Sixty years of environmental change in the world's largest freshwater lake – Lake Baikal, Siberia

High-resolution data collected over the past 60 years by a single family of Siberian scientists on Lake Baikal reveal significant warming of surface waters and long-term changes in the basal food web of the world's largest, most ancient lake. Attaining depths over 1.6 km, Lake Baikal is the deepest and most voluminous of the world's great lakes. Increases in average water temperature (1.21 °C since 1946), chlorophyll a (300% since 1979), and an influential group of zooplankton grazers (335% increase in cladocerans since 1946) may have important implications for nutrient cycling and food web dynamics. Results from multivariate autoregressive (MAR) modeling suggest that cladocerans increased strongly in response to temperature but not to algal biomass, and cladocerans depressed some algal resources without observable fertilization effects. Changes in Lake Baikal are particularly significant as an integrated signal of long-term regional warming, because this lake is expected to be among those most resistant to climate change due to its tremendous volume. These findings highlight the importance of accessible, long-term monitoring data for understanding ecosystem response to large-scale stressors such as climate change.     

Diversification along a benthic to pelagic gradient contributes to fish diversity in the world's largest lake (Lake Baikal,Russia)

Insights into the generation of diversity in both plants and animals have relied heavily on studying speciation in adaptive radiations. Russia's Lake Baikal has facilitated a putative adaptive radiation of cottid fishes (sculpins), some of which are highly specialized to inhabit novel niches created by the lake's unique geology and ecology. Here, we test evolutionary relationships and novel morphological adaptation in a piece of this radiation: the Baikal cottid genus, Cottocomephorus, a morphologically derived benthopelagic genus of three described species. We used a combination of mitochondrial DNA and restriction site associated DNA sequencing from all Cottocomephorus species. Analysis of mitochondrial cytochrome b haplotypes was only able to two resolve two lineages: C. grewingkii and C. comephoroides/inermis. Phylogenetic inference, principal component analysis, and faststructure of genome-wide SNPs uncovered three lineages within Cottocomephorus: C. comephoroides, C. inermis and C. grewingkii. We found recent divergence and admixture between C. comephoroides and C. inermis and deep divergence between these two species and C. grewingkii. Contrasting other fish radiations, we found no evidence of ancient hybridization among Cottocomephorus species. Digital morphology revealed highly derived pelagic phenotypes that reflect divergence by specialization to the benthopelagic niche in Cottocomephorus. Among Cottocomephorus species, we found evidence of ongoing adaptation to the pelagic zone. This pattern highlights the importance of speciation along a benthic-pelagic gradient seen in Cottocomephorus and across other adaptive fish radiations.     

Depleted methane-derived carbon in waters of Lake Baikal,Siberia

Results of hydrochemical and stable isotope measurements during the ice-breaking period on Lake Baikal indicate an apparent lack of relationship between measured δ¹³C of dissolved inorganic carbon (DIC) and phytoplankton below the trophogenic layer. While planktonic values of −31.7 to −33.5‰ are within a typical lacustrine range, the δ¹³C values of DIC turned out to be very negative, from −28.9 to −35.6‰. These isotopic values of DIC appear to be associated with oxidation of methane that accumulated during winter ice cover period. At the time of sampling, however, the observed depletion did not affect the phytoplankton/DIC fractionation relationship, because the difference between phytoplankton and DIC (−20 to −22‰ in surface waters) lies within the expected range of the fractionation coefficient. By analogy with small lakes, we explain this lack of relationship by the time lag between peak productivity and peak methane oxidation. Our interpretation of the Baikal DIC isotopic signature is consistent with methanogenesis in bottom sediments and with the known presence of widespread unstable gas hydrates and active methane seeps on the lake floor. Our findings suggest that methane is an important component of the Baikal carbon cycle, that late winter concentrations of methane in Baikal under ice may be 3–4 orders of magnitude higher than previously reported values for summer, and that the lake may be emitting a significant amount of methane to the atmosphere.     

The consortium of the sponge Lubomirskia baicalensis in Lake Baikal,East Siberia

The spatial distribution of the fauna associated with a branched sponge, Lubomirskia baicalensis, endemic of Lake Baikal has been quantitatively studied. The biomass and numbers of three amphipod species which inhabit the sponge correlate (linearly or non-linearly) with the weight of the sponge.     

Lake-wide assessment of microplastics in the surface waters of Lake Baikal,Siberia

Limnology - Small microplastic particles < 330 µm, sometimes called mini-microplastics (MMP), are far more abundant than those larger than 330 µm....     

Temperature,growth and seasonal succession of phytoplankton in Lake Baikal,Siberia

• 1 Growth rates of two dominant Lake Baikal phytoplankton, the winter diatom Aulacoseira baicalensis and the summer cyanobacterium Synechocystis limnetica, were measured in the laboratory under varied temperature and light regimes to determine the potential role of these abiotic factors in seasonal species succession in the lake.
• 2 Aulacoseira baicalensis grew best at low temperature and not at all above 8 °C. Its maximum instantaneous growth rate was 0.15 d^‐1 recorded at 2–3 °C. Cells grew faster as temperature decreased, apparently in contrast to conventional Q₁₀‐based temperature‐growth relationships.
• 3 The picoplankter Synechocystis limnetica did not grow at 2–3 or 5–6 °C, but grew at a rate of 0.24 d^‐1 at the highest incubation temperature of 17 °C. Maximum growth rate was 0.35 d^‐1 at 8 °C.
• 4 Saturation irradiances (I_k) for growth of Aulacoseira baicalensis and Synechocystis limnetica were near pre‐acclimation values of 40 µmol m^‐2 s^‐1. At temperatures conducive to growth, both phytoplankters grew at all irradiances tested, except for A. baicalensis which would not grow at values above 300 µmol m^‐2 s^‐1 at 8 °C.
• 5 We conclude that temperature is a major driving force for the seasonal succession of species in Lake Baikal. Other factors, including vertical mixing of the water column and grazing by zooplankton, may also play important roles.

     

Biodiversity,biogeography, and connectivity of polychaetes in the world's largest marine minerals exploration frontier

Aim

The abyssal Clarion-Clipperton Zone (CCZ), Pacific Ocean, is an area of commercial importance owing to the growing interest in mining high-grade polymetallic nodules at the seafloor for battery metals. Research into the spatial patterns of faunal diversity, composition, and population connectivity is needed to better understand the ecological impacts of potential resource extraction. Here, a DNA taxonomy approach is used to investigate regional-scale patterns of taxonomic and phylogenetic alpha and beta diversity, and genetic connectivity, of the dominant macrofaunal group (annelids) across a 6 million km² region of the abyssal seafloor.

Location

The abyssal seafloor (3932–5055 m depth) of the Clarion-Clipperton Zone, equatorial Pacific Ocean.

Methods

We used a combination of new and published barcode data to study 1866 polychaete specimens using molecular species delimitation. Both phylogenetic and taxonomic alpha and beta diversity metrics were used to analyse spatial patterns of biodiversity. Connectivity analyses were based on haplotype distributions for a subset of the studied taxa.

Results

DNA taxonomy identified 291–314 polychaete species from the COI and 16S datasets respectively. Taxonomic and phylogenetic beta diversity between sites were relatively high and mostly explained by lineage turnover. Over half of pairwise comparisons were more phylogenetically distinct than expected based on their taxonomic diversity. Connectivity analyses in abundant, broadly distributed taxa suggest an absence of genetic structuring driven by geographical location.

Main Conclusions

Species diversity in abyssal Pacific polychaetes is high relative to other deep-sea regions. Results suggest that environmental filtering, where the environment selects against certain species, may play a significant role in regulating spatial patterns of biodiversity in the CCZ. A core group of widespread species have diverse haplotypes but are well connected over broad distances. Our data suggest that the high environmental and faunal heterogeneity of the CCZ should be considered in future policy decisions.     

Trophic coupling of the microbial and the classical food web in Lake Baikal,Siberia

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A schizophrenia-susceptibility locus at 6q25, in one of the world's largest reported pedigrees

We have completed a genome scan of a 12-generation, 3,400-member pedigree with schizophrenia. Samples from 210 individuals were collected from the pedigree. We performed an "affecteds-only" genome-scan analysis using 43 members of the pedigree. The affected individuals included 29 patients with schizophrenia, 10 with schizoaffective disorders, and 4 with psychosis not otherwise specified. Two sets of white-European allele frequencies were used-one from a Swedish control population (46 unrelated individuals) and one from the pedigree (210 individuals). All analyses pointed to the same region: D6S264, located at 6q25.2, showed a maximum LOD score of 3.45 when allele frequencies in the Swedish control population were used, compared with a maximum LOD score of 2.59 when the pedigree's allele frequencies were used. We analyzed additional markers in the 6q25 region and found a maximum LOD score of 6.6 with marker D6S253, as well as a 6-cM haplotype (markers D6S253-D6S264) that segregated, after 12 generations, with the majority of the affected individuals. Multipoint analysis was performed with the markers in the 6q25 region, and a maximum LOD score of 7.7 was obtained. To evaluate the significance of the genome scan, we simulated the complete analysis under the assumption of no linkage. The results showed that a LOD score >2.2 should be considered as suggestive of linkage, whereas a LOD score >3.7 should be considered as significant. These results suggest that a common ancestral region was inherited by the affected individuals in this large pedigree.     

Influence of climate seasonality on the effectiveness of the use of aquatic macroinvertebrates in urban impact evaluation in central Amazonia

Limnology - Natural fluctuations in ecosystems, such as those associated with climate, are a fundamental factor structuring macroinvertebrate assemblages. Given that macroinvertebrates are widely...     

Inferring population trends for the world's largest fish from mark-recapture estimates of survival

1. Precise estimates of demographic rates are key components of population models used to predict the effects of stochastic environmental processes, harvest scenarios and extinction probability. 2. We used a 12-year photographic identification library of whale sharks from Ningaloo Reef, Western Australia to construct Cormack-Jolly-Seber (CJS) model estimates of survival within a capture-mark-recapture (CMR) framework. Estimated survival rates, population structure and assumptions regarding age at maturity, longevity and reproduction frequency were combined in a series of age-classified Leslie matrices to infer the potential trajectory of the population. 3. Using data from 111 individuals, there was evidence for time variation in apparent survival (phi) and recapture probability (p). The null model gave a phi of 0.825 (95% CI: 0.727-0.893) and p = 0.184 (95% CI: 0.121-0.271). The model-averaged annual phi ranged from 0.737 to 0.890. There was little evidence for a sex effect on survival. 4. Using standardized total length as a covariate in the CMR models indicated a size bias in phi. Ignoring the effects of time, a 5-m shark has a phi = 0.59 and a 9 m shark has phi = 0.81. 5. Of the 16 model combinations considered, 10 (63%) indicated a decreasing population (lambda < 1). For models based on age at first reproduction (alpha) of 13 years, the mean age of reproducing females at the stable age distribution (A) ranged from 15 to 23 years, which increased to 29-37 years when alpha was assumed to be 25. 6. All model scenarios had higher total elasticities for non-reproductive female survival [E(s(nr))] compared to those for reproductive female survival [E(s(r))]. 7. Assuming relatively slow, but biologically realistic, vital rates (alpha = 25 and biennial reproduction) and size-biased survival probabilities, our results suggest that the Ningaloo Reef population of whale sharks is declining, although more reproductive data are clearly needed to confirm this conclusion. Combining relatively precise survival estimates from CMR studies with realistic assumptions of other vital rates provides a useful heuristic framework for determining the vulnerability of large oceanic predators for which few direct data exist.     

A new interstitial cyclopoid copepod from a sandy beach on the western shore of Lake Baikal,Siberia

A new species of cyclopoid copepod, Diacyclops biceri sp. nov., is described from Lake Baikal. It was found in the interstitial water of a sandy beach at Buchta Peschanaya on the western shore of the central basin of Baikal. The new species is unique in possessing 2-segmented endopods in swimming legs 3 and 4. Swimming legs 2 to 4 have 3-segmented exopods. The slender body form, the lack of the antennal exopodal seta, and the presence of a secondary pseudosomite anterior to the genital double somite of the adult female are interpreted as adaptations to the interstitial habitat. The harpacticoid Epactophanes richardi Mrazek was found in the same interstitial habitat as D. biceri.     

Bacterial diversity in the cecum of the world's largest living rodent (Hydrochoerus hydrochaeris)

The capybara (Hydrochoerus hydrochaeris) is the world's largest living rodent. Native to South America, this hindgut fermenter is herbivorous and coprophagous and uses its enlarged cecum to digest dietary plant material. The microbiota of specialized hindgut fermenters has remained largely unexplored. The aim of this work was to describe the composition of the bacterial community in the fermenting cecum of wild capybaras. The analysis of bacterial communities in the capybara cecum is a first step towards the functional characterization of microbial fermentation in this model of hindgut fermentation. We sampled cecal contents from five wild adult capybaras (three males and two females) in the Venezuelan plains. DNA from cecal contents was extracted, the 16S rDNA was amplified, and the amplicons were hybridized onto a DNA microarray (G2 PhyloChip). We found 933 bacterial operational taxonomic units (OTUs) from 182 families in 21 bacterial phyla in the capybara cecum. The core bacterial microbiota (present in at least four animals) was represented by 575 OTUs. About 86% of the cecal bacterial OTUs belong to only five phyla, namely, Firmicutes (322 OTUs), Proteobacteria (301 OTUs), Bacteroidetes (76 OTUs), Actinobacteria (69 OTUs), and Sphirochaetes (37 OTUs). The capybara harbors a diverse bacterial community that includes lineages involved in fiber degradation and nitrogen fixation in other herbivorous animals.     

New Data on the Distribution of True Bugs (Heteroptera) in the South of Baikal Siberia

New data on the distribution of ten species of true bugs in the south of Baikal Siberia are reported based on the authors’ material. The collection localities and dates, biotopes, the number and sex of the specimens, and the general distribution are given for each species.     

Depth distribution of oligochaetes in Lake Baikal (Siberia - Russia)

In the course of a preliminary sampling program, oligochaetes were collected along two transects in soft sediments in Lake Baikal. The number of oligochaetes present in the samples was counted, without distinguishing between species. The results suggest an exponential decrease in number of individuals (N) relative to depth (11,165 N m^–2 at 21 m, 265 N m^–2 at 1200 m). Most oligochaetes were found in the top 7 cm of sediment. The orange colour of the sediments suggests a high oxygen availability, even at the greatest water depths.

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Résumé Au cours d'un programme d'échantillonnage préliminaire, les oligochètes du lac Baïkal ont été récoltés dans le sédiment mou prélevé le long de deux transects. Les oligochètes présents dans les échantillons ont simplement été dénombrés, sans identification déspèces. Les résultats suggèrent une diminution exponentielle du nombre d'individus en fonction de la profondeur du lac (11165 N m^–2 à 21 m, 265 N m^–2 à 1200 m). La plupart des oligochètes ont été trouvés dans les 7 premeirs cm de la couche supérieure du sédiment. La couleur orangée du sédiment suggère une grande disponibilité en oxygène, même aux profondeurs les plus grandes.

     

Microbial biodiversity in the Lake Baikal water

The investigation of the microbial community of Lake Baikal by the methods of general and molecular microbiology showed that culturable bacterial strains were represented by various known genera. The lake water contains a great number of bacterial morphotypes, as revealed by electron microscopy, and a great diversity of nonculturable microorganisms belonging to different phylogenetic groups, as revealed by 16S rRNA gene fragment sequencing. The inference is made that the microbial community of Lake Baikal contains not only the known species but also new, possibly endemic to the lake, bacterial species.     

Rapid increase in fish numbers follows creation of world's largest marine reserve network

No-take marine reserves (NTMRs) are much advocated as a solution to managing marine ecosystems, protecting exploited species and restoring natural states of biodiversity [1,2]. Increasingly, it is becoming clear that effective marine conservation and management at ecosystem and regional scales requires extensive networks of NTMRs [1,2]. The world's largest network of such reserves was established on Australia's Great Barrier Reef (GBR) in 2004. Closing such a large area to all fishing has been socially and politically controversial, making it imperative that the effectiveness of this new reserve network be assessed. Here we report evidence, first, that the densities of the major target species of the GBR reef line fisheries were significantly higher in the new NTMRs, compared with fished sites, in just two years; and second, that the positive differences were consistent for multiple marine reserves over an unprecedented spatial scale (>1,000 km).