Physical mechanisms influencing localized patterns of temperature variability and coral bleaching within a system of reef atolls
Interactions between oceanic and atmospheric processes within coral reefs can significantly alter local-scale (< km) water temperatures, and consequently drive variations in heat stress and bleaching severity. The Scott Reef atoll system was one of many reefs affected by the 2015–2016 mass coral bleaching event across tropical Australia, and specifically experienced sea surface temperature anomalies of 2 °C that caused severe mass bleaching (> 60%) over most of this system; however, the bleaching patterns were not uniform. Little is known about the processes governing thermodynamic variability within atolls, particularly those that are dominated by large amplitude tides. Here, we identify three mechanisms at Scott Reef that alleviated heat stress during the marine heatwave in 2016: (1) the cool wake of a tropical cyclone that induced temperature drops of 1.3 °C over a period of 8 days; (2) air–sea heat fluxes that interacted with the reef morphology during neap tides at one of the atolls to reduce water temperatures by up to 2.9 °C; (3) internal tidal processes that forced deeper and cooler water (up to 2.7 °C) into some sections of the shallow reefs. The latter two processes created localized areas of reduced temperatures that led to lower incidences of coral bleaching for parts of the reef. We predict these processes are likely to occur in other similar tide-dominated reef environments worldwide. Identifying locations where physical processes reduce heat stress will likely be critical for coral reefs in the future, by maintaining communities that can help facilitate local recovery of reefs following bleaching events that are expected to increase in frequency and severity in the coming decades.
KeywordsTide-dominated Atoll Hydrodynamics Temperature variability Coral bleaching Northwestern Australia
We would like to thank the Captain, crew and scientists of the R/V Solander cruises 6392, 6430 and 6551. This research was supported by the Australian Federal Government through the Australian Institute of Marine Science and the Browse LNG Development Joint Venture Participants, through the operator Woodside Energy Limited. Funding to R.H.G. was provided by the ARC Centre of Excellence for Coral Reef Studies, and a UWA University Postgraduate Award for International Students. On behalf of all authors, the corresponding author states that there is no conflict of interest. We certify that this article was prepared as part of official duties at the US Geological Survey. The article is thus in the public domain and cannot be copyrighted.
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