If you are interested in Marine Biology as a hobby, volunteer programs like Reef Check are a great way to go. If you actually want to become a Marine Biologist, you best have a 4.0 from a reasonable university, and go for a masters, and then a PHD. My Cuz is one of the rare exceptions in that she has managed to work as a Marine Biologist for over 30 years. However she is Highly trained, and poorly paid. It also comes with a pricetag.. either a required amount of teaching, or a large amount of kissing private ass and bending to capitalism. She has done both.. last I talked with her, she was considering becoming a grade school teacher, and getting out of the field all together...
On the plus side, she has logged countless hours on board ships, and a ton of hours at great depth on-board a Johnson Sea Link among other vessels. She specializes in the Deep Ocean. She tries not to act like it, but she is rather a genius.. and that helps as well.
