The work presented in this dissertation is composed of six chapters, one of which has been published (Wirt et al. 2015). Chapters 2 – 5 are intended to stand alone, with relevant figures, tables and references therein. The sixth and final chapter reviews the previous chapters, notes future work in progress, and makes recommendations for future research directions. Each chapter of the dissertation contributes to, or fully addresses one of two overarching goals. The first goal focuses on ways to best refine the current Acropora spp. critical habitat map originally generated by NOAA, at the time of listing of the species. The second goal of this study is to identify suitable A. cervicornis restoration sites using a species distribution modeling approach and existing monitoring data throughout Florida. Chapter 1 serves as a literature synthesis related to Acropora spp. history and environmental requirements.
The topic addressed in Chapter 2 examines whether the methods developed in Wirt (2011), for southeast Florida and the Florida reef tract, are applicable to the U.S. Virgin Islands and Puerto Rico. This work was published by Wirt et al. (2015) in Global Ecology and
Conservation.
Chapter 3 describes the compilation and processing steps used to amass relevant reef ecosystem data to use for multiple spatial modeling and mapping purposes. The primary use in this dissertation for the data described is to identify suitable Acropora restoration sites using a species distribution modelling (SDM) approach (Chapters 4 and 5). There are a variety of other
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uses for the compiled data, however the specific steps required to format the data into a suitable format for SDM development is described herein.
In Chapter 4, two statistical models used for species distribution modeling are compared and evaluated, random forest and boosted classification trees. The methods were chosen based on their ability to handle multinomial response data and their non-parametric nature. Both methods have also been shown to perform well in ecological prediction studies. The models are used with repeat A. cervicornis monitoring data to assess the regional stability of these
populations. The results of this work can be used to predict appropriate restoration locations.
Chapter 5 further examines the best statistical model identified in Chapter 4. The purpose of this chapter is to analyze the environmental parameters identified as most important by the model, and to provide an ecologically-guided approach to spatial prioritization of restoration efforts. The results of the model are also compared to current restoration locations.
The resulting models from this this research define and predict where conservation and restoration actions will be most effective. With existing populations mapped, the results will also aid in protecting the limited areas in which these species still occur. The resulting dataset on existing populations can also be used by researchers to compare characteristics of locations where these species are still thriving with the characteristics of areas from which they have disappeared. Such comparisons could, for example, inform choices for likely sites for successful restoration projects. By protecting and restoring populations of these species that provide habitat for many reef fish, the commercial and recreational fishing industries will also potentially be enhanced. Preservation of these species will have benefits for many other organisms that rely on Acropora thickets for shelter.
17 1.8 References
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2 Potential Habitat of Acropora spp. on Reefs of Florida, Puerto Rico, and the US Virgin Islands
Note to Reader
This chapter has been published in full (Wirt et al. 2015), and is included with the permission of the publisher.
2.1 Abstract
Elkhorn and staghorn corals (Acropora palmata, Acropora cervicornis) were listed in 2006 as threatened under the Endangered Species Act. The goal of this study was to create model potential-habitat maps for A. palmata and A. cervicornis, while identifying areas for possible re-establishment. These maps were created using a database of reported field observations in combination with existing benthic habitat maps. The mapped coral reef and hardbottom
classifications throughout Florida, Puerto Rico, and the US Virgin Island reef tracts were used to generate potential-habitat polygons using buffers that incorporated 95% and 99% of reported observations of Acropora spp. Locations of 92% of A. palmata observations and 84% of A.
cervicornis observations coincided with mapped coral reef or hard-bottom habitat throughout the study area. These results indicate that potential habitat for A. palmata is currently well defined throughout this region, but that potential habitat for A. cervicornis is more variable and has a wider range than that for A. palmata. This study provides a novel method of combining data sets
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at various geographic spatial scales and may be used to inform and refine the current National Oceanic and Atmospheric Administration critical habitat map.
2.2 Introduction
Corals of the genus Acropora have epitomized coral reefs worldwide because of their typical distribution in shallow water (making them more accessible and therefore more familiar) and characteristic branching morphologies. Two species occur in the western Atlantic and
Caribbean region, Acropora cervicornis (Lamarck 1816) and Acropora palmata (Lamarck 1816).
The precipitous decline of Acropora spp. in the western Atlantic and Caribbean is a primary issue of discussion in coral reef conservation. Their formal listing as threatened in 2006 (Federal Register, 2006) highlighted the concern for these historically important reef-building corals, bringing attention to the overall decline in reef-building corals over the past several decades. Fortunately for conservation and management purposes, their distribution in shallow water makes their habitats relatively accessible and amenable to mapping techniques based on satellite or aircraft-based remote sensing.
2.2.1 Recent threats to Acropora populations
During the past three decades many western Atlantic coral communities, including Acropora spp. populations, have been affected by a series of disturbances. The most notable of these include the spread of white-band disease (WBD) through Atlantic and Caribbean Acropora populations beginning around 1976 (Gladfelter, 1982; Porter et al., 2001), a cold-water event in 1976–1977 (Davis, 1982; Lessios, 1988; Lirman et al., 2011; Porter et al., 1982; Roberts et al., 1982), a region-wide Diadema (sea urchin) die-off in 1983 (Lessios, 1988), widespread mass-bleaching events in 1983 (Jaap, 1985; Lang et al., 1992; Hoegh-Guldberg, 1999), and numerous
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hurricanes (Lirman and Fong, 1996). In addition, the increase in frequency of such disturbances has limited recovery of extensive Acropora thickets in most of the western Caribbean.
The spread of WBD is widely considered one of the most significant disturbances affecting A. palmata and A. cervicornis. White-band disease was first documented in the early 1970s at Buck Island National Reef Monument in St. Croix, US Virgin Islands (Gladfelter et al., 1977). Prior to the spread of the disease, areas of the reef in St. Croix were composed of more than 50% live A. palmata (Mayor et al., 2006). Unfortunately, and as is the case for many populations throughout the species range, the combination of WBD and other disturbances has reduced populations more than 90% (Mayor et al., 2006). Similarly, WBD drastically reduced A.
cervicornis populations in both the shelf lagoon and spur-and-groove zones of the Belizean
cervicornis populations in both the shelf lagoon and spur-and-groove zones of the Belizean