Award: OCE-1233027

Lionfish (Pterois volitans/miles) are predators on Pacific and Indian Ocean coral reefs that were introduced to the coastal waters of Florida in the 1980s, likely by the aquarium trade (Fig. 1). Voracious consumers of small native coral-reef fishes, including the juveniles of both fisheries species (such as juvenile grouper and snapper) and ecologically important species (such as parrotfishes), the invader has undergone a population explosion that now ranges from the U.S. southeastern seaboard to the Gulf of Mexico and across the greater Caribbean region (Fig. 2). The lionfish invasion has been recognized as one of the major conservation threats worldwide. Our study region -- the Bahamas -- supports the highest abundances of invasive lionfish globally. Our research has focused on two key questions: (1) Do any native coral-reef species provide resistance to the invasion by inhibiting lionfish? (2) What are the ecological effects of the lionfish invasion? Our previous NSF project focused on question (1) and found that native predators, parasites, and potential competitors do not inhibit invasive lionfish in any substantial way. This NSF project focused on several aspects of question (2) regarding how invasive lionfish affect Atlantic coral reefs (Fig. 3). These studies benefit reef managers and the public by documenting the negative effects of lionfish and conveying the importance of controlling the invasion by means of lionfish derbies and targeted fisheries: (a) How does lionfish predation directly affect populations of native coral-reef fishes? Multiple field experiments where we manipulated the abundance lionfish on reefs of various sizes showed that lionfish cause severe population declines in many species of native fish. In extreme cases, some species were driven to local extinction. In some cases, baby fish avoided native predators yet not lionfish, which increased their susceptibility to predation by the invader. (b) How does lionfish predation indirectly affect the broader native coral-reef ecosystem? Field experiments showed, first, that lionfish reduce the feeding rate of seaweed-eating fishes. Because seaweeds can smother corals, this effect may indirectly allow seaweeds to displace corals, hastening the demise of already stressed coral reefs in the invaded region (Fig. 4). Second, lionfish have almost no effects on native cleaner gobies, and so do not inhibit this mutualism that benefits the native fish community. Third, lionfish are not attacked by territorial damselfishes, and so have access to small prey that live in damselfish territories. Fourth, lionfish attack one species of basslet more than another, which alters the level of competition between basslet species. (c) Are lionfish populations reaching levels where natural population limits are evident? Field experiments indicated that lionfish must reach very high abundances before their growth rate slows. When lionfish deplete a reef, they start feeding in surrounding habitats, such as seagrass beds, where they also lower native fish abundance. Toward the end of our study, we noticed that lionfish abundances in the central Bahamas were starting to decline despite there being no lionfish removals there. At this time, we are unsure whether this trend will continue. Dissemination of this research has included numerous public presentations and over 30 peer-reviewed publications in scientific journals, with additional publications in preparation. These papers and other media coverage and outreach materials, including a TEDx talk, are available at our lionfish web page (http://hixon.science.oregonstate.edu/content/highlight-lionfish-invasion/). This grant supported the PhD research of 6 graduate students, one of whom is now an assistant professor, four of whom are now post-doctoral researchers in marine ecology and conservation biology at other universities, and one of whom is writing her dissertation. Of these 6 graduate students, one is African-American, one is Asian-American, and four are women. This grant also partially supported a postdoctoral fellow who is now an assistant professor. Finally, several undergraduate students served as lab and field assistants, most of whom are now graduate students at other universities. Importantly, the lionfish invasion is bringing much needed media attention to the issue of invasive species and the role of all citizens in preventing the introduction and spread of harmful alien species. Last Modified: 01/18/2018 Submitted by: Mark A Hixon