All powers and duties of the city specified in the city charter in the general laws of the state are vested in the city council. The city council is composed of five members who are elected at large by the registered electors of the city. Two members are elected each year to three-year terms, except on every third year only one member, who is also the mayor, is elected to a three-year term. Further, should any general election include the election of a council person due to a vacancy in that office pursuant to article III, section 4, of the charter, then the unexpired term shall be filled by the candidate receiving the third greatest number of votes, or the second greatest number of votes in third year elections involving only the mayor. Should more than one vacancy be filled at the election, then those receiving the greatest number of votes shall be declared elected for the longest terms.