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.

     

Oxygen concentration profiles in sediments of two ancient lakes: Lake Baikal (Siberia,Russia) and Lake Malawi (East Africa)

Oxygen concentration profiles have been measured, by means of with microelectrodes in sediments of Lake Baikal and Lake Malawi, along transects allowing to give a survey of two major ancient Rift lakes: Lake Baikal (Eastern Siberia) and Lake Malawi (East Africa), along depth transects in the constitutive basins of the lakes and/or of relevant depths with regard to oxygen (including including the deepest point, 1680 m, in Lake Baikal). Sediment oxygen penetration depths (SOPs) display very different patterns, depending on the lake in the two lakes. In Lake Baikal, SOPs are variable, show no significant relationship with bathymetric depth and are surprisingly deep on Akademichesky ridge (> 50.0 mm), emphasizing the distinctive feature of this region in the lake. While the Selenga river is an important source of eutrophication, the similarity of SOP-values in the Selenga shallow with those of most other sites suggests either a dilution of organic material by allochthonous matter, or a strong south-to-north transport of particles. In Lake Malawi, available oxygen is restricted to a maximum of three millimetres of the sediment, and there is a negative relationship with bathymetric depth, as a result of a steady decline of oxygen concentration with depth through the water column. Amongst the few parameters known to affect SOPs, the oxygen consumption by the sediment seems the most significant in both lakes. SOP-values furthermore confirm differences in the trophic status of Baikal and Malawi, respectively. The importance of oxygen as a factor likely to create ecological segregation for benthic organisms is discussed. Lake Malawi offers possibilities of bathymetric segregation but no vertical segregation in the sediment. In contrast, no bathymetric segregation related to oxygen is possible in Lake Baikal, but vertical segregation in the sediment is very likely. This revised version was published online in July 2006 with corrections to the Cover Date.     

The evolutionary history of two species of Orthocladiinae (Diptera: Chironomidae) from Lake Baikal (Eastern Siberia)

The evolutionary history of two species belonging to the genus Orthocladius van der Wulp, 1874 van der Wulp, F.M. (1874), ‘Dipterologische Aanteekneningen’, Tijdschrift voor Entomologie, 17, 109–148. [Google Scholar] (Diptera: Chironomidae) from Lake Baikal was investigated using the mitochondrial gene coding the first subunit of the cytochrome c oxidase (CO1 mtDNA). The phylogenetic analysis indicated that the Baikal Orthocladius species were divided into two well-defined clades where O. (Orthocladius) gregarius Linevitsh, 1970 was a sister species to Palaearctic O. (Orthocladius) nitidoscutellatus Lundstrom, 1915 and the O. (Eudactylocladius) sp. was a sister species to Nearctic O. (Eudactylocladius) subletteorum Cranston, 1998 Сranston, P.S. (1998), ‘Nearctic Orthocladius Subgenus Eudactylocladius Revised (Diptera: Chironomidae)’, Journal of the Kansas Entomological Society, 71(3), 272–295.[Web of Science ®] , [Google Scholar]. Divergence time estimates indicated that these species had been evolving independently for about 18 Ma (Neogene, Early Miocene), while emergence of the most recent common ancestors of the modern O. (Orthocladius) gregarius and O. (Eudactylocladius) sp. was dated to about 3.5 Ma (Neogene, Pliocene). The evolution of Baikal orthoclads occurred from the rheophilic fauna under conditions of global climate change during the geological history of the Baikal Depression in the Tertiary Period.     

Seasonal cycles in total chemical composition of two Lake Baikal benthic-pelagic sculpins (Cottocomephorus, Cottoidei)

Annual cycles in chemical composition of the body, liver, gonads, red and white muscles were determined for two medium fat sculpins, Cottocomephorus grewingki and C. inermis , endemic to Lake Baikal. Their total lipid content ranged from 3 to 9% during the year. The content of defatted dry substance was 14–17%, similar to the protein content of the other Baikalian cottoid fishes. The prespawning period was characterized by a positive lipid and protein balance in both species. In C. grewingki the liver performed largely a metabolic function, whereas in C. inermis it served also as a storage site for lipid reserves. During spawning, total body lipids of females of both species showed a two- to threefold decrease. Males of C. grewingki guarding nests deplete greatly their total body lipids, which decrease seven- to ninefold by the time of larval hatching in comparison with the prespawning period, and constitute 1–2%. After spawning, lipid reserves of C. grewingki were quickly restored to the initial level (from about 3 to 9%) and maintained during the long sexual maturation period. In C. inermis total body lipids increased only twofold in comparison to those observed during the spawning period.     

Late Quaternary palaeohydrology of Lake Huinaymarca (Bolivia)

In lake Titicaca, the distribution of the modern ostracod fauna appears to be controlled by a combination of two factors: a) the equilibrium between carbonates and organic matter, b) the ionic composition of the lake water and its tributaries. Therefore, the Limnocythere-Pampacythere group generally predominates on an alkaline-carbonate lake floor. In parts of the lake receiving an NaCl input from tributaries, Cyprideis and Cyprinotus occur. These are generally absent elsewhere. The Candonopsis group is found in the deepest part of the lake.Analysis of ostracod assemblages recovered from a number of cores permitted the reconstruction of the hydrological evolution of lake Huinaymarca for the last 10000 years. This included: low water levels, variations of oxygenation related to the position of the thermocline, and interconnections between different basins of the lake.     

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.     

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.     

Late Quaternary paleoenvironmental reconstruction of the Tremiti structural high (Central Adriatic Sea) from benthic foraminiferal assemblages

Foraminiferal analyses carried out on the VTR01/8 core (Tremiti Islands, Adriatic Sea) lead to the reconstruction of the paleoenvironmental evolution of the area. Although the core site is located at about 1000 km from the Po delta, this study shows that the installation of the recent sedimentological and run-off system (with a shore parallel clay-belt) is similar to that described at sites much closer to the Po delta. The statistical analysis singled out four associations that correspond to four distinct environments. The ecological preferences of the most abundant taxa that characterize each environment reveal that from the bottom of the core to − 50 cm, there is a slight increase of the water depth after which the water depth increases until the present level. Association A (that comprises subclusters A1, A2 and A3) is characterized by shallow-water taxa (e.g., Ammonia beccarii, Quinqueloculina spp. and Elphidium granosum) showing that in the past an infralittoral environment typified the Tremiti High. The subclusters of Association A show that during the deposition of the lower part of the core there had been an alternation of phases characterized by different degrees of riverine influence: the site was at first under the influence of river outflow (A2) that later bypassed the core site (A3) and then came back, although located further away than before (A1). With the rising of the sea level, the Tremiti High became only marginally affected by river influence because the core site is located at a considerable distance from the Po outlets and seaward with respect to the center of the modern mud-belt. As a matter of fact, association B (Bulimina marginata, Cassidulina carinata and Textularia spp.), which starts at − 46 cm, shows the typical characteristics of the modern mud-belt outer-shelf assemblage, although the presence of opportunistic species is limited by the distant position with respect to the Po delta.     

Precopulatory mate guarding in Harpacticella inopinata Sars (Copepoda: Harpacticoida) from Lake Baikal

Precopulatory mate guarding is reported for the first time from a freshwater harpacticoid, Harpacticella inopinata. Adult males were observed grasping onto juvenile females from the third copepodid stage onwards, but most commonly with the fifth copepodid. This behaviour is interpreted as a plesiomorphic trait of the family Harpacticidae.     

Abundance,growth and grazing loss rates of picophytoplankton in Barguzin Bay,Lake Baikal

The abundance, growth, and grazing loss rates of picophytoplankton were investigated in August 2002 in Barguzin Bay, Lake Baikal. Water samples for incubation were taken once at a near-shore station and twice at an offshore station. Contributions of picophytoplankton to total phytoplankton were high (56.9–83.9%) at the offshore station and low (5.8–6.8%) at the near-shore station. The picophytoplankton community in the offshore station comprised mainly phycoerythrin (PE)-rich cyanobacteria, with eukaryotic picophytoplankton being less abundant. In contrast, as well as PE-rich cyanobacteria and eukaryotic picophytoplankton, phycocyanin (PC)-rich cyanobacteria were found in the near-shore station. At the offshore station, growth and grazing loss rates on 25 August were 0.56 and 0.43 day⁻¹, respectively, and on 29 August, 0.69 and 0.83 day⁻¹, respectively. At the near-shore station, growth and grazing loss rates were 1.61 and 0.70 day⁻¹, respectively. These results show that there is a difference in the abundance, composition, and ecological role in the microbial food web of picophytoplankton between the near-shore and the offshore areas in Barguzin Bay.     

Mitochondrial and nuclear DNA phylogeography of Thymallus spp (grayling) provides evidence of ice-age mediated environmental perturbations in the world's oldest body of fresh water,Lake Baikal

Theories on the hydrological history of Lake Baikal, the world's oldest and deepest body of freshwater, and its surrounding great rivers, are currently based solely on geological evidence and are conflicting. Baikal is inhabited by numerous zoogeographical enigmas but their high level of endemism has hindered phylogeographic inferences. We provide a biological perspective of the region's palaeo-hydrological development based on the demographic and genealogical history of the widespread Thymallus spp. (grayling). Phylogenetic reconstruction reveals that old lineages of grayling (pre-Pleistocene) currently inhabit the Enisey, Lena and Amur River basins. For Lake Baikal however, we conclude that a mid-Pleistocene colonization (110000-450000 years ago) of an unoccupied niche has occurred. Population genetic inferences support an Enisey-Angara river route of colonization into Baikal, corresponding to the cataclysmic palaeo-hydrological event that led to the formation of the lake's only contemporary outlet, and a subsequent range expansion several thousand kilometres into the uppermost reaches of the Selenga River basin. The evolutionary history of Lake Baikal grayling is congruent with the controversial hypothesis of repeated glaciation. However, considering the extraordinary levels of endemism and proposed Miocene or Oligocene coalescence of other faunal lineages, a less profound but equally consequential cycle of environmental perturbations may have taken place. Bi-parentally inherited microsatellite DNA loci supported the phylogenetic relationships of Thymallus spp. and the geographical expansion of Baikal grayling strikingly well. A Markov Chain Monte Carlo modelling approach suggested severe contemporary population decline during the last century, possibly reflecting the influence of an uncontrolled fishery on this treasured ecosystem. These complementary pictures of the demographic history of grayling underscore the breadth of historical inquiry that can be entertained through the modelling of sufficient molecular data, and may significantly alter the zoogeographical and limnological perspectives of Baikal's history.     

Abundance and pigment type composition of picocyanobacteria in Barguzin Bay, Lake Baikal

In Lake Baikal, picocyanobacteria are the most important primary producers during the summer. Freshwater picocyanobacteria are discriminated into either the phycoerythrin (PE)-rich or the phycocyanin (PC)-rich types according to their pigment composition. The distributions of these two types of picocyanobacteria were investigated in Barguzin Bay. The PC-rich type accounted for >98% of the total picocyanobacteria at the station near the shore of the bay where river water flows directly in. In the offshore area of the lake, all of the picocyanobacteria cells were of the PE-rich type. In addition, the occurrence of the PC-rich type was restricted to the station, where the attenuation coefficient exceeded 0.25 m⁻¹. Near the shore, where the turbidity was high (>1 NTU), the cell densities of both the PE- and PC-rich types increased away from the river mouth. This indicates that the PC-rich type cells grow near the shore of the bay where turbidity is high. Since the PC-rich type could not grow well when cells were incubated in offshore lake water, restricted distribution of the PC-rich type could also be explained by their growth capability. The present study clearly demonstrated the shift in the pigment type composition of picocyanobacteria from the coastal to the pelagic zone of Lake Baikal. The co-existence of the two pigment types probably enables the abundance of the picocyanobacterial community to be stable over a broader range of environmental conditions than would be possible for a single pigment type.     

The evolutionary relationships of two families of cottoid fishes of Lake Baikal (East Siberia) as suggested by analysis of mitochondrial DNA

Fragments of mtDNA genes Cyt B, ATPase 6, and ATPase 8 of six cottoid fishes species of Lake Baikal (East Siberia) were amplified and sequenced. In addition mtDNAs of the same fish were subjected to restriction analysis. The data obtained were used to construct phylogenetic trees. The topology of the ATPase tree differs from those of the Res (restriction) and Cyt B trees. Clustering of species within the trees confirms the viewpoint of Taliev (1955, Baicalian Sculpins (Cottoidei)) according to which Baikalian cottoids originate from two ancestral forms. The times of branching obtained do not confirm the existing viewpoint according to which the two golomyankas (Comephorus baicalensis and Comephorus dybowskii) are pre-Baikal (Myocene) relicts: these two species may have originated 1.2–1.8 million years ago in Baikal, and they seem to represent an example of rapid morphological evolution which resulted in the formation of a new family. Correspondence to: S. Ja. Slobodyanuk     

Vertical planktonic structure in the central basin of Lake Baikal in summer 1999, with special reference to the microbial food web

Planktonic microbial interactions in the central basin of Lake Baikal were examined on a summer day in 1999. The subsurface maxima of bacterial abundance and chlorophyll concentration were recorded at the same depth, whereas the vertical distribution of heterotrophic nanoflagellates was the inverse of those of bacteria and picophytoplankton. Release of extracellular organic car-bon (EOC) from phytoplankton was estimated by the NaH¹⁴CO₃ method as 2.4µgCl^–1day^–1. Bacterial production (4.3µgCl^–1day^–1), estimated in a bottle incubation experiment using size-fractionated water samples, exceeded the EOC released. Thus, other supplying sources of organic matter are needed for the bacterial production. Grazing (2.6µgCl^–1day^–1) was also estimated in the experiment and accounted for 60% of the bacterial production. This is the first report on the microbial food web in the central basin of Lake Baikal.     

Influence of rainfall seasonality on African lowland vegetation during the Late Quaternary: pollen evidence from Lake Masoko, Tanzania

Aim  To determine if changes in the key bioclimatic parameters associated with rainfall seasonality can be quantified from fossil sequences and to distinguish them from changes in the total annual rainfall.
Location  Lake Masoko, southern Tanzania (9°20' S, 33°45' E, 840 m a.s.l.).
Methods  Fossil pollen was extracted from a long and well-dated sedimentary sequence spanning the period 45,000–4400 cal. yr bp . The modern habitat, geographical distribution and climatic range (mean annual rainfall and temperature, and length of the dry season) of selected East African plants were used to infer past rainfall attributes for the most characteristic fossil pollen taxa identified from the sediments of Lake Masoko.
Results  In the Masoko pollen sequence it has been possible to identify changes in the length/severity of the dry season during the last 45,000 cal. yr bp , which are interpreted to reflect shifts in the mean position of the Intertropical Convergence Zone (ITCZ) over the southern tropics. We suggest that this bioclimatic parameter has been the main driver of the vegetation dynamics in this area. The major inferred change occurred at the Younger Dryas–Holocene transition c . 11,800 cal. yr bp , when semi-deciduous forest disappeared, being replaced in the lake catchment by woodland, which persists to the present day in spite of locally high rainfall.
Main conclusions  In tropical regions under the influence of the ITCZ, the position and strength of which determine the distribution of rainfall through the year, more attention must be paid to the impact of the length and intensity of the dry season on the modern and past distribution and dynamics of the vegetation. This climatic parameter is as important as the total annual amount of rainfall, and probably one of the most relevant in lowland areas.     

Thermal stratification, nutrient dynamics, and phytoplankton productivity during the onset of spring phytoplankton growth in Lake Baikal, Russia

Lake Baikal, Russian Siberia, was sampled in July 1990 during the period of spring mixing and initiation of thermal stratification. Vertical profiles of temperature, dissolved nutrients (nitrate and soluble reactive phosphorus), phytoplankton biomass, and primary productivity were determined in an eleven-station transect encompassing the entire 636 km length of the lake. Pronounced horizontal variability in hydrodynamic conditions was observed, with the southern region of the lake being strongly thermally stratified while the middle and north basins were largely isothermal through July. The extent of depletion of surface water nutrients, and the magnitude of phytoplankton biomass and productivity, were found to be strongly correlated with the degree of thermal stratification. Horizontal differences likely reflected the contribution of two important factors: variation in the timing of ice-out in different parts of the lake (driving large-scale patterns of thermal stratification and other limnological properties) and localized effects of river inflows that may contribute to the preliminary stabilization of the water column in the face of intense turbulent spring mixing (driving meso-scale patterns). Examination of the relationships between surface water inorganic N and P depletion suggested that during the spring and early summer, phytoplankton growth in unstratified portions of the lake was largely unconstrained by nutrient supplies. As summer progressed, the importance of co-limitation by both N and P became more apparent. Uptake and regeneration rates, measured directly using the stable isotope ¹⁵N, revealed that phytoplankton in stratified portions of the lake relied primarily on NH₄ as their N source. Rates of NH₄ regeneration were in approximate equilibrium with uptake; both processes were dominated by organisms <2 µm. This pattern is similar to that observed for oligotrophic marine systems. Our study underscores the importance of hydrodynamic conditions in influencing patterns of biological productivity and nutrient dynamics that occur in Lake Baikal during its brief growing season.     

Understanding Late Quaternary extinctions: the case of Myotragus balearicus (Bate, 1909)

Aim In this study we present a new view on the extinction of Myotragus balearicus, an extinct highly modified dwarf caprine from the Gymnesic Islands (or eastern Balearic Islands), as a methodological case study for interpretation of Late Quaternary extinctions (LQEs). Methods We analyse all available ¹⁴C ages obtained from M. balearicus bones from the uppermost part of the Pleistocene and the Holocene, together with the available chronological data of the putative causes of Myotragus extinction. Results It has been possible to define two critical dates that allow us to establish an ‘uncertainty period for the Myotragus extinction’ (UPME) in each analysed island (Mallorca, Menorca and Cabrera). For Mallorca, the UPME corresponds to the interval c. 3700 to 2030 calbc (i.e. c. 1670 years of uncertainty). In the case of Menorca, the UPME spans from 10,000 to 1930 calbc (8070 years of uncertainity). In Cabrera the UPME is placed between 3650 and 300 calbc (3350 years of uncertainty). These periods, together with a review of the available information on the chronology of human arrival and the chronology of Holocene climatic change, shed light on the possible causes of the extinction of this species. Main conclusions Extinction of Myotragus because of climatic change can be definitively rejected. The Myotragus extinction must be attributed to the rapid effects of the first human occupation. The use of uncertainity periods for the disappearance of species represents a useful tool for the analysis of LQEs.     

Annotated checklist of the leech species diversity in the Maloe More Strait of Lake Baikal,Russia

In this paper, the very first checklist of the freshwater leeches of Maloe More Strait, a special part of Lake Baikal, is presented. It includes 14 free-living and parasitic species, of which four species belong to endemic Baikal genera – two species from Baicalobdella and one species each from Baicaloclepsis and Codonobdella. The checklist highlights six potentially new morphological species recorded for the first time in the area. The exact systematic position is stated for all leech species. Each species from the list is provided with information on taxonomic synonymy, data on its geographic distribution, and ecological characteristics. New species records are additionally provided with brief morphological characteristics and photos of their external morphology.     

The origin and recycling of sedimented biogenic debris in a subalphine eutrophic lake (Lake Bled, Slovenia)

The areal distribution of organic C contents, ¹³C values, total N and P and biogenic Si contents in surficial sediments were used to study the distribution, origin and diagenetic transformations of sedimented biogenic debris in the eutrophic subalpine Lake Bled (Slovenia), which for most of the yearhas an anoxic hypolimnion. The influence of an allochthonous input, restricted to the western basin, was clearly traced by higher organic C and total N and P contents, higher ¹³C values, and higher sedimentation rate in comparison to the eastern basin. The low ¹³C values of sedimentary organic matter in the major part of the lake, lower than the ¹³C values of different types of organic matter, suggest that this sedimentary organic matter is most probably the product of a microbial community and not a residue of primary production.The temporal variation of benthic diffusive fluxes of NH₄, Si and PO₄, derived from modelling the pore water profiles, was related to sedimentation of phytoplanktonic blooms, while the PO₄ fluxes were also dependent on changing redox conditions at the sediment-water interface in the period of the winter-spring overtum. The removal of PO₄ in pore waters is probably due to the adsorption of phosphate and precipitation of apatite and vivianite. The budget of C, N and P at the sediment-water interface revealed a high recycling efficiency (>70%), also confirmed by the rather uniform (or only slightly decreasing) vertical profiles of organic C, total N and P in sediment cores and C/N and C/P ratios. The percentage of biogenic Si recycling is low (<10%), suggesting its removal in sediments.