Effect of extreme pH levels on early larval stages of the Pacific abalone (Haliotis discus hannai Ino, 1953)

Abstract

Seawater pH, which can be altered by human activity-induced pollution, potentially affects developmental processes at the early larval stages of Pacific abalone (Haliotis discus hannai). This study aimed to examine the effects of extreme seawater pH on these stages in Pacific abalone. Abalone eggs and larvae were exposed to five pH levels (pHs 6, 7, 8, 9, and 10), and several parameters were measured: hatching rate, malformation rate, larval length, DNA damage, oxygen consumption rate, settlement rate, and expression levels of two biomineralization genes (calmodulin and carbonic anhydrase) and one heat stress gene (heat shock protein 90, HSP90). Hatching rates decreased under low (pH 6) and high (pH 9 and 10) pH levels, compared to the control (pH 8). Extremely low and high pHs significantly affected larval length, malformation rate, and DNA damage (p < 0.05). At 20 hours post-fertilization (hpf), the oxygen consumption rate was significantly decreased only at pH 6 (p < 0.05). However, at 30 hpf, a significant reduction in the oxygen consumption rate was observed only at pHs 9 and 10 (p < 0.05). The settlement rate decreased significantly only at pH 10 (p < 0.05). Seawater pH affected carbonic anhydrase gene expression in larvae at 30 hpf, but not at 20 hpf, while calmodulin and HSP90 gene expression remained unchanged. In conclusion, extremely acidic and alka line seawater pHs severely disrupt early larval development in Pacific abalone.