Effects of the bacterial algicide IRI-160AA on the microbial community composition of the Delaware Inland Bays

Abstract

Global increases in harmful algal blooms (HABs) have spurred interest in measures to control these blooms. Prevention, control, and mitigation of HABs are of human interest, and there are naturally-occurring compounds that may directly influence these processes. Use of these compounds appears promising, but effects to non-target organisms are also of concern. The Delaware Inland Bay (DIB; Delaware, United States) system is host to the algicidal marine bacterium Shewanella sp. IRI-160, which secretes one or more compounds having allelopathic effects to dinoflagellate algae. The research described here had three objectives: (1) to determine whether the algicide has a significant effect on microbial community composition during or after repeated dosing, (2) to determine whether the algicide has a significant effect on microzooplankton grazing rates in natural communities, and (3) to determine the extent to which ammonium contributes to the algicidal effect of IRI-160AA. ☐ In Chapter 2, Quantitative PCR and DNA sequencing indicated a decline in natural dinoflagellate community abundance with repeated algicide daily dosing; however, community photosynthetic biomass was not negatively altered by the final timepoint. Additionally, community composition was shown to play a major role in dissolved nutrient and organic carbon assimilation. ☐ In Chapter 3, microcosms were dosed with the algicide at EC50 concentrations and incubated for 24 hours at four dilution factors. Microzooplankton grazing rates did not significantly decrease in the presence of the algicide at EC50 concentrations yet dominant microeukaryotic groups within communities did shift after 24 hours of exposure. ☐ In Chapter 4, photochemical parameters were used to investigate the extent to which ammonium contributes to the algicidal effect of IRI-160AA. Maximum yield of photosystem II (Fv/Fm), photochemical connectivity between photosystem II reaction centers (ρ), and the re-oxidation rate of the primary quinone (τ) all indicated that ammonium negatively affects the photosynthetic machinery of photosystem II but not to the same extent as IRI-160AA with equal NH4+ concentrations.