Mussel Biomass Research Articles

Declining freshwater mussel diversity in the middle and lower reaches of the Xin River Basin: Threat and conservation.

Freshwater mussels provide important functions and services for aquatic ecosystems, but populations of many species have been extirpated. Information on biodiversity plays an important role in the conservation and management of freshwater mussels. The Xin River Basin is a biodiversity hotspot for freshwater mussels in China, with more than 43 species known, but populations of which are decreasing. Here, we quantify the diversity of freshwater mussels in the middle and lower reaches of the Xin River Basin and study the correlation of habitat characteristics and freshwater mussel diversity. Compared to the historical period, the number of species, density, and biomass of freshwater mussels decreased 33%, 83%, and 82% in the current period, respectively. Fifty two percent of recorded species were empty shells, and 14 native freshwater mussels were not found in the study area. Four species are currently listed as vulnerable species using IUCN criteria and their global status. The assemblage structure of freshwater mussels exhibits significant spatial differences, and there was a correlation with substrate and physicochemical parameters. The main tributary of the Xin River with higher freshwater mussel diversity should be established as one large protected area because the nestedness component was the main pattern of beta diversity. These results indicated freshwater mussel diversity was declining rapidly, which can help focus conservation effort for freshwater mussel biodiversity.

Silent invasion: Sinanodonta woodiana successfully reproduces and possibly endangers native mussels in the north of its invasive range in Europe

AbstractThe explosive global spread of Sinadonta woodiana, a large‐bodied unionid mussel of East Asian origin, potentially affects the functioning of freshwater habitats and threatens native mussels. Molecular data indicate that its invasion in Europe started with a single colonization event, followed by in situ adaptation. This study traces one of the possible routes of such adaptation. It documents a population of S. woodiana with a known history of a two‐stage introduction: first, from a heated water source to a production fish pond in northern Poland, and subsequently from that pond to the study site. As the latest local transfer occurred more than 15 years before the study, the abundance of young S. woodiana in various age classes provides proof of ongoing in situ reproduction and resolves the question of the ability of S. woodiana to permanently colonize thermally unpolluted water bodies in areas with prolonged and cold winters. The study also shows that translocations of glochidia‐infested fish and/or adult mussels between water bodies in such areas result in the establishment of new self‐recruiting populations. Together, these findings show that further expansion of S. woodiana into colder regions and establishment of new populations in already invaded areas are to be expected. The relative abundance of S. woodiana and the native unionids: Anodonta anatina and A. cygnea was 40%, 18%, and 42%, respectively. S. woodiana contributed to 65% of the total mussel biomass. Individuals in the first three size classes, corresponding to the 2‐ to 4 year age classes, composed 50% of S. woodiana, 37% of A. anatina, and 26% of A. cygnea. The high proportion of young individuals in S. woodiana indicates population trajectories toward a gradually increasing dominance of this species and possibly reflects its negative impacts via interactions with host fish and competition for resources.

Drought-Induced, Punctuated Loss of Freshwater Mussels Alters Ecosystem Function Across Temporal Scales

Punctuated, mass mortality events are increasing for many animal taxa and are often related to climatic extremes such as drought. Freshwater mussels are experiencing increased mass mortality events linked to hydrologic drought. Because mussels play important functional roles in rivers it is important to understand the ecosystem effects of these die-offs. Here, we address how mass mortality events of mussels caused by drought may impact stream ecosystem function. We first present a conceptual model, based on the literature, of how mussel mass mortality should affect different ecosystem functions across various ecological time scales, from hours to decades. Next, we highlight two case studies of drought-linked, mussel-mass mortality events from rivers in the southern U.S. We then present the results of an experiment we performed quantifying the ecosystem effects of a punctuated mussel die-off. Finally, we combine our experimental results with field data from a recent mussel die-off to predict how mussel losses will influence ecosystem function. Based on the presented case studies, our mesocosm experiment, and our extrapolated nutrient pulse due to a mussel die-off, we conclude that stream ecosystems are extensively altered following mussel mass mortality events. Mussel loss is governed by drought severity, location within the river network, and species-specific drought tolerances. In the short term, decomposing carrion from mussel die-offs releases a large pulse of nutrients into the water which stimulates food web productivity. In the long term, the overall loss of mussel biomass, and the loss of functional traits as more sensitive species decline, leads to decreases in ecosystem function which may take decades to recover. Drought and human demand for water will make mussel die-offs more likely in the future and it is unlikely that drought sensitive species will recover without changes in water management and restoration of populations through mussel propagation. Our research provides an example of how the loss of an abundant, long-lived organism has cascading and long-term impacts on ecosystems.

Creating a window of opportunity for establishing ecosystem engineers by adding substratum: a case study on mussels

AbstractEcosystem engineers typically exert positive feedback on their environment, which enhances their performance. Such positive feedback is lacking in the establishment phase, when densities are too low and/or patches are too small. There is a strong need to unravel the mechanisms for overcoming the resulting establishment thresholds, both for ecological restoration purposes and to be able to use their services. In the present study, we question whether providing a transient substratum can be used as tool to overcome establishment thresholds, by creating a window of opportunity for initial settlement, using mussels (Mytilus edulis) as a model system. Combining field and flume experiments, we study how biogenic substratum enrichment in the form of a shell layer on a soft mudflat affects the critical dislodgement thresholds and, thus, the chances of mussel establishment at different mussel densities and aggregation states. Flume results showed that the presence of a shell layer reduced dislodgement of mussel patches in low‐energy environments but was conditional for establishment in high‐energy environments. That is, in high‐energy environments with shells, aggregation into clumps enhanced dislodgement, while dislodgement was reduced with increasing overall mussel biomass and overall mussel patch weight. Without shells, dislodgement was always 100%. These findings agreed with our field studies, which showed that coarse shell material reduced mussel losses (by a factor of 3), reduced aggregation (by a factor of 2.4), and increased attachment strength (by a factor of 2.4). Overall, our results show that the local presence of biogenic substratum increases the chance of mussel establishment by enhancing the critical hydrodynamic dislodgement threshold. Thus, the local addition of a biogenic substratum may create a window of opportunity to initiate settlement in more dynamic environments, to shift at a local scale from a bare mudflat state into an established biogenic reef state. Our findings have clear implications for how to approach restoration and management of ecosystem engineers dominated systems. For instance, when positive feedback of ecosystem engineers is lacking, (1) the transient offering of suitable settling substratum may be a necessary step to overcome establishment thresholds, and (2) this becomes increasingly important with increasing abiotic stress.

Long‐term population dynamics of dreissenid mussels (Dreissena polymorpha and D. rostriformis): a cross‐system analysis

AbstractDreissenid mussels (including the zebra mussel Dreissena polymorpha and the quagga mussel D. rostriformis) are among the world's most notorious invasive species, with large and widespread ecological and economic effects. However, their long‐term population dynamics are poorly known, even though these dynamics are critical to determining impacts and effective management. We gathered and analyzed 67 long‐term (>10 yr) data sets on dreissenid populations from lakes and rivers across Europe and North America. We addressed five questions: (1) How do Dreissena populations change through time? (2) Specifically, do Dreissena populations decline substantially after an initial outbreak phase? (3) Do different measures of population performance (biomass or density of settled animals, veliger density, recruitment of young) follow the same patterns through time? (4) How do the numbers or biomass of zebra mussels or of both species combined change after the quagga mussel arrives? (5) How does body size change over time? We also considered whether current data on long‐term dynamics of Dreissena populations are adequate for science and management. Individual Dreissena populations showed a wide range of temporal dynamics, but we could detect only two general patterns that applied across many populations: (1) Populations of both species increased rapidly in the first 1–2 yr after appearance, and (2) quagga mussels appeared later than zebra mussels and usually quickly caused large declines in zebra mussel populations. We found little evidence that combined Dreissena populations declined over the long term. Different measures of population performance were not congruent; the temporal dynamics of one life stage or population attribute cannot generally be accurately inferred from the dynamics of another. We found no consistent patterns in the long‐term dynamics of body size. The long‐term dynamics of Dreissena populations probably are driven by the ecological characteristics (e.g., predation, nutrient inputs, water temperature) and their temporal changes at individual sites rather than following a generalized time course that applies across many sites. Existing long‐term data sets on dreissenid populations, although clearly valuable, are inadequate to meet research and management needs. Data sets could be improved by standardizing sampling designs and methods, routinely collecting more variables, and increasing support.

Lake Characteristics, Population Properties and Invasion History Determine Impact of Invasive Bivalves on Lake Nutrient Dynamics

Invasive species can have large impacts on ecosystems, including the cycling and distribution of nutrients. To determine the whole-ecosystem effects of invasive zebra mussels on lake nutrient dynamics, we sampled 10 invaded Minnesota lakes spanning a broad trophic status gradient. We conducted N and P excretion and biodeposition rate measurements and determined the C, N and P composition of dreissenid soft tissues and shell material in the study lakes. We also estimated the whole-lake biomass of live dreissenid mussels and their dead shell material, constructing comprehensive nutrient budgets for dreissenid populations in the study lakes. We used the results of our measurements and published data to estimate the contribution of dreissenids to P budgets in 24 additional lakes in Europe and North America. Results show that nutrient cycling rates and composition of soft tissues and shells vary with mussel size and lake trophic status. Zebra mussels made variable, but often large, contributions to cycling and storage of water column standing stocks of POC, PON and TP in the study and literature lakes. In some lakes, the effects of zebra mussels on P dynamics were also considerable in the context of estimated P external and internal loading, sediment sequestration and effects of other biota. We show that the impact of zebra mussels on whole-lake nutrient budgets depends on lake properties, dreissenid population characteristics and invasion history. This information can be used by ecosystem managers to prioritize invasion prevention efforts toward lakes likely to be most strongly impacted by zebra mussel invasions.

Variation in aggregate descriptors of rocky shore communities: a test of synchrony across spatial scales

Rocky shore communities usually show complex patterns of compositional variation in space and time. Yet, this does not rule out the possibility of observing coherent temporal trends in aggregate community variables (e.g., biomass and number of species or individuals within functional groups or whole communities) due to broad-scale, seasonal, or interannual environmental controls that operate independently of local species composition. The goal of this study was to evaluate whether five aggregate community variables (mussel density, mussel biomass, algal biomass, macroinvertebrate density, and species density) show synchronous patterns of short-term, temporal variation (2 years) across eight rocky shore sites located in the Southwestern Atlantic and within two biogeographic regions (Warm Temperate Southwestern Atlantic and Magellanic). The study predictions were (1) that synchrony will increase as the spatial scale of analysis becomes smaller and, (2) that pairs of nearby sites will be more synchronized than pairs of distant ones. These predictions were weakly, if at all, supported by the data. Synchrony in aggregate community descriptors rarely occurred across the studied rocky shore sites. It can be observed at any spatial scale, and it can even fail to happen among sites located a few hundred meters apart. This suggests that local processes are overarching sources of short-term variability at the regional level, highlights the caution needed in generalizing from spatially limited time series data, and also underscores the potential limitations of climate envelope models to predict how aggregate community variables and related ecosystems functions (e.g., primary and secondary production) will respond to global climate change.

Modeling potential impacts of three benthic invasive species on the Lake Erie food web

Assessing the potential for aquatic invasive species (AIS) to impact ecosystem function and services is an important component of ecological risk assessment. This study focuses on quantifying changes in biomass of food web groups in response to changes in AIS biomass as a function of variable AIS prey vulnerabilities (i.e. food availability) and AIS vulnerabilities to predators (i.e. predation pressure). We modified an existing Lake Erie food web model to assess the potential food web impacts of three benthic AIS (Eurasian ruffe Gymnocephalus cernua, killer shrimp Dikerogammarus villosus, and golden mussel Limnoperna fortunei) that may invade Lake Erie in the near future. Simulated biomass of golden mussels was most affected by bottom-up control, while killer shrimp and ruffe were affected by both top-down and bottom-up controls. AIS food web impacts showed both monotonic and non-monotonic responses to AIS biomass. Impacts from ruffe were highest when their biomass was high, while killer shrimp and golden mussels had maximal impacts at intermediate biomass levels on some food web groups. Our results suggest that golden mussels, which can feed at a lower trophic level and have fewer predators than ruffe or killer shrimp, may reach much higher equilibrium biomass under some scenarios and affect a broader range of food web groups. While all three species may induce negative effects if introduced to Lake Erie, golden mussels may pose the highest risk of impact for Lake Erie’s food web.

Invader invaded: population dynamics of zebra mussels (Dreissena polymorpha) and quagga mussels (Dreissena rostriformis bugensis) in polymictic Oneida Lake, NY, USA (1992–2013)

Invasive zebra (ZM) and quagga (QM) mussels continue to spread within and across inland waters worldwide. Oneida Lake, NY, USA, is a large (207 km2), mesotrophic, polymictic lake surveyed annually for dreissenids across substrates since 1992. We estimated abundance and distribution of ZMs and QMs across substrates, calculated lakewide density and biomass, analyzed seasonal and annual differences in veliger density, and explored dynamics of species replacement. ZMs and QMs were detected in 1991 and 2005, respectively. ZM density peaked at almost 30,000 ind/m2 in 1992, declined to between 2600 and 7600 ind/m2 until 2008, and further declined to 370–560 ind/m2 in 2010–2013 concurrent with increasing QM abundance. ZM biomass remained stable from 1992 to 2008 (140–530 g shell-on dry wt/m2) but declined to < 10 g from 2010 to 2013. QMs increased from 38% of the total biomass in 2008 to ≥ 90% from 2010 to 2013 which was accompanied by a decrease in ZM lengths and increase in QM lengths. In shallow (< 9 m) waters, both mussels were more abundant on rock than sand and silt substrate. Only QMs were abundant in deep silt substrate. The shift from ZM to QM dominance increased total biomass, but not density, due to larger QMs. Veliger densities were higher in May and August–November after arrival of QMs; however, there was no correlation between number of veligers and new recruits in fall or adult mussel biomass. The replacement of ZM occurred over about 4 years even though published mechanisms for QM dominance are not operating in summer in Oneida Lake.

Sediment contributing invasive dreissenid species in a calcareous shallow lake – Possible implications for shortening life span of lakes by filling

Although the ecosystem transforming impact of the invasive dreissenid mussels has been widely reported in short-to-mid time scale studies, little is known about the contribution of the spent shells to sediments accumulating on the lake bottom. The question whether the shell production significantly reduces the lifespan of the lake by increasing sedimentation rate is particularly interesting in those shallow lakes where the calcium supply is sufficient to maintain the high mussel biomass production permanently, and where the alkaline water does not favor shell dissolution. Lake Balaton, a large calcareous, shallow lake in Central Europe invaded by dreissenids (Dreissena polymorpha, Dreissena rostriformis bugensis), provides an ideal testing ground for this scenario. Therefore, we made calculations based on recent population abundance datasets (2000–2018), estimated the whole habitable, hard surface coastline and the muddy bottom of the pelagic area which is also gradually becoming inhabited by D. r. bugensis, using high resolution aerial photographs and analyzing seismic sections. We created four scenarios: (1) if no dreissenids are present (applying basic sedimentation rate); (2) if D. r. bugensis had not been introduced to the lake (only D. polymorpha); (3) if D. r. bugensis occupies the hard surfaces of the coastline (the current dominant situation); (4) if D. r. bugensis colonizes the entire lake bottom (a probable future model). Different sedimentation rates obtained from the literature were used to model the filling of Lake Balaton. The shell production of the new invader, D. r. bugensis can shorten the lake’s lifespan by one to two-thirds, depending on the model, and whether the mussel density currently observed at the shoreline is extended to the whole lake bottom. Attention is called to shallow calcareous lakes with low pre-invasion sedimentation rates in which the shell contribution of invasive mollusks has the potential to shorten lifespan.

Effect of round goby (Neogobius melanostomus) invasion on blue mussel (Mytilus edulis trossulus) population and winter diet of the long-tailed duck (Clangula hyemalis)

The invasive round goby has established a viable population within 9 years of its first introduction to Lithuanian coastal waters (SE Baltic Sea). During its expansion phase, abundances increased 23-fold, which led to the near complete eradication of its main prey, the blue mussel, at < 20 m depth. The round goby population showed a stabilizing trend after blue mussel biomass was depleted; however, their abundance has not declined. The round goby feeds efficiently on newly settled mollusks, causing a severe constraint for blue mussel recovery. Changes in blue mussel availability and size structure induced a dietary shift in wintering long-tailed duck towards fish prey. An energetically dense food source sustains a good body condition in long-tailed ducks, however the change in trophic position (from 3.1 to 4.3 trophic level) suggests the potential for a reduction in their carrying capacity. Results from this study also show that coastal habitats with low and unpredictable population dynamics of blue mussel become less attractive wintering sites for long-tailed duck in the Baltic Sea. We also document a cascading effect of invasive species in the food web.

Biomass distribution of fishes and mussels mediates spatial and temporal heterogeneity in nutrient cycling in streams.

Animals can play important roles in cycling nutrients [hereafter consumer-driven nutrient dynamics (CND)], but researchers typically simplify animal communities inhabiting dynamic environments into single groups that are tested under relatively static conditions. We propose a conceptual framework and present empirical evidence for CND that considers the potential effects of spatially overlapping animal groups within dynamic ecosystems. Because streams can maintain high biomass of mussels and fish, we were able to evaluate this framework by testing if biogeochemical hotspots generated by stable aggregations of mussels attract fishes. We predicted that spatial overlap between these groups may increase the flux of mineralized nutrients. We quantified how different fish assemblage biomass was between mussel bed reaches and reaches without mussels. We compared fish and mussel biomass at mussel beds to test whether differences in animal biomass mediate their contributions to nutrient cycling through nitrogen and phosphorous excretion. We estimated areal excretion rates for each group by combining biomass estimates with measured excretion rates. Fish biomass was homogeneously distributed, except following a period of low flow when fish were more concentrated at mussel beds. Mussel biomass was consistently an order of magnitude greater than fish biomass and mussel areal excretion rates exceeded fish excretion rates. However, the magnitude of those differences varied spatially and temporally. Mussel excretion stoichiometry varied with changes in assemblage composition, while fish excretion stoichiometry varied little. Biogeochemical hotspots associated with mussels did not generally overlap with fish aggregations, thus, under these conditions, animal processes appear to exert additive ecosystem effects.

Ecological-social-economic assessment of zebra-mussel cultivation scenarios for the Oder (Szczecin) Lagoon

The Systems Approach Framework with an integrated Ecological-Social-Economic assessment was applied to address the issue of zebra mussel (Dreissena polymorpha) farming in the large Oder (Szczecin) Lagoon, southern Baltic Sea. Heavy eutrophication hampers the use of the lagoon and zebra mussel farming is considered as new use and potential measure to improve water quality. Three alternative scenarios were developed in interaction with local stakeholders: 1) the production of mussels as fresh feed and meal on a commercial basis seemed not profitable, because of a limited market for fresh mussels (zoos, aquaculture) and low prices for organic feed. 2) Mussel cultivation to improve transparency and attractiveness of bathing waters near beaches had only a limited potential (0.2 m improvement of Secchi depth). A higher mussel biomass would increase the risk of temporary hypoxia. 3) Mussels farms for improving the environmental status (according to EU Water Framework Directive) by supporting macrophyte restoration were considered as the most promising scenario. Our model simulations suggested that as soon as a compensation for nutrient removal is considered, all mussel farm scenarios could cover the costs. Experiments and literature confirm that the conditions for an environmental friendly farming approach in the lagoon are suitable. Steps towards and problems associated with an implementation, e.g. invasion of Dreissena bugensis (quagga mussel), are discussed. Each step of the Ecological-Social-Economic assessment and major lessons learnt are documented in detail. Altogether, the approach turned out to be very suitable for this issue.

Chronic Toxicity of 4-Nonylphenol to Two Unionid Mussels in Water-Only Exposures.

Limited studies indicate that mussels are generally insensitive to organic chemicals; however, these studies were conducted in acute or short-term exposures, and little is known about the chronic sensitivity of mussels to organic chemicals. We evaluated the chronic (28days) toxicity of 4-nonylphenol (4-NP) to two commonly tested species of mussels: fatmucket (Lampsilis siliquoidea) and rainbow mussel (Villosa iris). By the end of the 28days chronic exposures, mean survival was ≥93% in all treatments, but the mean dry weight and biomass of mussels at the highest exposure concentrations were significantly reduced relative to the control. The 20% effect concentrations were similar between the two species. When compared to all other tested species, fatmucket and rainbow mussels are among the top four most sensitive species to 4-NP. However, U.S. Environmental Protection Agency chronic water quality criterion of 6.6μg 4-NP/L should protect the two mussel species.

Mechanisms and impact of differential fouling of the zebra mussel Dreissena polymorpha on different unionid bivalves

Abstract Macrobiofouling is an important phenomenon in the aquatic environment, resulting in economic losses and environmental changes, including negative impact on hard‐shelled animals. A freshwater invasive byssate bivalve, the zebra mussel Dreissena polymorpha (Dreissenidae), strongly affects bivalves from the family Unionidae by fouling their shells. We tested potential mechanisms explaining variable fouling of different unionids (four native species: Anodonta anatina, A. cygnea, Unio pictorum, U. tumidus and the non‐native Sinanodonta woodiana) by the zebra mussel. We conducted a field survey (unionids collected at a sandy and muddy site in a dam reservoir), field experiment (unionids exposed without sediments in suspended baskets to dreissenid settlement) and laboratory experiment (a multiple choice test with and without the possibility of unionid burrowing into sandy sediments). In the survey, zebra mussel density was highest on A. anatina and S. woodiana, intermediate on U. pictorum and lowest on A. cygnea and U. tumidus. In the field experiment, A. anatina and S. woodiana were more fouled than Unio spp. In the laboratory, zebra mussels less often attached to U. pictorum and, when unionids could burrow themselves, also to S. woodiana. However, no unionid species was positively selected in the presence of stone substrata. The percentage of zebra mussels attached directly to unionids (compared to those attached to conspecifics) in the field survey was negatively related to the overall zebra mussel biomass. Zebra mussel fouling negatively affected the biomass of an allopatric S. woodiana on muddy bottom. Dreissenids overgrow different unionid species to variable extent, not only due to the differences in their exposed surface area, but, as our experimental results show, also because of their active substratum selection. Moreover, mussels seem to prefer unionid surface over conspecific shells, the latter being fouled only when overall dreissenid fouling is heavy. As unionids often constitute the main source of hard substratum for zebra mussels in waterbodies, the species composition of a unionid assemblage may affect dreissenid success by offering them variable substratum quality.

Modelling the interactions of the hydrothermal mussel Bathymodiolus azoricus with vent fluid

In the 40 years since the discovery of the rich faunal community around hydrothermal vents, many studies have clearly shown that environmental conditions have a strong influence on species distribution in these habitats. Nevertheless, the mechanisms that determine the spatial and temporal dynamics of species’ responses to vent conditions remain elusive. Metabolic studies to assess faunal interactions with vent fluid are particularly difficult to perform in the deep sea and are generally executed in isolation ex situ. Available data mainly concern foundation species, which visually dominate these ecosystems. This work uses a modelling approach to integrate biotic and abiotic data that have been acquired through the years on Eiffel Tower, a large sulphide edifice located on the Lucky Strike vent field on the Mid-Atlantic Ridge, and particularly on its dominant species, Bathymodiolus azoricus. A carbon-flux model was built using seven state variables: the biomass of mussels and their associated thiotrophic (SOX) and methanotrophic (MOX) symbionts and the ambient concentrations of oxygen, dihydrogen sulphide, methane and (particulate and dissolved) organic carbon. Temperature of the surrounding water and mussel density were the forcing variables in the system. Results showed no statistically significant differences between predicted and observed mussel biomass and estimates of energy partitioning within the mussel were in the range of available data.Metabolic rates were generally rather low and greatly reduced by a temperature effect in the coldest samples. These low metabolic rates imply a long lifespan for B. azoricus. Simulations suggest that they would strongly hinder re-establishment and resilience of mussel biomass. However, because symbionts respond quickly to changes in vent fluid, mussels would be able to buffer strong variations in the hydrothermal fluid supply. The model showed that if mussels fed indifferently on both types of symbionts, coexistence of MOX and SOX cannot be reached, thereby likely favouring hypotheses of competition for space inside the mussel gills and/or a differential use of the production of each symbiont. Model predictions are highly dependent on current knowledge, and the results presented here highlight the need for more quantitative data on the biology of B. azoricus across different size classes, on its interactions with symbionts, and in varying environmental concentrations in its substrates.

Phytoplankton and benthic algal response to ecosystem engineers and multiple stressors in the nearshore of Lake Huron

Abstract Resurgence of nuisance benthic algae in the Great Lakes, despite substantial efforts to reduce phosphorus loading, has stimulated renewed interest in exploring the diverse drivers of near-shore water quality. Interestingly, broad similarity in the underlying causes of shore fouling by benthic algae in Lakes Ontario, Erie, and Michigan appear to contrast with Lake Huron where system productivity and dreissenid abundance are lower. While total phosphorus was the primary predictor of chlorophyll concentrations (70–90% of variation) in the water column, we identified a series of spatial patterns that underpin this relationship (up to 28% of variation) and which integrate catchment processes, tributary influences, shoreline complexity, and distance from shore. Dreissenid mussels were the most important predictors of benthic algae cover and biomass in our models, explaining between 20 and 52% of variation. Spatial patterns explained an additional 21–48% of the variation in benthic algae cover and biomass and highlight the importance of site-specific spatial heterogeneity in benthic algae growth. Our results are consistent with the nearshore shunt hypothesis, wherein higher algal cover and biomass coincided with higher mussel density and biomass, although correlative effects with lake depth and loss of algal and mussel biomass due to physical disturbance must also be considered. These results underscore the difficulty associated with identifying the potential drivers of nearshore water quality as the diverse processes of nutrient loading, changes in catchment land use, and ecosystem change associated with invasion by dreissenids all vary in relative influence over a range of spatial scales.

Distribution and foraging patterns of common loons on Lake Michigan with implications for exposure to type E avian botulism

Abstract Common loons (Gavia immer) staging on the Great Lakes during fall migration are at risk to episodic outbreaks of type E botulism. Information on distribution, foraging patterns, and exposure routes of loons are needed for understanding the physical and ecological factors that contribute to avian botulism outbreaks. Aerial surveys were conducted to document the spatiotemporal distribution of common loons on Lake Michigan during falls 2011–2013. In addition, satellite telemetry and archival geolocator tags were used to determine the distribution and foraging patterns of individual common loons while using Lake Michigan during fall migration. Common loon distribution observed during aerial surveys and movements of individual radiomarked and/or geotagged loons suggest a seasonal pattern of use, with early fall use of Green Bay and northern Lake Michigan followed by a shift in distribution to southern Lake Michigan before moving on to wintering areas. Common loons tended to occupy offshore areas of Lake Michigan and, on average, spent the majority of daylight hours foraging. Dive depths were as deep as 60 m and dive characteristics suggested that loons were primarily foraging on benthic prey. A recent study concluded that round gobies (Neogobius melanostomus) are an important prey item of common loons and may be involved in transmission of botulinum neurotoxin type E. Loon distribution coincides with the distribution of dreissenid mussel biomass, an important food resource for round gobies. Our observations support speculation that energy transfer to higher trophic levels via gobies may occur in deep-water habitats, along with transfer of botulinum neurotoxin.

Quantifying a shift in benthic dominance from zebra (Dreissena polymorpha) to quagga (Dreissena rostriformis bugensis) mussels in a large, inland lake

Abstract Dreissenid mussels are aggressive invasive species that are continuing to spread across North America and co-occur in the same waterbodies with increasing frequency, yet the outcome and implications of this competition are poorly resolved. In 2009 and 2015, detailed (700 + sample sites) surveys were undertaken to assess the impacts of invasive dreissenid mussels in Lake Simcoe (Ontario, Canada). In 2009, zebra mussels were dominant, accounting for 84.3% of invasive mussel biomass recorded. In 2015, quagga mussels dominated (88.5% of invasive mussel biomass) and had expanded into profundal (> 20 m water depth) sites and onto soft (mud/silt) substrates with a mean profundal density of 887 mussels/m2 (2015) compared to ~ 39 mussels/m2 in 2009. Based on our annual benthos monitoring, at a subset of ~ 30 sites, this shift from zebra to quagga mussels occurred ~ 2010 and is likely related to a population decline of zebra mussels in waterbodies where both species are present, as recorded elsewhere in the Great Lakes Region. As the initial invasion of dreissenid mussels caused widespread ecological changes in Lake Simcoe, we are currently investigating the effects this change in species dominance, and their expansion into the profundal zone, will have on the lake; and our environmental management strategies. Areas of future study will include: changes in the composition of benthos, fish, or phytoplankton communities; increased water clarity and reduction of the spring phytoplankton bloom; energy/nutrient cycling; and fouling of anthropogenic in-lake infrastructures (e.g. water treatment intakes) built at depths > 25 m to avoid previous zebra mussel colonization.

Changes in Freshwater Mussel Communities Linked to Legacy Pollution in the Lower Delaware River

Freshwater mussels are among the most-imperiled organisms worldwide, although they provide a variety of important functions in the streams and rivers they inhabit. Among Atlantic-slope rivers, the Delaware River is known for its freshwater mussel diversity and biomass; however, limited data are available on the freshwater mussel fauna in the lower, non-tidal portion of the river. This section of the Delaware River has experienced decades of water-quality degradation from both industrial and municipal sources, primarily as a function of one of its major tributaries, the Lehigh River. We completed semi-quantitative snorkel surveys in 53.5 of the 121 km of the river to document mussel community composition and the continued impacts from pollution (particularly inputs from the Lehigh River) on mussel fauna. We detected changes in mussel catch per unit effort (CPUE) below the confluence of the Lehigh River, with significant declines in the dominant species Elliptio complanata (Eastern Elliptio) as we moved downstream from its confluence—CPUE dropped from 179 to 21 mussels/h. Patterns in mussel distribution around the Lehigh confluence matched chemical signatures of Lehigh water input. Specifically, Eastern Elliptio CPUE declined more quickly moving downstream on the Pennsylvania bank, where Lehigh River water input was more concentrated compared to the New Jersey bank. A definitive causal link remains to be established between the Lehigh River and the dramatic shifts in mussel community composition, warranting continued investigation as it relates to mussel conservation and restoration in the basin.