A scientist that studies fungi is called a mycologist.
A chemist
A scientist who studies gems such as rubies and diamonds is called a gemologist. They are experts in identifying and evaluating the quality and characteristics of gemstones.
A scientist who studies DNA double helix is called a molecular geneticist or a geneticist specializing in molecular biology.
A thunderstorm, though most thunderstorms are not disasters.
A catastrophist. Catastrophe theory describes how systems can suddenly become unstable. You might have seen the video of the bridge that built up a harmonic motion in a strong wind, until it swayed from side to side so much that it collapsed. Catastrophe theory describes such things.
A biotechnology scientist.
An Oceanographer. Marine Biologist, that sort of thing.
A scientist that studies viruses is called a virologist.
A scientist who studies mollusks is called a teuthologist.
A scientist that studies bears would be called an ursinologist.
virologist
An aviologist.
A meteorologist.
biologist
A vulcanologist
Mineralogists