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Despite growing recognition of the importance of ecosystem services and the economic and ecological harm caused by invasive species, linkages between invasions, changes in ecosystem functioning, and in turn, provisioning of ecosystem services remain poorly documented and poorly understood. We evaluate the economic impacts of an invasion that cascaded through a food web to cause substantial declines inwater clarity, a valued ecosystem service. The predatory zooplankton, the spiny water flea (Bythotrephes longimanus), invaded the Laurentian Great Lakes in the 1980s and has subsequently undergone secondary spread to inland lakes, including Lake Mendota (Wisconsin), in 2009. In Lake Mendota, Bythotrephes has reached unparalleled densities compared with in other lakes, decreasing biomass of the grazer Daphnia pulicaria and causing a decline in water clarity of nearly 1 m. Time series modeling revealed that the loss in water clarity, valued at US$140 million (US$640 per household), could be reversed by a 71% reduction in phosphorus loading. A phosphorus reduction of this magnitude is estimated to cost between US$86.5 million and US$163 million (US$430–US$810 per household). Estimates of the economic effects of Great Lakes invasive species may increase considerably if cases of secondary invasions into inland lakes, such as Lake Mendota, are included. Furthermore, such extreme cases of economic damages call for increased investment in the prevention and control of invasive species to better maximize the economic benefits of such programs. Our results highlight the need to more fully incorporate ecosystem services into our analysis of invasive species impacts, management, and public policy.

The role of phenotypic plasticity in adaptive evolution has been debated for decades. This is because the strength of natural selection is dependent on the direction and magnitude of phenotypic responses to environmental signals. Therefore, the connection between plasticity and adaptation will depend on the patterns of plasticity harbored by ancestral populations before a change in the environment. Yet few studies have directly assessed ancestral variation in plasticity and tracked phenotypic changes over time. Here we resurrected historic propagules of Daphnia spanning multiple species and lakes in Wisconsin following the invasion and proliferation of a novel predator (spiny waterflea, Bythotrephes longimanus). This approach revealed extensive genetic variation in predator-induced plasticity in ancestral populations of Daphnia. It is unlikely that the standing patterns of plasticity shielded Daphnia from selection to permit long-term coexistence with a novel predator. Instead, this variation in plasticity provided the raw materials for Bythotrephes-mediated selection to drive rapid shifts in Daphnia behavior and life history. Surprisingly, there was little evidence for the evolution of trait plasticity as genetic variation in plasticity was maintained in the face of a novel predator. Such results provide insight into the link between plasticity and adaptation and highlight the importance of quantifying genetic variation in plasticity when evaluating the drivers of evolutionary change in the wild.

Rising temperatures are leading to permafrost thaw over vast areas of the northern hemisphere. In the Canadian Arctic, permafrost degradation is causing significant changes in surface water quality due to the release of solutes that can alter conductivity, water clarity, and nutrient levels. For this study, we examined how changes in water quality associated with permafrost thaw might impact zooplankton, a group of organisms that play an important role in the food web of Arctic lakes. We conducted a biological and water quality survey of 37 lakes in the Mackenzie Delta region of Canada’s Northwest Territories. We then used this data set to develop models linking variation in the abundance, diversity, and evenness of zooplankton communities to physicochemical, biological, and spatial variables. Subsequently, we used these models to predict how zooplankton communities might respond as water quality is altered by permafrost thaw. Our models explained 47%, 68%, and 69% of the variation in zooplankton abundance, diversity, and evenness, respectively. Importantly, the most parsimonious models always included variables affected by permafrost thaw, such as calcium and conductivity. Predictions based on our models suggest significant increases in zooplankton abundance (1.6–3.6 fold) and decreases in diversity (1.2–1.7 fold) and evenness (1.1–1.4 fold) in response to water quality changes associated with permafrost thaw. These changes are in line with those described for significant perturbations such as eutrophication, acidification, and the introduction of exotic species such as the spiny water flea (Bythotrephes). Given their important role in aquatic food webs, we expect these changes in zooplankton communities will have ramifications for organisms at higher (fish) and lower (phytoplankton) trophic positions in Arctic lakes.

Bythotrephes is presently extending its distribution to basins throughout Europe and North America. We used long term data (1880-1997) on Bythotrephes longimanus in Eurasian waterbodies to characterize its ecology and tolerance to different ecological factors. Depending on season and environmental conditions of the waterbody, Eurasian B. longimanus may undergo cyclomorphosis and can exist as two distinct forms (B. longimanus or B. cederstroemi). Regional forms of the species (B. l. var. balticus, B. l. var. transcaucasicus, and B. l. var. arcticus) have also been described. Occurrence and density of Bythotrephes populations varies across geographical scales, and are apparently affected primarily by water temperature and salinity. Bythotrephes is limited to regions where water temperature ranges between 4 and 30 degree C, although the species prefers waters between 10 and 24 degree C. Bythotrephes tolerates salinity values between 0.04 and 8.0ppm, though it prefers water between 0.04 and 0.4ppm. These factors strongly restrict Bythotrephes' distribution in warmer and more saline waters of the Commonwealth of Independent States (CIS), particularly in southern Russia and Kazakhstan. Local abundance and distribution of Bythotrephes is affected by abiotic factors, including basin morphometry and flushing rate, temperature, oxygen concentration and pH, as well as by lake trophic status and fish predation. Planktivorous fish may restrict habitat use by Bythotrephes to regions of basins where overlap between these groups is minimized. Rivers, canals, and ephemeral waterbodies serve as important modes of Bythotrephes' dispersal throughout the CIS and western Europe. Morphological adaptations (e.g. a long caudal process, cyclic parthenogenesis, and production of resting eggs) permit Bythotrephes to tolerate seasonally inhospitable conditions, assist in its dispersal and range extension, and minimize fish predation.

Bythotrephes cederströemi are a predatory cladoceran zooplankter that have invaded numerous inland lakes in North America, many of which are stratified and support offshore fishes like Cisco ( Coregonus artedi ). While changes in zooplankton community composition following Bythotrephes invasion predict an increase in Cisco mercury concentrations (Hg), this phenomenon was not detected from a survey evaluating temporal changes in Cisco Hg across a broad range of lakes varying in the presence or absence of Bythotrephes . Here, we compare temporal changes in Cisco bioaccumulation slopes (i.e., slopes of relationships between Cisco Hg and trophic position) from lakes experiencing Bythotrephes invasion over the study period to those already invaded (as a reference) over similar time periods. Our results show that bioaccumulation slopes after Bythotrephes invasion either changed direction entirely (from positive to negative relationships) or decreased in elevation relative to those prior to invasion. No such pattern was observed in previously invaded reference lakes. Reductions in Cisco bioaccumulation slopes and/or intercepts following Bythotrephes invasion suggest that conversion efficiency (and therefore growth) of Cisco increased after invasion (i.e., less Hg accumulates in fish at an equivalent trophic position after vs. before invasion). Back-calculated Cisco growth rates and size-at-age from a second complimentary study were greater in the presence of Bythotrephes than without, further supporting the hypothesis that changes in Hg bioaccumulation are likely due to increased conversion efficiency among invaded populations. These findings highlight the potential importance of foraging energetics over and above shifts in trophic position in modifying fish contaminant concentrations.

We present a comprehensive survey of the scientific literature pertaining to non-indigenous and invasive zooplankton published across the first decades of the twenty-first century (i.e., 2000–2018). We provide a concise summary of the manner in which the scientific community has allocated its efforts to this issue in recent decades, and to illuminate trends that emerge from the literature. Our search yielded 620 publications encompassing 139 invasive zooplankton species, with invasive zooplankton reported from every region of the planet—including the Arctic and Antarctic. Most taxa were reported in a small number of publications, with the majority being mentioned in only a single paper. In contrast, approximately half of the surveyed publications concerned just four species: Bythotrephes longimanus, Mnemioposis leidyi, Cercopagis pengoi, and Daphnia lumholtzi. Our survey reveals strong geographic patterns among the literature, with most publications arising from economically developed western nations. We found that the majority of publications pertained to holoplanktonic organisms from freshwater habitats, especially from the North American Great Lakes. Based on these results, we present several recommendations for future research topics that may hold considerable opportunity for growth in our understanding of the invasion process.

Invasive species have extensive negative consequences for biodiversity and ecosystem health. Novel species also drive contemporary evolution in many native populations, which could mitigate or amplify their impacts on ecosystems. The predatory zooplankton Bythotrephes longimanus invaded lakes in Wisconsin, USA, in 2009. This invasion caused precipitous declines in zooplankton prey (Daphnia pulicaria), with cascading impacts on ecosystem services (water clarity). Here, we tested the link between Bythotrephes invasion, evolution in Daphnia and post-invasion ecological dynamics using 15 years of long-term data in conjunction with comparative experiments. Invasion by Bythotrephes is associated with rapid increases in the body size of Daphnia. Laboratory experiments revealed that such shifts have a genetic component; third-generation laboratory-reared Daphnia from ‘invaded’ lakes are significantly larger and exhibit greater reproductive effort than individuals from ‘uninvaded’ lakes. This trajectory of evolution should accelerate Daphnia population growth and enhance population persistence. We tested this prediction by comparing analyses of long-term data with laboratory-based simulations, and show that rapid evolution in Daphnia is associated with increased population growth in invaded lakes.

Calcium (Ca) concentrations are decreasing in softwater lakes across eastern North America and western Europe. Using long-term contemporary and palaeo-environmental field data, we show that this is precipitating a dramatic change in Canadian lakes: the replacement of previously dominant pelagic herbivores (Ca-rich Daphnia species) by Holopedium glacialis, a jelly-clad, Ca-poor competitor. In some lakes, this transformation is being facilitated by increases in macro-invertebrate predation, both from native (Chaoborus spp.) and introduced (Bythotrephes longimanus) zooplanktivores, to which Holopedium, with its jelly coat, is relatively invulnerable. Greater representation by Holopedium within cladoceran zooplankton communities will reduce nutrient transfer through food webs, given their lower phosphorus content relative to daphniids, and greater absolute abundances may pose long-term problems to water users. The dominance of jelly-clad zooplankton will likely persist while lakewater Ca levels remain low.

Bythotrephes longimanus (spiny waterflea) and Cercopagis pengoi (fishhook waterflea) are large invasive predatory cladocerans that alter the composition, density, and behavior of native zooplankton communities. Lake Champlain was invaded by Bythotrephes and Cercopagis in 2014 and 2018, respectively. This study was conducted to determine the changes in crustaceous zooplankton diel vertical migration (DVM) associated with the presence of these two invasive species. Daytime and nighttime zooplankton samples were collected from vertical net tows at 5 m intervals using 153 µm and 250 µm closing plankton nets at a 50 m deep site in Lake Champlain during the month of August (2013–2016, 2019, 2023, and 2024). Sampling dates encompassed years before and after each invader entered the lake. The results show increased DVM activity in several native zooplankton taxa associated with invasion years, including Daphnia retrocurva, Bosmina longirostris, and Diacyclops thomasi. Zooplankton in Lake Champlain appear to occupy deeper depths during the daytime after Bythotrephes and Cercopagis invaded than in previous years. Alterations associated with Bythotrephes were more extreme, whereas changes associated with Cercopagis were longer lasting. These shifts in DVM behavior have potential implications for trophic dynamics in Lake Champlain by altering competitive interactions and foraging behavior of zooplankton and their predators.

In light of the ongoing spread and adverse impacts of invasive species, there is an urgent need to develop more effective monitoring and management strategies. Such efforts are constrained by our limited capacity to efficiently detect invasive species. Here, we present the case of Bythotrephes longimanus (spiny water flea) invasion into Wisconsin lakes. Detecting Bythotrephes has proven to be challenging due to its capacity to persist at low densities and its highly seasonal population dynamics. We use Bythotrephes to explore detection using three monitoring methods: zooplankton net tows, environmental DNA (eDNA), and sampling of Bythotrephes tail spine subfossils in sediments. Detection probabilities were highly seasonal for both the net tow and eDNA sampling methods—though detections occurred one to two weeks earlier in net tows—and seasonal targeting substantially improved detection by both methods. Conversely, Bythotrephes spine subfossils were found in all 10 lakes with confirmed Bythotrephes populations and in all five samples taken from each lake, except for a single lake where four of the five samples had subfossils. This method was insensitive to seasonally varying population densities as sediments integrate over variation in population densities. In this case, detection and abundance estimation were well covered by sediments and zooplankton nets, respectively, and eDNA provided little additional benefit to surveillance. Our work highlights the importance of choosing methods that address both species life history and monitoring objectives when designing surveillance programs.