Georgia Tech have been doing expirements in the ocean. They have recently found out that seaweed also kills coral. Other coral killing objects are heat, pollution, and even sunscreen. They found that some seaweed cause coral bleaching and give off anti-coral chemicals. For the past decades, scientists have found coral reefs being dominated by seaweed, but they aren't sure if algae is also to blame. Don't think that seaweed is useless, because scientists thik it has a reson to live.