I watched this special on Discovery HD
about the Crown of Thorns sea star eating the reefs around the world. It was quite disturbing. The Crown of Thorns looks kinda cool and moves really wierd...but it's a monster. They feed only on hard corals. Now for the really bad news.... they've been propogating in record numbers. Large portions of the Great Barrier Reef and other reefs all around the world have been destroyed by this sea star.
One marine biologist has linked the record numbers of these monsters to the use of fertilizers and pesticies. When humans use these on their farms, golf courses, etc....these fertilizers then errode off the land during heavy rains and end up in the waterways and eventually the ocean. The problem with this is that the Crown of Throns sea star loves these chemicals and when subjected to them, they propogate much faster.
They don't know how bad it's going to get but in the mean while they're trying to fight back these monsters. The entire documentary was depressing. THey showed video of completely destroyed reefs. I believe the show was called something about the "Monster destroying the reefs"