Abstract:Intertidal bivalves experience broad fluctuations of abiotic factors including pH, salinity and temperature, which could affect their physiology and biochemistry. They are also exposed to trace metals such as copper (Cu) and cadmium (Cd) that accumulate in their tissues and may negatively affect respiration and cardiac activity. Therefore, understanding the impact of pH and heavy metals on intertidal bivalve physiology is of prime importance especially in the context of global ocean acidification. We determined the interactive effects of low pH (7.7 and 7.3) and the addition of heavy metals (Cu or Cd) on the physiological functions including oxygen consumption rate (OR), filtration rate (FR) and heart rate of a common intertidal bivalve, Ruditapes philippinarum. The experiment was conducted under laboratory conditions with pH 8.2 as the control treatment. Addition of Cu at concentrations of 0.06 and 0.60 mg/L suppressed OR, FR, and heart rate (P<0.05). The clams’ heart rate decreased from 23.8 bpm (beats per minute) to 10.5 bpm after being exposed to 0.06 mg/L Cu for 20 min. No significant effect of Cd (0.03, 0.30 mg/L) was found on OR or FR (P>0.05), however clams incubated in the 0.30 mg/L Cd group had a significantly higher heart rate (39.0 bpm) than the control (25.3 bpm) (P<0.05). Low pH had no effect on OR and FR (P>0.05), but clams´ heart rate in the pH 7.3 treatment decreased at the beginning of incubation and recovered rapidly. Our findings suggest that short-term exposure to Cu, Cd, or low pH, all impact the cardiac activity of clams, and the order of toxicity was Cu>Cd>pH. Heart rate was a more sensitive endpoint than OR and FR. There were no interactive effects of low pH and Cu or Cd on the respiration of clams. Our study provides referential data for studying the response of intertidal bivalves to heavy metal exposure and ocean acidification, which may be helpful in the prevention and biological reparation of potential heavy metal pollution in coastal areas.
