The role of both natural and artificial ponds in supporting biodiversity and as an infrequent habitat for aquatic organisms in urban areas may be greater than that in more rural landscapes. Moreover, biological succession and the dynamics of zooplankton can differ in urban ponds where we may observe a specific combination of environmental factors (e.g., an increase of eutrophication and pollution) compared to other water ecosystems. Therefore, ten urban artificial ponds were examined and the type of direct catchment area was established as the most important factor in the determination of zooplankton distribution. Different environmental factors structured zooplankton distribution between forest and meadow ponds. Low concentrations of oxygen as well as lack of fish, which was an effect of high concentrations of ammonium nitrogen, were responsible for the occurrence of littoral species and large crustacean species (e.g., Daphnia hyalina and Megacyclops viridis) in the case of forest ponds. Fish predation on large crustaceans and favourable food conditions (high concentration of chlorophyll a) created suitable conditions for the occurrence of pelagic species (e.g., Keratella cochlearis and K. quadrata) in the case of meadow ponds. Moreover, soon after the ice cover melted and before new macrophytes developed, previous-year dry rush stems created valuable refuge conditions for zooplankton in this type of pond. Despite anthropogenic pollution resulting from the close vicinity of the agglomeration of Poznań and unfavourable conditions attributed to the spring season a diverse zooplankton community occurred, reaching the level of 119 species in total.

Host-parasite interactions are shaped by the co-evolutionary arms race of parasite virulence, transmission success as well as host resistance and recovery. The virulence and fitness of parasites may depend on host condition, which is mediated, for instance, by host energy constraints. Here, we investigated to what extent stress imposed by predation threat and environmental pollutants influences host-parasite interactions. We challenged the crustacean host Daphnia magna with the sterilizing bacterial endoparasite Pasteuria ramosa and simultaneously exposed the host to fish kairomones, the pesticide carbaryl or both stressors. While parasite virulence, measured as impact on host mortality and sterilization, increased markedly after short-term pesticide exposure, it was not influenced by predation threat. Parasite fitness, measured in terms of produced transmission stages, decreased both in fish and pesticide treatments. This effect was much stronger under predation threat than carbaryl exposure, and was attributable to reduced somatic growth of the host, presumably resulting in fewer resources for parasite development. While the indirect impact of both stressors on spore loads provides evidence for host condition-dependent parasite fitness, the finding of increased virulence only under carbaryl exposure indicates a stronger physiological impact of the neurotoxic chemical compared with the effect of a non-toxic fish kairomone.

Gammarus spp. (Crustacea: Amphipoda) are widespread throughout a diverse range of marine, freshwater and estuarine/brackish habitats, often dominating benthic macroinvertebrate communities in terms of both numbers and/or biomass. Gammarus spp. are the dominant macroinvertebrate prey items of many fish, whether as a seasonal food source or a year-round staple. Selective predation by fish on Gammarus spp. is often linked to parasitism and the body size of the prey. Gammarus spp. populations are under increasing threat from both pollution and replacement/displacement by introduced species. Loss of populations and species invasions/replacements could have significant impacts on native predator species if the predator(s) cannot successfully adapt their feeding patterns to cope with non-indigenous Gammarus prey species. Despite this, many fish predation studies do not identify Gammarus prey to species level. This lack of precision could be important, as Gammarus spp. exhibit wide variations in physiochemical tolerances, habitat requirements, abilities to invade and susceptibility to replacement. Although rarely acknowledged, the impacts of non-piscean predators (particularly macroinvertebrates) on Gammarus prey species may frequently be stronger than those exerted by fish. A major aim of this review is to ascertain the current importance of Gammarus as a prey species, such that the implications of changes in Gammarus spp. populations can be more accurately assessed by interested groups such as ecologists and fisheries managers. We also review the dynamics of Gammarus spp. as prey to a diverse array of mammals, birds, amphibians, insects, flatworms, other crustaceans such as crabs and crayfish and, perhaps most importantly, other Gammarus spp.