Q:

Could be an union/synergy between Math, Computer Science and Marine Biology? 

I'm studing for my bachelor's degree in Natural Science and I have to chose the path for my future life.  I have to chose the right kind of graduate studies.  Since I love computer science, maths and marine biology more in details I love the tropical ecology especially that of the coral reefs and atols in the pacific ocean, the whales (e.g. the humpback whales and their migrations), the computer simulations and mathematical models.  Thus, I want to ask you if is there a branch of marine biology that allow me to study and specialize myself in tropical ecology and in math & computer science too, because in my current course we don't have any exams of computer science and only one of maths, and I'm feeling sad for this.  The right path coul be the computational biology?  Exist in biology, some field called "Computational Marine Biology" or "Computational Marine Tropical Ecology"?  One last thing, what about Ecoinformatics? 

A:

This advice is America-centric; graduate programs in other countries may be different, especially in regards to assigned course work, etc.  But this should more-or-less be solid.  Also, I'm assuming you're interested in a PhD.
I don't know if what you're looking for is a proper field, but that doesn't matter.   Ideally, grad school is where you do research on your own terms, and what lab you join is the single most important consideration.  What you want is a competent program that:

gives you the flexibility to create your own subfield
has supportive and knowledgeable faculty that you can work under
has excellent computer science AND marine biology programs (or analogs)

First, find faculty who are doing research you are interested in, and look at the programs available at their schools.  Since they're the most important consideration, everything else will fall into place after that.  
Next, email 5 of those professors with an introduction of what you're interested in, particularly about their research.   Ask them what programs are most appropriate at their university, and how flexible you can be in taking appropriate coursework.  
At some point, you'll probably want to decide if you want to be more of a marine biologist or a computer scientist.  Your diploma at the end of the decade is only going to say one of those things.   That shouldn't make a huge difference as to your job outlook, but is worth thinking about.   Practically, the question is whether you want to get your hands dirty, go out on a boat, and collect your own data.   Alternatively, if you join a CS program, you are more likely to be analyzing large datasets collected by other scientists.  
At most universities, you'll likely only have the option to join a biology program.  But there are certainly excellent CS programs with biology oriented faculty.   Even then, the CS faculty is more likely to be doing genomics and such.   
For practical recommendations, the University of Washington in Seattle would probably have something appropriate to your interests.  While I was there, my lab was adjacent to an Oceanography lab that had a video wall for visualizing ocean currents and such.  Not precisely marine biology, but UW has a very collaborative faculty and I'm sure the two departments work together.   
UW also has a strong computational biology program that you can go into either through CS or through one of the many biology programs.  You should also check out the Institute for Systems Biology at UW.  I saw a presentation there specifically about DNA exchange between marine microorganisms.   I'm not saying UW is your best option, I just know that school because I did my PhD there.  
A final word of advice.  Once you're in a program, it's very likely your interests will change as you learn about other research going on.  And also, it's quite possible you won't get into the lab you want simply because of money or logistics.  With both of these in mind, be flexible about where you're willing to go.  What you do during your PhD isn't really that important anyway.   If you're going to be research scientist, it's what you do during your Postdoc that will establish your career.  Just take the opportunity to learn everything you can and see what's out there. 
Hope this helps.   Good luck!