Toxic Cyanobacteria

The objective of this study was to investigate the movement of selected contaminants (jour heavy metals) and conventional limnological variables through the lower Saginaw River. We related limnological variables to concentrations of contaminants, determined if sources of these contaminants existed in the lower 8 km of the river, and calculated loadings of materials to Saginaw Bay. Concentrations of most variables changed significantly among the six sampling dates in 1990-1991, while relatively few variables were different among the six sampling stations. Causes of changes in concentrations of variables in the river over time appeared to stem from two factors, seasonality and river discharge. One phase of the sampling program was conducted on six different dates which encompassed river flows ranging from greater than 700 m 3 sec-i to less than 25 m 3 sec-i. The date on which the least river discharge was observed included a flow reversal when Saginaw Bay water intruded into the lower Saginaw River. Statistical analyses showed that temporal variation among variables was due, in part, to fluctuating river discharge and in part to seasonal factors. The relative importance of these two components varied among parameters. For example, total suspended solids were positively correlated with river discharge, while chlorophyll varied more seasonally. In contrast to temporal trends, few parameters varied significantly among the six sampling stations. This was especially true for dissolved and particulate metals. Loadings of key materials to Saginaw Bay from the Saginaw River were generally positively correlated with river discharge. We concluded that most substances entered the river upstream of our study section in the lower 8 km ofthe Saginaw River.

Hydrogen peroxide (H2O2) can be used as an emergency method to selectively suppress cyanobacterial blooms in lakes and drinking water reservoirs. However, it is largely unknown how environmental parameters alter the effectiveness of H2O2 treatments. In this study, the toxic cyanobacterial strain Microcystis aeruginosa PCC 7806 was treated with a range of H2O2 concentrations (0 to 10 mg/L), while being exposed to different light intensities and light colors. H2O2 treatments caused a stronger decline of the photosynthetic yield in high light than in low light or in the dark, and also a stronger decline in orange than in blue light. Our results are consistent with the hypothesis that H2O2 causes major damage at photosystem II (PSII) and interferes with PSII repair, which makes cells more sensitive to photoinhibition. Furthermore, H2O2 treatments caused a decrease in cell size and an increase in extracellular microcystin concentrations, indicative of leakage from disrupted cells. Our fi...

Experiments were run to determine the effect of filtrate from incubated Aphanizomenonflos-aquae on the thoracic appendage beat rate and frequency of postabdominal rejections by Daphnia carinata. Comparisons were made between the response to Aphanizomenon filtrate and to purified saxitoxin (STX). The short-term response pattern to the filtrate included an immediate 30-50% depression of thoracic appendage beat rate and elevation of postabdominal rejection rate followed by slowly decreasing thoracic appendage beat rate and increasing postabdominal rejection rate during the 1 O-min exposure. Animals recovered to pretreatment activity rates in <5 min. A similar response was observed in STX, except that Daphnia began to recover immediately from the thoracic appendage beat rate inhibition. Animals recovered to -60% of pretreatment activity after l-2 h in Aphanizomenon filtrate, whereas in STX they returned to pretreatment activity levels after -1 h of exposure to the neurotoxin. Water from a lake with a winter bloom of A. Jlos-aquae produced the same pattern of thoracic appendage beat rate and postabdominal rejection rate response as seen with the cultured Aphanizomenon. A comparison of responses to STX and the Aphanizomenon filtrate indicates the effect on D. carinata is through chemosensory stimulation rather than neuromotor inhibition.

While transfer of freshwater cyanobacteria to estuaries has been observed worldwide, the associated transfer of cyanotoxins is less often reported, in particular the sediment contribution. During fall 2018, we monitored the co-occurrence of cyanobacteria and microcystin (MC) in both the water column and in surface sediments at 5 stations along a river continuum, from a freshwater reservoir to the coastal area in Brittany, France. Cyanobacteria dominated the phytoplankton community in the water column with high densities at the freshwater sites. Microcystis cells and intracellular MC transfer to estuarine and marine sites were observed with decreasing concentrations in accordance with flow dilution. Extracellular MC showed the opposite trend and increased from upstream to downstream in accordance with the lysing of the cells at elevated salinities. Surface sediment samples contained high densities of colonial Microcystis in freshwater and with decreasing concentrations along the salinity gradient, similarly to cells concentrations in the water column. Intracellular MC was detected in sediment at all sites except at the marine outlet suggesting the survival of intact cells. Extracellular MC concentrations in sediment were up to 5 times higher than intracellular

The trials involved 60,132 GBEBI rice (Oryza glaberrima) seedlings and 4,703 tilapia juveniles with an average weight of 38 ±9.16 g fed with two complementary diets: (AC), (ASF) and a natural food (AN). Stocking density was 1.5 fish/m2. Nine ponds were used, 3 of which were randomly allocated to each feeding treatment to assess fish growth and rice production. Daily rations of 3% of the reared fish biomass were distributed in two meals (9 am and 3 pm). Rice seedlings were transplanted at a spacing of 25 cm x 20 cm. After 180 days of testing, for the complementary ASF and AC diets, the best nutrient quotients (Qn) (2.74 ±0.75) and daily growth (3.47 ±0.88 g/day) were obtained with AC. On the other hand, the highest Qn (4.56 ±1.15) and the lowest daily growth (2.36 ±0.56 g/day) were recorded with ASF.Comparison of all batches showed that fish fed only natural feed (AN) had the lowest daily growth (1.27 ±0.64 g/day). Rice yields where the supplementary feeds ASF (3.04 ± 0.04 t/ha) and AC (3.91 ± 0.40 t/ha) were fed were better than those of AN (control) (2.59 ±0.54 t/ha). This study shows that it is possible to improve the production of O. niloticus merchantable tilapia and the yield of GBEBI rice (Oryza glaberrima) with the use of supplementary feeds in the rice-fish system.

Limited predictability of cyanobacteria and algal harmful blooms (CyanoHABs) impairs the development of adequate water management programs. The Microcystis aeruginosa complex (MAC) is ubiquitous worldwide. Their large colony size and relatively low numerical abundance imply that MAC abundance and presence are usually underestimated in traditional phytoplankton quantifications, which are based on samples of small volume. The objective of this work was twofold: (a) evaluate four sampling strategies of increasing sampling size to detect MAC organisms and (b) asses the predictability of MAC presence using easy-to-measure environmental variables. Sampling strategies were (I) 5-25 mL sedimented water samples inspected under inverted light microscope; (II) 20 L of water samples inspected by on-board naked-eye; (III) samples collected by towing a 25 μm pore size net inspected under light microscope; (IV) naked-eye inspection of 1000-7000 L concentrated water samples collected using a 115 μm-pore plankton net. We evaluated these objectives in a large environmental gradient (800 km) from freshwater to marine water (salinity range = 0-33) covering a wide range of temperatures (10-33°C), underwater turbidity (0-158 NTU) and wind intensity (0-8 ms −1). Classification Random Forest models (presence/absence of MAC organisms) were constructed and evaluated for each strategy by randomly partitioning data into training (2/3) and test (1/3) sets. A systematic increase in average accuracy (from 51 to 90%) and sensitivity (from 45 to 94%) towards methods with larger sampling size was found (i.e. I-IV). The best obtained model showed a high accuracy (90%) and sensitivity (94%) to detect MAC presence. These results suggest that the presence of MAC organisms can be accurately predicted using easyto-measure environmental variables once sampling size is adequate. The proposed methodology demands very low costs and could be readily incorporated in most water monitoring plans to provide early warning of MAC occurrence, even when there is a low biomass of organisms. environment allows the improvement of predictability (Hulot et al., 2000; Kruk et al., 2011; Millie et al., 2014). The Microcystis aeruginosa complex (MAC) is composed by species belonging to Microcystis and similar genera (e.g. Sphaerocavum and Radiocystis) and are among the most common bloom-forming freshwater cyanobacteria around the world (Huisman et al., 2005). MAC species can potentially produce hepato-and neurotoxins (generally known as cyanotoxins) that cause cattle and human intoxication (Azevedo et al., 2002; Giannuzzi et al., 2011; Pearson et al., 2016). Therefore, accurate prediction of their presence is necessary to assist government institutions involved in water resource management, use and conservation. The blooms developed by MAC are superficial, dense and composed by colonies of varying sizes able to regulate their vertical position in the

Modern aquaculture in southern Côte d'Ivoire has encountered difficulties in recent decades, resulting in the closure of several production sites. HYDROFISH in Binger Ville, for example, has been shutting down operations since the end of 2015. As a result, it has enjoyed rigorous management, a production system Super-industrial and the collaboration of the Quebec firm HYDRONOV, a world giant of aquaponics culture. The purpose of this study is to identify the determinants of the modern aquaculture crisis in southern Côte d'Ivoire based on the case of HYDROFISH. The working method used is documentary research and a field survey. Investigations show that the shutdown of the farm's activities is linked to malfunctions in its production system resulting in the death of more than 06 tonnes of fish. Inadequacies in the management of the farm were also noted, with thefts of fish sometimes estimated at more than 4 tonnes per day and selling prices deemed too high by consumers.

Cyanobacteria blooms can be a threat to human health. Drastic changes in cyanobacteria concentrations are often rapid; thus high frequency sampling is required for effective bloom detection and control. Traditional monitoring methods are unsuited to such analysis and can be onerous. On the other hand, in-situ fluorescence probes are currently employed by a number of water utilities in order to obtain near real time water quality monitoring. Nevertheless, to date fluorescence probes can only derive rough estimates of total cyanobacteria concentrations, without discretizing bloom composition to species/genus level. The knowledge of the bloom species' composition can be helpful since some species are known toxin and/or taste and odour producers. The literature shows that different species of cyanobacteria have different tolerances for environmental conditions such as water temperature, pH and nutrition status. In this research, we argue that approaches such as machine learning can be applied to explain and predict species-specific cyanobacteria blooms based on environmental conditions. In particular, the feasibility of a model to predict cyanobacteria bloom species composition through a combination of real-time fluorescence biological data and routine environmental conditions data is discussed. As an example, preliminary analysis from an Australian drinking water reservoir was conducted and showed patterns of dominance and appearance of key species according to environmental conditions. Further, laboratory work combined with fluorescence monitoring of the reservoir indicates potential to couple data-driven species predictions with real time total cyanobacteria monitoring through calibration. The development of such a model could be useful for decision makers to evaluate risk and establish proper management responses.

Cyanobacteria blooms are frequent in freshwaters and are responsible for water quality deterioration and human intoxication. Although, not a new phenomenon, concern exists on the increasing persistence, scale, and toxicity of these blooms. There is evidence, in recent years, of the transfer of these toxins from inland to marine waters through freshwater outflow. However, the true impact of these blooms in marine habitats has been overlooked. In the present work, we describe the detection of Planktothrix agardhii, which is a common microcystin producer, in the Portuguese marine coastal waters nearby a river outfall in an area used for shellfish harvesting and recreational activities. P. agardhii was first observed in November of 2016 in seawater samples that are in the scope of the national shellfish monitoring system. This occurrence was followed closely between November and December of 2016 by a weekly sampling of mussels and water from the sea pier and adjacent river mouth with sa...

Cyanobacteria are a source of potent toxins among which the microcystin (a hepatotoxic peptide encoded by the mcy gene cluster of Microcystis spp.) is a frequent cause of poisoning in inland waters worldwide. Although the molecular basis of microcystin production is known, its role is still unknown. It was suggested that microcystin production have a metabolic cost that could be offset by some benefit (e.g. protection from grazing). We check that: i) microcystin-producing and non-producing strains occurs simultaneously in the Microcystis spp. blooms, ii) evolutionary forces (mutation, genetic drift) control frequencies of microcystin production and non-production strains, and iii) microcystin producing strains have diminished fitness compared with non-producing strains. We employ evolutionary game theory to explain the maintaining of microcystin-producing genotypes in natural populations of Microcystis spp. A two-strategy (to produce or not microcystin), two-players game of cooperators (microcystin-producing genotypes) and cheaters (non-producing genotypes) explains the coexistence of both genotypes in the same bloom. A bloom composed mostly by the microcystin-producing "cooperators" genotype, the "temptation of defection" (increase of non-producing genotypes) is counteracted by kin selection, which enable that natural selection can favour the cooperators. The closest related individuals occur within cyanobacteria blooms, cyanobacteria reproduces asexually providing sets of clones.

The use of iron salts in the control of eutrophication of surface water reservoirs can only be successful if there are no environmental effects. We examined the acute and chronic effects upon Daphnia longispina, the dominant member of the zooplankton. Laboratory tests established that, although dissolved iron had no measurable effect, the presence of particulate iron caused mortalities in acute

Cyanobacteria blooms are frequent in freshwaters and are responsible for water quality deterioration and human intoxication. Although, not a new phenomenon, concern exists on the increasing persistence, scale, and toxicity of these blooms. There is evidence, in recent years, of the transfer of these toxins from inland to marine waters through freshwater outflow. However, the true impact of these blooms in marine habitats has been overlooked. In the present work, we describe the detection of Planktothrix agardhii, which is a common microcystin producer, in the Portuguese marine coastal waters nearby a river outfall in an area used for shellfish harvesting and recreational activities. P. agardhii was first observed in November of 2016 in seawater samples that are in the scope of the national shellfish monitoring system. This occurrence was followed closely between November and December of 2016 by a weekly sampling of mussels and water from the sea pier and adjacent river mouth with sa...

Changing ecological communities in response to anthropogenic activities and climate change has become a worldwide problem. The eutrophication of waterbodies in freshwater and seawater caused by the effects of human activities and nutrient inputs could result in harmful algae blooms (HABs), decreases water quality, reductions in biodiversity and threats to human health. Rapid and accurate monitoring and assessment of aquatic ecosystems are imperative. Environmental DNA (eDNA) analysis using high-throughput sequencing has been demonstrated to be an effective and sensitive assay for detecting and monitoring single or multiple species in different samples. In this study, we review the potential applications of eDNA approaches in controlling and mitigating eutrophication and HABs in freshwater and marine ecosystems. We use recent studies to highlight how eDNA methods have been shown to be a useful tool for providing comprehensive data in studies of eutrophic freshwater and marine environ...

Ivorian aquaculture production reached an estimate of 4500 tons/ year (FAO, 2021a) and that of milled rice recorded an average of 1336446 tons/year (FAO, 2021b). These productions remain low to cover the enormous demands of the Ivorian population despite many years of practice and immense natural potentials (FAO, 2014; ONDR, 2020). Notably,

Ivorian aquaculture production reached an estimate of 4500 tons/ year (FAO, 2021a) and that of milled rice recorded an average of 1336446 tons/year (FAO, 2021b). These productions remain low to cover the enormous demands of the Ivorian population despite many years of practice and immense natural potentials (FAO, 2014; ONDR, 2020). Notably,

This study aimed to evaluate the influence of agricultural by-products on the
proliferation of potentially toxic microalgae in rice-fish farming. For this purpose, an
experiment was carried out in rice-fish culture ponds growing Oreochromis niloticus
with four dietary treatments: corn bran input (RSM), rice bran input (RSR), mixed byproduct input (RPC) and no feed input (RC). Phytotoxic Dinoflagellata and
Cyanobacteria from these ponds were collected monthly for six months. Sampling of
these microalgae was done by water filtration and scraping of the algal biofilm
attached to the submerged parts of the rice stems. In addition, the physico-chemical
parameters of the water in these ponds were measured. The analyses recorded a total of
44 phytotoxic microalgal taxa, including 33 Cyanobacteria and 11 Dinoflagellata with
eight taxa constant in the ponds. The majority of these taxa are likely to produce
hepatotoxins and neurotoxins in the ponds. The absolute density of potentially toxic
pelagic microalgae was significantly higher in RPC (15339 to 24450 Individuals/L)
than that in RC (5586 to13078 Individuals/L). Moreover, the density of potentially
toxic microalgae epiphytic on submerged rice stems was higher in RPC (113.5 to 160.5
Individuals/cm2) than that in RC (85.5 to 115.96 Individuals/cm2). In contrast to other
ponds. Anabaena affinis, Microcystis aeruginosa, Peridinium cinctum and
Protoperidinium sp. were the most abundant. The use of rice bran and its combination
with other agricultural by-products in rice-fish farming results in the proliferation of
toxic Cyanobacteria that would be harmful to fish health.

Cyanobacterial harmful algal blooms (CyanoHABs), mainly composed of the genus Microcystis, occur frequently throughout the Laurentian Great Lakes. We used artificial neural networks (ANNs) involving 31 hydrological and meteorological predictors to model total phytoplankton (as chlorophyll a) and Microcystis biomass from 2009 to 2011 in western Lake Erie. Continuous ANNs provided modeled-measured correspondences (and modeling efficiencies) ranging from 0.87 to 0.97 (0.75 to 0.94) and 0.71 to 0.90 (0.45 to 0.88) for training-cross-validation and test data subsets of chlorophyll a concentrations and Microcystis biovolumes, respectively. Classification ANNs correctly assigned up to 94% of instances for Microcystis presenceabsence. The influences of select predictors on phytoplankton and CyanoHAB niches were visualized using biplots and threedimensional response surfaces. These then were used to generate mathematical expressions for the relationships between modeled CyanoHAB outcomes and the direct and interactive influences of environmental factors. Based on identified conditions (ϳ40 to 50 g total phosphorus (TP)•L −1 , 22 to 26°C, and prolonged wind speeds less than ϳ19 km•h −1) underlying the likelihood of occurrence and accumulation of phytoplankton and Microcystis, a "target" concentration of 30 g TP•L −1 appears appropriate for alleviating blooms. ANNs generated robust ecological niche models for Microcystis, providing a predictive framework for quantitative visualization of nonlinear CyanoHAB-environmental interactions. Résumé : Les fleurs d'eau de cyanobactéries nuisibles (CyanoHAB), constituées principalement du genre Microcystis, sont fréquentes dans tous les Grands Lacs laurentiens. Nous avons utilisé des réseaux neuronaux artificiels (« ANNs ») incluant 31 prédicteurs hydrologiques et météorologiques pour modéliser la biomasse de phytoplancton totale (chlorophylle a) et de Microcystis, de 2009 à 2011, dans la partie occidentale du lac Érié. Des ANNs continus ont fourni des correspondances modèle-mesures (et des valeurs d'efficacité de la modélisation) allant de 0,87 à 0,97 (0,75 à 0,94) et de 0,71 à 0,90 (0,45 à 0,88) pour des sous-ensembles de données d'entraînement-de contrevalidation et d'essai des concentrations de la chlorophylle a et des biovolumes de Microcystis, respectivement. Les ANNs de classification ont affecté correctement jusqu'à 94 % des cas d'absence ou de présence de Microcystis. Les influences de prédicteurs sélectionnés sur les niches de phytoplancton et de CyanoHAB ont été visualisées à l'aide de diagrammes de double projection et de surfaces de réponse tridimensionnelles, qui ont ensuite été utilisés pour produire des expressions mathématiques pour les relations entre les CyanoHAB modélisées et les influences directes et interactives de facteurs environnementaux. À la lumière des conditions cernées (ϳ40 à 50 g phosphore total (PT)•L −1 , de 22 à 26°C et des vitesses du vent soutenues inférieures à ϳ19 km•h −1) sous-tendant la probabilité de présence et d'accumulation de phytoplancton et de Microcystis, une concentration « cible » de 30 g PT•L −1 semble adéquate pour réduire les fleurs d'eau. Les ANNs ont produit des modèles de niche écologique robustes pour Microcystis, fournissant ainsi un cadre prévisionnel pour la visualisation quantitative d'interactions non linéaires entre le milieu ambiant et les CyanoHAB. [Traduit par la Rédaction]

Cyanobacteria are a source of potent toxins among which the microcystin (a hepatotoxic peptide encoded by the mcy gene cluster of Microcystis spp.) is a frequent cause of poisoning in inland waters worldwide. Although the molecular basis of microcystin production is known, its role is still unknown. It was suggested that microcystin production have a metabolic cost that could be offset by some benefit (e.g. protection from grazing). We check that: i) microcystin-producing and non-producing strains occurs simultaneously in the Microcystis spp. blooms, ii) evolutionary forces (mutation, genetic drift) control frequencies of microcystin production and non-production strains, and iii) microcystin producing strains have diminished fitness compared with non-producing strains. We employ evolutionary game theory to explain the maintaining of microcystin-producing genotypes in natural populations of Microcystis spp. A two-strategy (to produce or not microcystin), two-players game of cooperat...

Relationships of body length (L) and filtering rate (fl of four Daphnia species and Holopedium gibber-urn were examined in situ during the day' and night, During the day filtering rates were low and variable. At night filtering rates were higher and more consistent, with large animals filtering at disproportionately high rates. This resulted in regressions of log F vs. log L with intercepts, slopes, and correlation coefficients that were generally lower in the day than at night. Feeding rates u) of Daphnia were calculated with seston ~3 1 pm dry weight as a measure of fcod concentration (c). There were striking differences in the day and night response of feeding rates to food concentration. In the day Daphnia feeding rates increased slowly with increasing food level, reaching fmsX at a relatively high incipient limiting food concentration (ILC), whereas at night feeding rates rose rapidly with food concentration to a maximum about twice the day.&,,, at about half the day ILC. Multiple regression equations were developed to predict F from L and C. Exceptionally high filtering and feeding rates shortly after the upward migration of Daphnia may be due to a daily hunger cycle, although hunger alone does not account for the high filtering activity sustained throughout the night. Diel feeding patterns of large and small D. pulex were asynchronous, resulting in a reversal of the F:L relationship in the early morning when small animals filtered more rapidly than did large animals. Haney Description of the study areas Experiments were done in three hardwater lakes in southern Michigan (Lawrence Lake: 4.

High densities of cyanobacteria can interfere with the use of lakes and reservoirs for recreation and as sources for drinking water, and one approach for reducing the amount of cyanobacteria is to reduce nutrient concentrations in the waterbody. 2. An approach is described for deriving numeric targets for concentrations of total phosphorus (TP) and total nitrogen (TN) that are associated with a pre-specified probability of cyanobacterial biovolume that exceeds the recommended World Health Organization thresholds for recreation in the water. The analysis consisted of two phases. First, a divisive tree algorithm was used to identify groups of lakes in which the relationship between nutrients and cyanobacterial biovolume was similar. Second, hierarchical Bayesian models were used to estimate relationships between cyanobacterial biovolume, TP and TN, while partitioning the observed variance in biovolume into components associated with sampling variability, temporal variability, and among-lake differences. 3. The final model accounted for 91% of the variance in cyanobacterial biovolume among different lakes and was used to identify nutrient concentrations that maintain a low probability of excessively high cyanobacterial biovolumes. 4. When no classes of lakes were specified and the relationship between cyanobacterial biovolume and nutrient concentrations was modelled using a national data set, mean targets of 87 and 1100 lg L À1 were derived for TP and TN, respectively, to maintain cyanobacterial biovolume below moderate risk levels as defined by the World Health Organization. After classification, mean nutrient targets in lakes that were found to be most susceptible to high biovolumes of cyanobacteria (i.e. deep lakes) were 61 and 800 lg L À1 for TP and TN, while higher nutrient thresholds were observed for other classes of lakes.

Phytoplankton abundance and composition and the cyanotoxin, microcystin, were examined relative to environmental parameters in western Lake Erie during late-summer (2003-2005). Spatially explicit distributions of phytoplankton occurred on an annual basis, with the greatest chlorophyll (Chl) a concentrations occurring in waters impacted by Maumee River inflows and in Sandusky Bay. Chlorophytes, bacillariophytes, and cyanobacteria contributed the majority of phylogenetic-group Chl a basin-wide in 2003, 2004, and 2005, respectively. Water clarity, pH, and specific conductance delineated patterns of group Chl a, signifying that water mass movements and mixing were primary determinants of phytoplankton accumulations and distributions. Water temperature, irradiance, and phosphorus availability delineated patterns of cyanobacterial biovolumes, suggesting that biotic processes (most likely, resource-based competition) controlled cyanobacterial abundance and composition. Intracellular microcystin concentrations corresponded to Microcystis abundance and environmental parameters indicative of conditions coincident with biomass accumulations. It appears that environmental parameters regulate microcystin indirectly, via control of cyanobacterial abundance and distribution.

Seasonal variation in phytoplankton size classes was studied over the period of a year in a small, mesotrophic, brown-water lake. Throughout the sampling period, species from 2-16 pm (GALD) dominated the phytoplankton community. Small phytoplankters (2-8 pm) were predominant in winter and early spring populations while algae of 8-16 pm became important in summer (phytoplankton < 2 pm was not counted). Principal coordinate analysis resulted in a cyclic pattern of dates in the reduced space, winter and early spring samples being well separated from the other dates. In multiple linear regressions between environmental parameters and important variable.

We examined changes in phytoplankton community composition in Lake Simcoe, Ontario, Canada, from 1980 to 2007. Diatom and total algal biovolume decreased significantly (P b 0.01) in Cook's Bay, the most eutrophic part of the lake, and the abundance of chlorophytes and cyanobacteria decreased significantly in all basins (P b 0.01). These group-level changes coincided with phosphorus load reductions during the 1980s and early 1990s. There was a period of low and interannually consistent total algal biovolume at stations in Cook's Bay and the main basin of the lake following the establishment of zebra mussels in the mid-1990s. However, there were increases after 2004 that are inconsistent with a sustained zebra mussel grazing effect. In contrast, there was a notable and sustained shift in community composition at the genus and species level that coincided with the invasion of the lake by zebra mussels, in particular a decrease in the abundance of Stephanodiscus spp. and an increase in the abundance of Fragilaria spp. This shift was related to an increase in reactive Si concentration and increased water clarity and occurred during a period of increasing water column stability. Overall, there have been notable changes in the biomass and community composition of the phytoplankton of Lake Simcoe over the last three decades related to nutrient load reductions, the timing of the invasion of the lake by zebra mussels, and increasing water column stability.

Individual Daphnia l?tlZex were tested for activity responses in different wavelengths of light at the same intensity and at different times of day in white light at fixed intensity. The distance a claphnid moved in 5 min varied invcrscly with the wavelength of incident light. Daphnids tcndecl to move vertically between 480 nm (blue) and 735 nm (red) and horizontally at 440 nm (violet) and in white light; this observation corroborates Smith and Baylor's description of color dances. Daphnia pulex has a circadian activity rhythm. Total activity was low at night, increased to a peak in the morning, then declined through the afternoon.

Individual Daphnia l?tlZex were tested for activity responses in different wavelengths of light at the same intensity and at different times of day in white light at fixed intensity. The distance a claphnid moved in 5 min varied invcrscly with the wavelength of incident light. Daphnids tcndecl to move vertically between 480 nm (blue) and 735 nm (red) and horizontally at 440 nm (violet) and in white light; this observation corroborates Smith and Baylor's description of color dances. Daphnia pulex has a circadian activity rhythm. Total activity was low at night, increased to a peak in the morning, then declined through the afternoon.

Phytoplankton and Microcystis aeruginosa (Kütz.) Kütz. biovolumes were characterized and modeled, respectively, with regard to hydrological and meteorological variables during zebra mussel invasion in Saginaw Bay (1990-1996). Total phytoplankton and Microcystis biomass within the inner bay were one and one-half and six times greater, respectively, than those of the outer bay. Following mussel invasion, mean total biomass in the inner bay decreased 84% but then returned to its approximate initial value. Microcystis was not present in the bay during 1990 and 1991 and thereafter occurred at ⁄ in 52% of sample sites ⁄ dates with the greatest biomass occurring in 1994-1996 and within months having water temperatures >19°C. With an overall relative biomass of 0.03 ± 0.01 (mean + SE), Microcystis had, at best, a marginal impact upon holistic compositional dynamics. Dynamics of the centric diatom Cyclotella ocellata Pant. and large pennate diatoms dominated compositional dissimilarities both inter-and intra-annually. The environmental variables that corresponded with phytoplankton distributions were similar for the inner and outer bays, and together identified physical forcing and biotic utilization of nutrients as determinants of system-level biomass patterns. Nonparametric models explained 70%-85% of the variability in Microcystis biovolumes and identified maximal biomass to occur at total phosphorus (TP) concentrations ranging from 40 to 45 lg AE L)1. From isometric projections depicting modeled Microcystis ⁄ environmental interactions, a TP concentration of <30 lg AE L)1 was identified as a desirable contemporary ''target'' for management efforts to ameliorate bloom potentials throughout mussel-impacted bay waters.

Phytoplankton biomass within the Saginaw Bay ecosystem (Lake Huron, Michigan, USA) was characterized as a function of select physical/chemical indicators. The complexity and variability of ecological systems typically make it difficult to model the influences of anthropogenic stressors and/or natural disturbances. Here, Artificial Neural Networks (ANNs) were developed to model chlorophyll a concentrations, a measure for water-column phytoplankton biomass and a proxy for system-level health. ANNs act like "black boxes" in the sense that relationships are encoded as weight vectors within the trained network and as such, cannot easily support the generation of scientific hypotheses unless these relationships can be explained in a comprehensible form. Accordingly, the 'knowledge' and/or rule-based information embedded within ANNs needs to be extracted and expressed as a set of comprehensible 'rules'. Such extracted information would enhance the delineation and understanding of ecological complexity and aid in developing usable prediction tools. Comparisons of various computational approaches (including TREPAN, an algorithm for constructing decision trees from neural networks) used in extracting rule-based information from trained Saginaw Bay ANNs are discussed.

An artificial neural network (ANN)-based technology e a 'Grey-Box', originating the iterative selection, depiction, and quantitation of environmental relationships for modeling microalgal abundance, as chlorophyll (CHL) a, was developed and evaluated. Due to their robust capability for reproducing the complexities underlying chaotic, non-linear systems, ANNs have become popular for the modeling of ecosystem structure and function. However, ANNs exhibit a holistic deficiency in declarative knowledge structure (i.e. a 'black-box'). The architecture of the Grey-Box provided the benefit of the ANN modeling structure, while deconvolving the interaction of prediction potentials among environmental variables upon CHL a. The influences of (pairs of) predictors upon the variance and magnitude of CHL a were depicted via pedagogical knowledge extraction (multi-dimensional response surfaces). This afforded derivation of mathematical equations for iterative predictive outcomes of CHL a and together with an algorithmic expression across iterations, corrected for the lack of declarative knowledge within conventional ANNs. Importantly, the Grey-Box 'bridged the gap' between 'white-box' parametric models and black-box ANNs in terms of performance and mathematical transparency. Grey-Box formulations are relevant to ecological niche modeling, identification of biotic response(s) to stress/disturbance thresholds, and qualitative/quantitative derivation of biota-environmental relationships for incorporation within stand-alone mechanistic models projecting ecological structure.

Phytoplankton samples were collected during July, August, and October of 1981 from 16 stations located in the nearshore of Lake Ontario and in the Oswego Harbor and river. Phytoplankton assemblages observed represented many species widely recognized as associated with eutrophic environments and environments possessing high chloride levels. Picoplankton and diatoms were the dominant groups on a numerical and biovolume basis, respectively. The eutrophic species Stephanodicus tenuis, Fragilaria capucina, and Scenedesmus spp. were present in the Oswego Harbor and river with substantially higher abundances than in the nearshore region of Lake Ontario. A decrease in abundance of the historically prevalent Asterionella and Tabellaria and an increase in cryptomonads is suggestedfor the Oswego area. Halophilic species dominated the diatom assemblage of the Oswego Harbor and mouth of the Oswego River. The abundance of halophilic species was correlated with high conductivity and chloride levels. Cyclotella atomus, Cyclotella cryptica, and Cyclotella meneghiniana, the dominant halophilic species at the harbor and river stations, accounted for 36.6% of the total diatom abundance.

The feeding abilities of Daphnia pulex were investigated by offering it suspensions of the small alga Chlamydomonas minutissima and its larger congener Chlamydomonas capensis. The suspensions differed in the relative abundance of the two algae and in tl e presence or absence of intermediately sized latex spheres. The experiments were designed to distinguish between mechanistic and behavioral modes of feeding. Daphnia showed marked flexibility in its feeding patterns, consistent with the behavioral hypothesis. It preferred to feed on C. minutissima. Significant feedir g on C. capensis occurred only when C. capensis-conditioned animals were presented suspensions relatively low in C. minutissima or in the presence of latex spheres. Analysis of gut contents revea.ed a reduction in the ingestion of latex spheres over time. Total carbon and life history analyses suggest that the preferred food, C. minutissima, is the superior food as well.

Phytoplankton are an important element in the ecology of lakes and reservoirs and therefore often included in lake monitoring programmes. However, algal distribution is often highly variable in both time and space, thereby posing difficulties when designing lake monitoring strategies. This study describes the spatial distribution of both total phytoplankton community structure and cyanobacterial biovolume during a period of high algal abundance in Lake Mulwala, a water-storage reservoir in Australia. The distribution of phytoplankton is then used for the rational design of monitoring strategies with sufficient statistical power to determine both changes in overall phytoplankton community structure over time, as well as to fulfil statutory cyanobacterial biovolume monitoring obligations.

The management of lakes requires the definition of physico-chemical thresholds to be used for ecosystem preservation or restoration. According to the European Water Framework Directive, the limits between physico-chemical quality classes must be set consistently with biological quality elements. One way to do this consists in analyzing the response of aquatic communities to environmental gradients across monitoring sites and in identifying ecological community thresholds, i.e. zones in the gradients where the species turnover is the highest. In this study, fish data from 196 lakes in France were considered to derive ecological thresholds using the multivariate method of gradient forest. The analysis was performed on 25 species and 36 environmental parameters. The results revealed the highest importance of maximal water temperature in the distribution of fish species. Other important parameters included geographical factors, dissolved organic carbon concentration and water transparency, while nutrients appeared to have low influence. In spite of the diversity of species responses to the gradients, community thresholds were detected in the gradients of the most important physico-chemical parameters and of total phosphorus and nitrate concentrations as well. The thresholds identified in such macroecological study may highlight new patterns of species natural distribution and improve niche characterization. Moreover, when factors that may be influenced by human activities are involved, the thresholds could be used to set environmental standards for lake preservation.

Long-term monitoring of aquatic ecosystems is essential to distinguish the effects of human-induced stressors from natural patterns of ecologic variation, especially in Great Lakes Area of Concern such as Muskegon Lake. Samples collected between 2003-2009, as part of a continuing long-term monitoring study of the lake, were analyzed to: 1) detect spatial and temporal patterns in the phytoplankton biovolume and species composition; 2) evaluate the environmental variables that regulate phytoplankton community composition changes; and 3) determine the ecological conditions under which toxin-producing Microcystis species occur. Distinct patterns in Muskegon Lake phytoplankton were not evident among sites, which can be explained, at least in part, by the well-mixed waters in this drowned river mouth system. However, surface and bottom samples within sites had significantly different biovolume and species composition, suggesting that horizontal mixing did not extend throughout the water column. Surface samples had greater phytoplankton biovolume than bottom samples, possibly because of greater irradiance. Seasonally, the least biovolume was recorded in spring samples, which were dominated by diatoms. Phytoplankton biovolume was greatest in the summer when cyanobacteria were abundant. Environmental variables that correlated highly with the ordination space defined by species composition included sulfate, specific conductance, total dissolved solids, and chloride. Results from regression tree analysis predicted increasing biovolume of Microcystis aeruginosa with increasing concentrations of the total Kjeldahl nitrogen. The seven-year period of this study did not reveal major changes in the lake's environment and phytoplankton communities, but the presence of invasive and toxin-producing species warrants their continued monitoring.

The use of iron salts in the control of eutrophication of surface water reservoirs can only be successful if there are no environmental effects. We examined the acute and chronic effects upon Daphnia longispina, the dominant member of the zooplankton. Laboratory tests established that, although dissolved iron had no measurable effect, the presence of particulate iron caused mortalities in acute tests (48 hours) and reduced number of broods per female and numbers of young hatching in chronic tests (21 days). At 11.48 mg Fe l −1 , 50% mortalities occurred in the population, whilst 4.49 mg Fe l −1 caused reductions in reproduction and increased mortality rates over 21 day tests. In inert china clay, similar results were observed, suggesting that it was the particulate nature of the ferric sulphate that caused the effects, rather than any toxic properties. A safe level of 1.69 mg Fe l −1 was calculated. The area of the filter of the third thoracic limb of the daphnids, from both the laboratory cultures and the south arm of Rutland Water (which received ferric-dosed inlet water) increased in size in the presence of ferric sulphate and china clay in chronic tests. This is a response to low food concentrations. Abnormal feeding behaviour was also observed in ferric sulphate. Thoracic beat rate, decreased in ferric sulphate but was unaffected in china clay. This suggested that the feeding rate depression was a response to the chemical nature of the ferric sulphate, rather than its particulate nature. The number of times that particles were rejected from the food groove increased in both ferric sulphate and china clay, in response to large clumps of these substances collecting there.

Resumo A estimativa do biovolume celular, baseada em medidas de dimensões lineares da forma, adaptadas a modelos geométricos padronizados, é importante para o estudo da ecologia do fitoplâncton. Contudo, cálculos demorados são demandados para a estimativa do biovolume a partir de medidas lineares. Neste trabalho, uma ferramenta de software simples é apresentada para auxiliar no cálculo do biovolume das amostras de fitoplâncton, usando modelos geométricos e observações microscópicas convencionais. O software BioCalc implementa as fórmulas mais recentes disponíveis na literatura para calcular o biovolume celular com base em um conjunto de 31 formas geométricas. Palavras-Chave: biovolume, fitoplâncton, morfometria, software. Abstract The estimate of cell biovolume, based on measurements of linear dimensions of shapes adapted to standard geometric models, is important for the study of phytoplankton ecology. However, time-consuming calculations are required for the estimation of biovolume from linear measurements. In this paper, a simple, user-friendly multiplatform software tool is presented to aid in the calculation of the biovolume of phytoplankton samples, using geometric models and conventional microscopic observations. The BioCalc software implements the most recent formulae available in the literature for calculating cell biovolume on the basis of a set of 31 geometric shapes.

Zooplankton grazing was measured in Albufera of València (Spain), a shallow turbid hypertrophic lagoon dominated by filamentous bluegreens, during the period of Daphnia magna growth, to evaluate the role of this cladoceran in maintaining a clear water phase which takes place after flushing for rice cultivation practices. We found extremely low ingestion and clearance rates (CR) on latex beads in situ, using a Haney trap suggesting potentially strong inhibition of grazing by the filamentous cyanobacteria, still flourishing in the lagoon. To test the effect of filaments, we undertook laboratory feeding experiments using six different dilutions of the lagoon water to vary filament concentrations, and four different bead concentrations. A highly significant power function between CR and water dilution associated with filament concentrations was found, indicating that the ability of Daphnia to exploit smaller edible algae and thereby control phytoplankton growth would depend on filament concentration levels in the lagoon. From our results only the two more diluted treatments, 9 · 10 3 and 18 · 10 3 filament ml À1 showed CRs not far from the range of what would be normally expected on the basis of the general relationship of feeding rate as a function of total food concentration. This means that at lower food concentrations, filaments reduce D. magna CR by increasing total food concentration beyond the incipient limiting level, as well as by moderate mechanical interference with the animal's feeding. However, at lagoon water concentrations above 25% (corresponding to filament concentrations of 75 · 10 5 filaments ml À1 ), extremely low CR's, which did not respond to any food addition, were obtained for D. magna. From these results we can infer that at concentrations beyond the above-mentioned critical level, feeding inhibition by filamentous cyanobacteria is most probably due entirely to mechanical interference.

Predictive models based on broad scale, spatial surveys typically identify nutrients and climate as the most important predictors of cyanobacteria abundance; however these models generally have low predictive power because at smaller geographic scales numerous other factors may be equally or more important. At the lake level, for example, the ability to forecast cyanobacteria dominance is of tremendous value to lake managers as they can use such models to communicate exposure risks associated with recreational and drinking water use, and possible exposure to algal toxins, in advance of bloom occurrence. We used detailed algal, limnological and meteorological data from two temperate lakes in south-central Ontario, Canada to determine the factors that are closely linked to cyanobacteria dominance, and to develop easy to use models to forecast cyanobacteria biovolume. For Brandy Lake (BL), the strongest and most parsimonious model for forecasting % cyanobacteria biovolume (% CB) included water column stability, hypolimnetic TP, and % cyanobacteria biovolume two weeks prior. For Three Mile Lake (TML), the best model for forecasting % CB included water column stability, hypolimnetic TP concentration, and 7-d mean wind speed. The models for forecasting % CB in BL and TML are fundamentally different in their lag periods (BL ¼ lag 1 model and TML ¼ lag 2 model) and in some predictor variables despite the close proximity of the study lakes. We speculate that three main factors (nutrient concentrations, water transparency and lake morphometry) may have contributed to differences in the models developed, and may account for variation observed in models derived from large spatial surveys. Our results illustrate that while forecast models can be developed to determine when cyanobacteria will dominate within two temperate lakes, the models require detailed, lake-specific calibration to be effective as risk-management tools.

Grazing rates of Daphnia sp. and Diaptomus oregonensis measured using an in situ method (Haney 1971) were compared with rates measured by collecting animals in vertical townets and placing them in experimental chambers either immediately or after a 24-h acclimation period. Experiments with acclimation yielded grazing rates of Daphnia that were statistically higher than in situ rates, whereas experiments conducted without acclimation yielded significantly lower rates. In situ grazing rates of Diaptomus were statistically higher than those for both townet techniques; experiments without an acclimation yielded higher rates than those for experiments with a 24-h acclimation period.

In the Laurentian Great Lakes, phytoplankton growth and biomass are secondarily limited by silica (Si), as a result of phosphorus (P) enrichment. Even modest levels of P enrichment can induce secondary Silimitation, which, in turn, promotes a shift from the native diatom phytoplankton flora to chlorophyte and cyanobacteria species. However, very little is known about the nutritional status of benthic populations and their response to nutrient enrichment. Two experiments were performed in the littoral zone of Lake Michigan where nutrients were delivered to in situ benthic algal (episammic and epilithic) assemblages using nutrient-diffusing substrata. In order to test the hypothesis that benthic algae in Lake Michigan are Si limited, a 2 Â 3 factorial experiment was used to deliver all combinations of Si, N, and P to resident assemblages growing on artificial substrata composed of natural (Si rich) versus calcium carbonate (Si poor) sand. A second experiment utilized a serial enrichment to evaluate the role of Si in mediating changes in taxonomic composition. These findings indicate that benthic algae in Lake Michigan exhibit signs of secondary Si limitation, and that their response to enrichment is similar to the phytoplankton. Moreover, natural sand substrata may provide a source of Si to resident benthic algae.

Morphological variation in Daphnia cucullata Sars was studied from 1994 to 2001 when fast increasing water trophy of the Siemiano´wka Reservoir was related to high TP and chlorophyll concentrations. During this period, D. cucullata biomass, as well as its contribution to the total cladocerans biomass clearly decreased. We found that among the six morphological parameters analyzed in D. cucullata, body length, height of the head and length of the tail spine had a tendency to decrease. The maximum values of these traits and carapace length also decreased. The morphology of D. cucullata appeared to be influenced by factors such as food availability, fish predation and an exclusive presence of D. cucullata among Daphniidae species. Increased water mixing in the reservoir may have also affected the changes in the head inclination of D. cucullata.

Microalgal biovolume is commonly calculated to assess the relative abundance (as biomass or carbon) of co-occurring algae varying in shape and/or size. However, a standardized set of equations for biovolume calculations from microscopically measured linear dimensions that includes the entire range of microalgal shapes is not available yet. In comparison with automated methods, the use of microscopical measurements allows high taxonomic resolution, up to the species level, and has fewer sources of error. We present a set of geometric shapes and mathematical equations for calculating biovolumes of Ͼ850 pelagic and benthic marine and freshwater microalgal genera. The equations are designed to minimize the effort of microscopic measurement. The similarities and differences between our proposal for standardization and previously published proposals are discussed and recommendations for quality standards given.

Length-weight relationships, feeding rates, and surface area and morphology of the third and fourth thoracic limbs of Daphnia carinata and Ceriodaphnia quadrangula s.1. were examined. Weight ( W ) increased between the square and cube of body length (L), W = 7 . 8 8 X lo-' L2.23, W = 1 .7 X L2.26 for D. carinata and C. quadrangula s.l., respectively. Both cladocerans had small (<0.3 pm) intersetular distances. Surface areas (A) of limbs I11 and IV increased as a power function of body length: A = 5 . 3 5 X L2.0 (D. carinata); A = 1 . 2 2 L 1 , 6 (C. quadrangula s.1.). Reynolds number was < 1; boundary layers surrounding the setules overlapped at beat rates of 5 and 16 cycles s-I. Filtering rates ( K ) for both species increased with increasing body length according to K = 1 . 8 x L2.0 (D. carinata) and K = 1 . 3 X 10+ L2.2 (C. quadrangula s.1.). K also increased as a power function of limb surface area. Filtering rates on Ankistrodesmus falcatus decreased above cell concentrations of c. lo4 cells ml-I. Hourly feeding rates (No. of cells per animal) increased with increasing cell concentration up to the incipient limiting concentrations and thereafter remained relatively stable. Weight-specific feeding rates for D. carinata decreased with increasing body size but for C. quadrangula s.1. remained relatively constant. D. carinata positively selected particles in the size range 4 . 8 -7 . 0 pm, whereas C. quadrangula s.1. showed no particle preference within the size range 3-12 pm. Both cladocerans showed differences in their feeding behaviour when offered a range of phytoplankton species but both fed most efficiently on A. falcatus. Although these cladocerans had limb morphologies that differentiated them from their Northern Hemisphere counterparts, this was not reflected in their feeding behaviour.

Experiments were run to determine the effect of filtrate from incubated Aphanizomenonflos-aquae on the thoracic appendage beat rate and frequency of postabdominal rejections by Daphnia carinata. Comparisons were made between the response to Aphanizomenon filtrate and to purified saxitoxin (STX). The short-term response pattern to the filtrate included an immediate 30-50% depression of thoracic appendage beat rate and elevation of postabdominal rejection rate followed by slowly decreasing thoracic appendage beat rate and increasing postabdominal rejection rate during the 1 O-min exposure. Animals recovered to pretreatment activity rates in <5 min. A similar response was observed in STX, except that Daphnia began to recover immediately from the thoracic appendage beat rate inhibition. Animals recovered to -60% of pretreatment activity after l-2 h in Aphanizomenon filtrate, whereas in STX they returned to pretreatment activity levels after -1 h of exposure to the neurotoxin. Water from a lake with a winter bloom of A. Jlos-aquae produced the same pattern of thoracic appendage beat rate and postabdominal rejection rate response as seen with the cultured Aphanizomenon. A comparison of responses to STX and the Aphanizomenon filtrate indicates the effect on D. carinata is through chemosensory stimulation rather than neuromotor inhibition.

Experiments were run to determine the effect of filtrate from incubated Aphanizomenonflos-aquae on the thoracic appendage beat rate and frequency of postabdominal rejections by Daphnia carinata. Comparisons were made between the response to Aphanizomenon filtrate and to purified saxitoxin (STX). The short-term response pattern to the filtrate included an immediate 30-50% depression of thoracic appendage beat rate and elevation of postabdominal rejection rate followed by slowly decreasing thoracic appendage beat rate and increasing postabdominal rejection rate during the 1 O-min exposure. Animals recovered to pretreatment activity rates in <5 min. A similar response was observed in STX, except that Daphnia began to recover immediately from the thoracic appendage beat rate inhibition. Animals recovered to -60% of pretreatment activity after l-2 h in Aphanizomenon filtrate, whereas in STX they returned to pretreatment activity levels after -1 h of exposure to the neurotoxin. Water from a lake with a winter bloom of A. Jlos-aquae produced the same pattern of thoracic appendage beat rate and postabdominal rejection rate response as seen with the cultured Aphanizomenon. A comparison of responses to STX and the Aphanizomenon filtrate indicates the effect on D. carinata is through chemosensory stimulation rather than neuromotor inhibition.

Analysis ofphytoplankton samples from the Straits of Mackinac region yielded high species diversity and species richness values at the outfall of the St. Marys River due to entrained benthic diatoms. Epilithic, psammonic, epipelic, and epiphytic diatoms originating in the St. Marys River and Detour Passage area were removed from their primary habitats and transported into northern Lake Huron. Southward movement of the St. Marys River plume, as determined from suspended benthic diatom distribution and abundance, was strongly indicated for 3 km. Moderate influence of the plume was noted at 6 km and weaker association with the plume was detected for as far as 32 km. Apparently, loss of suspended riverine species from the upper water column in this area was primarily due to sinking. Sinking, calculatedfrom residence times based on river discharge data, was estimated to range between 0.76 and 5.99 mjday. Total phytoplankton abundance and chlorophyll a values were lower near the rivermouth. Conversely, l4C uptake was significantly greater near the river. Benthic populations comprised as much as 40% of the assemblage and an additional amount of dead and fragmentary diatoms was also observed. Viable benthic diatoms may contribute as much as 25% of the algal assemblage on a cell volume basis. Upon death and decomposition, they may constitute an important source of carbon and nutrients in the immediate vicinity. ADDITIONAL INDEX WORDS: Distribution, water mass, sinking rates, zooplankton grazing, benthic diatoms.