ALA has some websites and links that relate to ocean life on their science tab - http://gws.ala.org/category/sciences

I'd also suggest Curriki (http://www.curriki.org/) and entering ocean life as a search term with a preschool or k-2 grade. This should give you a range of information on ocean life from text and videos to webcasts, which you could filter using the media tab.

Magic School Bus series has some books on ocean life, but this may be a little advanced for son.