Habitat alters the effect of false starts on seasonal‐wetland invertebrates

Abstract

Habitat alters the effect of false starts on seasonal-wetland invertebrates. 2. A laboratory emergence experiment was used to determine whether the abortive hatching caused by false starts alters assemblage composition in the subsequent hydroperiod; and whether the length of the dry period following a false start alters subsequent assemblage composition. Sediment for the experiment was collected from Lake Joondalup South, Swan Coastal Plain (SCP), Western Australia, because it has a relatively diverse assemblage of desiccation-resistant invertebrate propagules. Most wetlands on the SCP are seasonal and groundwater-fed and the region has a mediterranean-type climate 3. Two different habitat types (open water (OW) and fringing trees (FT)) with distinct freshwater invertebrate assemblages are commonly found in SCP wetlands. We repeated the experiment in sediment from both habitats to determine whether false starts had the same effect on the two assemblages. Replicate sediment samples from both habitats were placed in microcosms randomly allocated to treatments or controls.To simulate false starts of differing dry-period duration, treatments were inundated for five days, then allowed to dry out for different time periods (10, 20, 30 days) then inundated for five days. Controls were inundated for time periods equivalent to the total duration of each false start treatment (20, 30, 40 days). 4. FT sediment had higher organic matter and moisture content than OW sediment. The composition of the emerging assemblage differed between habitats, and emergence was slower from OW than FT sediment. Abortive hatching followed the false start in OW sediment, but subsequently the same assemblage emerged, showing reliance on the egg bank to re-supply lost populations. Abortive hatching was not observed in FT sediment, where invertebrates survived drying during the false start, continuing to develop for up to 30 d without surface water, because those sediments retained moisture.5. Provided that winter-spring hydroperiods continue to inundate OW for several months, these results indicate that invertebrates will be able to complete their life cycles and replenish egg banks following abortive hatching, demonstrating resilience to false starts. False starts to winter inundation rarely occur more than a month prior to the start of 'true' winter rains, so FT assemblages are resistant to false starts, showing the ability to survive dry periods of up to 30 days. Furthermore, survival in damp FT sediment also gave these populations a 'head start', because the surviving assemblage was identical to the continuously inundated control. 6.Assemblages emerging from beneath FT may potentially recolonise inundated OW habitat. So far, changes to SCP seasonal-wetland hydroperiods will be within the coping range of their invertebrate assemblages. As FT assemblages were more resistant to false starts, restoration schemes that increase shading by fringing vegetation should be encouraged.

An unexpected source of invertebrate community recovery in intermittent streams from a humid continental climate

“…water abstraction, land‐use alterations, climate change) flow intermittence. Contrary to what is reported from mesic climates, where natural flow intermittence promoted a development of physiological resistance to desiccation (Strachan et al., , ; Stubbington & Datry, ), and owing to the high relative air humidity, riparian cover, and the short duration of drying events, we expected taxonomically and functionally rich communities to persist in the dry streambed during phases with no surface water. This prediction was supported, showing how stream invertebrate communities may survive through periods of anthropogenically‐induced flow intermittence, in continental regions of Europe where increasing numbers of streams are affected by anthropogenic flow intermittence.…”

“…22 taxa in Boulton, ; 24 taxa in Datry et al., ) and which included eggs and other desiccation‐resistant forms. The pool of taxa surviving moist conditions during the dry phase in the 10 riverbeds of this study is richer than previously expected (Datry et al., ; Strachan et al., , ; Stubbington, Gunn, Little, Worrall, & Wood, ), indicating that it could be an important source of resilience in continental areas, as suggested previously (Strachan et al., ). On average, only 30% of organisms were found dead during the dry period, indicating that their large proportion was able to cope with the temporary lack of surface water.…”

Pond permanence is a key determinant of aquatic macroinvertebrate community structure in wetlands

“…Leslie & Lamp, ; Lillie, ; Schriever & Williams, ; Silver & Vamosi, ; Wiggins et al., ; Williams, ) and globally (e.g. Strachan, Chester, & Robson, ; Waterkeyn et al., ). As expected, the abundance of wet layers, which require ponded water to lay eggs, and that of dispersers, which can relocate to permanently‐ponded habitats, were both positively associated with increasing hydroperiod, revealing that these two strategies are particularly sensitive to pond permanence.…”

Macroinvertebrate seedbank composition in relation to antecedent duration of drying and multiple wet‐dry cycles in a temporary stream

“…Emergence may be immediate, allowing organisms with rapid development to persist in systems with ephemeral flow (Jackson & Sweeney, 1995;Williams, 2006). However, brief flow events are a potential risk to seedbank integrity if developing organisms perish when sediments redry (Dieterich & Anderson, 1995;Strachan, Chester & Robson, 2016). Life-history strategies promoting persistence despite such hydrological unpredictability include delayed emergence following immersion (Wickson, Chester & Robson, 2012) and asynchronous egg hatching (Zwick, 1996;Strachan et al, 2016).…”

“…However, brief flow events are a potential risk to seedbank integrity if developing organisms perish when sediments redry (Dieterich & Anderson, 1995;Strachan, Chester & Robson, 2016). Life-history strategies promoting persistence despite such hydrological unpredictability include delayed emergence following immersion (Wickson, Chester & Robson, 2012) and asynchronous egg hatching (Zwick, 1996;Strachan et al, 2016). Such 'bet-hedging' development strategies reflect taxon-specific adaptations to a historical flow regime (Lytle & Poff, 2004;Williams, 2006), be that seasonally intermittent, or ephemeral and unpredictable with repeated cycles of short flow events and subsequent dry phases (hereafter, 'wetdry cycles').…”