Abstract
This study investigated the effects of long-term incubation to near-future combined warming (+2 °C) and ocean acidification (−0.3 and −0.5 pH units) stressors, relative to current conditions (−0.3 °C and pH 8.0), on the energetics of food processing in the Antarctic sea urchin, Sterechinus neumayeri. After an extended incubation of 40 months, energy absorbed, energy lost through respiration and lost as waste were monitored through two feeding cycles. Growth parameters (mass of somatic and gonad tissues and the CHN content of gonad) were also measured. There were no significant effects of combined ocean acidification (OA) and temperature stressors on the growth of somatic or reproductive tissue. Despite more food being consumed in the low temperature control, once food processing and maintenance costs were subtracted, there were no significant effects of treatment on the scope for growth. The biggest significant differences were between amounts of food consumed during the two feeding cycles. More food was consumed by the low temperature (0 °C) control animals, indicating a potential effect of the changed conditions on digestive efficiency. Also, in November, more food was consumed, with a higher absorption efficiency, which resulted in a higher scope for growth in November than September and may reflect increased energetic needs associated with a switch to summer physiology. The effect of endogenous seasonal cycles and environmental variability on organism capacity is discussed.
Acknowledgements
Thanks to Paul Geissler for completing the CHN analysis and Tim Brand at SAMS for analysing the urea samples. Also thanks to Andy Clarke for advice on conducting the ammonia assay. We also thank Joelle Richard, Laura Weir and Guy Hillyard for assisting in animal husbandry and carbonate chemistry. The full dataset can be found at http://doi.org/r34.