The control and management of the port district shall be exercised through a port commission consisting of 5 members who shall be appointed by the boards of supervisors. In port districts the boundaries of which are coterminous with a single county at least 2 members shall be residents of the city constituting the seat of the county in which the port district lies. In any port district located in more than 1 county, representation on the port commission from each county covered by the port district shall be, as near as may be, in proportion to the state equalized value of the county in relation to the total state equalized value of the port district. The terms of office of the persons appointed shall be so arranged and designated at the time of their appointment that the term of 2 members shall expire in 3 years, 2 in 2 years, and 1 in 1 year, from July 1 following the appointment. Annually thereafter the boards of supervisors shall appoint the member or members to serve for 3 years as the term of any member or members appointed by them shall expire; any vacancy occurring among the commissioners shall be filled for the unexpired term by the board of supervisors. In any port district, the boundaries of which are coterminous with a city or township or coterminous with 1 or more whole cities or coterminous with 1 or more whole townships, the appointment of members of the port commission shall be made by the governing body of the city or township or cities or townships in which the port district is located, and such members shall hold office and be appointed in the same manner for the same term and subject to the same conditions as members of port districts appointed by the boards of supervisors.