Introduction

Lake Erie is a large, naturally dynamic, and heterogeneous ecosystem that supports diverse biological communities integral to ecosystem functioning and the provision of services valued by society (Allan et al., 2017; Fraker et al., 2022; Reutter, 2019; Sly, 1976). Despite its importance, a comprehensive accounting of Lake Erie’s biological diversity is lacking as is a thorough understanding of the mechanisms driving variation in community structure (e.g., species composition) during recent decades (Fraker et al., 2022). These information gaps reflect multiple challenges, including inconsistent monitoring, reporting, and data accessibility (Budnik et al., 2024; Fraker et al., 2022), the impacts of multiple, interacting human-driven stressors (e.g., climate change, altered nutrient inputs, invasive species, habitat destruction; Smith et al., 2015; Smith et al., 2019), and the need for more mechanistic research and modeling tools (Mohamed et al., 2019; Neumann et al., 2021) – challenges common across the Great Lakes (Jenny et al., 2020; Munawar and Hecky, 2001; Sterner et al., 2017). These uncertainties are especially conspicuous in Lake Erie’s coastal wetlands, which are characterized by complex hydrology and biology and have been dynamic in part due to human-driven environmental change (Cvetkovic and Chow-Fraser, 2011; Herdendorf, 1992; Kowalski and Wilcox, 1999; Munawar and Heath, 2008). Thus, investigations that assess how and why wetland community structure has varied during recent decades, as well as the implication of these changes for ecosystem function and ecosystem-service provisioning, are needed, as such information could benefit ongoing and planned wetland restoration efforts (Cvetkovic and Chow-Fraser, 2011; Rumball et al., 2025; Sierszen et al., 2012).

Although much recent research has focused on understanding the causes and consequences of aquatic community change in Lake Erie’s open waters (e.g., phytoplankton: Barbiero et al., 2019; O’Donnell et al., 2023a; zooplankton: Bailey and Hood, 2024; O’Donnell et al., 2023b; benthic macroinvertebrates: Burlakova et al., 2018; Karatayev et al., 2014; fish: Sinclair et al., 2021; Sinclair et al., 2023a), important information gaps persist in this habitat zone as well. These gaps were a major motivating factor for the Aquatic Ecosystem Health & Management (AEHM) Lake Erie special issue series to which this special issue belongs (see AEHM volumes:issues 26:4, 27:1, 28:1). The previous three special issues provided new insights into how and why Lake Erie’s open-lake phytoplankton (e.g., Lesht et al., 2024), benthic invertebrate (e.g., Howell et al., 2024), zooplankton (e.g., Ludsin et al., 2025), and fish (e.g., DeBruyne et al., 2024) communities have varied through time. Even so, substantial work remains to understand open-lake community dynamics and their drivers better.

This fourth and final AEHM special issue devoted to Lake Erie aims to help address information deficits in both wetland and open-lake systems. The first section of this special issue (Wetland Communities) consists of five research contributions and focuses on Lake Erie’s coastal wetlands. The first three contributions use long-term, binational (USA – Canada) monitoring data to provide detailed assessments of macrophyte (Gathman et al., 2025), benthic invertebrate (Dobrin et al., 2025), and fish (Johnson et al., 2025) communities in more than 50 wetlands across the lake, providing insight into their structuring mechanisms through time. The remaining two papers of this section examine fish community change in smaller set of wetlands; Lamothe et al. (2025) quantify fish community change in Point Pelee National Park of Canada (hereafter Point Pelee National Park) over the past two decades, whereas Kowalski et al. (2025) report on a four-year study that assess how restored wetland connectivity influences wetland function (as measured by fish abundance and movement patterns). By contrast, this special issue’s second section (Open-lake Communities) focuses on open waters of Lake Erie. The first paper, Fitzpatrick et al. (2025), provides new information on spatiotemporal variation in primary productivity during recent years, whereas Watkins et al. (2025) examine how Lake Erie’s zooplankton communities have varied through time across all three lake basins. Together, these studies advance our understanding of drivers of changes within Lake Erie’s lower food web.

Below, we summarize the major findings of these seven papers. We then offer concluding remarks to help generalize and contextualize the suite of findings presented in this special issue.

Wetland Communities

Lake Erie historically supported vast coastal wetland habitat (> 120,000 ha; Herdendorf, 1992; Mitsch, 2017). However, agricultural, residential, and urban development throughout the watershed resulted in extensive wetland loss and degradation. By the end of that 20^th century, studies estimated that 80 to 95% of Lake Erie’s wetlands were destroyed or degraded beyond proper function (Herdendorf, 1992; Lyon and Greene, 1992; Mitsch, 2017), leaving ~16,000 ha remaining today (WHSRN, 2025). Given the many benefits that wetlands provide (e.g., functional habitat for recreationally and culturally important species; reducing nutrient and chemical pollution in the open lake; bolstering economies through food production and nonconsumptive recreation; Carter et al., 2022; Mitsch, 2017; Sierszen et al., 2012; Trebitz and Hoffman, 2015), efforts to restore and protect Lake Erie wetlands have begun to expand of late (Rumball et al., 2025; USEPA, 2025). This growth has been supported by initiatives at multiple levels, including international (Great Lakes Water Quality Agreement; Great Lakes Coastal Wetland Monitoring Program, GLCWMP), federal (US Great Lakes Restoration Initiative; Canadian Federal Policy on Wetland Conservation), provincial (Conservation Authorities Act), and state (e.g., H2Ohio Initiative). Despite increased monitoring activity and restoration research, information on the flora and fauna of Lake Erie’s wetlands and their capacity to support key aspects of ecosystem functioning (e.g., fish movement) remains limited. The first three papers of this AEHM special issue therefore provide some of the first comprehensive results from the U.S. Environmental Protection Agency’s (USEPA’s) Great Lakes Coastal Wetland Monitoring Program (GLCWMP).

Gathman et al. (2025) provide baseline data on vegetation in Lake Erie’s coastal wetlands. The data, which were collected through the GLCWMP, characterize plant community composition in 58 coastal wetlands distributed along the northern and southern shorelines across the lake during 2011–2022. The authors also evaluate how observed changes in community composition relate to latitude and water-level fluctuations. They documented 310 species, consistent with estimates made more than 40 years ago (Herdendorf, 1992), with wetland-level species richness ranging from 4 to 58 species. Two notable patterns emerged: 1) species richness increased from west to east across the lake; and 2) the richness of submergent and floating-leaved vegetation increased with water level.

Dobrin et al. (2025) similarly provide baseline data that can support future efforts to explain changes in wetland macroinvertebrate assemblages. Using a standardized sweep-net protocol, they sampled 71 distinct coastal wetlands across US and Canadian waters of all three Lake Erie basins during 2004–2022. Their paper characterizes these assemblages, which consist of more than 150 genera across 80-plus families. Most wetlands were dominated by taxa that are indicative of good ecological condition (e.g., Ephemeroptera, Odonata, Amphipoda) and surprisingly few non-native species (with only the faucet snail, Bithynia tentaculata, being consistently abundant). Even so, wetlands clustered distinctively based on relative taxon abundances. Dobrin et al. conclude by emphasizing the value of this monitoring dataset to test whether Indices of Biotic Integrity show spatial structure that mirrors invertebrate assemblage clustering, which could help clarify the ultimate and proximal factors (likely lake-level and landscape-level variables interacting with local wetland conditions) shaping these invertebrate communities.

Similar to Dobrin et al. (2025), Johnson et al. (2025) present results from 52 coastal wetlands monitored as part of the GLCWMP, but with a focus on fish communities. During 2011–2022, they captured 115,844 individuals across 63 fish species. Johnson et al. examine how wetland fish community composition differed between Lake Erie’s northern and southern coastlines and among lake basins. Overall, catches were dominated by catfishes, non-native common carp (Cyprinus carpio), and goldfish (Carassius auratus). However, they detected substantial differences in species composition among Lake Erie’s three basins (e.g., more catfishes and non-native cyprinids to the west and more centrarchids to the east), and northern and southern shorelines (e.g., higher species richness in northern versus southern wetlands). As with the previous studies, Johnson et al. provide baseline data that could help identify the how wetland-specific habitat features influence the composition of coastal wetland fish communities, as well as how this composition relates to Lake Erie’s open-lake fish communities to which they are connected. Given the known susceptibility of wetland fish communities to anthropogenic change (Trebitz et al., 2009), Johnson et al.’s (2025) baseline data can also provide a foundation for assessing wetland responses to current and future pressures, including changes in ecosystem productivity, invasive species, and climate change.

Lamothe et al. (2025) also examine change in wetland fish communities during recent decades, applying multivariate statistical approaches to samples collected within Point Pelee National Park on the north shore of Lake Erie’s westernmost basin. Unlike the standardized data used in the three previously summarized papers, Lamothe et al. compiled data from sampling conducted using different net types during 2002, 2003, 2019, and 2021 as part of individual projects. This sampling captured more than 35,000 individuals spanning 40 species, with centrarchids (bluegill, Lepomis macrochirus, and warmouth, L. gulosus) among the most frequently captured species. The authors documented site-specific changes in abundance for some species and the first occurrence of tubenose gobies (Proterorhinus spp.) in this coastal complex (first documented in 2021). However, overall, their analyses showed that the Point Pelee National Park’s fish community remained largely unchanged during the past two decades. Observed interannual variations likely reflect, at least in part, differences in sampling gear and known changes in the hydrologic connectivity among study sites (e.g., intermittent connectivity of wetland habitat with Lake Erie after a recent breach of the barrier beach).

In the other spatially restricted study, Kowalski et al. (2025) describe fish movement within and between a recently reconnected diked wetland within Lake Erie’s westernmost basin. This work aligns with broader efforts to understand the ecological responses of wetland communities to restoration efforts in general (e.g., Rumball et al., 2025), as well as responses to increased wetland connectivity (e.g., Carter et al., 2022). Kowalski et al. (2025) used acoustic sonar during 2011–2014 to document the timing and frequency of fish movements (including daily, seasonal, and annual trends), an approach that overcomes key limitations of conventional techniques (e.g., netting, visual surveys). Their study provides insight into the timescale, seasonality, and magnitude of fish movements in newly connected wetland ecosystems. Strong diel and seasonal patterns of fish activity were observed and were largely consistent among years. These results have clear implications for optimizing the timing of management actions that depend on differentiating periods of high fish activity (e.g., surveying the fish assemblage) from low activity (e.g., restricting fish access to undertake non-native species removal).

Open-lake Communities

Similar to Lake Erie’s coastal wetlands, its open-water communities have experienced major changes through time due to anthropogenic stress (Burlakova et al., 2018; Karatayev et al., 2014; O’Donnell et al., 2023a; O’Donnell et al., 2023b; Munawar and Munawar, 1999; Sinclair et al., 2021; Sinclair et al., 2023a). Arguably the most impactful stress has been the alteration of nutrient (especially phosphorus, P) inputs, which has caused major shifts in lake-wide ecosystem productivity (Sinclair et al., 2023b). Most conspicuously, excessive point-source loading of total P loading during the 1950s to 1970s caused widespread eutrophication (Di Toro et al., 1987; Sly, 1976; Vollenweider et al., 1974). Subsequent P abatement efforts enacted as part of the Great Lakes Water Quality Agreement contributed to the rehabilitation of the lake (e.g., oligotrophication; Di Toro et al., 1987; Ludsin et al., 2001; Makarewicz and Bertram, 1991). Since the turn of the 21^st century, however, Lake Erie has re-eutrophied, largely due to changes in agricultural land-use practices that have led to excessive inputs of bioavailable P (Kane et al., 2014; Scavia et al., 2014; Sinclair et al., 2021; Sinclair et al., 2023b; Watson et al., 2016).

These changes in P availability, combined with other anthropogenic stressors, including invasive species established during the late 1980s and early 1990s (e.g., sessile, filter-feeding dreissenid mussels, Dermott and Munawar, 1993; predatory zooplankton species like Bythotrephes longimanus, Barbiero and Rockwell, 2008) and climate change (e.g., increased temperature and storm events; Dobson et al., 2020; Kaul et al., 2024), have complicated efforts to understand and predict biological responses through interactive and synergistic effects (Smith et al., 2019). These drivers can also create novel conditions in which previously reliable predictive relationships and the mechanistic understanding underpinning them no longer remain valid (Haltuch et al., 2019; Tamburello et al., 2019). In ecosystems experiencing such widespread environmental change (e.g., Lake Erie), it is critical to reevaluate established relationships and to identify indicators of ecosystem change so that management agencies can continue to rehabilitate, maintain, and/or sustain the many services these ecosystems provide (Haltuch et al., 2019; Rodríguez et al., 2016; Tamburello et al., 2019). The last two papers of this special issue attempt to do just that.

Recognizing the importance of revisiting assumptions about Lake Erie primary productivity and the models used to predict it, Fitzpatrick et al. (2025) used a radioisotope (¹⁴Carbon) approach to measure primary productivity in all three of Lake Erie’s basins and develop updated predictive models. Their results confirmed the established west-to-east decrease in primary productivity rate, but they also yielded several surprising results. First, they showed that the historically strong relationship between algal biomass (as measured by chlorophyll a; Munawar and Burns, 1976) and primary production has weakened. Rather than chlorophyll a being the strongest predictor of primary productivity, it is now better predicted by total P and surface temperature. This finding reinforces the need for agencies managing water quality to consider nutrient form/availability and climate when estimating rates of primary production. Second, Fitzpatrick et al. (2025) show that, despite having lower rates of volumetric primary production than the Western Erie Basin (hereafter Western Basin), the Central Erie Basin (hereafter Central Basin) accounts for the bulk (56.9 – 71.0%) of the lake’s total primary production (i.e., carbon fixation) by virtue of its large size. Finally, these authors report differences in phytoplankton communities among basins; although picoplankton (cells 0.2 to < 2 μm in diameter) were important primary producers in all three basins, “net” plankton (cyanophytes and diatoms with colonies and cells > 20 µm in diameter, respectively) dominated the Western Basin, consistent with Lake Erie’s continued eutrophic state.

With a similar goal of providing information useful to management decision-making, Watkins et al. (2025) used zooplankton community data to assess the ecological health of Lake Erie’s three basins. Zooplankton was used as an indicator because of its central position in the food web; shifts in community composition can reflect changes in the phytoplankton upon which they graze and the fish to which they fall prey (e.g., Johannsson et al., 1999; Mills et al., 1987). Watkins et al. (2025) describe changes in Lake Erie’s zooplankton communities using long-term (1997–2022) USEPA Great Lakes National Program Office monitoring data. This period encompasses the 1) the expansion of non-native invertebrates (e.g., Bythotrephes longimanus and dreissenid mussels; Barbiero and Rockwell, 2008; Dermott and Munawar, 1993), 2) the re-eutrophication of Lake Erie (Scavia et al., 2014; Watson et al., 2016; Sinclair et al., 2023b), and 3) continued climate change in the basin (Dobson et al., 2020; Kaul et al., 2024). Watkins et al. (2025) show that Lake Erie’s zooplankton communities changed from the most recent reported values (Barbiero et al., 2019), with the degree of change varying among lake basins. For example, in the Central and Eastern (Erie) basins, trends included increases in Calanoida during spring and a decrease in Bosminidae and Daphniidae during summer. By contrast, the Western Basin showed little long-term change. Watkins et al. (2025) conclude by offering insights into the role that anthropogenic stressors, including invasive Bythotrephes longimanus and changes in water temperature, have played in driving these basin-specific changes through time.

Conclusions

As with other Great Lakes of the world (Jenny et al., 2020; Sterner et al., 2017), understanding how Lake Erie’s biological communities have changed through time in response to both natural and human-driven environmental change remains a pressing need. Although this need is evident in Lake Erie’s open waters, it is especially conspicuous in its coastal wetlands, which have received less monitoring and research attention (Cvetkovic and Chow-Fraser, 2011). Thus, we envision that the data and results presented in this AEHM special issue will be of interest to a wide readership.

Most notably, papers in this AEHM special issue provide baseline data and analyses of wetland plant (Gathman et al., 2025), invertebrate (Dobrin et al., 2025), and fish (Johnson et al., 2025; Lamothe et al., 2025) communities. Beyond establishing reference conditions, these studies begin to identify causal mechanisms of community change (e.g., water-level fluctuations, Gathman et al., 2025; temporary hydrologic connectivity, Lamothe et al., 2025). The datasets presented also create opportunities for others to develop more synthetic indicators of wetland condition and change (e.g., Indices of Biotic Integrity, Johnson et al., 2025) and to explore the impacts of other ecosystem drivers like altered land-use practices, invasive species, and meteorological variation. Further, Kowalski et al. (2025) demonstrate the utility of acoustic telemetry for quantifying fish abundance and movement over short and long timescales in wetlands. Together, these long-term data and assessment tools will be invaluable for evaluating the effectiveness of restoration practices (e.g., restored hydrologic connectivity) within Lake Erie and elsewhere (Carter et al., 2022; Rumball et al., 2025), and for forecasting how continued or novel anthropogenic stressors (Amani et al., 2022; Anderson et al., 2023; Ward et al., 2025) might influence wetland communities and the ecosystem services they support (e.g., clean water, fisheries production, recreational opportunities).

Although this special issue emphasized Lake Erie’s coastal wetlands, the two open-water studies of plankton assemblages also yield important insights. These studies indicate that Lake Erie’s phytoplankton (Fitzpatrick et al., 2025) and zooplankton (Watkins et al., 2025) assemblages have responded to anthropogenic stress during recent decades. For example, Fitzpatrick et al. (2025) show that the historically strong relationship between chlorophyll a (a proxy for phytoplankton biomass) and primary production has weakened, apparently reflecting shifts in phosphorous loading (e.g., increased bioavailable P of late; Kane et al., 2014; Scavia et al., 2014). Watkins et al.’s (2025) results also suggest that warming, together with increased bioavailable P, have increased carbon fixation by large “net” plankton such as cyanophytes and diatoms (especially in Lake Erie’s Western Basin). Likewise, these authors demonstrate basin-specific shifts in the abundance of crustacean zooplankton, including summer declines in important prey taxa for fish, which they suggest are related to the non-native predatory zooplankter Bythotrephes longimanus.

Further, both studies highlight the growing importance of Lake Erie’s Central Basin. While Fitzpatrick et al. (2025) confirm that volumetric primary productivity rates decrease from west to east, they also show that the vast majority of primary production (carbon fixation), largely driven by picoplankton, occurs in Lake Erie’s Central Basin (also see Lesht et al., 2024). Interestingly, Watkins et al. (2025) found that crustacean zooplankton biomass during summer is greater in the Central Basin than the Western Basin, a result somewhat surprising given that nutrient loading (Scavia et al., 2014) and volumetric primary production rates (Fitzpatrick et al., 2025) are higher in the Western Basin than in the Central Basin. These findings suggest that the efficiency of energy transfer through the food web is lower in the Western Basin than Central Basin, perhaps due to the increased presence of harmful algal blooms dominated by cyanophytes during summer (Gobler et al., 2024; Watson et al., 2016). Studies that better integrate these plankton community findings with additional physicochemical (e.g., temperature, nutrient loading, dissolved oxygen) and biological components (e.g., consumers, including both non-native and native invertebrates and fish) could help resolve this uncertainty. More broadly, Fitzpatrick et al. (2025) and Watkins et al. (2025) underscore the need to periodically reassess ecological assumptions and update predictive models as lake conditions change (sensu Haltuch et al., 2019; Tamburello et al., 2019).

Another important information gap that this AEHM special issue identifies is the need to integrate wetland and open-lake studies. Wetlands can reduce nutrient (P) loading into Lake Erie (e.g., Carter et al., 2022; Mitsch, 2017), which should help mitigate eutrophication-related problems such as harmful algal blooms in its Western Basin, bottom hypoxia in the Central Basin, and Cladophora outbreaks in the Eastern Basin (Higgins et al., 2006; Scavia et al., 2014; Watson et al., 2016). However, the contribution of Lake Erie’s coastal wetlands to offshore biological productivity has not been fully evaluated. Similarly, while previous research has shown that Great Lakes wetland and open-lake fish communities share many species and wetlands are used for spawning and as nursery areas (Trebitz and Hoffman, 2015), we are unaware of any study that has linked open-lake fisheries productivity with wetland use in Lake Erie. Such integrative work could provide insights to guide future management planning (sensu Levin et al., 2009; Tallis et al., 2010) and strengthen the case for wetland restoration that is explicitly aligned with their ecological functions.

Given the brief insights and overarching conclusions presented, we encourage readers to explore the papers in this issue, as well as those in the three previous AEHM special issues focused on Lake Erie (volumes:issues 26:4, 27:1, 28:1)ⁱ. Collectively, these special issues deepen our understanding of Lake Erie, point to new research directions, and may inform more effective management so that the well-being of those who rely on Lake Erie for food, water, recreation, or other services can be sustained now and under future environmental change.