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High predatory efficiency and abundance drive expected ecological impacts of a marine invasive fish

Emma M. De Roy*, Ryan Scott, Nigel E. Hussey, Hugh J. MacIsaac

*Corresponding author:

ABSTRACT: Invasive species’ ecological impacts are highly variable and mediated by myriad factors, including both habitat and their population abundance. Lionfish Pterois volitans are an invasive marine fish which have high reported detrimental effects on prey populations, but whose effects relative to native predators are currently unknown for the recently colonized eastern Gulf of Mexico. We assessed the ecological impact of lionfish relative to 2 functionally similar native grouper species – red (Epinephelus morio) and graysby (Cephalopholis cruentata) – foraging in a heterogeneous environment using functional response (FR) methodology. We then combined the per capita impact of each species with their field abundance to obtain a Relative Impact Potential (RIP). RIP assesses the broader ecological impact of invasive relative to native predators, the magnitude of which predicts invasive species’ community-level negative effects. Lionfish FR and overall consumption rate was intermediate to that of red grouper (higher) and graysby grouper (lower). However, lionfish had the highest capture efficiency of all species, which was invariant of habitat. Much higher field abundance of lionfish resulted in high RIPs relative to both grouper species, demonstrating that lionfish ecological impact in this region will be driven mainly by high abundance and high predator efficiency rather than per capita effect. Our comparative study is the first empirical assessment of lionfish per capita impact and RIP in this region and one of few such studies to quantify the FR of a marine predator.