|dc.description.abstract||Understanding the mechanisms that facilitate the establishment of non-indigenous species is imperative for devising techniques that will assist in reducing the establishment rates of non-indigenous species. The establishment non-indigenous species can have negative ecological, economic, and human health effects. Non-indigenous passively dispersing organisms such as zooplankton, have been reported to invade constructed lakes (e.g., dams, water supply reservoirs and ornamental ponds) at much faster rates than natural lakes. For example, in New Zealand, a high proportion constructed waters, including dams for hydroelectricity generation, ornamental ponds and disused mine pits, have been invaded by non-indigenous zooplankton, including a number of calanoid copepods that are seemingly currently confined to these habitats. This has lead to a number of theories that have attempted to explain what makes constructed water bodies more vulnerable to invasion than natural lakes. One common attribute of these water bodies is their relatively young age, leading to the assertion that low biotic resistance leads to higher vulnerability of zooplankton communities in early stages of development.
The aim of this study was to determine if seeding water bodies with sediments containing native zooplankton eggs in early stages of their development will accelerate community colonisation, leading to greater biotic resistance to subsequent establishment of new zooplankton species. Twenty outdoor tanks were filled with tap water, and nutrients added to provide eutrophic conditions. Sediments were added to all tanks. Ten treatment tanks contained sediments and associated diapausing zooplankton eggs, sourced from local water bodies. The sediments were autoclaved in the remaining ten, which acted as controls, and thus received zooplankton colonised via natural means only. Tanks were left to colonise for 12 months and community composition and environmental variables were regularly monitored. During the 12 month colonisation period, species richness increased to a mean of 4.6 species in the treatment tanks and 2.6 in control tanks. Community composition also rapidly diverged between control and treatment tanks. Treatment tanks acquired a greater proportion of species adapted to pelagic conditions, such as cladocerans and copepods, with control tanks generally acquiring a high proportion of small, littoral dwelling rotifers. New species were added at 12 months, comprising of two copepods, four rotifers, and one cladoceran species, which were not established in the tanks already. After the introduction of these species, the unseeded control tanks had a much higher proportion of establishment of the new species during the three month post-introduction period. For example, the non-indigenous calanoid copepod Skistodiaptomus pallidus established exclusively in tanks that were void of any other calanoid copepod species. These were primarily control tanks, suggesting that native calanoid copepods play a key role in reducing establishment rates of this taxon. At 12 months, when the new species were added, none of the environmental variables measured (temperature, chlorophyll a, conductivity, specific conductance, DO concentration, DO saturation and pH) were statistically different between treatment and control tanks. This infers that at the time the new species were introduced to the tanks, they experienced similar abiotic conditions, and environmental variability was therefore not responsible for the differing establishment rates.
This study proves that biotic resistance plays an important role in reducing the establishment rate of non-indigenous zooplankton. It also provides strong evidence that seeding constructed water bodies with sediments containing diapausing eggs from locally sourced communities can be used as an effective management tool to reduce establishment rates of non-indigenous zooplankton.||en_NZ