Description: The Mariana Islands are a chain of fifteen high islands of volcanic origin, with numerous submerged banks and seamounts, oriented in an arc from north to south on the Marianas Ridge, and surrounded by deep to very deep waters. Guam, the largest, southern-most and populous island, has extensive fringing reefs. The islands to the north, notably Rota, Tinian and Sapan, also have fringing reefs, best developed on Saipan's western side. The northern islands have little of no recent reef development, with coral communities developed on non-reefal hardgrounds, or raised fossil reefs (eg. Farallon De Medinilla). This ecoregion also includes MinamiToriShima (Marcus Island) a very isolated atoll ca 1000km to the north-east. The larger islands of the main Marianas arc have been heavily modified for urban, agricultural or military purposes, including construction of ports, with impacts to incident reefs. The region is episodically in the path of tropical typhoons, and reefs have also been impacted by repeated outbreaks of Crown-of-thorns seastars and high temperature bleaching. Reef waters are mostly clear

Distinguishing ecoregion characteristics: The Marianas island arc is separated from neighbours by broad expanses of deep oceanic waters. Yap, the Caroline Islands and the Bonin Islands are ca 700km to the south-west, south-east and north respectively. With reef development largely restricted to the southern group of large islands, notably Guam and Saipan, this ecoregion is likely to be meaningfully subdivided

Additional Information: Marianas Islands corals currently appear to have no meaningful affinities with other ecoregions in the western-central Pacific (Veron, Stafford-Smith, DeVantier et al., 2015)

General Ecoregion References: Randall (1995); Spalding, Ravilious and Green (2001); Paulay (2003); Goldberg, Adams, Albert et al. (2008); Riegl, Purkis, Houk et al. (2008); Burke, Reytar, Spalding et al. (2011); Chin, Lison de Loma, Reytar et al. (2011); Blyth-Skyrme, Rooney, Parrish et al. (2013); Veron, Stafford-Smith, DeVantier et al. (2015);

Principal Coral Distribution References: In preparation