Sediment in the water off the coast of Taranaki during a marine ‘darkwave’ event.
Photo: Supplied / Jean Thoral
Recent research has brought to light a previously understudied phenomenon impacting New Zealand’s coastal waters: darkwaves. These events,characterized by significant reductions in water clarity,are gaining attention as scientists work to understand their causes,consequences,and potential links to broader environmental changes. I’ve found that understanding these events is crucial for maintaining the health of our marine ecosystems.
What are Darkwaves?
Simply put, darkwaves are significant decreases in light penetration through coastal waters. They aren’t caused by typical weather events like storms, but rather by increased levels of suspended sediment and organic matter. This murky water impacts everything from the growth of marine plants to the behavior of fish and other marine life. A key aspect of these events is their often localized nature, meaning they can affect specific areas while leaving nearby waters relatively clear.
Several factors can contribute to the formation of darkwaves. Anything that makes the water murky
can be a trigger, as one researcher noted. Common causes include runoff from land after heavy rainfall, resuspension of sediment from the seafloor, and blooms of phytoplankton or chlorophyll. According to data from the National Institute of Water and Atmospheric Research (NIWA), sediment runoff from land accounts for approximately 60% of total suspended solids in nearshore waters during rainfall events (NIWA, 2024).
Did You Know? Darkwaves can reduce light penetration by up to 90%, severely impacting photosynthetic organisms.
The Connection to Marine Heatwaves
Many regions of New Zealand are currently experiencing unusually warm sea temperatures and marine heatwaves. These warmer waters can stimulate phytoplankton blooms, which, while a natural occurrence, can also contribute to reduced water clarity. However, the precise relationship between marine heatwaves and darkwaves remains an area of ongoing investigation. More research is needed to determine if heatwaves directly trigger darkwaves or simply exacerbate existing conditions.
Establishing a standardized definition and measurement framework for darkwaves is a critical step. This allows for consistent monitoring and comparison of events across different locations and time periods. Now, with improved measurement techniques, scientists can accurately track these events and assess their impact on marine ecosystems.
