We're all doomed. DOOMED I say! Yes, the world will not be inherited by rats, cockroaches or investment bankers. The jellyfish will outlive us all. Although for those who read depressing non-fiction books on the destruction of the world's waterways already know of their destructive power, a new article came out today. http://www.livescience.com/animalworld/060710_jellyfish_explosion.html reported that man's heavy fishing has taken a toll, and now the jellyfish are increasing in numbers. "In fact the jellyfish are so numerous in the study area that they now represent more biomass than all the fish combined," says the article. "Their numbers, ironically, are beginning to "significantly interfere with fishing operations," the researchers report in the July 12 issue of the journal Current Biology." Alas, the total biomass of jellyfish in the Namibian shelf is now estimated to be more than three times that of fish.
You can read more at this site http://www.ocean.udel.edu/blacksea/chemistry/jellyfish.html where I plucked the following neato cool piccie of a jelly (hope they don't mind):

They're gorgeous to watch, but having experienced the sting, I can say emphatically you shouldn't touch the little buggers.