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Reef-Building Corals Acclimating to Elevated Water Temperatures
Mayfield, A.B., Fan, T.-Y. and Chen, C.-S. 2013. Physiological acclimation to elevated temperature in a reef-building coral from an upwelling environment. Coral Reefs 32: 909-921.

The authors write that "recent work has found that pocilloporid corals from regions characterized by unstable temperatures, such as those exposed to periodic upwelling, display a remarkable degree of phenotypic plasticity," and they say that "some recent works have shown that not all corals bleach, or even manifest signs of stress, at elevated temperatures predicted to characterize reefs in the coming decades (Barshis et al., 2013)," while simultaneously noting that "corals from highly variable temperature environments of both American Samoa (Oliver and Palumbi, 2011) and southern Taiwan (Mayfield et al., 2011, 2013) have previously been shown to withstand exposure to temperatures (e.g., 30-31°C) that induce bleaching or even mortality in conspecifics from other regions (Jokiel and Coles, 1990; Brown, 1997)."

What was done
"To uncover the long-term impacts of elevated temperature exposure to corals from reefs that experience episodic upwelling," as Mayfield et al. describe it, a mesocosm-based experiment was conducted whereby P. damicornis specimens collected from an upwelling coral reef on Houbihu (a small embayment within Nanwan Bay, southern Taiwan) were exposed for nine months to nearly 30°C, a temperature that the corals normally encounter in situ for just a few hours per year (Mayfield et al., 2012).

What was learned
Quoting the three researchers, "upon nine months of exposure to nearly 30°C, all colony (mortality and surface area), polyp (Symbiodinium density and chlorophyll a content), tissue (total thickness), and molecular (gene expression and molecular composition)-level parameters were documented at similar levels between experimental corals and controls incubated at 26.5°C, suggesting that this species can readily acclimate to elevated temperatures that cause significant degrees of stress, or even bleaching and mortality, in conspecifics of other regions of the Indo-Pacific."

What it means
In light of their findings, as well as those of other scientists studying the subject, Mayfield et al. say "there is now a growing body of evidence to support the notion that corals inhabiting more thermally unstable habitats outperform conspecifics from reefs characterized by more stable temperatures when exposed to elevated temperatures," citing Coles (1975), Castillo and Helmuth (2005) and Oliver and Palumbi (2011). And they report that "in other systems, provocative gene expression changes, such as the constitutive up-regulation of genes involved in thermotolerance (e.g., hsps; Heath et al., 1993; Feder, 1996), underlie the capacity for organisms to inhabit high and/or variable temperature environments," such as has more recently been documented in corals by Barshis et al. (2013).

Barshis, D.J., Ladner, J.T., Oliver, T.A., Seneca, F.O., Traylor-Knowles, N. and Palumbi, S.R. 2013. Genomic basis for coral resilience to climate change. Proceedings of the National Academy of Sciences USA 110: 1387-1392.

Brown, B.E. 1997. Coral bleaching: causes and consequences. Coral Reefs 16S: 129-138.

Castillo, K.D. and Helmuth, B.S.T. 2005. Influence of thermal history on the response of Montastraea annularis to short-term temperature exposure. Marine Biology 148: 261-270.

Coles, S. 1975. A comparison of effects of elevated temperature versus temperature fluctuations on reef corals at Kahe Point, Oahu. Pacific Science 29: 15-18.

Feder, M. 1996. Ecological and evolutionary physiology of stress proteins and the stress response: the Drosophila melanogaster model. In: Johnston, I.A. and Bennett, A.F. (Eds.). Animals and Temperature: Phenotypic and Evolutionary Adaptation. Cambridge University Press, Cambridge, United Kingdom, pp. 79-102.

Heath, A.G., Turner, B.J. and Davis, W.P. 1993. Temperature preferences and tolerances of three fish species inhabiting hyper-thermal ponds on mangrove islands. Hydrobiologia 259: 47-55.

Jokiel, P.L. and Coles, S.L. 1990. Response of Hawaiian and other Indo Pacific reef corals to elevated temperatures. Coral Reefs 8: 155-162.

Mayfield, A.B., Chan, P.H., Putnam, H.P., Chen, C.S. and Fan, T.Y. 2012. The effects of a variable temperature regime on the physiology of the reef-building coral Seriatopora hystrix: results from a laboratory-based reciprocal transplant. Journal of Experimental Biology 215: 4183-4195.

Mayfield, A.B., Chen, M., Meng, P.J., Lin, H.J., Chen, C.S. and Liu, P.J. 2013. The physiological response of the reef coral Pocillopora damicornis to elevated temperature: results from coral reef mesocosm experiments in southern Taiwan. Marine Environmental Research 86: 1-11.

Mayfield, A.B., Wang, L.H., Tang, P.C., Hsiao, Y.Y., Fan, T.Y., Tsai, C.L. and Chen, C.S. 2011. Assessing the impacts of experimentally elevated temperature on the biological composition and molecular chaperone gene expression of a reef coral. PLOS ONE 6: e26529.

Oliver, T.A. and Palumbi, S.R. 2011. Do fluctuating temperature environments elevate coral thermal tolerance? Coral Reefs 30: 429-440.

Reviewed 19 February 2014