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It is one of 50 million sponges along 1,000 kilometres of Fiordland coastline, the largest mass bleaching event ever recorded.
photo: supply
Massive bleaching occurred along 1,000 kilometres of the Fiordland National Park coastline, killing more than 50 million sponges. It is the largest and most destructive bleaching event ever recorded in the world, with tens of millions of sponges dying.
A new study published in the journal Environment Global Change BiologyStudies estimate that the 2022 bleaching will cause the number of marine sponges to drop by nearly half, making it the world’s largest “sponge die-off event.”
Lead author of the study, Te Herenga Waka marine biologist Professor James Bell, said the bleaching occurred during an intense marine heatwave that lasted 259 days, causing water temperatures to be 4.4ºC above average.
Mass bleaching has caused the cup sponge Cymbastella lamellata to turn from its usual chocolate brown to bone white.
Nearly a year later, the researchers found that almost 50 percent of the sponges at the sampling site had died.
“Not only is this the largest sponge bleaching event globally, it’s also the largest mass die-off of sponges ever recorded,” Professor Bell said.
It is one of 50 million sponges along 1,000 kilometres of Fiordland coastline, the largest mass bleaching event ever recorded.
photo: supply
As the climate warms, marine heatwaves are becoming more frequent and more intense, with significant impacts on marine life.
“During the 2022 Fiordland heatwave, more than 90% of C. lamellata sponges were bleached. These sponges are one of the most abundant species in the Fiordland and play a vital role in the ecosystem, including providing habitat and recycling nutrients that support marine life.
“We found that sponges are key contributors to the production of dissolved organic carbon in water columns. This food source has the potential to fuel the microbial food chain and support organisms higher up the food chain. The mass die-off of sponges following the 2022 heatwave meant this potential fuel source was reduced – we estimate a reduction of up to 850 tonnes.”
Professor Bell and his colleagues found that some sponges were able to recover from bleaching, suggesting they may be able to adapt to heat stress.
“We found that these sponges were experiencing changes in the microbial communities that they inhabit. The changes we observed suggest that sponges are showing a rapid evolutionary response to warming waters in order to survive.”
He said the findings gave scientists reason to be optimistic that sponges might be able to adapt to warmer water temperatures, but added that more research needed to be done.
“We need to…test this and monitor how more frequent and more intense marine heatwaves will affect this important species”.
It is one of 50 million sponges along 1,000 kilometres of Fiordland coastline, the largest mass bleaching event ever recorded.
photo: supply
The researchers also observed that dry conditions and unusually low rainfall coinciding with the marine heatwave may have allowed more light to reach the normally dark waters of the fjord region, exacerbating bleaching and mortality among sponges.
“This event highlights the importance of considering the impacts of extreme events, such as coastal temperature and freshwater extremes, on marine ecosystems, and how the likelihood of such events may change in the future,” said Dr Robert Smith, a physical oceanographer at the University of Otago and a member of the research team.
The research was funded by Victoria University of Wellington’s Te Herenga Waka, the Department of Conservation, the George Mason Charitable Trust, Fiordland Lobster Company and the Leslie Huggins Conservation Foundation.
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