Millions of sea sponges hit by rising ocean temperatures

Marine scientists in New Zealand have discovered millions of once-velvety brown sea sponges bleached bone white, the worst mass bleaching event of its type ever.

The discovery comes amid a continued rise in ocean temperatures, a trend scientists say is due to planet-warming fossil fuel emissions.

Thousands of bleached sea sponges were discovered in May in cold waters off the country’s southwestern coast. Further findings showed the damage was far worse, with millions – possibly tens of millions – of sea sponges affected.

Sponges rely on symbiotic organisms that photosynthesise inside them, providing food for the sponge and sometimes deterring predators. While bleaching does not necessarily kill the sponges, it evicts those organisms – lowering the chemical defences of the sponges and depriving them of food.

“As far as we’re aware, it’s the largest scale and largest number of sponges bleached in one event that’s been reported anywhere in the world certainly in cold waters,” said marine ecologist Professor James Bell of Victoria University in Wellington.