Katya E. Kovalenko

Aquatic invasive species: challenges for the future

Humans have effectively transported thousands of species around the globe and, with accelerated trade; the rate of introductions has increased over time. Aquatic ecosystems seem at particular risk from invasive species because of threats to biodiversity and human needs for water resources. Here, we review some known aspects of aquatic invasive species (AIS) and explore several new questions. We describe impacts of AIS, factors limiting their dispersal, and the role that humans play in transporting AIS. We also review the characteristics of species that should be the greatest threat for future invasions, including those that pave the way for invasions by other species (“invasional meltdown”). Susceptible aquatic communities, such as reservoirs, may serve as stepping stones for invasions of new landscapes. Some microbes disperse long distance, infect new hosts and grow in the external aquatic medium, a process that has consequences for human health. We also discuss the interaction between species invasions and other human impacts (climate change, landscape conversion), as well as the possible connection of invasions with regime shifts in lakes. Since many invaders become permanent features of the environment, we discuss how humans live with invasive species, and conclude with questions for future research.

Aquatic invasive species: general trends in the literature and introduction to the special issue

Invasion rates are increasing worldwide and most are due to the actions of humans. Deliberate introductions, escapes, and hitchhiking with global commerce transport species to other continents. While most species fail to thrive or have minor impacts on their new ecosystems, the large number of introductions has led to numerous problems. Aquatic invasive species are particularly pervasive and may cause food web disruption, biodiversity loss, and economic harm. Biological invasions appear in an increasing number of publications in the aquatic and general ecology literature. This special issue of Hydrobiologia includes 31 papers on aquatic invasive species and the factors that influence their dispersal and success, along with their impacts. Ecosystems include freshwater ponds, lakes and reservoirs, small streams and large rivers, and coastal marine systems. Study regions occur in temperate, as well as less-studied tropical and sub-tropical regions of four different continents. We discuss the dynamics of invasive species research in the current literature and provide a brief overview of the contributions to this issue.

Congruence of community thresholds in response to anthropogenic stress in Great Lakes coastal wetlands

Abstract: Biological attributes of ecosystems often change nonlinearly as a function of anthropogenic and natural stress. Plant and animal communities may exhibit zones of change along a stressor gradient that are disproportionate relative to the incremental change in the stressor. The ability to predict such transitions is essential for effective management intervention because they may indicate irreversible changes in ecological processes. Despite the importance of recognizing transition zones along a stressor gradient, few, if any, investigators have examined these responses across multiple taxa, and no community threshold studies have been reported at large geographic scales. We surveyed benthic macroinvertebrate, fish, bird, diatom, and plant communities in coastal wetlands across a geospatially referenced gradient of anthropogenic stress in the Laurentian Great Lakes. We used Threshold Indicator Taxon Analysis (Baker and King 2010) to analyze each communitys response to identify potential zones of disproportionate change in community structure along gradients of major watershed-scale stress: agriculture and urban/suburban development. Our results show surprising congruence in community thresholds among different taxonomic groups, particularly with respect to % developed land in the watershed. We also analyzed uncertainty associated with the community-specific thresholds to understand the ability of different assemblages to predict stress. The high and congruent sensitivity of assemblages to development demonstrates that watershed-scale stress has discernible effects on all biological communities, with increasing potential for ecosystem-scale functional changes. These findings have important implications for identifying reference-condition boundaries and for informing management and policy decisions, in particular, for selecting freshwater protected areas.

Functional changes in littoral macroinvertebrate communities in response to watershed-level anthropogenic stress

Watershed-scale anthropogenic stressors have profound effects on aquatic communities. Although several functional traits of stream macroinvertebrates change predictably in response to land development and urbanization, little is known about macroinvertebrate functional responses in lakes. We assessed functional community structure, functional diversity (Rao’s quadratic entropy) and voltinism in macroinvertebrate communities sampled across the full gradient of anthropogenic stress in Laurentian Great Lakes coastal wetlands. Functional diversity and voltinism significantly decreased with increasing development, whereas agriculture had smaller or non-significant effects. Functional community structure was affected by watershed-scale development, as demonstrated by an ordination analysis followed by regression. Because functional community structure affects energy flow and ecosystem function, and functional diversity is known to have important implications for ecosystem resilience to further environmental change, these results highlight the necessity of finding ways to remediate or at least ameliorate these effects.

Life after Dreissena : The decline of exotic suspension feeder may have significant impacts on lake ecosystems

It is well documented that the introduction of dreissenid bivalves in eutrophic lakes is usually associated with decreases in turbidity and total phosphorus concentrations in the water column, concomitant increases in water clarity, as well as other physical changes to habitat that may have cascading effects on other species in the invaded waterbody. In contrast, there is a paucity of data on the ecological ramifications of the elimination or decline of dreissenids due to pollution, bottom hypoxia, or other mechanisms. Using data collected by the U.S. Environmental Protection Agency Great Lakes National Program Offices Long-Term Biology and Water Quality Monitoring Programs, we analyzed the impacts of the hypoxia-induced declines in Dreissena densities in the central basin of Lake Erie on major water chemistry and physical parameters. Our analysis revealed that the decline in Dreissena density in the central basin was concomitant with a decrease in spring dissolved silica concentrations and an increase in total phosphorus and near bottom turbidity not seen in the western or eastern basins. In contrast, opposite patterns in water quality were observed in the eastern basin, which was characterized by a high and relatively stable Dreissena population. We are the first to report that dreissenid-related shifts in water quality of invaded waterbodies are reversible by documenting that the sharp decline of Dreissena in the central basin of Lake Erie was concomitant with a shift from clear to turbid water.

Watershed Land Use and Local Habitat: Implications for Habitat Assessment

Our understanding of anthropogenic stressor effects on wetland biota and ecosystem processes would benefit from better defined relationships between landscape and local stressors. We assessed the connection between watershed land use and local habitat and local disturbance in Great Lakes coastal ecosystems across a full range of anthropogenic stress. In addition, we identified dominant structuring variables, described redundancy, and assessed the relative influence of local versus watershed scale features on local habitat quality with on-site assessments conducted at 143 sample sites. Associations between habitat variables and watershed stressors were found, but only a small proportion of variation was explained. Overall, watershed agriculture was a stronger predictor of local habitat variables than was development. Variance partitioning revealed that disturbance and land use accounted for more variance in habitat than spatial factors or wetland type. This indicates that local and watershed-scale assessments are discrete approaches that document stress at different hierarchical scales and an assumed direct connection between watershed stress and local habitat and disturbance is an over-simplification. Therefore, assessments of stress should include both watershed scale and on-site habitat assessments. Furthermore, these results indicate that local scale mitigation/restoration could minimize negative impacts of changing land use.