What kinds of living and nonliving things do you think a marine biologist studies?

Marine biology is the study of organisms that lives in the marine environment, the environment that found in sea and oceans. They also study the interaction between these organisms and their environment.  

Marine biologists study both living and non-living things in their surroundings where they do research. The living things they study are marine organisms like fishes, sharks, whales, crustaceans, deep-sea organisms, sea plants, microbes and many more living creatures present in the marine environment.

They study their behavior, feeding habits, interaction with other organisms, their role in the ecosystem, mating behavior, etc.

The non-living things a marine biologist study are physical and chemical environment of marine habitat, geology of the area, concentration of salt, and other molecules that affect marine biology.