Another contributor focused on volunteering, which is certainly valuable, but I see that your location is 300 miles from the ocean, so I'll take a different tack. Not knowing where you are on your educational journey, I take a risk that the advice I'm about to give may not be useful immediately.
I would correspond online with biologists and college students; graduate students if you are lucky enough to befriend some (they are typically pretty busy). They may help you explore the "field work vs. lab work" conundrum mentioned in your profile. They'll also have valuable experience navigating the university:
1) Professors. If you become a grad student you will have a sponsor professor and likely a thesis committee. Those people can make all the difference, so before you choose, find out everything you can about how they've dealt with students. I had a great mentor professor as an undergrad, and would go on field trips with him and his grad students. He was a pioneering conservation biologist. But over the course of a couple years it became clear that he was not doing well emotionally and was taking it out on his grad students, sadly. I was lucky to not be directly impacted by that.
2) Peers. One hopes they all will be fun and supportive, but some can be overly competitive.
3) Politics, alas. You know that schools have different strengths and weaknesses in their programs. Some are better funded than others. And for field biologists, they critically depend on relationships the school has built with government agencies and private foundations. So that's worth investigating. And some schools have intra- or inter-departmental feuds, turf battles, and petty jealousies. It helps to be aware of the arena you're walking into.
You may already have an idea of what does and does not interest you as a focus of research (like plankton vs. marine mammals, for instance), or you will at some point. But try to be open minded. Find an area that's tangential to your main focus. For example, environmental law, or fisheries management, or parks and preserves management, or marine weather. Being well rounded will give you credibility when you go interviewing for volunteer and employment opportunities. Because marine biologists will at some point encounter legal, fisheries, parks and weather issues and specialists. (But I stress that those are just a few examples.) I thought I was mainly a forest ecosystems, big picture kind of guy. But I also became fascinated with evolutionary microbiology (after college) when I discovered the work of Dr. Lynn Margulis of the University of Massachusetts. But during college I probably thought of microbiology as only slightly more palatable than math and chemistry, with which I struggled.
Upon completing your undergrad degree you may be able to find a job in environmental education. In my country those jobs don't pay well but do provide networking opportunities. I found a gig leading grade school students on Everglades field trips, which I did for a year, although I had no plans to become a teacher.
Enough with the cold, matter-of-fact advice. Find something marine-ish that you love to read about! And read, and read. Become a close reader. When you get to the point of reading scientific research, pay attention to how the studies were designed.
Thank you for choosing a career with the earth in mind. Marine bio is fascinating! I wish you every good fortune.