Phylogenetic relationships and historical population reconstruction of Asian members of the genus Epischura (Copepoda,Calanoida)

We have reconstructed major demographic and phylogenetic events for two closely related copepod species: Epischura baikalensis Sars, 1900 (Copepoda, Calanoida), a key endemic species of the plankton community from Lake Baikal, and E. chankensis Rylov, 1928, a key zooplankton species from Lake Khanka. The reconstructions were based on the nucleotide sequences of mitochondrial DNA (mtDNA) cytochrome oxidase subunit 1 (CO1) using the BEAST software package and recently identified calibrations for the Baikal amphipods Gmelinoides fasciatus. The time span to a common ancestor for E. baikalensis and E. chankensis is 13.7 million years (95% confidence interval is 8.3–21.4 million years. Both species studied have experienced abrupt changes in the effective population size in the past. These changes are likely associated with climate and geological shifts in their habitat areas. For E. baikalensis, these changes can be associated with alternating glacier and interglacial periods as well as an increase in depth of Lake Baikal; for E. chankensis with formation and increase in the area of Lake Khanka, which was also due to climate and geological shifts in the Khanka basin.     

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.     

Warming overcomes dispersal-limitation to promote non-native expansion in Lake Baikal

Non-native species and climate change pose serious threats to global biodiversity. However, the roles of climate, dispersal, and competition are difficult to disentangle in heterogeneous landscapes. We combine empirical data and theory to examine how these forces influence the spread of non-native species in Lake Baikal. We analyze the potential for Daphnia longispina to establish in Lake Baikal, potentially threatening an endemic, cryophillic copepod Epischurella baikalensis. We collected field samples to establish current community composition and compared them to model predictions informed by flow rates, present-day temperatures, and temperature projections. Our data and model agree that expansion is currently limited by dispersal. However, projected increases in temperature reverse this effect, allowing D. longispina to establish in Lake Baikal’s main basin. A strong negative impact emerges from the interaction between climate change and dispersal, outweighing their independent effects. Climate, dispersal, and competition have complex, interactive effects on expansion with important implications for global biodiversity.     

First data on cyanobacterial biodiversity in benthic biofilms during mass mortality of endemic sponges in Lake Baikal

This study investigates in detail species diversity of cyanobacteria which proliferated on the surface of diseased sponges and bedrock in Lake Baikal (Siberia, Russia) during the ecological crisis that has been progressing in the littoral zone since 2011 and caused numerous negative changes in biota. In 2014–2015, we examined samples from diseased and healthy sponges as well as rock substrates using Sanger sequencing and high-throughput 16S rRNA gene analysis. Based on morphology, we identified 15 cyanobacterial species in biofoulings. Tychonema sp., Symplocastrum sp., Pseudanabaena galeata and Tolypothrix distorta dominated on diseased sponges. In communities of healthy sponges, we detected mainly picocyanobacteria Synechococcus. Fascicles of Symplocastrum sp. and T. distorta dominated on bedrock substrates. Phylogenetically, most 16S rDNAs clustered among Tychonema, Pseudanabaena, Geitlerinema, Kamptonema, Leptolyngbya, and Tolypothrix spp. Cyanobacterial proliferation in the littoral zone of Lake Baikal should be considered as one of the most important negative ecological processes in recent times which requires an urgent study in order to understand the causes of its emergence and development. Mat-forming cyanobacteria Tychonema characterized by the highest tropism to sponges plays a special role in the disease and death of sponges.     

Analysis of rDNA Regions of Five Freshwater Unionid Mussel Species in Presque Isle Bay,Southeastern Lake Erie

Population structure and fecundity of freshwater mussels can be difficult to assess due to the benthic habitat and complex life cycles of these organisms. However, rapid and reliable classification of unionids can be accomplished with polymerase chain reaction if species-specific DNA primers are established. In this report we describe the sequence analysis of the ITS1 and ITS2 regions from five mussel species (Amblema plicata, Fusconia flava, Lampsilis siliquoidea, Ligumia nasuta, and Pyganodon grandis) isolated from a refuge in Lake Erie. Sequence comparison revealed strong similarities between A. plicata and F. flava and between L. siliquoidea and L.nasuta. P. grandis contained regions of additional DNA not present within the other species. Our study confirmed the placement of Ligumia nasuta within the Lampsilinae. The analysis also revealed DNA sequences within the ITS1 and ITS2 regions that are species-specific. Thus, the development of species-specific PCR primers can be utilized for analysis of adult populations and for glochidia on host fish.     

New Records of Freshwater Sponges (Porifera) for Southern Lake Michigan

Four species of freshwater sponge were identified in southern Lake Michigan: Spongilla lacustris (Linneaus), Eunapius fragilis (Leidy), Ephydatia fluviatilis (Linneaus), and Ephydatia muelleri (Lieberkuhn). Samples were collected from artificial substrates in Calumet (IL), Hammond (IN), and Michigan City (IN) harbors and represent the first reports of sponges in these waters. Numerical densities for all species combined were as high as 698 sponge colonies/m² on the iron hull of the permanently moored 110-m-long ship Milwaukee Clipper in Hammond Harbor. These densities were lowest at 1-m depth and greater at 2- and 3-m depths. A positive correlation (r² = 0.74) was found between the density of sponge colonies and the angle of the hull as it changed from near vertical at the water line to overhanging at greater depth (toward the keel). Ephydatia muelleri was the most common species based on frequency of occurrence and percent surface area covered. Observations of epizoic growth of sponges on live zebra mussels (Dreissena polymorpha Pallas) suggest that an ecological interaction exists between these two groups of organisms on these artificial substrates.     

Having the balls to colonize – The Ephydatia fluviatilis group and the origin of (ancient) lake “endemic” sponge lineages

Spongillida (freshwater sponges) constitute an integral part of the world's lacustrine ecosystems. Their radiation and worldwide distribution into nearly every freshwater habitat is predominantly facilitated by the formation of so-called gemmules, i.e., globular endurance and propagation stages. Widespread species produce gemmules in a wide array of morphs, while in (ancient) lake endemic lineages gemmules are absent. Contrary to current classification, earlier molecular studies on non-type material indicated that gemmule-lacking lineages are unrelated, and endemic taxa were derived from a cosmopolitan (and paraphyletic) founder lineage. In this study we investigate this hypothesis with type material, particularly focussing on endemic taxa potentially derived from common ancestor shared with the widespread Ephydatia fluviatilis. We demonstrate that taxa regarded as endemic from Lake Ohrid (Ochridaspongia), Lake Kinneret/Tiberias (Cortispongilla) and Lake Titicaca (Balliviaspongia) are derived from the founder lineage, but unrelated to other, particularly Afrotropical, ancient lake sponges, and discuss implications for understanding freshwater sponge phylogeny and evolution.     

Diversity and biogeography of bacteriophages in biofilms of Lake Baikal based on g23 sequences

Here, we report on the sequences of the g23 communities of phages from biofilms and the surface microlayer in the most ancient lake of the world. The data are interpreted in terms of biogeography of the g23 communities. We show that bacteriophages from biotopes of biofilms of stones and sponges from the littoral zone and of the water from the pelagic zone of Lake Baikal form a common Baikal cluster. Viruses of the surface microlayer in the shallow Maloye More Strait of Lake Baikal group into one cluster with the sequences from polar lakes forming a sisterly clade with the Baikal cluster.     

Distribution,seasonality and putative origin of the non-native red alga Bangia atropurpurea (Bangiales,Rhodophyta) in the Laurentian Great Lakes

Bangia atropurpurea was first observed in Lake Erie in 1964 and subsequently spread to the lower Laurentian Great Lakes by the mid to late 1970s. The present study was initiated to examine the recent distribution of B. atropurpurea in the Great Lakes, the seasonal variation of the alga and the putative origin of this species based on DNA sequence analysis. From surveys in 1995 and 2002, this species has clearly spread, with newly identified populations observed in Lakes Huron, Michigan, Georgian Bay and the St. Lawrence River. Morphological analyses showed that Great Lakes populations from individual lakes or neighboring populations did not group together in cluster analyses. Correlation analysis, however, revealed significant relationships between the presence or absence of Bangia among the studied sites with pH and specific conductance as those locations that had stable populations had a mean pH and conductance of 8.2 and 353 μS·cm^− 1 respectively. Seasonal variation in morphology of a population from Burlington, Ontario (Lake Ontario, Canada) was examined monthly for one year. Maximum filament length occurred in April, with the greatest diameter and archaeospore production observed in May. Significant correlations were also noted for many morphological characteristics with water temperature, population height on the shoreline relative to the waterline and total phosphorus. Collections of B. atropurpurea analyzed from the Great Lakes were observed to be identical in sequence to collections of European freshwater Bangia in the cox2–3 gene spacer, the nuclear internal transcribed spacers (ITS 1 and 2) and the 5.8S rRNA gene (between the small and large subunits of the rRNA gene). These results suggest a recent European origin; however, further global collections of B. atropurpurea and microsatellite analyses are necessary to confirm this hypothesis.     

Invader amphipods Gmelinoides fasciatus (Stebbing, 1899) inhabiting distant waterbodies demonstrate differences in tolerance and energy metabolism under elevated temperatures

Gmelinoides fasciatus is a successful invasive amphipod (Amphipoda, Crustacea) that dispersed from Lake Baikal to various waterbodies. Here we studied whether Baikal conditions are optimal for G. fasciatus in terms of thermotolerance and investigated lethal temperatures, 70 kDa heat shock protein level, energy metabolism, and antioxidant defense of animals from three geographically distant waterbodies under changing temperatures. We used acute heat exposure to 28 °C to assess the median lethal times and gradual temperature increase from 6 °C to determine the lethal temperatures. Mortality under heat shock was explainable by the baseline content of Hsp70 that correlated with thermal history. But it was not the case under gradual temperature increase where Hsp70 levels became similar and the mortality pattern changed. The most thermotolerant amphipods from the Gulf of Finland demonstrated a higher amount of free glucose during the temperature increase that may be related to the higher salinity of this waterbody and less energy required for ion regulation. Even though concentrations of major physiological ions in Lake Baikal are lower than in Lake Ladoga, G. fasciatus from Ladoga was slightly more sensitive to the gradual temperature increase. This difference could be explained by the influence of high levels of humic and other potentially toxic substances in Lake Ladoga indicated by increased activities of catalase and glutathione S-transferase. Importantly, all G. fasciatus populations accumulated relatively low levels of lactate during the temperature increase, which may reflect the ability of this invasive species to effectively maintain aerobic metabolism under various conditions.     

First data on lipids and microorganisms of deepwater endemic sponge Baikalospongia intermedia and sediments from hydrothermal discharge area of the Frolikha Bay (North Baikal,Siberia)

In this report, we study lipid components (fatty acids with various degrees of unsaturation, aldehydes and sterols) of deep-water sponges Baikalospongia intermedia and sediments sampled using deep-water manned submersibles “Mir” at a hydrothermal vent of Frolikha Bay at depths of 400–450 m. It was found that unsaturated fatty acids predominate in the FA-composition of the sponges: very long chain demospongic acid 26:3, as well as monounsaturated 24:1 and isomers of acids 16:1 and 18:1. Among the saturated fatty acids in addition to the stearic 18:0, palmitic 16:0 and heptadecanoic 17:0 acids, significant amounts of acids of microbial origin (iso-palmitic i16:0, isostearic i18:0, oxy-stearic 10 h18) were detected. Using the method of mass spectrometry of microbial markers, we conclude, that the main microbial components of sponges B. intermedia and sediments from Frolikha Bay are methanotrophic microorganisms.     

Spatial segregation of cisco (Coregonus artedi) and lake whitefish (C. clupeaformis) larvae in Chaumont Bay,Lake Ontario

Two of the remaining coregonine species in Lake Ontario, cisco (Coregonus artedi) and lake whitefish (C. clupeaformis), spawn in Chaumont Bay, New York. Larvae co-occur in the spring but are difficult to distinguish morphologically. We applied genetic species identification using microsatellite DNA loci of 268 larvae from known locations in nearshore and offshore habitats in Chaumont Bay to determine the extent of mixing of these species in each habitat. Cisco dominated the larvae (95%) in offshore habitats and lake whitefish dominated (84%) in nearshore habitats, where seven of eight putative hybrids occurred. Habitat segregation between these two species at the larval stage has implications for productivity estimates, as changing environmental conditions may differentially affect shallow and deep waters, larval survival, and possibly subsequent recruitment. Discrimination between cisco and lake whitefish larvae will help to characterize habitat and basic life history needs and to focus research collections. Genetic species identification should be applied to larger samples of larvae to evaluate changes in larval distributions and associations with environmental conditions.     

Genomics reveals identity,phenology and population demographics of larval ciscoes (Coregonus artedi,C. hoyi,and C. kiyi) in the Apostle Islands,Lake Superior

We demonstrate, for the first time, the ability to reliably assign an assemblage of larval coregonines [Salmonidae Coregoninae] to shallow and multiple deepwater species. Larval coregonines from the Apostle Islands, Lake Superior, were genotyped using restriction site-associated DNA sequencing (RADseq) and were assigned to species using reference genotypes from adult corgonines from the same region. Of the 193 genotyped larvae, 101 were assigned as Coregonus artedi (average assignment probability = 97.6%), 57 were assigned as C. kiyi (average assignment probability = 95.5%), and 28 were assigned as C. hoyi (average assignment probability = 89.0%). Coregonus artedi were collected earliest in the season, followed by C. kiyi and then C. hoyi. Estimates of genetic diversity within each species provide a baseline for future monitoring in the Apostle Islands. Our success with species assignment indicates the promise of leveraging genomic data for larval coregonine identification, which could enable assessing and evaluating early life history dynamics and recruitment processes at the species level to the benefit of ongoing coregonine restoration and management efforts.     

Groundwater contamination by sewage causes benthic algal outbreaks in the littoral zone of Lake Baikal (East Siberia)

Lake Baikal, an ancient lake in Siberia, contains more endemic species than any other lake in the world with most of them residing in the benthic littoral zone. Explosive growth of benthic Spirogyra, a filamentous green alga, began approximately in 2011 in localized coastal areas, with the most severe examples occurring near coastal towns that lack a wastewater treatment facility or have a malfunctioning system. At other sites (small settlements, harbors), however, the cause of its excess growth is less obvious. Multiple hypotheses have been offered including lake level fluctuations, climate warming, a relaxation of grazing pressure, and coastal eutrophication. We assessed these hypotheses using data on historical lake levels, water temperature, the spatial-temporal distribution of Spirogyra along inhabited and non-inhabited shorelines, and measurements of fecal coliform bacteria and nutrients in ground water, interstitial water, and lake water. These data suggest that groundwater contamination is the primary cause of coastal eutrophication. Most houses and buildings in small settlements around Lake Baikal lack septic tanks but use unlined cesspools to collect human waste. This untreated human waste enters groundwater via passive filtration through permeable soils and flows to the coastal zone where it drives excess growth of Spirogyra. Remediation — including installation of septic systems, modernization of existing sewage treatment plants in coastal towns, and the adoption of non-phosphate containing detergents — as well as a reconsideration of the federal monitoring system regarding the coastal zone is urgently needed to protect this extraordinary lake.     

How ancient is Lake Lugu (Yunnan,China)? The gastropods’ viewpoint with focus on Radix (Lymnaeidae)

Lake Lugu has been termed an “ancient lake” in several publications. Ancient lakes, such as Baikal or Tanganyika have in common an age of several million years and an outstanding biodiversity and rate of endemism. Lake Lugu’s age is unknown, however, and has been inferred from the presumed Pliocene increased tectonic activity on the Yunnan-Guizhou Plateau. The lake was thus considered to be of tectonic origin, but supporting studies do not exist. Here we report and describe seven endemic species. The endemic gastropod Gyraulus luguhuensis exhibits an aberrant pseudo-dextral shell morphology, which is predominantly known from undisputed ancient lakes. To better understand the origin of the lake and of its biodiversity, we present a preliminary geological study, which shows that Lake Lugu is a tectonic-solution lake. During a survey of the aquatic habitats up to 21 gastropod morphospecies could be differentiated macro-morphologically. An aberrant neritid-like Radix was genetically studied for the first time. The genetic data suggest that Lugu-Radix, typical and neritid shell shapes, constitute a clade, comprising four possibly endemic evolutionary lineages, which potentially represent four different species. The molecular-clock approach indicates a Late Pliocene to Early Pleistocene origin of the clade, which we consider the minimum age of Lake Lugu. Our study reveals that the biodiversity in general and that of gastropods in particular is significantly higher than previously known. Against this background and considering the co-occurrence of aberrant Gyraulus and Radix with an evolutionary history of more than two million years, Lugu is putatively an ancient lake.     

Current state of phytoplankton in the littoral area of Lake Baikal,spring 2017

To assess the current state of phytoplankton in the littoral area of Lake Baikal and provide a baseline for future comparisons, we sampled spring plankton communities from the 44 littoral and 3 pelagic stations covering all three basins of the lake. The study examined chemical parameters of water (NH₄⁺, NO₂⁻, NO₃⁻, PO₄⁻³, Si, COD), species composition, abundance, and biomass of phytoplankton in Lake Baikal during late spring 2017. Sharp spatial heterogeneity was observed in the distribution of phytoplankton biomass along the western (399 ± 72 mg/m³) and eastern (1319 ± 220 mg/m³) shores of the lake. The phytoplankton were diverse, with 79 species; dominant algae were different from site to site and from south to north throughout the lake. In Southern and Central Baikal, we recorded an intense bloom of the diatom Synedra acus subsp. radians (28–1400 cells/mL), similar to that observed for the past 10 years, while the chrysophyte Dinobryon cylindricum dominated in Northern Baikal. The diatoms Aulacoseira baicalensis, A. islandica, and Stephanodiscus meyeri that were dominant in the 1960s–1990s were not numerous in 2017 (0.5–10 cells/mL). This change in dominant species indicates structural changes in the phytoplankton of Lake Baikal, which have led to the disappearance of the main distinctive feature of the Baikalian phytoplankton – the alternation of extremely high (with the algal biomass over 1000 mg/m³) and extremely low (less than 100 mg/m³) productivity years. The ecological equilibrium appears to have shifted towards a new steady state.     

Nearshore benthic blooms of filamentous green algae in Lake Baikal

For the first time, species of the genus Spirogyra, non-typical of the open nearshore waters of Lake Baikal, formed algal mats with Ulothrix zonata, Ulothrix tenerrima, and Ulothrix tenuissima near the village of Listvyanka, Russia. Normally widely distributed in the 0- to 1.5-m depth range, the growth of U. zonata was now evident and dominant (63% of the biomass) in the 2- to 5-m depth range. The overgrowth of the lake bottom by filamentous green algae, changes in distributional boundaries, the emergence and mass development of species of the genus Spirogyra, the presence of the eutrophic diatom indicator Fragilaria capucina var. vaucheriae, elevated abundances of coliform bacteria, and elevated levels of nutrients suggest an early stage of cultural eutrophication in the nearshore of Lake Baikal near Listvyanka, a popular tourist destination. The unusual abundance of Fragilaria associated with the filamentous green algae consisted of long-ribbon colonies of F. capucina var. vaucheriae, a eutrophic species, wound around the filamentous green algae, enhancing the dense algae mats. Historically dominant species, such as Didymosphenia geminata, Tetraspora cylindrica var. bullosa, and Draparnaldioides baicalensis typically observed at deeper depths of Lake Baikal, are now subdominants or minor species in the nearshore along the shoreline near Listvyanka.     

Fractioning of petroleum hydrocarbons from seeped oil as a factor of purity preservation of water in Lake Baikal (Russia)

Polycyclic aromatic hydrocarbons (PAHs) and n-alkanes were found in five different types of oil-containing samples emanating from deep oil seeps in Lake Baikal, the deepest and oldest lake in the world containing 20% of the world’s surface freshwater. The n-alkanes were the dominant component of the seeped oil on the water surface. PAHs were minor compounds of the oil, but this group is included in a priority series of organic contaminants that are subject to environmental regulation. The set of studied samples from the seep included: (i) freshly-emitted oil on the lake surface, (ii) oil at the lake bottom, (iii) samples of asphalt towers at the lake bottom, (iv) oil from voids within the sediment core and (v) samples of water from different depths. High variability in the concentrations of n-alkanes and PAHs suggested the presence of oil fractionation at the sediment-water interface. A light fraction of oil enriched by n-alkanes migrates to the surface of the lake’s water column, where n-alkanes are biodegraded by the Baikal microbial community while heavy oil fractions remain at the lake bottom and form asphalt towers in which PAHs with maximum toxicity accumulate. In the lake’s photic water layer, PAHs from light oil can be accumulated by phytoplankton. In the lake’s water column, benzo[a]pyrene was not detected over their detection limit (0.1 ng/L). The Toxic Equivalent (TEQ) value of PAHs identified in the Baikal water ranged from 0.001 to 0.012 ng/L.     

Recent quantitative values of Macrohectopus branickii (Dyb.) (amphipoda) from Lake Baikal

Macrohectopus branickii is the only amphipod with an exclusively pelagic lifestyle. Although this species plays an important role in the diet of pelagic fish of Lake Baikal, there is no regular monitoring of its abundance. We present data on the status of the population from a lake-wide 2015 survey and compare these data with available historical information. The survey was conducted with a modified Juday net and simultaneous hydroacoustics profiling from up to 700 m depth to the surface. The abundance of M. branickii in the pelagic zone over depths >300 m in 2015 averaged 1700 ind/m² (range 320–4090 ind/m²) and the biomass averaged 3.7 g/m² (range 1.1–14.4 g/m²). Sites with the greatest abundance of M. branickii were located in the South and Middle Basins off the eastern shore. These values are comparable to the published data from 1950s to 1980s. The characteristics of nearshore aggregations of larger mature females were more variable and need further study.