Do you think a population besides the moon jellies’ consumer population (sea turtles) and resource population (zooplankton) could have caused the moon jelly population to increase in size?

Answer:
I didn't quite understand your question, but the moon jelly population will increase if there are either more zooplankton or less sea turtles.
More zooplankton means more food => higher population
Less sea turtles means that the moon jelly will be lest often consumed => higher population