Using an online phycocyanin fluorescence probe for rapid monitoring of cyanobacteria in Macau freshwater reservoir

Monitoring of cyanobacteria and their toxins are traditionally conducted by cell counting, chlorophyll-a (chl-a) determination and cyanotoxin measurements, respectively. These methods are tedious, costly, time consuming, and insensitive to rapid changes in water quality and cyanobacterial abundance. We have applied and tested an online phycocyanin (PC) fluorescence probe for rapid monitoring of cyanobacteria in the Macau Storage Reservoir (MSR) that is experiencing cyanobacterial blooms. The relationships among cyanobacterial abundance, biovolume, cylindrospermopsin concentration, and PC fluorescence were analyzed using both laboratory and in-the-field studies. The performance of the probe was compared with traditional methods, and its advantages and limitations were assessed in pure and mixed cyanobacterial cultures in the laboratory. The proposed techniques successfully estimated the species including Microcystis and Cylindrospermopsis, two toxic species recently observed in the MSR. During February–November, 2010, the PC probe detected high correlations between PC and cell numbers (R ² = 0.71). Unlike the chl-a content, which indicates only the total algal biomass, the PC pigment specifically indicates cyanobacteria. These results support the PC parameter as a reliable estimate of cyanobacterial cell number, especially in freshwater bodies where the phytoplankton community and structure are stable. Thus, the PC probe is potentially applicable to online monitoring of cyanobacteria.     

Estimates of subtropical forest biomass based on airborne LiDAR and Landsat 8 OLI data

 快速、定量、精确地估算区域森林生物量一直是森林生态功能评价以及碳储量研究的重要问题。该研究基于机载激光雷达(LiDAR)点云与Landsat 8 OLI多光谱数据, 借助江苏省常熟市虞山地区55块调查样地数据, 首先提取并分析了87个特征变量(53个OLI特征变量, 34个LiDAR特征变量)与森林地上、地下生物量的Pearson’s相关系数以进行变量优选, 然后利用多元逐步回归法建立森林生物量估算模型(OLI生物量估算模型和LiDAR生物量估算模型), 并与基于两种数据建立的综合生物量估算模型的结果进行比较, 讨论预测结果及其精确性。结果表明: 3种模型(OLI模型、LiDAR模型和综合模型)在所有样地无区分分析时, 地上和地下生物量的估算精度均达到0.4以上, 基于不同森林类型(针叶林、阔叶林、混交林)分析时地上和地下生物量的估算精度均有明显提高, 达到0.67及以上。利用分森林类型模型估算生物量, 综合生物量估算模型精度(地上生物量: R²为0.88; 地下生物量: R²为0.92)优于OLI生物量估算模型(地上生物量: R²为0.73; 地下生物量: R²为0.81)和LiDAR生物量估算模型(地上生物量: R²为0.86; 地下生物量: R²为0.83)。     

Relationships between cyanobacterial production and the physical and chemical properties of a Midwestern Reservoir,USA

Drinking water reservoirs in agricultural dominated watersheds are particularly vulnerable to cyanobacterial blooms. A major byproduct of cyanobacteria is the production of objectionable taste and odor compounds such as geosmin. During May 1997 to September 1998, we studied spatial and temporal patterns of cyanobacterial abundance and composition with respect to a series of physical and chemical properties in Clinton Lake, located in east central Kansas, USA. Our results suggest that nutrients (in particular TN, NO₃–N concentrations), turbidity, and hydrologic regime all played potentially important roles in regulating cyanobacterial production. Specifically, low levels of nitrogen coupled with the internal release of phosphorus from the lake sediment under brief periods of anoxia may have helped promote cyanobacterial blooms. There was also a strong association between cyanobacterial blooms, geosmin production, and most taste and odor events in Clinton Lake. Anabaena circinalis appeared to be the source for geosmin production as a result of senescing algal cells just after the primary die-off of cyanobacteria.     

Hyperspectral remote sensing of cyanobacterial pigments as indicators of the iron nutritional status of cyanobacteria-dominant algal blooms in eutrophic lakes

Iron can stimulate cyanobacterial growth. Determining iron availability to cyanobacteria is therefore essential for timely warnings of bloom development. The objectives of this study were to determine the key spectral parameters indicating cellular iron status in cyanobacteria and to establish reliable equations for estimating iron nutrition in cyanobacterial cells. Cells, pigments, cellular iron, and spectra of cyanobacteria were measured monthly at 17 sites in Meiliang Bay of Taihu Lake during the summer period of cyanobacterial blooms from 2010 to 2013. Pronounced spatial and temporal variability of cellular iron of cyanobacteria was observed. The previously developed structure-insensitive pigment index (SIPI) and plant senescence reflectance index (PSRI) and the newly proposed chlorophyll a/phycocyanin index (R_Chl/PC) exhibited strong relationships with cyanobacterial cellular iron content. The relationships between the cellular iron concentration and SIPI, PSRI and R_Chl/PC could be expressed as linear, quadratic and cubic functions, respectively. The equations derived herein were tested using independent data from 2008 to 2009, obtained from 31 sites within Taihu Lake. For the three models that included SIPI, PSRI and R_Chl/PC as predictors, the coefficients of determination (R²) between the measured and estimated cellular iron concentration were 0.549, 0.584 and 0.909, and the mean relative errors (RE) were 17.1%, 18.1% and 8.0%, respectively. The overall results indicated that use of the three key hyperspectral parameters, SIPI, PSRI and R_Chl/PC, could be used for non-destructive and real-time monitoring of the iron nutritional status of cyanobacteria-dominant algal blooms in eutrophic lakes.     

Charismatic microfauna alter cyanobacterial production through a trophic cascade

The trophic ecology of cyanobacterial blooms is poorly understood on coral reefs. Blooms of toxic cyanobacteria, Lyngbya majuscula, can quickly form large mats. The herbivorous sea hare, Stylocheilus striatus, and the predatory nudibranch, Gymnodoris ceylonica, often associate with these blooms, forming a linear food chain: nudibranch—sea hare—cyanobacteria. Using laboratory studies, this study quantified (1) the functional response of nudibranchs, (2) the effect of sea hare size on predation rates, and (3) the strength of the indirect effect of sea hare predation on cyanobacteria (i.e., a trophic cascade). Nudibranchs consumed on average 2.4 sea hares d^?1, with the consumption of small sea hares 22 times greater than the consumption of large sea hares. Predation of sea hares reduced herbivory. Cyanobacterial biomass was 1.5 times greater when nudibranchs were present relative to when nudibranchs were absent. Although sea hare grazing can substantially reduce cyanobacterial biomass, predation of sea hares may mitigate grazing pressure, and therefore increase the abundance of cyanobacteria.     

Role of Predatory Bacteria in the Termination of a Cyanobacterial Bloom

Changes in cyanobacterial abundance and in the occurrence of bacteria of bacteria capable of lysing cyanobacteria were monitored over a period of 6 months (May to October 1998) in eutrophic Brome Lake (Quebec, Canada), in which dense cyanobacterial blooms recur regularly. By screening lake water, we isolated two strains of lytic bacteria, from the family Cytophagaceae. When tested on 12 cyanobacteria and 6 heterotrophic bacteria, strain 1 lysed only Anabaena flos-aquae and strain 2 lysed only Synechococcus cedorum, Synechococcus leopoliensis, Synechococcus elongatus, and Anacystic nidulans: both liquid and agar-grown cultures of these cyanobacteria were lysed. The number of plaque forming units of bacteria increased dramatically during the decline of the bloom. The results are consistent with an important role for these host-specific lytic bacteria in control and elimination of cyanobacterial blooms in this lake.     

Algal Diet of Small-Bodied Crustacean Zooplankton in a Cyanobacteria-Dominated Eutrophic Lake

Small-bodied cladocerans and cyclopoid copepods are becoming increasingly dominant over large crustacean zooplankton in eutrophic waters where they often coexist with cyanobacterial blooms. However, relatively little is known about their algal diet preferences. We studied grazing selectivity of small crustaceans (the cyclopoid copepods Mesocyclops leuckarti, Thermocyclops oithonoides, Cyclops kolensis, and the cladocerans Daphnia cucullata, Chydorus sphaericus, Bosmina spp.) by liquid chromatographic analyses of phytoplankton marker pigments in the shallow, highly eutrophic Lake Võrtsjärv (Estonia) during a seasonal cycle. Copepods (mainly C. kolensis) preferably consumed cryptophytes (identified by the marker pigment alloxanthin in gut contents) during colder periods, while they preferred small non-filamentous diatoms and green algae (identified mainly by diatoxanthin and lutein, respectively) from May to September. All studied cladoceran species showed highest selectivity towards colonial cyanobacteria (identified by canthaxanthin). For small C. sphaericus, commonly occuring in the pelagic zone of eutrophic lakes, colonial cyanobacteria can be their major food source, supporting their coexistence with cyanobacterial blooms. Pigments characteristic of filamentous cyanobacteria and diatoms (zeaxanthin and fucoxanthin, respectively), algae dominating in Võrtsjärv, were also found in the grazers’ diet but were generally avoided by the crustaceans commonly dominating the zooplankton assemblage. Together these results suggest that the co-occurring small-bodied cyclopoid and cladoceran species have markedly different algal diets and that the cladocera represent the main trophic link transferring cyanobacterial carbon to the food web in a highly eutrophic lake.     

Spatial and seasonal shifts in bloom‐forming cyanobacteria in Lake Chaohu: Patterns and driving factors

The patterns of spatial and temporal shifts in bloom‐forming cyanobacteria and the driving factors for these patterns were determined by analyzing the distribution of these cyanobacteria in Lake Chaohu using data from satellite images and field samples collected during 2012 and 2013. The cyanobacterial blooms primarily occupied the western region of Lake Chaohu, and the direction and speed of the prevailing wind determined the spatial distribution of these blooms. The cyanobacteria in Lake Chaohu were dominated by species of Microcystis and Anabaena. Microcystis reached its peak in June, and Anabaena had peaks in May and November, with an overall biomass that was higher than that of Microcystis. Microcystis generally occupied the western region of the lake in summer, whereas Anabaena dominated in other regions and seasons. Temperature may be responsible for these seasonal shifts. However, total phosphorus (TP), pH, temperature, turbidity and nitrate/nitrite nitrogen determined the coexistence of the two genera in different regions in summer. TP was correlated with Microcystis dominance, and pH and light availability were correlated with Anabaena dominance. Our results contribute to the understanding of shifts in bloom‐forming cyanobacteria and are important for the control of cyanobacterial blooms.     

Understanding cyanobacteria‐zooplankton interactions in a more eutrophic world

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湖泊蓝藻水华发生机理研究进展

蓝藻水华是富营养化湖泊常见的生态灾害,通过产生毒素、死亡分解时使水体缺氧和破坏正常的食物网威胁到饮用水安全、公众健康和景观,会造成严重的经济损失和社会问题,揭示其发生机理是进行防治的基础。综述了蓝藻水华发生机理的主要假说和证据,主要分为环境因子(营养盐、氮磷比、温度、微量元素、浮游动物牧食、水文和气象条件等)和生理生态特性(伪空泡、胶质鞘、CO2浓缩机制、适应低光强、贮藏营养物质、防晒、产毒素和固氮等)两个方面;评述了主要新理论,展望了今后的研究。到目前为止的研究表明寻找一两个关键因子并不能阐明蓝藻水华的发生机理。现存的理论或假说尽管已经在蓝藻水华的防治实践中产生重要作用,但仍然未能清楚地阐释其发生的客观规律。认为蓝藻水华是在各种环境因子(外因)的耦合驱动下,水华蓝藻由于其独特的生理生态特性(内因),产生巨大的生物量而在浮游植物群落中占绝对优势,在合适的水文气象条件下集聚于水表而形成。因此水华机理的研究应同时关注水华蓝藻的生理生态学规律和蓝藻水华发生的各种环境条件。不同环境因子协同影响水华蓝藻的不同生理生态特性的表达,从而影响水华的发生过程,将可能是以后研究的重点。蓝藻水华机理的研究在微观方面正趋向于应用分子生物学手段分析蓝藻生理过程,宏观方面则将广泛应用遥感遥测技术观测全湖蓝藻的变化规律。今后加强对水华蓝藻生理生态特性的基因表达与调控和环境多因子耦合作用于蓝藻水华过程的研究将有重要意义。蓝藻水华的机理研究包括现象、过程和原因3个层次的问题,通过大量的现象和过程的研究,不断揭示其发生过程中水华蓝藻的群落演替、种群发展、细胞活性和分子机理等变化规律,才能找到其发生的真正原因,为其防治提供理论依据和更好的治理措施。在蓝藻水华防治方面,控制营养盐和生态修复可能将是今后很长时间内最根本最有效和最具操作性的方法。     

Metabolism and foraging strategies of mid‐latitude mesozooplankton during cyanobacterial blooms as revealed by fatty acids,amino acids,and their stable carbon isotopes

Increasing sea surface temperatures (SST) and blooms of lipid‐poor, filamentous cyanobacteria can change mesozooplankton metabolism and foraging strategies in marine systems. Lipid shortage and imbalanced diet may challenge the build‐up of energy pools of lipids and proteins, and access to essential fatty acids (FAs) and amino acids (AAs) by copepods. The impact of cyanobacterial blooms on individual energy pools was assessed for key species temperate Temora longicornis and boreal Pseudo‐/Paracalanus spp. that dominated field mesozooplankton communities isolated by seasonal stratification in the central Baltic Sea during the hot and the cold summer. We looked at (a) total lipid and protein levels, (b) FA trophic markers and AA composition, and (c) compound‐specific stable carbon isotopes (δ¹³C) in bulk mesozooplankton and in a subset of parameters in particulate organic matter. Despite lipid‐poor cyanobacterial blooms, the key species were largely able to cover both energy pools, yet a tendency of lipid reduction was observed in surface animals. Omni‐ and carnivory feeding modes, FA trophic makers, and δ¹³C patterns in essential compounds emphasized that cyanobacterial FAs and AAs have been incorporated into mesozooplankton mainly via feeding on mixo‐ and heterotrophic (dino‐) flagellates and detrital complexes during summer. Foraging for essential highly unsaturated FAs from (dino‐) flagellates may have caused night migration of Pseudo‐/Paracalanus spp. from the deep subhalocline waters into the upper waters. Only in the hot summer (SST>19.0°C) was T. longicornis submerged in the colder subthermocline water (~4°C). Thus, the continuous warming trend and simultaneous feeding can eventually lead to competition on the preferred diet by key copepod species below the thermocline in stratified systems. A comparison of δ¹³C patterns of essential AAs in surface mesozooplankton across sub‐basins of low and high cyanobacterial biomasses revealed the potential of δ¹³C‐AA isoscapes for studies of commercial fish feeding trails across the Baltic Sea food webs.     

Ten-year survey of cyanobacterial blooms in Ohio’s waterbodies using satellite remote sensing

Cyanobacterial blooms are on the rise globally and are capable of adversely impacting human, animal, and ecosystem health. Blooms dominated by cyanobacteria species capable of toxin-production are commonly observed in eutrophic freshwater. The presence of cyanobacterial blooms in selected Ohio lakes, such as Lake Erie and Grand Lake St. Marys, has been well studied, but much less is known about the geographic distribution of these blooms across all of Ohio’s waterbodies. We examined the geographic distribution of cyanobacterial blooms in Ohio’s waterbodies from 2002 to 2011, using a nested semi-empirical algorithm and remotely sensed data from the Medium Resolution Imaging Spectrometer (MERIS) onboard the European Space Agency’s Envisat. We identified: 62 lakes, reservoirs, and ponds; 7 rivers; 6 marshes and wetlands; and 3 quarries with detectable cyanobacteria pigment (phycocyanin) concentrations. Of the 78 waterbodies identified in our study, roughly half (54%; n = 42) have any reported in situ microcystins monitoring results from state monitoring programs. Further, 90% of the waterbodies identified reached phycocyanin pigment concentrations representative of levels potentially hazardous to public health. This gap in lakes potentially impacted by cyanobacterial blooms and those that are currently monitored presents an important area of concern for public health, as well as ecosystem health, where unknown human and animal exposures to cyanotoxins may occur in many of Ohio’s waterbodies. Our approach may be replicated in other regions around the globe with potential cyanobacterial bloom presence, in order to assess the intensity, geographic distribution, and temporal pattern of blooms in lakes not currently monitored for the presence of cyanobacterial blooms.     

Targeted deep sequencing reveals high diversity and variable dominance of bloom-forming cyanobacteria in eutrophic lakes

Cyanobacterial blooms in eutrophic lakes are severe environmental problems worldwide. To characterize the spatiotemporal heterogeneity of cyanobacterial blooms, a high-throughput method is necessary for the specific detection of cyanobacteria. In this study, the cyanobacterial composition of three eutrophic waters in China (Taihu Lake, Dongqian Lake, and Dongzhen Reservoir) was determined by pyrosequencing the cpcBA intergenic spacer (cpcBA-IGS) of cyanobacteria. A total of 2585 OTUs were obtained from the normalized cpcBA-IGS sequence dataset at a distance of 0.05. The 238 most abundant OTUs contained 92% of the total sequences and were classified into six cyanobacterial groups. The water samples of Taihu Lake were dominated by Microcystis, mixed Nostocales species, Synechococcus, and unclassified cyanobacteria. Besides, all the samples from Taihu Lake were clustered together in the dendrogram based on shared abundant OTUs. The cyanobacterial diversity in Dongqian Lake was dramatically decreased after sediment dredging and Synechococcus became exclusively dominant in this lake. The genus Synechococcus was also dominant in the surface water of Dongzhen Reservoir, while phylogenetically diverse cyanobacteria coexisted at a depth of 10 m in this reservoir. In summary, targeted deep sequencing based on cpcBA-IGS revealed a large diversity of bloom-forming cyanobacteria in eutrophic lakes and spatiotemporal changes in the composition of cyanobacterial communities. The genus Microcystis was the most abundant bloom-forming cyanobacteria in eutrophic lakes, while Synechococcus could be exclusively dominant under appropriate environmental conditions.     

Harmful cyanobacteria and their cyanotoxins in Egyptian fresh waters – state of knowledge and research needs

Cyanobacterial blooms have increased in freshwater ecosystems worldwide in the last century, mostly resulting from eutrophication and climate change. These blooms represent serious threats to environmental and human health because of the production of harmful metabolites, called cyanotoxins. Like many countries, Egypt has been plagued with cyanobacterial blooms in most water sources, including the Nile River, irrigation canals, lakes and fishponds. However, the data about cyanotoxins produced in these blooms are limited. Only two types of cyanotoxins, microcystins and cylindrospermopsin, have been identified and characterised, mainly from Microcystis and Cylindrospermopsis blooms. The data revealed the presence of microcystins in raw and treated drinking waters at concentrations (0.05–3.8 µg l^?1), exceeding the WHO limit (1 µg l^?1) in some drinking water treatment plants. In addition, Nile tilapia Oreochromis niloticus caught from ponds containing heavy cyanobacterial blooms have accumulated considerable amounts of cyanotoxins in their edible tissues. The data presented here could be the catalyst for the establishment of a monitoring and management programme for harmful cyanobacteria and their cyanotoxins in Egyptian fresh waters. This review also elucidates the important research gaps and possible avenues for future research on cyanobacterial blooms and cyanotoxins in Egypt.     

Modelling lake cyanobacterial blooms: Disentangling the climate‐driven impacts of changing mixed depth and water temperature

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The influence of water circulation on chlorophyll-turbidity relationships in Lake Okeechobee as determined by remote sensing

The spatial distribution of phytoplankton can be difficult toassess in shallow, productive aquatic systems due to frequentalgal blooms, high turbidity and sediment-resuspension events.We conducted a study to assess the distribution of suspendedparticles in Lake Okeechobee, Florida, utilizing both Landsat(1974–75) or Advanced Very High Resolution Radiometer(AVHRR) (1987) satellite remote sensing. Surface water sampleswere collected by helicopter to determine in situ chlorophyll-aand turbidity levels at 20 stations on four dates in 1974–75and six dates in 1987. Remotely sensed reflectance values agreedwell with in situ particle densities at the 20 in-lake stations(average R²: Landsat = 0.81, AVHRR = 0.53) and independent,synoptic boat mapping of algal blooms (r² = 0.79, P < 0.01).Basin-wide maps of chlorophyll and turbidity, as well as additionalspatial sampling, both indicated that these parameters are notnecessarily coupled in Lake. Our data concur with the hypothesisthat the spatial distributions of chlorophyll and turbidityare shaped by different forces. The highest concentrations ofchlorophyll occurred in the vicinity of tributary nutrient inputsat the lake's perimeter, while turbidity increased towards thecenter of the lake, reflecting predominant water circulationpatterns. ²Present address: Department of Biology & Romberg TiburonEnvironmental Center, San Francisco State University, San Francisco,CA 94132, USA ³Present address: Idaho Division of Environmental Quality, 1420North Hilton, Boise, ID 83706-1260, USA ⁴Present address: 5642 Santiago Circle, Boca Raton, FL 33433,USA     

Bloom dynamics and chemical defenses of benthic cyanobacteria in the Indian River Lagoon,Florida

Cyanobacterial blooms are predicted to become more prominent in the future as a result of increasing seawater temperatures and the continued addition of nutrients to coastal waters. Many benthic marine cyanobacteria have potent chemical defenses that protect them from top down pressures and contribute to the persistence of blooms. Blooms of benthic cyanobacteria have been observed along the coast of Florida and within the Indian River Lagoon (IRL), a biodiverse estuary system that spans 250 km along Florida’s east coast. In this study, the cyanobacterial bloom progression at three sites within the central IRL was monitored over the course of two summers. The blooms consisted of four unique cyanobacterial species, including the recently described Okeania erythroflocculosa. The cyanobacteria produced a range of known bioactive compounds including malyngolide, lyngbyoic acid, microcolins A–B, and desacetylmicrocolin B. Ecologically-relevant assays showed that malyngolide inhibited the growth of marine fungi (Dendryphiella salina and Lindra thalassiae); microcolins A–B and desacetylmicrocolin B inhibited feeding by a generalist herbivore, the sea urchin Lytechinus variegatus; and lyngbyoic acid inhibited fungal growth and herbivore feeding. These chemical defenses likely contribute to the persistence of cyanobacterial blooms in the IRL during the summer growing period.     

Retrieval of phycocyanin concentration from remote-sensing reflectance using a semi-analytic model in eutrophic lakes

With the rapid development of the economy in recent years, massive algal (blue-green algae in particular) blooms have often observed in Chinese eutrophic lakes. The concentration of the cyanobacterial pigment phycocyanin (PC), an accessory pigment unique to freshwater blue-green algae, is often used as a quantitative indicator of blue-green algae in eutrophic inland waters. The purpose of this study was to evaluate the semi-analytic PC retrieval algorithm proposed by Simis et al. and to explore the potential to improve this PC algorithm so that it is more suitable for eutrophic lakes, such as Taihu Lake. In this paper, we recalculated the correction coefficients γ and δ to calculate the absorptions of chlorophyll-a at 665 nm and the absorptions of phycocyanin at 620 nm in terms of in situ measurements and observed that the values of these coefficients differed from the values used by Simis et al. and Randolph et al. The two coefficients are site dependent due to the different bio-optical properties of lakes. We also observed that the specific PC absorption at 620 nm a_pc*(620) decreases exponentially with an increase in PC concentrations. Therefore, a non-linear power–function of a_pc*(620), instead of a constant value of a_pc*(620) as used by Simis et al., was proposed for our improved PC retrieval algorithm in Taihu Lake, yielding a squared correlation coefficient (R²) of 0.55 and a root mean square error (RMSE) of 58.89 μg/L. Compared with the original PC retrieval algorithm by Simis et al., the improved retrieval algorithm has generally superior performance. In evaluating the limitation of the PC retrieval algorithms, we observed that the ratio of the total suspended solids to phycocyanin can be used as a primary measure for retrieval performance. Validation in Dianchi Lake and an error analysis proved that the improved PC algorithm has a better universality and is more suitable for eutrophic lakes with higher PC concentrations.     

Structural Diversity of Bacterial Communities Associated with Bloom-Forming Freshwater Cyanobacteria Differs According to the Cyanobacterial Genus

The factors and processes driving cyanobacterial blooms in eutrophic freshwater ecosystems have been extensively studied in the past decade. A growing number of these studies concern the direct or indirect interactions between cyanobacteria and heterotrophic bacteria. The presence of bacteria that are directly attached or immediately adjacent to cyanobacterial cells suggests that intense nutrient exchanges occur between these microorganisms. In order to determine if there is a specific association between cyanobacteria and bacteria, we compared the bacterial community composition during two cyanobacteria blooms of Anabaena (filamentous and N₂-fixing) and Microcystis (colonial and non-N₂ fixing) that occurred successively within the same lake. Using high-throughput sequencing, we revealed a clear distinction between associated and free-living communities and between cyanobacterial genera. The interactions between cyanobacteria and bacteria appeared to be based on dissolved organic matter degradation and on N recycling, both for N₂-fixing and non N₂-fixing cyanobacteria. Thus, the genus and potentially the species of cyanobacteria and its metabolic capacities appeared to select for the bacterial community in the phycosphere.     

Mesozooplankton and microzooplankton grazing during cyanobacterial blooms in the western basin of Lake Erie

Lake Erie is the most socioeconomically important and productive of the Laurentian (North American) Great Lakes. Since the mid-1990s cyanobacterial blooms dominated primarily by Microcystis have emerged to become annual, late summer events in the western basin of Lake Erie yet the effects of these blooms on food web dynamics and zooplankton grazing are unclear. From 2005 to 2007, grazing rates of cultured (Daphnia pulex) and natural assemblages of mesozooplankton and microzooplankton on five autotrophic populations were quantified during cyanobacterial blooms in western Lake Erie. While all groups of zooplankton grazed on all prey groups investigated, the grazing rates of natural and cultured mesozooplankton were inversely correlated with abundances of potentially toxic cyanobacteria (Microcystis, Anabaena, and Cylindrospermopsis; p < 0.05) while those of the in situ microzooplankton community were not. Microzooplankton grazed more rapidly and consistently on all groups of phytoplankton, including cyanobacteria, compared to both groups of mesozooplankton. Cyanobacteria displayed more rapid intrinsic cellular growth rates than other phytoplankton groups under enhanced nutrient concentrations suggesting that future nutrient loading to Lake Erie could exacerbate cyanobacterial blooms. In sum, while grazing rates of mesozooplankton are slowed by cyanobacterial blooms in the western basin of Lake Erie, microzooplankton are likely to play an important role in the top-down control of these blooms; this control could be weakened by any future increases in nutrient loads to Lake Erie.