The municipality at La Rochelle seem to be doing their bit to be eco-friendly. There is a park-and-ride just outside the city, that seemed to be well-frequented, with a little bus that shuttles between all the important stop-offs in the town.
You can rent little electric runabouts (4-door) in a car-share scheme, and there are charging stations available for your use. The land around is quite flat, and so well-suited to bicycles; these are available to be rented by the hour (the first half-hour is free) and we passed a number of bike parks as we wandered around. I would think that half an hour would be plenty of time to get between bike parks, so you could probably do everything you needed for free.
There are regular (every hour, but tide-dependent) ferries to shuttle you around the port, and take you to and from the marina. These are solar powered, you can see the panels on the roof, so no throbbing diesel engines when we got on, and not much noise either, just a gentle glide over the water.
The whole system seems to be branded Yélo, is managed via a yellow smartcard, and the bright yellow colour cheme is used on all the transport vehicles and notices.