Assessing seascape-wide ecological connectivity in support of conservation and restoration efforts in the Florida Keys, USA
Creators: Stuart, Courtney E
Publisher: name: University of Alberta Library
Year: 2022

<p>Multi-habitat use is a widespread strategy for marine organisms, including numerous coral reef fish and invertebrate species of ecological and economic importance. Through daily, seasonal, or ontogenetic migrations, these species play vital roles in maintaining functional connectivity, i.e., the exchange of organisms, energy, nutrients, and other matter between habitats in spatially and topographically heterogeneous seascapes. However, stressors operating over multiple spatiotemporal scales, including global ocean warming and acidification, land-use change, and resource overexploitation, are degrading and fragmenting marine habitats, threatening functional connectivity. Identifying, protecting, and restoring habitat patches and corridors responsible for maintaining multi-scale and multi-species functional connectivity is essential for marine conservation. In this thesis, I address key knowledge gaps in our understanding of the spatial and environmental conditions supporting the cross-shelf (&gt; 5 km) ontogenetic migrations of two mesopredatory reef fish species occupying a heavily modified coastal seascape in the Florida Keys, USA—gray snapper (Lutjanus griseus) and bluestriped grunt (Haemulon sciurus). In addition to supporting local fisheries, both species play a critical role in shaping ecosystem function by delivering allochthonous nutrient subsidies and modifying rates of herbivory, corallivory, and predation by other community members, yet their ontogenetic habitat shifts remain difficult to track using conventional techniques due to their small body size at migration and the broad spatiotemporal scales over which they move. In Chapter 2, I first compared two techniques for modeling seascape-wide habitat suitability for the migratory sub-adults of each species—penalized logistic regressions and Maximum Entropy (MaxEnt) modeling—using fish records from SCUBA-diver surveys and high-resolution spatial data on bathymetry, seasonal water conditions, habitat configuration, and seascape surface geomorphology. I found that across species and suitability thresholds, MaxEnt’s discriminatory ability exceeded that of the penalized regressions. Furthermore, MaxEnt’s patchy suitability predictions, which were driven primarily by benthic habitat composition, depth, and broad-scale seafloor features, more closely aligned with the known ecology of the study species. Then, in Chapter 3, I modeled potential functional connectivity for sub-adult L. griseus and H. sciurus using a spatial graph-theoretic approach in which MaxEnt-derived nodes (i.e., suitable habitat patches) and edges (i.e., least-cost paths predicted over species-specific resistance surfaces) were used to quantify and visualize the probability of connectivity at both the local and seascape scales. I then used the resulting connectivity networks to evaluate and rank the contributions of candidate sites prioritized for coral restoration as part of the spatial design of a broad-scale, multi-million dollar (USD) coral reef restoration program recently established in the Florida Keys—Mission: Iconic Reefs—to seascape-wide connectivity. I hypothesized that sites located adjacent to potential mangrove and seagrass nurseries would support higher levels of connectivity for both species, and thus be of the greatest value for restoration. Spatial graph analyses revealed that, across scales, the Florida Keys seascape presently supports a higher level of potential connectivity for sub-adult H. sciurus relative to L. griseus. Moreover, these models suggest that the Mission: Iconic Reefs sites are more likely to benefit from ecological interactions with migrating H. sciurus compared to L. griseus based on their spatial configuration. Contrary to my hypothesis, however, site-specific connectivity contributions were not found to be related to nursery proximity. This thesis demonstrates how spatial graph connectivity analyses informed by habitat suitability modeling can be leveraged as a tool in support of marine habitat restoration planning through the development of data-driven spatial priorities and joins previous research showcasing the ecological benefits of integrating multi-species connectivity in marine reserve design, including productivity and diversity enhancements.</p>