A critique of Mumby et al. 2011 “Grouper as a natural biocontrol of invasive lionfish”

Mumby et al. (2011) tested the biotic resistance hypothesis by comparing the biomass of invasive lionfish (introduced from the Indo-Pacific) and native grouper (Serranidae) at 12 sites within and adjacent to the Exuma Cays Land and Sea Park, The Bahamas. They reported that mean lionfish biomass was slightly lower within the reserve, compared to adjacent fished sites, and that there was a negative relationship between the biomass of lionfish and grouper. However, their study has a number of limitations and does not constitute sufficient evidence of a level of biotic resistance that would be ecologically meaningful. For example, the study design is pseudoreplicated and the biomass of lionfish is extremely low relative to observed values across the Caribbean. Furthermore, the effect size (assuming that there is an effect of native grouper) is very small compared to the natural range of lionfish biomass. Given the problems with Mumby et al. (2011) and evidence from other studies (e.g., Hackerott et al. 2013) that the biomass of lionfish and grouper is unrelated, it seems clear that managers cannot rely on native grouper populations to control the lionfish invasion.