Juvenile Atlantic sea scallop, Placopecten magellanicus, energetic response to increased carbon dioxide and temperature changes

Abstract

This study assessed the energy budget for juvenile Atlantic Sea Scallop,Placopecten magellanicus, during a natural drop in temperature (15.6°C to 5.8°C) over an 8-week time period during the fall at three different enrichment levels of carbon dioxide (CO2). Every 2 weeks, individuals were sampled for ecophysiological measurements of feeding activity, respiration rate (RR) and excretion rate (ER) to enable the calculation of scope for growth (SFG) and atomic oxygen:nitrogen ratios (O:N). In addition, 36 individuals per treatment were removed for shell height, dry tissue weight (DTW) and dry shell weight (DSW). We found a significant decrease in feeding rates as CO2increased. Those rates also were significantly affected by temperature, with highest feeding at 9.4°C. No significant CO2effect was observed for catabolic energy processes (RR and ER); however, these rates did increase significantly with temperature. The O:N ratio was not significantly affected by CO2, but was significantly affected by temperature. There was a significant interaction between CO2and temperature for ER and the O:N ratio, with low CO2levels resulting in a U-shaped response that was not sustained as CO2levels increased. This suggests that the independent effects of CO2and temperature observed at low levels are different once a CO2threshold is reached. Additionally, there were significant differences in growth estimators (shell height and DSW), with the best growth occurring at the lowest CO2level. In contrast to temperature variations that induced a trade-off response in energy acquisition and expenditure, results from this research support the hypothesis that sea scallops have a limited ability to alter physiological processes to compensate for increasing CO2.