M. J. Vander Zanden

What a difference a species makes: a meta–analysis of dreissenid mussel impacts on freshwater ecosystems

We performed a meta-analysis of published studies and long-term monitoring data sets to evaluate the effects of dreissenid mussels (Dreissena polymorpha and D. rostriformis bugensis), two of the worlds most problematic biological invaders, on the biogeochemistry, flora, and fauna of lakes and rivers across North America and Eurasia. Dreissenid effects were structured along two distinct energy pathways. For the pelagic–profundal pathway, large mean reductions in phytoplankton (−35% to −78%) and zooplankton (−40% to −77%) biomass occurred and were dependent on habitat type. The largest effects were found in rivers, followed by littoral and pelagic habitats in lakes. In contrast, benthic energy pathways within littoral habitats of lakes and rivers showed dramatic increases in mean benthic algal and macrophyte biomass (+170% to +180%), sediment-associated bacteria (about +2000%), non-dreissenid zoobenthic biomass (+160% to +210%), and total zoobenthic biomass, which includes dreissenid mussel soft tissues (+...

Twenty years of invasion: a review of round goby Neogobius melanostomus biology, spread and ecological implications.

The round goby Neogobius melanostomus is one of the most wide-ranging invasive fish on earth, with substantial introduced populations within the Laurentian Great Lakes watershed, the Baltic Sea and several major European rivers. Rapid expansion and deleterious ecosystem effects have motivated extensive research on this species; here this research is synthesized. Maps of the global distribution are provided and the invasion history of N. melanostomus, which spread more rapidly at first in North America, but has undergone substantial expansion over the past decade in the Baltic Sea, is summarized. Meta-analyses comparing their size at age, diet, competitors and predators in North American and European ecosystems are provided. Size at age is region specific, with saline habitats typically supporting larger and faster growing individuals than fresh water. Neogobius melanostomus prey differs substantially between regions, demonstrating a capacity to adapt to locally abundant food sources. Neogobius melanostomus comprise at least 50% of the diet of eight taxa in at least one site or life stage; in total, 16 predator taxa are documented from the Laurentian Great Lakes v. five from Eurasia. Invasive N. melanostomus are the only common forage fish to heavily exploit mussels in the Laurentian Great Lakes and the Baltic Sea, facilitating the transfer of energy from mussels to higher trophic levels in both systems. Neogobius melanostomus morphology, life history, reproduction, habitat preferences, environmental tolerances, parasites, environmental effects, sampling strategies and management are also discussed. Neogobius melanostomus inhabit a wide range of temperate freshwater and brackish-water ecosystems and will probably continue to spread via ballast water, accidental bait release and natural dispersal worldwide. Climate change will probably enhance N. melanostomus expansion by elevating water temperatures closer to its energetic optimum of 26° C. Future research needs are presented; most pressing are evaluating the economic effects of N. melanostomus invasion, determining long-term population level effects of egg predation on game-fish recruitment and comparing several variables (density, ecological effects morphology and life history) among invaded ecosystems. This review provides a central reference as researchers continue studying N. melanostomus, often as examples for advancing basic ecology and invasion biology.

The effect of dreissenid invasions on chlorophyll and the chlorophyll:total phosphorus ratio in north-temperate lakes

We investigated the effects of dreissenid mussel (Dreissena polymorpha and D. rostriformis bugensis) invasions on the concentrations of chlorophyll a (Chl) and total phosphorus(TP), and the Chl:TP ratio within 27 north-temperate lakes that spanned large gradients in lake size and trophic status, using two approaches: (i) regression analysis and (ii) hierarchical modeling. Overall, Chl declined by 40%–45% after dreissenid invasion and the magnitude of effect was structured by epilimnetic volume within stratified, but not nonstratified (mixed) lakes. Declines in TP over the invasion period were significant only for stratified systems and were smaller (∼16% reduction from pre-invasion values) than for Chl. Across the complete trophic gradient (i.e., among lakes) the regression approach (analysis of covariance) indicated a significant decline in the intercept of the Chl:TP, but not the slope. In contrast, hierarchical modeling indicated a decline in the slope of Chl:TP among lakes between pre- and post-invasi...

Potential for large‐bodied zooplankton and dreissenids to alter the productivity and autotrophic structure of lakes

While limnological studies have emphasized the importance of grazers on algal biomass and primary production in pelagic habitats, few studies have examined their potential role in altering total ecosystem primary production and its partitioning between pelagic and benthic habitats. We modified an existing ecosystem production model to include biotic feedbacks associated with two groups of large-bodied grazers of phytoplankton (large-bodied zooplankton and dreissenid mussels) and estimated their effects on total ecosystem production (TEP), and the partitioning of TEP between phytoplankton and periphyton (autotrophic structure) across large gradients in lake size and total phosphorus (TP) concentration. Model results indicated that these filter feeders were capable of reducing whole-lake phytoplankton production by 20-70%, and increasing whole-lake benthic production between 0% and 600%. Grazer effects on TEP were constrained by lake size, trophic status, and potential feedbacks between grazing and maximum rates of benthic photosynthesis (BP(MAX)). In small (mean depth Z < 10 m) oligotrophic and mesotrophic (TP < 100 mg P/m2) lakes, both large-bodied zooplankton and dreissenids were capable of increasing the benthic fraction (Bf) by 10-50% of TEP. Small lakes were also the only systems where TEP had the potential to increase in the presence of large-bodied grazers, but such increases only occurred if grazer-induced changes in water clarity, macrophyte coverage, or nutrient availability stimulated specific growth rates of periphyton. In other scenarios, TEP declined by a maximum of 50%. In very large lakes (Z > 100 m), Bf was minor (< 10%) in the presence or absence of grazers, but increases in littoral habitat and the stimulation of benthic production in these ecosystems could be of ecological relevance because littoral zones in large lakes contain a relatively high proportion of within-lake biodiversity and are important for whole-lake food webs.

Invasive Species Research to Meet the Needs of Resource Management and Planning

As zebra mussels (Dreissena polymorpha) continue to spread among inland lakes of the United States and Canada, there is growing interest from professionals, citizens, and other stakeholders to know which lakes are likely to be colonized by zebra mussels. Thus, we developed a classification of lake suitability for zebra mussels on the basis of measured or estimated concentrations of dissolved calcium in lake water and applied the classification to >11,500 lakes in Wisconsin and the Upper Peninsula of Michigan. The majority of lakes (58%) were classified as unsuitable (<10 mg/L Ca) for survival and reproduction of zebra mussels, 27% were identified as suitable (≥21 mg/L Ca), and 15% were classified as borderline suitable (≥10 and <21 mg/L Ca). Of the 77 inland lakes with confirmed zebra mussel records for which data on dissolved calcium were available, our method classified 74 as suitable and 3 as borderline suitable. To communicate this lake-specific suitability information and to help prioritize regional efforts to monitor and prevent the expansion of zebra mussels and other invasive species, we developed a web-based interface (available from http://www.aissmartprevention.wisc.edu/). Although we are still uncertain of how access to suitability information ultimately affects decision making, we believe this is a useful case study of building communication channels among researchers, practitioners, and the public.