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Constructed stormwater wetlands are one strategy for mitigating the negative effects of urbanization on aquatic ecosystems. However, the biotic community in these wetlands generally is dominated by organisms able to tolerate poor water quality. Reduced macroinvertebrate diversity and abundance in comparison to natural wetlands, and prevalence of invasive species, such as Gambusia, can influence the flow of energy through food webs. We used stable-isotope analysis (δ13C and δ15N) of food webs to assess whether the amount of catchment urbanization (total imperviousness [imperviousness] = % catchment covered in impervious surfaces) influenced basal resources and trophic relationships in constructed wetlands in Melbourne, Australia. As imperviousness increased, the abundance and diversity of macroinvertebrates decreased significantly and the values of δ13C and δ15N recorded for fishes and macroinvertebrates increased significantly. An increase in imperviousness was associated with a decrease in the me...

The effects of pharmaceuticals on aquatic ecosystems are the subject of increasing environmental concern. Of particular interest are a suite of drugs known as selective serotonin reuptake inhibitors (SSRIs), commonly prescribed to treat depression. SSRIs are now detected in the environment worldwide, but their effects on ecosystems are not well understood. We conducted replicated experiments testing for an ecosystem effect of SSRIs in streams. We used artificial stream mesocosms to expose natural biofilms and aquatic insect communities to concentrations (20 µg/L) of fluoxetine or citalopram or a mix of both (totaling 40 µg/L). These concentrations are the lowest found to have an effect on aquatic invertebrates in other studies. Treatments suppressed gross primary production by 29% and community respiration by ≥43% on rock biofilms but did not affect algal biomass or whole-stream metabolism. A common group of dipteran midges emerged earlier in all SSRI treated streams compared with the controls. To...

We experimentally assessed the interaction between a globally invasive snail (Potamopyrgus antipodarum) and an Australian native snail (Austropyrgus angasi) under temperatures based on current (1990–2000, mean = 17.94–19.02°C) and future (2100, mean = 19.42–21.65°C) predicted conditions. Temperature treatments were scenarios identified from down-scaled global circulation models. Growth rates (mm/d) for juveniles and adults were measured at low (1000 individuals [ind]/m2) and high (20,000 ind/m2) densities in intraspecific and interspecific interaction trials under the 2 temperature regimes. Juveniles of both species grew at similar rates regardless of temperature and density. On the other hand, adults had dissimilar growth rates among treatments. Under current temperatures, P. antipodarum adults grew significantly faster than A. angasi adults when both species were kept at high densities in the interspecific treatment (interspecific-high) and faster than when they were kept at high densities but w...

Loss of riparian vegetation surrounding streams can affect instream biota by altering stream characteristics, such as terrestrially derived detrital inputs and instream productivity. Omnivorous crayfish can be a dominant component of stream biota and are considered a keystone species because of their ability to forage at multiple trophic levels. Resource shifts caused by changes in riparian canopy have the potential to influence crayfish diet and growth. We investigated the effects of changes in canopy cover on the crayfish Cherax destructor in a southeastern Australian lowland stream. We compared the diet of C. destructor between sites with and without riparian cover and determined how differences in the quantity of food resources between sites affected crayfish growth. The availability of basal (plant, algae, and detrital) resources was related to the presence of a riparian canopy. Aquatic macrophytes were more common at sites with no canopy cover and terrestrially derived leaf litter was more a...