The results of a jellyfish tagging programme carried out by a team from Swansea University indicate that they may be active hunters and as such a threat to depleted fish stock recovery.
Until now jellyfish were largely considered to be inactive drifters on the world's oceans, obtaining prey whilst aimlessly floating on the tides, but the latest results from the Ecojel Project, a £575,000 long term study of increasing jellyfish populations and their potential impact on the economy, suggest otherwise.
The team tagged specimens of the large, Barrel jellyfish, Rhizostoma octopus, in Carmarthen Bay, Wales. The tags took water pressure and temperature readings every minute with the data being retrieved from tags washed up on beaches after the jellyfish die. So far 25 of the 72 tags deployed have been recovered.
Once deductions were made for unintentional movement caused by waves and so on, it was found that far from being at the whim of tides and ocean currents, the tags showed the jellyfish actively moving around 600m vertically on average each day instead of staying at fixed depths as previously believed.
At the same time gut content analysis showed stomachs full of varied prey wherever they were caught demonstrating the success of this technique.
Jellyfish have already been noted for their ability to adapt to fill ecological niches left vacant by overfishing. The uncovering of these intentionally complex movement patterns adds significant detail to our sparse knowledge of jellyfish behaviour, indicating an ability to become more dominant as ocean conditions change with this new found talent for hunting could give them greater advantage when competing with struggling fish larvae stocks for planktonic food.
If you find one of the remaining data-loggers on the beach, please email Victoria Hobson at [email protected]
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