Variation in the size structure of corals is related to environmental extremes in the Persian Gulf Andrew G. Bauman a, * , Morgan S. Pratchett a , Andrew H. Baird a , Bernhard Riegl b , Scott F. Heron c, d , David A. Feary e a ARC Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, QLD 4811, Australia b National Coral Reef Institute, Nova Southeastern University, Dania, FL, USA c Coral Reef Watch, National Oceanic and Atmospheric Administration, Townsville, QLD 4811, Australia d Marine Geophysical Laboratory, Physics Department, School of Engineering and Physical Sciences, James Cook University, Townsville, QLD 4811, Australia e School of the Environment, University of Technology, Sydney, New South Wales, Australia article info Article history: Received 31 July 2012 Received in revised form 14 November 2012 Accepted 18 November 2012 Keywords: Coral reefs Arabian Gulf Coral bleaching Climate change Disturbance Effects-population abstract The size structure of coral populations is the culmination of key demographic events, including recruitment, mortality and growth, thereby providing important insights to recent ecological dynamics. Importantly, the size structure of corals reflects both intrinsic (inherent life-history characteristics) and extrinsic (enhanced mortality due to chronic or acute disturbances) forcing on local populations, enabling post-hoc assessment of spatial and taxonomic differences in susceptibility to disturbance. This study examined the size structure of four locally abundant corals (Acropora downingi, Favia pallida, Platygyra daedalea, and massive Porites spp.) in two regions of the Persian Gulf: the southern Gulf (Dubai and Abu Dhabi) and eastern Gulf (western Musandam). Significant and consistent differences were apparent in mean colony sizes and size-distributions between regions. All corals in the southern Gulf were significantly smaller, and their size structure positively skewed and relatively more leptokurtic (i.e., peaky) compared to corals in the eastern Gulf. Sea surface temperatures, salinity, and the recent frequency of mass bleaching are all higher, in the southern Gulf, suggesting higher mortality rates and/or slower growth in these populations. Differences in size structure between locations were more pronounced than differences between species at each location, suggesting that extreme differences in environmental conditions and disturbance events have a greater influence on population dynamics in the Gulf than inherent differences in their life-history characteristics. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Scleractinian corals are fundamental to the biodiversity and function of coral reef ecosystems (Connell, 1978; Done et al., 1996). Yet, coral reef ecosystems are among the most threatened aquatic ecosystems (Hoegh-Guldberg and Bruno, 2010), and increasingly being degraded through multiple disturbances (e.g., over-fishing, coastal pollution, disease) that are becoming more frequent and severe (Hughes et al., 2003). Moreover, these enduring distur- bances are now being increasingly compounded by the more recent impacts of global climate change (Hughes et al., 2003; Bellwood et al., 2004). Over the next century, global sea surface temperatures (SSTs) are predicted to increase by at least 2  C(Parry et al., 2007). Consequently, fluctuations in a range of environmental variables are predicted to affect the growth rate, growth form, reproductive capacity of corlas (Brown, 1997; Kleypas et al., 1999), which are likely to directly impact the overall abundance, compo- sition and diversity of reef communities (Done, 1999; Baker et al., 2008), and may lead to further degradation of these reef systems globally (Hughes et al., 2003). Unless corals are able to adapt to changing environmental conditions, and predicted increases in the frequency and severity of coral bleaching events (Donner et al., 2005), benthic reef assemblages may ultimately become domi- nated by macroalgae (Hughes et al., 2010) or other non-coral organisms (Norström et al., 2009). Assessment of demographic consequences of time-varying influences of the environment, including the intensity and frequency of disturbance events requires long-term quantitative * Corresponding author. Tel.: þ61 467487757; fax: þ61 747816722. E-mail address: Andrew.Bauman@my.jcu.edu.au (A.G. Bauman). Contents lists available at SciVerse ScienceDirect Marine Environmental Research journal homepage: www.elsevier.com/locate/marenvrev 0141-1136/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.marenvres.2012.11.007 Marine Environmental Research 84 (2013) 43e50