Bleaching threat to Great Barrier Reef spawning

The annual massive coral spawning of Australia's Great Barrier Reef is underway.

Why it matters: Scientists are concerned that recent severe bleaching at the world’s largest coral reef may limit the size of the phenomenon, the Australian Broadcasting Corporation reports. The health status of the World Heritage-listed ecosystem has worsened from "significant concern" to "critical" for the first time, a new report finds.

• Climate change at the reef is driving ocean warming, acidification and extreme weather, contributing to "dramatic coral decline, and as a result decreasing populations of marine species," notes the report, published by UNESCO advisory body the International Union for Conservation of Nature Wednesday.
• Professor Terry Hughes, who co-authored a study released in October finding the reef has lost over half of its coral populations in the past three decades because of ocean warming, told the Australian ABC: "Dead corals don't breed."

What to watch: James Cook University researcher Katie Chartrand told the news outlet that she and colleagues have been conducting "large-scale larval seeding using these inflatable nursery systems" and will check on their progress in January.

• "In favour of corals this year is the La Niña event," she said. "So there is a strong chance that they're going to get a reprieve from [bleaching]."

Go deeper: Scientists discover reef that's taller than the Empire State Building