Great question. As with any science major, you will need you high school graduation and it is preferred if you can attend a 4 year undergraduate program. Depending on what your specialization is you might have to a a Master's program. So 6 years (4+2 years) of education.
If marine biology is your preference, start your research on the schools early. See if you can get an internship at a Science museum or local aquarium where they have marine animals and plants.
Lavanya recommends the following next steps:
You will most likely need a 4 year college degree in marine biology and possibly graduate education - depending on what you want to achieve with your degree. A 4 year degree is usually OK to work in the field. Advanced degrees can provide additional opportunities to direct research and other programs.
If you go to www.universities.com and search on marine biology you will find listings of all the marine biology programs available in the US.