Lessons learned from mesocosm experiments with curcumin: Pilot studies of a harmful algal bloom mitigation technique

Abstract Curcumin, a natural plant product derived from Curcuma longa , was assessed as a mitigation technique against the toxic bloom‐forming dinoflagellate Karenia brevis in two mesocosm experiments taking place in 2022 and 2024. In these experiments, curcumin was applied at a dosage of 5 mg L −1 to K. brevis concentrations of ~ 1.0 × 10 6 cells L −1 in 1400 L mesocosm tanks, and changes in cell concentrations, brevetoxins, and water chemistry parameters were examined over time. The 2024 experiment expanded on the 2022 experiment by examining nutrient dynamics and water clarity and explored the potential effects of curcumin on mortality rates, behavioral responses, and toxin content of hard clams ( Mercenaria spp.), sea urchins ( Lytechinus variegatus ), and blue crabs ( Callinectes sapidus ). In both experiments, curcumin treatment significantly reduced algal cells and total toxins within 24 h. In the 2024 experiment, curcumin caused a significant increase in turbidity above background levels but had no significant impact on total dissolved nitrogen or total dissolved phosphorus. Additionally, curcumin appeared to have no significant effect on animal mortality or behavior after 72 h of exposure. Here we present the results of these pilot studies with curcumin and share the challenges we experienced working with mesocosms for harmful algal bloom mitigation research.