pose threats to commercial fisheries, tourism, and coastal protections—ultimately resulting in significant economic repercussions."
As part of a comprehensive global study aimed at creating a framework to measure darkwaves, researchers have utilized satellite imagery to analyze the impacts of ex-Tropical Cyclone Seroja, which wreaked havoc in the Midwest in 2021, and ex-Cyclone Joyce from 2018.
This year has seen heightened cyclone activity in Western Australia, prompting officials to warn Pilbara residents to prepare their homes as Cyclone Mitchell approaches. Montie added that the increased frequency of storms could lead to more darkwave events along the coast. "Climate change is intensifying extreme weather patterns globally, resulting in stronger cyclones, heavier rainfall, and larger floods that are likely to become more common and severe," she explained. "Consequently, these darkwaves might persist for weeks or even months."
A Critical First Step
Montie expressed optimism about the future, stating that scientists anticipate darkwaves will "become more frequent." The newly designed framework developed by researchers will aid in identifying regions most at risk. "The encouraging news is that there are actionable steps we can take; darkwaves are also related to land management practices, such as controlling river sediment, agricultural runoff, and land clearing," she pointed out.
By pinpointing which watersheds contribute the most severe darkwaves, conservation efforts can be more effectively targeted. Implementing better land use strategies, erosion control measures, and restoring catchments can mitigate the intensity of these events when the next major storm strikes.
