Article: Anton A, Simpson MS, Vu I (2014) Environmental and Biotic Correlates to Lionfish Invasion Success in Bahamian Coral Reefs. PLoS ONE 9(9): e106229. doi:10.1371/journal.pone.0106229
One of the biggest issues conservationists face is the establishment of a non-native species in a habitat. If an invasive, non-native species is integrated into a new habitat, the dynamic of the whole ecosystem shifts. In many cases the exotic species will show up to a new habitat and declare it their own by outcompeting the native species for its resources. One example stems from the Argentine ant, which was accidently released in California and has now taken over Northern California by depressing the native ants of their habitat and food resources.
One of the most serious cases of invasion happened when the native Indo-Pacific Lionfish found its way into the tropical Caribbean oceans. While lionfish used to live peacefully in its old home, they now pose a huge threat to the Caribbean reefs. Lionfish are able to spawn almost continuously, releasing 2 million eggs a year, which has allowed their population density to blow up in the Caribbean to 5 times greater than it is in their native Indo-Pacific habitat. Researchers from North Carolina set out to quantify what physical and biological factors contribute to the success of lionfish in the Bahamas.
Field surveys were conducted around San Salvador Island, Bahamas (Fig.1). Eighteen (18) sites were selected, with care to avoid sites close to mooring balls, as to avoid any influence of spearfishing. Three separate 50 m transect lines were placed at each site and fish counts were run along the transect lines. Divers would swim along the line, counting any lionfish, potential lionfish prey species, and potential lionfish predator species. All sampling was done visually and no fishes were handled during the field study. All fish species noted were identified to species level and measured based on total length sight estimation.
Wave exposure and habitat complexity could be key environmental predictors to lionfish success. In order to estimate wave exposure, the average bottom velocity was taken at each site, or in other words, how much wave exposure there was near the seafloor. Wave direction, height, and depth were all obtained through probe meters or available data online. To determine the habitat complexity of each site, the benthic habitat was quantified based on coral cover, macroalgae, turf algal, and sponge coverage. The rugosity (or amplitude of the reef) of the reef was also determined in order to understand the reefs complexity.
Findings and Significance
Lionfish density was an average of 13 individuals, but some sites didn’t have any recorded lionfish sightings, while other sites had up to 73 individuals. Predator species of the lionfish averaged 540 individuals in the medium size category and 39 individuals in the large size category (Table 1). While lionfish density was positively related to large predator abundance, it was negatively correlated to wave exposure, as well as reef rugosity. When wave exposure was categorized based on high and low tide, dramatic differences were seen in lionfish densities. Lionfish density was about 22 times higher on low wave exposure environments, showing how lionfish prefer more sheltered sites.
The energetic cost of fighting against high wave exposure sites could potentially be the reason lionfish tend to stay in lower wave action sites. This could mean high energetic environments could serve as a refuge for lionfish prey. Unfortunately low exposure sites showed more abundance of macroalgae, which provides shelter and food for small fish. With a vast amount of prey hiding in the macroalgae, low wave exposure sites, this also might be a reason lionfish tend to hang out there. In this study small fish were indirectly related to low wave exposure sites and therefore no positive conclusions can be made, which suggests a potential lack of indirect bottom-up control of lionfish.
Direct lionfish management control is still strongly recommended through preservation and restoration, as lionfish numbers have not leveled out. This study has also provided an alternative management strategy, to safely guard lionfish prey. Energetic, high wave, environments might provide a refuge for small fish species against the lionfish invasion.