Cyanobacteria blooms in city parks: implications for urban ecology in a climate change scenario

• Autor(a) principal: Vieira, Bruna Soares
• Data de Publicação: 2023
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10773/40881
• topic: Cyanobacterial blooms; Climate change; Anthropogenic pressures; Cyanotoxins; Neurotoxicity; Multistress; Chemical contaminants; Urban ecology; Danio rerio embryos

Cyanobacteria can produce toxins that can have negative effects on aquatic organisms, wildlife, domestic animals and humans. In the current context of global change, urban parks, renowned for their multifaceted contributions to society, have been largely affected by blooms of toxic cyanobacteria. In the first chapter of this work, the effects of a cyanobacterial bloom, collected from an urban park in Aveiro, in two different stages of evolution on zebrafish embryos (Danio rerio) were assessed, evaluating toxicity in terms of mortality and hatching rates, behavior endpoints (total distance, slow and rapid movements, peripheral distance and different angle classes) and biochemical effects (oxidative stress - Glutathione-S-transferase (GST), Catalase (CAT), Glutathione Peroxidase (GPx) and Glutathione Reductase (GR); neurological damage - Acetilcholinesterase (AChE) and indicator of tissue damage - Lactate dehydrogenase (LDH)) after five days of exposure to cyanobacteria extract and filtered samples. The results showed that the exposure affected development (hatching and delayed development) and caused neurotoxicity, translated into hypoactive behavior, increased thigmotaxis and inhibition of ChE in zebrafish embryos, and that higher toxicity was observed for the cyanobacterial extract and filtered sample with more time of evolution. As an increasingly recurrent phenomenon, the occurrence of cyanobacterial blooms represents an additional layer of stress for ecosystems that are already facing the effects of anthropogenic activities, such as industrial and domestic effluents and agricultural runnoff. In a second chapter, the aim was to know if a sub lethal exposure to cyanotoxins changes the sensitivity of zebrafish embryos to a subsequent exposure to chemical stress. Zebrafish embryos were exposed for 96 hours to three concentrations of cyanobacterial extract from a toxic bloom collected in an urban park lake in Aveiro. After this period, the embryos were exposed to different concentrations of two compounds: the metal cadmium or the fungicide benomyl. The results showed an increase in LC₅₀ values in embryos pre-exposed to the cyanobacterial extract, suggesting that zebrafish embryos developing in cyanotoxins contaminated medium acquired resistance to a subsequent chemical stress, probably by activating detoxification mechanisms earlier than non-exposed embryos. This study showed that cyanotoxins may be an important factor modelling the toxicity of compounds in the aquatic environment that needs to be accounted for in risk evaluation studies.