Resistance Of Dormant Eggs Of Cladocera To Anthropogenic Pollutants

Many Cladocera species under unfavourable conditions produce resting eggs that can survive for years in deep diapause. Resting eggs form egg banks at the bottom sediments, which serve as a source of genetic diversity and replenish the population after periods of decline. Despite the obvious importance of resting eggs for the ecosystem functioning, studies assessing the sensitivity of resting eggs to different toxicants are scarce. We reviewed published data on the sensitivity of resting eggs to the effect of heavy metals, organic pollutants and ionizing radiation. Analysis shows that the effects of toxicants of different types on resting eggs will have different environmental consequences. Egg banks may suffer from prolonged contact of dormant eggs with heavy metals. However, the ecological relevance of these effects is low, since the effective concentrations of toxicants must be very high. In addition, the effect of heavy metals on resting eggs is not transmitted to hatchlings from exposed eggs. Taking into account high toxicity of heavy metals to active animals, we assume that the toxic effect of heavy metals is critical for active zooplankters and relatively safe for resting stages. Accumulation of artificial radionuclides in bottom sediments can have a significant impact on aquatic ecosystems through chronic effects both on survival of resting eggs and on the life cycle parameters of animals hatched from irradiated eggs. Resting eggs during reactivation are more sensitive to the effect of ionizing radiation. Pesticides and complex chemical compounds produce similar toxic effects on both resting eggs and life history parameters of hatchlings from exposed resting eggs. The bottom line is that to predict the effect of contamination of bottom sediments by different pollutants on the ecosystem structure and functioning, it is highly important to investigate the viability of the resting eggs under a wide range of concentrations of various toxicants and different durations of direct contact of eggs with toxicants.