Short- and long-term effects of culling invasive corallivorous gastropods

Eradicating invasive species and maintaining their populations at acceptable densities is both costly and challenging in marine environments, primarily due to the open water connectivity between culled and non-culled areas. This research aims to evaluate the short- and long-term effects of culling invasive species, considering the invasive gastropod Drupella rugosa (Born, 1778) from the coral reefs of Koh Tao (Gulf of Thailand) as a case study. Ecological, logistical, and behavioural factors that influenced the removal efforts were identified, highlighting key components that can inform future strategies aimed at managing outbreak events. Specific objectives included: (1) estimating gastropod densities and to study the behaviour of D. rugosa on Acropora-dominated reefs; (2) assessing short-term effects of D. rugosa removal by monitoring the fate of grazed corals; (3) examining the long-term impact of culling by analysing data from a removal campaign spanning over a decade, including an evaluation of the effort in terms of time and diver involvement. The relationship between damselfish and the feeding activity of corallivorous gastropods was also investigated. A key finding of this study is that poorly planned culling is ineffective in controlling outbreaks of invasive species such as those belonging to the genus Drupella. Long-term data from culling campaigns conducted between 2010 and 2024 revealed that the number of removed specimens remained relatively constant, despite significant differences in effort. This disparity underscores the lack of strategic coordination in the implementation of removal activities. Following a critical comparison with cases reported in the literature, common issues and transferable strategies were identified and thoroughly analyzed. Directions for management were provided, with the understanding that future actions should be grounded in a thorough knowledge of the species' ecological traits, the biotic and abiotic drivers of outbreak events, a quantitative assessment of its impact on Acropora reefs, and integration into with well-established international removal and prevention programs.