The salaries of members of the Council shall be established by Council by ordinance or resolution to be adopted no later than July 1, of each odd numbered year commencing in the year 1981. The salaries so established shall be effective for a two year period beginning January 1, of the year immediately following the adoption of the ordinance or resolution establishing them. In the event Council shall fail to establish salaries as required in this section, the salaries in effect for the prior two year period shall remain in effect until changed in accordance with this section. The initial salary of members of the Council under this Charter shall be that salary established for such office and in effect on January 1, 1981 and if none have been established, the Council first elected under this Charter shall establish such salaries within ninety days. Additional compensation may be established for the office of Mayor in the same manner as provided for establishing the compensation of the members of the Council. No increase shall be effective during the terms of the Mayor or Councilmembers in office at the time such ordinance is passed.