Aspectos ecofisiológicos da Cianobactéria tóxica Raphidiopsis Raciborskii: implicações para o monitoramento e manejo de reservatórios tropicais

Abstract

The objective of this study was to identify the environmental factors that regulate the biomass of Raphidiopsis raciborskii and the production of saxitoxins (STXs) in the tropical semi-arid reserve, and to determine the importance of two synergistic effects of temperatures and nutrients on the ecophysiology of strains of this species. Therefore, the study was composed of two chapters with the following objectives: (i) Identify the relationship between the biomass of R. raciborskii and the concentrations of STXs in the waters of tropical reservoirs and how the environmental factors are explained; (ii) Investigate the role of two synergistic effects of temperature and nutrient variation on toxic blooms of R. raciborskii. We evaluate the effects of environmental factors on the biomass of R. raciborskii and concentrations of STXs, as well as the relationship existing between the biomass of the species and the levels of STXs in 37 reserves of the State of Paraíba. We identified for the first time, the risk of exposure to STXs, using the risk ratio (HQ) and the risks of chronic exposure to toxin, by means of the cumulative distribution function (CDF) for the consumption of untreated water in supply reservoirs public in the semi-arid region of Brazil. We verified a correlation between the biomass of R. raciborskii and the concentrations of STXs. Phosphorus positively influences the biomass of the species while pH significantly influences the concentrations of STXs, indicating different factors that influence the biomass of R. raciborskii and the STXs. We found that the risks of exposure are generally low to moderate, or CDF highlights the risk of chronic exposure due to the low concentrations of toxins in more than 90% of the samples. Our results emphasize the potential expansion of R. raciborskii in tropical environments due to increased phosphorus, amplifying the levels of STXs transmitted through water and the associated risks of poisoning. To evaluate the synergistic effects of temperatures and nutrients on ecophysiological responses (growth, photosynthetic taxa, cyanotoxin content) in R. raciborskii strains, we tested 5 nutritional conditions, with high concentrations of nitrogen (N+) and phosphorus (P+), and low concentrations. of nitrogen (N-) and phosphorus (P-), I have as a control condition (C) or ASM-1 without modifications, and three temperatures (15, 25 and 35 ºC) that correspond to the minimum tolerable for the species at the exacerbated temperature, Above the proposed increase in IPCC hair at the end of this cycle. Changes in ecophysiological answers vary between strains, indicating the fragility of generalizing physiological answers based on some strains. The increase in biomass, as well as the production and release of toxins produced by R. raciborskii under ideal temperatures, especially at high levels of nutrients, highlights the need to control double the contribution of N and P to ecosystems to control the florações of R. raciborskii and the risks of intoxication. Finally, the present study contributes to the understanding of the influence of environmental factors on the regulation of the production and release of toxins produced by R. raciborskii, providing relevant information for the control of the populations of this cyanobacteria in scenarios of climatic changes and eutrophication. Keywords: cyanobacteria; cyanotoxins; toxic blooms; climatic changes; eutrophication.