Many zooplankton organisms produce resting eggs before harsh environmental conditions. After aquatic systems are recovered, animals hatch from resting eggs and help re-establish active communities. However, although the ability of resting eggs to survive desiccation is largely known, it is unclear to what extent the duration of desiccation affects the viability and hatching patterns of resting eggs. In this study, we assessed the viability of resting egg banks in naturally wet and dry sediments through ex-situ hatching experiments. In addition, we simulated dry out episodes of different durations (2 and 8 months) in wet sediments originating from temporary systems. We observed hatchlings of rotifers, cladocerans, copepods, ostracods, and anostracans in wet and dry sediments. Drying the sediments for different durations did not change the species richness and composition of hatchlings, possibly because temporary systems select for species and genotypes that are more prone to producing resting eggs, which survive desiccation. However, some species were stimulated to hatch after desiccation, suggesting that desiccation might help break the dormancy of resting eggs from temporary systems. Desiccation intervals up to 8 months likely do not affect the viability of resting eggs from temporary systems. Since many lakes are about to experience unpredictable droughts owing to human activities and ongoing global changes, the ability of resting eggs to tolerate desiccation will play a key role in zooplankton community recovery. K E Y W O R D S diapause, dormancy, drought, resilience, zooplankton 1 | INTRODUCTION Climate combined with river and lake features usually determine the probability of droughts in aquatic systems. Droughts are commonly observed in arid and semi-arid regions and in areas with strong seasonality in precipitation. Overall, shallow lakes and ponds and small aquatic systems, such as rock pools, are more prone to drought episodes. Moreover, the damming and regulation of rivers, water diverted from rivers and lakes, and ongoing changes in precipitation and temperature patterns may also reduce water availability, SUPPORTING INFORMATION Additional supporting information may be found online in the Supporting Information section at the end of the article. How to cite this article: Vargas AL, Santangelo JM, Bozelli RL. Recovery from drought: Viability and hatching patterns of hydrated and desiccated zooplankton resting eggs. Internat Rev Hydrobiol. 2019;104:26-33.

Many former permanent aquatic habitats now face occasional desiccation due to human activities. Zooplankton might recover from droughts after the hatching of resting eggs, but how desiccation duration affects the viability and hatching patterns of resting eggs is unclear. This study evaluated how desiccation of varying durations (0, 3, 6 and 9 months) affects the hatchling numbers of the freshwater calanoid Notodiaptomus iheringi inhabiting a permanent lake. Hatchlings were observed across all desiccation treatments, and hatchling abundance was higher in longer desiccation treatments. Resting eggs of N. iheringi survive desiccation for up to 9 months even though the tested population originated from sediments of a permanent lake. Desiccation may stimulate hatching by terminating dormancy and by weakening (wet) sediment adversity. Knowledge of the hatching patterns of resting eggs of varying taxa after desiccation can help to understand how zooplankton communities recover after droughts.

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We characterized the functional and taxonomic composition of the active and dormant communities from perennial lagoons and temporary ponds in a coastal plain. We sought to determine the degree of coherence between the egg bank and the active community within the same type of environment (temporary or perennial) and between environments subject to different hydrological cycles. We sampled the zooplankton community and environmental variables in six temporary ponds and five perennial lagoons in the dry and the wet periods of the hydrological cycle. Temporary ponds and perennial lagoons differed in abiotic conditions, with higher values of dissolved carbon in temporary ponds and higher values of salinity in perennial lagoons. The taxonomic coherence between active and dormant communities in temporary environments was greater than in perennial environments. In functional terms, we observed a high coherence between active and dormant communities for both types of environments. Our results highlight the need to conserve both temporary and perennial environments to assure the maintenance of zooplankton diversity. Although these environments are subject to the same set of climatic variables and pool of species, their idiosyncrasies are important forces promoting and sustaining biological diversity.