Effects of acid stress on life history traits of Eodiaptomus japonicus (Copepoda: Calanoida) from Lake Biwa, Japan

This study assessed the life history traits of Eodiaptomus japonicus when exposed to acid stress under a sufficient food supply. We aimed to evaluate the population dynamics of freshwater copepods in response to acidification. This was accomplished by determining somatic growth and fecundity under three pHs (6.0. 6.8 and 7.8) representing strong, weak and in situ proton stress levels, respectively. We observed similar post-embryonic development times and somatic growth until adulthood in all three treatments. However, acid stress lowered survival rates to <20% by adulthood, even at a mildly acidic pH of 6.8. The naupliar stages were more vulnerable to acid stress than the copepodid stages. Depressed female ratios under low pH indicated unfavorable conditions for population growth. Acid-stressed conditions had negative effects on copepod reproduction, such as delayed embryonic development, prolonged interclutch duration and reduced egg production rate. Population growth rate significantly declined as the pH decreased, primarily because of the decrease in survival rate, clutch size and prolonged interclutch duration. Eodiaptomus japonicus appears to prioritize somatic growth maintenance and survival over offspring production. Overall, our analysis revealed a potential 2.9% decrease in E. japonicus population growth for every 0.1 unit decrease in pH when food availability is not limiting.