Australian Broadcasting Corporation: Giant jellyfish are taking over parts of the world’s oceans due to overfishing and other human activities, researchers say. Nomura jellyfish are the biggest in the world and can grow as big as a sumo wrestler. They weigh up to 200 kilograms and can reach 2 metres in diameter. Dr Anthony Richardson and his colleagues from CSIRO Marine and Atmospheric Research says jellyfish numbers are increasing, particularly in South East Asia, the Black Sea, the Gulf of Mexico and the North …