High temperatures tolerated by a diverse assemblage of shallow-water corals in American Samoa

Corals in shallow waters are subjected to widely fluctuating temperatures on a daily basis. Using continuous temperature recordings, we examined the temperature regime in one such area, a backreef moat with low tide depths of 1-2 in on Ofu Island in American Samoa. The moat supports a high diversity of 85 coral species [H'((log2)) = 3.37] with 25 -26% live coral coverage. In one section of the moat, a 4,000-m pool inhabited by 52 coral species, the mean summer temperature was 29.3 degreesC, but daily temperatures fluctuated up to 6.3 degreesC and briefly reached a peak of 34.5 degreesC. The duration of hot water events, e.g., greater than or equal to 32 degreesC, averaged 2.4 h per event (maximum 5 h) and occurred on 35 summer days, although daily mean temperatures did not exceed 30.5 degreesC and were generally within 0.5 degreesC of that occurring outside the moat at an exposed coastal area. While there was a previous mortality of many acroporids during a long-term (several month) warming period in 1994, at least nine Acropora species and a diverse range of other taxa withstand the current temperature regime.