Resilience and acclimation to bleaching stressors in the scleractinian coral Porites cylindrica
Shakil Visram 1 , Angela E. Douglas ⁎
Department of Biology (Area 2), University of York, PO Box 373, York, YO10 5YW, UK Received 21 November 2006; received in revised form 28 March 2007; accepted17 April 2007
Abstract ‘Resilience’, the capacity of the coral symbiosis with dinoflagellate algal symbionts (‘zooxanthellae’) to recover after bleaching, is a little-studied but crucial aspect of coral responses to bleaching stressors. This study investigated the response of the zooxanthella population in the coral Porites cylindrica after bleaching either naturally on a shallow subtidal reefor experimentally in response to elevated temperature and darkness. Coral resilience was influenced by the nature and duration of the stressor. Corals strongly bleached by natural stressors were less resilient than those that had been partially bleached; and a similar recovery profile was obtained for corals experimentally bleached by exposure to elevated temperature, in which recovery wasslower for corals thermally-stressed 96 h than for 72 h. The opposite trend was evident for corals exposed to darkness, indicating that the bleaching trigger had a strong impact on coral resilience. When P. cylindrica recently recovered from bleaching was subjected to a repetition of bleaching stressors, it did not display acclimation, i.e. experience-mediated acquisition of resistance to bleachingstressors. The zooxanthella populations in all corals tested throughout the experiments were typed by PCR-RFLP as clade C, indicating that coral responses were not accompanied by any substantial change in zooxanthella composition at the cladal level. © 2007 Elsevier B.V. All rights reserved.
Keywords: Acclimatisation; Coral bleaching; Porites cylindrica; Resilience; Symbiodinium; Zooxanthellae1. Introduction Coral bleaching, the paling of tissues resulting from the drastic decline in zooxanthella densities and/or the loss of photosynthetic pigments, is a classic stress response of corals and allied symbiotic marine animals to perturbations in environmental conditions (Glynn, 1993;
⁎ Corresponding author. Tel.: +44 1904 328610; fax: +44 1904 328505. E-mail address: firstname.lastname@example.org(A.E. Douglas). 1 Current Address: CORDIO East Africa, PO Box 10135 Mombasa 80101, Kenya. 0022-0981/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jembe.2007.04.014
Brown, 1997). Among the various triggers of bleaching, elevated seawater temperature often in combination with high irradiance is of global significance (Glynn, 1993; Rowan et al., 1997; Brown et al.,2000), and has been predicted to result in global collapse of coral reef ecosystems by 2050 (Hoegh-Guldberg, 1999). These predictions are based on the simplifying assumption that the bleaching response of corals to elevated temperature is fixed. In principle, however, corals vary in their response to bleaching stressors in three ways: their degree of resistance, resilience and acclimatisation. Adetailed understanding of these three sources of variation is vital to the development of more accurate predictions of impacts of global climate change on coral reefs.
S. Visram, A.E. Douglas / Journal of Experimental Marine Biology and Ecology 349 (2007) 35–44
Resistance refers to the ability of corals to withstand bleaching stressors without bleaching (West and Salm, 2003). It isconvenient to consider resistance as the alternative response to susceptibility, where the coral does bleach; but in reality, corals display a continuum of responses of varying degrees of resistance/susceptibility. Factors contributing to resistance include antioxidant enzymes and fluorescent pigments in the coral (Lesser, 1996, 1997; Salih et al., 2000; Brown et al., 2002a) and physiological...