New Zealand sea sponge populations 'dying by the millions' due to climate change

New Zealand is seeing its worst-ever mass bleaching of important sea sponges. (CNN)

Shocking images have emerged from New Zealand showing millions of once-velvety brown sea sponges bleached bone white, the worst mass bleaching event of its type ever recorded, marine scientists say.

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

New Zealand scientists discovered thousands of bleached sea sponges in May of this year, 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 throughout the Fiordland region.

• Sign up for The Climate Barometer, delivered right to your inbox

"This is one of the most abundant sponges in Fiordland, and so it's a really wide-scale event," said James Bell, a marine biology professor from New Zealand's Victoria University.

Bell, who led the team responsible for spotting the initial bleaching event last month, told CNN that despite the extensive mass bleaching, some sponges were still alive and consuming oxygen.

"This region was so abundant and rich in marine life and it was almost like a white graveyard when we discovered it, it was really devastating and traumatic," he said. "We are able to conduct experiments on board our boat to try and understand how affected the sponges were by warmer temperatures. Unfortunately a lot of them were already very unhealthy and stressed."

Sea sponges come in a variety of sizes, colors and textures and play a crucial role in marine ecosystems, providing food and refuge for other marine animals like crabs, algae and fish.

"They pump out large volumes of water and capture tiny particles, bacteria, plankton and algae and also recycle carbon on the sea floor," Bell said. "They also provide shelter for marine creatures and increase habitat areas of the sea floor. They are very underappreciated creatures."

OCEANS HEATING UP AT RECORD SPEED

Last year was the hottest on record for the world's oceans for the third year in a row, placing massive additional stress on marine ecosystems.

This year, Australia's Great Barrier Reef suffered its sixth mass-bleaching event. Studies also confirmed coral bleaching at multiple reef sites.

The Great Barrier Reef is now believed to have lost more than half of its coral population to climate change in the past three decades, according to studies.

Sea sponges, like coral, are also heavily affected by extreme ocean temperatures and turn white as a stress response to temperatures that are too warm.

The sea creatures play an important role in marine ecosystems and scientists say their loss could affect millions of other marine animals.

Warming ocean temperatures are affecting sea sponge populations in other parts of New Zealand too, Bell noted. Swathes of dead sea sponges were discovered in the country's northern coastal areas. Some were found to be "melting" amid a lengthy marine heatwave.

"The mass bleaching event highlights again how dramatically oceans are changing due to global warming and climate change," he said. "It should serve as a wake-up call. We need climate action now, not in 10 or 15 years because by then it would be too late and we'd have lost all ecosystems and species."