The Phoenix Islands reefs are remarkable in many ways, which are mostly due to their remote geography. The lack of recent degradation due to the continued human presence has enabled the persistence of well-balanced reefs. There are 8 islands in the Kiribati Phoenix Islands, all of which are surrounded by reef. In addition, there are two submerged reefs in the Phoenix group: Carondelet Reef and Winslow Reef. Both are shallow platform reefs that are completely submerged, with Carondelet Reef being about 3-4 m underwater at low tide.
Coral reefs of the Phoenix Islands are greatly influenced by natural factors, such as wave energy on the southern, eastern and northern shores of the islands leading to high physical breakage. In the absence of local impacts such as pollution, overfishing, sedimentation, and coastal development, PIPA reefs serve as remnant examples of natural reefs. Researchers have identified over 250 coral species and preliminary assessments of the coral fauna indicate range extensions of 2 species from the Eastern Pacific (Pocillopora inflata, and Pavona gigantea) and at least one undescribed species. The number of documented shallow reef-fish species listed for the Phoenix Islands now stands at 518, with predictions of this number rising to over 570 species.
While the islands and surface waters of these islands have been long-known to history for their commercial and geographical importance, there is no evidence of systematic scientific exploration of these reefs prior to the first New England Aquarium expedition in 2000. The remoteness of this reef system has enabled it to persist without the day-to-day damage that most other reefs experience. As such, these reefs now serve as a restoration benchmark for other degraded hard coral ecosystems in the Central Pacific.
The Phoenix Islands have not been spared the threat of global warming, though they remain free from the local stresses that typically degrade reefs. In late 2002, the Phoenix Islands experienced one of the hottest ever-recorded warming events, followed by subsequent widespread coral mortality. Prior to the establishment of the MPA, PIPA reefs also suffered from a few shark-finning fishing vessels. Since then, expeditions have reported signs of recovery, including the resurgence of fast-growing coral species, evidence of new coral growth, and the continued persistence of fishes. Replenishment of sharks is also evident in some island lagoons, which act as nursery habitats for reef sharks and other species.