Sponges bleaching bone-white for the first time in New Zealand

Sea sponges off New Zealand s southern coastline have been found bleached bone-white for the first time after extreme ocean temperatures.

A group of scientists from Victoria University of Wellington were alarmed to discover the sponges, which are typically a rich chocolate brown, were bleached in more than a dozen sites near Breaksea Sound and Doubtful Sound in Fiordland.

The marine biology professor James Bell said as many as 95% of the sponges were bleached.

He said there are at least hundreds of thousands of sponges likely to have been bleached, and maybe even many more than that.

Bell's team discovered mass bleaching during a research trip in April. The species, which is common to the lower South Island, is one of 800 species of sponge found in New Zealand.

Sponge gardens dominate the sea floor around the country and play an important role in creating habitats for fish and releasing carbon that other species feed off.

There have been reports of sponges bleaching, including on the coast of Tasmania earlier this year, but generally they tend to be more tolerant to oceanic changes compared to other species such as corals, Bell said.

He said it was a really unusual event.

This is just a reminder of the climate crisis we are facing. There are so many species around New Zealand and we don't know what their thermal tolerances are. The oceans of the world were the hottest in recorded history last year due to climate change, which can cause the oceans to acidify and degrade reefs and ecosystems.

New Zealand was the hottest year on record, with 2021 being New Zealand's hottest year. In April, temperatures were still unseasonably high, with coastal water temperatures up to 2.6 degrees above average, according to the National Institute for Water and Atmospherics.

In Fiordland, those temperatures were even higher, said Rob Smith, a University of Otago oceanographer who works with the Moana Project researching marine heatwaves. He told RNZ that the region recorded temperatures up to 5 degrees higher than usual.

This summer is the strongest marine heat wave on the west coast of the South Island in 40 years. Further research was needed to determine whether ocean temperatures are causing the bleaching, Bell said. At this stage, the researchers had an observation and a very strong correlation between the bleaching and a severe temperature spike.

Bell said that some bleached sponges could come back to life, but the team would have to return to the site to see how they were faring towards the end of the month.

Some of them are a little bit manky and not very happy or healthy, but there is hope that they may not die.