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Why Do Some Jellyfish Bloom? A New Theory Emerges

Published on: 03/20/2013
Research Area(s): Marine Spatial Ecology
Region(s) of Study: Waterbodies / Chesapeake Bay
Jellyfish at Pearl and Hermes Atoll, Papahanaumokuakea Marine National Monument

Jellyfish at Pearl and Hermes Atoll, Papahanaumokuakea Marine National Monument. Credit: Greg McFall.

The authors of a study partially funded by NCCOS theorize that the recent global increase in jellyfish blooms is due to the proliferation of man-made structures such as sunken ship hulls, underwater aquaculture pens, and artificially hardened shorelines. Through observations and experimental evidence, the researchers learned that jellyfish larvae settle in larger numbers on these structures than they would normally on natural substrate alone, which leads to favorable conditions for dense local concentrations.

For those needing some jellyfish 101, the blooming “jelly” species in this study have a two-phase life history: a juvenile stage that requires something hard to attach itself to on the seafloor, and a free-swimming adult. Once the young, called polyps, detach from the substrate, they’re known as medusae. Swarms of thousands or millions of jellies can foul power plant or ship intake pipes, fishing nets, aquaculture enclosures, and beaches. Some species are armed with painful stingers that can kill fish and injure people.

The authors conclude that officials responsible for managing coastal waters should look into artificial structures designed to discourage polyp settling, manage water quality to reduce favorable conditions (murky, nutrient-rich water low in oxygen is ideal for them), and regulate garbage disposal to avoid introduction of additional jelly-friendly substrates.
Three co-authors of the paper are current or former NCCOS-sponsored scientists. Researchers funded by our grants forecast jellyfish in the Chesapeake Bay and ascertain what armored shorelines do to their natural surroundings.
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