Cyanobacteria Density Research Articles

Phytoplankton scenario and microcystin in water during extreme drought in semiarid tropical water supplies, Northeastern Brazil.

The objective of this study was to characterize the limnological, microystin and phytoplankton community of five tropical eutrophic reservoirs located in the Brazilian northeastern semi-arid region, used for domestic use at the time of extreme drought and reduction of water volume. The study was conducted in July and August 2015, and an integrated sample of the water column was collected at three points near the dam in each reservoir. Analysis of limnological parameters, identification and quantification of phytoplankton, with emphasis on cyanobacteria were performed, as well as detection of microcystin by means of immunoassay (ELISA). The reservoirs presented ~ 90% water volume reduction. High turbidity and concentrations of nitrogen and phosphorus, as well as high cyanobacterial densities, revealed an increase in the eutrophic state for hypereutrophy. The total biovolume of phytoplankton and cyanobacterial density is high, plus an average increase in relation to previous studies of 350% and 150%, respectively. The density of cyanobacteria and microcystin concentration presented values ​​above acceptable levels for drinking water according to Brazilian legislation. A phytoplankton community was represented by 17 functional groups, including potentially toxic cyanobacteria species such as Planktothrix agardhii (S1), Microcystis aeruginosa (M), Anabaena planktonica e Anabaena spp. (H1), Cylindrospermopsis raciborskii (Sn). Our results confirm that conditions of extreme drought and reduction of the volume of the reservoirs influence the composition, biovolume of phytoplankton and water quality, but not the increase of total microcystin in the analysed, although above 1μg-1 registered a significant decrease of water quality in used for human consumption.

Seasonal variation and potential risk assessment of microcystins in the sediments of Lake Taihu, China

High concentrations of microcystins (MCs) in sediment pose a serious hazard to aquatic and terrestrial organisms. Hence, we investigated the seasonal variation of dominant MCs (MC-LR, MC-RR and MC-YR) in sediments of Lake Taihu over four seasons for the first time. Sediment MCs varied seasonally (p < 0.01) with concentrations highest in August and lowest in February. The MCs were dominated by MC-LR (61.47%) with the content ranging from 0.02 to 2.37 μg/g dry weight in sediment. The three MC congeners and their proportions were significantly correlated with latitude and longitude. Meiliang Bay in the north had the highest MCs of all sites, while the eastern part of the lake had a high level especially in August. Variation of MC-LR and MC-RR concentrations was significantly correlated (p < 0.05) with water temperature, dissolved total organic carbon, cyanobacteria density, total suspended solid particles, and total organic carbon and total nitrogen in sediment, while MC-YR was negatively correlated (p < 0.01) with nutrients in the water column and heavy metals in sediments. An ecological risk assessment suggested the MCs already pose significant adverse effects on Potamopyrgus antipodarum; although the adverse effects on humans were weak, children were at greater risk than adults.

Morphological characteristics of cyanobacteria and dominant phytoplankton in reservoirs in Antioquia: a focus based in biovolume

Cyanotoxin contamination is of special interest in water bodies, especially those for human use, due to the various negative effects that blooms of potentially toxic cyanobacteria can cause on human health. Given the recreational and supply importance of the Abreo - Malpaso, Penol - Guatape and Playas reservoirs in the Department of Antioquia, Colombia. This study has estimated the biomass of the planktonic cyanobacteria, their geometric biovolume, the surface volume ratio (S / V) and the maximum linear dimension (MLD), during four sampling seasons in three different stations for each of these bodies. Water. We have identified from the Cyanophyta division with the production of cyanotoxins, the Microcystis complex and generates Woronichinia, Aphanocapsa and Oscillatoria, as well as the species Radiocystis fernandoi. When applying the nonparametric Kruskal - Wallis test, no significant differences were found between the studied reservoirs (p> 0.05); however, the Penol - Guatape reservoir presented the highest algae biomass and density of cyanobacteria, therefore, according to the levels of risk posed for the reservoirs studied and according to the morphological characteristics of these organisms, this reservoir presents a High Medium risk level in relation to the presence and morphology of the cyanobacteria, while the Abreo-Malpaso and Playas reservoirs are associated with a Medium Low risk. It is suggested to establish control and prevention measures to avoid a massive development of cyanobacteria, a possible presence of cyanotoxins and serious affectations in humans and animals.

An attempt to measure longitudinal connectivity based on the community structure of phytoplankton.

At present, there are few studies on the quantitative analysis of connectivity from the perspective of biocenology. This study aimed to develop a new quantitative assessment method for river connectivity based on the analysis of the effect of river connectivity on the phytoplankton community in the Shaying River, which has multiple gates. The results showed that from the view of the phytoplankton density and biomass, cryptophytes were the dominant phytoplankton group, but the cyanobacteria density was highest in the summer. In the top 10 of degrees of dominance, there were 4 species of cyanobacteria, 3 species of cryptophytes, 2 species of diatoms, and 1 species of chlorophytes. Based on the seasonal compositions and variations of the phytoplankton community, the river barriers had a great effect on the community. The community composition of the Shaying River has been transformed from a river-type community dominated by diatoms to a lake-type community dominated by cyanophytes. PCA (principal component analysis) indicated that there were obvious differences in the community structure among the sections partitioned by various river gates. According to the relative positions of the entire phytoplankton community and the relative sequence of the river gates, a potential gradient representing the river connectivity can be found; thus, the river connectivity can be quantitatively described from the perspective of the phytoplankton community, and hereby, the corresponding quantitative methods can be established. Characterizing the connectivity of rivers based on biota will facilitate assessing the effects of multiple barriers and understanding river connectivity, and provide the support for the effective management of rivers.

Removal efficiency of phosphorus, cyanobacteria and cyanotoxins by the “flock & sink” mitigation technique in semi-arid eutrophic waters

Geoengineering techniques have been used to control phosphorus and cyanobacteria in lakes promising greater and quicker chemical and ecological recovery. Techniques that use coagulants and clays to remove particulates and dissolved phosphorus from the water column have received great. In this study, bench-scale “flock & sink” assays were carried out to evaluate the efficiency of the coagulants aluminium sulphate (SUL), polyaluminium chloride (PAC) and chitosan (CHI), alone and combined with natural bentonite clays (BEN) and lanthanum-modified bentonite (LMB), to remove of phosphorus from a eutrophic reservoir in a semi-arid region of Brazil. In addition, the study seeks to assess the effects on the cyanobacteria density and the intra- and extracellular concentrations of cyanotoxins after the application of these geoengineering materials. The SUL and PAC coagulants effectively reduced the total phosphorus (TP), reactive soluble phosphorus (SRP), turbidity, chlorophyll-a, cyanobacteria density and intracellular microcystin, whereas CHI showed a low removal efficiency. Lanthanum-modified bentonite proved to be more effective than BEN; however, the application of the coagulants only was sufficient to successfully remove phosphorus and cyanobacteria from the water column. In addition, the efficiency of the “flock & sink” technique in cell removal varied among the cyanobacteria species. Small colonial species such as Aphanocapsa delicatissima, Merismopedia glauca and Merismopedia tenuissima were removed regardless of the treatment used, including those with CHI and BEN. As for the filamentous cyanobacteria, Cylindrospermopsis raciborskii, Geitlerinema amphibium, Planktothrix agardhii and Pseudanabaena catenata, removal was achieved only using PAC, SUL and LMB alone or when combined. The intracellular concentrations of saxitoxin and cylindrospermopsin and the extracellular fraction of these cyanotoxins and of microcystin were not influenced by the application of coagulants and clays. This indicates that cell lysis did not occur with the addition of the geoengineering materials. These results demonstrate that the “flock & sink” technique could be used for restoration of eutrophic waters.

Use of Sentinel 2 – MSI for water quality monitoring at Alqueva reservoir, Portugal

Abstract. Alqueva reservoir located in southeast of Portugal has a surface area of 250 km2 and total capacity of 4150 hm3. Since 2006 the water quality of this reservoir is explored by the authors using remote sensing techniques. First using MERIS multi-spectral radiometer on-board of ENVISAT-1 and presently with MSI multi-spectral radiometer on-board SENTINEL-2. The existence of two satellites (A and B) equipped with MSI enable the area to be revisited, under the same viewing conditions, every 2–3 days. Since 2017 the multidisciplinary project ALOP (ALentejo Observation and Prediction systems) expands the team knowledge about the physical and bio-chemical properties of the reservoir. This project includes an integrated field campaign at different experimental sites in the reservoir and its shores, at least until September 2018. Previous algorithms developed by the team for MERIS are tested with the new MSI instrument for water turbidity, chlorophyll a concentration and density of cyanobacteria. Results from micro-algae bloom occurred in late summer/early autumn 2017 on the reservoir are presented, showing the capabilities of MSI sensor for detection and high resolution mapping over the reservoir. The results are compared with in situ sampling and laboratorial analysis of chlorophyll a associated with the bloom.

Phytoplankton of Lake Bol’shie Shvakshty (Belarus) during the Shift of the Ecosystem from a Macrophyte–Weakly Eutrophic to a Phytoplankton–Hypereutrophic State

Changes in the quantitative characteristics and functioning of phytoplankton in Lake Bol’shie Shvakshty have been assessed. The changes are evoked by the introduction of herbivorous fishes into the lake and the resulting disturbance of ecological balance in the ecosystem and the shift of the lake into a hypertrophic state from a weakly eutrophic state. Human interference has caused the cyanobacteria density (abundance) and biomass values in the overall phytoplankton composition to strongly exceed (3.5 × 109 cells/L and above 68 μg/L chlorophyll-а, respectively) the threshold value for safe recreational use of water bodies (20 million cells/L and 10 μg/L chlorophyll-а) established by the World Health Organization (WHO). The lake can be assigned to the third level of hazard to human health within the classification proposed by the WHO, as the cyanobacteria density is higher than 100 million cells/L and chlorophyll-а content is higher than 50 μg/L. MC-producing Microcystis species were identified among the cyanobacteria that has propagated in the lake in recent years, and five microcystin variants, including the highly toxic MC-LR, have been detected in the water.

A Novel and Convenient Method for Early Warning of Algal Cell Density by Chlorophyll Fluorescence Parameters and Its Application in a Highland Lake.

The occurrence of algal blooms in drinking water sources and recreational water bodies have been increasing and causing severe environmental problems worldwide, particularly when blooms dominated by Microcystis spp. Bloom prediction and early warning mechanisms are becoming increasingly important for preventing harmful algal blooms in freshwater ecosystems. Chlorophyll fluorescence parameters (CFpars) have been widely used to evaluate growth scope and photosynthetic efficiency of phytoplankton. According to our 2-year monthly monitor datasets in Lake Erhai, a simple but convenient method was established to predict Microcystis blooms and algal cell densities based on a CFpar representing maximal photochemical quantum yield of Photosystems II (PSII) of algae. Generalized linear mixed models, used to identify the key factors related to the phytoplankton biomass in Lake Erhai, showed significant correlations between Chl a concentration and both the light attenuation coefficient and water temperature. We fitted seasonal trends of CFpars (Fv/Fm and ΔF/Fm′) and algal cell densities into the trigonometric regression to predict their seasonal variations and the autocorrelation function was applied to calculate the time lag between them. We found that the time lag only existed between Fv/Fm from blue channel and algal cell densities even both Fv/Fm and ΔF/Fm′ show the significant non-linear dynamics relationships with algal cell densities. The peak values of total algal cell density, cyanobacteria density and Microcystis density followed the foregoing peak value of Fv/Fm from blue channel with a time lagged around 40 days. Therefore, we could predict the possibilities of Microcystis bloom and estimate the algal cell densities in Lake Erhai ahead of 40 days based on the trends of Fv/Fm values from blue channel. The results from our study implies that the corresponding critical thresholds between Fv/Fm value and bloom occurrence, which might give new insight into prediction of cyanobacteria blooms and provide a convenient and efficient way for establishment of early warning of cyanobacteria bloom in eutrophic aquatic ecosystems.

Interspecific Relationship and Ecological Requirements of Two Potentially Harmful Cyanobacteria in a Deep South-Alpine Lake (L. Iseo, I)

In Lake Iseo (Lombardia, Italy), the predominant species in the cyanobacterial taxa was Planktothrix rubescens. However, since 2014, the presence of an allochthonous Cyanobacteria, Tychonema bourrellyi, able to produce consistent biomasses and harmful toxins, was detected. The causes of this expansion are poorly understood. Many studies have linked the development of allochthonous Cyanobacteria populations with climate change. This study shows the spatio-temporal dynamics, the ecological requirements, and the interspecific relationship of P. rubescens and T. bourrellyi. Samples were collected monthly in 2016 at six different depths in the water column; 20 chemico-physical characteristics were measured; and Cyanobacteria density, morphology, and biovolume were evaluated. The results allowed a comparison of the spatial pattern of the two species, which showed a greater distribution at a depth of 10–20 m, and their seasonal dynamics. Both Cyanobacteria were present throughout the year, with the greatest abundance during the period from March to May. A temporal shift was observed in their development, linked to different capacities for overcoming winter and mixing periods. Principal Component Analysis, performed on 20 observations (4 months × 5 depths), highlighted the important role of the stability of the water column in determining T. bourrellyi settlement in Lake Iseo and the role of solar radiation in spring population development.

Monitoring and research of microcystins and environmental factors in a typical artificial freshwater aquaculture pond.

Freshwater aquaculture ponds are important artificially regulated aquatic ecosystems which provide a large number of freshwater fish products in China. The cyanobacteria bloom and microcystin (MC) pollution caused by anthropogenic eutrophication have attracted much attention due to their toxic effects. To provide an insight into the cyanobacterial problem in the ponds, the environmental parameters and MCs of a typical artificial pond in the Yangtze River Delta region of China were monitored and studied from May to December 2015. During the monitoring period, the ponds were in serious eutrophication with total phosphorus (TP) concentrations between 0.95 and 1.80μg/L, and total nitrogen (TN) concentrations between 1.1 and 4.86μg/L. High feed coefficient and high fish stock were the main reasons for the eutrophication. The results showed that the water temperature was the key factor that affected the cyanobacteria blooming in the pond. The chlorophyll a concentration was significantly positively correlated with the cyanobacteria density during the blooming season. MC-LR and MC-RR existed simultaneously and showed a significant positive correlation. The peak concentrations of dissolved MC-LR and MC-RR in the pond water were 40.6 and 4.7μg/L, respectively, which is considered highly toxic. Free MC-LR and MC-RR were also found in the aquaculture products. MC-LR concentrations in the bighead carp (Aristichthys nobilis) liver and shrimp (Macrobrachium nipponense) muscle were up to 2.64 and 4.17μg/kg, respectively. MC-RR concentration was up to 1.89μg/kg in the black carp (Mylopharyngodon piceus) liver. The results implied the potential health risks for citizens and pets caused by current artificial freshwater aquaculture pond systems.

Phytoplankton community in the last undammed stretch of the Paraná River: considerations on the distance from the dam

Abstract Aim: To evaluate the influence of upstream reservoirs on the temporal and spatial variation of the phytoplankton community in the Paraná River channel and the importance of its main tributaries in reducing the oligotrophication process along this stretch of the river. Materials and Methods Sampling of phytoplankton and physical and chemical variables was performed quarterly between August 2013 and May 2015, in the Paraná River main channel and in the mouth of the main tributaries, at the stretch located between downstream Porto Primavera reservoir and the backwaters of Itaipu reservoir. To summarize the variation of phytoplankton density in relation to the main physical and chemical variables, we performed a Redundancy Analysis (RDA). Results A total of 214 taxa were identified throughout the study. We registered low values of phytoplankton species richness and abundance, which showed no patterns of temporal and spatial distribution, both for the Paraná River and the tributaries. However, RDA results showed spatial segregation among samples from the Paraná River main channel, such that the stretch located closer to the dam was associated with higher values of water transparency and Cyanobacteria density, exported by upstream reservoirs, whereas the middle and lower stretches were associated with higher phytoplankton complexity and higher nutrient concentration and turbidity. Conclusion Through the analysis of the phytoplankton community we could verify a reduction in the effects of oligotrophication along the longitudinal axis of the Paraná River and the important role of the tributaries in diminishing this effect.

Influence of Phoslock® on legacy phosphorus, nutrient ratios, and algal assemblage composition in hypereutrophic water resources.

Acceleration of eutrophication in freshwater resources can result in prolific growth of nuisance algae, notably cyanobacteria. In this research, we evaluated the ability of an in situ P binding technology (Phoslock®) to alter available water column and sediment P, and the subsequent impact on nutrient ratios and algal assemblage composition. Two golf course irrigation ponds with legacy nutrient loads and chronic cyanobacterial blooms were treated with Phoslock and monitored for 2years post-treatment. Phoslock significantly (P < 0.05) decreased water column total P levels and shifted mobile sediment P fractions (i.e., labile, reductant-soluble, organic) to the residual fraction. Total N/P ratios (by mass) significantly increased and were sustained at over 30:1 in the Hickory Meadows irrigation pond and 100:1 in the Chockyotte irrigation pond throughout the study. Consequent changes in the algal assemblage included decreases in dominance and overall density of cyanobacteria as well as a shift away from scum-forming genera (e.g., Microcystis spp. and Anabaena [Dolichospermum] sp.) to planktonic forms (e.g., Pseudanabaena sp. and Planktolyngbya sp.). This research provides information regarding mitigation of in situ water and sediment P toward shifting nutrient ratios and altering algal assemblage composition.

Cyanobacteria Community Dynamics and Trophic Status of Intensive Shrimp (Litopenaeus vannamei) Farming Pond in Situbondo East Java Indonesia

The objective of this study was to analyze the dynamics community structure of Cyanobacteria and trophic status in ponds of intensive shrimp culture ( Litopenaeus vannamei ) in Situbondo based on Trophic Diatom Index (TDI). The ex post facto research was conducted in situ in the hamlet of Pond Mutiara Mas III Klatakan Situbondo East Java Indonesia. Observation of Cyanobacteria and Diatoms community structure were done every week during four cycles of shrimp farming ponds. Cycle of shrimp farming ponds is the times for enlargement process of the shrimps from seed to mature which ranges from 90-120 days. The dependent variables were the density of Cyanobacteria and Diatoms community, as well as chemical parameters nitrite and orthophosphate. Trophic status was determined from TDI be counted from data of diatom density. All of the data were then classified using cluster and biplot analysis program PAST Ver. 3.11 to discribe the profile of ecosystem quality. The research results showed that there were four taxa of Cyanobacteria during farming cycle which the highest density was found from the genus of Oscillatoria . Based on the value of TDI, we found that the trophic status of water in shrimps pond during the production process was eutrophic until hyper-eutrophic. The water quality was decreases along with the length of incubation time.

The roles of cyanobacterial bloom in nitrogen removal

Annually occurred cyanobacterial bloom aggravated eutrophication situation and changed the lacustrine ecosystem components. Recently, high concentration of bloom cyanobacteria had been found to accelerate total nitrogen (TN) removal. However, the contribution of cyanobacterial bloom to TN removal remained unclear. In this study, microcosms with different density of bloom cyanobacteria were constructed and quantitative PCR and structural equation modelling (SEM) were used to analyze the microbes, environmental variables and the causal relationship to TN removal. Total bacteria, ammonia-oxidizing archaea and nirS gene abundances were indirectly influenced by cyanobacteria biomass and all of them had a direct effect on TN removal. SEM confirmed that cyanobacteria made a direct contribution to ammonium‑nitrogen (NH4+-N) level in water and induced nitrification activity, which favored the process of denitrification by supplying substrate and aggravating the anoxic status. These results strongly suggested that an increased cyanobacteria biomass had strong impacts on mineralization, nitrification and denitrification by mediating TN, dissolved organic carbon and dissolved oxygen directly and subsequently influenced the nitrifiers and denitrifiers.

Reduced Phytoplankton and Zooplankton Diversity Associated with Increased Cyanobacteria in Lake Champlain, USA

AbstractAnthropogenic inputs of nutrients threaten water quality around the world, causing eutrophication and altering phytoplankton communities. In freshwater systems, certain physiochemical conditions, including high TP, low TN:TP, and warm temperatures, can lead to problematic cyanobacteria blooms. Cyanobacteria can decrease phytoplankton diversity and phytoplankton diversity has been positively linked to zooplankton diversity, suggesting that cyanobacteria may have indirect negative effects on zooplankton diversity. Using monitoring data from Lake Champlain, we tested three hypotheses: (1) cyanobacteria density and phytoplankton diversity are inversely related; (2) phytoplankton diversity and zooplankton diversity are positively related; and by extension (3) cyanobacteria density and zooplankton diversity are inversely related. Relationships were investigated separately at shallow (4–15 m) and deep (25–100 m) sites using several diversity metrics. At deep sites, cyanobacteria density was only related (positively) to zooplankton Shannon diversity. At shallow sites, all three hypotheses were supported by three of four diversity metrics; low phytoplankton richness appears to be the link between high cyanobacteria density and low zooplankton diversity. Our results suggest that cyanobacteria may indirectly reduce zooplankton diversity by decreasing resource heterogeneity, although our results based on observational data were also consistent with well‐known direct pathways. Because low biodiversity can alter ecosystem processes and impair functioning, our results suggest that shallow systems may be more responsive to global change than deeper systems.

The Importance of Scientific Publishing: Teaching an Undergraduate How to Swim the Entire Length of the Pool

The Importance of Scientific Publishing: Teaching an Undergraduate How to Swim the Entire Length of the Pool

Biotic nitrogen fixation in the bryosphere is inhibited more by drought than warming.

The boreal forest is of particular interest to climate change research due to its large circumpolar distribution and accumulated soil carbon pool. Carbon uptake in this ecosystem is nitrogen (N)-limited, therefore factors affecting carbon or nitrogen dynamics in the boreal forest can have consequences for global climate. We used a 2-year field experiment to investigate the response of biotic nitrogen fixation by cyanobacteria associated with boreal forest bryophytes, in a factorial experiment combining simulated climate change with habitat fragmentation treatments. We simulated climate change conditions using open-top greenhouse chambers in the field, which increased mean and maximum temperatures, and created a precipitation gradient from ambient levels in the center to extreme drought conditions at the periphery of the chamber. The dry patches near the chamber walls exhibited almost no N-fixation, despite having similar densities of cyanobacteria (predominantly Stigonema sp.) as other patches. Rates of N-fixation were best explained by a model containing moisture, fragmentation, cyanobacteria density and time; warming was not a significant variable affecting N-fixation. There was no significant interaction between warming and fragmentation. These results suggest that cyanobacteria responded physiologically to drought by reducing N-fixation activity long before any changes in density. Ecosystem processes, such as N-fixation, can respond in the short term to environmental change much more rapidly than changes in the underlying community structure. Such rapid physiological responses may occur faster than demographic insurance effects of biodiversity.

Remoção de microcistina-LR de águas eutrofizadas por clarificação e filtração seguidas de adsorção em carvão ativado granular

RESUMO Usualmente, o tratamento convencional de águas com altas densidades de cianobactérias e concentração de cianotoxinas não garante efluente consoante o padrão de potabilidade vigente (1,0 µg.L-1 de microcistina). Etapas adicionais fazem-se necessárias, destacando-se a adsorção por carvão ativado granular ou pulverizado. Neste contexto, o objetivo geral deste trabalho foi avaliar em escala de bancada a remoção de microcistina em água natural por adsorção em colunas de carvão ativado granular de casca de coco, após as etapas de clarificação e filtração em areia. Os resultados mostraram que o transpasse no carvão de maior granulometria ocorreu em menor tempo de contato (2 h), quando comparado ao de menor granulometria. Tais resultados abrem perspectiva de emprego em escala real por garantir efluente com concentração inferior ao que estabelece a Portaria 2914 por mais tempo e utilizando menor massa de carvão.

&lt;b&gt;Cyanobacteria community in two tropical eutrophic reservoirs in northeastern Brazil

This study investigated the effect of seasonality on the Cyanobacteria community in two tropical eutrophic reservoirs in northeastern Brazil. Monthly samplings were conducted in the sub-surface of reservoirs. The following abiotic variables were analyzed: apparent color, turbidity, conductivity, alkalinity, calcium, magnesium, sodium, potassium, sulfate, total phosphorous, ammonia, nitrate, nitrite, chlorides, total hardness and chlorophyll-a, according to APHA (2012). Cyanobacteria density was quantified through biomass. Data were analyzed using one-way ANOVA and Redundancy Analysis (RDA). Higher mean values of Cyanobacteria biomass occurred in the dry (9.9mm 3 L -1 ) and rainy (19.0mm 3 L -1 ) season in Jucazinho and Carpina reservoirs, respectively, especially Planktothrix agardhii, Cylindrospermopsis raciborskii and Geiterinema amphibium, which occurred in 100% of the samples. RDA analysis revealed that the variables nitrite, ammonia, conductivity, calcium, sulfate, chlorides and alkalinity influenced most the Cyanobacteria community in both reservoirs. High trophic state index was observed throughout the year. Seasonality affected both biotic and abiotic variables.

Biotic or abiotic factors: which has greater influence in determining the structure of rotifers in semi-arid reservoirs?

ObjectiveThe objective of this study is to evaluate whether the distribution of structural attributes of rotifers in reservoirs in the semiarid region is more strongly influenced by abiotic or biotic environmental factors (density of cyanobacteria).MethodSampling occurred in two reservoirs in the Paraíba Basin, northeastern Brazil (Poções and Camalaú) during April and June 2012. Eight sampling points were distributed at two stations in each reservoir: the region near the entrance of the main tributary and region of the dam and collections were made in the limnetic and littoral zone in every season. To assess the abiotic influence and density of cyanobacteria in the distribution of the structural attributes of rotifers, environmental variables bivariate correlation was conducted in series.ResultsIn Poções reservoir, the distribution of rotifer biomass was negatively related to the density of cyanobacteria; among the environmental variables, chlorophyll-a and total nitrogen were negatively related to all of the tested structural attributes, while the concentrations of total phosphorus were strongly related to the abundance of rotifers. In the Camalaú reservoir, the biomass was a structural attribute with a stronger correlation to the density of cyanobacteria; between the environmental variables and Egeria densa, nitrate was negatively related to all of the attributes tested, while transparency was moderately related to the abundance, biomass and richness as well as Chara sp. with abundance.ConclusionsAssemblages of rotifers are more clearly related to environmental conditions, especially those indicative of trophic conditions, despite the density of cyanobacteria having been a factor that was positively related to the structural characteristics of rotifers and thus indicative of such structural assemblies. This can be used for analysis of local environmental condition factors.