Pelagic food web interactions among benthic invertebrates and trout in mountain lakes

1. Benthic chironomid larvae and the amphipod Gammarus lacustris have been observed in the pelagic habitats of many mountain lakes. The main goal of this study was to determine if chironomid larvae and gammarids potentially affect predator–prey and nutrient dynamics in pelagic food webs of mountain lakes. 2. Eighty‐six mountain lakes were surveyed in Alberta and eastern British Columbia during the years 1965–1984, 1991–2004 and 2005–2007. Pelagic chironomid larvae were found in 86% of these lakes, and pelagic gammarids were found in 29% of lakes. Densities of pelagic chironomid larvae were 92% lower in lakes with pelagic gammarids and 76% lower in lakes with trout (P < 0.05). Intraguild predation of trout on gammarids appeared to reduce predation pressure on chironomid larvae. Gammarids consumed in vitro about 1 chironomid per gammarid per day or about 20% of their body mass in chironomid biomass per day. 3. Concentrations of total dissolved P and N, particulate C, and chlorophyll‐a increased with increasing densities of pelagic gammarids and chironomid larvae in situ (R² = 0.14 ± 0.19 SD, P < 0.1) and in vitro (P < 0.001). 4. Our findings suggest that gammarids and chironomid larvae are linked as predators and prey in pelagic food webs, possibly stimulating phytoplankton abundance via nutrient release.     

淡水有害底栖蓝藻研究进展

底栖蓝藻在全球淡水水域内广泛分布,在河流、湖泊、湿地、泉水水域等均有发现。相比于浮游蓝藻,底栖蓝藻因其隐蔽性、采样困难等关注度较低。针对近十几年有害底栖蓝藻不断过量繁殖的情况,本文对有害底栖蓝藻种类、主要的环境影响因子、有害次级代谢物及监测分析方法进行了总结概括。阐述了在有害底栖蓝藻生物量集聚过程中,光照、温度、营养盐、基质、水流等主要环境因子间的交互关联,并指出藻垫小生境内有害底栖蓝藻与微生物群落间作用的重要性。分析了不同属种有害底栖蓝藻的代谢物种类及影响代谢物产出的因素,总结了目前定性和定量分析有害底栖蓝藻的方法并指出其不足,对预测、定位高水平的有害底栖蓝藻提出了建议。本文为进一步研究有害底栖蓝藻异常增殖机制和有效防控方法提供了参考和借鉴。     

Molecular techniques for the early warning of toxic cyanobacteria blooms in freshwater lakes and rivers

The aim of this work was to test the efficacy of molecular techniques for detecting toxigenic cyanobacteria in environmental water samples collected from freshwater lakes, rivers and reservoirs in Portugal. Of 26 environmental samples tested, 21 were found to contain Microcystis using a genus-specific polymerase chain reaction (PCR). Another primer pair was applied to the same DNA template to test for the presence of microcystin synthetase genes. This primer pair resulted in the formation of a PCR product in 15 of the samples containing Microcystis and one sample that did not give a positive result in the Microcystis genus-specific PCR. A restriction assay using the enzyme EcoRV was then applied to show that in most cases, the gene fragment was from toxigenic strains of Microcystis and, in one above-mentioned case, from a microcystin-producing strain of Planktothrix. All environmental samples were examined microscopically to confirm the presence of cyanobacteria species. Samples were also tested for the presence of microcystins using the ELISA plate assay. There was good agreement between the results obtained with molecular techniques and those obtained from microscopy and chemical methods. The PCR techniques applied in this paper were found to be useful, particularly when the concentration of the target organism was very low compared with other organisms. This technique can be used to detect inocula for cyanobacterial populations and therefore provide a useful tool for assessing under which conditions particular species can grow into bloom populations.     

Use of molecular markers as indicators for winter zooplankton grazing on toxic benthic cyanobacteria colonies in an urban Colorado lake

Laboratory experiments provide no general answer to the question of whether zooplankton affects cyanobacteria or are affected by prokaryotes. A cyanobacterium may be grazed upon as small colonies, and the same species, as larger colonies, may inhibit zooplankton feeding. Within zooplankton, different species or groups may be affected differently. With this background we set out to detect winter zooplankton grazing and toxicity of overwintering populations of Microcystis aeruginosa. A polymerase chain reaction (PCR) method with oligonucleotide primers for the mcy gene cluster that encodes microcystin synthetase was employed for detection of M. aeruginosa reminiscent products in grazing cladocera. In our field studies, we detected the mcy gene cluster in strains of overwintering colonies of benthic Microcystis and also confirmed the expression of toxicity by quantitative PCR, phosphatase inhibition and enzyme-linked immunosorbent assays (ELISA). We further confirmed the presence of the mcy gene cluster in DNA and RNA isolated from sampled Daphnia magna specimens, indicating that zooplankton in the natural environment may ingest toxic Microcystis cells as part of their diet during winter months.     

Environmental controls on benthic food web functions and carbon resource use in subarctic lakes

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Molecular and phylogenetic characterization of potentially toxic cyanobacteria in Tunisian freshwaters

This study presents a genetic characterization of 27 potentially toxic cyanobacterial strains isolated from seven reservoirs located in the north and centre of Tunisia. These strains belonged mainly to Microcystis aeruginosa, Cylindrospermopsis raciborskii and Planktothrix agardhii species. Their toxicological potential was evaluated by molecular biology tools, which showed that none of the isolated strains carried segments of the gene cluster responsible for the production of cylindrospermopsin and saxitoxin. The majority of Microcystis isolates were able to synthesize microcystin, since they presented the six characteristic segments of the microcystin synthetase mcy cluster (mcyA, -B, -C, -D, -E and -G). This was further confirmed by MALDI-TOF analysis that showed the presence of eight microcystin variants, including microcystin-LR. The taxonomic identification of the strains was assessed based on the variability of the 16S rRNA gene sequences. Furthermore, the 16S-23S rRNA ITS sequences of Microcystis isolates and rpoC1 sequences of Cylindrospermopsis strains were also used in the phylogenetic analysis.     

Viruses in subarctic lakes and their impact on benthic and pelagic bacteria

Virus–bacterium interactions were investigated in the pelagic and benthic habitats in a set of lakes along an altitudinal gradient in the subarctic northern Sweden. Viral and bacterial abundances showed a significant variation between the lakes, with the highest benthic microbial abundances recorded in a high-altitude lake [993 m above sea level (a.s.l.)], whereas the highest pelagic microbial abundances were found in a low-altitude lake (270 m a.s.l.). In the pelagic habitat, there was also a distinct difference in microbial abundances between the summer–autumn and the winter sampling occasion. A positive relationship was noted between viruses and bacteria in both the pelagic and the benthic habitats. Visibly virus-infected bacterial cells were uncommon in the pelagic habitat and undetectable in the benthos. Both lytic and lysogenic pelagic viral production rates were undetectable or low; thus, a possible explanation for the relative high viral abundances found in the water column could be an allochthonous input of viruses or release of sediment-derived viruses. Overall, our results provide novel information about the relevance of viruses in the subarctic region and indicate that viruses play only a minor role in the nutrient and carbon cycling in the microbial communities of subarctic lakes.     

Biogeographical distribution and ecological ranges of benthic cyanobacteria in East Antarctic lakes

For the first time, the cyanobacterial diversity from microbial mats in lakes of Eastern Antarctica was investigated using microscopic and molecular approaches. The present study assessed the biogeographical distribution of cyanobacteria in Antarctica. Five samples were taken from four lakes spanning a range of different ecological environments in Larsemann Hills, Vestfold Hills and Rauer Islands to evaluate the influence of lake characteristics on the cyanobacterial diversity. Seventeen morphospecies and 28 16S rRNA gene-based operational taxonomic units belonging to the Oscillatoriales, Nostocales and Chroococcales were identified. The internal transcribed spacer was evaluated to complement the 16S rRNA gene data and showed similar but more clear-cut tendencies. The molecular approach suggested that potential Antarctic endemic species, including a previously undiscovered diversity, are more abundant than has been estimated by morphological methods. Moreover, operational taxonomic units, also found outside Antarctica, were more widespread over the continent than potential endemics. The cyanobacterial diversity of the most saline lakes was found to differ from the others, and correlations between the sampling depth and the cyanobacterial communities can also be drawn. Comparison with database sequences illustrated the ubiquity of several cyanobacterial operational taxonomic units and their remarkable range of tolerance to harsh environmental conditions.     

Diversity of subaerial algae and cyanobacteria on tree bark in tropical mountain habitats

We report the species composition of subaerial epixylic algae and cyanobacteria from a South-East Asian mountain rainforest locality in Cibodas, West Java. Green algae (Trebouxiophyceae, Chlorophyceae, Trentepohliales) were dominant and Cyanobacteria were the second most frequent group. We specifically concentrated on the comparison of species composition of closed primary forest and open antropogenic spaces. Trentepohliales and Cyanobacteria dominated in open spaces with higher light intensities, whereas closed forest localities were dominated by trebouxiophycean coccal green algae. There was a significantly higher algal diversity in open spaces than in closed forest samples indicating the limiting effect of light on subaerial algal communities of closed tropical forests. A number of isolated strains and morphotypes probably represent undescribed taxa. Presented at the International Symposium Biology and Taxonomy of Green Algae V, Smolenice, June 26–29, 2007, Slovakia.     

Development of tolerance against toxic cyanobacteria in Daphnia

We tested whether previous exposure to a toxic strain of cyanobacteria (Microcystis) affects survival, growth, and reproduction of a common herbivore, Daphnia magna. Samples from three natural populations of D. magna were each divided into two parts; one part was fed a mixture of toxic Microcystis and the non-toxic green alga Scenedesmus whereas the other part was fed only Scenedesmus. After four weeks, we compared the ability of these two populations to withstand the toxic Microcystis by assessing survivorship, growth, and reproduction. We found that the ability of D. magna to cope successfully with toxic Microcystis is improved if the animals have experienced previous exposure to toxic Microcystis. This suggests that the toxin may less affect the D. magna populations that are repeatedly exposed to toxic cyanobacteria in their natural habitat than populations lacking prior exposure. Since the ability to tolerate toxins is manifested in both improved survival and larger size of the animals, it may have considerable impact on zooplankton community composition in fresh-waters.     

运用分子生物学技术监测水环境中产毒蓝藻

有毒蓝藻在形成水华破坏水体环境的同时,也对人畜产生危害。运用分子生物学技术对水环境中产毒蓝藻进行监测,由于其简单、快速和经济等优点,逐渐成为各国学者关注的热点。本文从以下3个方面对其进行了综述:1)早期分子生物学技术在产毒蓝藻诊断中的运用;2)以产毒基因为靶标进行的产毒蓝藻诊断;3)运用基因芯片技术对产毒蓝藻进行检测。与传统的分子生物学技术相比,生物芯片技术具有体积小、重量轻、便于携带、分析自动快速、高通量等许多传统方法所不能比拟的优势。因此,该技术在蓝藻毒素检测中的运用必将给目前的产毒蓝藻的检测带来一场新的革命。     

含微囊藻毒素的蓝藻水华提取物对小鼠抗氧化酶的毒性作用

在世界范围内发生的富含营养的废水中生长蓝藻水华已经造成了严重的水污染。已有报道显示水华中的有毒成分是一类单环七肽微囊藻毒素,它们对人和家畜有严重的毒害作用,本文所使用的蓝藻水华采集于我国的太湖地区。我们采用三个亚致死计量(16、32、64 mg冻干藻细胞/kg体重,相当于4.97、9.94、19.88μg藻毒素/kg体重)的蓝藻水华提取物(CBE),分析它们对小鼠肝脏抗氧化酶的影响。经过连续14d每天腹腔注射CBE,小鼠分别在第3、5、7、9、11、13、15天处死并检测三种主要的抗氧化酶:超氧化物歧化酶(SOD)、过氧化氢酶(CAT)和谷胱甘肽巯基转移酶(GST)的活性。SOD和CAT的活性均呈现了抑制效应,GST的活性也发生了明显的变化。为了进一步确定过氧化的程度,我们又通过检测丙二醛的含量分析了脂质过氧化的程度。经过14d CBE处理后脂质过氧化表现出了明显的浓度依赖性的上升趋势。我们的结果表明,CBE对小鼠的抗氧化酶有严重毒害作用,并且能够引起脂质的过氧化。     

Evaluation of sampling and screening techniques for tiered monitoring of toxic cyanobacteria in lakes

Exposure to cyanotoxins can pose serious human health consequences both through drinking water and recreational use of a contaminated waterway. We adapted a tiered framework proposed by the World Health Organization (WHO) for monitoring cyanobacteria populations and assessing public health risks and implemented the program in Lake Champlain. This study focused on evaluating the sampling protocols employed in this adapted monitoring program over two field seasons (2003 and 2004). Using a paired sampling design, we evaluated whether 63-μm Wisconsin net samples adequately represented whole-water conditions and whether chlorophyll a concentration could serve as a useful predictor of cyanobacteria density and microcystin concentration. We also evaluated the spatial and temporal dynamics of blooms and their implications for monitoring. Our results suggest that using threshold values of either potentially toxic cyanobacteria density counted using a rapid screening protocol or chlorophyll a concentration serve as initial indicators of potentially high levels of cyanotoxin; however, the utility of chlorophyll a is system-dependent. Whole-water samples provide more accurate estimates of population density and higher microcystin concentrations than net samples, offering a more cautionary approach to assessing risk to recreational lake users. Shoreline samples generally showed higher cyanotoxin concentrations than offshore, but restricting sampling to the shoreline may miss early warnings of bloom development.     

Changes in phytoplankton,benthic invertebrate and fish assemblages of boreal lakes following invasion by Gonyostomum semen

1. During recent decades, Gonyostomum semen populations have spread in northern temperate regions forming dense blooms that may dominate the phytoplankton assemblage for extended periods. In this study, we investigate the effects of G. semen blooms in boreal brown water lakes with special emphasis on phytoplankton, fish and benthic invertebrate assemblages using data from 10 boreal lakes sampled annually over a 10‐year period. 2. Significant differences in phytoplankton and benthic invertebrate assemblages were found between lakes with high (3.01 mm³ L^?1; >80% phytoplankton biomass) and lakes with low G. semen biomass (0.03 mm³ L^?1; <5% phytoplankton biomass). In particular, high G. semen lakes had lower biomass of smaller, edible phytoplankton and a higher abundance and biomass of benthic invertebrates, especially Chaoborus flavicans, and perch than low G. semen lakes. 3. The length distribution of fish also suggested a tendency towards large and older fish and a lower recruitment success in high G. semen lakes, as denoted by lower abundances of fish shorter than 10 cm and higher biomass and abundance of fish longer than 15 cm in high G. semen lakes. 4. This study shows that high G. semen lakes are characterised by less edible phytoplankton, dominance by a few species and enhanced benthic secondary and fish production. Hence, the conjecture that high biomasses of G. semen create a bottleneck in the energy transfer to higher trophic levels seems less likely in boreal lakes.     

Spatial scale and benthic community organisation in the littoral zones of large oligotrophic lakes: potential for cross-scale interactions

1. We studied the spatial organisation of littoral, benthic invertebrate communities in two large oligotrophic lakes with very extensive heterogeneous littoral zones, and report that littoral communities show significant variation in their structure at multiple spatial scales. 2. At coarser scales, littoral zone topography, riparian inputs and exposure may be important drivers of community spatial structure. At finer scales, the composition of substrates, particularly macrophytes and inorganic sediments, may be drivers of community spatial structure. 3. The effects of substrates on community spatial patterns were non‐additive across scales; community‐habitat correspondence became very noisy when we attempted to extrapolate results throughout the littoral. We present some evidence to suggest that this non‐additivity is because of the interaction among structuring processes that operate at different scales.     

Responses of benthic community metabolism to abiotic factors in a mountain river in southern Poland

Seasonal and longitudinal metabolic trends in benthic communities were studied in the five orders of a natural mountain river (the Stradomka) in southern Poland. The method of oxygen change of rocky substrata in chambers was applied. Metabolic data were compared with abiotic (light regime, channel geomorphology and stream hydrology), and water chemical variables. A tendency of downstream increase in gross production and community respiration was observed between 1st and 4th stream orders. The highest values of GP (0.94 g C m^-2 24 h ^-1) and CR (1.12 g C m^-2 24 h ^-1) were observed in the middle Stradomka course (3–4 orders) in spring. A distinct negative NDM (heterotrophy) of the benthic community was measured in autumn and spring. During winter NDM was almost constant and oscillated around zero. The P/R ratio changed according to season and fluctuated between heterotrophy (P/R < 1) and autotrophy (P/R > 1). In general, heterotrophy prevailed in the study system (except 5th order). A marked shift in P/R between 4th and 5th stream orders confirms the prediction included in the RCC. Water temperature and PAR accounted for 56% in GP variability, whereas CR and NDM were not related to these variables. The combined variables (PAR and PO₄–P) attributed to 69% in GP variability. The set of chemical factors was less related to Stradomka metabolic data. These results suggest that metabolic processes in this mountain river remarkably depend on physical variables (solar radiation, altitude, water temperature and conductivity). Metabolic parameters were similar to other geographical mountain systems. This revised version was published online in July 2006 with corrections to the Cover Date.     

Resource requirements of four freshwater diatom taxa determined by in situ growth bioassays using natural populations from alpine lakes

We performed a series of in situ batch culture experiments to assess the resource requirements of common diatom taxa in alpine lakes of the central Rocky Mountains of North America. While physiological data are available on the resource requirements of some of these taxa, it is unclear whether intraspecific generalizations can be made across aquatic systems due to the potential development of ecotypes. In these experiments, we used amended lake water for a culture medium and natural diatom populations. Growth kinetics were determined for Asterionella formosa Hassall, Fragilaria crotonensis Kitton, Staurosirella pinnata (Ehr.) Williams and Round and Tetracyclus glans (Ehr.) Mills. Staurosirella pinnata, a historically abundant alpine diatom, had very low N and P requirements. Asterionella formosa and F. crotonensis, generally considered meso- or eutrophic species, exhibited low P requirements if N and Si were in moderate supply. Tetracyclus glans had the highest Si requirement. These experiments reveal that the recent changes in diatom community structure in these alpine lakes may be driven by changes in nutrient supply. We suggest that local diatom taxa and a natural culturing medium should be used to obtain more representative algal physiological data from a particular area.     

Horizontal variation of biomass and C:N:P ratios of benthic algae in lakes

The horizontal variation of chlorophyll a (chl a) and C:N:P (carbon:nitrogen:phosphorus) ratio was estimated for benthic algal communities attached to living substrates (mussels and macrophytes) and to rocks and stones in three lakes of different trophy. Samples were taken in a nested hierarchical design with replicates separated by several cm, dm, 10 m, and km. The observed horizontal variation of chl a, C:N, and C:P ratios did not differ for horizontal scales, substrates, or lakes. Although the investigated lakes were quite unlike regarding nutrient status, light regime, or morphology, the patchiness was similar in all lakes. Moreover, patchiness was also similar on stones, macrophytes and mussels, although those substrates differed in longevity and surface structure. Similar patchiness regardless of scale, substrate, or sampled lake, implies the possibility of using an optimal sampling design calculated for one lake and substrate also in other lakes and on other substrates.     

Acidification and weathering processes in high mountain lakes in Southern Alps

About 200 lakes in Southern Alps (Italy and Switzerland) were studied in order to quantify their acidification. Although samplings were carried out in summer, long after the acid shock caused by snowmelt, some lakes were found to be acidic and 47% of them show alkalinity values of below 50 μeq 1^-1. Losses in alkalinity (acidification levels) were evaluated using a titration model with variable F-factor. Factor analysis shows that the main factors influencing water chemistry are related to rock weathering and nitrate uptake by vegetation. In watersheds containing carbonatic rocks the weathering of calcite is responsible for the most of the alkalinity production. We therefore focused on a set of 19 low-alkalinity lakes in the Maggia Valley lying in watersheds containing mainly acidic rocks. Results show that the weathering of silicate and calcite (present in small quantities, but highly soluble) and nitrate uptake account for most of the alkalinity production. Other watershed and in-lake processes may be important in some cases, but they never account for more than 27 % of the alkalinity production in these lakes.     

Studies on zooplankton in two acidified high mountain lakes in the Alps

Being located in remote areas, alpine lakes are good indicators of regional and global pollution, and are particularly sensitive to atmospheric depositions. When situated in areas where acidic rocks dominate, they are sensitive to acidification. In the framework of an international project partially funded by the EU, a two-year study on zooplankton was carried out on two lakes, Lake Paione Inferiore (LPI) and Lake Paione Superiore (LPS), selected because of their susceptibility to acidification. In particular, LPS is permanently acidified, with pH ranging between 5.3 and 6.2, and LPI is acidified during the ice melt, when pH drops to 6.1 units. In addition, LPI is subjected to further anthropogenic interference, since fish (Onchorynchus mykiss) have been repeatedly introduced into the lake during the last thirty years. Literature information is available on the species composition and the seasonal dynamics of the zooplankton communities of the two lakes before these anthropogenic disturbances took place. Previously, the two lakes had a similar species composition and abundant zooplankton. An analysis of the present-day situation reveals significant changes compared to the past. Both acidification and the introduction of fish are responsible for the marked alterations observed. By reconstructing of the past cladocera assemblages and by analysing the literature on lakes with different impacts of the two factors (pH and fish), we can estimate the relative importance of the two different anthropogenic disturbances on species composition and abundance of the zooplankton communities of the two lakes. This revised version was published online in August 2006 with corrections to the Cover Date.