Qualifications
To become a marine biologist, you don't necessarily need to go to a college that offers a marine biology degree. You don't even need to go to a school with an ocean nearby. The key to becoming a successful marine biologist starts with a solid background in basic science—biology, chemistry, and yes, physics. Taking more specific marine biology classes certainly won't hurt, but a broader science background will keep your options open and still set you on your way.
It's the volunteering or summer jobs that'll end up having the biggest influence on getting your first job. Unfortunately, most are unpaid—but then again, you don't become a marine biologist for the money. Those of you who desperately want BMWs and summer homes in the Hamptons can stop reading here.
These experiences will help to develop your niche within the aquatic ecosystem and set you apart from the other whale lovers out there. As many aspiring marine biologist realize, it's a tough and competitive field. Setting yourself apart from everyone else who loves the sea and has good grades in science is extremely beneficial. Learn to scuba dive in the community pool or take up photography. Even taking an extra class or two in computer programming will help.
Most aspiring marine biologists head to graduate school to get their master's degree so that they can become more specialized in their research interests. This is the point where you really begin to train for that specific aspect of marine biology that piques your interest.
Maybe you focus on population dynamics to understand how the introduction of new micro-bacteria will affect the aquatic food chain and the life expectancy of lobster. Focusing on genetics could lead you toward the path of developing vaccines for common diseases among salmon. A concentration in physics could be the jumping-off point for a life studying the ways that seals communicate fear.
The master's degree typically takes two to three years and costs a pretty penny, but it's often necessary to even get your foot in the door for certain types of marine biology research (source). A PhD becomes essential if you want to guide your own research or work as an associate professor at a university (source). And, if that's the route you take, invest in Band-Aids for all the paper cuts, since the workload tends to be a bit hefty. Professors don't just research; they teach, advise, and deal with the politics of research.