Coral bleaching and mortality in the Mexican Pacific during the 1997-98 El Niño and prediction from a remote sensing approach

Abstract

A coral reef monitoring program was initiated at Bahia Banderas (21°N, 105°W), on the Pacific coast of Mexico, on January 1997, several months before the onset of the El Nino-Southern Oscillation (ENSO) event of 1997-98. Live coral cover, sea surface temperature (SST) and salinity were monitored during 1997-98, in conjunction with hot spot' satellite bleaching predictions of NOAA's NESDIS. Coral reef bleaching during the 1997-98 El Nino at Bahia Banderas coincided closely with satellite bleaching predictions and with experimental observations on coral tolerance to thermal stress. The initial bleaching event rapidly evolved into an unprecedented massive coral mortality (96%), equivalent to the catastrophic coral mortalities observed in the Galapagos Islands during the 1982-83 ENSO. The sudden mass bleaching and mortality of corals at Bahia Banderas was most likely caused by the marked accelerated warming rate (+3.5°C mo -1 ), an order of magnitude higher than that observed during the 1982-83 El Nino in the Galapagos Islands (+0.35°C mo -1 ). Also, the SST anomaly observed during the 1997-98 ENSO at Bahia Banderas (+6.1°C) was 30% higher than in 1982-83 in the Galapagos area (+4.5°C). The recovery of the Bahia Banderas coral reefs is uncertain since the dead coral substrate has already been covered with filamentous fleshy algae. In contrast to the long-lasting existence of corals and coral reefs in the region, reef frameworks are typically very thin. This situation may indicate the frequent recurrence of mortality events due to environmental extremes, such as ENSO, that have limited reef development in the northeastern tropical Pacific Ocean.