Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
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Volume 15, issue 20
Biogeosciences, 15, 6277-6296, 2018
https://doi.org/10.5194/bg-15-6277-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Biogeosciences, 15, 6277-6296, 2018
https://doi.org/10.5194/bg-15-6277-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 26 Oct 2018

Research article | 26 Oct 2018

Coral reef carbonate budgets and ecological drivers in the central Red Sea – a naturally high temperature and high total alkalinity environment

Anna Roik1,a, Till Röthig1,b, Claudia Pogoreutz1, Vincent Saderne1, and Christian R. Voolstra1 Anna Roik et al.
  • 1Red Sea Research Center, King Abdullah University of Science and Technology, 23955 Thuwal, Saudi Arabia
  • acurrent address: Marine Microbiology, GEOMAR Helmholtz Centre for Ocean Research, 24105 Kiel, Germany
  • bcurrent address: Aquatic Research Facility, Environmental Sustainability Research Centre, University of Derby, Kedleston Road, Derby, DE22 1GB, UK

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 optimal reef production (5–10kg CaCO3m−2yr−1) and below maxima recently recorded in remote high coral cover reef sites. However, the erosive forces observed in the Red Sea nearshore reef contributed less than observed elsewhere. A higher TA accompanied reef growth across the shelf gradient, whereas stronger diurnal pH fluctuations were associated with negative carbonate budgets. Noteworthy for this oligotrophic region was the positive effect of phosphate, which is a central micronutrient for reef building corals. While parrotfish contributed substantially to bioerosion, our dataset also highlights coralline algae as important local reef builders. Altogether, our study establishes a baseline for reef growth in the central Red Sea that should be useful in assessing trajectories of reef growth capacity under current and future ocean scenarios.

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In this study we collected in situ accretion/erosion rates and abiotic/biotic variables to estimate carbonate budgets and ecological drivers of coral reef growth in the central Red Sea. Our data suggest that reef growth is comparable to estimates of other regions, but the erosive forces in the Red Sea are not as pronounced. Comparison with recent data suggests that Red Sea reef growth might not have decreased over the past decades, despite warming, calling for more detailed investigations.
In this study we collected in situ accretion/erosion rates and abiotic/biotic variables to...
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