The Swan Coastal Plain (SCP) is known for its highly biodiverse, groundwater-fed wetlands. However, since 1975, climatic drying has caused groundwater tables, runoff, and freshwater biodiversity to decline in streams and wetlands across SWA because once-permanent waterbodies are now dry for long periods. Although SCP wetlands have high conservation and community value, impacts of wetland drying on biodiversity are unknown.
In freshwaters, invertebrates are responsible for many ecosystem functions and provide the largest component of animal diversity. Loss of diversity and abundance of freshwater invertebrates will negatively affect biodiversity, and ecosystem function. Seasonal wetting and drying patterns (i.e. hydroperiod) are a strong filter on invertebrate communities. Many invertebrates can survive drying by using life stages (e.g., desiccation-resistant eggs) in sediment or in the damp bottoms of sediment fissures, but survival is proportional to sediment moisture content. Refuges such as fissures may be imperative to maintaining biodiversity in wetlands, but little is known about how they function. Once hydrological thresholds are crossed and wetlands fail to fill in successive years, the ability of invertebrate communities to recover may be diminished by both moisture loss and drying duration.
A comprehensive baseline dataset of 23 wetlands from 1989/90, when 16 of these wetlands were permanent, and 7 were seasonal. A subset of these wetlands has become seasonal due to climate drying as recently as 2011. A comparison of wetland invertebrate communities between the baseline years and 2024/25 was used to investigate whether this threshold change in hydroregime influences invertebrate communities and water quality. All wetlands experienced significant change between baseline and contemporary years, but, importantly, those that have transitioned to a drier hydroregime showed the largest shifts in their communities. While water quality variables were largely comparable, increases in colour and salinity and drops in TP in seasonal wetlands drove changes.