Simply put, a marine biologist studies sea creatures. In practice, however, the field of marine biology is vast and encompasses many different specialties and career paths. Marine biology is a subset of Oceanography, which is the broader study of all aspects of oceans. Many marine biologists study several specialized areas of expertise, or disciplines, before settling upon one career course that suits them. Marine biology is a combination of general biology and oceanography.
A marine biology graduate could specialize in studying large ocean animals, all the way down to microscopic organisms. Everything from whales to the plankton they eat, and everything else in between. Marine biotechnology, one of the possible specializations, involves developing and testing new drug treatments and protocols that are derived from ocean life. Another specialization is molecular biology, which is helpful in identifying microorganisms as well as diagnosing diseases that are caused by microorganisms.