New Zealand’s massive marine sponge bleaching is the largest on record

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.

As the climate warms, marine heatwaves are becoming more frequent and more intense, with significant impacts on marine life.

“During the 2022 heatwave in Fiordland, more than 90% of C. lamellata sponges were bleached. These sponges are one of the most abundant species in 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 communities of microbes that live with them. The changes we observed suggest that sponges are making 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.”

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.