Lower case letters that come after the capital letter(s), e. g., kjk, labeling a rock unit represent the rock unit's
-structure and depth
-age range
-rock type or name
-elevation

Apart from colors, geologic maps also use letter symbols to denote a property of a rock unit. Letter symbols are a combination of a capital letter followed by lower case letters. The capital letter represents the age of the geological unit, while the lower case letters represent the rock type or name.

Its decreasing because of illnesses

Ibelieve it's the pacific islands