West Flower Garden Banks Research Articles

The Flower Garden Banks Siderastrea siderea coral as a candidate Global boundary Stratotype Section and Point for the Anthropocene series

The proposed Anthropocene Global Boundary Stratotype Section and Point (GSSP) candidate site of West Flower Garden Bank (27.8762°N, 93.8147°W) is an open ocean location in the Gulf of Mexico with a submerged coral reef and few direct human impacts. Corals contain highly accurate and precise (<±1 year) internal chronologies, similar to tree rings, and their exoskeletons are formed of aragonite and can be preserved in the rock record. Here we present results from a large Siderastrea siderea coral (core 05WFGB3; 1755–2005 CE) sampled with annual and monthly resolutions that show clear markers of global and regional human impacts. Atmospheric nuclear bomb testing by-products (14C, 239+240Pu) have clear increases in this coral starting in 1957 for 14C and the first increase in 1956 for 239+240Pu (potential bases for the Anthropocene GSSP). Coral δ13C declined especially after 1956 consistent with the Suess effect resulting from the burning of fossil fuels. Coral skeletal δ15N starts to increase in 1963 corresponding with the increase in agricultural fertilizers. Coral Hg concentrations (1933–1980) loosely track fluctuations in industrial pollution and coral Ba/Ca increases from 1965–1983 when offshore oil operations expand after 1947. Coral temperature proxies contain the 20th-century global warming trend whereas coral growth declines during this interval.

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.

Insights from barium variability in a Siderastrea siderea coral in the northwestern Gulf of Mexico

Coral Ba/Ca is a proxy for seawater barium concentration that varies with upwelling, terrigenous input, and marine productivity whereas coral Sr/Ca varies with temperature. We examine monthly coral Ba/Ca and Sr/Ca before and during offshore oil exploration in a Siderastrea siderea coral from West Flower Garden Bank located on the continental shelf edge in the Gulf of Mexico. Coral Ba/Ca variations lack pulses driven by upwelling or river outflow and are not in sync with coral Sr/Ca that exhibit a different seasonal pattern. Seasonal variations in chlorophyll-a concentration negatively correlate with coral Ba/Ca explaining 25% of that variability. A significant increase in mean coral Ba/Ca of 1.76 μmol/mol between 1931–1944 and 1976–2004 corresponds to the increase in the United States barite production and consumption primarily used in offshore oil drilling, which escalated in the 1970s, suggesting oil drilling operations are increasing seawater Ba concentration in the Gulf of Mexico.

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.

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.

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.

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.

Persistence of coral assemblages at East and West Flower Garden Banks, Gulf of Mexico

Since 1989 a federally supported long-term coral reef monitoring program has focused on two study sites atop East and West Flower Garden Banks in the northwestern Gulf of Mexico. We examined 25 yr of benthic cover data to provide a multi-decadal baseline and trend analysis of the community structure for this coral reef system. Despite global coral reef decline in recent decades, mean coral cover at East and West Flower Garden Banks was above 50% for the combined 25 yr of continuous monitoring, and represented a stable coral community. However, mean macroalgal cover increased significantly between 1998 and 1999, rising from approximately 3 to 20%, and reaching a maximum above 30% in 2012. In contrast to many other shallow water reefs in the Caribbean region, increases in mean macroalgal cover have not been concomitant with coral cover decline at the Flower Garden Banks.

Gambierdiscus (Dinophyceae) species diversity in the Flower Garden Banks National Marine Sanctuary, Northern Gulf of Mexico, USA

Globally, ciguatera fish poisoning (CFP) is the principal cause of non-bacterial illness associated with seafood consumption. The toxins (ciguatoxins) responsible for CFP are produced by dinoflagellates in the genus Gambierdiscus, which are endemic to tropical and sub-tropical areas. Ciguatoxins are lipophilic and bioaccumulate in marine food webs, typically reaching their highest concentrations in fish. Following a CFP event in 2008, the U.S. Food and Drug Administration (USFDA) issued a ciguatera toxin alert that included fish harvested in the northern Gulf of Mexico in and near the Flower Garden Banks National Marine Sanctuary (FGBNMS). The East Flower Garden Bank (EFGB) and West Flower Garden Bank (WFGB) are characterized by thriving coral communities that support Gambierdiscus growth. This study was undertaken specifically to document the diversity of Gambierdiscus species present in the sanctuary that may be sources of ciguatoxins entering the food web. Samples collected from the FGBNMS over a three year period were screened using species-specific polymerase chain reaction assays. A diverse assemblage of Gambierdiscus species was distributed to depths of >45m, a new depth record for Gambierdiscus. Gambierdiscus belizeanus, Gambierdiscus caribaeus, Gambierdiscus carolinianus, Gambierdiscus carpenteri and Gambierdiscus ribotype 2 were all found on both East and West FGB with Gambierdiscus ruetzleri also recorded from the WFGB. The most common species was G. carolinianus, originally identified from samples collected between 35 and 40m off the coast of NC, USA. Our findings are consistent with recent physiological studies showing that some Gambierdiscus species can grow year round at the temperatures and salinities at the FGBNMS and at light levels as low as 10μmolphotonsm−2s−1. Such irradiances are estimated to occur in the FGBNMS at depths of ∼70–80m. The consistent recovery of Gambierdiscus species from deep sampling sites in areas known to produce ciguatoxic fish signals a substantial change in our concept of suitable habitats for Gambierdiscus to include depths greater than 50m.

Current and hydrographic conditions at the East Flower Garden Bank in 2011

The East Flower Garden Bank (EFGB), part of the Flower Garden Banks National Marine Sanctuary, is located in the northwestern Gulf of Mexico, about 185km southeast of Galveston, Texas. With a width of about 5km, the steep-sided bank rises from water depths of over 100m to within less than 20m of the surface. Four acoustic Doppler current profiler (ADCP) moorings and four temperature/salinity strings were deployed around the EFGB with an additional ADCP on top of the bank for about 1 year. The main objective was to understand the ocean processes over the EFGB and to examine the importance of the topographically induced processes on shelf edge circulation on longer (e.g. days to seasonal) time scales. Currents were generally eastward over the bank in the upper water column. Eddy events occasionally reversed the eastward flow for a few days. Currents in the lower water column tended to align with the bank's bathymetry and mostly were directed offshore at the southern edge of the bank. Wind and eddy events moved both shelf and off-shelf waters over the bank, including waters from as deep as 200m through upwelling and/or mixing processes. Mixed layers changed by as much as 50m in a couple of days. Inertial currents occurred throughout the year and were often much larger than the tidal currents. Commonly, the inertial currents were strong enough to reverse the predominantly eastward current flow on time scales of less than a day. Westward propagating cyclonic eddies (often associated with anticyclonic eddies) likely connect biological activities of the EFGB with the West Flower Garden Bank. Banks such as the EFGB, with large aspect ratios and heights, strongly alter circulation and enhance exchange processes at the shelf break.

Long-Term Persistence of Coral Assemblages on the Flower Garden Banks, Northwestern Gulf of Mexico: Implications for Science and Management

The coral reefs of the Flower Garden Banks (FGB) are among the most sensitive biological communities in U.S. Federal waters of the Gulf of Mexico. In 1973, the Minerals Management Service (MMS) established a program of protective activities at those reefs. The MMS and the National Oceanic and Atmospheric Administration (NOAA) have been monitoring coral populations on a long-term basis to detect incipient changes caused by oil and gas activities. The results also help in explaining the widespread degradation of reef ecosystems observed in the Caribbean region over the past few decades. Two sites, each 100 100 m and 17–26 m deep, have been monitored since 1988: one on the East FGB and the other on the West FGB. The mean coverage of living hard corals exceeded 50% at the two banks in 2002–2003, consistent with estimates of coral cover in previous years. We compared our results from 2002–2003 with data collected during the same period on protected reefs within the Florida Keys National Marine Sanctuary (FKNMS). Low values of coral cover on the reefs in the FKNMS exemplify how catastrophic mortality of the formerly dominant Acropora spp. led to degradation of coral assemblages throughout the Caribbean. The FGB remained in exceptionally good condition, largely for reasons of geography; their northern location excluded the cold-sensitive acroporids, so the regional-scale loss of acroporids did not reduce coral cover. The continuing multidecadal baseline of reef condition generated by the monitoring program at the FGB will enable managers to make informed decisions in the event of future changes to their biota.

Sedimentary Environments of East and West Flower Garden Banks Area

Sedimentary Environments of East and West Flower Garden Banks Area

51 Characterization of the northwestern gulf of Mexico macroalgae

The upper Northwestern Gulf basin is characterized by a relatively shallow but well developed continental shelf with an extensive system of mid‐ and outer shelf hard banks formed on unique tectonically created salt diapirs of varying origin and composition. Collections made by our laboratory from ∼30 m depth by SCUBA while participating in monitoring cruises to the National Marine Sanctuaries of the East and West Flower Garden Banks (Texas), Stetson Banks (Texas) and Sonnier Banks (Louisiana), and while dredging off Louisiana at ∼45–90 m depth, reveal a surprisingly different floristic composition among the sites. Several range extensions, new macroalgal records for the Gulf of Mexico, and the establishment of new species for the region indicate that the NW Gulf encompasses complex macroalgal biota. Our ongoing project includes the development of a modern taxonomic, phylogenetic, morphological and genetic database essential to informed management for preservation of biological diversity. It also provides a framework for seasonal algal composition against which long‐term trends and anomalies in algal distribution and health of the Gulf of Mexico can be assessed at future dates.

ALGAL COMMUNITY STRUCTURE OF THE EAST AND WEST FLOWER GARDEN BANKS, NORTHWESTERN GULF OF MEXICO

The algal communities of the Flower Garden Banks National Marine Sanctuary have not been comprehensively evaluated and only a few dominant macroalgal species have been reported. This study utilizes both destructive and non‐destructive sampling techniques to characterize and taxonomically identify the ‘algal mat’ community structure. The East and West Flower Garden Banks are located on the outer continental shelf approximately 200 km off the Texas‐Louisiana coastline. The average depth of both banks is 100 m with the crest approximately 20 m from the surface. Harvest and photogrammetric samples were collected during two extended cruises to the Flower Garden Banks in October 1998 and March 1999. Forty, 0.25‐m2 quadrats of standing stock material were randomly collected along with one hundred sixty‐one 0.25 m2 photo‐quadrats from an average depth of 27 m. Photo‐transparencies were projected to an actual size grid with 25 random points. Four thousand twenty‐five transparency points were evaluated and used to calculate percent composition of algal cover. Harvest samples were used to characterize the “algal mat” composition, species richness, abundance, and biomass. Forty‐two species were identified from the samples representing 14 Orders. The “red algal mat” was the dominant algal coverage comprising 38.4% of all photogrammetric samples. This mat was primarily composed of members from the Order Ceramiales. Centroceras, Ceramium, and Polysiphonia comprised 33.4% of the mat, Anotrichium and Hypoglossum, 22.4%.

Crustose Coralline Algae from the Flower Garden Banks, Northwestern Gulf of Mexico: Controls on Distribution and Growth Morphology

ABSTRACT The East and West Flower Garden Banks in the northwestern Gulf of Mexico represent the northernmost tropical coral reefs and Caribbean coralline algal flora on the North American continental shelf. Coralline algae are the dominant framework builders and sediment contributors below 50 m on the banks. On the basis of growth form and taxonomic composition, coralline algae on the Flower Garden Banks can be divided into four overlapping depth zones: upper coral reefs (20-30 m), Madracis-algal ridges (30-40 m), algal nodule zone (45-80 m), and deep algal reefs (50-90 m). Corallines on the upper coral reefs are dominated by Hydrolithon, Lithophyllum, and Porolithon. Their growth form as thick, laterally restricted crusts and knobs results from intensive grazing by parrotfish and urchins. Grazing is diminished on the Madracis-algal ridges below the upper reefs, and corallines grow here as laterally extensive plates, binding coral rubble. Dominant corallines on the ridges are Lithophyllum, Paragoniolithon, and Tenarea. Algal nodules (rhodoliths) o the deeper bank slopes are the most widespread algal growth form on the Flower Garden Banks. On the basis of shape, internal structure, and composition, rhodoliths are divided into an upper zone (where they have a spherical shape with concentric laminae) and a lower zone (discoidal shape with irregular laminae). Diminishing current velocity with increasing depth controls nodule morphology. The red alga, Peyssonnelia, and the foraminifer, Gypsina, are two non-coralline components that contribute substantially to nodule growth. Reduced current velocity in the lower nodule zone enables corallines and Peyssonnelia to develop laterally extensive pavements and 1-2 m high algal reefs. Taxonomic composition, high framework porosity, and irregular internal growth morphology f the deep algal reefs distinguish these structures from shallow algal ridges described elsewhere. The 90 m isobath at the Flower Garden Banks approximates the upward limit of a turbid nepheloid layer composed of continually resuspended sediment. Reefal structures within this water layer are dead and are now covered by fine sediment.

The structure of soft-bottom benthic communities in the vicinity of the Texas Flower Garden Banks, Gulf of Mexico

Biological and sedimentological samples were obtained in June 1980 from box cores taken in 100–200 m of water on sandy-mud sediments near the East and West Flower Garden Bank reefs, on the Texas-Louisiana Continental Shelf. The objective was to obtain baseline information about sedimentary parameters and organisms adjacent to the FGB environments in order to allow inferences to be made about potential effects of physical disturbance of the seafloor on the resident benthos. Most infaunal organisms are found in the upper 3–5 cm of the bottom. Permanent meiofauna dominate in both numbers and biomass. X-radiographs of sediment fabrics show all stations to be reworked by head-down deposit-feeders or errant bioturbators. Taxa responsible for this bioturbation were not quantitatively sampled. Macrofaunal densities range from 3000 to 25000 m −2 and total meiofauna from 221 to 892 × (10 cm) −2. Nematodes dominate followed in equal abundance by foraminiferans, polychaetes, and copepods. Seventy-five percent of the total sediment ATP in the top 3 cm is contributed by meiofauna. These benthic assemblages are hypothesized to represent a mixture of pioneering and high-order successional stages. Bacterial abundances are positively correlated with organic content and inversely correlated with macro- and meiofaunal densities. This inverse relationship may reflect consumer cropping intensities. Both microbial ATP and bacterial biomass are lower than reported for the Georgia Bight Shelf, Cape Blanc, West African Shelf, western coast of Norway, and Long Island Sound. Bacterial counts are lower than those recorded for the East China Sea and the Amazon River shelf. Moderate to low standing stocks of benthos, dominated by meiofaunal-sized taxa, further suggest that this area of the Gulf of Mexico is a relatively oligotrophic system for infaunal benthic consumers. Higher order successional stages are, in general, adversely affected to a greater extent than pioneering stages by physical disturbance. In the Texas-Louisiana shelf region, dilution of an already food limited system by inert barium sulphate would be expected to result in even lower standing stocks of benthic infaunal invertebrates.

Local Carbonate Production on a Terrigenous Shelf: ABSTRACT

During the past 10 years, the Department of Oceanography at Texas A&M University has been involved in investigating reefs and banks on the Texas-Louisiana outer continental shelf. Studies were conducted on the geologic structure, sediment distribution, biology, and water and sediment dynamics at over 30 reefs and banks. Because of the influence of the Mississippi River and other streams, the dominant sediments in this part of the Gulf of Mexico are terrigenous sands and muds. Uplift of the sea floor caused by salt diapirism exposes bed rock that serves as a substrate for colonization by calcareous organisms. Sediment facies and biologic zones at the Flower Garden Banks are closely related. The presence of a bathymetric high influences the direction and velocity of bottom currents. Factors that control sediment facies are biologic components and depth of the nepheloid layer (turbid water). Factors that control biologic zonation are the nature of the substrate, the water depth, and the depth of the nepheloid layer. No land-derived sediment (silt and clay) are present above a depth of 75 m. Studies of the physical characteristics of the water column indicate End_Page 1429------------------------------ that the nepheloid layer rarely rises to depths of 75 m. The 80-m depth contour marks a major boundary between biologic communities. That depth separates the turbid water fauna below from the clear water fauna and flora above. The east and west Flower Garden Banks serve as modern analogs of Tertiary reefs, such as the Oligocene reef at Damon Mound, Brazoria County, Texas. The sediment facies are similar, even to the muddy Porites gravels and Heterostegina sands that were deposited under an Oligocene nepheloid layer. End_of_Article - Last_Page 1430------------

Living Foraminifers of West Flower Garden Bank, Northernmost Coral Reef in the Gulf of Mexico

Living Foraminifers of West Flower Garden Bank, Northernmost Coral Reef in the Gulf of Mexico

Living Foraminifers of West Flower Garden Bank, Northernmost Coral Reef in Gulf of Mexico: ABSTRACT

At West Flower Garden Bank, on the outer Texas-Louisiana continental shelf, 104 species of living benthic foraminifers representing 73 genera were found in sediments and on hard substrates collected from the submerged coral reef and biostrome. Three habitat associations can be recognized. (1) An association of abundant sediment-dwelling species is formed by Cassidulina sp., Loxostromum limbatum forma costulatum, Peneroplis proteus, Pseudomassilina (?) sp., Quinqueloculina sp. A, Q. sp. B, Rosalina sp. B, and Rotaliammina trumbulli. (2) An association of abundant hard-substrate-dwelling species is formed by Carpenteria utricularis, Carterina spiculotesta, Gypsina plana, Homotrema rubra, Planogypsina squamiformis, Planorbulina acervalis, Planorbulina mediterranensis, Planor ulinoides retinaculata, Rotaliammina squamiformis, and Sporadotrema cylindrica. (3) An association dwelling in abundance both in the sediments and on hard substrates is formed by Amphistegina gibbosa, Eponides repandus, Miliolinella circularis, Neoconorbina orbicularis, Spirillina vivipara, and Tretomphalus atlanticus. Only 17 (16%) of the West Flower Garden Bank species are endemic to the Gulf of Mexico; 83 (80%) occur elsewhere in the Caribbean; and 53 (51%) also occur in the tropical Indo-Pacific. Thirty-two species (31%) are reported for the first time from the Gulf of Mexico, and 12 species (12%) are newly reported from the northwestern End_Page 1609------------------------------ Gulf; 18 species (17%) appear to be undescribed in previous literature. Many of the newly reported species are abundant at West Flower Garden Bank and several other species, known only sparsely from other Gulf and Caribbean reefs, are important constituents of the West Flower Garden Bank foraminiferal community. These results emphasize the value of direct sampling techniques that recover hard reef substrates. End_of_Article - Last_Page 1610------------