Another resource for those interested in ocean media, SeaOceanBooks is a website that sells maritime themed books. It contains a good collection of fiction and non-fiction on underwater environments: SeaOceanBooks.com.
Martin Leduc posts short reviews on maritime themed films and television. A good resource to start looking for longer format ocean media. Most of the documentaries are about seafaring and life on the oceans but, of course, are strongly imbricated with the life, resources, and politics of underwater spaces.