Desiccation increases the hatching of resting eggs of a freshwater calanoid copepod

Abstract

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.

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

“…Total hatchlings were less abundant and speciose in desiccated than in wet resting egg banks. These findings corroborate earlier observations showing lower hatching rates of cladocerans from permanent lakes after their resting eggs were desiccated for 6 h (Branstrator et al., 2013) or 4 months (Santangelo et al., 2011), but contrast with a calanoid copepod displaying higher hatching rates for eggs previously desiccated for 6 or 9 months (Brazil et al., 2022). In addition, tolerance to 1‐year desiccation was observed in the cladoceran I .…”

“…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).…”

“…Except for some anostracans and notostracans, as discussed below, few studies have evaluated how desiccation duration affects the viability of zooplankton resting eggs (Branstrator et al., 2013; Brazil et al., 2022; Vargas et al., 2019), and none have compared its effects on permanent and temporary habitats. While many studies have shown the establishment of active zooplankton after droughts and re‐inundation of aquatic habitats (Panarelli et al., 2008; da Silva Bandeira et al., 2020), few studies have determined how long lake sediments remained dry before re‐inundation.…”

“…After establishing all wet and dry replicates, sediments were kept in wrapped, closed flasks at 24 ± 1°C in dark conditions until their use 1 year later. A similar approach was used by Brazil et al (2022).…”

“…With few exceptions, limited studies have empirically evaluated the role of desiccation on the viability of zooplankton resting eggs. Earlier studies at the species level showed a decrease in hatching rates of Diaphanosoma birgei, Moina micrura and B. longimanus (Cladocera) resting eggs after desiccation and rehydration (Branstrator et al, 2013;Santangelo et al, 2011), whereas hatching rates of Notodiaptomus iheringi (Calanoida) may increase if eggs are desiccated shortly after sampling (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).…”