World Sees Scary Transition to Seas Full of Jellyfish, Not Fish

Every summer the surge of jellyfish seems to be getting worse and worse in the Mediterranean Sea. A new UN report says that may start seeing a future where jellyfish overtake fish in our great big seas. Ready for a jellyfish stirfry?

The new report assesses recent jellyfish blooms in the Mediterranean and Black Seas. At first it looks as though the blooms are happening where overfishing has depleted fish stocks. Turns out it’s a vicious circle likely manmade in nature.

Over-fishing removes top predators from the sea. Without top predators in place the jellyfish increase rapidly, then cause a vicious cycle where the over populating jellyfish feed wildly on juvenile fish and fish larvae.

The new report was released by the FAO’s General Fisheries Commission for the Mediterranean. 

The jellyfish problem on fish stocks was first shown in the early 1980s after the jellyfish species Mnemiopsis leidyi, from the Atlantic, was mistakingly introduced to the Black Sea, bringing the fish population to its knees. 

When an invader species Beroe ovate fed on the jellyfish the problem seemed to be resolved.

“In the past, the system could cope with episodes of jellyfish abundance, but in the case of the early 1980s blooms, the system went in another direction and is still not back to “normal” in pre-Pelagia years,” the report states.

According to the FAO report jellyfish have now become persistently abundant in almost all the oceans of the world,  and some experts actually are speaking of  “a global regime shift from a fish to a jellyfish ocean” in which  jellyfish supplant fish. 

Scary thought.

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Besides overfishing, here are some possible reasons for the shift:

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• Global warming, which enhances species that thrive at tropical latitudes.

• Eutrophication, which increases nutrients in the water.

• Widespread use of sea walls to prevent coastal erosion and the large number of tourist harbours, which make an ideal habitat for those jellyfish who go through a stage as polyps in their early lives.

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Seas with a bounty of jellyfish? If you missed it, you can catch our recipe for jellyfish stir fry here.