This groundbreaking NRDC documentary explores the startling phenomenon of ocean acidification, which may soon challenge marine life on a scale not seen for tens of millions of years. The film, featuring Sigourney Weaver, originally aired on Discovery Planet Green.
Acid Test: NRDC Documentary Explores Ocean Acidification
Scary stuff. I have a summary of various threats to the oceans here:
http://selfdestructivebastards.blogspot.com/2009/10/our-oceans-are-dying.html