No detectable effect of lionfish ( Pterois volitans and P. miles ) invasion on a healthy reef fish assemblage in Archipelago Los Roques National Park, Venezuela

There is an increasing concern that invasive lionfish will have dramatic impacts on native reef fish assemblages in the Caribbean. However, the intensity and speed of such changes will probably depend on the initial structure of each assemblage and on the lionfish population characteristics. The species composition of native fishes, diet and size structures were analyzed on a protected Venezuelan reef, through visual census on zones with and without lionfish, 1 and 3 years after the first sighting of Pterois (lionfish). Lionfish mean density ± SD increased from 30 ± 83.5 ( n = 22) to 121 ± 164 ind ha −1 ( n = 22), with an important increase in lionfish over 30 cm and the near absence of juveniles. Native species richness and densities remained stable through time. No significant change of native fish assemblage structure, species richness and density of potential Pterois prey, predators and competitors was found over time, but zones with lionfish had significantly higher levels of prey and predators, and significantly different fish assemblage structures. Most importantly, there was no interaction between time and the presence of Pterois on these metrics. Our results may suggest that: 1—a healthy composition of the initial structure of the reef fish assemblage may moderate the early impact of lionfish, and the observed lionfish densities (mean ± SD = 121 ± 164 ind ha −1 , n = 22) were not sufficient to induce a significant change in the assemblage; and 2—lionfish probably select zones where species richness and density of prey are the highest.