The salary of the Mayor shall be twenty-four hundred dollars ($2,400) per year for the first term beginning January 1, 1972. For terms thereafter, such salary shall be fixed  and determined by the Council, but the salary of the Mayor shall not be increased or decreased during the elective term of office which he is serving. If the established salary of the Mayor is to be changed in respect to a succeeding term of office, such change must be made by the Council prior to the first day of January of the last year of the term then being served by the Mayor. Unless and until such salary is so changed, it shall remain as last fixed.