All persons holding any administrative office on the date that the council-manager form of government under this article is made effective shall continue in office and in the performance of their respective duties until different provision shall be made for the performance of such duties or until the discontinuance of such office. The powers conferred and the duties imposed upon any office, department, board or agency of the municipality by the laws of the state shall, if such office, department, board or agency be abolished by this article or under its authority, be thereafter exercised and discharged by the office, department, board or agency designated by the council unless otherwise provided herein or by law.