AbstractPremiseA novel control technique was developed to mitigate an invasive siphonous green alga, Avrainvillea lacerata (Dichotomosiphonaceae), within a shallow degraded reef flat in Oʻahu, Hawaiʻi.Methods and ResultsReplicated treatments of 3% and 10% hydrogen peroxide (H2O2) were administered into individual basal attachments of the bed‐forming invasive seaweed on the Paikō reef, Oʻahu. Relative electron transport rate maxima (rETRm) were measured using a Walz Diving Pulse Amplitude Modulated Fluorometer in two replicate 100‐m2 plots in 2020. Over the period of this short‐term study, rETRm decreased following injections of either concentration of H2O2 in contrast with negative and positive controls.ConclusionsCompared with existing techniques that have used oxidizing agents in the marine environment in localized areas, the protocol described here has the potential to successfully decrease macroalgal carbon gain, potentially leading to loss of biomass at larger scales.