Stomach content and stable isotope analysis of invasive lionfish ( <i>Pterois volitans</i> ) in the Florida Keys

The invasive red lionfish, Pterois volitans, plays a unique role in seagrass and reef ecosystems, where it functions as a top predator and competitor for both food and shelter. Given the ubiquitous distribution of lionfish in the Gulf of Mexico and Caribbean basins, their species provides an excellent opportunity to understand how an invasive predator's diet and primary energy pathways change as a function of size and habitat type. To investigate these patterns, we studied lionfish from a mosaic of deep reef, shallow patch reef, and seagrass bed habitats in the Florida Keys using stomach contents and stable isotope analysis (δ¹³C and δ¹⁵N). In August 2020, lionfish (n = 48) and other native species were collected from coastal habitats in the Florida Keys, including deep (20-30 m), intermediate (12-18 m), and shallow (<8 m) reefs, to obtain representation of the local food web. Lionfish on shallow reefs were found to feed from different basal carbon sources than lionfish on intermediate and deep reefs. Bayesian mixing models predicted reef particulate organic matter to be the greatest source contributor to the primary energy pathways of lionfish and reef fish at similar trophic levels, and a high degree of resource use overlap between lionfish and native reef fish was documented. Over time, niche overlap with native species could lead to a decline in their populations through resource competition and/or direct predation, thus creating the need to further study the impact of lionfish in the Florida Keys ecosystem. With the increasing scientific consensus that lionfish diets and niche overlap are highly location-specific, this study further contributes to our collective understanding of the role that lionfish play in the food web of patch reefs in the Florida Keys.