Researcher disciplines and the assessment techniques used to evaluate Laurentian Great Lakes coastal ecosystems

The Laurentian Great Lakes of North America have been a focus of environmental and ecosystem research since the Great Lakes Water Quality Agreement in 1972. This study provides a review of scientific literature directed at the assessment of Laurentian Great Lakes coastal ecosystems. Our aim was to understand the methods employed to quantify disturbance and ecosystem quality within Laurentian Great Lakes coastal ecosystems within the last 20 years. We focused specifically on evidence of multidisciplinary articles, in authorship or types of assessment parameters used. We sought to uncover: 1) where Laurentian Great Lakes coastal ecosystems are investigated, 2) how patterns in the disciplines of researchers have shifted over time, 3) how measured parameters differed among disciplines, and 4) which parameters were used most often. Results indicate research was conducted almost evenly across the five Laurentian Great Lakes and that publication of coastal ecosystems studies increased dramatically ten years after the first State of the Great Lakes Ecosystem Conference in 1994. Research authored by environmental scientists and by multiple disciplines (multidisciplinary) have become more prevalent since 2003. This study supports the likelihood that communication and knowledge-sharing is happening between disciplines on some level. Multidisciplinary or environmental science articles were the most inclusive of parameters from different disciplines, but every discipline seemed to include chemical parameters less often than biota, physical, and spatial parameters. There is a need for an increased understanding of minor nutrient, toxin, and heavy metal impacts and use of spatial metrics in Laurentian Great Lakes coastal ecosystems.     

A pound of prevention,plus a pound of cure: Early detection and eradication of invasive species in the Laurentian Great Lakes

Ballast water regulations implemented in the early 1990s appear not to have slowed the rate of new aquatic invasive species (AIS) establishment in the Great Lakes. With more invasive species on the horizon, we examine the question of whether eradication of AIS is a viable management strategy for the Laurentian Great Lakes, and what a coordinated AIS early detection and eradication program would entail. In-lake monitoring would be conducted to assess the effectiveness of regulations aimed at stopping new AIS, and to maximize the likelihood of early detection of new invaders. Monitoring would be focused on detecting the most probable invaders, the most invasion-prone habitats, and the species most conducive to eradication. When a new non-native species is discovered, an eradication assessment would be conducted and used to guide the management response. In light of high uncertainty, management decisions must be robust to a range of impact and control scenarios. Though prevention should continue to be the cornerstone of management efforts, we believe that a coordinated early detection and eradication program is warranted if the Great Lakes management community and stakeholders are serious about reducing undesired impacts stemming from new AIS in the Great Lakes. Development of such a program is an opportunity for the Laurentian Great Lakes resource management community to demonstrate global leadership in invasive species management.     

Historical changes and current status of crayfish diversity and distribution in the Laurentian Great Lakes

Despite increasing recognition of the importance of invertebrates, and specifically crayfish, to nearshore food webs in the Laurentian Great Lakes, past and present ecological studies in the Great Lakes have predominantly focused on fishes. Using data from many sources, we provide a summary of crayfish diversity and distribution throughout the Great Lakes from 1882 to 2008 for 1456 locations where crayfish have been surveyed. Sampling effort was greatest in Lake Michigan, followed by lakes Huron, Erie, Superior, and Ontario. A total of 13 crayfish species occur in the lakes, with Lake Erie having the greatest diversity (n = 11) and Lake Superior having the least (n = 5). Five crayfish species are non-native to one or more lakes. Because Orconectes rusticus was the most widely distributed non-native species and is associated with known negative impacts, we assessed its spread throughout the Great Lakes. Although O. rusticus has been found for over 100 years in Lake Erie, its spread there has been relatively slow compared to that in lakes Michigan and Huron, where it has spread most rapidly since the 1990s and 2000, respectively. O. rusticus has been found in both lakes Superior and Ontario for 22 and 37 years, respectively, and has expanded little in either lake. Our broad spatial and temporal assessment of crayfish diversity and distribution provides a baseline for future nearshore ecological studies, and for future management efforts to restore native crayfish and limit non-native introductions and their impact on food web interactions.     

Stable isotope mass balance of the Laurentian Great Lakes

    We investigate the physical limnology of the Laurentian Great Lakes of North America using a new dataset of ¹⁸O/¹⁶O and ²H/¹H ratios from over 500 water samples collected at multiple depths from 75 stations during spring and summer of 2007. δ¹⁸O and δ²H values of each lake plot in distinct clusters along a trend parallel to, but offset from, the Global Meteoric Water Line, reflecting the combined effects of evaporative enrichment and the addition of precipitation and runoff along the chain lake system. We apply our new dataset to a stable-isotope-based evaporation model that explicitly incorporates downwind lake effects, including humidity build-up and changes to the isotope composition of atmospheric vapor. Our evaporation estimates are consistent with previous mass transfer results for Michigan, Huron, Ontario and Erie, but not for Superior, which has a much longer residence time. Calculated evaporation from Superior is ~300 mm per year, less than previous estimates of ~500 mm per year, likely arising from integration of the ‘isotopic memory' of lower evaporation rates under cooler climatic conditions with greater ice-cover than the present. Uncertainties in the estimates from the stable-isotope-based model are comparable to mass transfer results, offering an independent technique for evaluating evaporation fluxes.     

European frogbit (Hydrocharis morsus-ranae) invasion facilitated by non-native cattails (Typha) in the Laurentian Great Lakes

Plant-to-plant facilitation is important in structuring communities, particularly in ecosystems with high levels of natural disturbance, where a species may ameliorate an environmental stressor, allowing colonization by another species. Increasingly, facilitation is recognized as an important factor in invasion biology. In coastal wetlands, non-native emergent macrophytes reduce wind and wave action, potentially facilitating invasion by floating plants. We tested this hypothesis with the aquatic invasive species European frogbit (Hydrocharis morsus-ranae; EFB), a small floating plant, and invasive cattail (Typha spp.), a dominant emergent, by comparing logistic models of Great Lakes-wide plant community data to determine which plant and environmental variables exerted the greatest influence on EFB distribution at multiple scales. Second, we conducted a large-scale field experiment to evaluate the effects of invasive Typha removal treatments on an extant EFB population. Invasive Typha was a significant predictor variable in all AIC-selected models, with wetland zone as the other most common predictive factor of EFB occurrence. In the field experiment, we found a significant reduction of EFB in plots where invasive Typha was removed. Our results support the hypothesis that invasive Typha facilitates EFB persistence in Great Lakes coastal wetlands, likely by ameliorating wave action and wind energy. The potential future distribution of EFB in North America is vast due in part to the widespread and expanding distribution of invasive Typha and other invading macrophytes, and their capacity to facilitate EFB's expansion, posing significant risk to native species diversity in Great Lakes coastal wetlands.     

Polymethylene-interrupted fatty acids: Biomarkers for native and exotic mussels in the Laurentian Great Lakes

Freshwater organisms synthesize a wide variety of fatty acids (FAs); however, the ability to synthesize and/or subsequently modify a particular FA is not universal, making it possible to use certain FAs as biomarkers. Herein we document the occurrence of unusual FAs (polymethylene-interrupted fatty acids; PMI-FAs) in select freshwater organisms in the Laurentian Great Lakes. We did not detect PMI-FAs in: (a) natural seston from Lake Erie and Hamilton Harbor (Lake Ontario), (b) various species of laboratory-cultured algae including a green alga (Scenedesmus obliquus), two cyanobacteria (Aphanizomenon flos-aquae and Synechococystis sp.), two diatoms (Asterionella formosa, Diatoma elongatum) and a chrysophyte (Dinobryon cylindricum) or, (c) zooplankton (Daphnia spp., calanoid or cyclopoid copepods) from Lake Ontario, suggesting that PMI-FAs are not substantively incorporated into consumers at the phytoplankton-zooplankton interface. However, these unusual FAs comprised 4-6% of total fatty acids (on a dry tissue weight basis) of native fat mucket (Lampsilis siliquoidea) and plain pocketbook (L. cardium) mussels and in invasive zebra (Dreissena polymorpha) and quagga (D. bugensis) mussels. We were able to clearly partition Great Lakes' mussels into three separate groups (zebra, quagga, and native mussels) based solely on their PMI-FA profiles. We also provide evidence for the trophic transfer of PMI-FAs from mussels to various fishes in Lakes Ontario and Michigan, further underlining the potential usefulness of PMI-FAs for tracking the dietary contribution of mollusks in food web and contaminant-fate studies.     

Fish movement and migration studies in the Laurentian Great Lakes: Research trends and knowledge gaps

Resource management agencies in the Laurentian Great Lakes routinely conduct studies of fish movement and migration to understand the temporal and spatial distribution of fishes within and between the lakes and their tributaries. This literature has never been summarized and evaluated to identify common themes and future research opportunities. We reviewed 112 studies, published between 1952 and 2010, with the goal of summarizing existing research on the movement and migration of fishes in the Laurentian Great Lakes. The most commonly studied species were Lake Trout (Salvelinus namaycush), Walleye (Sander vitreus), and Lake Sturgeon (Acipenser fulvescens). Studies relied mainly on mark-recapture techniques with comparatively few using newer technologies such as biotelemetry, hydroacoustics, or otolith microchemistry/isotope analysis. Most movement studies addressed questions related to reproductive biology, effects of environmental factors on movement, stocking, and habitat use. Movement-related knowledge gaps were identified through the literature synthesis and a survey distributed to Great Lakes fisheries managers. Future studies on emigration/immigration of fishes through lake corridors, the dispersal of stocked fishes and of stock mixing were identified as being particularly important given their potential for developing lake- or region-wide harvest regulations and stocking strategies. The diversity of tools for studying fish movement across multiple years and various spatial scales gives researchers new abilities to address key science questions and management needs. Addressing these needs has the potential to improve upon existing fisheries management practices within the complexity of multi-jurisdictional governance in the Laurentian Great Lakes.     

Evaluation of sea lamprey-associated mortality sources on a generalized lake sturgeon population in the Great Lakes

Lake sturgeon populations in the Laurentian Great Lakes experience two age-specific mortality sources influenced by the sea lamprey Petromyzon marinus control program: lampricide (TFM) exposure-induced mortality on age-0 fish and sea lamprey predation on sub-adults (ages 7–24). We used a generic age-structured population model to show that although lampricide-induced mortality on age-0 lake sturgeon can limit attainable population abundance, sea lamprey predation on sub-adult lake sturgeon may have a greater influence. Under base conditions, adult lake sturgeon populations increased by 5.7% in the absence of TFM toxicity if there was no change in predation; whereas, a 13% increase in predation removed this effect, and a doubling of sea lamprey predation led to a 32% decrease in adult lake sturgeon. Our estimates of lake sturgeon abundance were highly dependent on the values of life history and mortality parameters, but the relative impacts of ceasing TFM treatment and increasing predation were robust given a status quo level of predation. The status quo predation was based on sea lamprey wounding on lake sturgeon, and improvements in this information would help better define tradeoffs between the mortality sources for specific systems. Reduction or elimination of TFM toxicity on larval lake sturgeon, while maintaining TFM toxicity on larval sea lamprey, can promote lake sturgeon restoration and minimize negative impacts on other fish community members.     

The deceptively complicated “elevation ordinary high water mark” and the problem with using it on a Laurentian Great Lakes shore

In 2013 the Laurentian Great Lakes are at historically low levels; but they will undoubtedly rise again as they always have in an ongoing pattern of seasonal, annual and decadal fluctuations. Those fluctuations, coupled with other physical dynamics unique to the Great Lakes system, will continue to shift shorelines lake-ward and land-ward dramatically over time, perhaps more so because of increased storminess from climate change. These shifting shores implicate legal doctrines that attempt to balance public interests and private property rights at the shore, and they complicate the Great Lakes states' efforts to effectively and fairly manage their Great Lakes shorelands. One challenge comes from using an elevation-based standard to mark ordinary high water, a method that is difficult conceptually to administer and that yields multiple marks over time. We describe briefly Great Lakes shoreline dynamics and the application of state Public Trust Doctrines to those shorelines, and we discuss in detail recent litigation in Michigan regarding use of an elevation-based standard to mark ordinary high water, illustrating the inherent problems with that standard. We conclude that the elevation-based standard should be abandoned, or if not abandoned applied in a manner to adequately safeguard public trust shorelands.     

Are PCB Levels in Fish from the Canadian Great Lakes Still Declining?

Long- and short-term levels and trends of polychlorinated biphenyls (PCBs) in lake trout (Salvelinus namaycush) and walleye (Sander vitreus) from the Canadian waters of the Great Lakes are examined using the bootstrap resampling method in light of the Great Lakes Strategy 2002 (GLS-2002) objective of decrease in concentrations by 25% during 2000–2007. This objective has been set as an indicator of progress toward the long-term goal of all Great Lakes fish being safe to eat without restriction. Lake Superior lake trout and walleye PCB concentrations were almost unchanged between 1990-2006, and the bootstrap analysis suggests that the probability of achieving the GLS-2002 objective is negligible (< 2%). The PCB levels in Lake Huron lake trout and walleye are decreasing; the declines between 2000–2007 are estimated to be 25–35% and 5–30%, respectively. In contrast, Lake Erie walleye concentrations will likely increase by 25–50% between 2000–2007. For Lake Ontario lake trout, achieving the 25% reduction target seems highly probable with a likely decrease of 45–55%; for Lake Ontario walleye, the probability of achieving such a reduction is only 8% with an expected change of −13 to +15%. Although the targeted reduction may not be achieved for walleye from Lakes Superior, Huron, and Ontario, their best projected 2007 PCB levels are below the unlimited fish consumption guideline of 105 ng/g wet weight used by the Ontario Ministry of the Environment. In contrast, although there are high probabilities of achieving the goal for lake trout from Lakes Huron and Ontario, their best projected 2007 PCB levels (160 and 370 ng/g ww, respectively) will continue to result in consumption restrictions. Lake Superior lake trout concentrations may remain unchanged at the current elevated level of 160 ng/g ww. For Lake Erie fish, the projected 2007 concentrations and the increasing trends are both worrisome. Additional measurements beyond 2007 are necessary to confirm these estimates because of the observed periodic oscillations in the concentrations.     

A systematic review of the literature on plastic pollution in the Laurentian Great Lakes and its effects on freshwater biota

Plastic pollution is ubiquitous in freshwater systems worldwide, and the Laurentian Great Lakes are no exception. We conducted a systematic review to synthesize the current state of the literature on plastic pollution, including macroplastics (>5 mm) and microplastics (<5 mm), in the Great Lakes. Thirty-four publications were used in our systematic review. We found ubiquitous contamination of microplastics in surface water, with maximum abundances exceeding those in ocean gyres. There are also high levels of plastic contamination reported across benthic sediments and shorelines of the Great Lakes. Citizen science data reveals macroplastic across Great Lakes shorelines, with more than three million pieces of plastic litter recorded over a span of three years. We completed a second systematic review of plastic pollution and its impact on freshwater ecosystems in general to inform how plastic in the Great Lakes may impact wildlife. Among studies published in the literature, we found 390 tested effects, 234 (60%) of which were detected and 156 (40%) of which were not; almost all of the freshwater effects (>98%) were tested on microplastics. Based on a subset of these papers, we found that the shape and size of a particle likely affects whether an effect is detected, e.g., more effects are detected for smaller particles. Finally, we identify gaps in scientific knowledge that need to be addressed and discuss how the state of the science can inform management strategies.     

Changes in mid-summer water temperature and clarity across the Great Lakes between 1968 and 2002

In recent decades, three important events have likely played a role in changing the water temperature and clarity of the Laurentian Great Lakes: 1) warmer climate, 2) reduced phosphorus loading, and 3) invasion by European Dreissenid mussels. This paper compiled environmental data from government agencies monitoring the middle and lower portions of the Great Lakes basin (lakes Huron, Erie and Ontario) to document changes in aquatic environments between 1968 and 2002. Over this 34-year period, mean annual air temperature increased at an average rate of 0.037 °C/y, resulting in a 1.3 °C increase. Surface water temperature during August has been rising at annual rates of 0.084 °C (Lake Huron) and 0.048 °C (Lake Ontario) resulting in increases of 2.9 °C and 1.6 °C, respectively. In Lake Erie, the trend was also positive, but it was smaller and not significant. Water clarity, measured here by August Secchi depth, increased in all lakes. Secchi depth increased 1.7 m in Lake Huron, 3.1 m in Lake Ontario and 2.4 m in Lake Erie. Prior to the invasion of Dreissenid mussels, increases in Secchi depth were significant (p < 0.05) in lakes Erie and Ontario, suggesting that phosphorus abatement aided water clarity. After Dreissenid mussel invasion, significant increases in Secchi depth were detected in lakes Ontario and Huron.     

Heterogeneity of bacterial communities within the zebra mussel (Dreissena polymorpha) in the Laurentian Great Lakes Basin

We analyzed and compared the structure of bacterial communities associated with zebra mussel mantle cavity fluid, gills, and gut samples collected from Lake Loon, an inland lake in Michigan's Lower Peninsula (U.S.A.) using partial 16S rRNA gene sequencing. A total of 713 cloned 16S ribosomal gene sequences were checked for similarity to existing 16S sequences in two public databases: the Ribosomal Database Project and BLAST. Based on a 98% sequence similarity threshold, a total of 355 phylotypes belonging to 12 bacterial phyla and the phylum Bacillariophyta (diatoms) were identified in zebra mussel samples. A dominance of sequences belonging to the class γ-proteobacteria was observed in the mantle cavity clone libraries (P < 0.0001). Significant sample-specific sequence associations (P < 0.001) included members of the orders Pseudomonadales and Vibrionales in mantle cavity fluid and gut clone libraries, members of both the phylum Actinobacteria and the class δ-proteobacteria in gill clone libraries, and the Cyanobacteria/Bacillariophyta group in gut clone libraries. Furthermore, our results suggest that the zebra mussel may serve as a reservoir for facultative and opportunistic pathogenic bacteria, e.g., Clostridium spp., Flavobacterium spp. and Mycobacterium spp., for many aquatic and terrestrial animals. This work constitutes the first account of the heterogeneity of bacterial communities associated with multiple compartments within the zebra mussel. The information gained in this study significantly contributes to what is known regarding the microbial ecology of the zebra mussel and its role in disease ecology and food-web shifts in the Great Lakes ecosystem.     

The benthic community of the Laurentian Great Lakes: Analysis of spatial gradients and temporal trends from 1998 to 2014

We used the results of seventeen years of Great Lakes benthic monitoring conducted by the U.S. EPA's Great Lakes National Program Office to describe the spatial and temporal patterns of benthic communities, assess their status, trends, and main drivers, and to infer the potential impact of these community changes on ecosystem functioning. Benthic abundance and diversity were higher at shallow (<70?m in depth) stations with chlorophyll concentrations above 3?μg/L than at deeper sites (<1?μg/L). We infer that lake productivity, measured by chlorophyll was likely the major driver of benthic abundance and diversity across lakes. Consequently, benthic diversity and abundance were the highest in the most productive Lake Erie, followed by lakes Ontario, Michigan, Huron, and Superior. Multivariate analysis distinguished three major communities shared among lakes (littoral, sublittoral, and profundal) that differed in species composition and abundance, functional group diversity, and tolerance to organic pollution. Analysis of temporal trends revealed that the largest changes occurred in profundal communities, apparent in significant shifts in dominant taxa across all lakes except Lake Superior. In lakes Michigan, Huron, and Ontario, the former dominant Diporeia was replaced with Dreissena and Oligochaeta. Profundal species, with the exception of dreissenids, became less abundant, and their depth distribution has shifted. In contrast, density and diversity of native littoral and sublittoral communities increased. The invasion of dreissenids was among the most important drivers of changes in benthic communities. Continued monitoring is critical for tracking unprecedented changes occurring in the Great Lakes ecosystem.     

Toxaphene trends in the Great Lakes fish

As part of the U.S. Great Lakes Fish Monitoring and Surveillance Program (GLFMSP), more than 300 lake trout (Salvelinus namaycush) and walleye (Stizostedion vitreum vitreum) collected from the Laurentian Great Lakes each year from 2004 to 2009, have been analyzed for total toxaphene and eight selected congeners. The analytical results show fish toxaphene concentrations are quite different among lakes. Between 2004 and 2009, Lake Superior lake trout had the highest concentration (119 to 482 ng/g) and Lake Erie walleye had the lowest concentration (18 to 47 ng/g). Combining these results with the historical total toxaphene data (1977–2003), temporal changes were examined for each lake. Because of different analytical methods used in the previous studies, the historical data were adjusted using a factor of 0.56 based on a previous inter-method comparison in our laboratory. Trend analysis using an exponential decay regression showed that toxaphene in Great Lakes fish exhibited a significant decrease in all of the lakes with t_1/2 (confidence interval) of 0.9 (0.8–1.1) years for Lake Erie walleye, 3.8 (3.5–4.1) years for Lake Huron lake trout, 5.6 (5.1–6.1) years for Lake Michigan lake trout, 7.5 (6.7–8.4) years for Lake Ontario lake trout and 10.1 (8.2–13.2) years for Lake Superior lake trout. Parlars 26, 50 and 62 were the dominant toxaphene congeners accounting for 0.53% to 41.7% of the total toxaphene concentration. Concentrations of these congeners generally also decreased over time.     

The flathead catfish invasion of the Great Lakes

A detailed review of historical literature and museum data revealed that flathead catfish were not historically native in the Great Lakes Basin, with the possible exception of a relict population in Lake Erie. The species has invaded Lake Erie, Lake St. Clair, Lake Huron, nearly all drainages in Michigan, and the Fox/Wolf and Milwaukee drainages in Wisconsin. They have not been collected from Lake Superior yet, and the temperature suitability of that lake is questionable. Flathead catfish have been stocked sparingly in the Great Lakes and is not the mechanism responsible for their spread. A stocking in 1968 in Ohio may be one exception to this. Dispersal resulted from both natural range expansions and unauthorized introductions. The invasion is ongoing, with the species invading both from the east and the west to meet in northern Lake Michigan. Much of this invasion has likely taken place since the 1990s. This species has been documented to have significant impacts on native fishes in other areas where it has been introduced; therefore, educating the public not to release them into new waters is important. Frequent monitoring of rivers and lakes for the presence of this species would detect new populations early so that management actions could be utilized on new populations if desired.     

Reviewing uncertainty in bioenergetics and food web models to project invasion impacts: Four major Chinese carps in the Great Lakes

Bioenergetics and food web models are tools available for understanding and projecting the impacts of aquatic species invasions on food web structure and energy allocation of an ecosystem. However, uncertainty is inherent in modeling the impact of invasive species in novel ecosystems as assumptions must be made about physiological responses to novel environments and interactions with existing (native and non-native) species. Here we use the four major Chinese carps (FMCC) in the Laurentian Great Lakes as a case study to categorize and describe the suite of uncertainties inherent in projecting the impact of invasive species with bioenergetics and food web models. We approach this case study in a decision analytic framework, describing structural uncertainties, environmental variation, partial observability, partial controllability, and linguistic uncertainty. Finally, we review and give suggestions for how the use of methods including adaptive management, scenario planning, sensitivity analyses, and value of information as well as efforts to ensure clarity in language and model structure can enable modelers and managers to reduce and account for key uncertainties and make better decisions for the control of invasive species.     

Risk-based classification and interactive map of watersheds contributing anthropogenic stress to Laurentian Great Lakes coastal ecosystems

We describe development anthropogenic stress indices for coastal margins of the Laurentian Great Lakes basin. Indices were derived based on the response of species assemblages to watershed-scale stress from agriculture and urbanization. Metrics were calculated for five groups of wetland biota: diatoms, wetland vegetation, aquatic invertebrates, fishes, and birds. Previously published community change points of these assemblages were used to classify each watershed as ‘least-disturbed’, ‘at-risk’, or ‘degraded’ based on community response to these stressors. The end products of this work are an on-line map utility and downloadable data that characterize the degree of agricultural land use and development in all watersheds of the US and Canadian Great Lakes basin. Discrepancies between the observed biological condition and putative anthropogenic stress can be used to determine if a site is more degraded than predicted based on watershed characteristics, or if remediation efforts are having beneficial impacts on site condition. This study provides a landscape-scale evaluation of wetland condition that is a critical first step for multi-scale assessments to help prioritize conservation or restoration efforts.