Garden Banks National Marine Sanctuary Research Articles

Growth characterization of mesophotic rhodoliths in the northern Gulf of Mexico using radiocarbon dating

Boxwork rhodoliths are characterized by a multitaxonomic composition and excessive void spaces, and they are distributed from intertidal to mesophotic depths. Growth rates and patterns in rhodoliths from shallower depths and simpler morphologies have been assessed using incremental and geochemical analyses, but rhodoliths from mesophotic depths have been harder to access and require more studies. Boxwork rhodoliths have proved too structurally complex for age and growth rate assessment techniques such as stable oxygen isotopes profiling or elemental mapping. We therefore utilized sequential radiocarbon analysis for growth characterization of mesophotic boxwork rhodoliths. Rhodoliths were collected from the Flower Garden Banks National Marine Sanctuary in the northern Gulf of Mexico from one location at 48–72 m and another at 103 m. Specimens were extensively sampled for radiocarbon concentrations from predicted nucleation points and along growth axes. From depths of 48–72 m, nucleation ages ranged from 795 ± 20 to 3270 ± 25 14C yr B·P. From depths of 103 m, nucleation ages ranged from 8960 ± 110 to 13,050 ± 150 14C yr B.P., dating back to the end of the Pleistocene in some cases. Several rhodoliths contained evidence of growth hiatuses, with deeper samples displaying age reversals that complicated the apparent growth history. We define age reversals to be non-sequential ages within a sampling sequence, typically a singular age before the return to normal age sequence. The research presented here includes the oldest known living rhodoliths, with the oldest rhodoliths grown before and after Holocene sea-level stabilization. These results have implications for the use of rhodoliths as paleoenvironmental indicators, and provide better understanding of the range and volume of carbonate production in these habitats.

Mesoscale Eddies Influence Coral Reef Environments in the Northwest Gulf of Mexico

AbstractCoral reefs globally are experiencing more frequent and severe warming events due to anthropogenic driven climate change. Subtropical reefs experience more seasonal variability than lower latitude reefs making them typically more resilient to climate change. With relatively stable coral cover in comparison to other global coral reefs, Flower Garden Banks National Marine Sanctuary (FGBNMS) in the Gulf of Mexico is a series of 17 reefs and banks located on the continental shelf‐edge containing a variety of shallow (0–30 m) and mesophotic (30–150 m) coral reef habitats. Here, we use satellite data products to associate open ocean Argo float profiles with eddy features over FGBNMS to study the shelf‐edge reef environment spanning nearly two decades (2003–2022). Satellite data show that FGBNMS is frequently influenced (∼15 days/month) by mesoscale eddies. The upper water column variability (0–25 m) is most influenced by the seasonal mixed layer despite eddy interaction. Subsurface seasonal ranges of temperature and salinity are enhanced or suppressed depending on the influence of eddies in relation to the mixed layer depth. Within the mesophotic zone (0–150 m), the largest range of thermal variability between anticyclonic and cyclonic eddies is between 50 and 150 m upwards of 5°C. However, these observed dynamics will likely change as a result of eddy variability associated with projected warming and Loop Current weakening, leading to increased thermal stress in the future.

Intersection of coral molecular responses to a localized mortality event and ex situ deoxygenation.

In July 2016, East Bank of Flower Garden Banks (FGB) National Marine Sanctuary experienced a localized mortality event (LME) of multiple invertebrate species that ultimately led to reductions in coral cover. Abiotic data taken directly after the event suggested that acute deoxygenation contributed to the mortality. Despite the large impact of this event on the coral community, there was no direct evidence that this LME was driven by acute deoxygenation, and thus we explored whether gene expression responses of corals to the LME would indicate what abiotic factors may have contributed to the LME. Gene expression of affected and unaffected corals sampled during the mortality event revealed evidence of the physiological consequences of the LME on coral hosts and their algal symbionts from two congeneric species (Orbicella franksi and Orbicella faveolata). Affected colonies of both species differentially regulated genes involved in mitochondrial regulation and oxidative stress. To further test the hypothesis that deoxygenation led to the LME, we measured coral host and algal symbiont gene expression in response to ex situ experimental deoxygenation (control = 6.9 ± 0.08 mg L-1, anoxic = 0.083 ± 0.017 mg L-1) in healthy O. faveolata colonies from the FGB. However, this deoxygenation experiment revealed divergent gene expression patterns compared to the corals sampled during the LME and was more similar to a generalized coral environmental stress response. It is therefore likely that while the LME was connected to low oxygen, it was a series of interconnected stressors that elicited the unique gene expression responses observed here. These insitu and ex situ data highlight how field responses to stressors are unique from those in controlled laboratory conditions, and that the complexities of deoxygenation events in the field likely arise from interactions between multiple environmental factors simultaneously.

An annotated and illustrated identification guide to common mesophotic reef sponges (Porifera, Demospongiae, Hexactinellida, and Homoscleromorpha) inhabiting Flower Garden Banks National Marine Sanctuary and vicinities.

Sponges are recognized as a diverse and abundant component of mesophotic and deep-sea ecosystems worldwide. In Flower Garden Banks National Marine Sanctuary region within the northwestern Gulf of Mexico, sponges thrive among diverse biological and geological habitats between 16-200+ m deep (i.e., coral reefs and communities, algal nodules, and coralline algae reefs, mesophotic reefs, patch reefs, scarps, ridges, soft substrate, and rocky outcrops). A synoptic guide is presented, developed by studying common sponge species in the region, through direct sampling and in-situ photographic records. A total of 64 species is included: 60 are Demospongiae (14 orders), two are Hexactinellida (one order), and two are Homoscleromorpha (one order). Thirty-four taxa are identified to species and 13 were identified to have affinity with, but were not identical to, a known species. Fifteen taxa could only be identified to genus level, and the species remain as uncertain (incerta sedis), with the potential to represent new species or variants of known species. One specimen received only a family assignation. This study extends geographic or mesophotic occurrence data for eleven known species and includes several potentially new species. This work improves our knowledge of Gulf of Mexico sponge biodiversity and highlights the importance of the region for scientists and resource managers.

Coral disease outbreak at the remote Flower Garden Banks, Gulf of Mexico

East and West Flower Garden Bank (FGB) are part of Flower Garden Banks National Marine Sanctuary (FGBNMS) in the northwest Gulf of Mexico. This geographically-isolated reef system contains extensive coral communities with the highest coral cover (>50%) in the continental United States due, in part, to their remoteness and depth, and have historically exhibited low incidence of coral disease and bleaching despite ocean warming. Yet in late August 2022, disease-like lesions on seven coral species were reported during routine monitoring surveys on East and West FGB (2.1–2.6% prevalence). A series of rapid response cruises were conducted in September and October 2022 focused on 1) characterizing signs and epidemiological aspects of the disease across FGB and within long-term monitoring sites, 2) treating affected coral colonies with Base 2B plus amoxicillin, and 3) collecting baseline images through photostations and photomosaics. Marginal and/or multi-focal lesions and tissue loss were observed, often associated with substantial fish and invertebrate predation, affecting the dominant coral species Pseudodiploria strigosa (7–8% lesion prevalence), Colpophyllia natans (11–18%), and Orbicella spp. (1%). Characterizing this disease event during its early epidemic phase at East and West FGB provides a critical opportunity to observe how coral disease functions in a relatively healthy coral ecosystem versus on reefs chronically affected by various stressors (e.g., Caribbean reefs adjacent to urban centers). Insights into the etiology, spread, and impacts of the disease can ultimately inform efforts to mitigate its effects on coral communities.

Fish community characterization of mid-shelf and shelf- edge mesophotic coral ecosystems in the expanded Flower Garden Banks National Marine Sanctuary

The mid to outer continental shelf in the northern Gulf of Mexico is composed of a patchy distribution of coral and rock reefs designated high priority for marine protection. To better understand the influence of deepwater habitat on fish community dynamics and conservation needs, we compared altiphotic-mesophotic transition (20– 40 m), upper mesophotic (40–60 m), and middle mesophotic (60–80 m) fish communities between mid-shelf (Sonnier Bank) and outer-shelf (McGrail Bank) banks from before their inclusion into the Flower Garden Banks National Marine Sanctuary. Surveys performed over two years with a remotely operated vehicle indicated that each bank and depth zone had distinct fish communities. Both banks were dominated by planktivores and piscivores, with an increase in depth specialists (e.g., deepwater anthiids and serranids) at the deeper zones surveyed, particularly in middle mesophotic depths at McGrail. An increased frequency of snappers, groupers, and amberjack was observed at Sonnier Bank, predominately in mesophotic depths, indicating the Sonnier Mesophotic Coral Ecosystem as either a hotspot or potential refuge for meso- and apex predators. This study fills a temporal gap in fish community dynamics of these two banks, serving to create a more continuous dataset available to assist in conservation assessments of the Flower Garden Banks National Marine Sanctuary.

Geological faulting a possible trigger for brine-induced reef mortality at East Flower Garden Bank, NW Gulf of Mexico

Localized mortality within reef crest depressions in Flower Garden Banks National Marine Sanctuary in 2016 may have resulted from inundation by brine that erupted when reef rock collapsed into a solution cavern in the salt dome below the bank. This mechanism offers an alternative explanation of mortality that has previously been attributed to hypoxia caused by either offshore movement of brackish, organically rich flood waters, upwelling, or both. Faults at the mortality site, discovered previously, and field observations of water conditions and mortality patterns during the event suggest that salt dissolution, undermining, and collapse may have driven a brine eruption. Elsewhere on the bank, anoxic, sulfurous brine flows have been found adjacent to areas of seafloor collapse, producing localized, brine-induced stress and mortality, but evidence of acute, lethal brine eruptions caused by active faulting would be novel for this system.

Characterizing the Biological Community before and after Partial Removal of an Offshore Gas Platform in the Northwestern Gulf of Mexico.

High Island A-389-A (HI-A-389-A) is a gas platform situated in 125 m water within Flower Garden Banks National Marine Sanctuary in the northwestern Gulf of Mexico, and provides habitat to a diverse array of benthic organisms and fish species. Platform production ceased in 2012, beginning the decommissioning process for structural removal. Rather than complete removal of the structure, the lower portion was left intact as an artificial reef and the upper 21 m was removed. The biological communities (benthic and fish) were characterized during diver and remotely operated vehicle surveys, both before and after removal of the upper structure. The platform's benthic community, primarily categorized as fouling organisms, was mainly composed of sponges, hydroids, macroalgae, bivalves, zoanthids, and stony corals. The dominant stony coral was orange cup coral (Tubastraea sp.), an exotic species, while native coral species were rare. Fish species were predominantly demersal planktivores. Analyses of the benthic and fish communities documented four distinct biological zones strongly associated with depth. Significant differences in the benthic community were observed after partial removal and varied with depth, including the loss of hydroids, increase in macroalgae cover, and sponge and coral community changes. Both demersal and pelagic fish communities exhibited significant differences by depth after removal but no significant changes were observed in federally managed species. Results reflect changes in benthic and fish communities after partial removal of the platform that is likely, in part, influenced by structure removal and temporal variations.

Improved biodiversity detection using a large-volume environmental DNA sampler with in situ filtration and implications for marine eDNA sampling strategies

Metabarcoding analysis of environmental DNA samples is a promising new tool for marine biodiversity and conservation. Typically, seawater samples are obtained using Niskin bottles and filtered to collect eDNA. However, standard sample volumes are small relative to the scale of the environment, conventional collection strategies are limited, and the filtration process is time consuming. To overcome these limitations, we developed a new large – volume eDNA sampler with in situ filtration, capable of taking up to 12 samples per deployment. We conducted three deployments of our sampler on the robotic vehicle Mesobot in the Flower Garden Banks National Marine Sanctuary in the northwestern Gulf of Mexico and collected samples from 20 to 400 m depth. We compared the large volume (∼40–60 L) samples collected by Mesobot with small volume (∼2 L) samples collected using the conventional CTD rosette – mounted Niskin bottle approach. We sequenced the V9 region of 18S rRNA, which detects a broad range of invertebrate taxa, and found that while both methods detected biodiversity changes associated with depth, our large volume samples detected approximately 66% more taxa than the CTD small volume samples. We found that the fraction of the eDNA signal originating from metazoans relative to the total eDNA signal decreased with sampling depth, indicating that larger volume samples may be especially important for detecting metazoans in mesopelagic and deep ocean environments. We also noted substantial variability in biological replicates from both the large volume Mesobot and small volume CTD sample sets. Both of the sample sets also identified taxa that the other did not – although the number of unique taxa associated with the Mesobot samples was almost four times larger than those from the CTD samples. Large volume eDNA sampling with in situ filtration, particularly when coupled with robotic platforms, has great potential for marine biodiversity surveys, and we discuss practical methodological and sampling considerations for future applications.

Assessment of Rhodolith Diversity in the Northwestern Gulf of Mexico Including the Description of Sporolithon gracile sp. nov. (Sporolithales, Rhodophyta), and Three New Species of Roseolithon (Hapalidiales, Rhodophyta)

In the past, non-geniculate coralline algae in the northwestern Gulf of Mexico have been identified based primarily on comparative morpho-anatomy. Recent studies employing DNA sequencing techniques combined with morpho-anatomical studies using SEM have revealed a wealth of previously undocumented diversity of rhodolith-forming non-geniculate coralline algae in the Corallinales, Hapalidiales and Sporolithales from mesophotic hard bank communities at 45-90 meters depth. Although many advances in the last decade have been made in clarifying species names and describing new species of corallines from offshore Louisiana and Texas, total diversity estimates are still incomplete and many species remain to be described. Collections from offshore Louisiana at Parker Bank in the newly expanded Flower Garden Banks National Marine Sanctuary yielded thin, finely branched rhodoliths. DNA sequence analyses of plastid-encoded psbA and rbcL loci, and nuclear-encoded LSU rDNA of these rhodolith-forming specimens revealed that some belong to an unnamed species of Sporolithon (Sporolithales) that we herein newly describe. Additionally, comparative DNA sequence analyses of rhodolith collections from Ewing Bank and other hard banks offshore Louisiana were conducted to assess rhodolith diversity in these mesophotic communities. The results revealed new reports of taxa for the region, including new rhodolith-forming species of Roseolithon (Hapalidiales) to be described herein as well. Our new biodiversity findings will be compared with historical studies from the NW Gulf of Mexico.

Key Life History Attributes and Removal Efforts of Invasive Lionfish (Pterois volitans) in the Flower Garden Banks National Marine Sanctuary, Northwestern Gulf of Mexico

Indo-Pacific lionfish (Pterois volitans and P. miles) are the first marine teleost to have successfully invaded and become established in the Western Atlantic Ocean of the United States, Gulf of Mexico (GoM), and Caribbean Sea. Pterois volitans were first reported in the Flower Garden Banks National Marine Sanctuary (FGBNMS), a protected coral reef system in the northwestern GoM, in 2011. Little is understood about the life history characteristics of lionfish in this ecosystem. This study assessed population characteristics (size, density, age and growth) and removal efforts of lionfish (n = 1,665) at two coral reef sites within FGBNMS for 2015, 2016, and 2018. The annual increment formation in sagittal otoliths was examined to assess the age and growth of lionfish collected in 2018 (n = 100). Lionfish ranged in size from 75 to 444 mm total length (TL) and 4–1,153 g in total weight (TW). Six hundred and ten fish were randomly dissected for sex determination (females = 256, males = 354), females ranged in size from 137 to 348 mm TL and 21–586 g, while males ranged from 118 to 444 mm TL and 18–1,153 g. Interannual variation in mean lionfish density ranged from 26.7 individuals per hectare (ind ha–1) in 2016 to 81.1 ind ha–1 in 2018, while removal effort significantly increased ranging from 1.92 to 5.42 kg diver h–1. Lionfish age ranged from 0 to 10 years, with a mean age of 3.9 years. The observed values of the asymptotic maximum total length (L∞) and Brody’s growth coefficient (K) were 345 mm and 0.30 for females and 415 mm and 0.18 for males. Results suggest lionfish from FGBNMS exhibit markedly lower mean densities, a lower L∞ and growth rate, but attain older ages than lionfish in the Caribbean Sea, Western Atlantic Ocean, and other ecoregions in the northern GoM. This study describes the first key life history parameters and removal efforts for lionfish in a protected, healthy coral reef system in the northwestern GoM that may provide insight into environmental population controls (e.g., ecological resilience). Metrics from this study could be integrated into mechanistic ecological models to determine if FGBNMS is in fact exhibiting natural resilience to the lionfish invasion.

Gene expression associated with disease resistance and long-term growth in a reef-building coral.

Rampant coral disease, exacerbated by climate change and other anthropogenic stressors, threatens reefs worldwide, especially in the Caribbean. Physically isolated yet genetically connected reefs such as Flower Garden Banks National Marine Sanctuary (FGBNMS) may serve as potential refugia for degraded Caribbean reefs. However, little is known about the mechanisms and trade-offs of pathogen resistance in reef-building corals. Here, we measure pathogen resistance in Montastraea cavernosa from FGBNMS. We identified individual colonies that demonstrated resistance or susceptibility to Vibrio spp. in a controlled laboratory environment. Long-term growth patterns suggest no trade-off between disease resistance and calcification. Predictive (pre-exposure) gene expression highlights subtle differences between resistant and susceptible genets, encouraging future coral disease studies to investigate associations between resistance and replicative age and immune cell populations. Predictive gene expression associated with long-term growth underscores the role of transmembrane proteins involved in cell adhesion and cell–cell interactions, contributing to the growing body of knowledge surrounding genes that influence calcification in reef-building corals. Together these results demonstrate that coral genets from isolated sanctuaries such as FGBNMS can withstand pathogen challenges and potentially aid restoration efforts in degraded reefs. Furthermore, gene expression signatures associated with resistance and long-term growth help inform strategic assessment of coral health parameters.

Oldest Indo-Pacific Lionfish (Pterois volitans/P. miles) Recorded From the Northwestern Gulf of Mexico

Indo-Pacific lionfish (Pterois volitans/miles) were first detected off the coast of Florida in the 1980s, with aquaria release being the most likely mechanism for introduction. Since then, lionfish have proliferated through the Western Atlantic Ocean, Caribbean Sea, and Gulf of Mexico (GOM). Here, we report the oldest lionfish aged on record in the Western Atlantic, removed from Flower Garden Banks National Marine Sanctuary (FGBNMS) in the GOM. In August 2018, a research expedition removed 745 lionfish from FGBNMS, of which a subset were retained for age and growth estimation. The oldest lionfish was a 10 y old male, with total length 375 mm and weight 805 g. The back-calculated birth date (2008) preceded the first observation of lionfish at FGBNMS by 3 years (2011). It is not well understood if lionfish are having negative impacts at FGBNMS, but this report signifies the importance of continued monitoring and removal efforts of this protected area.

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.

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.

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