Would the answer be 'ecologist'? That's what comes to mind. To 'check my work' I did a Google definition search. cf. http://en.wiktionary.org/wiki/ecologist. Using my library's online edition of the Oxford English Dictionary I found this definition of ecologist: "An expert in or student of ecology."
A person who studies physics is called a physicist, a person who studies chemistry is called a chemist, and a person who studies biology is called a biologist.
A person who studies a lot is often called a "bookworm" or a "knowledge enthusiast."
A person who studies organisms is called a biologist.
A person who studies flowers and plants is called a botanist.
A person who studies lichens is called a lichenologist.
If you mean Marine Biologist, it's someone who studies marine life (stuff that lives in the sea)
a person that studies gems is called a gemologist.
The Person Who studies about mamals , he is called mamalogist....
A person who studies animals is called a zoologist.
A person who studies physics is called a physicist, a person who studies chemistry is called a chemist, and a person who studies biology is called a biologist.
A person who studies or writes history is called a historian.
A person who studies the mind and behavior is called a psychologist.
A person who studies alligators is called a herpetologist.
A person who studies a lot is often called a "bookworm" or a "knowledge enthusiast."
A person who studies optometry is called an optometry student or an optometry student.
A person who studies culture is called an anthropologist.
A person who studies sound is called an acoustician.