Comparing key drivers of cyanobacteria biomass in temperate and tropical systems.

There is growing evidence that cyanobacterial blooms are becoming more common in different parts of the world; within this context, predictive cyanobacteria models have an essential role in lake management. Several models have been successfully used in temperate systems to describe the main drivers of cyanobacterial blooms, but relatively less work has been conducted in the Tropics. We analyzed data from six Brazilian reservoirs and from five Canadian lakes using a combination of regression tree analyses and variation partitioning to evaluate the similarities and differences between regions. Our results, together with a synthesis of the literature from different latitudes, showed that trophic state (i.e. nutrients), climatic variables (e.g., temperature and/or precipitation) and hydrodynamic regimes (i.e. water residence time) are significant drivers of cyanobacteria biomass over several scales. Nutrients came out as the primary predictor in both regions, followed by climate, but when all systems were pooled together, water residence time came out as most important. The consistency in variables identified between regions suggests that these drivers are widely important and cyanobacteria responded quite similarly in different geographical settings and waterbody types (i.e. lakes or reservoirs). However, more work is needed to identify key thresholds across latitudinal gradients. Taken together, these results suggest that multi-region syntheses can help identify drivers that predict broad-scale patterns of cyanobacteria biomass.

Lack of nitrogen as a causing agent of Cylindrospermopsis raciborskii intermittent blooms in a small tropical reservoir.

Cylindrospermopsis raciborskii is the focus of many studies due to its toxicity and increasing blooms frequency. The comprehension of the factors that might trigger these blooms is fundamental for the maintenance of good freshwater quality. To better understand the autoecology of C. raciborskii and to identify the factors controlling its dominance, general limnological features were evaluated in Pedalinhos reservoir, Brazil. Samplings were performed monthly between 2011 and 2013. Although C. raciborskii is considered a relatively perennial species in the tropics, it presented an interesting nonunimodal variation, with biovolume varying from 0 to c. 30 mm³ L⁻¹ in short time intervals (< 30 days). These temporal trends allowed the evaluation of the isolated effects of nonclimatic variables. Cylindrospermopsis raciborskii was connected with several variables, but nitrogen was the major determinant of its dynamics. Blooms were observed when dissolved inorganic nitrogen (DIN) was scarce (< 50 µg L⁻¹), mainly in relation to the availability of phosphorus and total-N (DIN : total-P < 3 and DIN : total-N < 0.04). This paper contributes to establish strategies to avoid C. raciborskii blooms, suggesting that a management in P levels would be not sufficient. It is necessary to consider N availability to avoid its dominance in the reservoir.

Feeding of Limnoperna fortunei (Dunker 1857): filtration rates with emphasis on Cyanobacteria use - DOI: 10.4025/actascibiolsci.v26i4.1523 / Alimentação de Limnoperna fortunei (Dunker 1857): taxas de filtração com ênfase ao uso de Cyanobacteria- DOI: 10.4025/actascibiolsci.v26i4.1523

Limnoperna fortunei is an invasive species in South America. The massive growth of this species became a great problem for environment and for the companies that use raw water. Limnoperna fortunei is a filter-feeding mollusk that feed on phytoplankton and other suspended particles. Filtering mollusks are great toxin bioaccumulators. Then L. fortunei has a potential cyanotoxin bioaccumulation and transfer in the food chain. In this study, in vitro experiments showed that L. fortunei is able to feed on Cyanobacteria toxic species, Microcystis viridis and Pseudanabaena sp. The filtration rates were 17.20 and 24.52mL.mgDW-1.h-1, respectively. They were similar as for the Chlorophyta Selenastrum capricornutum 11.91mL.mgDW-1.h-1. Results showed that cyanotoxins bioaccumulation by Limnoperna fortunei could be a future problem because of the high densities reached by these organisms and their feeding utilization by fish.

Limnoperna fortunei é uma espécie invasora na América do Sul que, devido ao seu crescimento excessivo, tornou-se um sério problema para o ambiente e para os setores usuários de água bruta. L. fortunei é um molusco filtrador que se alimenta de fitoplâncton e outras partículas suspensas. Moluscos filtradores são grandes bioacumuladores de toxinas. Desta forma, L. fortunei apresenta um potencial de bioacumulação e transferência na cadeia trófica de cianotoxinas. Neste estudo, experimentos in vitro demonstraram que L. fortunei é capaz de alimentar-se de espécies de Cyanobacteria potencialmente tóxicas, Microcystis viridis e Pseudanabaena sp. As taxas de filtração foram 17,20 e 24,52mL.mgPS-1.h-1, respectivamente, sendo similares à encontrada para a Chlorophyta Selenastrum capricornutum 11,91mL.mgPS 1.h-1. Os resultados indicaram que a bioacumulação de cianotoxinas por L. fortunei pode tornar-se um problema futuro visto as grandes densidades que esses organismos atingem e a sua utilização como item alimentar de peixes