Not to appear condescending, but a degree in Marine Biology would be appropriate. Many schools offer such programs. These are often Masters and PhD degrees though.

A Bachelor's degree in a discipline other than Marine Biology could still be good preparation. There is more choice at this lower and less-specialized level, such as biochemistry , ecology, and zoology.

UCSB offers a number of these related majors at the undergraduate level, as well as graduate-level options.

It depends on what job you're interested in pursuing as a marine biologist. A Bachelor of Science degree is a good place to begin and will qualify you for many marine biology positions. If you're interested in research, a Master's degree might be needed. If you're interested in leading your own research and/or teaching college students, a PhD is most likely required. For now, I suggest:
1) looking for people that have a job you'd like to have and see what degree they have (e.g., what experience(s) did they have that helped them get that job?) and
2) volunteer, intern or work with a marine biologist or an organization that focuses on marine biology to get your own sense of the field and which direction you may want to pursue. It's just as important knowing what you like to do as it is knowing what you don't like to do! Good luck!

Marine Biology is a wonderful and exciting career option. Possible paths are ocean engineering, conservation, education, health sciences, or research.

Marine and ocean sciences are becoming increasingly important as we try to clean and maintain our oceans and save our ocean creatures. Choosing a school with water nearby is important because the programs will center around you actually getting some hands on experience! I would say of all the marine biology programs, those focusing on ecology and conservation will be in the highest demand over the next decade and provide a very rewarding career path.

UCSB is now ranked 7th in the US and has a wonderful hands on marine biology program that allows you to actually interact with the ocean around campus!

Some universities (like UC Santa Barbara) actually have a degree in marine biology. Barring that, I would go for a degree in ecology or organismal biology, depending on what kind of marine biology you want to do.