Abstract
The structural framework provided by corals is crucial for reef ecosystem function and services, but high seawater temperatures can be detrimental to the calcification capacity of reef-building organisms. The Red Sea is very warm, but total alkalinity (TA) is naturally high and beneficial for reef accretion. To date, we know little about how such detrimental and beneficial abiotic factors affect each other and the balance between calcification and erosion on Red Sea coral reefs, i.e., overall reef growth, in this unique ocean basin. To provide estimates of present-day reef growth dynamics in the central Red Sea, we measured two metrics of reef growth, i.e., in situ net-accretion/-erosion rates (Gnet) determined by deployment of limestone blocks and ecosystem-scale carbonate budgets (Gbudget), along a cross-shelf gradient (25km, encompassing nearshore, midshore, and offshore reefs). Along this gradient, we assessed multiple abiotic (i.e., temperature, salinity, diurnal pH fluctuation, inorganic nutrients, and TA) and biotic (i.e., calcifier and epilithic bioeroder communities) variables. Both reef growth metrics revealed similar patterns from nearshore to offshore: net-erosive, neutral, and net-accretion states. The average cross-shelf Gbudget was 0.66kg CaCO3m−2yr−1, with the highest budget of 2.44kg CaCO3m−2yr−1 measured in the offshore reef. These data are comparable to the contemporary Gbudgets from the western Atlantic and Indian oceans, but lie well below
We thank the Coastal and Marine Resources Lab (CMOR) at King Abdullah University of Science and Technology (KAUST) for logistics and operations at sea (Esam Al-Jahdali, Abdullah Al-Jahdali, Ghazi Al-Jahdali, Ramzi Al-Jahdali, Haitham Al-Jahdali, Francis Mallon, Paul Müller, and David Pallett), as well as for the assistance with the deployment of oceanographic instruments (Lloyd Smith, Mark D. Pantalita, and Samer Mahmoud). We would like to acknowledge field assistance by Cornelia Roder and Christoph Walcher in setting up the reef monitoring sites. We thank Maha Khalil for providing a map of the study sites. We are grateful for the comments and suggestions from two anonymous reviewers and Steeve Comeau (Laboratoire d’Océanographie de Villefranche) for his critical comments and helpful suggestions to improve the manuscript. Research reported in this publication was supported by funding to Christian R. Voolstra from KAUST.