Hidden Resilience: How Resting Egg Banks Shape Zooplankton Diversity Across Salinity Gradients in Neighbouring Lakes

ABSTRACT Resting egg banks are crucial for the restoration and stability of zooplankton communities in aquatic ecosystems. In geographically adjacent lakes with varying salinities, bottom sediments harbour resting eggs of species adapted to different salinities, which can enhance the stability and functioning of the zooplankton metacommunity amid changing environmental conditions. To evaluate the capacity of resting egg banks to restore and sustain zooplankton communities under fluctuating salinities, we compared zooplankton diversity across four closely located lakes with salinities of 0.9 g L −1 , 2.3 g L −1 , 3.4 g L −1 , and 5.1 g L −1 . We conducted a series of experiments using resting eggs collected from the bottom sediments of these lakes, placing eggs from each lake into each of the four salinity treatments. We then compared the diversity of resulting zooplankton communities with natural communities and between lakes. The species diversity of zooplankton in natural samples was not consistently lower than that derived from resting egg banks. In two small, fishless, nutrient‐rich lakes, the diversity of zooplankton established from resting eggs exceeded that of natural communities. Conversely, in larger lakes with fish populations, natural samples exhibited greater diversity than those from resting eggs. The maximum species diversity of zooplankton established from resting eggs occurred at salinities corresponding to those of the originating lakes. Furthermore, increasing salinity (salinization) adversely affected zooplankton communities derived from less saline lakes—resulting in decreased species diversity, biomass, and ability to control phytoplankton abundance—more than decreasing salinity (desalinization) affected communities from more saline lakes. Notably, zooplankton communities formed at similar salinities from different lakes displayed distinct differences. The highest species diversity was recorded in natural samples from the largest and least saline lake, as well as in the zooplankton community established from resting eggs from the smallest lake and one exhibiting significant water level variability over recent decades. These results show that the species diversity of both active and resting stages of zooplankton in geographically proximate lakes with differing salinities can significantly overlap due to resting egg banks. Additionally, factors such as lake size, trophic status, and food web structure are also associated with the species diversity of active zooplankton. Importantly, even a small lake perceived to have low ecological and economic value—such as a nutrient‐polluted fishless lake—can serve as a reservoir of hidden biodiversity within its resting egg bank. This study enhances our understanding of the mechanisms underpinning aquatic ecosystem resistance to salinization, the structure and maintenance of zooplankton species diversity, and contributes to the theory of metacommunities.