Jellyfish threaten to 'dominate' oceans
By Anna Salleh Giant jelly fish are taking over parts of the world’s oceans due to overfishing and other human activities, say researchers. Dr Anthony Richardson of CSIRO Marine & Atmospheric Research and colleagues, report their findings in the journal Trends in Ecology and Evolution. “We need to take management action to avert the marine systems of the world flipping over to being jellyfish dominated,” says Richardson, who is also a marine biologist at the University of Queensland. Richardson says jellyfish numbers are increasing, particularly in Southeast Asia, the Black Sea, the Gulf of Mexico and the North Sea. He says the Japanese have a real problem with giant jellyfish that burst through fishing nets. “[They’re] 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,” says Richardson. Richardson and colleagues reviewed literature linking jellyfish blooms with overfishing and eutrophication – high levels of nutrients. Jellyfish are normally kept in check by fish, which eat small jellyfish and compete for jellyfish food such as zooplankton, he says. But, with overfishing, jellyfish numbers are increasing. Jellyfish feed on fish eggs and larvae, further impacting on 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. …
