Ephemeropteran and Trichopteran Assemblages Vary Across a Subtropical Rainforest Altitudinal Gradient: Useful Indicators for Climate Change

The subtropical rainforests of eastern Australia are expected to be greatly affected by climate change, with several studies predicting an upward shift in elevational distribution for many groups of fauna and flora. Freshwater streams have so far been neglected by most studies involving elevation, climate change and subtropical rainforest. This study is the first to explore changes in macroinvertebrates across an elevational gradient within subtropical streams to determine the effect of elevation. The study focussed on Ephemeroptera and Trichoptera (ET) and identified indicator taxa with the potential to be used for future monitoring of climate change. Stream macroinvertebrates, specifically of the Orders Ephemeroptera and Trichoptera, and environmental data was collected from pools, riffles and runs at 13 sites across three subtropical streams that spanned an elevation gradient from 300 m to 1100 m a.s.l. Water temperature, substrate composition, stream width and riparian canopy cover were the most notable environmental changes observed across the gradient. Trichopteran taxa richness was negatively correlated with elevation; however, ephemeropteran taxa richness did not respond to elevation. Water temperature, canopy cover, stream width and substrate composition explained the highest variation in ET assemblages across the gradient, with ET assemblages separating into distinct 'low' (300 m-500 m a.s.l.) and 'high' (700-900 m a.s.l.) assemblages; the 1100 m elevational zone was distinct, with an observed sharp decline in species richness. Elevation, along with reach scale environmental factors, are influential in structuring ET assemblages in subtropical rainforest streams, with specific ET taxa having the potential to be useful indicators of climate change in these systems.