This was a field experiment conducted on artificial patch reefs to test for effects of invasive red lionfish density on native coral-reef fishes. Four reefs were used as 0-lionfish control reefs and there was one reef per remaining lionfish treatment (2, 4, 6, 8, 10, and 12 lionfish/m²). Using SCUBA and handnets, we collected lionfish ranging in initial size from 40 to 71mm total length [TL] from nearby reefs.  Each lionfish was given a unique elastomer tag (Northwest Marine Technology Inc., Shaw Island, WA, USA) to differentiate between lionfish at the start of the experiment and any new immigrants over the course of the study and to monitor demographic rates as part of another study (see related files and references). Treatments were started on all reefs within a 2-week period. To maintain treatments, we monitored lionfish density during weekly visits and removed any new lionfish recruits (total of 15 throughout experiment) and immigrants (total of 5 throughout experiment). In addition, we removed resident native piscivores and standardized the number of Nassau grouper (Epinephelus striatus) and territorial damselfishes (Stegastes spp.) weekly to mitigate any confounding effects of these strong interactors on fish recruitment. Of the lionfish initially placed on the reefs, only 6 out of 40 disappeared. To account for the small changes in lionfish density throughout the experiment, we averaged the weekly lionfish densities on each reef over the course of the experiment (1, 2, 4, 7, 10, and 12 lionfish/m²).

Following the establishment of lionfish density treatments, a pair of divers using SCUBA censused the entire fish community on each reef weekly for 7 weeks, recording the species, abundance, and body size (TL estimated to the nearest centimeter) of all fish present both on the reefs and within a 1-m radius around the reefs. Divers slowly approached the reefs and first counted all planktivorous and active species hovering above the reefs from a distance of approximately 3 m. From a distance of 1 m, the divers slowly circled the reefs and counted all other species, using dive lights to count cryptic species in holes.