This is not easy to answer, because the range is so great. Many, if not most, graduate students getting a Ph.D. are supported by the University they enter. The going rate these days is 13,000 to 17,000 dollars per year. On the Masters level, it is common for the student to have to pay tuition, which can vary from ca. 3,000 per year in a public university to 30,000 in a private university.
Many marine biologists are academics and therefore contribute to knowledge and teach students.
Many others work in government agencies monitoring pollution and fish stocks and making policy to manage fisheries and pollution control. Some work in conservation organizations that seek to protect marine environments and endangered species. In my course, I make students write three papers. On the professional side of matters, an academic marine biologist usually has earned a Ph.D. in the subject and usually has had at least 2 years of postdoctoral training. On the personal side, science is a subject that involves far more communication and cooperation skills than most people realize.