Okinawa coral reefs face race to survive heat threat

Scientists and conservationists in Japan's Okinawa are testing ways to protect coral reefs after a 2024 marine heatwave caused widespread bleaching in the subtropical island region.

Researchers are using controlled seawater tanks to simulate hotter, more acidic oceans, while local projects are breeding and transplanting corals that may be better able to survive future heat stress.

Timothy Ravasi, a professor at the Okinawa Institute of Science and Technology Graduate University, told AFP that another mass bleaching event was almost certain sooner or later in Okinawa and other reefs worldwide. He said his lab's heatwave simulator lets scientists change temperature and pH levels to study how coral, fish and other organisms respond.

Okinawa is a major resort region and depends on tourism for more than 80 percent of its economy. Ravasi said hotel construction, overfishing and pollution are adding to climate pressure on coral ecosystems.

The village of Onna has bred corals and transplanted them into the sea since 1999. Shoichi Ikeno, head of local diving company Lagoon, told AFP that some sceptics initially viewed coral cloning as an unnatural intervention, but later DNA analysis found minimal ecological impact.

In Yomitan, Koji Kinjo has bred what he calls “miracle coral” in an artificial sea at an indoor farm. He told AFP the corals were exposed to stressors including strong ultraviolet rays while growing, and said they survived the 2024 bleaching.

Kinjo said he believes Okinawa's corals will die out without intervention, while some traditionalists argue the ocean should be left to recover naturally.