When I used the ferries over the river Mersey the landing stages were cantilevered and the gaps covered with sliding plates. Water moves so you do need to allow your floating stages to rise and fall. I agree with pressonregardless and see you are adopting a similar system. Make sure the gap for the joints allows for the maximum wave size movement and use a hinged plate to cover the gap. There will be quite some pressure on the mountings so I suggest you do a trial with one to see if it needs to be made stronger. If I remember correctly the floating pontoons were attached to shore with heavy anchor chains.
Looking forward to see your finished product