Conservationists have raised fears that the Government will only approve a handful of protected areas in UK seas, missing a "once-in-a-lifetime opportunity" to protect marine wildlife.
A list of 127 marine conservation zones - covering around 27% of English waters - have been proposed following consultation with wildlife groups, fishing interests and other sea users, but there are concerns that in the face of lobbying from the marine industry only a few will be approved.
The UK's network of Sea Life centres has launched a campaign to collect 250,000 postcards from visitors backing the creation of a network of protected areas that will help species such as critically endangered European eels and native spiny seahorses.
The Marine Conservation Society was involved in the consultation on creating marine conservation zones.
The charity's Dr Jean Luc Solandt said: "There are fears that ministers will miss this once-in-a-lifetime opportunity to make a real difference to the future of our seas, and approve only a handful of these sites."
Biologists Chris Brown and Emily Madge, from the Sea Life centre at Weymouth, Dorset, have kicked off the appeal by posting the first postcard while waist-deep in the surf at the seaside town.
Weymouth appeal co-ordinator Kate Buss said: "Restrictions on fishing and other activities would benefit many species, including the now critically endangered European eel, the red-listed undulate ray and native spiny seahorses.
"The sites recommended amount to only 27% of English waters, but there are fears that ministers will bow to pressure from marine industry lobbyists and approve only a handful."
Sea Life aquariums across the UK are collecting postcards backing full approval of the 127 marine sites, as are Sea Life attractions at Alton Towers and Chessington World of Adventures, and the Cornish Seal Sanctuary.
School children will deliver the postcards to Westminster in the New Year.