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Freshwater gastropod (Mollusca: Gastropoda) assemblages, habitat, and the first detection of an invasive gastropod species in two large, dreissenid-influenced, connecting rivers ☆
Abstract
Native freshwater gastropods are a highly diverse and imperiled group of mollusks in North America and are influenced by a growing number of problematic invasive species. Consequently, there has been an increased need for understanding aquatic gastropod assemblages throughout North America to implement conservation and management strategies. In the Laurentian Great Lakes, gastropod surveys have been sparse, and most surveys have focused on invasive species. To investigate gastropod assemblages in two large connecting rivers of the Great Lakes, the Detroit and St. Clair rivers, benthic surveys were conducted in 2019 and 2021. Sites in the Detroit River (n = 56) and the St. Clair River (n = 51) were surveyed using petite PONAR grabs from which gastropod shells were identified and quantified to family or a group of two combined families. In both the Detroit and St. Clair rivers, the gastropod family Pleuroceridae (37 % and 56 % total composition, respectively) and combined families Amnicolidae + Hydrobiidae (42 % and 23 % total composition, respectively) contributed the most to overall gastropod composition. Invasive Potamopyrgus antipodarum shells were identified at 4 (7 %) Detroit River sites and 10 (20 %) St. Clair River sites and represent the first documented occurrence in the Detroit River. Although this study was limited to quantifying densities based on shells and cannot assume live-collected snail densities, these results provide a baseline knowledge of the gastropod assemblages and habitat use in these two large river systems which can be used to implement conservation and management strategies.
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The New Zealand mud snail (Potamopyrgus antipodarum) is an invasive mollusk that was first reported in Lake Ontario, a Laurentian Great Lake, in 1991. In 2022, we found a small population in the North Channel representing the first record of this snail in Lake Huron. To understand the status of this species in the Great Lakes, we combined data from the U.S. EPA Great Lakes National Program Office sampling efforts, data from publications, regional reports, and online databases. In the last three decades P. antipodarum has spread to all Great Lakes, and the number of official sightings per year increased fourfold during the last decade. The highest density was observed in Lake Michigan, followed by lakes Ontario, Erie, and Huron. In Lake Michigan in 2021, P. antipodarum lake-wide density increased 56-fold compared to 2015, comprising 93% of the total gastropod density and 79% of biomass. This spread may have been facilitated by invasive Dreissena spp. through stimulation of bottom algae and periphyton growth. While P. antipodarum is still spreading in lakes Michigan and Huron, its abundance remains stable in other lakes. Further monitoring is needed to understand the patterns of spread and P. antipodarum effects on Great Lakes benthic communities.
We examined three decades of changes in dreissenid populations in Lake Ontario and predation by round goby (Neogobius melanostomus). Dreissenids (almost exclusively quagga mussels, Dreissena rostriformis bugensis) peaked in 2003, 13 years after arrival, and then declined at depths <90 m but continued to increase deeper through 2018. Lake-wide density also increased from 2008 to 2018 along with average mussel lengths and lake-wide biomass, which reached an all-time high in 2018 (25.2 ± 3.3 g AFTDW/m²). Round goby densities were estimated at 4.2 fish/m² using videography at 10 to 35 m depth range in 2018. This density should impact mussel populations based on feeding rates, as indicated in the literature. While the abundance of 0–5 mm mussels appears to be high in all three years with measured length distributions (2008, 2013, 2018), the abundance of 5 to 12 mm dreissenids, the size range most commonly consumed by round goby, was low except at >90 m depths. Although the size distributions indicate that round goby is affecting mussel recruitment, we did not find a decline in dreissenid density in the nearshore and mid-depth ranges where goby have been abundant since 2005. The lake-wide densities and biomass of quagga mussels have increased over time, due to both the growth of individual mussels in the shallower depths, and a continuing increase in density at >90 m. Thus, the ecological effects of quagga mussels in Lake Ontario are likely to continue into the foreseeable future.
In 1985, remedial action plan development was initiated to restore impaired beneficial uses in 42 Great Lakes Areas of Concern (AOCs). A 43rd AOC was designated in 1991. AOC restoration has not been easy as it requires networks focused on gathering stakeholders, coordinating efforts, and ensuring use restoration. As of 2019, seven AOCs were delisted, two were designated as Areas of Concern in Recovery, and 79 of 137 known use impairments in Canadian AOCs and 90 of 255 known use impairments in U.S. AOCs were eliminated. Between 1985 and 2019, a total of $22.78 billion U.S. was spent on restoring all AOCs. Pollution prevention investments should be viewed as spending to avoid future cleanups, and AOC restoration investments should be viewed as spending to help revitalize communities that has over a 3 to 1 return on investment. The pace of U.S. AOC restoration has accelerated under the Great Lakes Legacy Act (GLLA) and Great Lakes Restoration Initiative (GLRI). Sustained funding through U.S. programs like GLRI and GLLA and Canadian programs such as Canada-Ontario Agreement Respecting Great Lakes Water Quality and Ecosystem Health and the Great Lakes Protection Initiative is needed to restore all AOCs. Other major AOC program achievements include use of locally-designed ecosystem approaches, contaminated sediment remediation, habitat rehabilitation, controlling eutrophication, and advancing science. Key lessons learned include: ensure meaningful public participation; engage local leaders; establish a compelling vision; establish measurable targets; practice adaptive management; build partnerships; pursue collaborative financing; build a record of success; quantify benefits; and focus on life after delisting.
The seminal work of Mills et al. (1993) lists 137 established aquatic species as nonindigenous to the Great Lakes (two plants are further subdivided into two subspecies groups). We have removed seven of these species: three have been redefined as probably native, and four plants (including both subspecies of Sonchus arvensis) have been reclassified as terrestrial. Thirty-five species that arrived prior to 1993 (some due to reclassification, some due to a time lag in discovery and reporting) have been added to the list. Twenty-four new species have become established post-1993, bringing the total to 188 (with Pluchea odorata including two subspecies). Notably, 21 of the 23 species were introduced between 1993 and 2006, but only 3 new species have been documented with new reproducing and overwintering populations in the last decade. Multiple revisions have been made to taxonomy and introduction dates based on additional review of literature and museum/herbarium collections. Over the most recent 25 years, the rate of introduction of nonindigenous species capable of becoming established has declined. With the 2006 expansion of ballast regulations to include residual ballast sediments in vessels declaring ‘No Ballast on Board’, the rate of new invasions has fallen to a low of only 0.25 species per year.
The faucet snail (Bithynia tentaculata) was introduced to the Great Lakes region in the late 1800s. Faucet snails alter native community dynamics and are an intermediate host for multiple trematode parasites that can be lethal to waterfowl when the snails are consumed. Although faucet snails have been established in the Great Lakes for over a century, their populations appear to have remained small for most of this period and their known distribution was limited to the lower Great Lakes, though basin-wide surveys were lacking until recently, so snails may have gone undetected. We compiled data from a five-year coastal wetland monitoring program spanning all of the Great Lakes, providing a basin-wide inventory of faucet snail populations and confirming the snail’s presence in every Great Lake. Further, we identified potential drivers of faucet snail occurrence and abundance (individuals per sampling replicate) across the basin and within individual lakes to identify factors that could lead to elevated risk of range expansion. Across the basin and within individual lakes, faucet snail occurrence was related to human recreational transport (proximity to a boat launch) and eutrophication (anthropogenic land-use, elevated nutrient concentrations). In addition, at sites where faucet snails occurred, they were most abundant at wetlands with surrounding forest cover, suggesting that the species can thrive in a range of environmental conditions. Our results suggest that limiting passive transport of faucet snails is vital to minimizing their spread to remote wetlands where the snails may thrive once established.
Freshwater mollusc diversity has repeatedly been found to peak in lowland stagnant waters, which are highly exposed to human-made degradation and the spread of non-native species. Despite the increasing loss of these habitats, little is known about the main predictors of their mollusc diversity patterns. Therefore, we aimed to determine the environmental drivers of mollusc assemblage variation between and within sites by sampling 62 water bodies in the Dyje River floodplain (south-eastern Czechia). We measured 14 environmental variables, categorized as site-specific or plot-specific. Species richness and abundances were analysed by GLM and GEE; species compositional variance was assessed by NMDS and db-RDA ordinations. Mollusc species richness, ranging between 0 and 15 species per site, and abundance sharply decreased towards high trophy sites, with the chlorophyll-a concentration and water pH highly correlated with species counts. Species compositional variation was driven mainly by water trophy and the quality of organic detritus. Site heterogeneity turned out to significantly control local assemblages of molluscs, while the presence of individual species seemed to be filtered by site trophy and the shoreline length. Thus, to maintain high regional diversity of aquatic molluscs in lowland agricultural landscapes, the presence of low trophy sites seems to be essential.
An upsurge in anthropogenic impacts has hastened the decline of the red panda (Ailurus fulgens). The red panda is a global conservation icon, but holistic conservation management has been hampered by research being restricted to certain locations and population clusters. Building a comprehensive potential habitat map for the red panda is imperative to advance the conservation effort and ensure coordinated management across international boundaries. Here, we use occurrence records of both subspecies of red pandas from across their entire range to build a habitat model using the maximum entropy algorithm (MaxEnt 3.3.3k) and the least correlated bioclimatic variables. We found that the subspecies have separate climatic spaces dominated by temperature‐associated variables in the eastern geographic distribution limit and precipitation‐associated variables in the western distribution limit. Annual precipitation (BIO12) and maximum temperature in the warmest months (BIO5) were major predictors of habitat suitability for A. f. fulgens and A. f. styani, respectively. Our model predicted 134,975 km² of red panda habitat based on 10 percentile thresholds in China (62% of total predicted habitat), Nepal (15%), Myanmar (9%), Bhutan (9%), and India (5%). Existing protected areas (PAs) encompass 28% of red panda habitat, meaning the PA network is currently insufficient and alternative conservation mechanisms are needed to protect the habitat. Bhutan's PAs provide good coverage for the red panda habitat. Furthermore, large areas of habitat were predicted in cross‐broader areas, and transboundary conservation will be necessary.
The Asian clam Corbicula fluminea is among the most prolific aquatic invaders in the world; but in colder mid-latitude areas, like the Laurentian Great Lakes, their population expansion has likely been limited by poor overwinter survival. In these areas, Asian clams are typically found in thermal refugia like warmwater discharges from industrial facilities. We sought to identify the current extent of Asian clam populations in Lake Michigan and waters immediately adjacent to it, specifically at locations most likely to harbor overwintering populations – industrial warmwater discharges. During April–May 2017, we surveyed 17 locations around Lake Michigan. Evidence of Asian clam populations was found at four sites, though live specimens (n = 3) were only found at the Indiana Harbor Ship Canal in East Chicago, IN. Shells or fragments of shells were found at Green Bay, WI, Waukegan, IL, and Port Sheldon, MI. Our findings indicate that although Asian clams are present in Lake Michigan, they are relatively rare, and remain isolated to a few small pockets of over-wintering habitat.
Egg deposition and use of restored spawning substrates by lithophilic fishes (e.g., Lake Sturgeon Acipenser fulvescens, Lake Whitefish Coregonus clupeaformis, and Walleye Sander vitreus) were assessed throughout the St. Clair–Detroit River system from 2005 to 2016. Bayesian models were used to quantify egg abundance and presence/absence relative to site-specific variables (e.g., depth, velocity, and artificial spawning reef presence) and temperature to evaluate fish use of restored artificial spawning reefs and assess patterns in egg deposition. Lake Whitefish and Walleye egg abundance, probability of detection, and probability of occupancy were assessed with detection-adjusted methods; Lake Sturgeon egg abundance and probability of occurrence were assessed using delta-lognormal methods. The models indicated that the probability of Walleye eggs occupying a site increased with water velocity and that the rate of increase decreased with depth, whereas Lake Whitefish egg occupancy was not correlated with any of the attributes considered. Egg deposition by Lake Whitefish and Walleyes was greater at sites with high water velocities and was lower over artificial spawning reefs. Lake Sturgeon eggs were collected least frequently but were more likely to be collected over artificial spawning reefs and in greater abundances than elsewhere. Detection-adjusted egg abundances were not greater over artificial spawning reefs, indicating that these projects may not directly benefit spawning Walleyes and Lake Whitefish. However, 98% of the Lake Sturgeon eggs observed were collected over artificial spawning reefs, supporting the hypothesis that the reefs provided spawning sites for Lake Sturgeon and could mitigate historic losses of Lake Sturgeon spawning habitat.
2,604 names at the rank of subtribe, tribe, subfamily, family and superfamily have been proposed for Recent and fossil gastropods, and another 35 for monoplacophorans. All names are listed in a nomenclator giving full bibliographical reference, date of publication, typification, and their nomenclatural availability and validity under the International Code of Zoological Nomenclature. Another 790 names, established for categories above the familygroup (infraorder to subclass) are listed separately. A fully ranked, hierarchical classification summarizes recent advances in the phylogeny of the Gastropoda and Monoplacophora. In all, the classification recognizes as valid a total of 721 gastropod families, of which 245 are known exclusively as fossils and 476 occur in the Recent with or without a fossil record; and 20 monoplacophoran families, of which 1 only occurs as Recent. Nomenclatural acts in this work: Amberleya bathonica Cox & Arkell, 1950, fixed as type species of Amberleya J. Morris & Lycett, 1851, under Art. 70.3; Ampezzopleura tenuis Nützel, 1998, fixed as type species of Ampezzopleura Bandel, 1991, under Art. 70.3; Proserpina nitida G. B. Sowerby II, 1839, designated type species of Despoena Newton, 1891; Buccinum glabratum Linnaeus, 1758, designated type species of Dipsaccus H. Adams & A. Adams, 1853; Murex ficus Linnaeus, 1758, designated type species of Ficula Swainson, 1835; Oncomelania hupensis Gredler, 1881, designated type species of Hemibia Heude, 1890; Murex metaxa Delle Chiaje, 1828, fixed as type species of Metaxia Monterosato, 1884 under Art. 70.3; Neridomus anglicus Cox & Arkell, 1950, fixed as type species of Neridomus J. Morris & Lycett, 1851, under Art. 70.3; Navicella clypeolum Récluz, 1843, designated type species of Orthopoma Gray, 1868; Trochus viadrinus M. Schmidt, 1905, fixed as type species of Parataphrus Chavan, 1954 under Art. 70.3; Helix pomatia Linnaeus, 1758, designated type species of Pentataenia A. Schmidt, 1855; Flammulina ponsonbyi Suter, 1897, fixed as type species of Phenacohelix Suter, 1892, under Art. 70.3; Cyrtolites corniculum Eichwald, 1860, fixed as type species of Pollicina Koken, 1895, under Art. 70.3; Purpurina elegantula d'Orbigny, 1850, designated as type species of Purpurina d'Orbigny, 1850, and lectotype of Turbo bellona d'Orbigny, 1850, designated as neotype of Purpurina elegantula; Pyramidella minuscula Monterosato, 1880, fixed as type species of Tiberia Jeffreys, 1884, under Art. 70.3; Cyclostoma delicatum Philippi, 1844, fixed as type species of Trachysma G. O. Sars, 1878, under Art. 70.3; Helix elegans Gmelin, 1791, fixed as type species of Trochoidea T. Brown, 1827, under Art. 70.3; Turritellopsis stimpsoni Dall, 1919, fixed as type species of Turritellopsis G. O. Sars, 1878, under Art. 70.3; Fusus averillii Gabb, 1864, fixed as type species of Volutoderma Gabb, 1876, under Art. 70.3; Voluta pepo Lightfoot, 1786, fixed as type species of Yetus Bowdich, 1822. Curnonidae d'Udekem d'Acoz, nom. nov., and Curnon d'Udekem d'Acoz, nom. nov., are established for Charcotiidae Odhner, 1926, and Charcotia Vayssière, 1906, (between 27 March and 1 May), non Charcotia Chevreux, 1906 (January) [Amphipoda]; Yuopisthonematidae Nützel, nom. nov., and Yuopisthonema Nützel, nom. nov., are established for Opisthonematidae Yu, 1976, and Opisthonema Yu, 1974, non Gill, 1862 [Pisces]. The new family-group name Burnupiidae Albrecht is established in this work; and the names Scolodontina and Orthalicoidei are first used here to denote, respectively, a suborder containing the family Scolodontidae, and an infraorder containing the superfamily Orthalicoidea.
The chief aim of the present study was to reveal changes in a littoral macroinvertebrate community induced by the invasion of the New Zealand mud snail (Potamopyrgus antipodarum). For that purpose, we compared relevant aspects of the lake littoral macroinvertebrate community in pre- and post-invasion periods and determined the trophic position of P. antipodarum in the lake food web by performing the stable isotope-ratio analysis. The analyses performed showed that P. antipodarum is a primary consumer that may utilise a wide range of primary food sources. Overall, our study showed the following effects of the P. antipodarum invasion on the macroinvertebrate community: A definite increase in the total macroinvertebrate biomass, a significant increase in the local macroinvertebrate family richness and diversity, a shift in the community composition from crustacean- to gastropod-dominated. However, P. antipodarum invasion was not found to affect the biomass of local macroinvertebrates, which remained unchanged.
In recent years, the number of areas remaining under the influence of acidity has increased. At all levels of ecosystems, biodiversity decreases with acidification, due to the elimination of species that are most sensitive to low pH. Forest ponds belong to a specific group that varied in location, a huge amount of leaf litter, and isolation from other aquatic environments. They are crucial in the industrial landscape with well-developed industry and human activity. The aim was to investigate the relative importance of water chemistry in explaining snail assemblage compositions and species richness in forest ponds of contrasting pH. Patterns in gastropod communities were determined from an analysis in 26 forest ponds with multivariate gradient analysis. Ponds ranged in a base mean pH from 3.0 to 9.0. pH has been found to be an important factor influencing gastropod fauna. Neutral ponds support diverse communities, typical of small water bodies. In two acidic pond types, snail fauna was different. Among the species characteristic for acidic ponds (pH < 6) were Anisus spirorbis and Aplexa hypnorum. The greatest distinct characterised alkaline ponds with the numerous appearance of alien Physa acuta. The most diverse gastropod fauna was found in neutral ponds, whereas the lowest degree of diversity was found in ponds with the lowest pH. Current knowledge of pH-associated changes in aquatic ecosystems is still incomplete because anthropogenic acidification is a recent phenomenon. It is extremely important in forest habitats, since they react more intensively to climatic factors and are often used in landscape management and planning.
Climate change and species invasions interact in nature, disrupting biological communities. Based on this knowledge, we simultaneously assessed the effects of climate change on the native distribution of the Amazonian fish Colossoma macropomum as well as on its invasiveness across river basins of South America, using ecological niche modeling. We used six niche models within the ensemble forecast context to predict the geographical distribution of C. macropomum for the present time, 2050 and 2080. Given that this species has been continuously introduced into non-native South American basins by fish farming activities, we added the locations of C. macropomum farms into the modeling process to obtain a more realistic scenario of its invasive potential. Based on modelling outputs we mapped climate refuge areas at different times. Our results showed that a plenty of climatically suitable areas for the occurrence of C. macropomum occurrence are located outside the original basins at the present time and that its invasive potential is greatly amplified by fish farms. Simulations of future geographic ranges revealed drastic range contraction in the native region, implying concerns not only with respect to the species conservation but also from a socio-economic perspective since the species is a cornerstone of artisanal and commercial fisheries in the Amazon. Although the invasive potential is projected to decrease in the face of climate change, climate refugia will concentrate in Paraná River, Southeast Atlantic and East Atlantic basins, putting intense, negative pressures on the native fish fauna these regions. Our findings show that short and long-term management actions are required for: i) the conservation of natural stocks of C. macropomum in the Amazon, and ii) protecting native fish fauna in the climate refuges of the invaded regions.
Freshwater gastropods often contribute significantly to freshwater ecosystem biomass and are a vital component of many consumers'
diets. They can also serve as a nutrient resource for terrestrial predators, representing an important example of nutrient
transfer across a habitat boundary. This study uses bankside middens to provide evidence of predation by the brown rat Rattus norvegicus on the native freshwater gastropod Viviparus viviparus in a closed, lentic system in Ely, southeastern England. Conchological analysis of shell remains in middens compared with
live snails in adjacent water sites suggested this predation could be size-selective for larger snails, and analysis of soft
tissue dry weights and the mechanical force required to break shells suggested that this was driven predominantly by maximizing
nutrient gain, rather than by optimizing handling effort. Aquatic gastropods represent a potentially important nutrient resource
for brown rat populations; this resource may be used continuously through time or exhibit ‘resource pulse’ dynamics. Predation
of this nature might also have important impacts on gastropod population structure, which may in turn impair ecosystem functioning.
The introduction of the invasive faucet snail (Bithynia tentaculata) and its associated trematodes, Cyathocotyle bushiensis, Sphaeridiotrema spp., and Leyogonimus polyoon, has resulted in recurring waterfowl die-offs during spring and fall migration in the Great Lakes Region, especially of Lesser scaup (Aythya affinis) and American coots (Fulica americana). Here we evaluated faucet snail habitat use and abundance in infested waterbodies in northcentral Minnesota (USA) during spring, summer, and fall of 2011–2013. We collected snail samples, along with data on abiotic and biotic variables, at 12 snail-infested waterbodies. We used Generalized Estimating Equations to develop models that explain variability in the distribution and abundance of snails within waterbodies. Models containing water depth consistently received considerable support in waterbodies where depth varied substantially; however the specific shape of these relationships varied among waterbodies. Snails used a wide range of depths, but were more likely to be present in deep portions (~6 m) of large lakes in all seasons. We found seasonal differences in the location of rafts of migrating scaup, with use of areas closer to shore in the spring, and use of areas shallower than those used most by faucet snails. Patterns in snail distribution likely influenced the availability of snails for consumption by migrating waterfowl; differences in portions of large lakes used by migratory waterfowl as stopover sites and by faucet snails may reduce exposure of migrating waterfowl to trematodes in infested lakes. However, some spatio-temporal overlap between snails and scaup occurs and explains the continuing loss of waterfowl to trematodiasis.
The New Zealand mud snail (Potamopyrgus antipodarum) is a world wide invasive species with established invasive populations in Australia, Europe, Japan, and North America. In the Laurentian Great Lakes, the snail has been found in each major water body except for Lakes Huron and St. Clair. Here we report data from samples taken from 78 sites in Lake St. Clair, the Mackinaw Straits, and two locations in western Lake Huron (Saginaw Bay and Thunder Bay) from time periods ranging from 1997 to 2009. Potamopyrgus was not found in the samples taken from any of the sites. Thus, there is no evidence from this study that the New Zealand mud snail has established populations in Lakes Huron and St. Clair.
Elimia livescens (Menke 1830) is a freshwater gastropod common in the Laurentian Great Lakes region. Geometric morphometric analysis was conducted to determine the variation in shell shape among sites along the shoreline of Lake Michigan (4 sites) and 3 inland lakes on Beaver Island and Manitou Island (8 sites) in Michigan, USA. Canonical Variates Analysis (CVA) showed significant variation in shell shape among the sites at inland lakes and those on the Lake Michigan shoreline. Eighty-two and a half percent of individual snails could be correctly assigned to their lake of origin and 62.8% could be correctly assigned to their site of origin based on shell shape. CVA axes were tested for correlations with the environmental variables. Shell shape in E. livescens correlated most strongly with fetch length and specific conductance. Higher fetch lengths produce higher-energy wave action and may select for individuals with a larger aperture, more globose shape, and lower spire (better for anchorage). Lower fetch lengths produce lower-energy wave action and may select for snails with a smaller aperture, more elongate shape, and higher spire (better for navigating above soft sediment). Environmental processes like those documented in classic studies on marine snails appear to affect shell shape in freshwater snails in similar ways. Furthermore, our study highlights that fetch plays a key role in structuring benthic communities and may play a parallel role in structuring populations. Our study suggests that shell shape variability is a critical factor in regional adaptation and success in this widely distributed gastropod.
Zebra mussels (Dreissena polymorpha) are not only an extremely aggressive invasive species, often dominating water bodies they invade, they are also very effective ecosystem engineers, altering the environments they invade. They are effective engineers, altering both ecosystem structure and function. They change existing and provide new habitat for other organisms, affect trophic interactions and the availability of foods for both pelagic species and other benthic species, and they affect the rates of other ecosystem processes including mineralization of nutrients, oxygen availability and sedimentation rates. These physical impacts on the environment feedback directly to other species that interact with or are impacted by zebra mussels, or indirectly through food chains, disturbance, succession, or other longer-term community and ecosystem processes.
Despite the mollusks being the second largest group in Kingdom Animalia, they have not been considered in environmental risk assessment so far, mainly due to the lack of standardized protocols. In this sense, the gastropods, with abundant species widely distributed in aquatic environments, have been employed in water and sediment quality assessments due their clear sensitivity to chemical compounds, as pollution indicators for different substances. Acute and chronic toxicity tests have been mostly used in ecotoxicological protocols to evaluate potential effects of contaminants on natural populations. However, with the need to assess potential sublethal hazards to ecosystems of pollutants at low concentrations, environmental monitoring programs have encouraged analyzing effects on gametes, fertilization, reproduction and embryo-larval development. Furthermore, among the myriad of chemicals reaching the environment, some compounds can directly affect the reproductive potential through induction of mutations in germ cells and vulnerable embryos. This work discusses some case studies of standardization assays with freshwater snails, especially good organisms for laboratory and in situ monitoring studies, to be considered for regulatory environmental agencies. In that context, this work also shows the prospects for using gastropods in monitoring freshwater environments in Latin America.
Presented here are keys and notes on distribution and ecology for the freshwater snails (Gastropoda), mussels (Unionidae). and fingernail clams (Sphaeriidae) which have been collected from the Laurentian Great Lakes.
Including subspecies and forms. 121 taxa are discussed: 47 Gastropoda. 39 Unionidae, and 35 Sphaeriidae. Relations to substrate preferences and pollution are summarized where known. Special emphasis is given to the sphaeriid genus Pisidium in discussions of morphological variability and characters which will separate the species and forms both in the adult and immature stages. Both drawings and scanning electron microscope
photomicrographs are presented for all sphaeriid taxa. A limited synonymy has been compiled from publications and reports on the Laurentian Great Lakes and the expanded reference section includes not only citations used in the text but also publications and reports which may aid researchers in more in-depth studies of the fauna.
Dreissena polymorpha, the zebra mussel, is one of the most aggressive and important invading aquatic species world wide. Its spread has followed the path of human activity, initially following human constructed canals connecting the Black Sea and Baltic Sea basins. One consequence of this invasion is the impact of zebra mussels on native bivalves. Overgrowth by Dreissena can cause a dramatic decrease in unionid density. The extent of this effect is determined by several factors including Dreissena density, time since invasion by Dreissena, biomass of attached Dreissena, and type of bottom sediments (sand versus silt). We found a correlation between overall Dreissena density and the number of zebra mussels per overgrown unionid, and between Dreissena density and the ratio of the mass of attached zebra mussels to the mass of the host unionid. The extensive overgrowth of unionids by Dreissena, resulting in mass mortality, is characteristic of periods of rapid population growth, when Dreissena invade a new waterbody.
The invasive New Zealand mudsnail, Potamopyrgus antipodarum, is a small freshwater hydrobiid snail with populations in western US rivers and streams and in the Laurentian Great Lakes. The snail has had established populations in the Great Lakes since at least 1991 and in one stream emptying into Lake Ontario since at least 2007. This study’s purpose was to broadly survey streams and rivers emptying into Lakes Ontario and Erie to determine the extent of the species’ lotic invasion in the Eastern US. In the summer of 2011, over 100 sites were sampled from the Niagara River, NY to Oswego, NY along Lake Ontario and over 80 sites from Buffalo, NY to the Pennsylvania-Ohio State line along Lake Erie. At each site, general observations of the stream were made and the organisms living in the stream were surveyed for the presence of New Zealand mud snails. Potamopyrgus was found at the site of original discovery and at one additional location along Lake Ontario. In addition an unusual snail was discovered that was a hybrid between a native species (Pleurocera livescens) and an invasive (Pleurocera virginica). This hybrid was extremely abundant in several locations and may be invasive.
The New Zealand mud snail, Potamopyrgus antipodarum, is a widely distributed non-native species of management concern on four continents. In a southern California stream, P. antipodarum abundance, which ranged from ca. −2, was related to discharge and temperature patterns. Laboratory experiments indicated that P. antipodarum (1) survivorship decreased from 13 to 27°C, but its growth rate was higher at 13 and 20°C than 27°C; (2) grazing rates were similar to those of native algivores in short-term trials; (3) grazing impact was greater than that of a native hydrobiid snail in longer-term trials; (4) ingested different diatom sizes than some other grazers; (5) reduced the abundances of medium-sized and large diatoms, and several filamentous cyanobacteria and chlorophytes, while increasing the relative abundances of tough filamentous chlorophytes (e.g., Cladophora); (6) impact on other grazing invertebrates was species specific, ranging from competition to facilitation; (7) reduced the survivorship of Anaxyrus boreas tadpoles; and (8) was consumed by non-native Procambarus clarkii and naiads of Aeshna and Argia. Ecological effects of introduced P.antipodarum are subtle, occurring primarily at transitory high densities, but flow regulation may enhance their effects by eliminating high flows that reduce their population sizes.
Alien species (those carried outside their original ranges by human activities) have strongly affected the distribution and abundance of mollusks in many North American fresh waters. The best known of these aliens in North America is the zebra mussel (Dreissena polymorpha), which has nearly extirpated native unionid clams from infested lakes and rivers by fouling their shells and outcompeting them for food. Zebra mussels also have reduced populations of native sphaeriid clams, and both increased and reduced populations of snails. The effects of the other well-known alien bivalve in North America, Corbicula fluminea, are surprisingly poorly known. Corbicula probably caused some populations of native bivalves to decline, but other native populations seem to coexist with Corbicula. Several plausible mechanisms of interaction between Corbicula and the native biota have been proposed, but not demonstrated. Other aliens, including the recently arrived snail Potamopyrgus antipodarum, probably compete strongly with native freshwater mollusks under some circumstances. Several alien species, such as round goby and some sunfishes and crayfishes introduced outside their native ranges in North America, are effective predators on native mollusks and have strong effects on their distribution and abundance. Other aliens (particularly aquatic plants) affect mollusks by altering the food base or the physicochemical environment. Alien species can affect water quality, cycling of contaminants, and performance of biological indices of water quality. Because of ineffective control of aliens in North America, they may be an increasingly important factor in molluscan distribution as new species arrive from other continents and established species spread throughout the continent.
Dreissena polymorpha (zebra mussel) and D. rostriformis bugensis (quagga mussel) continue to spread in Europe and in North America, and have large ecological and economic impacts where they invade. Today many more waterbodies are invaded by zebra mussels, and therefore the extent of their impact is greater than that of quagga mussels. Both species provide additional space and food for invertebrates in the littoral zone, increasing their diversity and density. In contrast, in the profundal zone, quagga mussels may compete for space and food resources with benthic invertebrates, decreasing their diversity and density. The system-wide effect of dreissenids depends on water mixing rates, lake morphology, and turnover rates. Because quagga mussels are found in all regions of a lake, and form larger populations, they may filter larger volumes of water and may have greater system-wide effects, especially in deep lakes, than zebra mussels, which are restricted to shallower portions of lakes. Shortly after initial invasion, as populations increase, both dreissenids will have their largest effects on communities, and most of them will be direct effects. After the initial stage of invasion, impacts are less predictable, and more likely to be caused by indirect effects through changes in the ecosystem.
Many North American freshwater mollusks are at risk of extinction. Knowledge of basic ecology and systematics of the pleurocerid and hydrobiid gastropods is lacking. Pleurocerids are most diverse in southeastern USA, and we know that periphyton food limits their growth, and that their grazing, in turn, limits periphyton biomass. However, we know little about the effects of spates and current velocity on pleurocerid populations, and more work is needed to determine whether interspecific competition or significant risk from predation occurs. Hydrobiids are extremely diverse, but many species inhabit only a few springs (especially in arid western USA) and are at risk of extinction. More work is needed on their population and community ecology. Invasions pose a risk to native snail species. For example, the New Zealand mudsnail (Potamopyrgus antipodarum) interacts negatively with several hydrobiids in the Snake River in western USA. We suggest several research avenues that are needed if we are to maintain and restore pleurocerid and hydrobiid snail populations.
We sampled Doe Run, Kentucky to search for habitat-mediated differences in the abundance and size distribution of a pleurocerid grazer, Elimia semicarinata, predicted by the literature. Adult density was 3x greater in a slow-flow, sunny habitat, than in faster flowing or shaded habitats where densities were similar. Adult size was greatest in slow-flow habitats, and smallest in habitats with faster current velocities. In comparison, juvenile densities were greater in habitats with faster current velocities. Linear regressions indicated that both adult density and size were negatively related to current velocity, but that juvenile abundance was positively related to current velocity; none of the variables were significantly affected by light levels. Periphyton biomass (both chlorophyll a concentration and ash-free dry mass) was generally greater in slow-flow, sunny habitats, and lower in habitats with faster current velocities, suggesting current velocity may indirectly affect snail size distributions by altering food resources. Differences in gastropod size and density were maintained among habitats even though a field experiment suggested rapid colonization rates in all habitats. An experiment with in situ flow baffles revealed that the number and size of snails colonizing flow refugia increased only in habitats with faster current velocities. Taken together, our results suggest that adults may select flow refugia, while juveniles avoid them, and that pleurocerid population dynamics are influenced by current velocity directly by shear stress, or indirectly by effects of current velocity on periphyton biomass. Future studies of grazer-periphyton interactions should take such complexities into account.
This is the first American Fisheries Society conservation assessment of freshwater gastropods (snails) from Canada and the United States by the Gastropod Subcommittee (Endangered Species Committee). This review covers 703 species representing 16 families and 93 genera, of which 67 species are considered extinct, or possibly extinct, 278 are endangered, 102 are threatened, 73 are vulnerable, 157 are currently stable, and 26 species have uncertain taxonomic status. Of the entire fauna, 74% of gastropods are imperiled (vulnerable, threatened, endangered) or extinct, which exceeds imperilment levels in fishes (39%) and crayfishes (48%) but is similar to that of mussels (72%). Comparison of modern to background extinction rates reveals that gastropods have the highest modern extinction rate yet observed, 9,539 times greater than background rates. Gastropods are highly susceptible to habitat loss and degradation, particularly narrow endemics restricted to a single spring or short stream reaches. Compilation of this review was hampered by a paucity of current distributional information and taxonomic uncertainties. Although research on several fronts including basic biology, physiology, conservation strategies, life history, and ecology are needed, systematics and curation of museum collections and databases coupled with comprehensive status surveys (geographic limits, threat identification) are priorities.
RESUMEN
esta es la primera evaluación sobre el estado que guarda la conservación de los gasterópodos (caracoles) de Canadá y los EE.UU., realizada por el Subcomité para los Gasterópodos (Comité de Especies Amenazadas) de la Sociedad Americana de Pesquerías. Esta revisión comprende 703 especies, pertenecientes a 16 familias y 93 géneros, de las cuales 67 se consideran extintas o probablemente extintas; 278 están en peligro, 102 amenazadas, 73 vulnerables, 157 cuentan con poblaciones estables y 26 especies presentan un estado taxonómico incierto. De la totalidad de la fauna, 74% de los gasterópodos se encuentran en alguna categoría de vulnerabilidad (amenazados, en peligro o vulnerables) o extintos, lo cual excede al nivel de amenaza al que está sujeto el grupo de los peces (39%) y los langostinos (48%), pero es similar al de los mejillones (72%). Comparando las tasas de extinción actuales contra las tasas de extinción de fondo en el grupo de los gasterópodos, se tiene que en la actualidad son las más altas registradas: 9,539 veces la tasa de extinción de fondo. Los gasterópodos son altamente susceptibles a la degradación y pérdida de hábitat, en particular aquellas especies endémicas cuya distribución está restringida a un solo manantial o a arroyos pequeños. La compilación realizada para esta revisión se dificultó por la falta de información sobre la incertidumbre en la distribución y taxonomía del grupo. Si bien se necesita desarrollar investigación en distintos frentes como biología básica, fisiología, estrategias de conservación, historias de vida y ecología, se consideran como prioridades la sistemática, curación de colecciones museográficas y bases de datos acopladas con muestreos sistemáticos integrales (para establecer límites geográficos, identificación de amenazas).
Island biogeography theory can be used to explain patterns of species richness on various types of habitat islands, including freshwater lake systems. Mollusk production in these systems also has been linked to various water-chemistry variables, such as pH, alkalinity, hardness, and specific conductance. We examined how mollusk diversity patterns were related to geographical and limnological factors in insular lakes of the Beaver and Manitou Archipelagos in Lake Michigan (Laurentian Great Lakes), USA. The strongest correlations observed were with shoreline development (r = 0.80), specific conductance (r = 0.87), and pH (r = 0.87). Principal components analysis revealed that isolation by distance and PO 4 32 concentration also may have affected species richness and abundance. Shoreline length was a better predictor of species richness than surface area, but both measures of habitat size were unable to account for much of the variation in species richness. The data suggest that shoreline length and development represent available habitat area more accurately than lake area for primarily littoral-dwelling mollusks. The relatively weak correlations observed with lake area and isolation from Lake Michigan suggest that application of island biogeography theory to predict mollusk species richness using only lake surface area and isolation by distance is limited for freshwater mollusks.
Although spatial scale is important for understanding ecological processes and guiding conservation planning, studies combining a range of scales are rare. Habitat suitability modelling has been used traditionally to study broad-scale patterns of species distribution but can also be applied to address conservation needs at finer scales. We studied the ability of presence-only species distribution modelling to predict patterns of habitat selection at broad and fine spatial scales for one of the rarest mammals in the UK, the grey long-eared bat (Plecotus austriacus). Models were constructed with Maxent using broad-scale distribution data from across the UK (excluding Northern Ireland) and fine-scale radio-tracking data from bats at one colony. Fine-scale model predictions were evaluated with radio-tracking locations from bats from a distant colony, and compared with results of traditional radio-tracking data analysis methods (compositional analysis of habitat selection). Broad-scale models indicated that winter temperature, summer precipitation and land cover were the most important variables limiting the distribution of the grey long-eared bat in the UK. Fine-scale models predicted that proximity to unimproved grasslands and distance to suburban areas determine foraging habitat suitability around maternity colonies, while compositional analysis also identified unimproved grasslands as the most preferred foraging habitat type. This strong association with unimproved lowland grasslands highlights the potential importance of changes in agricultural practices in the past century for wildlife conservation. Hence, multi-scale models offer an important tool for identifying conservation requirements at the fine landscape level that can guide national-level conservation management practices.
We examined the importance of the Eurasian zebra mussel (Dreissena polymorpha) in structuring macroinvertebrate communities on hard substrata in the Great Lakes - St. Lawrence River system. An experiment using artificial substrata (i.e., cement bricks with either a layer of living zebra mussels, a layer of intact empty shells that mimicked living mussels, or with no added layer) showed that macroinvertebrate abundance is enhanced in the presence of zebra mussels and that macroinvertebrate responses to physical versus biological attributes of mussel beds (e.g., spatial habitat created by clumped shells; biodeposition) vary among taxa. Moreover, densities of zebra mussels and associated epifauna have increased severalfold at various sites in the Great Lakes - St. Lawrence River system within the past decade; changes in community composition were similar to those observed in our artificial substrate experiment. Our results suggest that dense zebra mussel colonization alters macroinvertebrate communities on hard substrata by enhancing conditions for deposit-feeding organisms, small gastropods, and small predatory invertebrates, and by displacing large gastropods and certain large filterers. In the St. Lawrence River, these effects were associated with zebra mussel densities of 1500-4000 individuals/m2, which are likely to be supported by most waterbodies in North America.
Among the highest profile invasive species in the Laurentian Great Lakes region are Dreissena polymorpha and D. rostriformis bugensis (collectively dreissenids). Despite their abundance and ecosystem-wide effects, little is known about dreissenid distributions in large connecting channels between lakes. The objectives of this study
were to estimate and document dreissenid densities and their habitat characteristics throughout the St. Clair River, to compare dreissenid species demographics, and predict spatial distributions between two connecting waters of the Great Lakes: the St. Clair and Detroit rivers. Two types of species distribution models (SDMs),
MaxEnt and classification and regression tree analysis (CART), were created using dreissenid and habitat data collected in both the Detroit and St. Clair rivers. The SDMs were then used to predict presence of dreissenids in the St. Clair River. The St. Clair River had more D. r. bugensis (mean density = 486 ± 152 individuals/m2) than
D. polymorpha (mean density = 3 ± 1 individuals/m2). The SDMs created from the Detroit River data reliably predicted presence of dreissenids in the St. Clair River. Depending on the river and species, CART models identified velocity and depth to be important predictor variables, while distance to river inlet/outlet were the most influential variables in the MaxEnt models. Most research on dreissenid distribution modeling is focused on determining areas for potential spread; however, this study presents a unique perspective by modeling dreissenid presence, both D. polymorpha and D. r. bugensis separately and together, where they have been established for more than 30 years.
Native freshwater mussels (Bivalvia: Unionidae) were seemingly pushed to extirpation following the establishment of dreissenid mussels in the St. Clair (SCR)–Detroit River (DR) System and the current state of unionids in the main channels of the SCR remains unknown. To assess remnant unionid populations, the DR and SCR were surveyed in 2019 and 2021, respectively, using a mixture of stratified random, historical, potential refuge, and
model-selected (SCR sampling only) sites (n = 56 DR sites and 51 SCR sites). Data collected from the DR (2019) were used to create unionid species distribution models in MaxEnt, which produced the model-selected sites for sampling the SCR. A total of 14 live unionids representing 9 species were found among 7 sites in the SCR; however, the DR model projected to the SCR failed to be predictive for unionid presence in the SCR (0 % success).
Additional models were created for the DR and SCR using MaxEnt and classification and regression tree (CART)
Analysis to elucidate the characteristic differences between the two rivers. MaxEnt modelling showed the highest
contributing variable for the DR model was water velocity (m/s) while the highest contributing variable for the
SCR model was river distance to the outlet which could be one explanation for why the DR model did not
accurately predict unionid presence in the SCR. Additionally, when DR and SCR data were combined in the CARTmodel, the model failed to predict any live unionid sites from the SCR. Variability in model predictions demonstrate the characteristic differences between the DR and SCR. Therefore, model verification for both rivers specific models took place in 2022 (n = 8 DR sites and 6 SCR sites). The DR unionid species distribution model identified 3 additional sites with live unionids (38 % of predicted sites), but the SCR model did not locate any additional live unionid locations (0 % of predicted sites). This research updated our knowledge on native unionid distributions and habitat use in the DR and SCR which could contribute towards unionid conservation in the
future.
Some corbiculids (bivalve clams in the genus Corbicula ) are invasive, having spread nearly worldwide and are thought to impact native unionid mussels. To determine the density and distributional associations of invasive corbiculids co‐occurring with native unionids, corbiculid clam and unionid mussel surveys were conducted at 122 sites in the Kalamazoo River catchment, Michigan, U.S.A.
Unionid densities ranged from 0 to 97 (x̅ = 7.45 ± 15.38 SD ) live unionids found per person hour while corbiculid densities varied from 0 to 0.24 (0.012 ± 0.037) g/cm ³ . Corbiculid distributions were clumped (Moran's I test: Index = 0.281, Z = 2.228, p = 0.026) and highest along the main branch of the river. Unionid distributions, both individual species and at family level, were found to be randomly distributed throughout the catchment (Moran's I test: Index = 0.343 to −0.022, Z = 1.913 to −0.118, p value = 0.056 to 0.970).
Overall, unionid species richness, as well as the distribution of 13 unionid species, were negatively associated with corbiculid density. Although corbiculids can inhabit the same river reaches with unionids, unionid species richness and densities may be negatively influenced by the presence of corbiculids.
Although many species of unionids were negatively associated with corbiculid density, our research showed that they can co‐exist in the same river reaches. Overall, unionids were positively correlated with corbiculids throughout the catchment, probably because the two groups have similar habitat requirements. It is therefore important to consider unionids and corbiculids concurrently in conservation planning and the management of invasive corbiculids.
The freshwater pearl mussel Margaritifera margaritifera has been suffering major population declines in Europe. This endangered species is a host specialist and exclusively requires salmonid species ( Salmo trutta and Salmo salar ) to complete its life cycle. In theory, obligatory biotic interactions should deserve special conservation attention, because the loss or massive decline of fish hosts may elicit the extirpation of their affiliated species. While many threats disturbing M. margaritifera are similarly affecting salmonids, climate change is particularly alarming, with the potential to significantly change the fish‐mussel dynamics.
To evaluate the importance of including the occurrence of fish hosts for predicting the distribution of M. margaritifera in Europe, three datasets were used to build species distribution models (SDMs) with a maximum entropy (MaxEnt) approach: (1) environmental variables (ENV); (2) probability of fish hosts occurrence (FH); and (3) environmental variables and probability of fish hosts occurrence (ENV + FH). We identified the environmental variables that better explain M. margaritifera distribution and modelled its current and future distribution under a suite of climate change scenarios. Furthermore, projections were used to evaluate the adequacy of current networks of European protected areas in covering the suitable habitats for M. margaritifera .
Results showed that incorporating data about fish hosts into M. margaritifera SDMs avoided the overprediction of geographical projections and, to a minor extent, improved model performance (area under the curve: ENV = 0.851; FH = 0.848; ENV + FH = 0.867). The distribution range of M. margaritifera in Europe is expected to contract in all future timeframes and emission scenarios considered. Forecasts point to large contractions particularly in central and southern Europe and lowland regions. The European network of protected areas fails to protect 69% of the current and 66%–67% of the future predicted M. margaritifera distribution.
This study clearly illustrates the importance of including mussel–fish hosts interactions for accurately predicting M. margaritifera's distribution. The response of M. margaritifera to environmental variables highlights its vulnerability to the higher temperatures, particularly in southern Europe. While predictions indicate large contractions in M. margaritifera's distribution as a result of future climate change, the current European network of protected areas fails to safeguard M. margaritifera .
This work provides strong evidence for proposing the generalised use of biotic information about hosts in addition to purely environmental variables to model the distribution of freshwater mussels, as well as for other species with obligatory biotic interactions. Building SDMs such as those discussed here can inform political decision‐making about the likely scenarios for species occurrence in future decades, the requirements needed for an effective conservation strategy, and the regions where conservation should be a priority.
There are serious concerns for native freshwater mussel survival (Bivalvia: Unionidae) in the Laurentian Great Lakes region after populations were seemingly pushed to the brink of extirpation following the introduction of dreissenid mussels (Dreissena polymorpha and D. rostriformis bugensis) in the mid-1980s. The Detroit River was the first major river system in North America to be invaded by dreissenids, and unionids were considered extirpated from the river by 1998. Since then several unionid refuges (areas with relatively low dreissenid impact and surviving unionids) have been found in coastal areas of lakes St. Clair and Erie, but no documentation exists in the Detroit River. To assess dreissenid presence and potential unionid persistence, a mixture of stratified random, historical, and potential refuge sites were surveyed during summer 2019 in the Detroit River. Unionid and dreissenid habitat use was further investigated with analysis of variance and classification and tree analyses. Of the 56 sites surveyed, only five sites had live unionids totaling 220 animals of 11 species. More than 2000 unionid shells of 31 species were collected from 39 sites, confirming the large and diverse unionid populations that existed prior to the dreissenid invasion. Ninety-eight percent of live unionids found showed evidence of past or present dreissenid attachment. Estimated dreissenid densities were highly variable with river location and ranged from 0 to 5673 live individuals per m2, with the largest densities concentrated in the upstream half of the Detroit River. Despite their previously assumed extirpation from the Detroit River, live unionids were found during this comprehensive survey. Although only 40% of the historical species within the unionid assemblage remains, our results suggest, in the right conditions, some coexistence is possible among some species of unionids and dreissenids in this large river system.
Non-native species often lead to undesirable ecological and environmental impacts. Two hypotheses that predict establishment of non-native species are enemy release and biotic resistance. Support for these hypotheses in freshwater invasions is mixed. Experiments combined with field observations provide a complementary approach to understanding how interactions between native and non-native species lead to enemy release or biotic resistance. We tested experimentally whether these hypotheses provided insights into the invasion of the banded mystery snail (Viviparus georgianus), which has invaded the Great Lakes region and northeastern Unites States (US) from the southeastern US. Because freshwater systems vary widely in their nutrient concentrations due to natural and anthropogenic processes, we tested whether nutrient additions altered competitive and predatory interactions that regulate mechanisms of enemy release or biotic resistance. We evaluated the status of the mystery snail invasion in a 3-year field survey of Lake George (NY, US) to identify if field observations supported any experimental conclusions. The presence of the banded mystery snail led to a 14% and 27% reduction in biomass of a native competitor under low- and high-nutrient concentrations, respectively. The mystery snail also triggered a 29% biomass loss of a native snail predator, but only in low-nutrient concentrations. Field surveys indicated that the mystery snail dominated the snail community; of seven snail species, it comprised 77% of all snails. Results from the field surveys combined with experimental results indicate that neither competitors nor predators have likely suppressed the invasion of the banded mystery snail. This conclusion is consistent with competitive- and predatory-enemy release as we found no indication of biotic resistance via competition or predation from native species. Our results further highlight that the post-establishment impacts of invasive species are altered by the trophic state of freshwater ecosystems.
In the 12 years since Dudgeon et al. (2006) reviewed major pressures on freshwater ecosystems, the biodiversity crisis in the world's lakes, reservoirs, rivers, streams and wetlands has deepened. While lakes, reservoirs and rivers cover only 2.3% of the Earth's surface, these ecosystems host at least 9.5% of the Earth's described animal species. Furthermore, using the World Wide Fund for Nature's Living Planet Index, freshwater population declines (83% between 1970 and 2014) continue to outpace contemporaneous declines in marine or terrestrial systems. The Anthropocene has brought multiple new and varied threats that disproportionately impact freshwater systems. We document 12 emerging threats to freshwater biodiversity that are either entirely new since 2006 or have since intensified: (i) changing climates; (ii) e‐commerce and invasions; (iii) infectious diseases; (iv) harmful algal blooms; (v) expanding hydropower; (vi) emerging contaminants; (vii) engineered nanomaterials; (viii) microplastic pollution; (ix) light and noise; (x) freshwater salinisation; (xi) declining calcium; and (xii) cumulative stressors. Effects are evidenced for amphibians, fishes, invertebrates, microbes, plants, turtles and waterbirds, with potential for ecosystem‐level changes through bottom‐up and top‐down processes. In our highly uncertain future, the net effects of these threats raise serious concerns for freshwater ecosystems. However, we also highlight opportunities for conservation gains as a result of novel management tools (e.g. environmental flows, environmental DNA) and specific conservation‐oriented actions (e.g. dam removal, habitat protection policies, managed relocation of species) that have been met with varying levels of success. Moving forward, we advocate hybrid approaches that manage fresh waters as crucial ecosystems for human life support as well as essential hotspots of biodiversity and ecological function. Efforts to reverse global trends in freshwater degradation now depend on bridging an immense gap between the aspirations of conservation biologists and the accelerating rate of species endangerment.
This study examines how flow disturbance influences distributions of the snail Potamopyrgus antipodarum, a common grazer in New Zealand streams, at the drainage basin, substratum, and rock face scales. We analyzed survey data from 48 streams across New Zealand to relate snail densities to hydrological patterns and conducted experiments in a laboratory flow tank and in artificial streams in field conditions to evaluate refugium effects of different substrate types in high flows. The survey showed that local densities were significantly inversely related to flood frequency, suggesting flow disturbance influenced regional distributions of P. antipodarum. The survey also revealed that lake-fed streams and low-gradient streams in foothill regions tended to have fewer, less severe floods and higher snail densities than high-gradient (> 1%) streams in mountain and foothill regions. Results from both the flow tank and artificial stream experiments showed that finer-grained substrates provided better refugium from dislodgment conditions than larger substrates (i.e., cobbles) when bed sediments were artificially stabilized. In the flow tank where velocities were incrementally increased, dislodgment rates of snails were significantly lower on artificial gravels than on artificial cobbles or bedrock. Snails moved to low-velocity patches (i.e., crevices) on all substrates as current velocities increased. However, more snails accumulated in crevices between gravels and pebbles than between cobbles; the relatively high turbulence between cobbles, in part, contributed to high dislodgment rates from this substrate. Similar differences in dislodgment vulnerability and flow refugium effects were observed in experiments using real substrates in artificial streams in field conditions. A substrate size-flood duration experiment showed that significantly more snails were dislodged from cobbles and pebbles than from gravels and that more were dislodged in longer-lasting high discharge events (30 min) than in brief ones (1 min). Another experiment in which snails were transported downstream (1, 3, 6 or 9 m) from non-stabilized substrate patches similarly showed that snail dislodgment and mortality rates were generally higher from cobbles than from gravels and pebbles. Like other studies, we found that larger substrate particles were less likely to move than smaller ones (gravels) under similar hydraulic conditions. However, we discovered that the best refugium conditions for resisting dislodgment are not necessarily linked to larger substrate size. Our findings also suggest that flooding may alter local densities of snails by moving and relocating snails rather than by killing them. The observed patterns of distributions of these snails appear to result from complex interactions between hydrological/hydraulic features and substrate architecture.
The MaxEnt software package is one of the most popular tools for species distribution and environmental niche modeling, with over 1000 published applications since 2006. Its popularity is likely for two reasons: 1) MaxEnt typically outperforms other methods based on predictive accuracy and 2) the software is particularly easy to use. MaxEnt users must make a number of decisions about how they should select their input data and choose from a wide variety of settings in the software package to build models from these data. The underlying basis for making these decisions is unclear in many studies, and default settings are apparently chosen, even though alternative settings are often more appropriate. In this paper, we provide a detailed explanation of how MaxEnt works and a prospectus on modeling options to enable users to make informed decisions when preparing data, choosing settings and interpreting output. We explain how the choice of background samples reflects prior assumptions, how nonlinear functions of environmental variables (features) are created and selected, how to account for environmentally biased sampling, the interpretation of the various types of model output and the challenges for model evaluation. We demonstrate MaxEnt’s calculations using both simplified simulated data and occurrence data from South Africa on species of the flowering plant family Proteaceae. Throughout, we show how MaxEnt’s outputs vary in response to different settings to highlight the need for making biologically motivated modeling decisions.
We examined covariation of morphology with local and regional environmental variables in the widespread North American freshwater gastropod Elimia livescens (Menke, 1830). Geometric morphometrics was used to quantify shape of individuals collected at sites in Indiana, U.S.A. We used the Procrustes superimposition method and relative warp analysis to examine variation among individuals. We found that shape of E. livescens covaried significantly with flowing versus non-flowing habitats, drainage area, latitude and longitude, water temperature, conductivity, substrate type, and the presence of woody debris. Individuals with smaller apertures and streamlined shape occurred in smaller watersheds in the southeastern regions of Indiana, and in local habitats with low water flow, low conductivity, large, coarse substrate (rip-rap), low frequency of woody debris, and higher dissolved oxygen. We suggest that morphological variation is an integral part in maintaining a wide distribution and maximizing local success for an aquatic gastropod that occurs in a variety of environments.
We examined the importance of the Eurasian zebra mussel (Dreissena polymorpha) in structuring macroinvertebrate communities on hard substrata in the Great Lakes – St. Lawrence River system. An experiment using artificial substrata (i.e., cement bricks with either a layer of living zebra mussels, a layer of intact empty shells that mimicked living mussels, or with no added layer) showed that macroinvertebrate abundance is enhanced in the presence of zebra mussels and that macroinvertebrate responses to physical versus biological attributes of mussel beds (e.g., spatial habitat created by clumped shells; biodeposition) vary among taxa. Moreover, densities of zebra mussels and associated epifauna have increased severalfold at various sites in the Great Lakes – St. Lawrence River system within the past decade; changes in community composition were similar to those observed in our artificial substrate experiment. Our results suggest that dense zebra mussel colonization alters macroinvertebrate communities on hard substrata by enhancing conditions for deposit-feeding organisms, small gastropods, and small predatory invertebrates, and by displacing large gastropods and certain large filterers. In the St. Lawrence River, these effects were associated with zebra mussel densities of 1500–4000 individuals/m 2 , which are likely to be supported by most waterbodies in North America. Résumé : Nous avons examiné l'importance de la moule zébrée eurasienne (Dreissena polymorpha) dans la structuration des communautés de macroinvertébrés sur des substrats durs dans le réseau des Grands Lacs et du Saint-Laurent. Une expérience faisant appel à des substrats artificiels (c.-à-d., des briques de ciment soit couvertes d'une couche de moules zébrées vivantes, soit portant une couche de coquilles vides intactes ressemblant à des moules vivantes, soit sans recouvrement) a révélé que l'abondance de macroinvertébrés est accrue en présence de moules zébrées, et que les taxons de macroinvertébrés varient en fonction des attributs physiques ou des attributs biologiques des gisements de moules (p. ex., habitat spatial créé par les coquilles entassées; nourriture fournie par le dépôt de matières organiques). En outre, les densités des moules zébrées et de l'épifaune associée ont augmenté plusieurs fois à divers sites du réseau des Grands Lacs et du Saint-Laurent au cours de la dernière décennie; les changements dans la composition des communautés étaient similaires à ceux que nous avons observés pendant notre expérience sur les substrats artificiels. Nos résultats font ressortir que la colonisation par les moules zébrées modifie les communautés de macroinvertébrés sur les substrats durs en stimulant les conditions favorables aux organismes déposivores, aux petits gastropodes et aux petits invertébrés prédateurs, et en déplaçant les gros gastropodes et certains filtreurs de grande taille. Dans le Saint-Laurent, ces effets étaient associés à des densités de moules zébrées de 1500–4000 individus/m 2 , qui sont susceptibles d'être observées dans la plupart des masses d'eau de l'Amérique du Nord. [Traduit par la Rédaction]
We collected aquatic gastropods at 137 sites in lakes and streams of Indiana and tested for patterns of assem- blages with environmental variables. The survey resulted in 32 species with a mean of 2.8 species at each site, and a mean abundance at each site of 144 individuals. Nonmetric multidimensional scaling (NMS) multivariate analyses resulted in watershed drainage area, water conductivity, substrate category frequency, and dissolved oxygen as significant correlates of gastropod assemblage structure. Gastropod assemblages of lakes were not significantly different than assemblages of streams in the ordination. Prosobranch taxa occurred in higher abundances than pulmonate taxa at sites with lower con- ductivity in larger watersheds. There were no pairs of gastropod species that tended to co-occur more frequently than ran- dom. Our analyses resulted in local environmental variables providing explanation of aquatic gastropod assemblage struc- ture.