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With climate change and re-oligotrophication of lakes due to restoration efforts, the relative importance of benthic cyanobacteria is increasing, but they are much less studied than their planktonic counterparts. Following a major water level rise event that inundated massive reed stands in Lake Kinneret, Israel, we discovered the appearance in vast abundance of Gloeotrichia pisum (cyanobacteria). This provided an opportunity to investigate the biology and ecology of a benthic epiphytic colonial cyanobacterium, proliferating under altered environmental conditions, with possible toxin production potential and as a model for an invasive epiphyte. The species was identified by its typical morphology, and by sequencing its 16S rRNA gene and the intragenic space. We report on the abundance and spatial distribution of the detected colonies, their morphological characteristics and pigment composition. High phycoerythrin content provides the brownish color and supports growth at low light levels. Genomic community composition analysis revealed that G. pisum colonies host a diverse microbial community of microalgae, cyanobacteria, bacteria, and archaea with a conserved and characteristic taxonomic composition. The Synechococcales order showed high relative abundance in the colony, as well as other prokaryotes producing secondary metabolites, such as the rhodopsin producer Pseudorhodobacter. The microbial consortium in the colonies performed nitrogen fixation. The diazotroph's phylogenetic relations were demonstrated. Tests for presence of cyanotoxins (microcystin, cylindrospermopsin) proved negative. This study is the first documentation of the genus in Israel, providing insight on the invasive nature of G. pisum, and on the ecological implications of its appearance in a lake ecosystem.

On May 31, 2012, thousands of dead fish were found along the north-western shore of the Sea of Galilee. Analysis of fish gill tissue revealed no evidence of poisoning, and the fish looked healthy. This event adds to reports of similar fish kills at the same location, from the early 1990s, from May 2007, and a subsequent event on June 27, 2012, a month after the May 31 event. The common hypothesis for the massive kill suggests that a seiche induced by strong winds caused the upwelling of colder and anoxic hypolimnetic water along the western shores of the lake. Still, this hypothesis has not yet been tested.The WRF (The Weather Research and Forecasting) atmospheric model was recently coupled with the ocean model MITgcm (MIT general circulation model). The coupled model was named SKRIPS (Scripps–KAUST Regional Integrated Prediction System). The two SKRIPS model components (WRF and MITgcm) are well-tested at high resolution, allowing us to investigate the physical mechanism of the fish-kill event in an interactive system. To test the hypolimnetic water upwelling hypothesis for the massive fish-kill, we have set up and integrated the SKRIPS model for the May 31, 2012, event at a horizontal grid resolution of 400 m2, both for the atmospheric and lake component of the model.In this talk, I will present results from a high-resolution coupled atmosphere-lake regional simulation indicating an upwelling of cold anoxic hypolimnetic water into the surface during the event. The upwelling of cold water is increased close to the shore. The discussion will be supplemented by field data of temperature and oxygen concentrations, collected before, during, and after the fish-kill event. Our simulation results agree with the field observations, adding confidence to the anoxic hypolimnetic water upwelling hypothesis. Such fish-kill events may explain the biblical ‘miraculous catch of fish’ and the ‘miracle of the loaves and fish’. Also, it may provide a possible seasonal time frame (spring) for their occurrence in the past.

Little is known on the dynamics of under-ice phytoplankton communities. We investigated phytoplankton communities in the upper (0–20 m) and lower (30–35 m) layer of oligotrophic Lake Tovel, Brenta Dolomites (Italy) over 6 years during summer and under ice. Winter conditions were different from one year to another with respect to ice thickness and snow cover. Proxies for light transmission (Secchi disc transparency, light attenuation) were similar between seasons, even though the incident solar radiation was lower in winter. Algal richness and chlorophyll-a were not different between seasons while biomass was higher during summer. In four of the 6 years, Bacillariophyta dominated during summer and Miozoa (class Dinophyceae) under ice while in 2 years Bacillariophyta also dominated under ice. Generally, a shift to larger size classes from summer to under ice was observed for Bacillariophyta, Chlorophyta, and Ochrophyta (class Chrysophyceae) while Dinophyceae showed the opposite pattern. No strong links between phytoplankton community composition and abiotic factors (under-ice convective mixing, snow on ice, under-ice light) were found. We suggest that inter-species relationships and more precise indicators of under-ice light should be considered to better understand under-ice processes.

In many regions across the globe, extreme weather events such as storms have increased in frequency, intensity, and duration due to climate change. Ecological theory predicts that such extreme events should have large impacts on ecosystem structure and function. High winds and precipitation associated with storms can affect lakes via short‐term runoff events from watersheds and physical mixing of the water column. In addition, lakes connected to rivers and streams will also experience flushing due to high flow rates. Although we have a well‐developed understanding of how wind and precipitation events can alter lake physical processes and some aspects of biogeochemical cycling, our mechanistic understanding of the emergent responses of phytoplankton communities is poor. Here we provide a comprehensive synthesis that identifies how storms interact with lake and watershed attributes and their antecedent conditions to generate changes in lake physical and chemical environments. Such changes can restructure phytoplankton communities and their dynamics, as well as result in altered ecological function (e.g., carbon, nutrient and energy cycling) in the short‐ and long‐term. We summarize the current understanding of storm‐induced phytoplankton dynamics, identify knowledge gaps with a systematic review of the literature, and suggest future research directions across a gradient of lake types and environmental conditions., Our understanding of ecosystem‐scale responses to storm events is fragmented, and terminological variability in defining a “storm” hinders resolution of generalizable impacts. We provide a comprehensive synthesis of the interactions between physical properties and biological responses in lakes that demonstrates the context‐dependency of storm impacts; lake/watershed attributes and their antecedent conditions mediate the extent to which storms impact lake ecosystems. We develop a framework which conceptualizes how abrupt, storm‐induced changes in the lake environment influence phytoplankton community dynamics through functional traits, identifies current limitations, and highlights several avenues of research to narrow knowledge gaps in synthetic and interdisciplinary ways.

The Lake Suwa (Japan) has a history of non-N-fixing Microcystis blooms. Lake Kinneret (Israel) experienced multiannual periods of sole domination by the dinoflagellate Peridinium gatunense and periods dominated seasonally by P. gatunense or cyanobacteria. Extensive studies have been carried out in both lakes regarding the role of dissolved inorganic nitrogen and phosphorus as drivers of primary productivity. There is growing evidence that dissolved organic nitrogen (DON) compounds also influence not only biomass and structure of phytoplankton communities but also microcystin production. This study focuses on relationships of DON with: (1) population dynamics of Microcystis spp. and concentrations of microcystins in Lake Suwa, and (2) population dynamics of P. gatunense as well as N- and non-N-fixing cyanobacteria in Lake Kinneret. Modelling results for historical data of Lake Suwa by means of the hybrid evolutionary algorithm HEA revealed that the prediction of abundances of four Microcystis species and concentrations of cyanotoxins achieved higher coefficients of correlation when DON/DIN-ratios were included as drivers. Population dynamics of P. gatunense in Lake Kinneret appeared to have a strong inverse relationships with DON/DIN-ratios reflected by inferential models of HEA with higher coefficients of correlation when driven by DON/DIN-ratios. When DON/DIN-ratios were included as drivers, models of Microcystis spp. in Lake Kinneret performed higher coefficients of determination compared to models of N-fixing cyanobacteria. The study highlights the need to consider DON for improved understanding and management of population dynamics of cyanobacteria and dinoflagellates in freshwater lakes.

Kaplan-Levy R, Alster A, Lnag-Yona N, Zohary T2021.The Israel National Culture Collection of Algae (INCCA) for biodiversity conservation. SILNews77

The Andalusian International University held a workshop entitled Temporary wetlands’ future in drylands under the projected global change scenario in March 2020 in Baeza, Spain, with 26 participants from 10 countries. The workshop objectives were to promote international cooperation and scientific exchange on the conservation and protection of temporary wetlands. The participants highlighted the extreme conditions that temporary and permanent wetlands, ponds, and shallow lakes are currently facing and predicted a dismal future for these systems due to climate change. To foster a holistic view of these ecosystems, the workshop included wetland watersheds. It was concluded that the main threats are those affecting water quality and quantity as well as egg-seed banks, species population dynamics, and food webs. The inherent characteristics of waterbodies in drylands, including high resilience and resistance to harsh conditions, are already negatively impacted by direct human actions and climate change. Another threat is the time lag between scientific warnings about threats and the social and political concern leading to mitigating actions. Thus, more effective actions to protect and conserve temporary wetlands are essential. Research networks could help stimulate the necessary conservation actions, but the global recession due to the COVID-19 pandemic will pose a challenge as economies are burdened with urgent expenditure. This special issue of the journal Inland Waters is the outcome of the workshop presentations and is composed of the ensuing papers on wetlands in drylands. This work was supported by UNIA. Universidad Internacional de Andalucia [grant number: UNIA-WORKSHOP-2019]; Centro de Estudios Avanzados en Ciencias de la Tierra [grant number: CEACTIERRA-2020]. SB was supported by the PONDERFUL project (Pond ecosystems for resilient future landscapes in a changing climate) funded by European Union's Horizon 2020 research and innovation programme under grant agreement No. 869296. EJ was supported by the TUBITAK researchers program BIDEB 2232 (project 118C250). TZ was supported by the Israel Water Authority.

We review the literature on the relationship between water temperature and size of freshwater phytoplankton, to examine the hypothesis that freshwater phytoplankton, like marine phytoplankton and many other groups of organisms, conform to Bergmann’s Rule and become smaller with warming. We provide both experimental and field evidence in support of the above hypothesis, much of this evidence was hidden in studies focused on other issues, but presenting temperature and phytoplankton size data. Freshwater phytoplankton size shrinks with increasing temperature at both the species level (by cells or colonies becoming smaller) and at the community level (shift to smaller species). Exceptions to the Rule do occur but in most cases those exceptions can be explained by indirect effects of temperature on phytoplankton size, via processes such as grazing or nutrient availability. With global warming, freshwater phytoplankton are likely to be of smaller size. This article is dedicated to Colin S. Reynolds, who has had a leading role in our personal education and understanding of phytoplankton ecology.

The Mediterranean in general and the Eastern Mediterranean in particular is a unique ocean. The concentration of dissolved nutrients in the deep waters of the Eastern Mediterranean is much lower than those in other oceans of the world, and when these are mixed into the surface waters they support very low primary productivity. The Mediterranean in general, and the Eastern Mediterranean in particular, has a large excess of evaporation over precipitation. The structure of the water column across the Eastern Mediterranean carries many of the characteristics of a typical tropical structure. Heterotrophic bacteria are an important component of oligotrophic pelagic environments in general and of the Eastern Mediterranean in particular. The Eastern Mediterranean is unusual in being the largest body of water in the world in which the primary productivity is phosphorus limited. The annual phytoplankton bloom occurs in winter as soon as deep mixing occurs and ceases when the phosphate is depleted.

Limnology as a multidisciplinary science has a major role to play in achieving sustainable solutions for Africa’s water shortage and environmental problems and ensuring they are protected, ...

Mougeotia (Zygnematales, Charophyta) first appeared in the plankton of Lake Kinneret in 1998. While initially rare, from 2004 onwards it was present in the plankton continuously, forming massive blooms in spring (2005, 2006, 2012) or in winter (2010), occasionally appearing in different morphological and life cycle forms. Mougeotia maintained its population under a wide range of water temperatures, nutrient concentrations, solar radiation, pH levels and stratification patterns, making it a highly versatile alga. In multiple regression, year and month as the only predictors explained 36% of the pattern of Mougeotia biomass. However, Mougeotia biomass could not be explained by any of the environmental parameters considered. Modeling the temporal dynamics of Mougeotia biomass using an autoregressive integrated moving average (ARIMA(1,0,0)) explained 56% of variability indicating that intraspecific factors (e.g., competition for nutrients or self-shading) may determine the dynamics of Mougeotia biomass. To explain the lack of relationships with the environmental parameters, we hypothesize that (1) Mougeotia possesses exceptional physiological plasticity and/or (2) Lake Kinneret may host two or more genetically distinct cryptic species of Mougeotia with different environmental niches. Both explanations may hinder any inference on Mougeotia–environment relationships and require confirmation by experimental work.

Climate change and human overexploitation of freshwaters jointly lead to extreme fluctuations in lake water levels. The latter induces changes in the structure and availability of littoral habitats...

We modify an existing water quality index of Lake Kinneret to better match the objective of sustaining the ecosystem over time. The Kinneret Sustainability Index (KSI) provides a quantitative indication of how similar the current ecosystem is in relation to a reference state that managers are striving to achieve and sustain once accomplished. As Lake Kinneret is the only freshwater lake in Israel, it is vital to sustain the lake ecosystem over time. The KSI provides lake managers with a means for assessing the state of the lake. The KSI is based on nine ecosystem variables and provides information on each variable and the combined index. We present examples of application of the KSI to lake management and conduct a sensitivity analysis of the underlying assumptions demonstrating its robustness to the assumptions. While the index presented here is specific to Lake Kinneret, it is a general approach that can be readily applied to lakes worldwide and can assist, for example, in achievement of the required good status for European lakes.

Cyanobacteria are notorious for producing water blooms and for toxin formation. Toxic cyanobacterial blooms present an ever-increasing serious threat to both the quality of drinking water and recreational uses and severely disrupt aquatic ecosystems, worldwide. In many cases, such blooms are dominated by toxic Microcystis sp. that produce a family of structurally similar hepatotoxins, known as microcystins (MCs). Here we present a retrospective analysis of Microcystis seasonal blooms from Lake Kinneret (Sea of Galilee, Israel) indicating that the population is composed of at least 25 different genotypes and two different chemo-types, whose relative abundance changes over decades. Based on a long-term record of biotic and abiotic parameters and laboratory experiments we propose that minor increase in water temperature, but not in salinity, may affect Microcystis community structure by changing the relative abundance of species/strains from toxic to less or non-toxic species.

In European countries, hydromorphological (HyMo) pressures are the second most commonly occurring types of pressures on aquatic ecosystems (after eutrophication). HyMo pressures (i.e., man-made alt...

We developed a computerized image-analysis system, PlanktoMetrix, the first system to conduct all steps of conventional microscope-based phytoplankton and zooplankton analyses (counting, measuring sizes, entering data, computations, storage in database) simultaneously using real-time digital imaging. The microscope field that displays the sample is continuously scanned by a digital camera and screened on a computer monitor, on which cell counts and measurements of linear dimensions are made by mouse clicks. When the microscope tasks are completed, computations of species abundances, estimates of biovolume per individual, species biomass per unit volume, and total assemblage biomass concentration are made automatically and stored into a database. All raw and computed data are exportable to common spreadsheet platforms. PlanktoMetrix offers the production of high-quality data in less time, with lower user fatigue and fewer typing errors; therefore, more time can be devoted to data analysis rather than generation. Furthermore, PlanktoMetrix allows collecting organism size data regularly, thus offering plankton ecologists a tool for following seasonal, ontogenetic, and other well-documented but generally ignored changes in plankton size and morphology. An example of PlanktoMetrix-generated cell size time series shows that the dinoflagellate Peridiniopsis elpatiewskyi undergoes a distinct annual cycle with larger cells in winter and smaller cells in summer. PlanktoMetrix is distributed free to interested users and will likely be available in the future as an open-source platform.

Lakes undergoing major changes in phytoplankton species composition are likely to undergo changes in carbon (C) cycling. In this study we used stable C isotopes to understand how the C cycle of Lake Kinneret, Israel, responded to documented changes in phytoplankton species composition. We compared the annual δ 13 C cycle of particulate organic matter from surface water (POM surf ) between (1) years in which a massive spring bloom of the dinoflagellate Peridinium gatunense occurred (Peridinium years) and (2) years in which it did not (non-Peridinium years). In nonPeridinium years, the spring δ 13 C–POM surf maxima were lower by 3.3‰. These spring δ 13 C maxima were even lower in POM sinking into sediment traps and in zooplankton (lower by 6.8 and 6.9‰, respectively). These differences in the isotopic composition of the major organic C components in the lake represent ecosystem-level responses to the presence or absence of the key blooming species P. gatunense. When present, the intensive, almost monospecific bloom lowers the concentrations of CO 2(aq) , causing a reduction in the isotopic fractionation of the algae (higher δ 13 C of POM surf ) and massive precipitation of calcium carbonate (CaCO 3 ). In non-Peridinium years, the phytoplankton cannot deplete CO 2(aq) to similar levels; the algae maintain higher isotopic fractionation, leading to lower δ 13 C maxima. These changes are reflected higher up in the food web (zooplankton) and in sedimenting organic matter. The consequences for the ecosystem in non-Peridinium years are lower export of both organic and inorganic C.

Alon Rimmer, an outstanding tenacious hydrologist and a devoted editor and mentor passed away on April 22, 2018, at the age of 62, after fighting cancer. Alon was an eloquent writer and speaker who could express difficult concepts in simple terms with well-illustrated drawings. He applied a system approach with mathematical modeling to provide simple and practical solutions to complex problems. He expressed and publicized his scientific opinion even if it opposed the consensus. We will remember Alon’s resolute personality as well as his strong physique. His sense of wisdom, wit, sensitivity, humor, modesty and incredible courage, and continue to apply the computational tools he left us.

Raphidiopsis raciborskii is a tropical toxic cyanobacterium that is rapidly expanding to diverse lake habitats in different climate zones by sophisticated adaptation mechanisms. This meta-analysis investigated correlations of R. raciborskii with water temperature and N:P (nitrogen to phosphorus)-ratios across four lakes with different climates and trophic states by means of long-term time series and the hybrid evolutionary algorithm HEA. The results have shown that in the lakes with temperate and Mediterranean climate, R. raciborskii is strongly correlated with water temperature since germination and growth rely on rising water temperatures in spring. In contrast, there was a weaker correlation with water temperature in subtropical and tropical lakes where pelagic populations of R. raciborskii are overwintering, and are present all year round. However, the highest abundances of R. raciborskii coincided with highest water temperature for the Mediterranean, subtropical and tropical lakes, whilst in the temperate Langer See the highest abundances of R. raciborskii occurred at 24.1 °C, even though temperatures of up to 27 °C were recorded in 2013 and 2014. The correlation of R. raciborskii with N:P-ratios proved to be strongest for the meso- to eutrophic Lake Kinneret (r2 = 0.8) and lowest for the eutrophic Lake Paranoa (r2 = 0.16). However, the assumption has been confirmed that R. raciborskii is growing fastest when waters are N-limited regardless of trophic states. In terms of phenology, the temperate and Mediterranean lakes displayed “fastest growth” in spring and early summer. In contrast, the growing season in subtropical and tropical lakes lasted from spring to autumn most likely because of overwintering populations, and growing importance of direct and indirect biotic regulating factors such as competition, grazing, remineralisation of nutrients along warming climate. In order to carry out a meta-analysis of time series across four different lakes, HEA served as powerful tool resulting in inferential models with predictive capacity for population dynamics of R. raciborskii just driven by water temperature or N:P-ratios, whilst coefficients of determination r2 served as criteria for hypotheses testing.

Allelopathic species can alter biodiversity. Using simulated assemblages that are characterised by neutrality, lumpy coexistence and intransitivity, we explore relationships between within-assemblage competitive dissimilarities and resistance to allelopathic species. An emergent behaviour from our models is that assemblages are more resistant to allelopathy when members strongly compete exploitatively (high competitive power). We found that neutral assemblages were the most vulnerable to allelopathic species, followed by lumpy and then by intransitive assemblages. We find support for our modeling in real-world time-series data from eight lakes of varied morphometry and trophic state. Our analysis of this data shows that a lake's history of allelopathic phytoplankton species biovolume density and dominance is related to the number of species clusters occurring in the plankton assemblages of those lakes, an emergent trend similar to that of our modeling. We suggest that an assemblage's competitive power determines its allelopathy resistance.

The Kinneret phytoplankton biodiversity has been monitored on a regular basis since 1969, with the taxonomic information stored as a digital online catalog ( http://kinneret.ocean.org.il/phyt_cat_listView.aspx ) containing photographs and morphological descriptions. Our aim was to upgrade this ID tool by adding to it a consensus DNA sequence as a species identifier—DNA barcode. A two-gene system approach was applied, sequencing DNA fragments from the Ribulose-1,5-bisphosphate carboxylase oxygenase large subunit (rbcL) and the rRNA small subunit and intragenic space (SSU-ITS). Today, 72 species isolated from Lake Kinneret, are at different stages of processing. The barcoding process was completed for 26 of those. Barcoding has enabled us to support current nomenclature, clarify the taxonomic names of species whose identification was previously inconclusive, classify to species level taxa previously identified to genus only, discover species new to the lake, and update current nomenclature. The construction of the DNA barcode database stands as the first brick of knowledge upon which further experimental work can be conducted, enabling fast and accurate identification of the Kinneret phytoplankton.

The widely used term “stability” has multiple meanings and is rarely quantified in limnological studies. The main objective of this study was to develop an approach for quantifying the stability of a phytoplankton community using Lake Kinneret as a case study. It is a first attempt of calculating an index of stability for each of the five main taxonomic groups of the Kinneret phytoplankton (Bacillariophyta, Chlorophyta, Cryptophyta, Cyanophyta and Dinophyta), and for the entire community. A simple statistical approach to calculate the stability index was devised, using phytoplankton wet-weight biomass as the parameter being manipulated. The period 1970–1979 was selected as a reference period. The following stability indices were established and applied (each at three time scales): (1) a stability index for each of five main taxonomic groups; (2) a combined index of the stability, aggregating the stabilities of the individual taxonomic groups and (3) a stability index of entire community based on total phytoplankton biomass. The dynamics of these indices during 1969–2011 were examined. Destabilization of the community structure was triggered by an increase in the variability of Bacillariophyta biomass shortly after the reference period, in 1981–1983. Only 10 years later, the community destabilization become associated with progressively increasing biomass of Cyanobacteria. Dinophyta were the last to destabilize in the mid 1990s. Despite notable changes in the community structure, the total phytoplankton biomass remained relatively stable. Therefore, in 1969–2011 the stability index based on total phytoplankton biomass was higher than the combined index based on the stabilities of the individual taxonomic groups. Only weak relationships were found between the stability index values and potential driving forces (lake water level fluctuations and nutrient loads). While this approach was applied to Lake Kinneret, the concept presented is not lake specific and could be applied to other lakes.

We examined an 8.5-year record (2004-2012) of cell size data for phytoplankton species from Lake Kinneret, Israel, sampled weekly or at 2-week intervals and determined microscopically by the same person. Many of the species abundant enough to be counted year-round showed a typical seasonal cell size pattern that repeated annually: cell diameter was maximal in winter and minimal in summer. This pattern was shared by species from different taxonomic groups including cyanobacteria, chlorophyta, and dinoflagellates. Similarly, in colonial species of diatoms, chlorophyta, and cyanobacteria the number of cells per colony was larger in winter and smaller in summer. We postulated that the seasonal changes in cell or colony size constituted an adaptation that enabled species to overcome temperature-dependent changes in water density and viscosity and adjust their sinking velocities in the different seasons. A series of computations based on Stokes' law supported our hypothesis. If this phenomenon of larger cells or colonies of the same species at lower temperatures is widespread in lake phytoplankton, then (1) phytoplankton biomass estimates should be based on seasonally determined biovolume per species data rather than fixed values; and (2) we would expect to see smaller-sized organisms in the future as global warming changes ambient temperatures.

The Mediterranean region is both a global biodiversity hot spot and one of the biomes most strongly affected by human activities. Ecologists and land managers are increasingly required to advise on threats to biodiversity under foreseeable climate change. We used expert surveys to evaluate current understanding and uncertainties regarding climate change impacts on biodiversity in terrestrial, inland freshwater, and marine ecosystems of Israel. Finally, we propose a response strategy toward minimizing these changes. The surveys and the published literature indicated that the main climate change impacts in Israel include ongoing deterioration of freshwater habitats, decline of shrubland and woodland areas, and increased frequency and severity of forest fires. For the Mediterranean Sea, the surveys predict further introduction and establishment of invasive species from the Red Sea, accelerated erosion of coastal rocky habitat, and collapse of coastal rocky platforms. In the Gulf of Aqaba, Red Sea, corals may be resilient to foreseen climate change due to their high tolerance for rising water temperatures. Despite these predictions, science-based knowledge regarding the contribution of management toward minimizing climate change impacts on biodiversity is still lacking. Habitat loss, degradation, and fragmentation are presently the primary and immediate threats to natural ecosystems in Israel. Protection of natural ecosystems, including local refugia, must be intensified to maintain existing biodiversity under pressure from mounting urban development and climate change. This protection policy should include ecological corridors to minimize the consequences of fragmentation of existing natural habitats for species survival. A longer-term strategy should mandate connectivity across environmental and climatic gradients to maintain natural resilience by allowing reorganization of natural ecosystems facing climate change.

The hybrid evolutionary algorithm (HEA) was implemented to model and analyze population dynamics of the different phytoplankton phyla (chlorophyta, bacillariophyta, cyanophyta and dinophyta) in relation to physical, chemical, and biological determinants and their combinations in a large lake. Biweekly measurements over a 12-year period were used as input. The validation of models obtained with HEA showed the best results for bacillariophyta and dinophyta resulting in coefficients of determination (r(2)) between the modeled and measured data of 0.54-0.79 and 0.29-0.76 for these phyla, respectively, suggesting good predictability of their dynamics. The lowest adequacy of HEA models was found for cyanophyta (r(2) of 0.28-0.46). Models that combined physical, chemical and biological inputs scored highest, whilst zooplankton-based models scored lowest in all experiments and indicated that top-down control of algal biomass could have only secondary effect. The input sensitivity analysis was used for testing the best phytoplankton models with threshold values determining high or low algal biomass and inhibitory-excitatory effects of specific parameters. Wavelets were tested to analyze two extreme cases of dinophyta dynamics in years of its exceptionally high and low developments to gain insights into lag times between the exert of key factor and algae response. Lag times extracted from daily interpolated data of highly correlated inputs of dinophyta in 1998 varied between 2 and 4 days. Crown Copyright (C) 2013 Published by Elsevier B.V. All rights reserved.

Microcystis sp. are major players in the global intensification of toxic cyanobacterial blooms endangering the water quality of freshwater bodies. A novel green alga identified as Scenedesmus sp., designated strain huji (hereafter S. huji), was isolated from water samples containing toxic Microcystis sp. withdrawn from Lake Kinneret (Sea of Galilee), Israel, suggesting that it produces secondary metabolites that help it withstand the Microcystis toxins. Competition experiments suggested complex interaction between these two organisms and use of spent cell-free media from S. huji caused severe cell lysis in various Microcystis strains. We have isolated active metabolites from the spent S. huji medium. Application of the concentrated allelochemicals interfered with the functionality and perhaps the integrity of the Microcystis cell membrane, as indicated by the rapid effect on the photosynthetic variable fluorescence and leakage of phycobilins and ions. Although some activity was observed towards various bacteria, it did not alter growth of eukaryotic organisms such as the green alga Chlamydomonas reinhardtii.

A long-term record dating back to the 1960s indicates that Peridinium gatunense, an armored dinoflagellate, dominated the phytoplankton of Lake Kinneret (Sea of Galilee, Israel) until the mid-1990s, with a relatively stable spring bloom. However, since 1996, these blooms became irregular, failing to develop in 10 out of the past 16 years. During the later period, a significant correlation (R2 = 0.605, P = 0.013) was found between annual peak P. gatunense biomass and riverine inflow volume. In-lake surveys showed that patches of high P. gatunense densities were associated with water enriched with fresher inflowing Jordan River water. Supplementing laboratory cultures of P. gatunense with Hula Valley water stimulated its growth relative to un-enriched controls. A likely explanation to the recent irregular blooms of this dinoflagellate is a hydrological modification that was made in the catchment in the mid-1990s, preventing Hula Valley water from reaching Lake Kinneret in most years—except for exceptionally wet years. We propose that until the mid-1990s, the Jordan River water enriched Lake Kinneret with a growth factor (a microelement and/or organic compound) originating in the Hula Valley, which in recent years has arrived in sufficient quantities to support a bloom only in high-rainfall years.

A set of satellite images of chlorophyll a concentration for Lake Kinneret (Israel) from the period February to April 2007 captured the temporal evolution of horizontal patchiness that developed during the typical spring bloom of the dinoflagellate Peridinium gatunense. Narrow bands of high concentration located adjacent to the shoreline at the start of the bloom were followed by progressive propagation of this high-concentration region from the shoreline toward the center of the lake as the bloom proceeded. A three-dimensional (3-D) hydrodynamic numerical model and an analytical model for a flat-bottomed elliptical basin together explain the observed phenomenon. The spatial structure of Kelvin waves, which were demonstrated to most likely be present in February and April due to resonance, produced regions of high velocity gradient, contributing to horizontal dispersion close to the shoreline. This region of high dispersion was narrow and close to the shoreline at the start of the bloom when the Burger number was relatively small, but it widened over the course of the season as the Burger number increased due to increasing stratification. In addition, an increase in the dispersion rate with time in the lake interior was inferred from numerical simulation due to increasing wind speeds and a thinner surface layer. Physical processes, in this case, horizontal dispersion as a result of both Kelvin waves and wind, can play an important role in governing the dynamics and spatial evolution of dinoflagellate blooms in lakes. Spatial heterogeneity of phytoplankton is a ubiquitous occurrence in lakes, coastal waters, and the open ocean. Phytoplankton patchiness can be defined by localized, abruptly elevated concentrations. Phytoplankton patches may occur at a broad range of spatial scales, and such

Water levels of lakes fluctuate naturally in response to climatic and hydrological forcing. Human over-exploitation of water resources leads to increased annual and interannual fluctuations of wate...

The association of water level changes and the relative (%) contributions of crustacean zooplankton to particulate N (PNz) and particulate P (PPz) in Lake Kinneret, Israel were studied. The PNz and PPz were assessed for a period of 10 years (1999–2008) in relation to water level (WL) changes which occurred during that period. We estimated PNz and PPz, based on crustacean N and P content measured seasonally over 2 years, and a 10-year record of zooplankton densities. Mean cladoceran N and P contents were 8.7 and 1.2% of dry weight, respectively, while for copepods they were 9.5 and 1.5% of dry weight, respectively. Zooplankton density, and hence PNz and PPz, changed dramatically during the 10 years, concurrent with extreme variations in the lake’s WL. The lowest mean values of PNz and PPz occurred during high WL years and the highest PNz and PPz were during low WL years. PNz and PPz were negatively correlated with the total PN and PP concentrations, respectively, in the lake. The reduction in zooplankton contribution to the particulate N and P during high WL is probably due to higher loading of particulate matter in wet years, causing an increase of PN and PP concentration in the lake, as well as lower densities of zooplankton, caused by higher fish predation pressure, both are a by-product of the large water influx during extreme wet winters.

The hypothesis that physical constraints may be as important, if not more important, than biological ones in shaping the structure of phytoplankton assemblage was tested by analyzing longterm (11–29 years) phytoplankton series in eight lakes and nine sites located along a latitudinal gradient in the Northern hemisphere. Phytoplankton biomass was used and similarity of assemblages in same months of the annual data sets was then calculated by subtracting the Bray–Curtis dissimilarity index from 1. The extent of biological and physical forcing was partly based on ‘‘expert evaluation’’: the importance of four physical (light availability, temperature, conductivity, and sediment stirring up) and five biological variables (basic nutrients [SRP-, DIN-, SRSi-availability] as estimators of competition straight, importance of grazing, and importance of parasitism) was evaluated month by month by arbitrarily scaling from 1 to 5 the intensity of each variable and then summing them in the appropriate subgroup. Since the number of physical variables is less than that of the biological ones, the latter was rescaled to reach the same maximum attainable value of physical variables. The results showed an extremely high variability, making evident that each lake, although showing the same metabolic processes, behaves as an individual with regard to its phytoplankton structure. More generally, it was possible to highlight a largely more important role of physical constraints in shaping both biomass and composition of phytoplankton. This is especially true in winter. In addition, the results were compared to the outcomes of the PEG model, since a plasticity in the structure of phytoplankton much greater than that reported in this widely acknowledged model has been recorded in the data set used. This high variability found in this study in relation to physical constraints might also explain the different patterns of phytoplankton growth observed from Northern temperate to Mediterranean lakes as well as those occurring in shallow and deep lakes.

A member of the cyanobacterial genus Cylindrospermopsis Seenayya et Subba Raju (Order Nostocales) invaded Lake Kinneret (Israel) in 1998. Since then it has been found in the water column nearly every summer, initially at low concentrations, but since 2003 it formed major summer blooms. The goals of the present study were to identify the invading species based on its morphology, annual life cycle, toxicity, genetic markers, and its phylogeny, and to examine its range of morphological variability. Cell counts, allometric measurements, and filament morphology were determined on samples collected weekly from a mid-lake station throughout 2005. Akinetes, heterocytes, filament end types, cellular contents, and the annual cycle of filament morphology were described, supporting the identification as Cylindrospermopsis raciborskii (Woloszynska) Seenayya et Subba Raju. Cells had many small, few large, or no dark granules presumed to be polyphosphate bodies. Filament fragmentation was observed and six types of filament ends were described. Sequence analysis of the 16SrRNA and ITS-L DNA fragment from a laboratory isolate of the cyanobacterium also confirmed the identification as C. raciborskii. Biomass of this species collected from Lake Kinneret during a bloom did not show toxicity in Artemia bioassays, and the toxin cylindrospermopsin was not detected in a methanolic extract of the isolate. Genetic examination indicated that C. raciborskii from Lake Kinneret lacked the cyrJ component of the cylindrospermopsin synthase cluster and, thereby, was incapable of producing the toxin. Due to the morphological plasticity of this species, the identification of C. raciborskii from Lake Kinneret was not straight forward and required taking multiple approaches, including microscopic observations over a full annual cycle, culture isolation, and molecular taxonomy.

Suggett, David J. et. al.-- Contribution to AME Special 2 ‘Progress and perspectives in aquatic primary productivity’.-- 13 pages, 5 figures, Bioassay experiments were performed to identify how growth of key groups within the microbial community was simultaneously limited by nutrient (nitrogen and phosphorus) availability during spring in the Gulf of Aqaba’s oceanic waters. Measurements of chlorophyll a (chl a) concentration and fast repetition rate (FRR) fluorescence generally demonstrated that growth of obligate phototrophic phytoplankton was co-limited by N and P and growth of facultative aerobic anoxygenic photoheterotropic (AAP) bacteria was limited by N. Phytoplankton exhibited an increase in chl a biomass over 24 to 48 h upon relief of nutrient limitation. This response coincided with an increase in photosystem II (PSII) photochemical efficiency (Fv/Fm), but was preceded (within 24 h) by a decrease in effective absorption crosssection (σPSII) and electron turnover time (τ). A similar response for τ and bacterio-chl a was observed for the AAPs. Consistent with the up-regulation of PSII activity with FRR fluorescence were observations of newly synthesized PSII reaction centers via low temperature (77K) fluorescence spectroscopy for addition of N (and N + P). Flow cytometry revealed that the chl a and thus FRR fluorescence responses were partly driven by the picophytoplankton (, We thank the Batsheva de Rothschild Foundation, Bar-Ilan University, the Moshe Shilo Center for Marine Biogeochemistry, and the staff of the Interuniversity Institute for funding and logistic support. Attendance at the workshop was also supported by an international travel grant from the Texas Institute of Oceanography (A.Q.) and EUROCEANS (D.J.S., E.V.D. and T.L.)

A modified type of species size-frequency distribution or "taxonomic size spectrum" (TSS) was applied to analyze phytoplankton structural change under environmental impacts, using Lake Kinneret as a monitoring database. While the ‘traditional’ TSS (TTSS) describes the distribution of the operational taxonomic unit (OTU) number into size classes, the frequency-weighted TSS (FTSS) distributes the frequency of occurrence of OTUs in water samples, accounting for the water mass occupancy by algal species, i.e., the time-spatial structure of the studied assemblage. FTSS consistency was proven for two dramatically different monitoring periods, where the "extreme" period (1996-1999) was characterized by pronounced deformations of the established patterns of phytoplankton annual succession for the "stable" period (1982-1985). Quantitative similarity estimates for the phytoplankton assemblage taxonomic time-spatial structure were produced by cluster analysis. Specific changes in the FTSS fine structure were evident and helpful for diagnostics, being more pronounced during the extreme years. The descriptors providing quantitative similarity comparisons for the aquatic assemblage structure, while not requiring deep taxonomic knowledge, may be helpful for lake managers and environmental agencies.

Phytoplankton concentration in Lake Kinneret (Israel) has varied up to 10-fold in space and time, with horizontal patches ranging from a couple of kilometres to a basin scale. Previous studies have used a 1D model to reproduce the temporal evolution of physical and biogeochemical variables in this lake. The question that arises then is how appropriate is a 1D approach to represent the dynamic of a spatially heterogeneous system, where there are non-linear dependencies between variables. Field data, a N-P-Z model coupled to both a 1D and a 3D hydrodynamic model, a 1D diffusion-reaction equation and scaling analysis are used to understand the role of spatial variability, expressed as phytoplankton patchiness, in the modelling of primary production. The analysis and results are used to investigate the effect of horizontal variability in the forcing and in the free mechanisms that affect the growth of patterns. The study shows that the use of averaged properties in a 1D approach may produce misleading results in the presence of localised patches, in terms of both concentration and composition of phytoplankton. The reason lies in the fact that the calibration process of ecological parameters in the 1D model appears to be site and process specific. That is, it depends on the pattern's characteristics and the underlying physical processes causing them. And this is a critical point for the success of numerical simulations under spatial variability. In this study, it is also shown that a length scale based on diffusion and growth rate of phytoplankton could be used as a criterion to assess the appropriateness of the 1D assumption.

Both theoretical ecology and lake management practices acutely need quantitative assessment tools for the analysis of structural changes taking place in the plankton community. Size spectrum, a tool allowing such assessment, is usually based on size distributions of organisms irrespective of their taxonomy. The size-frequency distribution of taxonomic units in an assemblage, named by us ‘traditional taxonomic size spectrum’ (TTSS), has been applied for over 70 years, but seldom in aquatic ecology. Longterm consistency of phytoplankton TTSS, evidenced even during pronounced ecosystem changes, was described for the subtropical and eutrophic Lake Kinneret, Israel. In the present study, we examine whether consistent TTSS patterns prevail across ecosystems, and apply the TTSS to the phytoplankton of the temperate and oligotrophic Lake Tahoe, USA. A typical annual TTSS pattern was revealed, and its details were analyzed quantitatively by hierarchical cluster analysis. The Tahoe TTSS similarity level during 4 years (Pearson r=0.92 to 0.99) is comparable to that of the Kinneret during its stable period; even for pairs divided by>20 years, r>0.8. While the Tahoe TTSS general pattern resembles that of Lake Kinneret, the two lakes are distinguishable by means of cluster analysis. A high similarity (r=0.91) was found between the eight-year averaged TTSSs of the two lakes. The above results let us suppose that the longterm consistency of the aquatic assemblage taxonomic size structure pattern is a general phenomenon. This pattern deserves special attention at times of accelerated global climate change, acerbated by burgeoning anthropogenic impacts.

In a series of grazer-gradient and dilution microcosm experiments, we compared grazing and nutrient mineralization by naturally co-existing crustacean and microzooplankton assemblages from mesoeutrophic Lake Kinneret. Across two distinct seasonal plankton assemblages, microzooplankton dominated both phytoplankton and bacteria grazing and nitrogen (N) and phosphorus (P) mineralization. Mass-specific ingestion rates by microzooplankton were ,20 times higher than ingestion rates of crustaceans. Although most carbon ingested by microzooplankton was in the form of bacteria, microzooplankton inflicted substantially higher mortalities (both in absolute terms and relative to maximum potential growth rates) on both phytoplankton and bacteria compared with crustaceans. Mass-specific P and N excretion rates were also higher (by 70 and 50 times, respectively) than crustacean excretion rates. These results suggest that microzooplankton grazing and nutrient mineralization are driving forces affecting bacteria and phytoplankton dynamics, playing important roles in carbon and nutrient transfer to upper trophic levels even in pelagic freshwater systems containing abundant crustaceans.

The aim of the study was a search for typical structure patterns of phytoplankton assemblages, based on the long-term dynamics analysis. As a test case we used the interannual phytoplankton variability of Lake Kinneret (Israel). The dominant phytoplankton species (Peridinium gatunense) structure was presented as the frequency-weighted taxonomic size spectrum (TSS) which describes the size distribution of the operational taxonomic unit (OTUj) occurrence frequencies. Using 24 years monitoring data, the TSS annual patterns of P. gatunense were compared. Typical persistent TSS patterns were evident even during years of pronounced deviations from the typical patterns of phytoplankton biomass dynamics and species composition. By correlation analysis, hierarchical cluster analysis and ANOVA the TSS variability was quantified and compared. While the TSS general shape was almost constant, its amplitude variations allowed us to distinguish between three levels of annual bloom intensity.

SUMMARY 1. Through analyses of a 34-year record of phytoplankton, zooplankton and physicochemical parameters from Lake Kinneret, Israel, we show that distinct and persistent phytoplankton assemblage states occurred from winter to summer. 2. The most obvious characteristic of these states was the presence or absence of a spring bloom of the dinoflagellate, Peridinium gatunense. 3. Analyses of the data within the framework of the alternative states model revealed a possible complex triggering mechanism, and system hysteresis. 4. A change in zooplankton biomass and body size coincident with changes in predation pressure associated with the collapse of the Kinneret Bleak, Acanthobrama terraesanctae, fishery appeared to be the ‘slow changing’ variable in the context of the alternative states model. Alternative phytoplankton states were only possible after this variable crossed a threshold in 1993‐94, following the collapse of the fishery. 5. When alternative states were possible, some physicochemical parameters and the structure of the zooplankton assemblage appeared to control which phytoplankton state emerged in a given year. In years without a P. gatunense bloom, important physicochemical parameters in winter included low NO3 loading, high water temperature, high water level, a deeper thermocline, low transparency, high concentrations of NO3 and Cl in the epilimnion, and low concentration of epilimnetic total phosphorus. In addition, the cladoceran Chydorus sphaericus and adults of the copepod Mesocyclops ogunnus were observed in winter in years without a bloom. 6. Zooplankton biomass and body size of some taxa have recovered since the 1993‐94 collapse of the fishery, yet incidence of both phytoplankton states in Lake Kinneret was still possible. Within the framework of the alternative states model, this suggests that the slow changing variable threshold where alternative states became possible is different from the threshold where alternative states will no longer be possible. In other words, the system is characterised by a hysteresis.

Epidemic chytrid fungal infection of Peridinium gatunense, the major bloom-forming dinoflagellate in Lake Kinneret, Israel, is reported for the first time. The fungus, identified as Phlyctochytrium sp. based on morphological and life cycle characteristics, was first observed in December 2000. It rapidly developed into an epidemic, coinciding with a 1000-fold decline in Peridinium density within 9 days of the initial observation of the chytrid. In August 2001 a second fungal epidemic occurred, which was again associated with a Peridinium population crash. In 2002–2003 less dramatic fungal epidemics were recorded, infection prevalence was low and the Peridinium population did not crash. Laboratory experiments demonstrated that healthy Peridinium cells are not prone to fungal infection, mostly stressed or dead cells were infected. In other words, Phlyctochytrium is a saprophyte, possibly a facultative parasite of Peridinium. Probably another pathogen was responsible for the observed bloom crashes and the saprophytic Phlyctochytrium was a secondary parasite, infecting the already moribund cells. The emergence of fungal epidemics in Lake Kinneret could be interpreted as an early signal of ecosystem response to increasing anthropogenic stress.

International audience; Over the last decades, mass developments by the filamentous conjugating green alga Mougeotia have been followed in three large peri-alpine lakes (Lake Geneva, Lake Garda, Lake Maggiore) and in the sub-tropical Lake Kinneret. The aim of this study is to highlight annual and interannual patterns of Mougeotia biomass in the studied lakes and select key environmental parameters that may favour and maintain its mass development. Our results confirm former studies that planktic Mougeotia favours meso-oligotrophic conditions and becomes dominant when annual mean total phosphorus concentrations in the epilimnion fall below 20 A mu g l(-1). This triggering factor has effect with interactions of other environmental circumstances such as the water column stability. Physiological and morphological features of the taxon make it a successful competitor under stratified conditions. Results also showed that in three out of the four studied lakes, the annual peak was higher when the annual population development started earlier. Focusing on Lake Geneva, depth and strength of the thermocline, as well as wind speed in the beginning of summer that can cause nutrient replenishment and mix the epilimnion are key factors in the blooming of the taxon.

It is of great theoretical interest and applied importance to assess the structural change of the aquatic community or assemblage as a whole. Size spectrum, a tool allowing such assessment, most often describes the size distribution of organisms, irrespective of their taxonomy. The size-frequency distribution of taxonomic units in an assemblage is applied more and more often as another special case of size spectrum, and is called here traditional taxonomic size spectrum (TTSS). The Lake Kinneret (Israel) phytoplankton database was used to compare two periods of four years each, one typical and one of an extremely abnormal, perturbed community state. All eight annual TTSS curves had a similar pattern. Hierarchical cluster analysis was used to quantify the similarity between TTSS histograms. For the stable period (1982–1985), the similarity measures (Pearson r) between TTSS of any pair of years were close to the ‘ideal’ value of 1, ranging from 0.927–0.985. For the extremely abnormal period (1996–1999), they had a wider range (0.896–0.980), where the lowest estimates correspond to explicit distortions of the TTSS pattern. So the similarity comparison of TTSS histograms reveals persistent ecosystem characteristics, also giving information on strong perturbations.