Background
The authors write that "whether corals can adapt to increasing temperatures over the course of generations will depend in part on heritable variation in thermal physiology and dispersal potential, which may serve as the raw material for natural selection."

What was done
Meyer et al. "performed controlled crosses between three genetically distinct colonies of the branching coral Acropora millepora," after which they "compared the families of larvae (which in this species naturally lack symbionts) for several physiological traits." This work was conducted at two different water temperatures - the standard culturing temperature of 28°C and an elevated temperature of 32°C - as well as an even higher temperature of 34°C that was maintained for two full days.

What was learned
The U.S., Canadian and Australian researchers confirmed the existence of phenotypic variance for several pertinent thermal and dispersive factors among the families of coral they studied, which finding, in their words, "suggests the existence of considerable heritable variation in natural coral populations," which in turn supports "the possibility of effective adaptive responses to climate change." In addition, they report that other analyses of the species they studied have found "high levels of genetic diversity both within and between reefs (Smith-Keune and van Oppen, 2006)," and that "studies in other coral species have also uncovered substantial genetic diversity within populations (Ayre and Hughes, 2000; Underwood, 2009; Wang et al., 2009)."

What it means
Myer et al. conclude that "additive genetic variance exists within coral populations for several traits that might reasonably be expected to have fitness consequences during global climate change," which finding, as they describe it yet again, "supports the possibility of effective adaptive responses to climate change."

References
Ayre, D.J. and Hughes, T.P. 2000. Genotypic diversity and gene flow in brooding and spawning corals along the Great Barrier Reef, Australia. Evolution 54: 1590-1605.

Smith-Keune, C. and van Oppen, M. 2006. Genetic structure of a reef-building coral from thermally distinct environments on the Great Barrier Reef. Coral Reefs 25: 493-502.

Underwood, J.N. 2009. Genetic diversity and divergence among coastal and offshore reefs in a hard coral depend on geographic discontinuity and oceanic currents. Evolutionary Applications 2: 222-233.

Wang, S., Zhang, L. and Matz, M. 2009. Microsatellite characterization and marker development from public EST and WGS databases in the reef-building coral Acropora millepora (Cnidaria, Anthozoa, Scleractinia). Journal of Heredity 100: 329-337.