Why so many jellyfish?

Science Corner

DAUPHIN ISLAND, Ala. (WKRG) — If you have been to the beach lately, you might have seen purple flags flying, which means to watch out for dangerous marine life. Right now, that is jellyfish.. .but why so many?

The reason we typically see more jellyfish in the summer is because their growth and reproduction are driven by warmer water, and their food source, plankton, is at its highest growth during the spring and summer.

While jellyfish do not have brains, different species have certain behaviors that cause some to swim towards light, some can sense wind, some respond to water temperatures, and some swim against currents. Dr. Monty Graham, Professor of Marine Science at the University of Southern Mississippi, said, “Those little changes in behavior can create what we call swarms or aggregations of jellyfish. Those are pretty natural.”

These swarms sometimes happen close to shore because as the water gets more shallow, things get more and more compressed, making the jellyfish groups more dense.

Dr. Graham also says that typically we have lots of jellyfish for 10 years, followed by another 10 years with fewer jellyfish, and this is due to large-scale environmental factors such as El Niño.


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