K.M. Trayler

The influence of changing hydroregime on the invertebrate communities of temporary seasonal wetlands

Abstract. Community dynamics in temporary waters are constrained by the hydroregime (depth, timing, duration, frequency, and predictability of water in an aquatic habitat), which in turn is influenced by climatic patterns and anthropogenic use of water in the landscape. Declining rainfall in regions with a Mediterranean climate, such as southwestern Australia, has decreased the depth and duration of water in temporary wetlands, potentially altering the composition of invertebrate communities. We used a long-term data set (6–25 y) to examine temporal changes in hydroregimes and aquatic invertebrate diversity (based on species presence/absence) at 9 seasonal wetlands. The study wetlands maintained distinctly seasonal hydroregimes, despite declining rainfall and the contraction of wetland hydroperiods. Distance-based redundancy analysis (dbRDA) indicated that conductivity, NO3−+NO2−, and turbidity were the most important factors explaining the changes in invertebrate community composition over time. Allocation of species into 4 trait-based groups based on their resilience to or resistance of drought and their mode of recolonization of a water body upon rewetting revealed that the fauna is dominated by active dispersers. This result suggests that the proximity of source wetlands from which mobile invertebrate species and vertebrate vectors, such as waterbirds, can recolonize seasonal wetlands is an important factor influencing the invertebrate community response to rewetting. Despite the decline in water availability, we found little evidence of a shift to a more arid-adapted fauna. We suggest that the maintenance of a mosaic of wetlands of varying hydroregimes at the whole-landscape scale will be critical to the future persistence of aquatic invertebrate communities in Mediterranean regions where the frequency and intensity of droughts is predicted to increase.