Coral Bleaching in the Persian/Arabian Gulf Is Modulated by Summer Winds

Abstract

Corals in the Persian/Arabian Gulf are the most thermally tolerant in the world, but live very near the thresholds of their thermal tolerance. Warming sea temperatures associated with climate change have resulted in numerous coral bleaching events regionally since the mid-1990s, but it has been unclear why unusually warm sea temperatures occur some years but not others. Using a combination of 5 years of observed sea-bottom temperatures at three reef sites and a meteorologically linked hydrodynamic model that extends through the past decade, we show that summer sea-bottom temperatures are tightly linked to regional wind regimes, and that strong 'shamal' wind events control the occurrence and severity of bleaching. Sea bottom temperatures were primarily controlled by latent heat flux from wind-driven surface evaporation which exceeded 300 W m −2 during shamal winds, double that of typical breeze conditions. Daily temperature change was highly correlated with wind speed, with breeze winds (<4 m s −1) resulting in increased warming, while faster winds caused cooling, with the magnitude of temperature decline increasing with wind speed. Using observed and simulated data from 2012 to 2017, we show that years with reported bleaching events (2012, 2017) were characterized by low winds speeds that resulted in temperatures persisting above coral bleaching threshold temperatures for >5 weeks, while the cooler intervening years (2013-2016) had summers with more frequent and/or strong shamal events which repeatedly cooled temperatures below bleaching thresholds for days to weeks, providing corals temporary respite from thermal stress. Using observed data from 2012 onward and simulated data from 2008 to 2011, we show that the severity of bleaching events over the past decade was linked to both the number of cumulative days above bleaching thresholds (rather than total days, which obfuscates the cooling effects of occasional brief shamal events), as well as to maxima. We show that winds of 4 m s −1 represents a critical threshold for whether or not corals cross bleaching threshold temperatures, and provide simulations to forecast sea-bottom temperature change and recovery times under a range of wind conditions. The role that wind-driven cooling may play on coral reefs globally is discussed.

Assessment of Climate Change Impacts on Sea Surface Temperatures and Sea Level Rise—The Arabian Gulf

“…The effect of the Shamal (northern) winds in modulating SST is reported by [18], where during weak Shamal wind the SST was observed to rise and during strong winds, the SST decreases due to the cooling effect of these winds. Paparella et al, [18] noticed that this weakness occurred in 2012 and 2017. In addition, coral assemblages have been heavily degraded as a result of coastal and marine development activities [20].…”

“…Corals living in symbiosis with unicellular algae are primarily responsible for the formation of tropical shallow water reefs [17]. Corals in the Gulf are the most thermally tolerant in the world, but they live very close to the thresholds of their thermal tolerance [18]. Yet, mass coral bleaching and mortality in 1996 and 1998 were reported in many areas in the Arabian Gulf due to El-Niño related climate change [19].…”

“…Yet, mass coral bleaching and mortality in 1996 and 1998 were reported in many areas in the Arabian Gulf due to El-Niño related climate change [19]. The effect of the Shamal (northern) winds in modulating SST is reported by [18], where during weak Shamal wind the SST was observed to rise and during strong winds, the SST decreases due to the cooling effect of these winds. Paparella et al, [18] noticed that this weakness occurred in 2012 and 2017.…”

“…However, temperature trends in the Gulf are increasing, particularly at the areas of coral reefs, which could exceed the upper tolerability level of these organisms. Coral bleaching is noticeable in some parts of the Gulf [18], and the SSTs are warming in some areas at rates three times the global average [44]. In the Gulf, the shallowness of water, the high salinity, and the extreme seasonal variations in water temperatures are considered to be the major stressors for coral reefs [42].…”

Identifying potentially invasive non‐native marine and brackish water species for the Arabian Gulf and Sea of Oman

“…The RSA, which is bordered by the countries of Bahrain, Iran, Iraq, Kuwait, Oman, Qatar, Saudi Arabia and the United Arab Emirates, has unique environmental features, including a marine environment characterized by extreme oceanographic and meteorological conditions (Riefl et al, 2012;Sale et al, 2011;Van Lavieren et al, 2011;Vaughan, Al-Mansoori, & Burt, 2019). Sea surface temperatures (SST) in the RSA regularly exceed 37°C during the extreme summer months (Paparella, Xu, Vaughan, & Burt, 2019), and mean salinity is 42 ppt, with >50 ppt common in the south and up to 70 ppt in coastal lagoons Wabnitz et al, 2018).…”