I think we are going to start seeing a number of studies that question the conventional wisdom regrading the dramatic impacts lionfish are having on reef fish communities. Here is one from Los Roques in Venezuela. They find no effect on native species richness or abundance 3 years after the invasion (abstract pasted below). It seems the initial studies identifying large impacts were on isolated patches where lionfish could reduce recruitment of new prey. Yet at larger spatial scales (an entire reef tract), perhaps lionfish are not causing major shifts in prey communities.
Abstract. 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.