It will only benefit you if you can find a college with a marine bio department. But you can still go to marine bio graduate study without any marine biology background (you do want to have biology background).

Undergraduate education is preparation for graduate education, so if you want to go into marine biology as a graduate student, it would be well to have a strong background in it as an undergraduate.

As an undergraduate, you will be required to select a Major, which is a field of study where you apply a heavy degree of your studies. You should try to major in biology, preferably in ecology, if you want to go into marine bio.

UCSB has one of the best undergraduate marine biology programs in the world, btw.

This is a pretty important question, but you are about to make some pretty important decisions.

As a graduate student in marine biology, I would say that it is never too early to start doing what you want to do. In this case, if you want to study marine biology, go to a school that has a strong marine biology department or program. Once you get there, find people (professors, graduate students, etc.) who are doing research that is interesting to you, and go work for them (you'll probably have to start off as a volunteer). You'll see much more about what being a marine biologist really is from working along side of them than just from taking classes. And if you work hard enough for them, you may get opportunities to do fieldwork with them (I took an undergraduate assistant to the Galapagos Islands for 9 months, and friends of mine have taken undergraduate assistants to other places all over the world including St. Croix in the Caribbean, Tahiti, Mexico and even Antarctica, to name a few).

So, if you think marine biology is really what you want to do:
1) find a school that has a good program (examples on the West Coast: UCSB, UCSC, UCSD, UCD, CSU Northridge, CSU Long Beach, CSU Fullerton, Stanford, SDSU, Humboldt State, Oregon State, Univ. of Oregon, U. Washington, U. British Columbia).
2) Go there.
3) Meet the people doing interesting work.
4) Work for them.
5) Have amazing experiences.
Then you can decide if grad school and a career in marine biology is right for you.

It's good that you are thinking about these issues now. I went through your same situation, but much later). I realized I wanted to study marine science when I was a sophomore/junior in college.

I went to UC Berkeley, where there are a couple marine science faculty members teaching courses, but which does not have a major in marine science. Then I went to graduate school at UC Santa Barbara (I have a PhD) which does offer a marine biology major (actually, aquatic biology). Then I was a researcher at University of Hawaii, which initially did not offer an undergraduate marine biology major because the faculty there feel that students should major in something more basic (biology, chemistry, geology, physics) and then specialize in grad school (marine biology, marine chemistry or chemical oceanography, etc). They've since changed their minds. Now I actually teach at a small university that is known for having a very good marine biology undergraduate major.

You're not going to like this answer, but I'd have to say it depends on what you want to do.
(1) If you want to be a university professor:You could go either way. What really matters is developing your interest in the subject (i.e. narrowing it down to something to you want to become a "world expert" in) as well as any research you do as an undergraduate. It doesn't have to be marine biology research, and you don't have to do the same type of research for the rest of your life, but it is very important that you get involved in a research project. Both small schools and large schools are good for this. Small schools will give you more contact with professors who do research, and large schools will give you more opportunities to do different kinds of research. A teaching college will not help you. It's better if you go to a well-known college and get good grades, since you'll be applying to graduate school afterwards.

The types of classes you take will help focus your interest and provide a good foundation, but shouldn't matter too much.

Be prepared to be AT LEAST 30 before you get a permanent job (nowadays most young professors are closer to 35), and even then your starting salary won't be much over $50,000. And the jobs are not that common, so you might not get to pick where you'll live, which can be a pain if you already have a family and have to move or if you move somewhere where you can't afford to buy a house. These are the realities, and you might as well face them now.

(2) If you want to work in marine conservation (designing marine protected areas, doing public education, working at an aquarium or captive breeding program, doing biological surveys, making laws to protect natural resources, working at a nonprofit group): You should pick a college that has a good marine biology program, with classes in the areas you are interested in and opportunities to do internships.

Consider a school that offers classes in marine policy as well as marine biology. Smaller colleges might be better here, since you'll need to get a job right after your undergraduate study and so you'll need to do most of your networking in college. Consider picking a school in an area or region where you want to live. (Don't go to school in Florida if you'd rather work in the South Pacific on Humpback whales. Likewise, don't go to Hawaii if you want to work on manatees.) Also, seriously consider volunteering for a non-profit organization if you want a long-term job there.

(3) If you want to do research:
It's rare to get a job where you only do research and you are the one in charge of designing that research. They do exist (Monterey Bay Aquarium Research Institute, e.g.). Most of the time researchers also teach at a university, so read the advice for becoming a university professor in (1).
Laboratory technicians get to do almost 100% research, but they work for someone else (usually a university professor or government laboratory), so they don't get to pick what they do research on. In my opinion, these are good jobs. You do a lot of laboratory work, with often little formal reward other than a paycheck, but you get to travel and do really interesting field research at spectacular places (think Antarctica, coral reef diving, shark tagging, etc.). The jobs are often temporary (a typical research grant is 3 years), but some are longer-term. These jobs are a lot of work, but if you work for a good boss, they can be fun and rewarding. You can live and work anywhere there is a research lab. They often require a Masters but not a PhD.

These are highly specialized jobs, and the best way to prepare is to get involved in as many different research projects as you can, with exposure to as many different techniques as possible. Pick a school that does a lot of marine biology research.

There are two ways of thinking about this. You could save marine bio for graduate school and go to a smaller school without a strong marine program. You tend to get more attention and a broader education from a program like this, and when you head to graduate school you'll have the basic preparation for a very wide range of specialties and you can decide what aspect of marine bio you want to pursue. This is the strategy I chose -- the downside is that it can be difficult to 'break into' a field if you haven't had much marine biology experience and you're competing against other students who have marine bio experience and letters of reference from marine bio profs. The upside is that you may be better prepared in general for the academic rigors of grad school.

The second strategy is to go for a school (usually a larger school) with a strong marine bio program and specialize right away. This way you get lots of experience, a chance to work with profs and grad students, and exposure to what it's really like to be a marine biologist. The downsides are that at larger schools you don't get as much personal attention from the professors and you can get lost in a sea of undergrads, and you'll be tempted to take cool specialty classes (like "Deep-Sea Ecophysiology" or crazy things like that) in place of less cool but highly important classes (like organic chemistry, advanced calculus, English literature): on the other hand, you have no idea how important it is to exposure yourself to good writing.

If you really want to go to grad school, you'll need to spend more time on those basics and less time with the specialty classes -- there will be plenty of time for that later.

I suppose there is a third option of going to a larger school that doesn't have a marine program, but there's no clear advantage to that strategy. This is not to say that you can't become a marine biologist if you go to a large school that doesn't have a marine program, but if you're going to choose a school without a marine program, why not choose a smaller one with a lower faculty-student ratio, a strong humanities program, that sort of thing. Good luck making a decision!