Long-term physiological responses to combined ocean acidification and warming show energetic trade-offs in an asterinid starfish

While organismal responses to climate change and ocean acidification are increasingly documented, longer-term (> a few weeks) experiments with marine organisms are still sparse. However, such experiments are crucial for assessing potential acclimatization mechanisms, as well as predicting species-specific responses to environmental change. Here, we assess the combined effects of elevated pCO(2) and temperature on organismal metabolism, mortality, righting activity, and calcification of the coral reef-associated starfish Aquilonastra yairi. Specimens were incubated at two temperature levels (27 degrees C and 32 degrees C) crossed with three pCO(2) regimes (455 mu atm, 1052 mu atm, and 2066 mu atm) for 90 days. At the end of the experiment, mortality was not altered by temperature and pCO(2) treatments. Elevated temperature alone increased metabolic rate, accelerated righting activity, and caused a decline in calcification rate, while high pCO(2) increased metabolic rate and reduced calcification rate, but did not affect the righting activity. We document that temperature is the main stressor regulating starfish physiology. However, the combination of high temperature and high pCO(2) showed nonlinear and potentially synergistic effects on organismal physiology (e.g., metabolic rate), where the elevated temperature allowed the starfish to better cope with the adverse effect of high pCO(2) concentration (low pH) on calcification and reduced skeletal dissolution (antagonistic interactive effects) interpreted as a result of energetic trade-offs.

Automated summary

This study assesses the long-term effects of increased temperature and pCO(2) on the physiology and calcification of a coral reef-associated starfish. The results show that temperature is the main stressor, but the combination of high temperature and high pCO(2) has nonlinear and potentially synergistic effects on organismal physiology.