Spatial and temporal aquatic–terrestrial transitions in the temporary Albarine River, France: responses of invertebrates to experimental rewetting

Abstract

1. In temporary rivers, viewed as coupled terrestrial-aquatic ecosystems, spatial and temporal transition zones between aquatic and terrestrial conditions are common and occur simultaneously. 2. The effects of artificial rewetting on terrestrial and aquatic invertebrate assemblages were examined in dry sediments collected from the Albarine River, France. Rewetted sediments had previously been dry for between 0.1 and 142 days. Dry sediments were collected directly from the streambed (DS) and from riparian gravel bars (RGB). 3. We first predicted that invertebrate responses to rewetting would vary with the duration of the preceding dry period. Second, we predicted convergence of the invertebrate assemblages in DS and RGB sediments with increasing duration of the dry period. Third, we predicted that an aquatic 'invertebrate seedbank' (aquatic life stages that persist within streambed sediments during dry periods) would contribute substantially to the resilience of benthic assemblages. 4. Results indicated that the duration of the dry period was the primary driver of aquatic and terrestrial responses to artificial rewetting. The density and richness of aquatic taxa decreased with the duration of the dry period in both DS and RGB sediments, whereas the density of terrestrial invertebrates increased in DS sediments. 5. No convergence between DS and RGB assemblage composition was observed with an increasing dry period. Although there were more aquatic organisms in DS sediments than in RGB sediments, there was no difference in taxonomic richness between sediment types. Even after prolonged dry periods (142 days), there was typically a lower density and taxonomic richness of terrestrial invertebrates in DS sediments than in adjacent RGB sediments. 6. The results suggest that the aquatic invertebrate seedbank could contribute substantially to the resilience of benthic assemblages in the Albarine River, in addition to other mechanisms such as drift and oviposition. Of the taxa in the benthos before and after the summer dry period, 65% were also recovered from artificially rewetted DS sediments. The simultaneous presence of temporal and spatial terrestrial-aquatic transition zones in temporary rivers increases successional diversity (i.e. mosaics of dry and saturated streambed patches at various stages of terrestrial and aquatic succession). This contribution to biodiversity emphasises the need to protect dry reaches of temporary rivers.

Fringing trees may provide a refuge from prolonged drying for urban wetland invertebrates

“…Declines in the diversity and abundance of invertebrates emerging from sediments as the duration of drying increases have been observed in several studies (e.g. Larned et al 2007;Datry et al 2012). Also, Jenkins and Boulton (2007) found that for microinvertebrate egg banks, drying for a period greater than 10-20 years resulted in marked declines in species richness.…”

“…Decanting was repeated at days 20 and 30. A 30 day duration was chosen as sufficient to stimulate hatching and emergence in most species, based on similar studies (Jenkins and Boulton 2007;Larned et al 2007;Chester and Robson 2011;Datry et al 2012). These studies all used similar methods of inundation with non-chlorinated water, decanting and filtering with the exception that, as in Jenkins and Boulton (2007), samples were not aerated because the sediments were from lentic rather than lotic habitats.…”

Regionalization of patterns of flow intermittence from gauging station records

“…Aquatic and terrestrial species colonize and emigrate from intermittent rivers in response to shifts between wet and dry habitat (Acuña et al, 2005;Corti and Datry, 2012;Datry et al, 2012;Davey and Kelly, 2007;Steward et al, 2011). A smaller number of intermittent river specialists persist through multiple wet-dry cycles; this group includes aestivating fish and encysting invertebrates (Kikawada et al, 2005;Perry et al, 2008;Sayer, 2005).…”

Microrefuges from drying for invertebrates in a seasonal wetland

“…Some crustaceans produce drought resistant eggs or cysts (Datry et al, 2012;Stubbington & Datry, 2013). Other groups, such as many large predators (e.g.…”