Giant jellyfish are taking over parts of the world’s oceans due to overfishing and other human activities, researchers say.
Nomurajellyfish are the biggest in the world and can grow as big as a sumowrestler. They weigh up to 200 kilograms and can reach 2 metres indiameter.
Richardson says jellyfish numbers are increasing, particularly inSoutheast Asia, the Black Sea, the Gulf of Mexico and the North Sea.
Richardson and his colleagues have reviewed literature linking jellyfish bloomswith overfishing and eutrophication – high levels of nutrients.
The team recommends a number of actions in its paper, published inthe journal Trends in Ecology and Evolution and released to coincidewith World Oceans Day.
They say it is important to reduce overfishing, especially of small pelagic fish like sardines, and to reduce run-off. They also say it is important to control the transport of jellyfish around the world in ballast water and aquariums.
Jellyfish are considered simple jelly-like sea animals, which are related to the microscopic animals that form coral. They generally start their life as a plant-like polyp on the sea bed before budding off into the well-known bell-shaped medusa. Jellyfishhave tentacles containing pneumatocyst cells, which act like littleharpoons that lodge in prey to sting and kill them.