Emily Shaw (1)*, Peter Edmunds (1), Robert Carpenter (1), Coulson Lantz (1)
1 Department of Biology, California State University, Northridge, California, 91330, USA
Calcification in several species of reef-building corals has been shown to be sensitive to future ocean pH and temperature conditions. This has raised concerns that warming and acidification will lead to a shift in reef community composition. However, future population trajectories of corals will depend on whether there is genetic variability for which natural selection can occur. Whilst there is evidence showing different responses between species to elevated CO2 (resulting in “winners and losers”), we have little understanding of intraspecific variation in the response of coral calcification to ocean acidification.
In this study we documented intraspecific variability of in situ growth rates of corals in Moorea, French Polynesia. We also performed a common garden experiment on genotypes of the coral Acropora pulchra to determine intraspecific variability in the response of calcification to elevated temperature (27 and 30°C) and CO2 treatments (ambient and ~1000μatm).
In situ surveys showed large intraspecific variation in the growth rate of corals on the reef at Moorea. Similarly, we found significant differences in calcification rates of different genotypes of A. pulchra under control conditions. All genotypes showed a negative calcification response to high CO2, however, the temperature response was variable with some genotypes significantly affected and others not.
We show that genotypes of a single species can respond to future temperature and CO2 conditions differently compared with the mean response for the same species. Wide intraspecific variation in growth rates of corals in situ indicates that similar variation occurs on the reef. Understanding intraspecific genetic variation is important for determining how populations will respond to global change and should be investigated further in other species. Just as there will likely be winning and losing species in a high-CO2 ocean, there will also be winning and losing genotypes that can fuel evolutionary change.