Mass bleaching of sea sponges possibly devastating for NZ marine life

Marine scientists are concerned for the ecosystem of our nation’s biggest National Park, fearing the mass bleaching of native sea sponges in Fiordland might be just the tip of the damage done by climate change.

Researchers have discovered bleached sea sponges for the first time in New Zealand – and it’s not good news.

“It's quite alarming,” says Victoria University’s marine biology professor James Bell.

He says the sponges, once healthy and brown, have been bleached white in the wake of a dramatic shift in temperature due to global warming, in some areas of Fiordland, up to 95% of the sponges are affected.

Bleaching, like this, is a first in New Zealand - and rare in cold waters internationally.

He says the true extent of the damage has yet to be discovered.

Sea sponges are an essential part of Fiordland’s marine ecosystem, they provide a habitat for organisms to live and filter feed for fish.

“Given the wide-scale area that this species occurs within Fiordland, you could be talking about you know hundreds of thousands maybe millions of individual sponges that have actually been bleached.”

The heatwave may have also directly impacted other native marine species.

“It's quite possible that there could be other species that have been impacted by this heat wave, it just so happened that the bleaching and changing colour is very obvious to spot.”

The Fiordland Marine Guardians were established to advise the Government on the management of the Fiordland Marine Area.

Chairperson Rebecca McLeod says the news has come as a shock to the group.

“James Bell came along to our meeting a couple of weeks ago and presented some of the photos and videos to us and I think just everyone was very quiet, just it took us a while to process the gravity of this discovery.

"We were hoping this would be a really localised mortality event, but it seems to be throughout the Fiordland marine area, which is a massive area of New Zealand’s coastline.

“Generally, we feel pretty powerless… it's a pretty crushing blow.”

The damage comes as climate change causes a rise in fluctuating ocean temperatures in recent years.

Dr Robert Smith is a lecturer at Otago University's Department of Marine Science and works with the Government-funded Moana Project to record and study ocean temperatures.

He says marine heatwaves are becoming increasingly common in the wake of global warming. In April, parts of the South Island were hit by some of the hottest water on record.

“I've been really surprised by just how warm these temperatures got particularly off the coast of Fiordland.

“Water temperatures peaked at 5 degrees Celsius above normal the actual temperatures were around 20 degrees, and that's a record for this time of year.”