To become a marine biologist , it depends the collegue, but most of cases you have to study biology in general and the be study a post degree in marine biologist, because is a very specific field, but is such a good field , you can develop many skills and to be in the investigation field, in both animals and marine plants, and such other categories I imagine they may exist, also you may investigate by now where you can find the career, because the best ones are near the coast
I have worked for a university, the federal government, a tribe, a consulting firm, a state agency, and a city. In fisheries there are many job opportunities. I would suggest you study biology, chemistry, and math. Consider volunteering to gain knowledge and experience. Some volunteer opportunities may exist at aquariums, hatcheries, or in surveys done by agencies.