which locally may have vertical sides. Between the reefs, however, the shelf is a mostly flat and featureless surface with water depths of 20–50 m. Water depths increase rapidly to the east of the GBR, which is located on the shelf margin of the Coral Sea basin in water 120–140 m deep. The moderate- to low-relief mid- to outer shelf zone lies north of the incised valleys and offshore from the deltaic zone. Although the 60 m to 80 m isobaths suggest the existence of east-west trending valleys, these are much lower in relief than those to the south. Generally, this zone forms a low-relief plain, gently dipping towards the shelf break which is in about 140 m of water. A drowned barrier reef system forms a rim near the shelf break along the southeastern part of the Gulf. Demographics and economy Communities inhabiting the Papuan Gulf primarily live in both villages on the shore or in coastal mangrove forests, as well as in key regional centers (Kikori, Baimuru, Ihu, Kerema and Malalaua). These semi-urban centers are where the health services are located, as well as high schools, and large trade stores. The provincial government of the Gulf Province, which administers the bulk of the Papuan Gulf, is located in Kerema. As a result of the services available in these centers they all composed of a mixture of Papuan Gulf ethnic groups. Since the 1950s, people of the Gulf of Papua have been migrating to PNG's national capital Port Moresby to find work. As a result of these demographic shifts, Port Moresby is home to a sizable community of Papuan Gulf residents. They are located primarily in the settlements of Kaugere, Kila Kila and Horse Camp. Gulf Communities have access to a regional airservice which connects them to the wider nation. A sealed road links communities near Malalaua to Port Moresby. When not washed out a dirt road connects Kerema to Malalaua. Despite this infrastructure, the primary means of travel remains canoes, and fiber-glass dinghies with outboard motors. Within the Purari Delta and among the Elema it is common for individuals, particularly men, to travel to Port Moresby at least once a year to see relatives and to earn money. Today, people primarily rely on fishing and hunting, sago palms, and depending on the area agriculture and horticulture. Communities in the eastern Gulf (Toaripi and Elema), where the soil is