Jellyfish swimming skills help explain blooms

Jellyfish can detect the direction of ocean currents and swim strongly against them, a finding that could help in predicting and avoiding problematic jellyfish blooms.

Barrel-jellyfish were observed to actively swim in a particular direction at the surface of the ocean. The jellyfish were also tagged and tracked using GPS and found to have directional swimming preferences.

“Jellyfish are not just bags of jelly drifting passively in the oceans,” said Deakin University’s Professor Graeme Hays in a statement. “They are incredibly advanced in their orientation abilities.

“Detecting ocean currents without fixed visual reference points is thought to be close to impossible and is not seen, for example, in lots of migrating vertebrates including birds and turtles.”

The model the researchers developed of the jellyfishes’ behaviour, together with ocean currents, helps to explain how jellyfish form blooms that include hundreds to millions of individuals for periods up to several months.

Jellyfish blooms appear to be on the increase. En masse jellyfish can destroy fisheries, clog fishing nets, cause power plant outages and sting holiday-makers.

It’s not clear exactly how the jellyfish figure out which way to go.

The researchers suggest the animals could detect current shear across their body surface, or they may indirectly assess the direction of drift using other cues such as the Earth’s magnetic field or infrasound.

“Now that we have shown this remarkable behaviour by one species, we need to see how broadly it applies to other species of jellyfish,” Hays said. “This will allow improved management of jellyfish blooms.”

This study has been published in Current Biology.