Characterizing changes in density, space use, and diel behavior of Lionfish (Pterois volitans) on mesophotic coral reefs in the US Virgin Islands Marine Biology

Lionfish that live in mesophotic reef environments (30 to 150 m depth) are potentially undermining invasive species management efforts on shallower reefs. Understanding the behavior of lionfish in these deeper habitats is critical to characterizing the impacts of mesophotic lionfish on their home reefs as well as on adjacent shallow reefs. In this study, we combined long term monitoring and acoustic telemetry data to characterize the density and behavior of lionfish on mesophotic reefs in the United States Virgin Islands (USVI). Across 10 years of monitoring, significantly higher densities of lionfish were observed on mesophotic reefs as compared to nearshore and offshore reefs in the USVI. We tagged lionfish at two mesophotic reef sites in the territory and found that most of them were resident to the mesophotic areas and had comparable home range sizes to those reported on adjacent shallow coral reefs. We found that a majority of fish displayed crepuscular diel activity patterns, but some individuals had unusually high activity during daytime periods as compared to previous studies of the species. There was variability within the crepuscular activity pattern, with some individuals being more active in the morning and others in the evening crepuscular periods. The persistence of lionfish in mesophotic reef habitats in the USVI suggests that they could be impacting these environments, and future studies and management efforts should focus on identifying, quantifying, and mitigating those effects. Grant no. NA17NOS4820086 Grant no. NA16NOS4820054