Here is proof that our oceans have harbored monstrous beings for a very long time.

http://giantology.typepad.com/giantology/2005/10/tsunami_giant_c.html

I hate to break it too you, but like the comments on that site say, the CGI in that clip is painfully obvious.
I won't disagree that there aren't creatures we haven't discovered yet in the sea, but I have to agree that this video clip is a hoax.