Recent seawater temperature histories, status, and predictions for Madagascar’s coral reefs

Abstract

Recent temperature histories and benthic surveys of Madagascar’s coral reefs are presented from 3 disparate regions in order to develop an understanding of the relationship between sea surface temperature (SST) and benthic cover, coral diversity, and community structure. Results indicate the presence of distinct temperature zones influenced by windward and seaward positions, latitude, intra- and inter-annual cycles, and local hydrodynamics. Southwest reefs had SSTs with the lowest mean, highest variation, fastest rise, strongest periodicities and highest cumulative degree heating weeks during recent warm events. These reefs were distinguished by a low number of coral taxa and a high cover of erect algae and had recently undergone a major decline in coral cover and change in community structure. Northwestern and eastern reefs had SSTs with moderate means and variation, lower temperature rises, and weaker periodicities. They also had higher coral cover and numbers of coral genera, and communities more typical of Indian Ocean coral communities undisturbed by temperature anomalies. Northwestern reefs had the lowest cumulative degree heating weeks and a high frequency of rare ‘boutique’ taxa that are usually found deeper or in lowdisturbance environments. Eastern reefs had a developed reef structure and may have the greatest potential for surviving climate change, while the northwest may be more amenable to protecting rare taxa. The more temperate reefs of the south showed large-scale degradation and no evidence for a refuge for coral communities, and require increased herbivory and associated fisheries management to reduce erect algal abundance.