Reading is always a good thing in fact that is how I got interested in Marine Biology.
Contacting your a councelor would be a good start.
Since you are still in High School I will not go into what college courses you need.
I would recommend the following math and science courses if your school offers them. Biology, Chemistry, Math (Algebra, Physics, Calculus, Trig, Geometry), Earth Science, Botany, as well as any other science course offered. A writing course would also be useful. Also make sure your grades in your other classes are good as well most Universities don't want students who Ace science but do bad in Composition and History.
Also even though you have a lot of time before you need to think about college don't hesitate to contact a univeristy for advice on what Highschool classes you need.
Some things you need to know about marine biology are: You will write constantly; you cannot escape math; A's and B's are acceptable in classes C's, D's, and F's are not; and last but not least, you will not get rich.
Marine biology is a great field to study and work in. I wish you the best of luck.