Microscopic eukaryotes living in a dying lake (Lake Koronia, Greece)

The morphological and phylogenetic diversity of the microscopic eukaryotes of the Lake Koronia water column was investigated during a mass kill of birds and fish in August–September 2004. The dominant morphospecies corresponded to the known toxin-producing species Prymnesium parvum , followed by Amoebidium sp., a taxon belonging to the group of parasitic Mesomycetozoea , and the common chlorophyte Pediastrum boryanum. Prymnesium exhibited heteromorphic life-cycle stages (flagellate and nonmotile coccoid cells). Phylogenetic analysis with 18S rRNA gene suggested that these heteromorphic stages belonged to the Platychrysis – Prymnesium monophyletic group. The most abundant phylotype was almost identical to P. boryanum . The fungal phylotypes were related to the Chytridiomycota , and the ciliate-like ones were closely related to Enchelys polynucleata and Pattersoniella vitiphila . Two phylotypes representing novel members belonging to the Jakobida and the Apicomplexa were also found. The microscopic eukaryotes of Lake Koronia include several organisms that are related to parasitic life modes.     

Consumption of crucian carp (Carassius carassius L., 1758) by restocked pike (Esox lucius L., 1758) in a lake with frequent winter hypoxia

To assess the effects of stocked pike (Esox lucius L.) on crucian carp (Carassius carassius L.) biomasses, the annual consumption of pike was estimated and compared with removal fishery catches. The studied lake, Lake Savijärvi, is a small (40 ha), shallow and eutrophicated lake in southern Finland with frequent algal blooms during summers and fish kills during winters. Until the 1980s, the fish fauna consisted of pike, perch (Perca fluviatilis L.), roach [Rutilus rutilus (L.)], crucian carp, and tench (Tinca tinca L.). Since 2003, when crucian carp were abundant in the extreme and with only a few roach and tench individuals, the lake has been biomanipulated by removal seining. To enhance the effects of seining, piscivorous pike were restocked in the spring of 2008. During the 3‐year study, the catch of crucian carp decreased from 243 to 136 kg while the catch of pike increased from 0.1 to 5.7 kg per seining hectare due to their spawning in the lake as of 2009. The total crucian carp consumption by captured pike was 588 kg during the 2008–2010 study period. When applying the number of pike estimated with the mark‐recapture method, consumption estimate increased to 917 kg, or 22.9 kg per lake hectare in 2010. Thus, pike consumption of crucian carp was about 17% of the removal catch in 2010.     

Unveiling fungal zooflagellates as members of freshwater picoeukaryotes: evidence from a molecular diversity study in a deep meromictic lake

This study presents an original 18S rRNA PCR survey of the freshwater picoeukaryote community, and was designed to detect unidentified heterotrophic picoflagellates (size range 0.6-5 microm) which are prevalent throughout the year within the heterotrophic flagellate assemblage in Lake Pavin. Four clone libraries were constructed from samples collected in two contrasting zones in the lake. Computerized statistic tools have suggested that sequence retrieval was representative of the in situ picoplankton diversity. The two sampling zones exhibited similar diversity patterns but shared only about 5% of the operational taxonomic units (OTUs). Phylogenetic analysis clustered our sequences into three taxonomic groups: Alveolates (30% of OTUs), Fungi (23%) and Cercozoa (19%). Fungi thus substantially contributed to the detected diversity, as was additionally supported by direct microscopic observations of fungal zoospores and sporangia. A large fraction of the sequences belonged to parasites, including Alveolate sequences affiliated to the genus Perkinsus known as zooparasites, and chytrids that include host-specific parasitic fungi of various freshwater phytoplankton species, primarily diatoms. Phylogenetic analysis revealed five novel clades that probably include typical freshwater environmental sequences. Overall, from the unsuspected fungal diversity unveiled, we think that fungal zooflagellates have been misidentified as phagotrophic nanoflagellates in previous studies. This is in agreement with a recent experimental demonstration that zoospore-producing fungi and parasitic activity may play an important role in aquatic food webs.     

Evolution of Resistance to Quorum-Sensing Inhibitors

The objective of this study was to explore the succession of planktonic unicellular eukaryotes by means of 18S rRNA gene tag pyrosequencing in the eastern English Channel (EEC) during the winter to summer transition. The 59 most representative (>0.1 %, representing altogether 95 % of total reads), unique operational taxonomic units (OTUs) from all samples belonged to 18 known high-level taxonomic groups and 1 unaffiliated clade. The five most abundant OTUs (69.2 % of total reads) belonged to Dinophyceae, Cercozoa, Haptophyceae, marine alveolate group I, and Fungi. Cluster and network analysis between samples distinguished the winter, the pre-bloom, the Phaeocystis globosa bloom and the post-bloom early summer conditions. The OTUs-based network revealed that P. globosa showed a relatively low number of connections—most of them negative—with all other OTUs. Fungi were linked to all major taxonomic groups, except Dinophyceae. Cercozoa mostly co-occurred with the Fungi, the Bacillariophyceae and several of the miscellaneous OTUs. This study provided a more detailed exploration into the planktonic succession pattern of the EEC due to its increased depth of taxonomic sampling over previous efforts based on classical monitoring observations. Data analysis implied that the food web concept in a coastal system based on predator–prey (e.g. grazer–phytoplankton) relationships is just a part of the ecological picture; and those organisms exploiting a variety of strategies, such as saprotrophy and parasitism, are persistent and abundant members of the community.     

Evidence of repeated long-distance movements by lake charr <Emphasis Type="Italic">Salvelinus namaycush</Emphasis> in Lake Huron

Movements and dispersal distances of acoustically-tagged adult lake charr Salvelinus namaycush were estimated based on detections at acoustic receivers in Lake Huron during 2010–2014. Most lake charr were detected only at receivers proximate to their release location or were not detected at all, but 3–9% of tagged lake charr were detected at receivers located over 100 km from their release location. Several fish made extensive repeated migrations within the lake, some at the scale of the entire main basin. Our observations show that some lake charr individuals repeat a similar pattern each year of moving long distances, and some fish were observed to show annual fidelity to presumed foraging sites in the spring at a spatial scale of approximately 200 km. Our telemetry-based estimates were minimum estimates of dispersal, as the placement of receivers within Lake Huron was not optimal for detection of lake charr and did not cover the majority of the lake. Further study of long-distance movement in lake charr is necessary to fully understand the implications of this behavior to lake charr ecology, population dynamics, and management in the Great Lakes.     

Toxicity of a soluble peptide from Microcystis sp. to zooplankton and fish

SUMMARY.

• 1 A soluble cell fraction lethal to Daphnia magna was isolated by the disruption of net phytoplankton from eutrophic Aculeo Lake. The phytoplankton of this lake is dominated by Microcystis sp.
• 2 The soluble fraction was also lethal to common native zooplankton, including the rotifers Keratella sp., Trichocerca similis, the copepod Boeckella sp., and the cladoceran Chydorus sphaericus. In addition, a partially purified soluble component of the lethal fraction caused the death of the fish Gambusia affinis.
• 3 The specific toxicity of the soluble fraction from phytoptankton varied four- to six-fold seasonally with peaks during periods of warm temperature.
• 4 Our results suggest that releases of a toxic peptide from Microcystis sp. may be the cause of massive fish kills at the study site, Aculeo Lake.

     

The present state of an Arctic charr (Salvelinus alpinus L.) population in Lake Imandra subjected to over-fishing

The influence of fishery on the state of Arctic charr (Salvelinus alpinus L.) population in Lake Imandra. The largest freshwater water body of the Kola Peninsula, is considered. Retrospective analysis of the catches during the period 1930–2010 revealed that the consequences of uncontrolled fishing are comparable with those of technogenic pollution. As a result of intensive and long-term antropogenic influence on the lake the number of age-groups decreased; the weight and length indices changed; the structure of fish population was simplified. Even after improving of environmental conditions, the numbers of fish continued to decrease due to uncontrolled angling and poaching which led to almost complete extinction of charr in the lake.     

Habitat coupling in a large lake system: delivery of an energy subsidy by an offshore planktivore to the nearshore zone of Lake Superior

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Community Structure and Dynamics of Small Eukaryotes Targeted by New Oligonucleotide Probes: New Insight into the Lacustrine Microbial Food Web

The seasonal dynamics of the small eukaryotic fraction (cell diameter, 0.2 to 5 μm) was investigated in a mesotrophic lake by tyramide signal amplification-fluorescence in situ hybridization targeting seven different phylogenetic groups: Chlorophyceae, Chrysophyceae, Cryptophyceae, Cercozoa, LKM11, Perkinsozoa (two clades), and Fungi. The abundance of small eukaryotes ranged from 1,692 to 10,782 cells ml⁻¹. The dominant groups were the Chrysophyceae and the Chlorophyceae, which represented 19.6% and 17.9% of small eukaryotes, respectively. The results also confirmed the quantitative importance of putative parasites, Fungi and Perkinsozoa, in the small heterotrophic eukaryotic assemblage. The relative abundances recorded for the Perkinsozoa group reached as much as 31.6% of total targeted eukaryotes during the summer. The dynamics of Perkinsozoa clade 1 coincided with abundance variations in Peridinium and Ceratium spp. (Dinoflagellates), while the dynamics of Perkinsozoa clade 2 was linked to the presence of Dinobryon spp. (Chrysophyceae). Fungi, represented by chytrids, reached maximal abundance in December (569 cells ml⁻¹) and were mainly correlated with the dynamics of diatoms, especially Melosira varians. A further new finding of this study is the recurrent presence of Cercozoa (6.2%) and LKM11 (4.5%) cells. This quantitative approach based on newly designed probes offers a promising means of in-depth analysis of microbial food webs in lakes, especially by revealing the phylogenetic composition of the small heterotrophic flagellate assemblage, for which an important fraction of cells are generally unidentified by classical microscopy (on average, 96.8% of the small heterotrophic flagellates were identified by the specific probes we used in this study).Recently developed molecular methods based on the amplification and sequencing of rRNA genes have made it possible to investigate picoeukaryote assemblage composition (pigmented or nonpigmented unicellular eukaryotes with cell diameters of <2 μm or <5 μm according to the studies) in various aquatic systems, independently of morphological identification and cultivation (14, 23, 27, 28, 29, 39). The essential role of picoplankton (both eukaryotic and prokaryotic) as a contributor to plankton biomass and to carbon and nutrient cycling has long been established (9), but the unexpected diversity among the smallest eukaryotes (cell diameters, <5 μm) was only recently revealed. Most of these data were obtained in oceanic systems, but a few recent studies conducted in lakes have also highlighted the broad diversity of 18S rRNA sequences affiliated with numerous phylogenetic groups: Chlorophyceae, Chrysophyceae, Cryptophyceae, Cercozoa, Fungi, Choanoflagellida, Bicosoecida, Ciliophora, Haptophyceae, Perkinsozoa, LKM11, Hyphochytridiomycota, Katablepharidaceae, Dinophyceae, and Eustigmatophyceae (22, 23, 24, 34). Thus, it has been possible to observe clear seasonal changes in small-eukaryote structure in an oligomesotrophic lake (23), and the lake-based studies generally report a dominance of heterotrophic cells within the lacustrine small-eukaryote assemblage. Moreover, the recurrent presence of sequences affiliated with parasitic groups has been highlighted in lakes of various trophic statuses (22, 23). Lepère et al. (25) reported the unexpected importance of two groups: first, fungi affiliated with two clades of chytrids known as parasites of various groups of microalgae; and second, members of the phylum Perkinsozoa belonging to two clades closely related to Perkinsus marinus and Parvilucifera infectans, which are parasites of bivalves and dinoflagellates, respectively (30), and whose systematic position has been controversial, since they are phylogenetically related to the Apicomplexa or the Dinoflagellata (6, 13).Although these data brought new insight into the structural diversity of lacustrine small eukaryotes, the relative importance, dynamics, and functional roles of these microorganisms from various phylogenetic groups are still largely unknown. We now need to research specific in situ abundances of previously undetected taxa. In this study, specially developed oligonucleotide probes, designed on the basis of molecular data obtained from sequencing (20, 21, 22, 23, 24, 25, 34), were used for fluorescence in situ hybridization (FISH) coupled with tyramide signal amplification (TSA) to investigate the composition, abundance, and dynamics of lacustrine small eukaryotes (<5 μm) in the mesotrophic Lake Bourget over 1 year. Special attention was paid to the dynamics of putative parasitic groups (Perkinsozoa, Fungi, Cercozoa).     

Fish habitat suitability and community structure in the equatorial Lake Naivasha,Kenya

Habitat suitability indices indicate how fish species respond to different habitat types. We assessed effects of habitat characteristics on fish distribution in an equatorial lake, Lake Naivasha, Kenya, where habitats vary according to substrate, depth and turbidity. Using monthly data between 2008 and 2010 using multi-mesh gill nets, catch per unit effort was used as a relative abundance measure to identify how habitat variables drive fish distribution. The focus was on commercial fishes: two introduced species (Cyprinus carpio and Micropterus salmoides) and two naturalised species (Oreochromis leucostictus and Tilapia zillii). Analyses revealed distinct preferences for different habitat variables by all commercial species except for C. carpio. For example, O. leucostictus preferred shallow waters with silt–clay substrates whilst M. salmoides preferred deeper waters with sandy/rocky substrates. Conversely, C. carpio showed no specialised habitat requirements. Niche overlaps were significantly lower between O. leucostictus and its respective sympatric species than between other species, a likely result of its territorial behaviour. The continued environmental degradation of Lake Naivasha may imperil the preferred habitats of the niche restricted M. salmoides, O. leucostictus and T. zillii. By contrast, the ubiquity of C. carpio may facilitate their invasion, and consequently sustain their dominance in the lake’s commercial fishery.     

Spatial and temporal distribution of Caulobacter spp. in two mesotrophic lakes

The seasonal distribution of Caulobacter spp. has been determined in the water column of two mesotrophic lakes using most probable number (MPN) viable counting techniques from April, 1972 to March, 1973. Concentrations in Lake Washington, a monomictic lake, peaked at 1000–3300 per ml in the epilimnion during the late spring and summer and reached lows in October of less than 2 per ml prior to fall turnover. The reason for the decrease in viable numbers is not known. Caulobacter spp. began to increase gradually in December, during the winter mixing period well before the spring bloom. Concentrations in Hall Lake, a small kettle lake, were somewhat higher than in Lake Washington, ranging from 0.27 per ml in October to over 5000 per ml during May. In contrast to Lake Washington, the highest populations were found in the metalimnion and upper hypolimnion of Hall Lake. Caulobacter spp. were also found in the anaerobic depths of the hypolimnion. However, these did not grow anaerobically, suggesting that they had settled into the hypolimnion and survived in the cold anaerobic zone. The populations of Caulobacter spp. reached maximum numbers at the approximate times and depths at which algal biomass would be expected to be greatest.     

A wide window of migration phenology captures inter‐annual variability of favourable conditions: Results of a whole‐lake experiment with juvenile Pacific salmon

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Observations on limnological conditions associated with a fish kill of Oreochromis niloticus in Lake Chivero following collapse of an algal bloom

Possible causes of deaths of Oreochromis niloticus in Lake Chivero were examined in relation to changes in limnological conditions monitored over a 25‐month period. The fish deaths coincided with the collapse of an algal bloom that had developed and builtup in the lake for 8 months. Chlorophyll a and dissolved oxygen increased to average concentrations of 42.4 μg l^?1 and 10.9 mg l^?1 respectively prior to the collapse of the bloom. Dissolved oxygen decreased when the bloom started to die off and coincided with the fish deaths when the average surface dissolved oxygen concentration in the lake was 3.9 mg l^?1 and was at a depth of 5 m <2 mg l^?1. Mortality probably resulted from depressed oxygen levels caused by the high oxygen demand from the massive algal die‐off and released algal toxins. This is the first time that die‐off of algae has been linked to fish‐kills in Lake Chivero as occurs in other hypereutrophic systems.     

Phylogenetic Estimation of Community Composition and Novel Eukaryotic Lineages in Base Mine Lake: An Oil Sands Tailings Reclamation Site in Northern Alberta

Reclamation of anthropogenically impacted environments is a critical issue worldwide. In the oil sands extraction industry of Alberta, reclamation of mining‐impacted areas, especially areas affected by tailings waste, is an important aspect of the mining life cycle. A reclamation technique currently under study is water‐capping, where tailings are capped by water to create an end‐pit lake (EPL). Base Mine Lake (BML) is the first full‐scale end‐pit lake in the Alberta oil sands region. In this study, we sequenced eukaryotic 18S rRNA genes recovered from 92 samples of Base Mine Lake water in a comprehensive sampling programme covering the ice‐free period of 2015. The 565 operational taxonomic units (OTUs) generated revealed a dynamic and diverse community including abundant Microsporidia, Ciliata and Cercozoa, though 41% of OTUs were not classifiable below the phylum level by comparison to 18S rRNA databases. Phylogenetic analysis of five heterotrophic phyla (Cercozoa, Fungi, Ciliata, Amoebozoa and Excavata) revealed substantial novel diversity, with many clusters of OTUs that were more similar to each other than to any reference sequence. All of these groups are entirely or mostly heterotrophic, as a relatively small number of definitively photosynthetic clades were amplified from the BML samples.     

Influences of ENSO and PDO phenomena on the local climate variability can drive extreme temperature and depth conditions in a Pampean shallow lake affecting fish communities

The aim of this study was to characterize occurrence of extreme temperature and depth conditions affecting fish community in a shallow lake as result of local climate variability, in turn influenced by the ENSO and PDO phenomena. Extreme depth and water temperature events (modeled from local weather conditions) were characterized from 1966 to 2012 to estimate changes in Chascomús lake fish communities. The ENSO and PDO influences on the occurrence probability of these ecosystem changes were investigated. Four significant changes in Chascomús Lake fish assemblage were identified during period assessed, as response to extreme temperature and depth events. Extreme high depth conditions would have changed fish community during 1987 and 2002, leading to a configuration characterized by the absence of the most emblematic fish species in Chascomús Lake, the pejerrey (Odontesthes bonariensis). On the other hand, extreme low water temperatures would have promoted a fish community characterized by the dominance of this last species during 1966–1986, 1997–2001 and 2008–2013 periods. Furthermore, extreme shortening in pejerrey spawning season was significantly related with decrease of its relative abundance. The occurrence probability of the extreme physical conditions modifying Chascomús Lake fish communities was significantly explained by ENSO (by depth influences) and by PDO (by water temperature influences). Thus, this study showed strong correlations between the ENSO and PDO influences and the occurrence probability of the extreme physical conditions changing fish community in Chascomús Lake.     

西藏夯错水鸟多样性及斑头雁繁殖活动区的变化

于2009年4 11月,对西藏夯错的水鸟资源状况进行了调查,旨在了解该地区水鸟资源状况的了解,并为禽流感的防控提供了科学依据。在夯错全年共记录到水鸟26种,隶属于6目10科。夯错也是斑头雁和棕头鸥重要的繁殖地。水鸟春秋季迁徙高峰期在4月份和10月份,这也是水鸟多样性较高的2个月,其主要原因是由于迁徙鸭类数量和种类的增加。卫星跟踪研究表明,在繁殖前期,斑头雁活动区面积较大,主要在夯错及其周围的湿地取食;进入繁殖中期,斑头雁的活动范围减少了许多;繁殖后期,随着幼鸟陆续出壳,父母随即带领幼鸟离开夯错,到其它湿地取食和育雏,因此此期的活动区面积较大。由于夯错面积较小,不能满足斑头雁对食物的需求,因此部分斑头雁选择其它湿地作为主要的取食地,但部分扩散到其它湿地的斑头雁在迁徙前期重新返回夯错,使得该时期斑头雁的数量有呈上升趋势。通过与青海湖水鸟资源状况的比较发现,夯错水鸟种类较少,这可能主要是由于两个湖泊所处地理区划的不同,并由此带来的气候环境的差异,以及植被条件的不同所造成的。这种差异主要是由于夯错海拔较高,紫外线很强,气候干燥,植被单一,栖息地类型多样性较低,因此水鸟的种数也相对较少一些。     

Resident Nongame Waterbird Use Following Biomanipulation of a Shallow Lake

Abstract: We examined the use of Lake Christina, Minnesota, USA, by nongame waterbirds following an autumn 2003 application of rotenone to eliminate its fish base and enhance migrating canvasback (Aythya valisineria) habitat. The only nongame waterbirds observed attempting to nest in 2004 were black terns (Chlidonias niger), but they failed to hatch any young. We recorded 246 Western grebes (Aechmophorus occidentalis) on Lake Christina in the spring of 2004, but by mid-June most had left the lake. During this period, few fish were available, and we suggest that although the emergent vegetation was suitable for nesting, the lack of food prevented colony formation. In spring 2005, small fish were again available on the lake, and numbers of all nongame species were greater than in 2004. We located 315 western grebe nests, of which 198 hatched ≥1 young (63% of all attempts). Landscape-level manipulation may enhance habitat for some species but also has the potential to exclude trophic levels from future use and should be considered when manipulating large-scale systems.     

Spatiotemporal distribution of bacteriochlorophylls in the meromictic Lake Suigetsu, Japan

The spatiotemporal distribution of chlorophyll pigments (chloropigments) in the water column of a meromictic lake, Lake Suigetsu (Fukui, Japan), was investigated. Water samples were collected from the central basin of Lake Suigetsu bimonthly between May 2008 and March 2010 at appropriate depths, including the oxic surface, oxic–anoxic interface, and anoxic bottom layers. Chlorophyll a, related to cyanobacteria and eukaryotic phytoplankton, was detected throughout the water column during the years of the study, whereas bacteriochlorophyll e, related to brown-colored green sulfur bacteria, was detected in the anoxic layers below the chemocline at a maximum concentration of 825 μg L^?1. The concentration of bacteriochlorophyll e was generally maximal at or just below the chemocline of the lake. The cellular content of bacteriochlorophyll e was estimated to be low in the upper part of the chemocline and tended to increase with increasing water depth. Bacteriochlorophyll a, which was presumably related to purple sulfur bacteria, was only detected at the chemocline during summer and autumn at concentrations of 5.4–16.3 μg L^?1. Our analysis of the chloropigment distribution for the two years of the study suggested that brown-colored green sulfur bacteria are the predominant phototroph in the anoxic layers of Lake Suigetsu, and that these play a significant role in the carbon and sulfur cycling of the lake, especially from spring to summer.     

青海可鲁克湖水鸟季节动态及渔鸥活动区分析

2008-2010年,对青海可鲁克湖的水鸟季节动态进行了调查。共记录到54种34828只水鸟,隶属于6目11科,雁鸭类水鸟最多,共统计到28445只,占水鸟总数的81.7%;其次是鸥类和鸻鹬类。可鲁克湖在水鸟春秋季迁徙高峰期在4月和10月,这也是水鸟多样性较高的两个月,其主要原因是由于迁徙鸭类数量和种类的增加。卫星跟踪表明,可鲁克湖是青海湖繁殖渔鸥重要的停歇地,渔鸥在可鲁克湖的停歇天数每年也有所不同,2007年和2008年秋季较2006年停歇时间短一些,初步判断与当地的人为干扰有关。当地政府对道路进行修建,其正好位于渔鸥的活动区内,这对渔鸥的日常活动造成较大影响,迫使渔鸥提前离开可鲁克湖。春季停歇天数的不同主要与青海湖面冰融的时间有关,若青海湖由于温度较高,冰融的时间早一些,渔鸥可能提前离开可鲁克湖,前往青海湖进行繁殖活动。     

Genetic diversity of microbial eukaryotes in anoxic sediment around fumaroles on a submarine caldera floor based on the small-subunit rDNA phylogeny

Recent culture-independent molecular analyses have shown the diversity and ecological importance of microbial eukaryotes (protists) in various marine environments. In the present study we directly extracted DNA from anoxic sediment near active fumaroles on a submarine caldera floor at a depth of 200 m and constructed genetic libraries of PCR-amplified eukaryotic small-subunit (SSU) rDNA. By sequencing cloned SSU rDNA of the libraries and their phylogenetic analyses, it was shown that most sequences have affiliations with known major lineages of eukaryotes (Cercozoa, Alveolata, stramenopiles and Opisthokonta). In particular, some sequences were closely related to those of representatives of eukaryotic parasites, such as Phagomyxa and Cryothecomonas of Cercozoa, Pirsonia of stramenopiles and Ichthyosporea of Opisthokonta, although it is not clear whether the organisms occur in free-living or parasitic forms. In addition, other sequences did not seem to be related to any described eukaryotic lineages suggesting the existence of novel eukaryotes at a high-taxonomic level in the sediment. The community composition of microbial eukaryotes in the sediment we surveyed was different overall from those of other anoxic marine environments previously investigated.