No abstract

Mass-bleaching events (in which corals and other symbiotic invertebrates lose their zooxanthellae) have been occurring every 3 to 4 yr since 1979 The last report of widespread mass-bleaching in the Pacific (which included bleaching around French Polynesia) was in February-April 1991. This paper reports on mass-bleaching along the outer reef slope of Moorea. French Polynesia, in April 1994. Mass-bleaching was extensive at all sites visited, with corals being bleached down to 25 m. Colour loss by corals was due to low area1 densities of zooxanthellae and the percentage of live coral affected ranged between 39.6 (* 7.12, SEM) ( N W sites) and 72.4 (t 7.1 l , SEMI (NE sites). Bleaching also varied as a funct~on of depth and included a wide range of species Acropora spp. showed the most severe bleaching (89.0 to 100% of all colonies completely bleached) and Pontes spp. showed the least amount of bleaching (12 9 to 42.5'K of all colonies partly bleached). Pocillopora spp. showed intermediate bleaching (73.9 to 92.1 % of all colonies either partly or completely bleached). The results of this report indicate that current bleaching is on a scale equal to that of the 1991 bleaching event. Temperatures recorded hourly at 14 m off the outer reef slope from July 1991 to August 1994 (and those from satellite sea surface temperature readings) indicate unusually warm sea temperatures in March 1994, which were approximately l.O°C higher than the highest temperatures recorded in 1992 and 1993, years in which bleaching on a massive scale did not occur. The appearance of warmer temperatures preceded the onset of bleaching by 2 to 3 wk, which strongly confirms the hypothesis that positive thermal anomalies are responsible for recent bleaching events in the Central and Western Pacific.