Salinity sensitivity of Moina macrocopa post-diapause females hatched from resting eggs of different ages

Worldwide freshwater salinization may significantly alter ecosystem functioning and affect biodiversity. We studied the effect of salinity on hatching success of resting eggs of different ages and life history traits of post-diapause females of cladoceran Moina macrocopa. The hatching success of resting eggs was almost unaffected by the salinity we tested (up to 5.9 g L⁻¹). We observed a distinct difference in the hatching success of resting eggs of different ages, which was lower by ca. 50% for 4-year-old resting eggs compared with 1-year-old resting eggs. We found a decrease in the values of the life-history traits of the females hatched from 4-year-old resting eggs compared with the females hatched from 1-year-old resting eggs exposed to salinity within the range of 0.08–3.5 g L⁻¹: a shorter lifespan, a lower juvenile somatic growth rate, a delay in the day of the first reproduction, and a smaller number of parthenogenetic clutches produced. Analysis showed that at a salinity of 3.5 g L⁻¹, females hatched from resting eggs are more vulnerable to the effect of salinity than directly developing females. The post-diapause females exposed to salinity showed a shorter lifespan and reduced reproduction parameters (produced fewer clutches and neonates) compared with the directly developing females. Thus, the hatching of resting eggs can be considered as a critical period of the development of a species with the diapause in its life cycle due to the vulnerability of post-diapause females to increased salinity, which can be crucially important for the ecological success of the population.