well it depends. If you're talking about already native species like Eledone cirrhosa then I wonder if they would eat them. If you're talking about bringing in a new species to the ecosystem then you've got a problem of 2 alien species instead of one! Who knows? Maybe we'll see a bloom of our own native species? I don't know if the local cephs would eat Chinese mitten crabs though.
Yes, these crabs are edible. (At least the Chinese like them...)
Most famous of its "crab butter" or whatever you call it. Heck a party of 20 can scoff 50-80 of these crabs, since they really don't grow much larger than a bit larger than your palm.
... not so far fetched really. When i was studying in London for my MSc, a mate had this big plan of getting a contract from the Environment Agency to remove some invasive crayfish from rivers and selling them to local restaurants.
When I was working for Sealife in Weymouth we got a call from customs as someone had tried to import them in a box with all the chinese writing on it... we kept them as a display and got some good PR out of it. It's amazing the sort of things which people will try and do...
They were fairly big though... dont think there are many bigger in this country than them... the big edible and the spiny spider crab will be but thats about it...
I used to feed edibles to my GPO... what a showdown!