Bitcoins are a decentralized, electronic currency ( http://www.bitcoin.org ). They are derived from people “mining” Bitcoins on their computers. People make money by just running Bitcoin mining rigs.
I can see two advantages of having a setup out in the water.
You can set up a mining rig to be overclocked and create heat using the seawater to provide some of the cooling of your mining rig.
Using tidal forces and waves you can generate the electricity needed to run the machines.
Plus you have full use of Bitcoins in your community. It would be like building a community around a gold mine. You all trade in gold and have the benefit of being able to create something that is traded internationally.