There is no marriage registration office in Changxing Island, Dalian. If you are in Changxing Island or a foreigner, you need to register at your domicile or the domicile of the object. Locals come to Wafangdian or Dalian to register. Wafangdian registration office is located in the courtyard of the Municipal Maternal and Child Health Station in the west of Xinhua Bridge.
I hope this helps.