 In marine terms, the Houtman Abrolhos is located within the Southwest Shelf Transition, an Integrated Marine and Coastal Regionalisation of Australia (IMCRA) biotone that takes in the continental shelf from Perth to Geraldton.This province is defined as the area of shelf where tropical waters intergrade into temperate, thus supporting both tropical and temperate biota.In addition, this area contains the highest concentration of west coast endemics.