Larval development, juvenile survival, and burrowing rate of geoduck clams (Panopea japonica) under different pH conditions

Abstract

Changes in seawater pH in the culture environment have numerous effects on marine bivalves. To investigate the effect of pH on larval development, juvenile survival, and burrowing rate of geoduck clams (Panopea japonica), specimens were cultured under different experimental pH conditions (6.8, 7.2, 7.6, 8.0, 8.4, and 9.2). The pH range for optimal growth and development differed among different larval stages. However, significant changes in larval development (p < 0.5) relative to the control (pH 8.0) were detected at very high or low pH. The best hatching rate occurred at pH 7.6–8.8, and it was significantly lower (p < 0.5) at pH 6.8, 7.2, and 9.2. Larval survival was only 4% at pH 6.8. Growth rate of larvae increased with increasing pH and the optimal range was 8.0 to 8.8. This finding suggests that alkaline conditions favor growth and development of larvae and allow them to reach the metamorphic stage promptly. Prolonged metamorphosis was a common feature in larvae in the different experimental pH groups. pH below 7.6 and above 8.8 resulted in a significantly (p < 0.5) lower metamorphosis rate, suggesting that high acidity and alkalinity were deleterious to larval metamorphosis. Thus, the suitable pH range for metamorphosis was 8.0 to 8.8. Lower and higher pH also affected the digging behavior of geoduck clams, and the suitable pH range for burrowing was 7.2 to 8.8. Geoduck clams stopped burrowing in the sand at pH 6.8 and 9.2, possibly due to impairment of biological process caused by acidic and alkaline seawater. These findings provide valuable information about the larval and juvenile responses of P. japonica in variable pH.