Reef-building coral populations throughout the world are being threatened by numerous stressors and continue to decline. As potent endocrine-disrupting compounds, exogenous sex steroid contamination has been a largely overlooked stressor to corals. Previous research indicates these compounds are prevalent in marine environments, fluctuate annually along with reproductive cycles, can bioaccumulate, and have had variable effects on growth and reproduction in several cnidarian species. This project had three primary objectives: (1) establish environmental estradiol and progesterone concentrations in Broward County and lower Florida Keys reef environments, (2) conduct 17 β-estradiol and progesterone larval assays on P. astreoides larvae to determine the effects of these compounds on settlement and viability, and (3) conduct 17 β-estradiol and progesterone dosing experiments on adult Acropora cervicornis and Porites astreoides fragments to determine the effects on growth, zooxanthellae, reproduction, and overall tissue health. Estradiol was detected in surface and at-depth water samples from Broward County and lower Keys reef sites at effect level concentrations for marine organisms. Broward County larvae treated with low progesterone (5 ng/L) had decreased survival, while lower Keys larvae in low estradiol treatments (1 ng/L) had increased on-disc settlement. No other treatment effects were observed, however, lower Keys larvae had greater overall survival in comparison to Broward County larvae. There were no significant differences between estradiol and progesterone treatments in the adult-dosing experiment for growth, zooxanthellae density, reproduction, and overall tissue health. This is the first study to detect estradiol at Broward County reefs sites and our results, while inconclusive, indicate these compounds may have the potential to affect coral reef ecosystems.

White Band disease has devastated the staghorn coral Acropora cervicornis in recent decades, and it continues to impinge upon restoration efforts. The etiological agent(s) remain unknown as Koch’s postulates have yet to be satisfied, but disease may originate when opportunistic pathogens in the surface mucus layer exploit a stressed host. Using 16s rRNA sequencing, differences in the taxonomic diversity and relative abundances of bacteria within the mucus of A. cervicornis were documented between colonies of the same genotype, genotypes (n=8) categorized as having either high or low WBD susceptibility, and during a transplantation event. A. cervicornis colonies suspended from midwater PVC trees via monofilament were sampled for mucus, after which half of the sampled colonies were relocated to the unconsolidated sediments below. Temporal changes in the microbiome of the pelagic and benthic corals were then monitored by sampling the same apical tip over time. Incidentally, all benthic colonies for this experiment became afflicted with WBD; thereby differences in healthy vs. diseased colonies and the effects of disease progression on the microbiome were documented. Water was sampled concurrently with all mucus experiments to resolve the degree of commonality in bacterial species between the two environments, and sediments were sampled in the transplant experiment to determine if sediments may act as a pathogen reservoir. In addition, sediment samples were collected to assess site and temporal differences in the benthic microbiome along a nearshore to offshore transect off Key Largo, Florida. Irrespective of the inclusion of water operational taxonomic units (OTUs), no differences between colonies of the same genotype were observed with regards to the bacterial communities sampled from mucus in either alpha diversity metrics [species richness, Shannon, Inverse Simpson] or phylogenetic relatedness as determined by weighted unique fraction (UniFrac) were detected between colonies. However, differences were observed in the Bray-Curtis dissimiliarity matrices based on relative abundance and presence/absence of either [with and without water OTU] scenarios. Bacterial communities associated with different coral genotypes differed in species richness and Inverse Simpson in both water scenarios, as did weighted UniFrac and Bray-Curtis relative abundance and presence/absence transformed dissimilarity matrices. Alpha diversity of mucus bacteria was similar between corals of different disease-susceptibilities when water OTUs were either included or excluded, except for the Inverse Simpson index upon removal of water OTUs. Removal of aqueous bacteria also revealed significant differences between disease-susceptibility groups in Bray-Curtis relative abundance and presence/absence dissimiliarity values that was not detected with the incorporation of water OTUs. Regardless of the presence of water OTUs, weighted UniFrac was similar between corals of different disease susceptibilities. Most notably, dispersion increased in the microbiome of coral genotypes with high disease susceptibility in all cases except for the relative abundance transformed Bray-Curtis dissimilarity matrix when water OTUs were incorporated. This finding is in accordance with the Anna Karenina Principle, which states that loss of microbial regulation leads to an unpredictable microbiome in diseased individuals. In the sediment experiment, location was the only factor influencing microbiome composition. These findings may be due to the short duration of the experiment and differences between the carbonate content of the sediments and hydrological regimes between sites.

Since the 1970s, loss of herbivores, coral bleaching, pollution, and disease epidemics have reshaped the ecological framework of coral reefs. Staghorn coral, Acropora cervicornis, was a major reef-building scleractinian coral found throughout Florida and the Caribbean that experienced unprecedented population declines primarily due to disease and coral bleaching. These two stressors are coupled; the highest coral disease prevalence occurs after periods of thermal stress caused by increased sea surface temperature. Previous research documented three disease-resistant A. cervicornis genotypes in Panama, but it is unknown if disease-resistant genotypes exist in the Florida Keys. Thermal tolerance has been found to be variable among different species of corals and is relatively unknown in A. cervicornis. To investigate disease resistance and thermal tolerance in corals collected from the Florida Keys, pathogen transmission, thermal tolerance experiments, and coral outplanting studies were conducted, along with histological work to assess the condition of coral tissues. Corals were challenged in situ with exposure to rapid tissue loss (RTL) and bleaching resistance was evaluated ex situ in temperature-controlled seawater tanks, using 39 A. cervicornis genotypes. Disease and bleaching were further characterized in the wild using outplanted colonies. In a pathogen transmission pilot study, 7 out of 39 genotypes developed signs of rapid tissue loss transmission. An expanded transmission experiment that used 12 potentially disease resistant genotypes (based on anecdotal information and results from the pilot study), all genotypes developed signs of RTL transmission. However, susceptibility was variable but not statistically different among genotypes (p>0.05), ranging from 40-100% transmission. Histological analyses revealed significant (p0.05) related to photosynthetic efficiency and tissue condition metrics. No significant differences in mortality, disease, or predation were found between disease resistant and disease susceptible genotypes in outplanting experiments (p>0.05). This study reports the first evidence that disease resistance is present in Florida A. cervicornis genotypes. The variability of disease resistance found within genotypes suggests that genotype is not the only factor influencing disease transmission. Short-term exposure to thermal stress revealed heat tolerant A. cervicornis genotypes, which corroborates with recent published studies. Taken together, these results provide insights into how Caribbean Acropora and other scleractinian species persist through multiple disease and coral bleaching events.

Since the 1980’s, there has been an unprecedented decline in the reef-building Caribbean corals, Acropora cervicornis and A. palmata, which has led to their listing as “threatened” under the U.S Endangered Species Act. Despite this protective status, these Acropora species continue to experience declines primarily attributed to disease, global climate change, and storm damage. Recent evidence suggests the hybrid of these threatened species (A. prolifera) is found at abundances similar to or higher than the parental species at many sites throughout the Caribbean. However, there is still much that is unknown as to how and why hybrids may be increasing in abundance at select sites. In 2007, scientists from NOAA NMFS established 9 permanent transects at three sites in the USVI to quantify fish diversity and coral tissue condition in A. cervicornis thickets. Over the years, they observed that A. prolifera seemed to be increasing in abundance on transects that were once dominated by A. cervicornis. This dataset provided a unique opportunity to investigate whether a shift from a threatened parental species to its hybrid may have occurred. This study has two objectives, (1) to quantify the change in A. cervicornis and A. prolifera percent cover and colony health over a 9-year period, and (2) to compare the genotypic diversity among the three Caribbean acroporids on and near the transects to determine the primary method of propagation, i.e., sexual versus asexual. For this study, I used transect photographs taken in March, July and November 2009, April 2012, and August 2017 to compare intra- and interannual variation in acroporid cover and colony health. Striking losses were observed in A. cervicornis cover between March 2009 and August 2017. At Thatch Cay, A. cervicornis declined from 25.7% to 8.9% between March 2009 and November 2009, but remained stable (10.2%) up to August 2017. Acropora cervicornis cover declined from 13.2% to 0% at Lovango Cay, and from 8.2% to 0% at No-Name Bay. At the one site (No-Name Bay) that A. prolifera was present during the original surveys of the transects, the percent cover remained relatively high and stable over the sample period. At No-Name Bay, A. prolifera percent cover (18.2%) was significantly higher than A. cervicornis (5.4%) by November 2009. It appears that A. prolifera expanded in the habitat left void by the decline in A. cervicornis. The general health of A. cervicornis based on the amount of healthy versus white and pale tissue appeared to decline at all sites between March 2009 and November 2009. To determine if the high percent cover on some transects was derived from asexual propagation or sexual recruitment, 139 tissue samples were collected in 2017 and genotyped using five microsatellite markers. No significant difference in genotypic richness (number of unique genotypes divided by the sample size) was observed among A. cervicornis (0.62), A. prolifera (0.64), and A. palmata (0.68). This suggests that the hybrid colonization is from multiple sexually derived individuals, not just asexual propagation from a rare hybridization event. High genotypic diversity, stable population abundance, and healthier colonies, suggest acroporid hybrids may become the primary habitat building coral of shallow reefs in the U.S. Virgin Islands. Due to considerable differences in morphologies between A. cervicornis and A. prolifera, it is unclear how a shift to the hybrid may affect the organisms that occupy acroporid structure and if the same ecological functions can be fulfilled.

Over the last 40 years, the Caribbean has lost half of its live coral cover, mostly in the form of Acropora cervicornis and A. palmata, due to disease, bleaching from rising water temperatures, and other stressors. To help restore these corals to reefs in Florida, the Coral Restoration Foundation (CRF) created nearshore nurseries and transplanted over 30,000 acroporid colonies across the Florida Keys. The objective of this thesis was to evaluate the growth, survivorship, and condition of nursery-raised A. cervicornis colonies that were part of two transplant projects: 1) photographic analyses of 17 past CRF transplant projects over the last seven years; and 2) a transplant experiment at Little Conch Reef to additionally assess the effects of depth, colony density, and the genetic composition of transplants. The photographic analyses included 2,428 individual colonies, 38 genotypes, and six reefs from 2007 to 2013. Results from the photographs were combined with one in situ monitoring effort that used SCUBA in 2014. In the Little Conch Reef experiment, 1,288 colonies from 14 genotypes were transplanted in October and November, 2013 at two depths (5m and 12m) in either cluster or thicket configurations. At each depth, clusters comprised 14 colonies, each placed within in 1m diameter radius, with ten monogenetic and six multigenetic structures. Thickets were 3.5m by 1.5m in size, with 10 colonies from each genotype forming its own subunit within the larger configuration. In June 2014, 963 additional colonies were added to the shallow site by stacking them on top of six existing clusters and one thicket to evaluate whether larger three-dimensional structures affected growth or survival. The Little Conch Reef experiment was monitored through January 2015. Results from the photographic analyses were: 1) maximum size of A. cervicornis transplants was approximately 40cm in diameter; 2) mortality increased after approximately two years; 3) despite high mortality, some colonies survived the duration of each project; and 4) frequent and long-term monitoring is required to assess factors that affect survival and condition. Results from the Little Conch Reef experiment suggest: 1) maximum skeletal diameter was unaffected by any of the treatments; 2) percent survival and percent live tissue were higher at the shallow site compared to the deep site, and similarly, the clusters outperformed the thickets, and multigenetic clusters outperformed their monogenetic counterparts; 3) location within the shallow site had an impact on survival and condition, with clusters doing better on the south side than on the north; and 4) stacking did not positively impact growth, survival, or condition. In general, the sizes and condition of natural populations of A. cervicornis throughout the Florida Keys are similar to results from both experiments and with other transplant projects conducted in the Caribbean. Remarkably, despite high mortality in nearly all of the projects, small numbers of colonies transplanted for most projects, a few colonies survived to 2014/2015. These colonies have the potential to act as a “seed population” that might produce sexually dispersed larvae better adapted at surviving mortality events and asexual fragments that may be better acclimated to the stressors related to their location. Evidence of persistence in this species and expansion northward in Florida suggest that it is too early to consider coral reefs a lost cause, and that coral restoration holds promise for enhancing recovery of A. cervicornis.

Human activities have substantially increased the atmospheric concentrations of greenhouse gases, resulting in warmer ocean temperatures that are having a negative impact on reef corals, which are highly susceptible to changes in temperature. Understanding the degree to which species vary in their tolerance to elevated temperatures and whether this variation is heritable is important in determining their ability to adapt to climate change. In order to address this, Acropora cervicornis fragments from 20 genetically distinct colonies were kept at either ambient or elevated temperatures, and mortality was monitored for 26 days. Heritability of thermal tolerance was estimated using a clonal method comparing the difference in lifespan within and among clones in a one-way ANOVA, as well as a marker based method using the program MARK (Ritland 1996) to estimate relatedness between colonies. To understand the physiological basis of thermal tolerance, tissue samples from both treatments were taken after 12 hours to investigate gene expression associated with sub-lethal temperature stress at both the mRNA and the protein level. The results revealed that this population of A. cervicornis has a relatively high amount of total genetic variation in thermal tolerance (H2 = 0.528), but low additive genetic variation for this trait (h2 = 0.032). In addition, both gene expression and protein expression among colonies were highly variable and did not show consistent patterns related to differences in thermal tolerance among colonies. These results reveal that this population of A. cervicornis may have a limited capacity to respond to projected increases in ocean temperatures. In addition, the results suggest that the molecular basis of thermal tolerance in this species is complex and that there are potentially many genotypic combinations that can result in a heat-tolerant phenotype.

Coral nurseries have become a popular and successful method to produce coral fragments for reef-restocking and restoration projects worldwide. Numerous in-situ coral nurseries have been established and many studies have focused on the most effective way to produce coral fragments in offshore nurseries. In contrast, production of coral fragments in land-based nurseries is rarely studied despite a growing knowledge of coral husbandry and coral aquaculture. Little data exist on the success of tank-raised corals when transplanted back into reef environments. This thesis presents the results of a study designed to assess the use of land-based coral nurseries in production of fragments of the Atlantic staghorn coral Acropora cervicornis for the purposes of reef re-stocking and restoration. The first objective of the study was to assess if A. cervicornis fragments can be produced in aquarium conditions at comparable rates to offshore nurseries. Fragments from the same wild donor colonies were placed in an offshore nursery and a land-based nursery and monitored for survival, growth, branch production, and branch thickness for 16 months. Survival was lower in the land-based nursery, largely due to a mechanical failure. Linear extension was lower in the land-based nursery until nursery conditions were evaluated and optimized. The optimization process included changes to water quality, temperature control, and lighting. Post-optimization, linear extension in the land-based nursery exceeded the offshore nursery, with a maximum monthly growth rate of 16.0 ± 5.3 mm month-1. The maximum monthly rate in the offshore nursery was 10.6 ± 4.1 mm month-1. Branch number and thickness were also lower initially in the land-based nursery, however both metrics increased rapidly after optimization. This experiment shows that A. cervicornis can be successfully grown in a land-based nursery, and that linear extension and fragment production can be higher than in offshore nurseries if environmental conditions are maintained within optimum ranges. This experiment highlights some of the conditions that promoted high linear extension rates in this species. The second objective of this study was to examine the success of corals outplanted from land-based nurseries and to determine whether corals reared in a land-based nursery would show the same growth and survival after transplantation as those reared in a traditional offshore nursery. This was examined in two experiments. In the first experiment, small fragments were outplanted from colonies reared offshore and from colonies reared in a land-based system. In the second experiment, larger colonies reared in the two separate land-based systems were outplanted to the same location. All transplanted corals were monitored for survival, growth, branch number, and incidence of predation, breakage, and disease over one year. Two major storm events occurred during this portion of the study, so the potential for differences in breakage or storm damage were also assessed. There were no significant differences in survival or growth of fragments outplanted from a land-based nursery and an offshore nursery. Colony outplants from one land-based location had better survival and growth than colonies from a second land-based location. Tropical storm activity greatly increased the occurrence of breakage and tissue loss in all groups, resulting in decreases in colony volume and additional mortality. Survival ranged from 85% to 100% after six months, and survival ranged from 70% to 89% after one year and the passing of two tropical storms. Small (5 cm) transplants did not have significantly lower survivorship than large transplants. Overall, the transplant of fragments and colonies raised in land-based nurseries was successful, as measured by growth and survival rates that were comparable to or exceeded those observed for corals raised in offshore nurseries. Large colony transplants exhibited the best survivorship and extension rates, but were also highly prone to breakage.