New Zealand is experiencing the biggest bleaching of sea sponges ever, scientists say, as extreme ocean temperatures turn millions of aquatic creatures white.
The discovery came after researchers sounded the alarm in May, when bleached sea sponges were first found off the south coast of New Zealand.
Initially, researchers estimated that hundreds of thousands of sponges had been bleached – but over the past month, scientists checked in on beaches across the country, and found that millions – possibly tens of millions – had been bleached into bone-white color. was changed.
Professor James Bell, a marine ecologist at Victoria University, said: “As far as we know, this is the largest scale and largest number of sponges bleached in a single event reported anywhere in the world… Definitely in cold water.”
When members of Bell’s team first saw the May bleaching event in Fiordland, they put the word to the Department of Conservation and other charter ships in the area to see if it had been observed in other sounds.
“They reported bleaching everywhere,” he said. The team now believes that “there are at least millions of sponges, perhaps many millions of sponges that have undergone this bleaching”.
Marine sponges, such as coral, rely on symbiotic organisms to photosynthesize inside them, providing food for sponges and sometimes deterring predators.
While bleaching doesn’t necessarily kill sponges completely, it dislodges those organisms—reducing the sponge’s chemical defenses and depriving them of food. While some species can recover from severe bleaching, Bell said others do not.
Dr Robert Smith, an oceanographer at the University of Otago, said two oceanic heatwaves in New Zealand have created record sea temperatures – with some areas becoming five degrees warmer than normal.
“At New Zealand’s northern and southern border, we have seen the longest and strongest ocean heatwave in 40 years since satellite-based measurements of ocean temperatures began in 1981,” he said.
Smith said that in some areas, marine heatwaves began in September last year, and were only ending — lasting 213 days.
“It’s a really unusual aspect to see these unusually hot temperatures for so long,” Smith said.
“Some organisms are going to recover a day or a week above average temperatures — but once you start accumulating that heatstroke … we’re really going to start feeling the effects.”
Smith said it was difficult to attribute a single heatwave event to a man-made climate crisis, but ocean temperatures were rising around the world.
“What we can say is that there has been a significant increase in the frequency, duration, and intensity of ocean warming globally over the past century,” he said — and projections indicate that those heat waves will become more extreme and more extreme in the future. are getting longer.
“What we are seeing now is a window into what our oceans are likely to see for our children and our grandchildren.”