Abstract: The purpose of this study was to estimate the effects of seawater acidification and elevated temperature on the carbon budget of clam Sinonovacula constricta. Adult clams were exposed to various treatments under conditions of three pH values and three temperatures. The ingestion, respiration, defecation, and excretion of S. constricta were detected. The results showed that the carbon source obtained by S. constricta was mainly consumed through breathing, and then they were directly discharged as dejection, with a small part being discharged by excretion. The remaining carbon was mainly used for growth and development. At 23 ℃, the utilization rate of carbon at pH 8.2 was greater than that at pH 7.6 and pH 7.9. In pH 8.2 seawater, the utilization rate of carbon reached the peak at 23 ℃ when the water temperature ranged from 15 ℃ to 31 ℃. Oneway ANOVA showed that the ingestion rate was significantly influenced by low pH and temperature (P<0.05). In 23 ℃ seawater, with pH declining, S. constricta fed less Isochrysis sphaerica. At pH 8.2, the ingestion rate reached the peak at 23 ℃ when temperature changed from 15 to 31 ℃. Moreover, the oxygen consumption was significantly influenced by low pH and temperature (P<0.05). In 23 ℃ seawater, the respiration rate declined with pH decreasing. At pH 8.2, the respiration rate reached the peak at 23 ℃ when the temperature ranged from 15 ℃ to 31 ℃. However, no significant differences in excretion rate and defecation rate under low pH and temperature were found in this study (P>0.05).

Key words: altitude, litter, P, C, N, soil