I would just look for graduate school placement in the natural sciences. Marine science is too specific. The thing to ask would be how many biology majors go on to graduate programs (as opposed to med school or HS teaching or whatever). I’m not sure there are any web sites that track that sort of thing. but it would be the sort of thing to ask schools when you visit in person or virtually.
Here is a list of programs (undergrad and grad):
You should look through the programs and see where the faculty did their undergraduates and PhDs, especially the assistant professors. Also, many PhD programs provide the CVs of their graduate students or simply where their graduate students earned undergraduate degrees .
Finally, look at the Survey of Earned Doctorates, and see how many people who earned their doctorate in ocean sciences (more correctly physical and earth sciences) earned their undergrad from different colleges. You’ll likely need to export the table to Excel, so that you can cull the hundreds of colleges which don’t have the major, and than compare this number to the number of undergraduates each college has. It’s a bit of a hassle, but it is invaluable information.
Of course, you’d have to tease out the Marine Biology PhDs, so the PhDs of U Maine graduates are likely almost all oceanography, but those of UIUC and U Oklahoma graduates are much more likely to be earth sciences at UIUC and atmospheric sciences at Oklahoma.