Abstract
Coral bleaching events due to elevated temperatures are increasing in both frequency and magnitude worldwide. Mass bleaching was recorded at five sites in the northern Persian Gulf during August and September 2012. Based on available seawater temperature data from field, satellite and previous studies, we suggest that the coral bleaching threshold temperature in the northern Persian Gulf is between 33.5 and 34°C, which is about 1.5 to 2.5°C lower than that in the southern part. To assess the bleaching effects, coral genera counted during 60-minute dives were categorized into four groups including healthy, slightly bleached ( 50% bleached tissue) and fully bleached colonies. The anomalously high sea surface temperature resulted in massive coral bleaching (~84% coral colonies affected). Acropora spp. colonies, which are known as the most vulnerable corals to thermal stress, were less affected by the bleaching than massive corals, such as Porites , which are among the most thermo-tolerant corals. Turbid waters, suggested as coral refugia against global warming, did not protect corals in this study since most affected corals were found in the most turbid waters. The 2012 bleaching in the northern Persian Gulf was relatively strong from the viewpoint of coral bleaching severity. Long-term monitoring is needed to understand the actual consequences of the bleaching event on the coral reefs and communities.
Highlights
Loss of symbiotic algae and/or their photosynthetic pigments by zooxanthellate reef-builders is considered a major threat for coral reefs worldwide (Lesser 2011), especially because large-scale bleaching events have been related to global warming (Goreau and Hayes 1994, 2005)
This paper studies the spatial variation in bleaching susceptibility of corals from some Iranian islands in the northern and central Persian Gulf during a coral bleaching event observed in 2012
From the analysis of temperature data sets available, we suggest 33.5 to 34°C as the coral bleaching threshold temperature in the northern Persian Gulf, which is about 1.5 to 2.5°C lower than the threshold suggested for the southern part of the Gulf (35 to 36°C)
Summary
Loss of symbiotic algae (zooxanthellae) and/or their photosynthetic pigments by zooxanthellate reef-builders is considered a major threat for coral reefs worldwide (Lesser 2011), especially because large-scale bleaching events have been related to global warming (Goreau and Hayes 1994, 2005). Coral bleaching events have increasingly affected coral reefs on a global scale in recent years (Goreau and Hayes 1994, 2005, Coles and Brown 2003, Meissner et al 2012). The most destructive global coral bleaching events reported have occurred worldwide in the last three decades (Goreau and Hayes 1994, 2005, Goreau et al 2000, Wilkinson 2004, 2008, Riegl et al 2011, Guest et al 2012), including in the Persian Gulf (Rezai et al 2004, Riegl and Purkis 2009, Riegl et al 2011)
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