Flower Garden Banks Research Articles

Transcriptomic plasticity of mesophotic corals among natural populations and transplants of Montastraea cavernosa in the Gulf of Mexico and Belize.

While physiological responses to low-light environments have been studied among corals on mesophotic coral ecosystems worldwide (MCEs; 30-150m), the mechanisms behind acclimatization and adaptation to depth are not well understood for most coral species. Transcriptomic approaches based on RNA sequencing are useful tools for quantifying gene expression plasticity, particularly in slow-growing species such as scleractinian corals, and for identifying potential functional differences among conspecifics. A tag-based RNA-Seq (Tag-Seq) pipeline was applied to quantify transcriptional variation in natural populations of the scleractinian coral Montastraea cavernosa from mesophotic and shallower environments across five sites in Belize and the Gulf of Mexico: Carrie Bow Cay, West and East Flower Garden Banks, Pulley Ridge, and Dry Tortugas. Regional site location was a stronger driver of gene expression patterns than depth. However, mesophotic corals among all sites shared similar regulation of metabolic and cell growth functional pathways that may represent common physiological responses to environmental conditions at depth. Additionally, in a transplant experiment at West and East Flower Garden Banks, colonies transplanted from mesophotic to shallower habitats diverged from the control mesophotic group over time, indicating depth-regulated plasticity of gene expression. When the shallower depth zone experienced a bleaching event, bleaching severity did not differ significantly between transplants and shallow controls, but gene expression patterns indicated variable regulation of stress responses among depth treatments. Coupled observational and experimental studies of gene expression among mesophotic and shallower M. cavernosa provide insights into the ability of this depth-generalist coral species to persist under varying environmental conditions.

Morphological and molecular characterization of a new species of black coral from Elvers Bank, north-western Gulf of Mexico (Cnidaria: Anthozoa: Hexacorallia: Antipatharia: Aphanipathidae: Distichopathes)

AbstractThe continental shelf edge of the NW Gulf of Mexico supports dozens of reefs and banks, including the West and East Flower Garden Banks (FGB) and Stetson Bank that comprise the Flower Garden Banks National Marine Sanctuary (FGBNMS). Discovered by fishermen in the early 1900s, the FGBs are named after the colourful corals, sponges and algae that dominate the region. The reefs and banks are the surface expression of underlying salt domes and provide important habitat for mesophotic coral ecosystems (MCE) and deep coral communities to 300 m depth. Since 2001, FGBNMS research teams have utilized remotely operated vehicles (e.g. ‘Phantom S2’, ‘Mohawk’, ‘Yogi’) to survey and characterize benthic habitats of this region. In 2016, a Draft Environmental Impact Statement proposed the expansion of the current sanctuary boundaries to incorporate an additional 15 reefs and banks, including Elvers Bank. Antipatharians (black corals) were collected within the proposed expansion sites and analysed using morphological and molecular methods. A new species, Distichopathes hickersonae, collected at 172 m depth on Elvers Bank, is described within the family Aphanipathidae. This brings the total number of black coral species in and around the sanctuary to 14.

The Influence of Eddies on Coral Larval Retention in the Flower Garden Banks

While coral larval exchange among reef patches is crucial to the persistence of coral metapopulations, larval retention within patches is critical for local population maintenance. In isolated systems such as the Flower Garden Banks (FGB) of the NW Gulf of Mexico (GoM), local retention is thought to play an important role in maintaining high levels of coral cover. Numerous mesoscale cyclonic and anticyclonic features (eddies) are known to spin off from the GoM’s Loop Current, many of which pass over the FGB. We developed a biophysical model of coral larval dispersal (2004–2018) to investigate the extent to which eddies may facilitate coral larval exchange between and within the East and West FGB. Virtual larvae of the broadcast spawning Orbicella faveolata and the brooding Porites astreoides were released and tracked with species-specific reproductive and larval behaviors to investigate differences in retention and connectivity in corals with contrasting life histories. Eddies were detected and tracked using sea surface altimetry and compared with larval trajectories to assess the retentive characteristics of these features. Results suggest consistently high, but species-specific, levels of local retention and cross-bank connectivity in both coral species. High local retention is possible early in the dispersal of P. astreoides, and both species routinely experience retention due to recirculation in eddy features as late as 30 days after planulation or spawning. Eddies passing over the FGB were associated with pulses of between- and within-bank retention, indicating that larvae are capable of dispersing from and returning to coral reefs in the NW GoM. Although opportunities for retention are inherently ephemeral and stochastic due to the nature of Loop Current eddy shedding, eddy propagation should serve as a reliable reseeding mechanism for FGB coral populations. In particular, peaks in late summer eddy propagation correspond with mass coral spawning and may enhance larval retention. These findings support the assertions that healthy FGB reefs may be largely self-sustaining, and that persistent, self-sustaining populations at the FGB may supply downstream reefs with larvae and behave as a remote climate change refugium.

Range extension of Mesophyllum erubescens (Foslie) Me. Lemoine (Hapalidiales, Rhodophyta): first report from mesophotic rhodolith beds in the northwestern Gulf of Mexico offshore Louisiana and Texas, including the Flower Garden Banks National Marine Sanctuary

DNA sequence analysis of plastid-encoded psbA and UPA, mitochondrion-encoded COI, and nuclear-encoded LSU rDNA of rhodolith-forming crustose coralline algal specimens from the northwestern Gulf of Mexico reveals that Mesophyllum erubescens (Foslie) Me. Lemoine is present in mesophotic rhodolith beds offshore Louisiana and Texas at 39–57 m depth. Morpho-anatomical characters viewed with SEM support the identification of these specimens. Mesophyllum erubescens is reported for the first time offshore Louisiana at Ewing Bank, the Louisiana–Texas border at Bright Bank, and Texas in the Flower Garden Banks National Marine Sanctuary.

Community Dynamics of Fish Assemblages on Mid-Shelf and Outer-Shelf Coral Reefs in the Northwestern Gulf of Mexico

Offshore natural banks in the Gulf of Mexico (GOM) are unique model systems for examining the mechanisms structuring reef fish communities due to their substantial geographic isolation, and the presence of replicate experimental units of both low (mid-shelf) and high coral diversity (shelf-edge) reef habitats. Here, we examined the species assemblage structure of juvenile and adult fishes at two mid-shelf reefs (Sonnier and Stetson Bank) and two shelf-edge reefs (East and West Flower Garden Banks) in the northwestern GOM to evaluate the relative importance of habitat (i.e. coral diversity) vs. recruitment in structuring resident fish assemblages. Visual reef fish surveys (n = 400) were conducted at the four coral reefs during two seasons, spring-early summer and late summer-fall in 2009 and 2010. Two depth zones were surveyed at each reef, representing the reef crest (15-23 m depth) and upper slope (23-30 m depth) habitats. Seasonal variability in recruitment to both mid-shelf and shelf-edge reefs was observed, with higher mean juvenile density and diversity (Hʹ) observed during the late season at all reefs in 2009 and all but Stetson in 2010, supporting an early fall recruitment peak. Likewise, considerable inter-annual variability in juvenile recruitment was observed, with significantly lower juvenile density and Hʹ observed at mid-shelf reefs in 2010 relative to 2009. Species diversity was strongly linked to coral diversity, with greater reef fish diversity consistently observed at shelf-edge relative to mid-shelf reefs. Observed differences in the composition of juvenile and adult assemblages at mid-shelf reefs suggest that reef fish communities at these reefs were more strongly influenced by post-settlement processes (e.g. juvenile mortality) than shelf-edge reefs, which may be a function of several limiting factors (e.g., predation, coral diversity, water quality). Results indicate that reef fish assemblages associated with mid-shelf and shelf-edge reefs in the northwestern GOM have sufficient stabilizing mechanisms in place to facilitate recovery from anomalous recruitment events and maintain consistent resident assemblages. The strong, reef type-specific differences in assemblage composition observed throughout the study indicate that mid-shelf and shelf-edge coral reef habitats may fill different functional roles for demersal fishes in the northwestern GOM.

Predictive modelling of mesophotic habitats in the north‐western Gulf of Mexico

Abstract Effective management of marine resources requires an understanding of the spatial distribution of biologically important communities. The north‐western Gulf of Mexico contains diverse marine ecosystems at a large range of depths and geographic settings. To better understand the distribution of these marine habitats across large geographic areas under consideration for marine sanctuary status, presence‐only predictive modelling was used. Results confirmed that local geographic characteristics can accurately predict the probability of occurrence for marine habitat types, and include a novel technique for assigning a single, most likely habitat in areas where multiple habitats are predicted. The highest resolution bathymetric data (10 m) available for the region was used to develop raster layers that represent characteristics that have been shown to influence species occurrence in other settings. A georeferenced historical photo record collected via remotely operated vehicle was classified according to six commonly found mesophotic habitats across the 18 reefs and banks under consideration for Flower Garden Banks National Marine Sanctuary boundary expansion. Using maximum entropy modelling, the influence of local geographic characteristics on the presence of these habitats was measured and a spatial probability distribution was developed for each habitat type across the study area.

Coral Reefs in the Gulf of Mexico Large Marine Ecosystem: Conservation Status, Challenges, and Opportunities

The importance of coral reefs (CR) within marine ecosystems has become widely recognized. Although shallow CR are not as abundant in the Gulf of Mexico (GoM) as in other areas such as the Caribbean, their uniqueness, singularity, isolation and conservation status make their conservation highly important. Corals and CR, both shallow and deep, are more widely distributed throughout the GoM than previously thought, providing new venues of research but also new challenges for their sustainable management. They are widely present in the three countries circumscribing the GoM (Cuba, Mexico and the United States). Corals are also distributed throughout different depths, from the keys of corals of Florida and Cuba, to the mesophotic reefs in Flower Garden Banks, Pulley Ridge and submerged banks in the southern GoM; additional coral presence occurs even beyond mesophotic depths (~30-150 m). Like reefs around the world, they are subject to an increased threat from anthropogenic causes, including overfishing, pollution and climate change. But there is also hope. Some reefs in the area, such as those in Flower Garden Banks National Marine Sanctuary are probably the best-preserved reefs in the region, with coral cover greater than 50%, which is unusual in the Wider Caribbean. Others are experiencing new protections through the work of government and local communities. The objectives of this manuscript are to summarize the overall status of corals and CR in the GoM, analyze some of the current and future threats, and explore opportunities for their conservation in the region. Aside from the above mentioned anthropogenic threats bleaching, coral diseases and hurricanes have been identified as main contributors for CR declines not only in the GoM but abroad; some nowadays present but likely to increase threats are invasion by alien species or by Sargassum spp. Among some of the opportunities identified are to capitalize on existing and emerging multilateral agreements and initiatives (e.g., GoM Large Marine Ecosystem, trinational sanctuaries agreement); increase financial support for conservation through international initiatives and the private sector; and a need to comprehend the inherent interconnection among corals, CR and deeper bank ecosystems as they do not function in isolation.

Localized hypoxia may have caused coral reef mortality at the Flower Garden Banks

On July 25, 2016, turbid water and dead corals, sponges and other invertebrates were discovered at the East Bank (EB) of the Flower Garden Banks (FGB) National Marine Sanctuary. Mortality was spread over 0.06 km2, with up to 80% coral mortality reported in some areas. Within days, response efforts were underway to investigate the potential mechanisms leading to the mortality event. Hydrographic surveys, moored buoy data, and a regional hydrodynamic model were used to characterize water chemistry, hydrography, and microbial communities within the FGB. Low salinity (~ 31–33), total alkalinity (~ 2284–2330 µmol kg−1), and dissolved inorganic carbon (DIC, ~ 1968–2011 µmol kg−1) were detected in surface waters over the EB and eastern stations, revealing the presence of river-derived water. The Mississippi/Atchafalaya rivers were the primary sources of freshwater during the event, although Texas rivers, all of which had unusually high discharge during 2016, contributed approximately one-fifth to the total freshwater mass. At 75 m depth, high density, salinity, DIC, ammonium, and abundance of microbial taxa associated with deep waters were coincident with low temperature and aragonite saturation state at the northern and eastern stations, indicating a deeper source water at these stations. Cross-slope density gradients were also consistent with an upwelling circulation pattern. Using these observations and data, we hypothesize that the mortality event was most likely caused by the combination of two processes. The turbid freshwater layer inhibited photosynthesis, leading to net respiration of coral reef organic matter. Additionally, deep, dense waters upwelled onto the bank and formed a stratified bottom layer, which prevented re-oxygenation from the overlying water column and led to localized areas of hypoxia within pockets on the reef. Hypoxia likely formed rapidly, within two days. Moving forward, high-frequency temporal measurements of oxygen and carbonate chemistry are critical for monitoring risks (e.g., hypoxia and acidification) associated with freshwater discharge and upwelling, since these processes may adversely affect coral reef health.

Gene Expression of Endangered Coral (Orbicella spp.) in Flower Garden Banks National Marine Sanctuary After Hurricane Harvey

About 190 km south of the Texas–Louisiana border, the East and West Flower Garden Banks (FGB) have maintained >50% coral cover with infrequent and minor incidents of disease or bleaching since monitoring began in the 1970s. However, a mortality event, affecting 5.6 ha (2.6% of the area) of the East FGB, occurred in late July 2016 and coincided with storm-generated freshwater runoff extending offshore and over the reef system. To capture the immediate effects of storm-driven freshwater runoff on coral and symbiont physiology, we leveraged the heavy rainfall associated with Hurricane Harvey in late August 2017 by sampling FGB corals at two time points: September 2017, when surface water salinity was reduced (~34 ppt); and one month later when salinity had returned to typical levels (~36 ppt in October 2017). Tissue samples (N = 47) collected midday were immediately preserved for gene expression profiling from two congeneric coral species (Orbicella faveolata and Orbicella franksi) from the East and West FGB to determine the physiological consequences of storm-derived runoff. In the coral, differences between host species and sampling time points accounted for the majority of differentially expressed genes. Gene ontology enrichment for genes differentially expressed immediately after Hurricane Harvey indicated increases in cellular oxidative stress responses. Although tissue loss was not observed on FGB reefs following Hurricane Harvey, our results suggest that poor water quality following this storm caused FGB corals to experience sub-lethal stress. We also found dramatic expression differences across sampling time points in the coral’s algal symbiont, Breviolum minutum. Some of these differentially expressed genes may be involved in the symbionts’ response to changing environments, including a group of differentially expressed post-transcriptional RNA modification genes. In this study, we cannot disentangle the effects of reduced salinity from the collection time point, so these expression patterns could also be related to seasonality. These findings highlight the urgent need for continued monitoring of these reef systems to establish a baseline for gene expression of healthy corals in the FGB system across seasons, as well as the need for integrated solutions to manage stormwater runoff in the Gulf of Mexico.

Sanctuary islands in a hostile matrix: The perception, representation, and protection of the Flower Garden Banks National Marine Sanctuary, Gulf of Mexico

Sanctuary islands in a hostile matrix: The perception, representation, and protection of the Flower Garden Banks National Marine Sanctuary, Gulf of Mexico

Coral mortality event in the Flower Garden Banks of the Gulf of Mexico in July 2016: Local hypoxia due to cross-shelf transport of coastal flood waters?

Remotely sensed and in situ data, in tandem with numerical modeling, are used to explore the causes of an episode of localized but severe mortality of corals, sponges, and other invertebrates at the Flower Garden Banks (FGB) National Marine Sanctuary in July 2016. At about 190 km off the Texas coast, at the top the seamount in the East FGB, up to 82% of coral reef organisms were affected in a 1–2 m thick layer on the local seafloor at ∼23 m depth. Analysis of available data pointed to low levels of dissolved oxygen being the most likely contributing factor in the observed mortality (Johnston et al., 2019).Observations show that upwelling-favorable winds in June and July 2016 carried brackish and turbid coastal waters across the northwestern Gulf of Mexico continental shelf to the FGB. This plume of coastal water was the result of exceptionally high precipitation and local river run-off. Field data provide clear evidence of thin, localized, subsurface near-hypoxic layers immediately below this turbid, low salinity coastal plume. These mid-water layers extended over longer distances (30–40 km), and reached further offshore (∼100 km), than previously reported in the region, associated with large quantities of organic matter carried offshore by the brackish plume.The surface brackish layer was observed to cover the East FGB in satellite ocean color imagery and in situ salinity measurements in late June and July 2016. Model results and sparse observations on the shelf suggest that this surface layer was ∼20 m thick. It is expected that organic matter carried in the surface layer accumulated on the seafloor of the East FGB, which was just below the brackish plume. In the absence of ventilation, this led to the local formation of a bottom hypoxic layer, similar to what is observed on the Gulf of Mexico inner to mid-shelf every summer.The conditions experienced at FGB in July 2016 are likely to affect other reefs exposed to brackish plumes with high organic matter loads. The processes of physical connectivity by transport of material is critical for reef colonization and survival, but can also be fatal to coral ecosystems. The monitoring of coral reefs should take the threat of hypoxia due to distant sources of organic matter into account.

Protecting juveniles, spawners or both: A practical statistical modelling approach for the design of marine protected areas

Abstract Fish populations undertaking ontogenetic or spawning migrations pose challenges to marine protected area (MPA) planning because of the large extent of their distribution areas. There is a need to identify the juvenile and spawner hotspots of these populations that could be set aside as MPAs. Species distribution models making comprehensive use of available monitoring data and predicting the realized juvenile and spawner hotspots of migratory fish populations will assist resource managers with MPA planning. We developed a statistical modelling approach relying on multiple, regional monitoring datasets for assisting spatial protection efforts targeting the juveniles, spawners, or both life stages, of migratory fish species and species complexes. This approach predicts juvenile and spawner hotspot indices, and critical life stage (CLS) hotspot indices, which integrate both juvenile and spawner hotspot indices. We applied the approach to 11 vulnerable species of the grouper–snapper complex of the U.S. Gulf of Mexico, which all form fish spawning aggregations (FSAs). The CLS hotspot index was predicted to be highest in the Pulley Ridge and Flower Garden Banks areas, followed by the West Florida Shelf, southwestern Florida waters and portions of the Louisiana‐Mississippi‐Alabama shelf. The Pulley Ridge Habitat Area of Particular Concern and Flower Garden Banks National Marine Sanctuary are two important existing MPAs of the U.S. Gulf of Mexico, whose possible expansion is being considered. The predicted CLS hotspot indices suggest that expanding these MPAs or increasing harvest regulations within them would offer substantial protection to both the juveniles and spawners of many FSA‐forming species of the grouper–snapper complex. Synthesis and applications. As the number of marine protected areas (MPAs) continues to increase worldwide, statistical modelling approaches making comprehensive use of available data are urgently needed to support resource managers’ abilities to establish sound and efficient spatial protection plans. The outputs of our statistical models can serve as inputs to conservation planning software packages seeking optimal marine protected areas configurations or can be directly employed by resource managers for formulating spatial protection plans.

Patterns of benthic cover with depth on Caribbean mesophotic reefs

Tropical mesophotic reefs, which span the transition between shallow reefs and the bottom of the photic zone (30–150 m), are an understudied ecosystem. It has been proposed that sponge abundance increases with depth through 150 m on reefs throughout the Caribbean and perhaps globally (the “sponge increase hypothesis”). A recent review concluded that there was not sufficient evidence in the literature to support this hypothesis for the Caribbean and that further data quantifying changes in sponge abundance with depth on mesophotic reefs are needed. In this study, percentage cover of sponges, macroalgae, and hard corals was estimated using 1123 images taken by remotely operated vehicles on 58 dive tracks on mesophotic reefs off the coasts of Puerto Rico (to 180 m) and St. Thomas (US Virgin Islands; to 100 m), and on the Flower Garden Banks (Gulf of Mexico; to 100 m). Off Puerto Rico, sponge cover decreased with increasing depth below ~ 100 m, driven primarily by a decline in the cover of emergent (non-encrusting) sponge species. Sponge cover did not change with depth off St. Thomas or on the Flower Garden Banks and was an order of magnitude lower on the Flower Garden Banks. The data from these three locations did not support the sponge increase hypothesis. Mean cover of hard coral off Puerto Rico and St. Thomas was less than 8% between 20 and 80 m and negligible below these depths, but much higher ( ~ 15–30%) between 30 and 40 m on the Flower Garden Banks and negligible below these depths. Off Puerto Rico, cover of macroalgae decreased with depth in a manner similar to sponge cover, which may reflect a positive relationship between sponges and macroalgae in the lower mesophotic zone ( > 100 m). Off St. Thomas and on the Flower Garden Banks, which were both shallower sites with more abundant macroalgae, sponge abundance was likely limited due to competition for space. Generalizations about patterns of sponge abundance across mesophotic depths await further studies, but our data suggest a depth-dependent relationship with macroalgal abundance.

Detection of gaps in the spatial coverage of coral reef monitoring projects in the US Caribbean and Gulf of Mexico.

As part of the US Coral Reef Task Force's National Program to Map, Assess, Inventory, and Monitor US Coral Reef Ecosystems, a comprehensive survey of projects/programs monitoring coral reef ecosystems and related habitats (i.e., seagrass beds and mangroves) in the US Caribbean and Pacific was undertaken. Information was gathered on a total of 296 monitoring and assessment projects conducted since 1990 in the US Caribbean and the Gulf of Mexico. Substantial gaps in monitoring coverage of US coral reef ecosystems were revealed through geographic information system (GIS) analysis of survey metadata. Although southern Florida contains approximately two-thirds of all marine monitoring projects found in the US Caribbean and Gulf of Mexico, we were unable to identify any ongoing projects that monitor coral reefs along Florida's western coast and off of the Florida Middle Grounds. Additionally, Florida is covered by approximately 1 900 km2 of mangroves, yet there were only four ongoing projects that monitor this ecosystem, leaving gaps in coverage in the Lower and Middle Keys and along the eastern and western coasts. The Flower Garden Banks National Marine Sanctuary, located offshore of the Texas/Louisiana border, has an integral long-term monitoring program, but lacks a monitoring project that gathers long-term, quantitative data on reef lish abundance and certain water quality parameters. Numerous coral reef monitoring projects in Puerto Rico are concentrated on the island's southwestern coast surrounding La Parguera, while far fewer monitoring projects are conducted along the northern and southeastern coasts and around Vieques Island. In the US Virgin Islands, the paucity of monitoring projects in large areas of St. Croix and St. Thomas contrasts with monitoring activity in three marine protected areas (MPAs), where 66% of the US Virgin Islands' coral reef monitoring sites were found. Only a series of assessments have been conducted at Navassa, a small, uninhabited island located 55 km west of Haiti and 137 km northeast of Jamaica. In order to better understand changes in coral reef communities and to produce a series of biennial reports on the status of US coral reef ecosystems, the National Oceanic and Atmospheric Administration (NOAA) is developing a national coral reef monitoring network. This network has already begun to fill some of these gaps in monitoring coverage through issuing cooperative grants to states and territories to build long-term monitoring capacity.

Localized coral reef mortality event at East Flower Garden Bank, Gulf of Mexico

Flower Garden Banks National Marine Sanctuary contains the northernmost coral reef ecosystem in the Gulf of Mexico, with >50% living coral cover. Historically, this reef system has harbored a healthy coral community, relatively free of disease with limited mortality from bleaching or other factors. In July 2016 an unprecedented localized mortality event was documented at East Flower Garden Bank affecting an area of approximately 5.6 ha (2.6% of the coral reef). Within this area, up to 82% of the coral colonies succumbed to partial or total mortality, along with invertebrates spanning numerous taxa, including cnidarians, poriferans, echinoderms, crustaceans, and mollusks. Within the affected area, the impact was highly stratified, with many coral colonies exhibiting a clear line of delineation with polyps above appearing healthy, and those below exhibiting paling, bleaching, tissue sloughing, and/or mortality. The mortality of sessile invertebrates across multiple taxa was similar to observations from coral mortality events in other regions associated with low dissolved oxygen (DO) concentrations. While instrumentation for measuring DO was not in place on East Flower Garden Bank, DO sensors at similar depths located 50–70 km northwest of East Flower Garden Bank confirmed low DO levels (<3.5 mg L–1) at the time of the event. The mortality event likely resulted from a combination of stressors, but localized low DO is implicated as the primary contributing factor.

Genetic connectivity dynamics of the giant barrel sponge, Xestospongia muta, across the Florida Reef Tract and Gulf of Mexico

Resolving the genetic connectivity of coral reef taxa is necessary to understand the community dynamics of these increasingly threatened ecosystems. Herein, we assess the fine scale genetic connectivity of six populations of the Atlantic giant barrel sponge, Xestospongia muta (Schmidt, 1870), using microsatellite markers. This survey included populations from across the Florida Reef Tract and the Gulf of Mexico, including sponges from the Pulley Ridge Habitat Area of Particular Concern, a mesophotic coral reef located approximately 250 km from Florida's (USA) southwestern coast, and the Flower Garden Banks National Marine Sanctuary, the northernmost western Atlantic coral reef ecosystem. Overall, significant population structure was found (F ST = 0.020, 95% CI: 0.011–0.031), with X. muta individuals from the Flower Garden Banks showing the highest levels of genetic differentiation relative to all other surveyed populations (F ST > 0.048). Despite the high levels of population structuring observed, some horizontal and/ or vertical connectivity was found between neighboring reef systems, including evidence of gene flow between mesophotic (Pulley Ridge Habitat of Particular Concern) and photic (Dry Tortugas) reef tracts. Furthermore, largely negligible levels of first-generation migration among discrete genetic populations was observed, suggesting that the persistence of most populations of X. muta is highly dependent on self-recruitment. Thus, while the Pulley Ridge mesophotic reef may provide sponge recruits to shallow photic reefs, its role as a potential refuge and propagule source appears limited to only small geographic scales.

Montastraea cavernosa corallite structure demonstrates distinct morphotypes across shallow and mesophotic depth zones in the Gulf of Mexico.

This study assessed morphological variation of the depth-generalist coral Montastraea cavernosa across shallow and mesophotic coral ecosystems in the Gulf of Mexico (GOM) using thirteen corallite metrics. While corallite structure differed significantly across sites, we observed that mean corallite diameters were smaller and spacing was greater in mesophotic corals as compared to shallow corals. Additional corallite variation, including greater mean corallite height of mesophotic samples, are hypothesized to be photoadaptive responses to low light environments. Multivariate analyses also revealed two distinct morphotypes identified by significant variation in corallite spacing with >90% accuracy. A ‘shallow’ morphotype was characterized by larger, more closely-spaced corallites, while a ‘depth-generalist’ type exhibited smaller, further-spaced corallites. Variable presence of morphotypes within some sites suggests genotypic influence on corallite morphology as there was a slight, but significant, impact of morphotype on genetic structure within shallow zones in the Flower Garden Banks. Patterns of increased algal symbiont (Symbiodiniaceae) density and chlorophyll concentration were retained in the depth-generalist morphotype even in shallow zones, identifying multiple photoadaptive strategies between morphotypes. The results of this study suggest that morphological variation among M. cavernosa represents a combination of genotypic variation and phenotypic plasticity rather than responses to environmental stimuli alone.

Recruit symbiosis establishment and Symbiodiniaceae composition influenced by adult corals and reef sediment

For most reef-building corals, the establishment of symbiosis occurs via horizontal transmission, where juvenile coral recruits acquire their algal symbionts (family Symbiodiniaceae) from their surrounding environment post-settlement. This transmission strategy allows corals to interact with a diverse array of symbionts, potentially facilitating adaptation to the newly settled environment. We exposed aposymbiotic Pseudodiploria strigosa recruits from the Flower Garden Banks to natal reef sediment (C−S+), symbiotic adult coral fragments (C+S−), sediment and coral fragments (C+S+), or seawater controls (C−S−) and quantified rates of symbiont uptake and Symbiodiniaceae community composition within each recruit using metabarcoding of the ITS2 locus. The most rapid uptake was observed in C+S+ treatments, and this combination also led to the highest symbiont alpha diversity in recruits. While C−S+ treatments exhibited the next highest uptake rate, only one individual recruit successfully established symbiosis in the C+S− treatment, suggesting that sediment both serves as a direct symbiont source for coral recruits and promotes (or, potentially, mediates) transmission from adult coral colonies. In turn, presence of adult corals facilitated uptake from the sediment, perhaps via chemical signaling. Taken together, our results reinforce the key role of sediment in algal symbiont uptake by P. strigosa recruits and suggest that sediment plays a necessary, but perhaps not sufficient, role in the life cycle of algal Symbiodiniaceae symbionts.

Coral bleaching and recovery from 2016 to 2017 at East and West Flower Garden Banks, Gulf of Mexico

East Flower Garden Bank (EFGB) and West Flower Garden Bank (WFGB), part of Flower Garden Banks National Marine Sanctuary (FGBNMS) in the northwestern Gulf of Mexico, support tropical coral reefs that exhibit over 50% living coral cover. These reefs have been monitored annually since 1989, and in 2016 were exposed to higher than normal seawater temperatures leading to a severe bleaching event. Corals at EFGB and WFGB showed no signs of bleaching until September 2016, occurring later in the year compared to other reefs in the Caribbean region. Coral bleaching and subsequent recovery at each bank were documented through a time series of repetitive photographs within previously established long-term monitoring stations. Preceding the event, mean live coral cover within monitoring stations was collectively 64 ± 2%. Prior to signs of bleaching from July to September 2016, seawater temperatures on the reef were above 30 °C for a total of 36 d at EFGB and 21 d at WFGB. By October 2016, 67 ± 5% of the coral cover within EFGB monitoring stations and 25 ± 3% within WFGB monitoring stations exhibited signs of bleaching or paling stress, with dissimilarities in the amount of bleaching most likely due to significant differences in thermal profiles between banks. Significantly increasing long-term trends for daily mean seawater temperature indicate that temperatures on the banks have become warmer over time, and calculated bleaching threshold curves suggest that more than 50 d above 29.5 °C would initiate a bleaching year at EFGB and WFGB. Even though recovery within monitoring stations at both banks was documented with no significant declines in mean coral cover from 2016 to 2017 (64% and 62%, respectively), it is likely FGBNMS will be subject to additional and more frequent bleaching events in the future as ocean temperatures continue to rise.

Correction to: Important juvenile manta ray habitat at Flower Garden Banks National Marine Sanctuary in the northwestern Gulf of Mexico

In a recent paper (Stewart et al. 2018), we reported on the presence of juvenile manta rays in the Flower Garden Banks National Marine Sanctuary (FGBNMS) and suggested that the region serves as a nursery habitat for the species. Unfortunately we failed to consider the Masters thesis by Jeffrey N Childs (2001) entitled: ‘The occurrence, habitat use, and behavior of sharks and rays associating with topographic highs in the Northwestern Gulf of Mexico’. Childs (2001) was the first to document the presence of juvenile manta rays at the Flower Garden Banks and he suggested that the Flower Garden Banks serve as a nursery habitat for juvenile manta rays. We regret this oversight and apologize for failing to acknowledge and cite this relevant work.