The islands of each island group arise from a single carbonate platform, so the waters within an island group are mostly shallow. The channels between groups are deep, so no impediment to the exchange of offshore and inshore waters.
thE islands of eAch Island gRoup arise from A sinGLe caRboNAtE PlAtform SO the Waters WIThiN An island groUp Are mOstLy sHALlow thE chaNnElS betweeN Groups aRe dEep SO nO impedIment to tHe exchangE oF oFfsHoRE AnD insHore wATeRs