Montastraea

Coastal development shifts natural hydrology through water redirection, increased impervious surfaces, and increased connectivity to the coastal ocean through inlets. In Southeast Florida, watershed alterations can cause flash-freshening in nearshore coastal habitats, threatening coral reef ecosystems. This study assessed the hyposalinity tolerance threshold of two prominent scleractinian corals in Southeast Florida. In a series of experiments, we determined that Montastraea cavernosa corals have an LC50 of 19 PSU but can survive for at least 21 days at an intermediately stressful salinity of 25 PSU. Porites astreoides corals demonstrated an LC50 of 19 PSU, but experienced mortality when exposed to 25 PSU for 17–18 days. Prior to mortality, corals displayed decreased polyp activity, altered coloration, and decreased tissue integrity. These data suggest that lower-volume, longer-duration releases of freshwater from reservoirs may preserve coral health in Southeast Florida.

Coral reef ecosystems across the Tropical Western Atlantic, are rapidly degrading due to a combination of anthropogenic stressors including coastal development, overfishing, and climate change-induced coral bleaching and disease outbreaks. Despite this general pattern, certain reef ecosystems are less exposed to these stressors due to a lack of/or distance from coastal development and/or their depth. These characteristics protect these coral reef ecosystems from rapid degradation and these coral populations potentially serve as important refugia. Developing an understanding of the connectivity dynamics among these refugia and to more degraded reefs is critical to developing networks of marine protected areas and management to ensure the persistence and recovery of coral metapopulations. In particular, increased research focus has been placed on mesophotic coral ecosystems (MCEs, 30-150 m) which are deeper and more buffered from anthropogenic stressors than shallow reefs (<30 m). A collection of hypotheses known as the Deep Reef Refugia Hypothesis surmises that MCEs may serve as larval sources to reseed shallow coral populations following a disturbance-driven decline. This dissertation research focuses on quantifying the population genetic structure of a dominant, depthgeneralist, coral species, Montastraea cavernosa, across previously understudied shallow and mesophotic reefs throughout the Gulf of Mexico and Western Caribbean to quantify the refugia potential of these reefs and characterize their roles in the regional coral metapopulation. Chapter 1 provides a review of the ecology and population genetic connectivity dynamics of shallow and mesophotic coral populations in the Tropical Western Atlantic.

Stony coral tissue loss disease (SCTLD) has been spreading throughout Caribbean coral reefs since 2014, heavily impacting scleractinian corals. To mitigate losses, this experiment assessed the effectiveness of two SCTLD intervention treatments in situ. SCTLD-affected Montastraea cavernosa colonies offshore of Broward County were divided into three treatment groups: 1) chlorinated epoxy, 2) Base 2B plus amoxicillin, and 3) untreated controls, plus a fourth group of healthy untreated controls. These colonies were monitored over 11 months to record SCTLD status, lesion activity, colony mortality, and changes in healthy tissue area with 3D modelling. The Base 2B plus amoxicillin treatment was more effective at halting SCTLD lesions, slowing the rate of tissue loss, and decreasing the overall proportion of tissue lost as compared to chlorinated epoxy or no treatment. However, neither treatment prevented new SCTLD lesions from developing. These findings can enhance the effectiveness of Caribbean management efforts to mitigate SCTLD impacts.

Since 2014 stony coral tissue loss disease (SCTLD) has contributed substantially to declines of reef-building corals in Florida. Monthly surveys were conducted throughout the northern Florida reef tract to monitor the spread and impacts of SCTLD on a larger spatial scale. SCTLD disease prevalence was lower in Palm Beach County than in Broward or Martin County, but there were no significant changes in prevalence over time. To assess colony level impacts of the disease, this study optimized a 3D photogrammetry technique for fate-tracking infected Montastraea cavernosa coral colonies with a low-cost, rapid protocol that measured tissue area over three time points. Total colony area and healthy tissue area decreased significantly over time, while disease area did not significantly vary. Traditional coral surveys combined with the 3D photogrammetry method provide greater insights into the spatial/temporal dynamics and impacts of this disease on individual corals and reef populations than surveys alone.

Coral reefs worldwide are experiencing unprecedented and rapid declines. However, deeper, mesophotic coral ecosystems (MCEs; 30–150 m) may act as refuges for coral species, providing larvae to recolonize degraded shallow reefs. This study assessed the genetic connectivity of shallow and mesophotic Montastraea cavernosa populations on the Belize Barrier Reef and the community structure of their endosymbiotic algae (Family Symbiodiniaceae) across a fine-scale depth gradient (10, 16, 25, 35 m). Evaluation of nine polymorphic microsatellite markers demonstrated that relatively shallow (10 and 16 m) M. cavernosa populations were genetically distinct from relatively deep (25 and 35 m) populations. High throughput sequencing of ribosomal coding DNA from Symbiodiniaceae communities of M. cavernosa revealed differences in community structure across depth, with shallow-specialist and depth-generalist community profiles. This research provides important information for the management of distinct deep and adds to the body of research on the understudied MCEs of the Mesoamerican Reef.

Coral reef ecosystems worldwide are facing increasing degradation due to
disease, anthropogenic damage, and climate change, particularly in the Tropical Western
Atlantic. Mesophotic coral ecosystems (MCEs) have been recently gaining attention
through increased characterization as continuations of shallow reefs below traditional
SCUBA depths (>30 m). As MCEs appear to be sheltered from many stressors affecting
shallow reefs, MCEs may act as a coral refuge and provide larvae to nearby shallow
reefs. The Deep Reef Refugia Hypothesis (DRRH) posits that shallow and mesophotic
reefs may be genetically connected and that some coral species are equally compatible in
both habitats. The research presented here addresses key questions that underlie this
theory and advances our knowledge of coral connectivity and MCE ecology using the
depth-generalist coral Montastraea cavernosa. Chapter 1 presents an overview of the
DRRH, a description of MCEs in the Gulf of Mexico (GOM), and the framework of
research questions within existing reef management infrastructure in the GOM. Through microsatellite genotyping, Chapter 2 identifies high connectivity among shallow and
mesophotic reefs in the northwest GOM and evidence for relative isolation between depth
zones in Belize and the southeast GOM. Historical migration and vertical connectivity
models estimate Gulf-wide population panmixia. Chapter 3 focuses on population
structure within the northwest GOM, identifying a lack of significant population
structure. Dominant migration patterns estimate population panmixia, suggesting
mesophotic populations currently considered for National Marine Sanctuary protection
benefit the Flower Garden Banks. Chapter 4 quantifies the level of morphological
variation between shallow and mesophotic M. cavernosa, revealing two distinct
morphotypes possibly representing adaptive tradeoffs. Chapter 5 examines the
transcriptomic mechanisms behind coral plasticity between depth zones, discovering a
consistent response to mesophotic conditions across regions. Additionally, variable
plasticity of mesophotic corals resulting from transplantation to shallow depths and
potential differences in bleaching resilience between shallow and mesophotic corals are
identified. The dissertation concludes with a synthesis of the results as they pertain to
connectivity of shallow and mesophotic corals in the Gulf of Mexico and suggests future
research that will aid in further understanding of MCE ecology and connectivity.

Coral reefs on Florida’s Reef Tract (FRT) are susceptible to many anthropogenic
influences including controlled freshwater discharges and agricultural runoff as well as
high natural environmental variability from seasonal rainfall, runoff and upwelling. To
better understand coral population structure and responses to sublethal stressors,
populations of the scleractinian coral Montastraea cavernosa in the northern FRT were
examined using a combination of genomic and transcriptomic techniques. Microsatellite
genetic markers identified high local retention among sites and a slight southward gene
flow. An in-situ temporal gene expression analysis utilizing a tag-based sequencing
transcriptomic approach was used to analyze baseline coral health at St. Lucie Reef
(SLR), off Stuart, FL. Temporal variation had the greatest influence of differential gene
expression among M. cavernosa at SLR. Results will be shared with local resource
managers and coupled with a complementary ex-situ experimental trial.