Catastrophic coral mortality in the remote central Pacific Ocean: Kirabati Phoenix islands

Abstract

Quantitative and qualitative surveys in November-to-December 2004 revealed near 100% coral mortality in the lagoon of Kanton Atoll and 62% mortality on the outer leeward reef slopes of this island as well as elsewhere throughout the Kiribati Phoenix islands in the Central equatorial Pacific Ocean. most dead colonies were in growth position. Colonies were encrusted with coralline algae indicating they had been dead for 1 to 2 years, thus dying just after an expedition by the New england Aquarium in July 2002 which declared the region one of the most pristine reefs left in the Central Pacific. Fish populations did not seem reduced to the same levels as the stony corals but only 153 species of fish were identified at the study sites. Apex predators and key indicator fish species were present suggesting little impact from overfishing. Populations of invertebrates, now dominated by sponges, were also seemingly reduced inside the Kanton Atoll lagoon. Thirty-six species of living corals were identified along 480 m2 of transects. Five of eight coral genera represented <1% of the bottom cover. many of the living corals found were less than 10 cm in diameter suggesting recruitment has occurred since the mass mortality. bleaching Hot Spot Analysis by National Oceanographic and Atmospheric Administration / National environmental Satellite, Data, and information Service (NOAA/NeSDiS) satellite monitoring revealed a record high of 16 degree heating weeks (DHW) around the Phoenix islands between August 2002 and march 2003. The Kanton Atoll lagoon has a residence time approaching 50 days, there is no significant source of land-based pollution and there was no sign of any destructive fishing practices. Hence, the exposure to excessively high water temperatures for over six months killed the coralreef community of Kanton Atoll lagoon and caused the excessive loss of coral species and cover throughout the Phoenix island group. These observations provide further evidence that coral reefs in the most remote part of the Central Pacific Ocean are not isolated from the effects of global warming. __________________________ 1Planetary Coral Reef Foundation, P.O. box 201, Pacific Palisades, CA 90272. 2Department of biology, College of Charleston, SC 29424. Manuscript received 14 September 2005; revised 18 September 2006.