Users who fail to return to the site at Panda.org or react to messages from WWF will see their site reduced to a puddle of mud.
As part of a £30,000 project, Moonfish is creating a host of potentially viral elements, including banners, buttons and a Flash movie of the living site, which is being emailed to about 40,000 users on the Panda Passport database.
"The living web site is our tool to reward activists and encourage viral activity,
explained Sarah Bladen, online campaign officer at WWF. "It will be the user's window into the sea, where they can see it thriving or slowly disintegrating."
Stuart Johnson, account director at Moonfish, said: "The graphic illustrates the campaign online, which had to be fun and interactive as well as getting the WWF's message across."