Except as otherwise provided, the term of office for each director shall be two years and until the appointment and qualification of his or her successor. A successor shall be appointed not later than 30 days immediately upon the expiration of a director’s term. A vacancy exists whenever a director ceases to hold office on the city council or board of supervisors from which he or she was appointed. Any vacancy shall, within 60 days of its occurrence, be filled for the balance of the term by the body that made the original appointment.