Krasnoyarsk scientists have revealed the negative impact of increased salinity on planktonic crustaceans. The study shows that salinity does not affect the hatching success of their resting eggs, but does reduce the survival and reproductive abilities of the crustaceans hatching from them. Thus, an increase in salinity reduces the number of resting zooplankton eggs, which are important for the natural population regeneration. The results of the study were published in the journal Aquatic Ecology.

Freshwater salinization is a global environmental problem associated with increasing salt concentrations in aquatic ecosystems. It is often the result of human activity, including natural resource extraction, agriculture and use of road deicing agents. Salts seep into nearby water bodies through groundwater and runoff, negatively influencing ecosystems, water quality and biodiversity. Increased salinity affects all parts of the aquatic ecosystem, including planktonic crustaceans, which are important for self-purification of water and serve as food for fish.

Most often, the development of populations of planktonic crustaceans in northern latitudes is cyclical. In summer, they typically reproduce rapidly, with females giving birth to live offspring every few days. By autumn, they change their reproductive strategy and form resting eggs in a protective chitinous capsule. It contains an embryo in the early stages of development in an inhibited state. In the spring, young crustaceans hatch from the eggs, and the population repeats the cycle of seasonal development. Such eggs are resistant to various unfavorable conditions, which include increased salinity of water. It is believed that the reserves of resting eggs accumulated at the bottom of the reservoir are a kind of insurance against extinction. They allow the crustaceans to recover when conditions become normal again.

Scientists from the Krasnoyarsk Science Center SB RAS, together with their colleagues, assessed the effect of increased salinity and the age of resting eggs on the survival and fertility of females of one of the widespread species of planktonic crustaceans. The experiment used water salinity levels that did not exceed critical values for the survival of animals and the hatching of resting eggs.

Specialists noted a significant difference in the intensity of hatching of resting eggs of different ages. Older 4-year-old eggs produced fewer individuals than fresher 1-year-old eggs. The researchers concluded that the supply of old eggs is less important for the recovery of the crustacean population. However, the salinity levels used in the experiments did not affect the hatching success of resting eggs.

However, the salinity affected the survival of hatched crustaceans. At the salinity of 3.5 g/l, animal survival rate decreased sharply for both young and old eggs. Females hatched in high salinity conditions had a shorter lifespan, reduced growth rate, and produced fewer clutches and offspring.

“We hypothesize that embryos are sensitive to the effects of increased salinity at an early stage of development. The salinity, which is a stress factor present when the females hatch, affects the life cycle of the crustaceans. Females live half as long and produce fewer offspring. Another important result is that we demonstrated differences in the hatching success of resting eggs of different ages. In addition, females from old eggs were more sensitive to salinity. Our results call into question the widely assumed ability of resting egg banks to ensure the survival of natural populations of crustaceans during temporary salinization of a reservoir and subsequent restoration of water quality. At low salinity, crustaceans still hatch from resting eggs, but they live and reproduce much worse than in fresh water. As a result, the supply of resting eggs is depleted. This may turn out to be critical for the conservation of biodiversity in the context of the global trend of salinization of natural ecosystems,” explained Tatyana Lopatina, Candidate of Biological Sciences, researcher at the Institute of Biophysics SB RAS.

Specialists from the Khakassky State Nature Reserve also took part in the study. The study was supported by the Russian Science Foundation and the Krasnoyarsk Regional Science Foundation (project No. 23-24-10044).