[msandford]

The tunnel will very likely be less disruptive to marine animals than ferry boats. During the construction yes it will be worse but 10 years after? The ecosystem will have forgotten the disruption and will have gained additional peace from reduced/eliminated ferries.

[lukan]

Ferries do not mess up the ground and the riffs which is where most sea life is to be found. Big ships are only a problem to sea life if they dump their old oil there, their anchors ... or well, trawling (which is forbidden there for a reason).

[gmueckl]

Ships also produce noise. At least marine mammals are affected by ship noises.