Box jellyfish
In Australia (mainly northern; however, box jellyfish can live in subtropical waters as far south as Sydney, with "Carybdea marsupialis" being recorded as far south as Bermagui, Sapphire Coast) the highest risk period for the box jellyfish is between October and May, but stings and specimens have been reported all months of the year. Similarly, the highest risk conditions are those with calm water and a light, onshore breeze; however, stings and specimens have been reported in all conditions.
Dead zone (ecology)
Despite most other life forms being killed by the lack of oxygen, jellyfish can thrive and are sometimes present in dead zones in vast numbers. These jellyfish blooms produce mucus and waste, leading to major changes in food webs in the ocean. The organic carbon is metabolised by bacteria which return it to the atmosphere in the form of carbon dioxide in what has been termed a "jelly carbon shunt".