This is science
the question is what caused the jelly population to increase.

When the walleye pollock population decreased, there were more zooplankton available for the moon jellies to eat. Since the jellies had more energy storage molecules, they were able to reproduce more. This lead to more births than deaths in the moon jelly population, which caused the jelly population to increase.

Explanation:

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supercell thunderstorms are perhaps the most violent of all thunderstorm types, and are capable of producing damaging winds, large hail, and weak-to-violent tornadoes