Coral bleaching and mortality on artificial and natural reefs in Maldives in 1998, sea surface temperature anomalies and initial recovery

The bleaching and subsequent mortality of branching and massive corals on a rtificial and natural reefs in the central atolls of Maldives in 1998 are e xamined with respect to sea surface temperature (SST) anomalies, SST normal ly peaks in April-May in Maldives. The UK Meteorological Office's Global se a-Ice and SST data set version 2.3b shows that in 1998 monthly mean SST was 1.2-4 S.D. above the 1950-1999 average during the warmest months (March-Ju ne), with the greatest anomaly in May of +2.1 degreesC. Bleaching was first reported in mid-April and was severe from late April to mid-May with some recovery evident by late-Mag. At least 98% of branching corals (Acroporidae , Pocilloporidae) on artificial structures deployed on a reef flat in 1990 died whereas the majority of massive corals (Poritidae, Faviidae, Agariciid ae) survived the bleaching, The pre-bleaching coral community on the artifi cial reefs in 1994 was 95% branching corals and 5% massives (n = 1589); the post-bleaching community mas 3% branching corals and 97% massives (n = 248 ), Significant reductions in live coral cover were seen at all natural reef s surveyed in the central atolls, with average Live coral cover decreasing from about 42% to 2%, a 20-fold reduction from pre-bleaching levels. A surv ey of recruitment of juvenile corals to the artificial structures 10 months after the bleaching event showed that 67% of recruits (greater than or equ al to0.5 cm diameter) were acroporids and pocilloporids and 33% were from m assive families (n = 202) compared to 94% and 6%, respectively, in 1990-199 4 (n = 3136), Similar post-bleaching dominance of recruitment by branching corals was seen on nearby natural reef (78% acroporids and pocilloporids; 2 2% massives), A Linear regression of April mean monthly SST against year wa s highly significant (p < 0.001) and suggests a rise of 0.16<degrees>C per decade, If this trend continues, by 2030 mean April SST in the central atol ls mill normally exceed the anomaly level at which corals appear there are susceptible to mass bleaching, (C) 2001 Elsevier Science Ltd. All rights re served.