Researchers are pointing to a new, problematic, consequence of overfishing in the world’s oceans – jellyfish domination.
Dr Anthony Richardson, an Australian marine biologist, says marine systems of the world run an acute risk of flipping over to being jellyfish dominated, and mentions Southeast Asia, the Black Sea, the Gulf of Mexico and the North Sea, as particular problem areas.
The Japanese today have a major problem with giant jellyfish that burst through fishing nets, he says, specifying “a jelly fish called Nomura, which is the biggest jellyfish in the world. It can weigh 200 kilograms, as big as a sumo wrestler and is 2 metres in diameter,”
Jellyfish are normally kept in check by fish, which eat small jellyfish and compete for jellyfish food such as zooplankton. With overfishing, jellyfish numbers are increasing. Also, jellyfish feed on fish eggs and larvae, further reducing fish numbers.
To add insult to injury, nitrogen and phosphorous in run-off cause red phytoplankton blooms, which create low-oxygen dead zones where jellyfish survive, but fish can’t.
“You can think of them like a protected area for jellyfish,” says Richardson.
He and his colleagues say it’s important to reduce overfishing, especially of small pelagic fish, like sardines, and to reduce run-off.
They also say it’s important to control the transport of jellyfish around the world in ballast water and aquariums.