Oral Presentation AFSS/NZFSS Joint Conference 2019

What’s life history got to do with it? Macroinvertebrate responses to drying flow regime in headwater streams of Southwestern Australia (#127)

Nicole Carey 1 , Edwin Chester 1 , Belinda Robson 1
  1. Murdoch University, Perth, WA, Australia

Southwestern Australia has experienced climate-change driven drying for at least 50 years, decades ahead of other mediterranean-climate regions. Groundwater decline caused most perennial (gaining) streams to become intermittent (losing) streams. Before these changes in flow regime, Bunn (1986) published detailed studies of invertebrate stream communities and documented the life histories of 13 then common species (amphipods, odonates, stoneflies, mayflies, caddisflies; 1988). We revisited these same streams in 2016-17, most of which are now intermittent, to compare current macroinvertebrate assemblages to historical (1980s) assemblages, and re-describe the life history phenology of the 13 species studied by Bunn. Several responses to intermittency were identified. Four species (2 caddisflies, 2 mayflies) disappeared from now-intermittent streams. Two stoneflies switched from summer to winter breeding. The amphipod has survived in all streams. Two mayflies, a shredding caddisfly and a dragonfly still occur in now-intermittent streams, but these are likely to be population sinks. The transition from perennial to seasonal streams has had profound impacts on fauna that were formerly the most abundant species. Furthermore, long-term climatic drying and flow regime change have significantly altered invertebrate assemblage composition. In particular, now- intermittent streams had lower diversity and abundance of key shredders and EPT taxa, most of which are endemic. The ability of a species to adapt its life history phenology was found to be a key determinant of its persistence following flow regime change. As drying progresses, the fauna may continue to lose longer lived endemic species, changing the identity of key species and inevitably altering in-stream processes.