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)?

People that live in the South Pacific island are called "Pacific islanders"