Abstract

Lionfish (Pterois volitans and P. miles) have become invasive across the western Atlantic and are believed to have caused up to 94% declines in fish abundance in some areas. However, their impacts are mostly estimated from small-scale patch reef studies over short timescales (weeks to months). Given that patch reefs, as small, isolated reef systems, are particularly vulnerable to invasive predator arrival, it has been suggested that regional lionfish impacts have been drastically overestimated. To investigate regional-scale lionfish impacts beyond patch reefs, we used an 18-year dataset comprising 11,000 transects, representing multiple reef types from eight countries. We gathered regional data to control for 14 biological, physical, social and management variables known to affect reef fish communities. Initial lionfish invasion occurred over six years in our dataset, thus reducing the potential influence of large- scale point impact events (e.g hurricanes, bleaching) on our results. We centred the data on year of lionfish arrival and investigated the effects of lionfish on native fish community composition, and on the abundance, richness and diversity of native fish communities. We detected clear shifts in native fish communities between pre-invasion and two or more years post-invasion, indicating a region-wide lionfish impact on native fish communities that resulted in a permanent and stable post-invasion fish community. We found that prior to lionfish arrival, most reefs were showing steady increases in fish abundance, species richness and diversity. These increases continued following initial lionfish invasion, however, we detected simultaneous declines in all metrics five years after invasion. With our staggered invasion dates and comprehensive set of contextual variables controlled for, our results strongly suggest a regionally significant negative impact of lionfish five years post-invasion. Our study builds on previous small-scale studies that have shown lionfish impacts over weeks or months, by identifying regional scale impacts detectable several years post-invasion.

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