Effects of geography, taxa, water flow, and temperature variation on coral bleaching intensity in Mauritius

This study describes the response of common coral taxa at 15 sites to a warm-water anomaly in Mauritius in March 2004. Sites circumscribed the island and differed in their water flow and thermal history as a result of variation in local current patterns. We observed 2 distinct positive responses of coral taxa to the anomaly that correlated with their local abundance, with a group of sparse (22 taxa covering < 5 cm m(-1)) and abundant taxa (7 taxa covering > 5 cm m(-1)). The 2 most dominant taxa Acropora and Montipora were among the most susceptible genera in the abundant group, while Seriatopora and Alveopora were the most susceptible taxa in the sparse group. This suggests that a temperature anomaly that is sufficient to cause mortality will remove taxa from 2 positions in the community spectrum with consequences for both ecological functions and diversity. We found that bleaching intensity at the sites was positively associated with water flow, with the most intense bleaching and highest currents on the windward and offshore sites. The algal symbiont communities in nearly all of the corals sampled on both sides of the island and 2 depths were dominated by diverse Symbiodinium in Clade C, indicating that the observed differences in response among coral taxa and sites were unlikely to be greatly affected by the types of symbionts they contained. We suggest that high water flow reduces background stress and acclimation, and results in corals that are less tolerant of rare temperature anomalies.