Abstract:Ocean acidification is one of the major changes in marine ecosystem in this century. This has a negative effect on the fertilization, development, growth, and survival of marine mollusks. Presently, physiological effects of ocean acidification on some economic shellfish are not clear. To study the effects of ocean acidification on the physiological ecology of economic shellfish is of great significance for environmental science, ecology, and aquaculture. The feeding, respiratory metabolism, and energy budget of Scapharca broughtonii at different pH levels (pH 8.2~7.6) were studied in the laboratory. The results showed that the feeding and defecation rates of S. broughtonii were significantly (P<0.05) affected by pH, and there was a declining trend on the feeding and defecation rates with a decrease in pH value. The oxygen consumption rate was also significantly (P<0.05) affected by pH, showing an obvious downward trend with decreasing pH value. There was an initial decrease in ammonia excretion rate, which then increased with a decrease in pH value. O : N ratio at low pH value was lower than that of normal seawater, indicating that low pH value could inhibit the respiratory metabolism of S. broughtonii to some extent. The energy budget at different pH values indicated that energy ingestion, respiratory consumption, fecal energy loss, and energy absorbed in the growth process all decreased with a decrease in pH value. Interestingly, energy loss during excretion decreased first and then increased. According to energy budget equation, we found that pH had a significant effect on energy distribution of S. broughtonii (P<0.05). As the pH value decreases, the proportion of energy consumed during respiration and excretion increases, while the proportion involved in excrement and growth decreases. Under low pH conditions, S. broughtonii will make appropriate physiological adjustments to reduce the feeding rate and increase the metabolic rate, resulting in a decrease in energy, which leads to a decrease in energy deposition in the growth process. This study suggested that the feeding and metabolism of S. broughtonii decreased significantly under short-term acidification, which may be a synergistic effect of increased cell energy demand and nitrogen loss.
