Question

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? Why or why not?


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Answer 1

Yes. Changes in other populations can indirectly cause moon jellies to increase through trophic and habitat interactions. Ways this can happen:

- Predator release: If populations of other jelly predators (e.g., certain fish, sunfish, or seabirds that eat jellyfish eggs/juveniles) decline, jelly mortality falls and populations can grow.
- Competitive release: If competitor populations (other gelatinous predators or planktivores that consume the same zooplankton) drop, more food becomes available to moon jellies and they can expand.
- Habitat engineers/invaders: Increases in organisms that create hard substrate (barnacles, mussels, oysters or fouling communities on piers and ship hulls) can provide more settlement area for jelly polyps, boosting recruitment of new medusae.
- Disease/parasite dynamics: A decline in populations of parasites or intermediate hosts that suppress moon jellies could allow jelly numbers to rise.
- Human population effects: Human activities (overfishing of jelly predators/competitors, coastal development that increases hard substrate, or nutrient runoff that indirectly benefits jellies) act through human population change and behavior to change jelly abundance.

So yes — you don’t need only changes in sea turtles or zooplankton to explain an increase; changes in other predator, competitor, or habitat-related populations (including indirect human effects) can produce the same outcome.