Coral reefs are the largest structures built by any living thing, including humans. As they lieunder the surface of the water, most people don't realize that they are actually like hugemountains rising from the ocean floor. Recently many reefs have begun to suffer seriousdamage, and some can no longer support the wide variety of plants and other life forms theydid in the past. The damage seems to come from three basic sources: direct physicaldestruction of the coral itself, pollution produced by humans, and the warming of ocean waterscaused by climate change.