Firstly, koalas are not bears.
There is no particular name for someone who studies koalas.
People who study the field of animal Biology are zoologists. While there are specialised areas within this broad parameter (such as ornithologists, who study birds), there is no particular name for one who studies koalas. It is too narrow a field.
A scientist that studies bears would be called an ursinologist.
Gemologists
you call it chemist i think
A magnetometer is a device used to measure the intensity and direction of a magnetic field.
scientest
A scientist that studies bears would be called an ursinologist.
Zoologist
You call someone that studies metal a metallurgist.
A physicist.
a person who studies planets is a planetologist.
florist
An Anthropologist.
Microbiologists
Brocollogist
A Zoologist
malacologist
A physicist.