Analysis of bulk stable isotopes and trophic positions of invasive lionfish (Pterois volitans) on deep versus shallow reefs at Curacao

In the decades since their introduction, invasive Red lionfish (Pterois volitans) have spread throughout reefs across the entire tropical western Atlantic Ocean (TWA). Adult lionfish are largely free from predation in the TWA, where they prey on native fish populations and compete with native mesopredatory fishes. Recent explorations of deep-reef habitats have found that lionfish are common on mesophotic and rariphotic reefs down to 304 m, bringing into question the extent of impact that invasive lionfish have on deep vs shallow reefs. A recent Caribbean study found that lionfish from mesophotic habitats are older, bigger, more reproductively active, and have denser populations compared to those from shallow reefs. However, variation in trophic ecology between these two populations is not well understood due to challenges collecting lionfish below traditional SCUBA-diving depths. In the present study, lionfish were collected at Curaçao from deep reefs (60–174 m) using the Curasub submersible and were compared to specimens collected from adjacent shallow reefs (5–37 m). From each fish, scale, muscle and heart tissue were subjected to bulk stable carbon and nitrogen isotope analyses to examine trophic differences over long, intermediate, and short-term temporal scales, respectively. We found that deep lionfish have a significantly higher (~ 0.3‰) trophic position than shallow lionfish. Our results also indicate that on intermediate and longer temporal scales, δ¹³C values of deep lionfish overlap with but are slightly broader than that of shallow lionfish. However, on shorter time scales, deep lionfish are depleted in δ¹³C. This may suggest lionfish migrations between deep and shallow reefs, or that the carbon signatures across depth are more similar than previously considered. These findings underscore the importance of understanding the impact invasive lionfish have on reef ecosystems and may have broad implications for the effectiveness of invasive-species management on deep reefs.