The recovery of stream fauna from supra-seasonal drought is highly variable. The factors influencing drought recovery are poorly understood, with many species able to recover quickly, and others eliminated for extended periods.
We investigated the effects of drought on two amphipod taxa Pseudomoera gabrieli (Eusiridae) and Austrogammarus spp. (Paramelitidae) through an analysis of 11 years of semi-quantitative macroinvertebrate monitoring data collected from three forested streams in the Dandenong Ranges and quantitative samples of amphipods from two upstream sites in 2003 and 2013.
Abundances of Austrogammarus and P. gabrieli in the lower reaches of Lyrebird Creek fell from 102 and 103 per unit effort respectively, to zero following cease-to-flow events in the summers of 2007 and 2008. Similar declines in abundances were not observed in the other two streams, which did not cease to flow, or in the springs at the heads of the catchments. P.gabrieli returned to the lower reaches of Lyrebird Creek in lower abundances after 3 years, but Austrogammarus remains absent 5 years later, despite upstream and downstream source populations within 1 km.
The failure of Austrogrammarus (which includes the threatened species, A. australis) to recover after 5 years, indicates a lack of suitable drought refugia and very low dispersal rates. The response of P. gabrieli suggests a similar lack of local refugia, but greater dispersal ability. With the threat of climate change and increasing demand for water extraction, this study highlights the challenges of protecting fauna with limited abilities to disperse or utilize local refugia.