Question

Review the Glacier Sea food web. Respond to the questions below based on what you have learned so far.

What could have caused births to increase in the moon jelly population?

Answer 1

Several plausible explanations — most fall into two big categories: something changed that let more jellyfish reproduce (bottom-up), or something changed that let more young survive (top-down). Specific possibilities for moon jellies:

- Increased food (bottom-up).
- More phytoplankton → more zooplankton (their prey) → polyps and medusae have more energy to grow and strobilate, producing more ephyrae/births.
- Causes: seasonal bloom, glacier melt releasing nutrients, or local nutrient runoff.

- Fewer predators or less predation (top-down).
- A decline in species that eat juvenile jellies or polyps (fish, some crustaceans, sea turtles, etc.) would raise survival and apparent births.
- Causes: overfishing, disease in predator populations, migration changes.

- Favorable environmental conditions for reproduction.
- Warmer temperatures, optimal salinity, or light cues can trigger polyp strobilation and increase reproductive output.

- Reduced competition or disease.
- Fewer competitors for plankton or a drop in jelly parasites/pathogens could increase reproduction and survival.

- Life-history/behavioral aggregation.
- Changes in currents or habitat that concentrate polyps/medusae can lead to locally higher reproductive output.

How to tell which caused it
- Check plankton surveys and nutrient levels (support bottom-up).
- Monitor predator abundances and fishing records (support top-down).
- Look at water temperature/salinity/time of year and polyp strobilation rates.
- Inspect jellies for disease/parasites and sample juvenile survival rates.

Any one or a combination of these could explain the birth increase; the most common drivers reported in coastal systems are nutrient-driven plankton blooms and declines in jelly predators (often from overfishing).