Recovery from drought: Viability and hatching patterns of hydrated and desiccated zooplankton resting eggs

Abstract

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.

Long‐term droughts change the hatching patterns of zooplankton resting eggs from permanent and temporary lakes

“…In addition, tolerance to 1-year desiccation was observed in the cladoceran I. spinifer and the ostracod B. gwelupensis originating from seasonal wetlands (Strachan et al, 2016a). Our results for temporary lakes in this study differ also from results for a set of temporary lakes where no changes in species richness and increased abundance were observed after egg banks were desiccated for 8 months (Vargas et al, 2019) TA B L E 4 PERMDISP results for the effects of lake category (permanent and temporary lakes) and sediment type (wet and dry sediments) on the hatchling communities.…”

“…For example, considering all taxonomic groups, species richness in the egg bank varied from one to 11, and from one to 18, in a set of five permanent and five temporary habitats, respectively (Araújo et al, 2013). Later, seven and 16 taxa were observed in a set of four permanent and four temporary lakes, respectively (Vargas et al, 2019) Hairston Jr et al, 1995), and long-term storage (9 months) of sediments with their water content might reduce the number of hatchlings in some species (Brazil et al, 2022).…”

“…At the community level, Ilyocryptus spinifer (Cladocera) and Bennelongia gwelupensis (Ostracoda) hatched from seasonal wetland sediments that remained dry for 1 year (Strachan et al., 2016a). More recently, one study developed in a set of temporary lakes has shown that the abundance of hatchlings may increase if sediments are previously desiccated for 8 months (Vargas et al., 2019), whereas no similar studies have been conducted in permanent lakes. Given such contrasting results, desiccating sediments may decrease the abundance and species richness of hatchling communities if some resting eggs fail to hatch as a consequence of previous desiccation, especially in permanent habitats.…”

Using topsoil translocation from natural wetlands to restore rice field systems

“…Some zooplankton animals, in particular rotifers and crustaceans, have dormancy capability (i.e. long-term resistant stages) that enables them to survive periods of unfavorable conditions (Fontaneto 2019;Vargas et al 2019). Thus, such dormant stages are crucial for colonization processes and community dynamics in freshwater wetlands, especially temporary ones (Shurin 2000;Badosa et al 2017;Brendonck et al 2017;Olmo et al 2020).…”

Cladocera resting egg banks in temporary and permanent wetlands

“…As the duration of the dry period increases the ability of a dormant egg to persist decreases (Nielsen et al, 2013;Eskinazi-Sant'Anna and Pace, 2018). In tropical systems, hatching of some cladoceran species or genotypes is benefited from short desiccation events, of at least 8 months (Vargas et al, 2019). However, Jenkins and Boulton (2007) suggests drying longer than a few decades may adversely impact recovery of microinvertebrate populations in Australian arid zone floodplain rivers.…”