You usually do not need to inform anyone about your bike transport. Only on large ships it is possible to take your bike with you (Blue Star Ferries, Anek Lines, etc.). However, on ships without a garage such as the route Paros to Mykonos, bicycles are usually not allowed inside. You will see if the ship has a garage when booking. Paros can be busy in the summer, so it is a good idea to tell a port staff member that you have a bicycle in case you need extra help.