Hi,
yep, heaps of hard work first. Make sure you know your maths (I had to do calculus, statistics, linear algebra and discrete maths), chemistry, physics, geography, geology, and of course biology because you need all of them. It is also a very time consuming course, I have about twice as many hours as some other students do. However, having said that it is also a fascinating course, well worthwhile. Here in Australia at least it is a growing field with more and more jobs coming up all the time.
I'm not too sure about Universities over there in the US, but perhaps you should take a look at a few Australian Universities because they have the reputation as being the best places for marine sciences in the world (in my course there are students from all over the world). Check out a place called James Cook University in Townsville, Queensland (they have a site on the net), it is right on the Great Barrier Reef and seems to be the best place in the world for pure Marine Biology. I am hoping to go up there to to a PhD or something, but at the moment I am just doing a Marine Science degree at the University of Sydney. It is not quite as good as JCU for marine biology, but is better at more general Marine Science degrees, which is better for me as I am not exactly sure what branch of marine biology I want to study yet, and it is easy to transfer later on.)
HTH,
Tom