Copper (Cu) is commonly used in aquaculture ponds to control cyanobacterial blooms. In Alabama, copper is often used when blooms become evident and there is not a strong understanding of how to use dosing to mitigate bloom development. To improve management plans to address harmful algal blooms, I carried out a number of studies characterizing the effects of copper on cyanobacterial species that are commonly found in Alabama catfish ponds. Three cyanobacteria: Microcystis, Anabaena, and Oscillatoria were isolated from a local catfish pond and culturing methods were developed. All three species were exposed to copper using a dose-response format ranging from 0-200 µg/L to identify decreases in cell density, impacts on growth rates, chlorophyll concentrations, and the phycocyanin: chlorophyll ratio. As these algal strains are grown in aquaculture ponds which have consistent copper exposure, Microcystis were compared to a lab strain (UTEX 3037). The results demonstrated that Cu affected biological performance of the algal species. Using chlorophyll-a concentrations to determine Cu toxicity, the 96-h EC50 values were 15.7, 19.8, 21.4, and 12.0 µg/L Cu for UTEX 3037, Microcystis, Anabaena, and Oscillatoria, respectively. Based on the results of cell density measurements, the 96-h EC50 values for UTEX 3037 and Microcystis were 15.6 and 19.9 µg/L Cu, respectively. These EC50 values indicate that both measurement endpoints gave consistent results. Among the algal species, Oscillatoria appeared to be the most sensitive to Cu. These results highlight the need for species-specific knowledge of how different species react to Cu pollution in order to effectively manage aquatic environments. The development of focused mitigation methods will be greatly impacted by the resolution of dose-response connections between Cu exposure and cyanobacterial populations as well as the validation of chlorophyll concentrations as a proxy for algal density. To formulate effective management methods that mitigate detrimental impacts of Cu contamination on cyanobacterial communities, more studies are necessary to fully understand the underlying processes regulating the observed responses.
Keywords: copper toxicity, harmful algal bloom, Microcystis, Oscillatoria, Anabaena