Ancient Lake Ohrid: biodiversity and evolution

Worldwide ancient lakes have been a major focal point of geological, biological, and ecological research, and key concepts in, for example, evolutionary biology are partly based on ancient lake studies. Ancient lakes can be found on most continents and climate zones with most actual or putative ancient lakes in Europe being restricted to the Balkan Region. The arguably most outstanding of them is the oligotrophic and karstic Lake Ohrid, a steep-sided graben of rift formation origin situated in the central Balkans. Here, an attempt is made to summarize current knowledge of the geological, limnological, and faunal history of Lake Ohrid. Additionally, existing data on biodiversity and endemism in Lake Ohrid are updated and evaluated, and patterns and processes of speciation are reviewed in the context of the Ohrid watershed, including its sister lake, Lake Prespa. Whereas the geological history of the Ohrid Graben is relatively well studied, there is little knowledge about the limnological and biotic history of the actual lake (e.g., the age of the extant lake or from where the lake first received its water, along with its first biota). Most workers agree on a time frame of origin for Lake Ohrid of 2–5 million years ago (Mya). However, until now, the exact limnological origin and the origin of faunal or floral elements of Lake Ohrid remain uncertain. Two largely contrasting opinions either favour the theory of de novo formation of Lake Ohrid in a dry polje with a spring or river hydrography or a palaeogeographical connection of Lake Ohrid to brackish waters on the Balkan Peninsula. Whereas neither theory can be rejected at this point, the data summarized in the current review support the de novo hypothesis. An assessment of the fauna and flora of Lake Ohrid confirms that the lake harbours an incredible endemic biodiversity. Despite the fact that some biotic groups are poorly studied or not studied at all, approximately 1,200 native species are known from the lake, including 586 animals, and at least 212 species are endemic, including 182 animals. The adjusted rate of endemicity is estimated at 36% for all taxa and 34% for Animalia. In terms of endemic biodiversity, Lake Ohrid is with these 212 known endemic species and a surface area of 358 km² probably the most diverse lake in the world, taking surface area into account. Preliminary phylogeographical analyses of endemic Lake Ohrid taxa indicate that the vast majority of respective sister taxa occurs in the Balkans and that therefore the most recent common ancestors of Ohrid- and non-Ohrid species likely resided in the region when Lake Ohrid came into existence. These data also indicate that there is relatively little faunal exchange and overlap between Lake Ohrid and its sister lake, Lake Prespa, despite the fact that the latter lake is a major water supplier for Lake Ohrid. Studies on selected species flocks and scatters, mostly in molluscs, point towards the assumption that only few lineages originally colonized Lake Ohrid from the Balkans and that the majority of endemic species seen today probably started to evolve within the lake during the early Pleistocene. Within the Ohrid watershed, endemism occurs at different spatial and taxonomic scales, ranging from species endemic to certain parts of Lake Ohrid to species endemic to the whole watershed and from subspecies to genus level and possibly beyond. Modes of speciation in the Ohrid watershed are largely affected by its degree of isolation. Observational evidence points towards both allopatric (peripatric) and parapatric speciation. Though sympatric speciation within a habitat is conceivable, so far there are no known examples. Today, the lake suffers from increasing anthropogenic pressure and a “creeping biodiversity crisis”. Some endemic species presumably have already gone extinct, and there are also indications of invasive species penetrating Lake Ohrid. The comparatively small size of Lake Ohrid and the extremely small range of many endemic species, together with increasing human pressure make its fauna particularly vulnerable. It is thus hoped that this review will encourage future research on the ecology and evolutionary biology of the lake’s taxa, the knowledge of which would ultimately help protecting this unique European biodiversity hot spot. Guest editors: T. Wilke, R. V?in?l? & F. Riedel Patterns and Processes of Speciation in Ancient Lakes: Proceedings of the Fourth Symposium on Speciation in Ancient Lakes, Berlin, Germany, September 4–8, 2006     

Rapid evolution of an ancient lake species flock: Freshwater limpets (Gastropoda: Ancylidae) in the Balkan Lake Ohrid

Ancient lakes have long been recognized as evolutionary theatres and hot spots of endemism; the evolution of their morphologically often highly diverse species flocks has received much attention. However, as each ancient lake has its own geological and evolutionary history, modes of speciation may differ from system to system. Ancient lakes can act as evolutionary reservoirs that assure the survival of relict species, but at the same time extant species may evolve through intralacustrine speciation. Other aspects of interest are the actual rates of immigration, diversification or extinction as well as the temporal framework of morphological change. Many of these questions have been addressed in the African (e.g. Lake Tanganyika) and Asian (e.g. Lake Baikal) ancient lakes. For an European ancient lakes (e.g. Lakes Ohrid and Prespa), such studies are largely missing. In the present paper, extraordinarily shaped endemic freshwater limpets of the genus Ancylus from the Balkan Lake Ohrid are used in a phylogeographic and phylogenetic context to test whether they represent an ancient lake species flock, to study the mode of speciation, and to assess the timing of morphological change. Based on DNA data from two mitochondrial genes (COI, LSU rDNA), it has been found that the Lake Ohrid Ancylus species form an endemic monophyletic group. In addition, the lake's feeder springs are inhabited by another, undescribed Ancylus species. All other studied waterbodies within the watershed do not support their own Ancylus lineages but are inhabited by a widespread Mediterranean taxon. The split between the species endemic to the lake and its sister taxon is dated to 1.4±0.6 million years ago. The study presents the first genetic confirmation for the existence of a species flock in a European ancient lake. Contrary to the prevailing opinion it shows that, concerning Ancylus, Lake Ohrid represents a site of intralacustrine speciation rather than an evolutionary reservoir. Moreover, it provides the first evidence for rapid morphological change in an European ancient lake species flock. See also Electronic Supplement at: http://www.senckenberg.de/odes/06-12.htm.     

Testing two contrasting evolutionary patterns in ancient lakes: species flock versus species scatter in valvatid gastropods of Lake Ohrid

Ancient lakes have long been recognized as “hot spots of evolution” and “evolutionary theatres” and they have significantly contributed to a better understanding of speciation and radiation processes in space and time. Yet, phylogenetic relationships of many ancient lake taxa, particularly invertebrate groups, are still unresolved. Also, the lack of robust morphological, anatomical, and phylogeographical data has largely prevented a rigorous testing of evolutionary hypotheses. For the freshwater gastropod genus Valvata—a group with a high degree of endemism in several ancient lakes—different evolutionary scenarios are suggested for different ancient lakes. Lake Baikal, for example, is inhabited by several endemic Valvata taxa that presumably do not form a monophyletic group. For such an evolutionary pattern, the term ancient lake species scatter is introduced here. In contrast, for the Balkan Lake Ohrid, workers previously suggested the presence of a monophyletic group of endemic Valvata species, that is, an ancient lake species flock. Sequence data of the mitochondrial cytochrome oxidase c subunit I gene (COI) from worldwide taxa, with a strong emphasis on Balkan species, are here used to test whether the putative Ohrid Valvata endemics represent an ancient lake species flock and to study patterns of speciation both on the Ohrid and the Balkan scale. The study reveals three distinct clades of endemic Valvata in Lake Ohrid. Monophyly of these taxa, however, is rejected, and they therefore do not represent an ancient lake species flock, but rather an ancient lake species scatter. Also, in contrast to many other gastropod groups in Lake Ohrid, the valvatids apparently did not radiate. Many Valvata taxa in ancient lakes are characterized by enhanced levels of shell complexity. However, it remains unclear whether these patterns are associated with ancient lake environments per se. It is here suggested that similarities in shell structure between North American and Balkan taxa might simply be due to convergent evolution.     

Biota of Lake Cheder (Tuva,Russia)

The algal flora and invertebrate fauna of Lake Cheder, located in the Central Tuva Basin, Russia, have been studied from collections made in August 1999. Eighteen taxa belonging to diatoms, blue–green and green algae, and seven species of fauna (two crustaceans and five insects) were present.     

Microbial communities of the stratified soda Lake Doroninskoe (Transbaikal region)

The physicochemical properties, species composition, and vertical distribution of microorganisms in the water column, shoreline microbial mat, and small shoreline mud volcanoes of the stratified soda Lake Doroninskoe were investigated in September 2007. The lake is located in the Transbaikal region, in the permafrost zone (51°25′N; 112°28′E). The maximal depth of the contemporary lake is about 6 m, the pH value of the water is 9.72, and the water mineralization in the near-bottom horizon is 32.3 g l⁻¹. In summer, the surface oxygen-containing horizon of the water column becomes demineralized to 26.5 g l⁻¹; at a depth of 3.5–4.0 m, an abrupt transition occurs to the aerobic zone containing hydrosulfide (up to 12.56 g l⁻¹). Hydrosulfide was also detected in trace quantities in the upper water horizons. The density stratification of the water column usually ensures stable anaerobic conditions until the freezing period (November and December). The primary production of oxygenic phototrophs reached 176–230 μg l⁻¹. High rates of dark CO₂ assimilation (61–240 μg l⁻¹) were detected in the chemocline. Within this zone, an alkaliphilic species of sulfur-oxidizing bacteria of the genus Thioalkalivibrio was detected (10⁴ cells ml⁻¹). Lithoheterotrophic bacteria Halomonas spp., as well as bacteriochlorophyll a-containing aerobic anoxygenic phototrophic bacteria (AAP) Roseinatronobacter sp. capable of thiosulfate oxidation, were isolated from samples collected from the aerobic zone (0–3 m). The water transparency in September was extremely low; therefore, no visible clusters of anoxygenic phototrophic bacteria (APBs) were detected at the boundary of the hydrosulfide layer. However, purple sulfur bacteria which, according to the results of the 16S rRNA gene analysis, belong to the species Thioalkalicoccus limnaeus, Ectothiorhodospira variabilis, “Ect. magna,” and Ect. shaposhnikovii, were isolated from samples of deep silt sediments. Ect. variabilis and Ect. shaposhnikovii were the major APB species in the shoreline algo-bacterial mat. The halotolerant bacterium Ect. shaposhnikovii, purple nonsulfur bacteria of the genus Rhodobacter, and AAP of Roseococcus sp. were isolated from the samples collected from mud volcanoes. All these species are alkaliphiles, moderate halophiles, or halotolerant microorganisms.     

The Radiation of Hydrobioid Gastropods (Caenogastropoda, Rissooidea) in Ancient Lake Poso, Sulawesi

A survey of the fauna of hydrobioid gastropods living in ancient Lake Poso in Sulawesi revealed a total of 16 species, 14 of them new, belonging to two genera, Sulawesidrobia and Keindahan gen. nov. Most species occurred on hard substrates, water plants or rootlets of trees. Since only the upper 0.5 m of the lake have been sampled, many more species probably remain to be discovered. Already, Lake Posoȁ9s fauna ranks among the four most diverse hydrobioid lake faunas worldwide. The Sulawesi lakes including Lake Poso and the Malili Lakes are the only lakes where sizeable radiations of hydrobioid and cerithioid gastropods coexist. Outside Lake Poso, hydrobioid gastropods have not been investigated so far apart from a single species reported from Lake Lindoe similar to or identical with S. bonnei [Abbott, 1945. Occasional Papers on Mollusks 1: 1–4], which has its type locality in Lake Poso and may in fact be a complex of species. Therefore endemicity in Lake Poso cannot be estimated nor is it possible to say, whether the radiation is of lacustrine origin. The introduction of alien fish has had a severe impact on the native fish fauna. The impact on the invertebrate fauna is not known but chances are that this survey based on collections from 1991 no longer reflects the original assemblage in the lake.     

Lake districts of north‐western Russia: identification of subregions based on analyses of hydrologic data

1. There are more than 400 000 lakes in the north‐western part of European Russia. Data from 50 gauging stations (located on lakes with water surface area ≤ 400 km²), within the region, was used to identify regions that exhibit common hydrologic patterns. 2. Analyses of common hydrologic patterns permitted the division of the overall area into four regions within which lakes exhibit common hydrologic and limnologic features.     

The Phototrophic Community Found in Lake Khilganta (an Alkaline Saline Lake Located in the Southeastern Transbaikal Region)

The structure of the phototrophic community found in Lake Khilganta (the Agin-Buryat Autonomous Area), a shallow saline soda lake (depth, 35–45 cm; water mineralization, 45 g/l; alkalinity, 30 mg-equiv/l; pH 9.5) has been studied. The bottom of the lake is covered with a 10- to 15-mm microbial mat, whose basis is formed by the filamentous cyanobacterium Microcoleus chthonoplastes. The mat exhibits pronounced layering and contains a significant amount of minerals. Six zones, which have characteristic colors and consistencies and are composed of intermittent layers, have been identified along the vertical profile. Live phototrophic bacteria have been found in the three upper zones. The bulk of the cyanobacteria is concentrated in the upper zone. In the lower zones, the development of purple bacteria has been observed. The diurnal dynamics of the vertical distribution of phototrophic microorganisms, which results from variations in the physicochemical environmental parameters, is described. Ectothiorhodospira sp. are dominant among the anoxyphotobacteria present. Their number, determined according to the inoculation method, is 10⁶–10⁷ cells/ml. The purple bacteria of the genera Allochromatium, Thiocapsa, and Rhodovulum are also present. Experiments with isolated pure cultures have shown that the anoxygenic photosynthetic bacteria of Lake Khilganta are halotolerant and alkalitolerant or alkaliphilic. In liquid enrichment cultures, at pH 9.5, the ratio of anoxyphotobacteria species is close to that observed in the lake. When the pH is increased to 10.4, it is Ectothiorhodospira, which is the most adapted to life under increased mineralization and alkalinity, that predominantly develops. Photosynthetic activity has been observed in the three upper mat zones and constitutes, on average, 1.5 g C/(m²h); the share of anoxygenic photosynthesis accounts for 75–95% of the total productivity. The main role in sulfide oxidation belongs to the phototrophic anoxyphotobacteria and cyanobacteria. In terms of the physicochemical conditions and structure of the phototrophic community, Lake Khilganta is similar to shallow saline water bodies of marine origin. The main differences consist in the increased alkalinity and in the consequent prevalence of alkaliphilic and alkalitolerant microorganisms and in the absence of representatives of the neutrophilic group of green sulfur bacteria.__________Translated from Mikrobiologiya, Vol. 74, No. 3, 2005, pp. 410–419.Original Russian Text Copyright © 2005 by Kompantseva, Sorokin, Gorlenko, Namsaraev.     

Concurrent evolution of ancient sister lakes and sister species: the freshwater gastropod genus <Emphasis Type="Italic">Radix</Emphasis> in lakes Ohrid and Prespa

Ancient sister lakes are considered to be ancient lakes lying in close geographic proximity, sharing a related origin and significant time of co-existence, usually having hydrological connection as well as a balanced degree of faunal overlap and distinctness. A paradigm for studying sister lake relationships are the ancient lakes Ohrid and Prespa in the Balkans, which are characterized by high degrees of endemicity. Three general patterns of endemic species can be distinguished for these lakes: (1) taxa that are endemic to either lake, with no close relatives in the respective sister lake, (2) closely related but distinct endemic taxa in both lakes (sister species) and (3) shared endemic taxa occurring in both lakes. In the present paper, two endemic freshwater pulmonate gastropod species, Radix relicta (Lake Ohrid) and R. pinteri (Lake Prespa), are used to study the evolution of presumed sister species based on biogeographical and comparative DNA data from world-wide Radix taxa. Phylogenetic, phylogeographical and parametric bootstrap analyses all suggest a sister group relationship of R. relicta and R. pinteri (pattern 2 of endemic diversity). Sister to these two taxa is the widespread R. ampla, which does not occur in the vicinity of lakes Ohrid and Prespa. The southern feeder spring complexes of Lake Ohrid are inhabited by another lineage (Radix sp. 1), which resembles Radix relicta in morphology/anatomy. For Lake Prespa, the widespread R. auricularia was reported in addition to the endemic R. pinteri. Comparative phylogenetic data favour a western Adriatic zoogeographical affinity of lakes Ohrid and Prespa over an Aegean-Anatolian faunal connection. The status of lakes Ohrid and Prespa as sister lakes is evaluated in the light of current knowledge on gastropod speciation and endemism in these hotspots of biodiversity.     

Correlation between algal species diversity index and phytoplankton community biomass in a mesotrophic lake (West Siberia, Russia)

The study deals with phytoplankton biodiversity in mesotrophic Sartlan Lake, a large natural saline water body in the south of West Siberia. Two different approaches are used: floristic and ecological cenotic. The former is good for determining and analyzing the phytoplankton species composition. The latter gives a quantitative estimation of the phytoplankton biodiversity from the equation of information theory: $ H_b = - \sum\limits_{i = 1}^n {\frac{{B_i }} {B}\log _2 \frac{{B_i }} {B}} The study deals with phytoplankton biodiversity in mesotrophic Sartlan Lake, a large natural saline water body in the south of West Siberia. Two different approaches are used: floristic and ecological cenotic. The former is good for determining and analyzing the phytoplankton species composition. The latter gives a quantitative estimation of the phytoplankton biodiversity from the equation of information theory: , where H _b is the biodiversity (bits); B _i is the population biomass of the species i; B is the entire phytoplankton community biomass (mg/l). A reliable stable negative correlation exists between the phytoplankton biomass and species diversity. Analytical equations and a diagram are given to illustrate the correlation between these values. Original Russian Text ? V.I. Ermolaev, 2009, published in Sibirskii Ekologicheskii Zhurnal, 2009, Vol. 16, No. 4, pp. 623–628.     

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.     

Distribution and population dynamics of ostracodes (Crustacea,Ostracoda) in a karstic lake: Lake Banyoles (Catalonia,Spain)

Qualitative and quantitative benthic samples were collected monthly between December 1986 and December 1987 from several stations at various depths and basins in the karstic Lake Banyoles (Catalonia, Spain), to study the spatial distribution and seasonality of ostracodes. A total of eight ostracode species were found in the lake. Of these, Candona neglecta Sars, Isocypris beauchampi Paris and Cypria ophtalmica Jurine were the most common ostracodes at all depth stations. Darwinula stevensoni Brady & Robertson, Ilyocypris species (I. bradyi Sars and I. gibba (Ramdohr)), Cyprideis torosa (Jones) and Cyclocypris ovum Jurine, on the other hand, were confined to sublittoral and littoral areas of the lake.Substrate and organic matter content appeared to be relevant factors determining the distribution of ostracode species at the different stations. The highest abundance of ostracodes were in the sublittoral (Basin IV–7 m and Basin I-5 m) where the substrate was coarse and sediment had a high organic matter content (>35% LOI). Low oxygen levels in the hypolimnetic waters (i.e. < 1 mg l^–1) may explain the absence of ostracodes at deeper zones in stations where the anoxic period lasts more than four months. On the other hand, low temperatures seem to favour the development of C. neglecta and D. stevensoni, while with higher temperatures I. beauchampi, C. torosa and C. ovum increased their abundances. However, no clear pattern can be observed, so ostracode species in Lake Banyoles, apparently, have non-seasonal life histories.     

Human impact as registered in the pollen record: some results from the western Lake Constance region,Southern Germany

Pollen analytical results from a littoral profile taken in Lake Constance compared with pollen profiles from small kettle holes nearby form the basis for conclusions concerning human population density, the economy and environment from the Neolithic period to the Middle Ages. Early Neolithic human impact is implicated in a lime decline and also the expansion of beech. The late Neolithic lakeshore settlements caused a decline of elm, beech and lime and, by shifting cultivation, considerably changed the forest cover. The settlements were abandoned after less than 100 years. There were long periods without distinct human impact in the middle and towards the end of the late Neolithic period. Since at least the Late Bronze Age there has been permanent habitation in the region. Human impact was greatest in the High Medieval period and later, and was also substantial in the late La Tène and Roman periods. Distinct declines in human impact can be observed between the La Tène and Roman periods and in the Migration and Merovingian periods. In these intervals, open land and grazed oak forest were replaced by birch and later on by beech forests. The decreases in human impact are not of the same intensity in all diagrams.     

300年来鄱阳湖营养盐演化重建与模拟

水体富营养化已经成为全球性的问题而受到广泛关注,然而其发生的过程和机制尚未完全明了。在湖泊营养演化过程中,水文和生态是两个最基本的制约因素。相对于短期的和试验性的研究,长时间尺度的营养盐变化过程能更全面地揭示营养盐的演化机制。以我国最大的淡水湖——鄱阳湖为例,采用湖泊水体交换周期模型和湖泊生态-营养盐动力耦合模型,重建鄱阳湖营养盐的长期变化,并利用沉积钻孔代用指标加以验证。在此基础上探讨其演化机制,模拟的时间序列中营养盐变化对气候水文与生态系统存在两种不同的响应模式。敏感因子分析显示:典型同步响应期中(1812—1828 AD),气候水文因子的贡献率达79.1%,生态因子为20.9%;典型异步响应期中(1844—1860 AD),两者贡献率分别为36.4%和63.6%。在模拟的营养盐变化时间序列中同步期占62.5%,说明气候因子在营养盐演化过程中起重要的作用;异步期虽只占12.5%,但对湖泊营养盐作用、营养盐反馈生物量同样至关重要。相关分析结果显示,生物量增长与TP含量基本呈线性关系,但存在一个阈值。在没有超过阈值前,生物量对TP具有较好的调节作用;当超过阈值之后,生物量的调节作用减弱。     

Molecular phylogeny and diversification of freshwater shrimps (Decapoda, Atyidae, Caridina) from ancient Lake Poso (Sulawesi, Indonesia)--the importance of being colourful

Ancient Lake Poso on the Indonesian island Sulawesi hosts a highly diverse endemic fauna, including a small species flock of atyid Caridina shrimps, which are characterized by conspicuous colour patterns. We used a mtDNA based molecular phylogeny to test the assumption of a monophyletic origin and intralacustrine radiation of the species flock and to assess the species specificity of some colour morphs. Our data reveal a rapid radiation of Caridina in the entire Poso drainage system, but provide no strong evidence for a monophyletic radiation of the lake species. Nevertheless each lacustrine species shows a varying degree of substrate or trophic specialization, usually considered a hallmark of adaptive radiation. Two distinct colour forms previously attributed to a single species, C. ensifera, lack distinguishing qualitative morphological characters, but are shown to be two different species. In contrast, morphologically rather distinct lake species lacking specific colour patterns may be hybridizing with riverine taxa. These results suggest that colour may play a similar role in species recognition and possibly speciation in ancient lake Caridina as hypothesized, e.g. for some African cichlids.     

Phylogeny and historical demography of endemic fishes in Lake Biwa: the ancient lake as a promoter of evolution and diversification of freshwater fishes in western Japan

To elucidate the origins of the endemic fish of Lake Biwa, an ancient lake in Japan, and the role of the lake in the diversification of freshwater fish in western Japan, we established a molecular phylogenetic framework with an absolute time scale and inferred the historical demography of a large set of fish species in and around the lake. We used mtDNA sequences obtained from a total of 190 specimens, including 11 endemic species of Lake Biwa and their related species, for phylogenetic analyses with divergence time estimations and from a total of 2319 specimens of 42 species (including 14 endemics) occurring in the lake for population genetic analyses. Phylogenetic analysis suggested that some of the endemic species diverged from their closest relatives earlier (1.3–13.0 Ma) than the period in which the present environmental characteristics of the lake started to develop (ca. 0.4 Ma), whereas others diverged more recently (after 0.4 Ma). In contrast, historical demographic parameters suggested that almost all species, including endemic and nonendemic ones, expanded their populations after the development of the present lake environment. In phylogeographic analyses, common or very close haplotypes of some species were obtained from Lake Biwa and other regions of western Japan. The phylogenetic and historical demographic evidence suggests that there was a time lag between phylogenetic divergence and population establishment and that phenotypic adaptation of some endemic species to the limnetic environment occurred much later than the divergences of those endemic lineages. Population structure and phylogeographic patterns suggest that Lake Biwa has functioned not only as the center of adaptive evolution but also as a reservoir for fish diversity in western Japan.     

Evaporation effects as reflected in freshwaters and ostracod calcite from modern environments in Central and Northeast Yakutia (East Siberia,Russia)

Taxonomical and geochemical investigations on freshwater ostracods from 15 waters in Central and Northeast (NE) Yakutia have been undertaken in order to estimate their potential usefulness in palaeoenvironmental reconstructions based on regional fossil records. Higher variability in environmental factors such as pH, electrical conductivity, and ionic content was observed in thermokarst-affected lakes in Central Yakutia than in NE Yakutia lakes. Species diversity of freshwater ostracods reached up to eight taxa per lake, mostly dominated by Candona weltneri Hartwig 1899, in Central Yakutia, whereas in NE Yakutian waters the diversity was lower and Candona muelleri jakutica Pietrzeniuk 1977 or Fabaeformiscandona inaequivalvis (Sars 1898) had highest frequencies. Coupled analyses of stable isotopes (δ¹⁸O, δ¹³C) and element ratios (Sr/Ca, Mg/Ca) were performed on both host waters and ostracod calcite, aiming to estimate the modern relationships. Correlations between host waters and ostracod calcite of single species were found for δ¹⁸O, δ¹³C and Sr/Ca and Mg/Ca ratios. The relationships between δ¹⁸O, Mg/Ca and Sr/Ca ratios and electrical conductivity (salinity) as an expression of solute concentrations in the waters mainly controlled by evaporation are more complicated but evident, and may be useful in future interpretation of geochemical data from fossil Siberian ostracods. Handling editor: K. Martens     

Lake Glubokoe (Moscow region,Eastern Europe), general characteristics

There have been almost a hundred years of continuous scientific activities at The Hydrobiological Station ‘Glubokoe Ozero’. The present volume of ‘Hydrobiologia’ contains summary papers reviewing previous and recent results of the studies on the hydrochemistry, zooplankton, zoobenthos, littoral fauna, food composition of fish, and historical biocenology (based on animal remains in bottom sediments), as well as on particular animal groups, such as Cladocera with special consideration of Daphnia, rotifers, fish, and parasitofauna. The present introductory paper provides data on the general characteristics of Lake Glubokoe, the history of its investigations and the station's modern programme which is aimed at biocenology with special consideration for morphological and physiological adaptations. Research both on general and on peculiar features of Lake Glubokoe is envisaged.     

The restoration of Lake Apopka in relation to alternative stable states: an alternative view to that of Bachmann et al. (1999)

Bachmann et al. (1999) postulated that wind energy initiated, and has maintained, high turbidity in hypertrophic (mean chlorophyll a = 92 g l^–1) Lake Apopka, Florida (mean depth = 1.6 m; area = 12500 ha). They asserted that the turbid condition was initiated by a hurricane in late 1947 that destroyed submersed plant beds and that high turbidity has since been maintained by wind-driven resuspension of fluid sediments. In their view, there has been sufficient light for re-establishment of submersed plants over about 38% of the lake bottom, but plant growth has been precluded by the fluid character of the sediments. They concluded that the restoration program of the St. Johns River Water Management District, which includes reduction of the phosphorus (P) loading rate, will not restore water clarity or submersed vegetation. An alternative explanation for Lake Apopka's turbid state is that it was initiated, and has been maintained, by excessive P loading that led to algal blooms and elimination of submersed vegetation through light limitation. The transition to the turbid state was contemporaneous with drainage of 7300 ha of the floodplain wetland to create polders for farming, beginning in the early 1940s. Lake P budgets indicate that drainage of the farms caused a seven-fold increase in the P loading rate (0.08 g TP m^–2 yr^–1 to 0.55 g TP m^–2 yr^–1). Paleolimnological analysis of lake sediments also indicates an increase in the P loading rate in mid-century, concomitant with the decline in submersed vegetation and the increase in phytoplankton abundance. After the increase in P loading, wind disturbance may have accelerated the transition to the turbid state; but, before the increase in P loading, wind disturbance was insufficient to elicit the turbid state, as evidenced by the stability of the clear-water state in the face of 14 hurricanes and 41 tropical storms from 1881 to 1946. Measurements of photosynthetically active radiation (PAR) indicate that light limitation has inhibited submersed plant growth except on the shallowest 5% of the lake bottom. Further, the correlation between the diffuse attentuation coefficient (K _PAR) and chlorophyll a (CHLA) indicates that light limitation would be removed over about 82% of the lake bottom with a reduction in CHLA from 92 g l^–1 to 25 g l^–1. Recently, following a 40% reduction in the P loading rate, the mean total P (TP) concentration, mean CHLA, and total suspended solids fell by about 30% while mean Secchi depth increased by more than 20%. Submersed plant beds appeared in areas devoid of macrophytes for nearly 50 years. These improvements, during a period with no change in mean wind speeds measured at Lake Apopka, provide the strongest evidence that the turbid state has been maintained by excessive P loading and that the current restoration program, which combines P load reduction with planting and removal of planktivorous fish, will be effective.