Quicklime-based eradication attempt of Xenopus laevis as a model for controlling pond invasions

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Aquatic non-native invasive species are notoriously difficult to eradicate, particularly in pondscapes where populations can spread rapidly, persist in unmanaged refugia, and recolonise treated sites.In such contexts, high-intensity management interventions may be justified, balancing short-term collateral impacts against the prevention of permanent establishment and long-term damages.Pondlevel interventions with chemical eradication methods, such as rotenone or herbicide application, can be effective but raise ethical and environmental concerns.Here, we evaluate quicklime (calcium oxide, CaO) application as a more environmentally friendly chemical control tool for pond invaders, using the African clawed frog (Xenopus laevis (Daudin, 1802)) invasion in Belgium as a case study.When applied to water, quicklime temporarily and rapidly increases pH to lethal levels.In winter 2023, three ponds with breeding populations of X. laevis were drained, pretreated with fyke netting to remove as many aquatic fauna individuals as possible, temporarily fenced, and treated with quicklime.Management costs were documented and treatment effectiveness was assessed through pH measurements, visual surveys, and environmental DNA (eDNA) quantification in a before-after study design.Immediately after treatment, large numbers of deceased post-metamorphic individuals were recovered, indicating treatment-induced mortality.While X. laevis eDNA concentrations in winter post-treatment were low and, in one pond, zero, posttreatment summer eDNA concentrations were consistently lower than pre-treatment summer eDNA concentrations, suggesting treatment-induced population decline, possibly followed by partial population recovery.Water pH returned to near baseline levels within one month.Total management costs were conservatively estimated at €43,880 (excluding VAT), of which the majority was attributable to quicklime purchase (€23,525) and manual labour (€17,600).We provide the first field-based preliminary evidence that quicklime can induce large-scale mortality and population size reductions in X. laevis populations in small to medium-sized ponds.These findings remain preliminary due to limited replication, the absence of control sites, and the inability to disentangle the effects of manual removal from quicklime application.We discuss practical considerations, limitations, and broader applicability, proposing quicklime as a high-intensity option within integrated management strategies for pond invaders.

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