Coral grief

Coral reefs are noisy living animals vital to other marine life, particularly in the South Pacific. As the oceans warm, quick action is needed to reverse their decline.

- NAT SELLERS

Once dazzling with colour O and life, coral reefs around the globe are turning a spectral white as climate change warms the world's seas. For Aotearoa New Zealand, this is not an immediate threat but for our South Pacific neighbours, the impacts are profound.

Simon Davy, professor of marine biology at Te Herenga Waka - Victoria University of Wellington, says Pacific coral reefs are declining at a rate of about 2% a year, and it may be only 40-50 years before they are completely gone.

With at least a quarter of all marine life found on coral reefs, their importance cannot be overstated. As Davy says, "The biodiversity is huge."

It follows that a healthy reef is one teeming with top predators. "The most healthy reef I've ever seen, Palmyra Atoll [northwest of Kiribati], is one of the remotest places on Earth and I've never seen so many sharks in my life," Davy says. However, even this lost corner of the planet occasionally gets bleached.

BLEACHED OUT 

"It depends where in the world, but when you start getting much above 30°C, corals tend to bleach and potentially die," he says. "Just one or two degrees above their normal summer temperatures, you're going to tip them over their physiological threshold."

When a coral bleaches, most of the algae that live in symbiosis within the coral die, leaving it without colour and its means to obtain food. If temperatures cool, a bleached coral has roughly a month for the algae to recover before its fate is likely sealed.

Another side effect of bleaching is that it reduces the coral's skeleton, making it more susceptible to erosion.