Graduate Thesis Or Dissertation
 

Habitat Use and Ecological Interactions of Invasive Lionfish in the Bahamas

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  • Invasive species are a growing global economic and ecological problem. Invasive Indo-Pacific lionfish (Pterois spp.) are known to have extreme negative effects on coral-reef communities in the Bahamas, so understating their distribution within and among reefs, what limits their local movements, and the effects they have on native prey species is crucial for managing the invasion. I studied invasive lionfish off the island of Eleuthera, the Bahamas, at multiple spatial scales. In Chapter 2, I examined their regional distribution and abundance. I used multiple predictive models with a variety of data sources to determine which model was best for predicting lionfish presence/absence and density among reefs. The model with the highest predictive capability included remotely sensed satellite data as well as diver collected microhabitat data for both presence/absence and density of lionfish. The ability to predict lionfish density increased in the model that included native Nassau grouper (a potential predator and competitor of lionfish), but decreased in the lionfish presence/absence model. In Chapter 3, I examined what biotic and abiotic factors influence lionfish site fidelity at particular reefs. Using dorsal spine clips, and detailed information about coloration, I tracked individual lionfish on reefs over two field seasons. I also collected abundance and size data on native grouper and prey species and conducted detailed habitat surveys focusing on reef structural complexity. I used linear mixed effects models to determine which factors were correlated to three different measures of site fidelity: frequency (number of times lionfish were seen/ number of surveys), duration (time between 1st and last sighting of lionfish), and distance (linear distance between sighting locations within a reef). Lionfish density was positively correlated with both frequency and duration, and prey density was negatively correlated with frequency. None of the variables were correlated with average distance moved on the reef. However, lionfish density was correlated with habitat complexity, which suggests that there is both the biotic influence of conspecifics and prey as well as an indirect effect of habitat on lionfish site fidelity. Finally, in Chapter 4, at the individual scale, I explored the potential for lionfish to have consumptive (lethal) and/or non-consumptive (nonlethal) effects on the common native prey Stegastes partitus, the bicolor damselfish. I observed the behavior of bicolor damselfish in the presence of either lionfish or native species (including a carnivore and an egg predator) to determine whether bicolor damselfish respond to lionfish similarly to native species. I found that bicolor damselfish do not change their behavior in the presence of lionfish, and even respond less aggressively to lionfish than non-threatening native species. I also measured bicolor fecundity as number and size of egg masses produced. Despite having no behavioral response to lionfish, bicolor damselfish inhabiting reefs with high lionfish densities had lower fecundity. This pattern may be due to the average adult bicolor being smaller in size, which could be a lagged non-consumptive effect of lionfish. These results show that investigation of invasive species at multiple spatial scales can increase our understanding of their overall effects on native communities. While both habitat and native grouper may have a large effect on the presence and densities of invasive lionfish, lionfish habitat fidelity is more strongly correlated to densities of conspecifics and prey. Additionally, lionfish have non-lethal effects on certain native species that are not apparent if only behavior is examined.
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