Kate Sparks (1)*, Shawna Foo (2), Sven Uthicke (2), Maria Byrne (3), Miles Lamare (1)
1 Department of Marine Science, University of Otago, Dunedin, New Zealand
2 Schools of Medical and Biological Sciences, University of Sydney, Sydney, New South Wales, Australia.
3 Australian Institute of Marine Science, Townsville, Queensland, Australia
The crown-of-thorns sea star Acanthaster planci is a key predator on the Great Barrier Reef, and is thought to be responsible for up to 42% of coral cover loss worldwide. A. planci populations on the Great Barrier Reef follow a periodic ‘outbreak’ cycle during which large areas of coral reef can be decimated. These are thought to be primarily driven by an increase in food availability linked to warming water temperatures. The pattern of future Acanthaster outbreaks, and therefore the health of the Great Barrier Reef, are likely linked to how A.planci larvae cope with ocean acidification and warming.
This study used a quantitative genetic approach and a modified North Carolina II breeding design to examine the range of A.planci genotypes expressed in response to combined ocean warming and acidification. Interactions between genotype and environment were tested using a permutational multivariate ANOVA and Restricted Error Maximum Likelihood (REML) calculations of variance. Response ratios were calculated for offspring of each dam/sire pair across all treatments.
High temperature (32°C) and pCO2 (900ppm) both reduced normal development at 16-cell cleavage stage. At gastrulation, temperature had a significant negative effect on development, but pCO2 did not. Sire identity, and the interactions between temperature and pCO2, generated significant variation in offspring gastrulation success, however no equivalent interaction between maternal genotype and environment was seen. Response ratios indicated that most larvae exhibit highest gastrulation success in ‘present-day’ conditions. However, additive genetic variance (from sire x environment interactions) indicated that a sub-set of individuals develop best in both high temperatures and high pCO2.
The capacity to tolerate high temperatures and high pCO2 is a trait which is dependent on both genetic identity and environment. Larval tolerance to environmental changes and genotypic variation make A.planci an evolutionary ‘winner’ in a climate change scenario.