Is South Pacifican the term for the population living on the islands commonly referred to as the S. Pacific?

When is it appropriate to use a geographical region to define the group the resides within the that region independent of political boarders (north american, south american, european, etc.)? Is there a difference between defining the geographic area by the body of water (i.e. caribbean or south pacific) or by the island groups (i.e. bahamas)?