Peatland forest ecosystems play a critical ecological, economic, and cultural role by sequestering carbon, supporting biodiversity, the provisioning of conventional and non-conventional wood products, and providing habitat for specialists. Historically, forest management in these systems has used clearcut harvests to maximize pulp production, often resulting in structurally simplified stands vulnerable to climate change. As climate change reshapes boreal systems through warming, altered hydrology, and increased disturbance, identifying structural features that promote resilience is increasingly important. Ecological forestry, which aims to emulate natural disturbance and subsequent forest development, is an alternative approach to support a broader suite of ecosystem processes. To inform this approach, we examined how forest structure, quantified through lidar-derived metrics, varies across peatland forest types and stand ages, and how these structural attributes influence avian communities, with emphasis on peatland associate species. We used field measurements, bird point count surveys, and lidar data across productive black spruce, stagnant black spruce, and tamarack stands in lowland conifer peatlands of northern Minnesota. Results showed that canopy height, canopy cover, heterogeneity, vertical canopy complexity, and overall complexity did not differ among cover types but increased significantly with stand age, reflecting the gradual development of structural complexity over time. Total bird species richness and diversity showed limited associations with forest type, stand age, or structural metrics, likely reflecting the broad distribution of generalist species across stands. In contrast, peatland-associated species exhibited clear positive responses: their richness and diversity increased significantly with stand age and were positively correlated with lidar-derived measures of canopy cover and the overall complexity index. These results underscore the ecological value of older, structurally complex peatland stands in sustaining specialist bird assemblages and highlight the importance of incorporating fine-scale structural metrics into biodiversity assessments and climate-adaptive management planning aimed at sustaining habitat function under increasing climatic variability. Further, our results have application to the development of silvicultural approaches that better reflect the natural, complex structural dynamics of these ecosystems. Silvicultural approaches that emulate natural structural development, such as irregular shelterwood with reserves or variable density thinning, may enhance canopy complexity while maintaining forest productivity and habitat for peatland specialist birds.

Abstract Coastal wetlands are among the most important ecosystems on the planet but are increasingly imperiled by accelerating sea‐level rise (SLR). In the past, biogeomorphic feedbacks have allowed coastal wetlands to adjust vertically and persist through periods of accelerated SLR. Recent rates of SLR are faster than any in recent geologic history, making the fate of coastal wetlands highly uncertain. Here, we synthesize surface elevation table marker‐horizon data from 442 stations in coastal wetlands across the conterminous United States to evaluate if they are largely persisting in the face of accelerated SLR, or if they are undergoing ecological transformations of submergence and/or migration. Across the conterminous United States, 11% of coastal wetlands in this sample are on a trajectory of submergence whereas 73% of sites are lagging SLR, but may be able to migrate upslope, and 16% of sites are gaining elevation at rates which exceed SLR indicating persistence and an ability to migrate seaward. Vulnerability of these systems to ecological transformation varies across the three coasts of the conterminous United States which, span large biogeomorphic gradients. These results serve as one of the first national syntheses of coastal wetland elevation trends and may help focus conservation and restoration efforts in a rapidly changing future.

Photosynthetic pigment fluorescence is commonly used in limnology and oceanography as a proxy for phytoplankton biomass. Fluorometry has been used to detect subsurface algal blooms, characterize dynamics of the deep chlorophyll layer, and to provide greater vertical resolution to phytoplankton monitoring. However, more studies are needed to better understand how fluorometric data relate to phytoplankton microscopic assessments across a wide range of natural conditions. We combined data generated using pigment fluorometry with simultaneously collected phytoplankton taxonomic data, assessed via microscopy, from the Laurentian Great Lakes to analyze the correspondence between the two approaches. Across the Great Lakes, chlorophyll a concentrations estimated using fluorometry were significantly correlated with the total phytoplankton biovolume from microscopy-based assessment. Stronger correlations between the two approaches were observed in spring samples compared to summer samples, with the weakest relationships for summer deep chlorophyll layer samples. For phytoplankton group-specific correlations, brown-pigmented algae (mostly diatoms) were the most consistent between the two methods, whereas only weak correlations were observed for green algae, cyanobacteria, and cryptophytes. Weak relationships for some taxa may reflect poor accuracy across the gradient of phytoplankton abundance observed in the Great Lakes. We further discuss potential reasons for discrepancies and implications for fluorometric data interpretation. Fluorometry may enable greater spatial, vertical, and temporal resolution of phytoplankton data critical for assessing lower food web dynamics, but it may not closely correspond to microscopy-based approaches in terms of predicting specific phytoplankton groups.

We present Laurentian Great Lakes phytoplankton trends from 2001 to 2021 in spring and summer. Trend analysis identified significant changes in phytoplankton abundance and taxonomic composition. This included the loss of phytoplankton biovolume, especially diatoms, in lakes Huron and Michigan following the quagga mussel invasion, an increase in cyanobacteria especially in the central basin of Lake Erie, and an increase in phytoplankton biovolume in Lake Superior. Within functional groups, we observed increases in the absolute and relative abundances of flagellated organisms, largely owing to increases in single-celled cryptophytes and dinoflagellates in the spring and colonial chrysophytes in the summer, and a rise in lightly silicified rhizosolenoid diatoms during summer. Random forest analysis identified potential drivers and mechanisms for phytoplankton changes alongside concurrently sampled invertebrate and water quality parameters. The quagga mussel invasion was an important driver of major phytoplankton shifts, but climate change-related stressors affecting stratification are also likely drivers of changes. We observed strong relationships between phytoplankton and microzooplankton, with rotifers and copepod nauplii showing positive relationships with many phytoplankton groups, though whether these are top-down or bottom-up associations is not clear. This study recognizes continuing reorganization of the Great Lakes phytoplankton community that is likely to have long-term impacts on food webs.

We hypothesize that aquatic ecosystem services are likely to be inequitably accessible and addressing this hypothesis requires systematic assessment at regional and national scales. We used existing data from large-scale aquatic monitoring programs (National Coastal Condition Assessment, National Lakes Assessment) to examine relationships between ecosystem condition, approximating a subset of cultural and provisioning services, and inequality (population below poverty level, minority population). We also assessed whether monitoring sites equitably represented the gradient of socioeconomic backgrounds. Several water quality indicators were associated with significantly different minority and low-income percentages; however, the effect size was generally small, with the exception of nitrogen condition status. Minority communities were somewhat under-represented when comparing the distribution of all census blocks to those in proximity to monitoring sites. Analyses were sensitive to the skewed distribution of monitoring sites with a low frequency of observations at the more socially vulnerable part of the gradient. We discuss implications of these findings for improving the representation of vulnerable communities in large-scale monitoring programs.

Quantifying the relationship between phytoplankton and zooplankton may offer insight into zooplankton sensitivity to shifting phytoplankton assemblages and the potential impacts of producer-consumer decoupling on the rest of the food web. We analyzed 18 years (2001-2018) of paired phytoplankton and zooplankton samples collected as part of the United States Environmental Protection Agency (U.S. EPA) Great Lakes Biology Monitoring Program to examine both the long-term and seasonal relationships between zooplankton and phytoplankton across all five Laurentian Great Lakes. We also analyzed effects of phytoplankton diversity on zooplankton biomass, diversity, and predator-prey (zooplanktivore/grazer) ratios. Across the Great Lakes, there was a weak positive correlation between total algal biovolume and zooplankton biomass in both spring and summer. The relationship was weaker and not consistently positive within individual lakes. These trends were consistent over time, providing no evidence of increasing decoupling over the study period. Zooplankton biomass was weakly negatively correlated with algal diversity across lakes, whereas zooplankton diversity was unaffected. These relationships did not change when we considered only the edible phytoplankton fraction, possibly due to the high correlation between total and edible phytoplankton biovolume in most of these lakes. Lack of strong coupling between these producer and consumer assemblages may be related to lagging responses by the consumers, top-down effects from higher-level consumers, or other confounding factors. These results underscore the difficulty in predicting higher trophic level responses, including zooplankton, from changes in phytoplankton assemblages.

The surface elevation table (SET) approach and two survey instruments, a digital level (DL) and a total station (TS), were used to evaluate elevation change at a 1-ha, micro-tidal, back-barrier salt marsh at Assateague Island National Seashore (Berlin, MD, USA) from 2016 to 2022. SET data were collected at 3 sampling stations along the perimeter of the plot, 36 pins per station, and the DL and TS data were collected adjacent to 36 stakes, four readings per stake, throughout the plot. The average elevation range of the marsh surface measurements at the SET stations was 2 cm, while the range was considerably greater within the larger 1-ha DL and TS sampling area (24 cm). The average elevation of the marsh surface only varied by 2 cm among the three methods. Elevation change trends of the three methods ranged from 2.8 to 3.5 mm year −1 and were not significantly different from each other. Despite differences in sample size and spatial distribution of measurements, these methods provided comparable measures of long-term trends in marsh surface elevation probably because the marsh at this site was structurally homogeneous with low topographic relief.

Tidal marshes build elevations by below- and aboveground organic and mineral soil processes. Marsh elevation and accretion data can be used to determine if marshes are keeping pace with sea-level rise. Using a network of 54 deep rod surface elevation tables with paired feldspar marker horizon plots, we tracked elevation and accretion trends across 16 marshes in California, USA. All sites had overall positive gains across years that included severe drought conditions and extreme rain events. Marsh elevation relative to tidal datum ( z *) was the key predictor for elevation and accretion rates, with higher change rates at lower z * sites. Marsh sites are clustered into three regional groups (Northern California, San Francisco Bay area, and Southern California), primarily defined by maximum temperature and annual rainfall differences. Elevation, accretion, and shallow subsidence rates were not significantly different between clusters, but their explanatory variables did vary. High-temperature days were a key predictor for elevation, accretion, and shallow subsidence rates in the state-wide analysis and San Francisco Bay regional analysis. The largest elevation gains were observed in the San Francisco Bay-Delta and some of the smallest in Humboldt Bay, with Morro Bay having the lowest accretion rate overall. Central and Southern California marshes were keeping pace or out-pacing sea-level rise, while none of the Humboldt Bay marshes were keeping pace. Marsh surface elevation data can inform management intervention and be a leading indicator for sea-level rise vulnerability. Long-term monitoring across geomorphic settings can help inform management and anticipate marsh change.

Several coastal ecosystems—most notably mangroves and tidal marshes—exhibit biogenic feedbacks that are facilitating adjustment to relative sea-level rise (RSLR), including the sequestration of carbon and the trapping of mineral sediment 1 . The stability of reef-top habitats under RSLR is similarly linked to reef-derived sediment accumulation and the vertical accretion of protective coral reefs 2 . The persistence of these ecosystems under high rates of RSLR is contested 3 . Here we show that the probability of vertical adjustment to RSLR inferred from palaeo-stratigraphic observations aligns with contemporary in situ survey measurements. A deficit between tidal marsh and mangrove adjustment and RSLR is likely at 4 mm yr −1 and highly likely at 7 mm yr −1 of RSLR. As rates of RSLR exceed 7 mm yr −1 , the probability that reef islands destabilize through increased shoreline erosion and wave over-topping increases. Increased global warming from 1.5 °C to 2.0 °C would double the area of mapped tidal marsh exposed to 4 mm yr −1 of RSLR by between 2080 and 2100. With 3 °C of warming, nearly all the world’s mangrove forests and coral reef islands and almost 40% of mapped tidal marshes are estimated to be exposed to RSLR of at least 7 mm yr −1 . Meeting the Paris agreement targets would minimize disruption to coastal ecosystems.

Walleye (Sander vitreus; WAE) and yellow perch (Perca flavescens; YEP; collectively percids) are freshwater fishes threatened by multiple stressors, including aquatic invasive species. Zebra mussels (Dreissena polymorpha; ZM) and spiny water fleas (Bythotrephes cederströmii; SWF) are aquatic invasive species that reduce pelagic zooplankton biomass, an important food resource for both age-0 percids and the prey fish of adult percids. Both percid species are generalist consumers, and it is unknown how they respond to reduced pelagic energy resources associated with invasions. We examined pelagic and littoral energy use in percids from nine large north temperate lakes which vary in invasion status. We sampled adult and age-0 percids from each lake in 2017 or 2018 and analyzed muscle tissue for δ13C and δ15N isotope ratios. We characterized isotope baselines with littoral and pelagic invertebrates to allow cross-lake comparisons. We estimated the proportion pelagic reliance using Bayesian mixing models and determined the variance contribution of ZM and SWF presence to estimates using model comparison. Pelagic reliance of percids sampled from ZM-invaded lakes was consistently lower than uninvaded lakes, while pelagic reliance of percids sampled from SWF-invaded lakes was greater than uninvaded lakes, although neither effect was statistically distinguishable from zero. Model comparison indicated pelagic reliance of adult WAE, age-0 WAE, and age-0 YEP was influenced by ZM presence, while pelagic reliance of adult YEP was influenced by SWF presence. If percid populations persistently rely on pelagic resources, despite those resources being reduced, there may be negative consequences to growth, survival, or recruitment.

Multiple aquatic ecosystem services (ES) sustain humanity, but some of them may not be equitably accessible to all people. We take a transdisciplinary approach to recent literature to highlight some of the inequalities specific to aquatic ecosystems, focusing on provisioning, supporting and cultural aquatic ES. We also explore feedbacks between access to ES, awareness, and public support for those services. Without targeted interventions, inequality in aquatic ecosystem service delivery is likely to continue to increase with the projected increase in wealth gaps, increasing global trade insensitive to local values, decreasing awareness of ES availability, and increasing urban population without access to green and blue spaces. We conclude by highlighting examples of potential research needs, emphasizing that systematic assessment of inequality is the first step in seeking equitable access to ES and ensuring continuing public support for protection of aquatic ecosystems.

Breeding birds in North America’s eastern and boreal forests have experienced significant population declines in recent decades due largely to habitat loss. The North American Great Lakes coastal zone provides critical stopover and breeding habitat for millions of migratory and resident birds with diverse life history traits. Extensive human land use in this region has resulted in significant forest loss. To understand how functional and taxonomic diversity of breeding bird communities have been affected by agriculture and urbanization in this region, we calculated measures of functional diversity, Shannon’s diversity index, and species richness along a gradient of human land use intensity. We analyzed bird survey data collected at 2982 locations within 1 km of the shoreline where upland forest was the dominant habitat. We used hierarchical partitioning to determine the extent to which spatial confounding factors (i.e., broad climatic and biogeographic gradients across the five Great Lakes) accounted for observed differences in diversity measures, and then used fourth-corner analysis to describe the relationship between species, functional traits, and land cover types. Although spatial confounding factors accounted for some variation, functional evenness, species richness, and Shannon’s diversity index declined significantly with increasing human land use. Species negatively associated with increasing human land use were those that eat primarily invertebrates by foraging on foliage or bark (75%) and species categorized as long-distance migrants (58%), which suggests increased vulnerability of forest-dependent species to habitat modification and reductions in habitat availability. Functional evenness declined with increasing human land use, while other measures of functional diversity (functional dispersion and Rao’s quadratic entropy) remained relatively constant. Understanding the disconnect between functional and taxonomic diversity of bird assemblages and quantifying the degree of resilience of functional community properties is critical for predicting long-term effects of both habitat loss and ecological restoration on biodiversity and ecosystem function.

We examined the recent paleolimnological diatom record from 109 mostly Minnesota (USA) lakes to determine whether anthropogenic impacts could be detected across a large geographic region and associated with a known stressor such as agriculture or climate change. Four periods of diatom assemblage reorganization were observed: (1) a pre-impact period; (2) a period of early Euro-American settlement and development; (3) a mid-20th century period of stabilization in impacts likely related to remediation and landscape recovery; and (4) a recent period of rapid change likely due to multiple stressors. Shallow and deep lakes expressed variations in their taxonomic character and historical changes in the diatom assemblages, but the amount of change was not specifically associated with contemporary agricultural or modern in-lake nutrient status. Lake depth is a major determinant of how a lake will respond to stressors and manifest change in primary producers; however, lake- or ecoregion-specific considerations will continue to inform lake management. Cultural eutrophication caused several of these historical changes to algal communities, but it is apparent that the amount of recent assemblage reorganization is a result of multiple concurrent stressors that may include climate change and the effects of non-native species infestations.

Ecological studies of the highly diverse groups of organisms, such as algae, can be particularly prone to taxonomic opinion bias. There is mounting pressure to recognize and report this bias across studies to facilitate reproducible science and data re-use; however, there are fewer studies which link taxonomic bias to loss of precision in modelling community responses or in bioassessments. We use long-term phytoplankton monitoring data to evaluate effects of taxonomic bias on relevant ecological metrics including algal biovolume, cell counts, diversity, and the performance of a species-based weighted-averaging model for inferring phosphorus concentrations. Despite the non-zero taxonomic bias between paired original and quality assurance samples, several important indicators derived from these data, including model-inferred phosphorus concentrations, total algal biovolume and cell density, and diversity were mostly unaffected. We discuss this as an example of using ecologically relevant model performance criteria for making recommendations about the acceptable level of taxonomic bias.

Much uncertainty exists about the vulnerability of valuable tidal marsh ecosystems to relative sea level rise. Previous assessments of resilience to sea level rise, to which marshes can adjust by sediment accretion and elevation gain, revealed contrasting results, depending on contemporary or Holocene geological data. By analyzing globally distributed contemporary data, we found that marsh sediment accretion increases in parity with sea level rise, seemingly confirming previously claimed marsh resilience. However, subsidence of the substrate shows a nonlinear increase with accretion. As a result, marsh elevation gain is constrained in relation to sea level rise, and deficits emerge that are consistent with Holocene observations of tidal marsh vulnerability.

Small nearshore fishes are an important part of lacustrine and functional diversity and link pelagic and benthic habitats by serving as prey for larger nearshore and offshore fishes. However, the trophic complexity of these small nearshore fishes is often unrecognized and detailed studies of their role in food webs are lacking. Here, we examined niche space patterns of small nearshore fish species using Bayesian analyses of carbon and nitrogen stable isotope data in nine freshwater lakes that are among the largest lakes in Minnesota. We found considerable variability in niche areas within species and high variability in niche overlap across species. At the assemblage level, niche overlap (average diet overlap of all species pairs at a lake) decreased as whole-lake species richness increased, possibly indicating a greater degree of resource specialization in more speciose lakes. Overall fish niche space was weakly but significantly related to niche space of their invertebrate prey. Although nearshore benthic resources contributed to fish diets in all lakes, all fish species also had non-negligible and variable contributions from pelagic zooplankton. This inter- and intraspecific variability in trophic niche space likely contributes to the multi-level trophic complexity, functional diversity, and potentially food web resilience to ecosystem changes.

Transgression into adjacent uplands is an important global response of coastal wetlands to accelerated rates of sea level rise. “Ghost forests” mark a signature characteristic of marsh transgression on the landscape, as changes in tidal inundation and salinity cause bordering upland tree mortality, increase light availability, and the emergence of tidal marsh species due to reduced competition. To investigate these mechanisms of the marsh migration process, we conducted a field experiment to simulate a natural disturbance event (e.g., storm-induced flooding) by inducing the death of established trees (coastal loblolly pine, Pinus taeda ) at the marsh-upland forest ecotone. After this simulated disturbance in 2014, we monitored changes in vegetation along an elevation gradient in control and treatment areas to determine if disturbance can lead to an ecosystem shift from forested upland to wetland vegetation. Light availability initially increased in the disturbed area, leading to an increase in biodiversity of vegetation with early successional grass and shrub species. However, over the course of this 5-year experiment, there was no increase in inundation in the disturbed areas relative to the control and pine trees recolonized becoming the dominant plant cover in the disturbed study areas. Thus, in the 5 years since the disturbance, there has been no overall shift in species composition toward more hydrophytic vegetation that would be indicative of marsh transgression with the removal of trees. These findings suggest that disturbance is necessary but not sufficient alone for transgression to occur. Unless hydrological characteristics suppress tree re-growth within a period of several years following disturbance, the regenerating trees will shade and outcompete any migrating wetland vegetation species. Our results suggest that complex interactions between disturbance, biotic resistance, and slope help determine the potential for marsh transgression.

Aquatic invasive species research has been surging in popularity, with the number of papers published in Hydrobiologia doubling since the previous decade. We overview contributions to the current Special Issue, including new studies on introduction and establishment, traits distinguishing high-impact invaders and their impacts, interactions between AIS and other human stressors as well as new developments in management. In addition, we analyze public interest in invasive species using 17 years of data (2004–2020) on absolute search volumes from Google extracted using Keywords Everywhere app. In particular, we analyze trends in searches for invasive species in general, several high-impact AIS, as well as the popularity of invasive species searches contrasted with other commonly recognized ecological problems in aquatic ecosystems. During the available search period, search volume for invasive species in general has increased and compared favorably with other ecological issues, whereas search volume patterns for high-impact AIS were species-specific and often exceeded search volumes for the general keyword. Public engagement is critical for all aspects of AIS research and management, and analysis of search volumes can be used to gauge, sustain and diversify this engagement.

The vulnerability of the world’s tidal marshes to sea-level rise threatens their substantial contribution to fisheries, coastal protection, biodiversity conservation and carbon sequestration. Feedbacks between relative sea-level rise (RSLR) and the rate of mineral and organic sediment accumulation in tidal wetlands, and hence elevation gain, have been proposed to ameliorate this risk. Here we report on changes in tidal marsh elevation and shoreline position in relation to our network of 387 fixed benchmarks in tidal marshes on four continents measured for an average of 10 years. During this period RSLR at these marshes reached on average 6.6 mm yr-1, compared to 0.34 mm yr-1 over the past millenia. While the rate of sediment accretion corresponded to RSLR, the loss of elevation to shallow subsidence increased in proportion to the accretion rate. This caused a deficit between elevation gain and RSLR which increased consistently with the rate of RSLR regardless of position within the tidal frame, suggesting that long-term in situ tidal marsh survival is unlikely. While higher tidal range (>3m) conferred a greater stability in measures of shoreline change and vegetation cover, other regions showed a tendency towards instability and retreat.