Cyanobacterium Cylindrospermopsis Raciborskii Research Articles

Variations in carbon-to-phosphorus ratios of two Australian strains of Cylindrospermopsis raciborskii

The toxic cyanobacterium Cylindrospermopsis raciborskii can form large blooms in freshwater systems, causing water quality problems. The availability of the essential macronutrient phosphorus (P), has a big impact on bloom formation but the variation in physiological response of different strains of C. raciborskii to available P has not previously been examined. This study investigated the carbon:phosphorus (C:P) ratio of two toxic Australian strains of C. raciborskii, AWT205 and NPD, under a range of P concentrations in batch and continuous cultures. P was added as a single dose to batch cultures and in continuous cultures at P concentrations of 0.032, 0.16, 0.64 and 16 μmol P l−1. Cellular carbon and phosphorus content of both strains increased under P-limited conditions (0 μmol P l−1 addition) with zero growth. Strain NPD had a lower C:P ratio (34:1) than AWT205 (150:1) indicating higher P storage capacity, and strain NPD survived P-limited conditions for longer. There was no significant difference in exponential growth rates (0.2 d−1, P ≥ 0.5) under all P concentrations for both strains, with the exception of no P, demonstrating non-P-limited growth even at the lowest concentration (0.032 µmol P l−1) and no increase in growth rate with additional P. 33P uptake measurements were used to show that these strains both have very low half saturation constants (Ks = 0.02 μmol P l−1) compared with other phytoplankton and strains of C. raciborskii. This is indicative of high uptake affinities and suggests that these strains are highly adapted to a low P supply. Overall the results of this study are consistent with the P strategy of storage prioritization over growth rate, and demonstrate differences between the strains in the C:P ratio under P-limitation, indicating variation in P storage.

Influence of environmental variables on saxitoxin yields by Cylindrospermopsis raciborskii in a mesotrophic subtropical reservoir.

Saxitoxins are a class of toxins produced by at least two groups of evolutionarily distant organisms (cyanobacteria and dinoflagellates). While the toxicity of these toxins is relatively well characterized, to date little is known about their drivers and ecological functions, especially in lower latitude tropical and subtropical freshwater ecosystems. In the present study, we aimed to obtain a better understanding of the main drivers of saxitoxin concentrations in aquatic environments. We investigated the relationships among saxitoxin concentrations in a mesotrophic subtropical reservoir dominated by the cyanobacteria Cylindrospermopsis raciborskii with physical, chemical and biological water variables. The highest saxitoxin concentrations were 0.20 μg·L-1, which occurred in the samples with the highest densities of C. raciborskii (maximum of 4.3 × 104 org·mL-1) and the highest concentration of dissolved nutrients (nitrate from 0.2 to 0.8 μg·L-1, ortophosphate from 0.3 to 8.5 μg·L-1). These correlations were confirmed by statistical analyses. However, the highest saxitoxin relative concentrations (per trichome) were associated with lower C. raciborskii densities, suggesting that saxitoxin production or the selection of saxitoxin-producing strains was associated with the adaptation of this species to conditions of stress. Our results indicate that C. raciborskii toxin yields vary depending on the enrichment conditions having potential implications for reservoir management.

Distribution of invasive Cylindrospermopsis raciborskii in the East-Central Europe is driven by climatic and local environmental variables.

Mechanisms behind expansion of an invasive cyanobacterium Cylindrospermopsis raciborskii have not been fully resolved, and different hypotheses, such as global warming, are suggested. In the East-Central Europe, it is widely occurring in western part of Poland but only in single locations in the East due to some limiting factors. Therefore, broad-scale phytoplankton survey including 117 randomly selected lakes in Poland and Lithuania was conducted. The results showed that C. raciborskii occurred widely in western part of Poland but was absent from other regions and Lithuania except one lake. The regions in which C. raciborskii was present had higher annual mean air temperature, higher maximum air temperature of the warmest month and higher minimum temperature of the coldest month, demonstrating that average air temperature, and indirectly, the duration of growing season might be more important factor driving C. raciborskii distribution than measured in situ water temperature. In turn, the presence of C. raciborskii in single localities may be more related to physiological adaptations of separated ecotype. Collectively, these results provide novel evidence on the influence of temperature on C. raciborskii distribution in East-European regions but also indicate high ecological plasticity of this species.

Effects of crude extracts of a saxitoxin-producer strain of the cyanobacterium Cylindrospermopsis raciborskii on the swimming behavior of wild and laboratory reared guppy Poecilia vivipara

The cyanobacterium Cylindrospermopsis raciborskii is an invasive species in water supply reservoirs worldwide, which can produces cylindrospermopsins and saxitoxins. In the wild, guppy (Poecilia vivipara) can be exposed to cyanotoxins, but those born and reared in laboratory are free of this contact. The aim of this paper was to comparatively measure the locomotor activity of ‘wild’ and ‘lab’ P. vivipara before and after exposure to crude extracts of two different cultures of C. raciborskii (CYRF-01), a saxitoxin-procucer strain. The movement of each fish was recorded using an image monitoring system (Videomex V®) before and after 48 h exposure to cyanobacterial extracts. Each experiment was performed during 4 h, with 1 h acclimation and 3 h recording period of the parameters Distance performed (DP), Swimming time (SwT), Stereotypic time (StT), Resting time (RT) and Average speed (AS). The quantification of saxitoxin in the solutions was performed by the enzyme-linked immunosorbent assay (ELISA). The weight or the total length did not influence the locomotor activity of fish in any of the experiments. The saxitoxin value was similar for both cultures (Culture 1: 7.3 μg L−1 and Culture 2: 8.6 μg L−1). However, in experiments with Culture 1 an increased activity in most parameters was observed, while in Culture 2, a decreased activity was observed only in ‘lab’ fish. Wild fish was less affected, showing higher resistance to both cyanobacterial crude extracts. This study showed that different cultures of the same strain of C. raciborskii and with similar contents of saxitoxin are able to change the locomotor activity of P. vivipara, contributing to the validation of the use of behavioral parameters to the evaluation of sublethal effects of toxic cyanobacteria on fish.

The invasion success of the cyanobacterium Cylindrospermopsis raciborskii in experimental mesocosms: genetic identity, grazing loss, competition and biotic resistance

The invasion success of the cyanobacterium Cylindrospermopsis raciborskii in experimental mesocosms: genetic identity, grazing loss, competition and biotic resistance

Isolation of cyanophage CrV infecting Cylindrospermopsis raciborskii and the influence of temperature and irradiance on CrV proliferation

A lytic virus that infects a European strain of the freshwater filamentous cyano-bacterium Cylindrospermopsis raciborskii was isolated from a lake in the Netherlands and partially characterised. With a genome size of 110 +/- 15 kb, an icosahedral capsid of 65 +/- 1 nm (n = 22) and a long non-contractile tail of 612 +/- 31 nm (n = 15), this dsDNA cyanophage CrV appears to belong to the Siphoviridae family. CrV was highly host specific, not infecting other filamentous cyano bacteria species isolated from the same lake, nor 4 Australian strains of C. raciborskii. The latent period of this cyanophage was 20-24 h. Varying the irradiance affected cyanophage-host inter actions: at low light (20 mu mol quanta m(-2) s(-1)) the latent period was 1.3 times longer compared with at mid light (90 mu mol quanta m-2 s(-1)); burst size at mid light was 332 CrV per lysed host cell, at low light it was halved (48%) and at high light (250 mu mol quanta m(-2) s(-1)) the burst size was further reduced to only 14% of that of mid light. Temperature also affected the virus growth characteristics: the CrV latent period at high temperature (30 degrees C) was reduced to just 11% (compared with a mid temperature of 22 degrees C), but still the burst size increased to 541 CrV per lysed host cell; at low temperature (15 degrees C) the latent period was prolonged 1.3-fold and the burst size was reduced to 43%. Our findings indicate that ecologically relevant environmental factors can affect the extent of viral lysis of C. raciborskii, advancing our understanding of the spread of this invasive cyanobacterium across Europe.

Influence of linoleic acid on growth, oxidative stress and photosynthesis of the cyanobacterium Cylindrospermopsis raciborskii

ABSTRACTIn this study, the effects of linoleic acid on the growth, photosynthetic activities and oxidative system of the invasive cyanobacterium Cylindrospermopsis raciborskii were investigated. The results indicated that linoleic acid decreased the growth rate and chlorophyll a concentration in C. raciborskii after 48 h incubation. The maximum photochemical efficiency (Fv/Fm) of photosystem II (PSII) and maximum relative electron transport rate (ETRmax) decreased significantly at concentrations higher than 1 mg L−1. However, non-photochemical quenching (NPQ) significantly increased when cultured at concentrations of 0.5, 1, 2 and 4 mg L−1. PSII electron transfer rate and chlorophyll a fluorescence transients appeared to be affected after the cells were exposed to higher concentrations of linoleic acid; the density of the reaction centres (RCs), quantum energy flux ratios and the performance index on absorption basis decreased, but absorption flux per RC and dissipated energy flux per RC increased. Malondialdehyde content, superoxide dismutase and catalase activities were enhanced when exposed to 2 and 4 mg L−1 of linoleic acid. This suggests that the blockage of electron transport on the donor and acceptor sides of PSII is the mechanism responsible for the toxicity of linoleic acid in PSII of C. raciborskii.

The success of the cyanobacterium Cylindrospermopsis raciborskii in freshwaters is enhanced by the combined effects of light intensity and temperature

<p>Toxic cyanobacterial blooms in freshwaters are thought to be a consequence of the combined effects of anthropogenic eutrophication and climate change. It is expected that climate change will affect water mixing regimes that alter the water transparency and ultimately the light environment for phytoplankton. Blooms of the potentially toxic cyanobacterium <em>Cylindrospermopsis raciborskii</em> are expanding from tropical towards temperate regions. Several hypotheses have been proposed to explain this expansion, including an increase in water temperature due to climate change and the high phenotypic plasticity of the species that allows it to exploit different light environments. We performed an analysis based on eight lakes in tropical, subtropical and temperate regions to examine the distribution and abundance of <em>C. raciborskii</em> in relation to water temperature and transparency. We then conducted a series of short-term factorial experiments that combined three temperatures and two light intensity levels using <em>C. raciborskii</em> cultures alone and in interaction with another cyanobacterium to identify its growth capacity. Our results from the field, in contrast to predictions, showed no differences in dominance (>40% to the total biovolume) of <em>C. raciborskii</em> between climate regions. <em>C. raciborskii</em> was able to dominate the phytoplankton in a wide range of light environments (euphotic zone = 1.5 to 5 m, euphotic zone/mixing zone ratio <0.5 to >1.5). Moreover, <em>C. raciborskii </em>was capable of dominating the phytoplankton at low temperatures (<15°C). Our experimental results showed that <em>C. raciborskii</em> growing in interaction was enhanced by the increase of the temperature and light intensity. <em>C. raciborskii </em>growth in high light intensities and at a wide range of temperatures, suggests that any advantage that this species may derive from climate change that favors its dominance in the phytoplankton is likely due to changes in the light environment rather than changes in temperature. Predictive models that consider only temperature as a drive factor can therefore fail in predicting the expansion of this potentially toxic cyanobacterium.<em></em></p>

Abiotic variables affect STX concentration in a meso-oligotrophic subtropical coastal lake dominated by Cylindrospermopsis raciborskii (Cyanophyceae)

The cyanobacterium Cylindrospermopsis raciborskii is capable of producing toxins including saxitoxin (STX). Few studies have verified the influence of environmental variables on the production of STX and most have only been studied in the laboratory. The goal of this work was to identify the abiotic variables related to STX concentration in situ. The relationship among STX concentration and the physical variables, nutrients and chlorophyll-a (chl-a) concentration was examined in a meso-oligotrophic subtropical coastal lake dominated by C. raciborskii. A generalized linear model was developed, incorporating all variables measured monthly over a 45-month monitoring period. Conductivity and dissolved inorganic nitrogen (DIN) concentration provided the greatest explanatory power for STX concentration in situ. Previous studies suggested that C. raciborskii cells exposed to stress associated with higher ionic concentrations appear to activate the biosynthesis of STX suggesting that STX can elicit changes cell permeability and may contribute to the homeostasis of this organism. An increase of DIN concentration results in a higher concentration of STX which may be related to a reduced metabolic demand, since the uptake of inorganic nitrogen requires less energy than N2-fixation. Thus, increased DIN can favor the growth of C. raciborskii population or improve cellular homeostasis, both potentially increasing STX concentration in the aquatic system, which was observed through a delayed response pattern. The developed model, while providing only a moderate predictive power, can assist in the understanding of the environmental variables associated with increases in STX concentration, and in monitoring and minimizing the risks of toxic blooms.

Behavioral alterations induced by repeated saxitoxin exposure in drinking water.

BackgroundBlooms of the saxitoxin-producing cyanobacterium Cylindrospermopsis raciborskii have been contaminating drinking water reservoirs in Brazil for many years. Although acute effects of saxitoxin intoxication are well known, chronic deleterious outcomes caused by repeated saxitoxin exposure still require further investigation. The aim of the present work is to investigate the effects of consumption of drinking water contaminated with C. raciborskii for 30 days on learning and memory processes in rats.MethodsThe effects of saxitoxin (3 or 9 μg/L STX equivalents) or cyanobacteria on behavior was determined using the open field habituation task, elevated plus maze anxiety model task, inhibitory avoidance task, and referential Morris water maze task.ResultsNo effects of saxitoxin consumption was observed on anxiety and motor exploratory parameters in the elevated plus maze and open field habituation tasks, respectively. However, groups treated with 9 μg/L STX equivalents displayed a decreased memory performance in the inhibitory avoidance and Morris water maze tasks.ConclusionsThese results suggest an amnesic effect of saxitoxin on aversive and spatial memories.

Morpho-physiological responses of a subtropical strain of Cylindrospermopsis raciborskii (Cyanobacteria) to different light intensities

The toxigenic cyanobacterium Cylindrospermopsis raciborskii previously restricted to tropical latitudes, has been increasingly reported in temperate lakes in recent decades. The causes of its biogeographical expansion are under investigation, but efficient physiological adaptation to changes in temperature and light regimes are likely to be involved. The present study evaluated the morpho-physiological responses of a strain of C. raciborskii from southern Brazil to nine light intensities, from 9 to 250 µmol photons m-2 s-1. Blooms of this cyanobacterium are regularly recorded in the region. Morpho-physiological responses were measured based on growth rate and trichome length. Cylindrospermopsis raciborskii showed slow growth at low light intensities, 9 and 20 µmol photons m-2 s-1, and responded morphologically by increasing the length of trichomes. In turn, the strain displayed constant maximum growth rates at light intensities higher than 50 µmol photons m-2 s-1. These results support the hypothesis that C. raciborskii can survive under low light conditions and continue to produce viable trichomes. Moreover, the strain achieved high growth rates under a relatively wide range of light intensities, a physiological adaptation that can potentially be a competitive advantage in the phytoplankton community.

Toxicity Overrides Morphology on Cylindrospermopsis raciborskii Grazing Resistance to the Calanoid Copepod Eudiaptomus gracilis.

Toxicity and morphology may function as defense mechanisms of bloom-forming cyanobacteria against zooplankton grazing. Yet, the relative importance of each of these factors and their plasticity remains poorly known. We tested the effects of chemical and morphological traits of the bloom-forming cyanobacterium Cylindrospermopsis raciborskii on the feeding response of the selective feeder Eudiaptomus gracilis (Calanoida, Copepoda), using a saxitoxin-producing strain (STX+) and a non-saxitoxin (STX−)-producing strain as food. From these two chemotypes, we established cultures of three different morphotypes that differed in filament length (short, medium, and long) by incubating the strains at 17, 25, and 32 °C. We hypothesized that the inhibitory effects of saxitoxins determine the avoidance of C. raciborskii, and that morphology would only become relevant in the absence of saxitoxins. Temperature affected two traits: higher temperature resulted in significantly shorter filaments in both strains and led to much higher toxin contents in the STX+ strain (1.7 μg eq STX L−1 at 17 °C, 7.9 μg eq STX L−1 at 25 °C, and 25.1 μg eq STX L−1 at 32 °C). Copepods strongly reduced the ingestion of the STX+ strain in comparison with STX− cultures, regardless of filament length. Conversely, consumption of shorter filaments was significantly higher in the STX− strain. The great plasticity of morphological and chemical traits of C. raciborskii and their resultant contrasting effects on the feeding behavior of zooplankton might explain the success of this cyanobacterium in a variety of aquatic environments.Electronic supplementary materialThe online version of this article (doi:10.1007/s00248-016-0734-8) contains supplementary material, which is available to authorized users.

Is bigger better? A possibility for adaptation of Daphnia to filamentous cyanobacteria in the face of global warming

Body size is a key determinant of fitness in Daphnia. Bigger size means higher feeding efficiency and reproduction. However, filamentous cyanobacteria have a more detrimental effect on larger daphnids. Predicted global warming is expected to reduce size of Daphnia and facilitate frequent occurrence of cyanobacteria. Therefore, we asked two questions: (i) does elevated temperature cause reduced size of daphnids, and (ii) is temperature-dependent size reduction adaptive in an environment dominated by filamentous cyanobacteria? To address these issues, we obtained 8 clones of the Daphnia longispina complex from artificially heated lakes and 8 clones from control lakes, and exposed them to a favorable food Scenedesmus obliquus and a mixture of S. obliquus and the filamentous cyanobacterium Cylindrospermopsis raciborskii in life table experiments at 16, 20, and 24°C. Individuals from heated lakes attained larger body size than those from control lakes. Moreover, exposure to the filamentous cyanobacterium led to reduced fecundity of Daphnia from the non-heated lakes and did not affect reproduction of Daphnia from the heated lakes. We conclude that Daphnia display some evolutionary adaptations to cope with filamentous cyanobacteria, linked to long-term exposition to elevated temperature. Our results violate broadly accepted assumptions that ectotherms are smaller in warmer environments.

Combining immunolabeling and catalyzed reporter deposition to detect intracellular saxitoxin in a cyanobacterium

We combined the use of polyclonal antibodies against saxitoxin with catalyzed reporter deposition to detect production of saxitoxin by the cyanobacterium Cylindrospermopsis raciborskii. The procedure is simple, allows detection of intracellular saxitoxin in cyanobacteria filaments by confocal laser microscopy and is a promising tool to study toxin production and metabolism.

Influence of UV-B radiation on the fitness and toxin expression of the cyanobacterium Cylindrospermopsis raciborskii

The harmful bloom-forming cyanobacterium Cylindrospermopsis raciborskii grows in freshwaters over a wide range of light conditions. This species has increased its global distribution recently. The influence of ultraviolet radiation (UVR) on the fitness and toxin production of C. raciborskii has not previously been explored. We performed short-term experiments with three C. raciborskii strains (MVCC19, LB2897, and CYP011 K), and we compared their responses with other bloom-forming species (Microcystis sp.1 and Plankthotrix agardhii) to determine the impact of UV-B radiation on pigments, biomass, and morphological traits. In addition, we analyzed the effect of UV-B on the saxitoxin content and sxtU gene expression in the strain MVCC19. C. raciborskii strains were stressed differentially by UV-B exposure as evidenced by changes in growth, morphology, and heterocytes number. A significant increase in saxitoxin concentration and sxtU gene expression under UV-B suggests that toxin production in C. raciborskii can be a response to UV-B stress. In comparison, Microcystis sp.1 was more tolerant, while P. agardhii was severely impacted by UV-B, indicating also different sensitivities among cyanobacteria to UVR. Our results underscore the influence of UVR on C. raciborskii and the differences between strains which showed phenotypic plasticity, which potentially could affect its distribution in freshwaters.

Can Cylindrospermopsis raciborskii invade the Baltic Sea?

Management actions against invasive species are usually most efficient during early stages of invasion. Monitoring for early detection is therefore part of many management plans. However, if monitoring efforts do not match suitable habitat areas, detecting the initial stages of an invasion may fail. We highlight this mismatch by assessing which areas have suitable habitats for an invasion of the cyanobacterium Cylindrospermopsis raciborskii in the Baltic Sea, and compare these with the areas that are currently monitored for algal blooms. Establishment of this potential toxin-producer in the Baltic Sea could have serious socio-economic consequences for tourism and recreation, as well as fisheries and aquaculture in the coastal regions. We estimate the coastal areas of the eastern Gulf of Finland as the most suitable area for establishment because of low salinity and high summer seawater surface temperatures. The species is not yet reported in the Baltic Sea, but in the suitable-habitat areas indicated by our assessment, very little monitoring is currently being done. We suggest several lines of research and monitoring to increase the probability of early detection and better predictions for the future distribution of the species.

Photo-acclimation to low light—Changes from growth to antenna size in the cyanobacterium Cylindrospermopsis raciborskii

Cylindrospermopsis raciborskii is a toxic cyanobacterium which is responsible for the formation of Harmful Algal Blooms (HABs) and it is commonly described to prefer low light conditions. To elucidate the mechanisms that makes this species successful in such environments, we studied the physiological characteristics of C. raciborskii (strain NPD) exposed to both saturating (80μmol photonsm−2s−1) and suboptimal (10μmol photonsm−2s−1) light intensities. When exposed to the low light of 10μmol photonsm−2s−1, C. raciborskii showed a slower cell division rate (μc), lower respiration rate (Rd) and higher cell quotas of Chl a and phycocyanin. However, no differences in the cellular light harvesting efficiency (α) and maximal photosynthetic rate (Pmax) were observed. Under low light, the unchanged photosynthesis was associated with both functional maintenance of the photosynthetic machinery and a larger cross-sectional area of PSIIα-centres (σPSIIα). In relation to the literature, our results indicate that C. raciborskii NPD responds to low light by changing the size of the light harvesting antenna. Ecologically, the physiological acclimations observed suggest that C. raciborskii NPD can perform well in environments where light intensity is low and relatively stable, as might occur during the final stages of HABs.

A bloom of cyanobacteria (Cylindrospermopsis raciborskii) in UHE Carlos Botelho (Lobo/Broa) reservoir: a consequence of global change?

; periodic turbulence with re-oxygenation of the whole water column, and high saturation of oxygen (80-100%); low retention time (< 20 days) and a extensive macrophyte grow in the headwaters that prevent high nutrient load. This is the picture for the last 44 years. The phytoplankton composition was consistent with the oligomesotrophic characteristic of the reservoir: predominance of diatoms and chlorophyceae with a maximum of 10µg/l chlorophyll. However in the winter of (july) 2014 the following changes were observed: a heavy bloom of cyanobacteria occurred for the first time in the reservoir. This cyanobacteria Cylindrospermopsis raciborskii, is a invasive species. Very high chlorophyll levels (up to 100µg/l) were measured and high concentration and input of phosphorus was also detected (Tundisi and Matsumura-Tundisi, 2014). The explanation for this sudden appearance of blooms, can be attributed to the following factors: increase of up to 2°C above the average water temperature during the winter; lower rainfall during summer (30% less of the yearly average of 1.500 mm). Increase in the retention time (from <20 days up to 60 days) in order to maintain volumes for hydroelectricity production. This cyanobacteria bloom can be attributed to changes in the regional climate and the hydrological regime, with consequences for the dam operation. As described by Paerl and Huisman (2008), global warming affects patterns of precipitation and drought. The changes in the hydrological cycle enhanced cyanobacterial dominance. Heavy rains after extensive drought periods, increase nutrient input promoting phytoplankton growth. During periods of drought ,residence time, increase, thus promoting blooms.

Biodiversity of cyanobacteria in Tunisian freshwater reservoirs: occurrence and potent toxicity – a review

In spite of the great environmental and sanitary importance of cyanobacteria, their biodiversity is little known in Tunisia. In this work, a review was carried out, based on literature data, of potentially toxic cyanobacteria occurrence in Tunisia. Microcystis, one of the most widely distributed toxic bloom-forming cyanobacteria genera, was represented by Microcytis wesenbergii, found only in Lebna water reservoir, and Microcytis aeruginosa recorded in different water bodies. The invasive potentially toxic cyanobacterium Cylindrospermopsis raciborskii , reported for the first time in Tunisia in October 2004, was observed in the semi-arid to arid areas. The harmful genus Planktothrix was represented in Tunisian freshwater by the green-pigmented species P. agardhii . The filamentous cyanobacteria dominance is increasingly reported in Tunisia in eutrophic water bodies. This dominance increases especially during the summer–autumn period. Recently, potentially toxic cyanobacteria blooms have been reported in some reservoirs in the north east of the country. These blooms were generated by the potentially toxic Chroococcale Microcystis aeruginosa. Harmful cyanobacteria tend to spatio-temporal expansion in the Tunisian inland waters. The toxicological potential evaluated by several methods showed that none of the Tunisian strains were proved to be cylindrospermopsin nor saxitoxin producers. However, the majority of Microcystis were able to synthesize microcystin.

Primary production of lake phytoplankton, dominated by the cyanobacterium Cylindrospermopsis raciborskii, in response to irradiance and temperature

We present the first data on the interacting effect of temperature and light on primary production of the toxic cyanobacterium Cylindrospermopsis raciborskii in situ. C. raciborskii can be a dominant component of the phytoplankton community in tropical and subtropical lakes and reservoirs. We examined the interacting effects of a range of light (0, 2, 7, 17, 30, and 100% of ambient light) and temperature (20, 24, 28, and 32 °C) conditions, in terms of primary production rate and primary production irradiance model parameters, for a C. raciborskii-dominated phytoplankton community in a subtropical reservoir. Based on 13C-uptake experiments, phytoplankton preconditioned to temperatures between 24 and 26 °C had highest maximum primary production rates (2.25 ± 0.45 μg C μg Chl-a−1 h−1) at 28 °C and lowest at 32 °C (0.58 ± 0.13 μg C μg Chl-a−1 h−1). Temperature also had an effect on the response to light conditions. Phytoplankton preconditioned to a shallow euphotic depth (~2.3 m deep) had the lowest half saturation of primary production, Ik, at 28 °C and highest at 32 °C, while the highest temperature treatment also had the highest level of photoinhibition at 100% of ambient light. This suggests that the cyanobacterial community is adapted to a low light environment under optimal temperature conditions for primary productivity. These conditions are consistent with other studies showing that C. raciborskii is highly adapted to low light conditions. This work demonstrates the importance of considering temperature when comparing calibrated primary production parameters.