Association of aerobic anoxygenic phototrophs and zebra mussels,Dreissena polymorpha,within the littoral zone of Lake Winnipeg

While nutrient loading has affected all levels of Lake Winnipeg’s ecology, its greatest influence has likely been on the microbial community. In addition to eutrophication, zebra mussels (Dreissena polymorpha) have recently invaded the ecosystem and threaten food web dynamics. Their filter-feeding predation and association with bacteria, specifically phototrophs, was investigated. A sampling trip to Lake Winnipeg in October 2017, focused on the isolation, enumeration, and identification of aerobic anoxygenic phototrophs in littoral water, sediment, and tissues of mussels. Gimli, Patricia, and Grand beaches, separated by >15 km across the South Basin, had similar bacterial counts when cultivated on rich organic, BG-11, purple non-sulphur, and K₂TeO₃-supplemented media. Culture-based enumeration on rich organic medium revealed 1.74% of heterotrophs from littoral waters were aerobic anoxygenic phototrophs, and represented 13.98% within sediments. In contrast, 0.48, 1.15, and 0.16% of cultured heterotrophs were aerobic anoxygenic phototrophs within zebra mussel gill, gut, and gonadal tissues, respectively. High-throughput sequencing of bacterial 16S V4 rDNA maintained similar trends in respective bivalve organs, where 0.22, 1.13, and 0.20% of total 16S genes belonged to these phototrophs. Several Sphingomonadaceae isolates were recovered from gut tissues, all with filamentous morphology large enough for predation. Bioaccumulation of metals was also studied in D. polymorpha. All tested associated aerobic anoxygenic phototrophs were capable of resisting the metalloid oxide tellurite. The consistent distribution of aerobic anoxygenic phototrophs within microbial communities across Lake Winnipeg, and their predominance in the gut tissues of zebra mussels suggested bacterial consumption by this invasive species.     

Limited evidence of zebra mussel (Dreissena polymorpha) consumption by freshwater drum (Aplodinotus grunniens) in Lake Winnipeg

Freshwater drum (Aplodinotus grunniens) may be a predator of the invasive zebra mussel (Dreissena polymorpha), which established in Lake Winnipeg in 2013. In this study, the diets, trophic position, and growth of 51 freshwater drum collected in 2019 (six years post-zebra mussel invasion) were compared to 64 freshwater drum sampled in 2000. Benthic insect larvae were the dominant food items in both years. Although mollusks occur in high densities in Lake Winnipeg, they were only consumed by a few freshwater drum in either sample year. Zebra mussels were not a frequent prey item in 2019 as they were only consumed by four of the sampled freshwater drum. Stable isotope analysis of white muscle tissue yielded similar δ¹³C and δ¹⁵N values in both years and were consistent with a benthic, insectivorous diet. Length-at-age data derived from otoliths revealed that the 2019 population had at least an equal growth rate to the 2000 population. Weight-at-length data suggested that fish condition was greater in 2019 than in 2000, which coincided with increased benthic macroinvertebrate density in Lake Winnipeg. Based on these findings, Lake Winnipeg freshwater drum continue to feed predominantly on insect larvae and not zebra mussels.     

Detection and expression of genes for phosphorus metabolism in picocyanobacteria from the Laurentian Great Lakes

The pelagic regions of Lake Superior and eastern Lake Erie (Laurentian Great Lakes) are typically phosphorus (P)-limited environments, and picocyanobacteria of the genus Synechococcus spp. are prominent primary producers during the summer. As a proxy for their utilization of organic P, the expression of two genes, phnD and phoX, was monitored. The phnD gene encodes the phosphonate binding protein of the ABC-type phosphonate transporter, whereas the phoX gene encodes a calcium-dependent alkaline phosphatase. Furthermore, to assess the ability of freshwater Synechococcus spp. to substitute sulfolipids for phospholipids, sqdX gene (cyanobacterial sulfolipid synthase) expression was examined. We employed PCR primers to detect the presence of all three genes in the endemic Synechococcus spp., and RT-PCR assays of cultured freshwater strains and environmental samples to assess the degree of P-stress in the phytoplankton. We show that the phnD gene was constitutively expressed, suggesting that freshwater picocyanobacteria were metabolizing exogenous phosphonate compounds in Lakes Erie and Superior. By contrast, phoX was regulated by P bioavailability. We also provide evidence that sqdX is expressed during increased growth rates in phosphorus-replete conditions, suggesting that sulfolipid synthesis is not a P conservation mechanism for freshwater Synechococcus spp.     

Spatial patterns of bacterial community composition within Lake Erie sediments

Lake Erie is a large freshwater ecosystem with three distinct basins that exhibit an east-to-west gradient of increasing productivity, as well as allochthonous inputs of nutrients and xenobiotics. To evaluate microbial community composition throughout this ecosystem, 435 16S rDNA environmental clones were sequenced from 11 sediment samples throughout the Western, Central, and Eastern basins, as well as the hypoxic “dead zone” of Lake Erie in the hypolimnetic region of the Central basin. Rank abundance distributions of bacterial taxa within each location revealed that Gamma- and Betaproteobacteria, microbes capable of metabolizing a wide range of organic matter pools, comprised a greater fraction of the microbial community within inshore sites of the Central and Western basins compared to the Eastern basin. While geophysical characteristics of the three major basins and the dead zone did not drive significant differences in species diversity, Fast UniFrac analyses revealed microbial community spatial structuring, with the Central basin showing higher phylogenetic uniqueness of bacterial lineages. Principal component analyses based on phylogenetic distances consistently grouped the dead zone with the Central basin and highlighted the distinctiveness of microbial communities from the Eastern basin. Results from this study provide evidence for the local adaptation of microbial communities and the potential role of riverine inputs in modulating taxonomic composition of lacustrine bacterial communities. These results are consistent with previous functional studies on microbial metabolism, which showed that differences in geochemistry across the three basins of Lake Erie play an important role in the local adaptation of microbial communities.     

Investigating the invasion of the nonindigenous zooplankter, Eubosmina coregoni, in Lake Winnipeg,Manitoba, Canada

The spread of nonindigenous species (NIS) over land and via interconnecting water bodies is threatening aquatic ecosystems worldwide. This study examines the invasion of the first known NIS zooplankter, Eubosmina coregoni, into Lake Winnipeg, Manitoba, Canada. Analyses of cladoceran microfossils from a sediment core collected in the North Basin of the lake indicate this species first appeared in sediments dated to the late 1980s. An increase in total cladoceran accumulation rates coupled with increasing N, C, P, and chlorophyll a over the last 40 years provides evidence of eutrophication. Extant samples from fall 2002-2005 indicate that E. coregoni is mainly restricted to the North Basin while Bosmina longirostris is present throughout the lake. Results from this study provide baseline data regarding the invasion and establishment of E. coregoni, a precursor to future NIS that may have substantial ecological and economic impacts on the Lake Winnipeg ecosystem.     

Diversity and distribution of free-living and particle-associated bacterioplankton in Sandusky Bay and adjacent waters of Lake Erie Western Basin

Studies on the bacterial communities in Lake Erie have been largely focused on cyanobacteria. To characterize the community structure of the other bacteria, we examined the 16S rRNA gene content of free-living (FL) and particle-associated (PA) bacterioplankton populations in Sandusky Bay (SD) and adjacent waters in the Western Basin (WB) of Lake Erie. A comprehensive survey of nutrients and other limnological variables was also performed in parallel. A total of 18,569 of 16S rRNA V6 pyrotag sequences were recovered, which were affiliated with 64 unique bacterial orders within 14 phyla. FL bacteria were composed differently from PA ones and contained significantly more Actinomycetales. In addition, FL bacteria were taxonomically more diverse. Despite the distinct environmental conditions, compositional variation was insignificant between bacteria in the SD and WB samples.     

Determination of the microbial diversity of anaerobic-aerobic activated sludge by a novel molecular biological technique

Sequential anaerobic-aerobic batch reactors were maintained on acetate/peptone and two different P/total organic carbon ratios that select for microbial communities enriched for either glycogen-accumulating organisms (GAO) or polyphosphate-accumulating organism (PAO). The community profiles of the eubacterial population and gram-positive high G-C bacteria (HGC) were characterized and compared by determining the terminal restriction fragment length polymorphisms (T-RFLP) of 16S rDNA. The Hhal+Rsal digested 5′ T-RFLP patterns of the eubacterial 16S rDNA amplified from the GAO- and PAOenriched communities were made up with 12 and 14 rank-abundant fragments (i.e., ribotypes), respectively. Among those ribotypes detected in the GAO-enriched community, only seven were found in the PAO-enriched community. The HGC group could only account for no more than 6% and 17% of the eubacterial 16S rDNA amplified from the GAO- and PAO-enriched communities, respectively. Within the HGC community, at least 16 and 10 rank-abundant ribotypes were observed m the Mspl digested T-RFLP patterns of GAO- and PAO-enriched communities, respectively. Among those HGC ribotypes observed in both communities, only five were in common. These indicate that the enrichment processes leading to the establishment of GAO- and PAO-specific communities caused the dramatic difference and complexity in the microbial population.     

Morphology and blood metabolites reflect recent spatial and temporal differences among Lake Winnipeg walleye,Sander vitreus

The invasive rainbow smelt (Osmerus mordax) was an abundant food source for Lake Winnipeg walleye (Sander vitreus), especially in the north basin of the lake, until the smelt’s collapse in approximately 2013. We quantified changing length-at-age (≈ growth rates) and relative mass (≈ body condition) in Lake Winnipeg walleye caught for a gillnet index data set. Here, walleye showed smaller length-at-age, particularly young fish in the north basin, over time. This approach to assessing growth suggests a constraint in the north basin fish, possibly a nutritional limitation between 2017 and 2018, that was not present in the south. We then analyzed a separate group of walleye (≥452 mm in fork length) sampled in 2017 as part of a large-scale tracking study, which had a similar slope in length-mass relationship to large walleye caught in that year for the gillnet index data. A panel of metabolites in whole blood samples associated with amino acid metabolism and protein turnover was compared. These metabolites revealed elevated essential amino acids in fish caught in the Dauphin River, and suggest that protein degradation may be elevated in north basin walleye. Therefore, based on both growth estimates and metabolites associated with protein balance, we suggest there were spatially distinct separations affecting Lake Winnipeg walleye with decreased nutritional status of walleye in the north basin of Lake Winnipeg being of particular concern.     

Historical and contemporary movement and survival rates of walleye (Sander vitreus) in Lake Winnipeg,Canada

Understanding patterns of fish movement in large lake ecosystems is essential for determining appropriate management actions as differences in movement behaviour can influence life history traits such as growth and survival. Lake Winnipeg in Manitoba, Canada supports the 2nd largest walleye (Sander vitreus) commercial fishery in North America. We used mark-recapture models to determine movement and estimate survival of walleye between basins of Lake Winnipeg in historical and contemporary contexts, comparing a tag-recovery study completed historically during 1974–1977 with a contemporary (2017–2019) acoustic telemetry study. Mark-recapture models revealed comparably low but detectable annual transitions between basins from historical (0.3–1.2%) and contemporary datasets (7–8.5%). Historically, fish > 300 mm more frequently moved in a south to north direction. Contemporary estimates suggest similar length-based directionality in that fish > 350 mm were always more likely to move in a south-north direction. Contemporary annual survival derived from mark-recapture models ranged between 27 and 45% and 64.3% when derived from catch curve analysis, while independently derived annual historical survival estimates ranged between 50 and 69% and 45.5% from catch curve analysis. Using the contemporary dataset, we also observed seasonal variation in movement and survival between basins, with the greatest movement across the lake occurring during the fall. Our results demonstrate a persisting pattern of low but measurable movement, suggesting between basin movement is not unusual for Lake Winnipeg. Further, low walleye survival rates reported here for the two time periods studied, support recent management actions to reduce fishing pressure across the lake.     

Patterns in the crustacean zooplankton community in Lake Winnipeg,Manitoba: Response to long-term environmental change

Changes in the crustacean zooplankton community composition and abundance in Lake Winnipeg (1969–2006) provide a rare opportunity to examine their response to environmental changes in the largest naturally eutrophic lake on the Canadian prairies. Since 1929, zooplankton species composition in Lake Winnipeg has changed little except for the addition of the invasive cladoceran, Eubosmina coregoni in 1994. The dominant taxa in the lake in summer include: Leptodiaptomus ashlandi, Acanthocyclops vernalis, Diacyclops thomasi, Daphnia retrocurva, Daphnia mendotae, Diaphanosoma birgei, Eubosmina coregoni, and Bosmina longirostris. Climate-accelerated nutrient loading to southern Lake Winnipeg over the last two decades has led to increased phytoplankton abundance and higher frequency of cyanobacterial blooms especially in its northern basin. Crustacean zooplankton have likewise increased especially in the North Basin, but less so in the more nutrient rich South Basin, possibly as a consequence of higher densities of pelagic planktivorous fish and light-limited primary production compared with the more transparent North basin (Brunskill et al., 1979, 1980). Calanoid copepods play a larger role in the South basin food web in contrast to cyclopoid copepods and Cladocera in the North basin. The study begins to fill the recognized gap in understanding of Lake Winnipeg's food web structure and provides a baseline for evaluating ongoing changes in the zooplankton community with the arrival of new non-indigenous taxa, e.g. Bythotrephes longimanus and Dreissena polymorpha. It reinforces previous work demonstrating that zooplankton provide valuable indices toward evaluating the health of an ecosystem.     

Developing habitat associations for fishes in Lake Winnipeg by linking large scale bathymetric and substrate data with fish telemetry detections

Understanding relationships between freshwater fishes and habitat is critical for effective fisheries and habitat management. Habitat suitability indices (HSI) are commonly used to describe fish–habitat associations in rivers and other freshwater ecosystems. When applied to large lakes however, standard sampling procedures are inadequate because of larger sampling areas and an increased risk of fish collection bias through one-time observations. Here, we use lake bathymetry, substrate, and multiple fish telemetry detections collected from a systematically deployed receiver grid to develop HSI for four fish species (lake sturgeon, freshwater drum, common carp, and walleye) in Lake Winnipeg. Seasonal variations in habitat use based on water depth and substrate were observed in three of four species. Lake sturgeon remained in shallow locations with predominantly gravel substrate near the mouth of the Winnipeg River regardless of season. Freshwater drum persisted over fine substrate in both summer and winter but had a broader depth range in the summer compared to winter. Common carp shifted from mid-range depths and silt substrate in the summer to shallow depths and gravel substrate in the winter. Walleye showed an unchanging association to fine substrate but expanded from primarily mid-range depths in the summer to include shallower depths in the winter. These findings show how multiple telemetry detections per fish can be combined with hydroacoustic data to provide informative habitat associations for fishes in a large lacustrine ecosystem.     

Population genetic diversity and phylogeographic divergence patterns of the yellow perch (Perca flavescens)

Great Lakes populations of yellow perch have fluctuated throughout past decades to the present due to unstable recruitment patterns and exploitation. Our study analyzes genetic diversity and structure across the native range in order to interpret phylogeographic history and contemporary patterns. We compare complete mitochondrial DNA control region sequences (912 bp) from 568 spawning individuals at 32 sites, encompassing all 5 Great Lakes and outlying watersheds from the upper Mississippi River, Lake Winnipeg, Lake Champlain, and Atlantic and Gulf coastal relict populations. These broad-scale divergences additionally are compared with fine-scale patterns from 334 individuals at 16 spawning sites across Lake Erie's 4 fishery management units. We identify 21 mtDNA haplotypes, including a widespread type that totals 87% of individuals across the Great Lakes. Overall genetic diversity is relatively low in comparison with other Great Lakes fishes, congruent with prior allozyme and microsatellite studies. The largest genetic demarcation separates 2 primary population groups: one in the Great Lakes, Lake Winnipeg, and upper Mississippi River watersheds and the other along the Atlantic and Gulf coasts, together with Lake Champlain; which diverged ∼ 365,000 years ago. In addition, the watersheds house genetically separable groups, whose patterns reflect broad-scale isolation by geographic distance. A few spawning groups show some fine-scale differentiation within Lake Erie, which do not reflect fishery management units and need further study with higher-resolution markers.     

Borders and Barriers: challenges of Fisheries Management and Conservation in Open Systems

Large rivers often bisect geopolitical boundaries where management goals may be at odds for a shared fishery, creating fragmented management zones. Fragmentation due to physical barriers may further impact the fishery by reducing fish passage. Our goal was to estimate basin‐wide parameters (i.e. movement, survival and capture probabilities) of a large‐river species known to move throughout watersheds. We tagged13 892 Channel Catfish in the Red River of the North (Red River) and Lake Winnipeg in Manitoba, Canada, and collected 553 recaptures. We estimated 2.2% of catfish are moving from the Red River to Lake Winnipeg each month and 9.4%, primarily large (>600 mm) individuals, moved upstream through a dam (monthly). Approximately 5.6% of catfish moved to the USA each month, and only one fish returned. Our results suggest the lower reaches of the Red River may be a source population for the USA, where survival is lower, and Lake Winnipeg. The complex movements of Channel Catfish throughout the Red River, across barriers and international boundaries, suggest conservation and management of fish populations should be watershed wide. Copyright © 2017 John Wiley & Sons, Ltd.     

Spatial ecology of common carp (Cyprinus carpio) in Lake Winnipeg and its potential for management actions

Common carp feeding and spawning behaviours negatively impact the functioning of marsh ecosystems. In the Netley-Libau Marsh, situated on the southern end of Lake Winnipeg, water level regulations, nonpoint source nutrient pollution, and the non-native common carp are thought to be the main contributors to the degradation of the marsh habitat. Using acoustic telemetry, we analysed the movement rate, frequency and timing of suspected spawning migrations, spatial ecology, and aggregation of common carp in the Lake Winnipeg drainage over a three year time period. Common carp moved the farthest during the open water period when water temperature was >5 °C. Their annual migration into Netley-Libau Marsh was correlated to ordinal date. Common carp left the marsh in late spring/early summer, presumably feeding in Lake Winnipeg, before moving to overwintering sites situated in Traverse Bay and Lake Winnipeg, where they arrived typically by October and formed aggregations. These findings will inform habitat and fisheries managers in the effort to undertake evidence-based management actions. The predictability of the movements and the tendency for common carp to aggregate indicates that exclusion techniques and commercial fishing may represent viable management solutions.     

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

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

Assessing the impacts of light synthetic crude oil on microbial communities within Laurentian Great Lakes’ sediment habitats

The ability of microbial communities to respond to and degrade crude oil in marine environments is well understood, yet fewer studies have examined freshwater environments. The Laurentian Great Lakes are one of the world’s largest surface freshwater sources. A pipeline that transports light synthetic crude oil crosses between two of the Great Lakes (the Straits of Mackinac, connecting Lakes Michigan and Huron, U.S.A.), and there is uncertainty on how the various habitats within this region would respond to accidental crude oil exposure. In this study, sediment microbial communities from three distinct habitats (coastal beach, freshwater coastal wetland, and Lake Michigan deep sediments) were used in microcosm experiments to document their community response (16S rRNA gene sequencing) to light synthetic crude oil (headspace gas chromatography). Microbial community structure (beta diversity) was impacted after exposure to crude oil in each of the habitats examined, with each habitat showing a different level of resistance to crude oil. Additionally, within each habitat, beta diversity distinguished sub-communities that increased in abundance in experimental treatments. Specifically, an increase in total abundance of Alphaproteobacteria, Betaproteobacteria, or Gammaproteobacteria was observed in microcosms exposed to crude oil regardless of habitat type. Methane, a potential hydrocarbon degradation byproduct, was observed in the headspace of the microcosms after exposure to crude oil, which may indicate methanogenic hydrocarbon degradation. These data suggest Great Lakes freshwater microbial communities will respond differently to crude oil exposure but may have shared community members involved in resisting and degrading light synthetic crude oil.     

Seasonal Hypoxia and the Genetic Diversity of Prokaryote Populations in the Central Basin Hypolimnion of Lake Erie: Evidence for Abundant Cyanobacteria and Photosynthesis

The reoccurring region of seasonal hypoxia in the central basin of Lake Erie (“the dead zone”) has been of significant interest to researchers over the past several years. Surprisingly however, no efforts to characterize the endemic microbial community, responsible for the consumption of oxygen in this system, have been published. To understand how the microbial community may be interacting with this event, we have begun to characterize microbial members by using molecular tools. Phycoerythrinrich cyanobacteria appear abundant and active in a narrow region (∼ 1.5 m) below the thermocline during hypoxic conditions, reaching abundances of greater than 10⁵ mL⁻¹ and being the primary agent releasing 1.5 mg O₂ L⁻¹ above the daytime demands in this region. Sequencing of 16S rDNA amplicons, generated with universal eubacterial primer sets, from the Lake Erie's hypolimnion during seasonal oxygen depletion demonstrated that cyanobacteria, most closely related to phycoerythrin-rich Synechococcus spp., dominate during rapid drawdown of oxygen (0.083 mg L⁻¹ d⁻¹ in 2004) in this region. Analyses of another conserved marker of phylogeny (RuBisCO) has been used to confirm the presence of these cell types. Numerous distinct taxa of heterotrophic bacteria are also represented in the 16S library. The results of this study suggest that novel groups of cyanobacteria may persist within the Lake Erie dead zone during hypoxic conditions and, along with the heterotrophic community, strongly influence system geochemistry.     

Carbon fixation by the phytoplankton community across Lake Winnipeg

Lakes are important sites for carbon fixation and carbon dioxide (CO₂) exchange with the atmosphere. Carbon fixation rates have not previously been published for Lake Winnipeg but are important for quantifying the lake’s role in the regional greenhouse gas budget and the lake’s trophic structure and fish habitat. This study measured net ecosystem production (NEP), gross primary production (GPP), and gross respiration (GR) across the lake using a custom-built automated incubator connected to a ship’s water intake during a research cruise between July 31 and August 17, 2018 on Lake Winnipeg. The incubator estimated NEP, GR, and GPP every 60 min while moving along the ship’s track and at anchor, providing high-resolution data that are not obtainable through conventional incubations. The mean NEP for Lake Winnipeg during our survey was ?8.4 ± 5.6 g C m^?2 d^?1, suggesting that the lake was net heterotrophic and thus a net CO₂ source to the atmosphere during the 2018 summer cruise. The high-resolution data revealed significant spatiotemporal variability, including short-lived, highly net productive events that preceded remotely sensed chlorophyll a blooms by several days. Conversely, in regions with high chlorophyll a concentrations, we observed strong net heterotrophy and low nutrients, suggesting respiration was fueled by the degradation of mature, nutrient-limited phytoplankton blooms. The incubator system used in this study demonstrated its utility for monitoring rapid changes in NEP over short spatial scales in a lake which shows heightened regional variability in its physical, biogeochemical, and biological make-up.     

The distribution,density, and biomass of the zebra mussel (Dreissena polymorpha) on natural substrates in Lake Winnipeg 2017–2019

The distribution, density, biomass and size-structure of the zebra mussel (Dreissena polymorpha) population in Lake Winnipeg were examined between 2017 and 2019. Zebra mussels have colonized most of the available hard substrate in the south basin and Narrows region, but colonization of the north basin remains low at present, even on suitable substrate. Numerical densities and shell free biomass peaked at 5530 ± 953 m^?2 and 64.7 ± 57.9 g shell free dry mass m^?2 respectively. The distribution appeared to be strongly limited by substrate type and availability, with further limitations on the distribution imposed by physical disturbance in shallow waters and unsuitable substrate in deeper areas of the lake. Zebra mussels <1 year old dominated the populations, and individuals >18 mm were exceedingly rare. Poor recruitment was observed at sites along the eastern side of the south basin compared to elsewhere in the lake. The proximate causes of these differences in colonization success and recruitment are not clear, but may be in part due to heterogeneous patterns of key physico-chemical environmental conditions such as calcium concentrations required for successful development of juvenile mussels and colder water temperatures in the north basin. This study provides a baseline of information on which to track further expansion of zebra mussels in Lake Winnipeg and assist efforts to develop an understanding of how zebra mussels may affect the ecology of Lake Winnipeg.     

Current state of the sponge fauna (Porifera: Lubomirskiidae) of Lake Baikal: Sponge disease and the problem of conservation of diversity

The spatial distribution of healthy and diseased sponges in Lake Baikal was investigated. The endemic sponges were studied in May ? June 2015 at 11 transects within the depth range of 0 to 40 m. More than 500 sponge specimens were collected, and 29 taxa including 12 species and 17 morphospecies (sp. taxa) were identified. Among the 29 taxa, only B. martinsoni specimens and 14 morphospecies were healthy, whereas specimens of the other 11 species and 3 morphospecies were diseased, making up 35% of the total number of specimens (512). The different body forms of sponge found among the specimens were encrusting (66%), globulous (21%), and branched (13%). Sponges with necrosis signs, discolored specimens or covered with violet film or brown spots, were found in all transects under study (37 stations of 68). The percent cover of the bottom (per m²) by various body forms of sponges was evaluated with a sponge faunal state assessment test. Changes in the diversity and abundance of sponges due to their disease may jeopardize the functioning of the entire ecosystem of Lake Baikal which is a World Heritage Site. This baseline data on patterns of sponges, including their spatial distribution and percent cover, will be utilized to support future management and monitoring of Lake Baikal. Data on the current state of Baikal endemic sponge fauna are essential for understanding the causes and prognosis of disease processes of freshwater sponges.