Overview: As part of a seven-year project on threatened ecosystems, we take a special in-depth look in this third episode at one of the habitats under most urgent threat from climate change, coral reefs. What are the innovative techniques that could provide a much-needed lifeline and hope for the future? Globally, coral reefs are at crisis point. Half of all coral reefs have already been lost or severely damaged, and experts predict that, without action, nearly all reefs could die off in the next 20 to 30 years. When the ocean is too warm for too long, corals bleach and die. 2023 saw record sea temperatures around the globe, and as bleaching events become more frequent, there's a race against time to find ways to help damaged reefs recover.