NCCOS sponsored an extensive investigation on a natural bacteria-produced algicide that kills harmful algal bloom dinoflagellates. Findings showed the algicide is mostly benign to other organisms. The research strongly suggests that certain natural algicidal compounds are promising tools to control toxic dinoflagellate blooms in an environmentally friendly way.
Natural compounds hold promise for combating harmful algal blooms (HABs), provided they minimally impact non-target organisms. One potential approach to mitigate HABs is to utilize naturally occurring species or the compounds they produce.
Long-term NCCOS research under multiple projects (2010, 2015 and 2020) showed the bacterium “Shewanella sp. IRI-160” can produce a compound lethal to HAB dinoflagellates such as Karenia brevis and Karlodinium veneficum. The algicide appears to trigger cell cycle arrest and programmed cell death. Investigators hope they can use bacterium and/or its chemical compound to prevent or mitigate toxic dinoflagellate blooms; however, effects on non-target organisms were unknown until now.
Published in the Springer Nature’s journal Scientific Reports, the algicide IRI-160AA was tested using bioassays on various developmental stages of the copepod Acartia tonsa, the blue crab Callinectes sapidus and the eastern oyster Crassostrea virginica. Bioassays with dinoflagellates demonstrated that a 1% addition of the algidce reduced dinoflagellate abundance by 50%. In contrast, mortality experiments with the copepod revealed that the 24-hour (h) Lethal Concentration 50 (LC50), the concentrations of the chemical that kills 50% of the test animals during the observation period, was 13.4% for adult females and 5.96% for early-stage nauplii larvae. For the blue crab, the 24-h LC50 for first-stage zoeae larvae was 16.8%; results were not significant for later-stage crab megalopae larvae or oyster larvae. Respiration rates generally increased for small percentages of larvae but rates of later crustacean larval stages and oysters were unaffected. Activity levels (swimming, feeding, etc.) were affected for young crab and oyster larvae. Activity levels of later larval stages and of adult copepods were unaffected and algicide effects were minimal or absent at the concentration required to inhibit dinoflagellate growth.
The researchers found that overall, smaller, non-target biota with higher surface to volume ratios (e.g., microzooplankton) could be negatively impacted from IRI-160AA algicide treatments. Collectively, the lethal and sublethal bioassays suggest earlier, smaller life stages are more sensitive to this algicide than later, larger stages. Overall, however, the taxa and stages assayed were tolerant to the algicide at concentrations required for dinoflagellate mortality.
In conclusion, isolated algicidal compounds such as IRI-160AA are promising in their role of controlling harmful dinoflagellate blooms. While there may be risks to higher animals (metazoans) at the site of initial application where locally high concentrations may be experienced, these effects are limited. Given the substantial negative impacts of HABs across higher trophic levels, the risk of direct exposure of metazoans to algicide during control seems tolerable. These effects should be confirmed in mesocosm studies where dinoflagellates and metazoans can be exposed to the algicide simultaneously.
Citation: Simons, Victoria E., Kathryn J. Coyne, Mark E. Warner, Margaret M. Dolan and Jonathan H. Cohen. 2021. Effects of a bacteria-produced algicide on non-target marine invertebrate species. Scientific Reports 11, 583. https://doi.org/10.1038/s41598-020-79814-w