Relative sensitivity of cyanobacteria and green algae to copper exposure: implications for increased treatment efficiency of harmful algal blooms and reducing environmental copper load

Copper (Cu) is commonly used to control harmful algal blooms (HABs), especially in pond aquaculture systems. The present study aimed to investigate the relative sensitivity of cyanobacteria and green algae to Cu to provide more scientific information that can be used to improve the efficiency of HAB treatments in aquaculture ponds. Three cyanobacterial species that are commonly present in earthen pond aquaculture systems in Alabama, USA (Microcystis spp., Anabaena spp., and Oscillatoria spp.) were isolated from an aquaculture pond used to produce channel catfish, Ictalurus punctatus, in Alabama and cultured under laboratory conditions in the Ecotoxicology and Risk Assessment Laboratory of Auburn University. All three algal species were exposed to Cu using a dose-response design with Cu concentrations ranging from 0 (control) to 150 µg/L Cu to determine their biological responses to Cu. The experiment was also conducted with a standard laboratory strain of cyanobacteria, UTEX 3037, for comparison with field-isolated cyanobacteria. Cell density and chlorophyll concentrations were measured to evaluate effect concentrations (ECs). Comparisons of ECs were conducted to assess the sensitivity of cyanobacteria and green algae to Cu, both from the current study and the literature. Results showed that EC values were dependent on algal species and exposure time. The EC50 ranged from 11.90 µg/L Cu (Oscillatoria spp. for 48 hours of exposure) to 96.70 µg/L Cu (UTEX 3037 for 24 hours of exposure). Among the algal species studied, Oscillatoria spp. appeared to be the most sensitive to Cu. Cyanobacteria were more sensitive to Cu than were green algae. The results of the present study highlight the need for cyanobacterial species-specific sensitivity to Cu, which is crucial for developing HAB treatment plans to enhance efficacy and prevent underdosing or overdosing of Cu, thereby reducing costs and minimizing Cu load into pond aquaculture systems.