Sea sponge bleaching a wake-up call for climate action
In a discovery reported around the world, the marine ecology team led by Professor James Bell from the School of Biological Sciences was shocked to find mass bleaching of marine sponges in Fiordland, Aotearoa’s largest national park.
A research trip found large numbers of sponges that should be a healthy velvety-brown have been bleached bone-white over a relatively short period.
This alarming event is thought to be linked to increasing ocean temperatures due to climate change. The area experienced a prolonged marine heat wave over the summer with water temperatures up to 5 degrees hotter than normal.
“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,” says Professor Bell. At least millions of sponges have been bleached—maybe even tens of millions. This is one of the most abundant sponges in Fiordland, so it's a really wide-scale event.”
After the initial discovery in May, the team asked scientists around the country to look out for other signs that sponges were changing and found it was not an isolated occurrence, with many sponges showing signs of tissue decay and death at many sites in the northeast of New Zealand. The heatwave may also have impacted other native marine species that have gone unnoticed.
Although bleaching doesn’t seem to kill the sponges outright, it strips them of tiny symbiotic organisms they rely on for food and potentially providing them defences against predators, causing them stress. It's currently unclear if the sponges will survive or not.
According to Professor Bell, sponges are underappreciated creatures that play a crucial role in the food chain. They create habitats on the sea floor, filter large volumes of water, and recycle carbon for other species higher up the food chain. There could be serious consequences for fish and other animals if sponges were wiped out.
"The mass bleaching event highlights again how dramatically our oceans are changing due to global warming and climate change," he says. "It should serve as a wake-up call. We need climate action now, not in 10 or 15 years. By then it will be too late and we may have lost many species and perhaps entire ecosystems."
The research in Fiordland has been supported by donations from the The Leslie Hutchins Foundation and the Fiordland Lobster Company. Worldwide interest in the sponge bleaching research has led us to set up a givealittle page to raise money through the Victoria University of Wellington Foundation. The aim is to revisit Fiordland to investigate how the sponges have fared over the winter.