The Great Barrier Reef (GBR) is the largest coral reef system in the world. It extends from 24° 30′ S in the south to 9° 30′ S in the north, a distance of about 2300 km along the north-east shelf of Australia (Fig. 1.1). Accurate estimates of dimensions and other geographical data are available only for the Great Barrier Reef Marine Park (345 500 km2) or the Great Barrier Reef World Heritage Area (348 000 km2) which also includes islands excluded from the Park. Within this area are 2900 reefs occupying over 20 000 km2 or 9% of the 224 000 km2 shelf area (Hopley et al., 1989). However, this administrative area does not include the contiguous shelf of Torres Strait, data for which are more scant. The Strait is 150 km wide and east of the line of high islands, which link Australia to Papua New Guinea, the shelf has a width of over 200 km. Estimated total shelf area here is about 37 000 km2 and, relying on comparative data from the adjacent Great Barrier Reef Marine Park (which ends at 10° 42′ S) there may be a further 750 reefs and shoals with a total area of about 6000 km2.
The GBR is also one of the best studied in the world. Although first described during James Cook's voyage of exploration in 1770, because of science's preoccupation with atolls, it did not become a major focus until after the establishment of the Great Barrier Reef Committee in 1922 and the ground-breaking year-long Royal Society Expedition to Low Isles near Cairns in 1928–29 (see below and Bowen and Bowen, 2002).