Evidence for interactions among environmental stressors in the Laurentian Great Lakes (original) (raw)
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Do Dreissenid Mussels Affect Lake Erie Ecosystem Stability Processes?
American Midland Naturalist, 2005
Ecosystem stability processes such as constancy, resilience and persistence are important, but often neglected, topics of invasive species research. Here we consider how invasive dreissenid mussels affect ecosystem stability processes in Lake Erie through both consumptive and excretory processes using the stability landscape heuristic . Consumption of phytoplankton by dreissenid mussels adds complexity to the system and potentially slows energy transfer from lower to higher trophic levels decreasing system constancy and lowering system resiliency. Excreting soluble waste products at low nitrogen to phosphorus ratios exacerbates these impacts on stability processes because low nutrient ratios favor growth of cyanobacterial blooms, less preferred food of zooplankton, further decreasing the transfer of energy from lower to higher trophic levels. We also provide evidence for recent changes in Lake Erie's stability landscape including a return towards eutrophy.
Net effects of multiple stressors in freshwater ecosystems: a meta-analysis
Global Change Biology, 2015
The accelerating rate of global change has focused attention on the cumulative impacts of novel and extreme environmental changes (i.e., stressors), especially in marine ecosystems. As integrators of local catchment and regional processes, freshwater ecosystems are also ranked highly sensitive to the net effects of multiple stressors, yet there has not been a large-scale quantitative synthesis. We analysed data from 88 papers including 286 responses of freshwater ecosystems to paired stressors, and discovered that overall, their cumulative mean effect size was less than the sum of their single effects (i.e., an antagonistic interaction). Net effects of dual stressors on diversity and functional performance response metrics were additive and antagonistic, respectively. Across individual studies, a simple votecounting method revealed that the net effects of stressor pairs were frequently more antagonistic (41%) than synergistic (28%), additive (16%) or reversed (15%). Here, we define a reversal as occurring when the net impact of two stressors is in the opposite direction (negative or positive) from that of the sum of their single effects. While warming paired with nutrification resulted in additive net effects, the overall mean net effect of warming combined with a second stressor was antagonistic. Most importantly, the mean net effects across all stressor pairs and response metrics were consistently antagonistic or additive, contrasting the greater prevalence of reported synergies in marine systems. Here, a possible explanation for more antagonistic responses by freshwater biota to stressors is that the inherent greater environmental variability of smaller aquatic ecosystems fosters greater potential for acclimation and co-adaptation to multiple stressors.
Journal of Great Lakes Research, 2011
Thirty-two biological variables (taxonomic and/or functional groups) representing the four major communities, phytoplankton, zooplankton, benthos and fish, characterizing the upper Bay of Quinte (Lake Ontario) ecosystem, were assembled for the 27-year period, 1982-2008. Coincident regime shifts were detected in phytoplankton, benthos, and fish in 1995, which was just after invasive zebra mussels (Dreissena spp.) became established in the bay in 1993-1994. Two independent methods were used to detect these shifts: 1) principal components analysis followed by a Regime Shift Detector test for a change point in the running mean of the first principal component scores and measurements of significant difference between pre-and post-Dreissena ecosystem structure based on measures of Bray-Curtis community similarity. Although a statistically significant shift was not detected in the zooplankton community by itself, zooplankton variables were instrumental in the overall ecosystem shift, determined for the combined four communities. All 32 variables were ranked for their individual contribution to the difference between the pre-and post-Dreissena ecosystem structures. The resolution of two distinct ecosystem structures, pre-and post-Dreissena, was greatly improved after employing a novel method of variable optimization that involved a selective and sequential removal of variables contributing least to the statistical difference between pre-and post-Dreissena ecosystem structures. The resultant 20-variable subset defined a 1995 ecosystem regime shift at very high level of statistical confidence (ANOSIM-R =0.970).
Ecological Applications, 2013
Ecosystems often experience multiple environmental stressors simultaneously that can differ widely in their pathways and strengths of impact. Differences in the relative impact of environmental stressors can guide restoration and management prioritization, but few studies have empirically assessed a comprehensive suite of stressors acting on a given ecosystem. To fill this gap in the Laurentian Great Lakes, where considerable restoration investments are currently underway, we used expert elicitation via a detailed online survey to develop ratings of the relative impacts of 50 potential stressors. Highlighting the multiplicity of stressors in this system, experts assessed all 50 stressors as having some impact on ecosystem condition, but ratings differed greatly among stressors. Individual stressors related to invasive and nuisance species (e.g., dreissenid mussels and ballast invasion risk) and climate change were assessed as having the greatest potential impacts. These results mark a shift away from the longstanding emphasis on nonpoint phosphorus and persistent bioaccumulative toxic substances in the Great Lakes. Differences in impact ratings among lakes and ecosystem zones were weak, and experts exhibited surprisingly high levels of agreement on the relative impacts of most stressors. Our results provide a basin-wide, quantitative summary of expert opinion on the present-day influence of all major Great Lakes stressors. The resulting ratings can facilitate prioritizing stressors to achieve management objectives in a given location, as well as providing a baseline for future stressor impact assessments in the Great Lakes and elsewhere.
Impact of Dreissenid Mussel Population Changes on Lake Erie Nutrient Dynamics
Fully understanding the importance of zebra and quagga mussels' effects on internal nutrient (especially nitrogen and phosphorus) cycling in large lakes like Lake Erie is essential when attempting to ameliorate their contribution to beneficial use impairments and to understand how invasive species perturb ecosystems in their invasive ranges. Here, we first used field surveys to determine the current (2004) dreissenid community structure on hard, preferred substrate in the western basin of Lake Erie. We then estimated the potential nutrient subsidy to the phytoplankton community by dreissenid nitrogen and phosphorus excretion by integrating the dreissenid community structure at these sites with published size-specific nutrient excretion regressions. We found that the total dreissenid community density had decreased dramatically (by > 50%) from previous estimates, that zebra mussels now comprised only a small fraction of the total density (< 3%), and that the quagga mussel-d...
Ecology, 2017
Dreissenid mussels, including the zebra (Dreissena polymorpha) and quagga (Dreissena rostiformus bugensis) mussel, are invasive species known for their capacity to act as ecosystem engineers. They have caused significant changes in the many freshwater systems they have invaded by increasing water clarity, reducing primary productivity, and altering zooplankton and benthic invertebrate assemblages. What is less clear is how their ecosystem engineering effects manifest up the food web to impact higher trophic levels, including fish. Here, we use a biological tracer (stable isotopes of carbon and nitrogen) to analyze long-term and broad-scale trends in the resource use of benthivorous lake whitefish (Coregonus clupeaformis) in the Laurentian Great Lakes, where dreissenid mussels have become established in each lake except Lake Superior. We measured stable isotope ratios from archived material (fish scale samples) collected over several decades by multiple agencies and from 14 locations...
Ecological Modelling, 2009
As invasion rates of exotic species increase, an ecosystem level understanding of their impacts is imperative for predicting future spread and consequences. We have previously shown that network analyses are powerful tools for understanding the effects of exotic species perturbation on ecosystems. We now use the network analysis approach to compare how the same perturbation affects another ecosystem of similar trophic status. We compared food web characteristics of the Bay of Quinte, Lake Ontario (Canada), to previous research on Oneida Lake, New York (USA) before and after zebra mussel (Dreissena polymorpha) invasion. We used ecological network analysis (ENA) to rigorously quantify ecosystem function through an analysis of direct and indirect food web transfers. We used a social network analysis method, cohesion analysis (CA), to assess ecosystem structure by organizing food web members into subgroups of strongly interacting predators and prey. Together, ENA and CA allowed us to understand how food web structure and function respond simultaneously to perturbation. In general, zebra mussel effects on the Bay of Quinte, when compared to Oneida Lake, were similar in direction, but greater in magnitude. Both systems underwent functional changes involving focused flow through a small number of taxa and increased use of benthic sources of production; additionally, both systems structurally changed with subgroup membership changing considerably (33% in Oneida Lake) or being disrupted entirely (in the Bay of Quinte). However, the response of total ecosystem activity (as measured by carbon flow) differed between both systems, with increasing activity in the Bay of Quinte, and decreasing activity in Oneida Lake. Thus, these analyses revealed parallel effects of zebra mussel invasion in ecosystems of similar trophic status, yet they also suggested that important differences may exist. As exotic species continue to disrupt the structure and function of our native ecosystems, food web network analyses will be useful for understanding their far-reaching effects.
Integrated Environmental Assessment and Management, 2014
The North Atlantic Landscape Conservation Cooperative LCC (NA LCC) is a publicprivate partnership that provides information to support conservation decisions that may be affected by global climate change (GCC) and other threats. The NA LCC region extends from southeast Virginia to the Canadian Maritime Provinces. Within this region, the U.S. National Climate Assessment documented increases in air temperature, total precipitation, frequency of heavy precipitation events, and rising sea level, and predicted more drastic changes. Here we synthesize literature on the effects of GCC interacting with selected contaminant, nutrient, and environmental processes to adversely affect natural resources within this region. Using a case study approach, we focused on three stressors with sufficient NA LCC region-specific information for an informed discussion. We describe GCC interactions with a contaminant (mercury), and two complex environmental phenomena-freshwater acidification and eutrophication. We also prepared taxa case studies on GCC-and GCCcontaminant/nutrient/process effects on amphibians and freshwater mussels. Several avian species of high conservation concern have blood mercury concentrations that have been associated with reduced nesting success. Freshwater acidification has adversely affected terrestrial and aquatic ecosystems in the Adirondacks and other areas of the region that are slowly recovering due to decreased emissions of nitrogen and sulfur oxides. Eutrophication in many estuaries within the region is projected to increase from greater storm runoff and less denitrification in riparian wetlands. Estuarine hypoxia may be exacerbated by increased stratification. Elevated water temperature favors algal species that produce harmful algal blooms (HABs). In several of the region's estuaries, HABs have been associated with bird die-offs.
Physiology and Biogeography: The Response of European Mussels (Mytilusspp.) to Climate Change*
American Malacological Bulletin, 2015
To understand how ecological communities may respond to climate change we have adopted the approach of determining the response of major ecosystem engineers that determine community composition and function. We utilize two approaches, correlative and mechanistic, to understand the current and future distributions of the marine mussels Mytilus edulis Linnaeus, 1758 and M. galloprovincialis Lamarck, 1819 in Europe. Both are dominant space-occupying species that control biodiversity in many coastal ecosystems and are the basis of the largest aquaculture production in Europe. A mechanistic analysis of physiological energetic response to temperature of the two species indicates that M. edulis cannot sustain a positive energy balance for sustained periods when sea surface temperature (SST) is greater than 23 °C, while M. galloprovincialis can maintain a positive energy balance at SST up to 30 °C. There is no difference in energetic response of the two species at cold temperatures (5-10 °C). The upper temperature threshold of positive energy balance in each species corresponds closely to the distribution of SST at their respective southern range limits in Europe. Alternatively, the northern range limit of M. galloprovincialis coincides with areas where winter SST is less than 9 °C, but there is no evidence of an energetic limit to this species at the cold end of its geographic range. Presently there is no mechanistic explanation for the difference between species in their northern range limits; however, as indicated by Random Forest modeling, M. galloprovincialis appears to be limited by cold temperatures during winter, suggesting the hypothesis of failure in reproductive development. These approaches allow for the ability to forecast changes in the distributions of these two species in Europe as SST continues to increase.