Thomas J. Bright

Chemosynthetic Mussels at a Brine-Filled Pockmark in the Northern Gulf of Mexico

A large (540 square meters) bed of Bathymodiolus n. sp. (Mytilidae: Bivalvia) rings a pool of hypersaline (121.35 practical salinity units) brine at a water depth of 650 meters on the continental slope south of Louisiana. The anoxic brine (dissolved oxygen ≤0.17 milliliters per liter) contains high concentrations of methane, which nourishes methanotrophic symbionts in the mussels. The brine, which originates from a salt-cored diapir that penetrates to within 500 meters ofthe sea floor, fills a depression that was evidently excavated by escaping gas. The spatial continuity of the mussel bed indicates that the brine level has remained fairly constant; however, demographic differences between the inner and outer parts of the bed record small fluctuations.

Meiofauna and the thiobios in the east flower garden brine seep

Special hydrodynamic-chemical conditions at the East Flower Garden brine seep have provided the opportunity to examine the community structure of the thiobios and the oxybiotic-thiobiotic boundary. The boundary between the thiobios, whose population maxima occur in sulfidedependent chemoclines and which presumably have an ecologic requirement for sulfide, and the oxybios, which occur in oxidized zones above the chemocline, is controlled by sulfide, not oxygen. The boundary, which may not be at zero sulfide, is determined by a time-concentration phenomenon based on a dynamic interplay of sulfide and oxygen supply rates and the biotas sulfide detoxification capabilities. In Gollums Canyon, where oxygen is plentiful, the boundary is at 10–40 μg-atoms·l-1 sulfide. Total abundances of organisms at thiobiotic stations were comparable to total abundances at oxybiotic stations. Highest thiobiotic abundance was 202 051 organisms per m2; highest oxybiotic abundance was 240 572 organisms per m2. The thiobios is dominated by representatives of the lower Bilateria (viz. Gnathostomulida, Platyhelminthes and Aschelminthes). These groups accounted for 50–80% of all the organisms present in the thiobiotic stations but less than 20% of all organisms in the oxybiotic stations. At two thiobiotic stations, over 50% of all organisms were gnathostomulids. Thiobios included macrofaunal as well as meiofaunal components. Peak abundances of amphipods were associated with the thiobiotic environment.

The effect of sulfide and an increased food supply on the meiofauna and macrofauna at the East Flower Garden brine seep

A sulfurous brine seep at the East Flower Garden Bank, northwest Gulf of Mexico, produces conditions conducive to the growth of a luxuriant prokaryotic biota. Hydrodynamic cropping continually harvests this biota and distributes it to sandy-bottom and hard-bank benthic communities downstream of the seep. Consequently, both macro- and meiofaunal abundances are dramatically increased above the regional norm in parts of the seep system. When sulfide is present, the lower Bilaterian groups belonging to the meiofauna dominate the community; without sulfide, macrofaunal groups, particularly crustaceans, dominate the community. Outside the influence of the seep, meiofaunal copepods predominate. Changes in taxonomic composition and abundance indicate that the sandy-bottom benthos at 70–80 m depth at the East Flower Garden bank is foodlimited and that, under these conditions, meiofauna, particularly the higher Bilaterian groups, dominate the community numerically. Perhaps, under food-limiting conditions, meiofauna compete favorably with macrofauna for food.

Seafloor instability at East Flower Garden Bank, northwest Gulf of Mexico

An increasing volume of evidence suggests that normal faulting and graben formation associated with salt diapirism may be catastrophic. The evidence includes: 1) removal of solid salt from the diapirs by dissolution, 2) the nature of rock outcrops at the crests of domes, 3) seismic profiles showing recent displacement of the seafloor, and 4) changes in coral growth rates at the East Flower Garden Bank. The possibility of catastrophic movement of the seabed is an engineering constraint that must be addressed prior to emplacing structures such as jack-up rigs and production platforms.

Effects of turbidity on calcification rate, protein concentration and the free amino acid pool of the coral Acropora cervicornis

Calcification rate in the coral Acropora cervicornis was reduced significantly when exposed for 24 h to 100-ppm kaolin, but was unchanged in corals exposed to 50-ppm kaolin. Calcification rate returned to control levels during a 48-h recovery period. Most free amino acids (FAA) in the FAA pool decreased significantly in corals exposed to 100-ppm kaolin, but were unchanged in corals exposed to 50-ppm kaolin. After a 48-h recovery period, the FAA pool remained considerably below control levels in the 100-ppm exposed corals and dropped below control levels in the 50-ppm exposed corals. Calcification rate dropped less and later during the exposure period in the growing tip than in sections further down the stalk. The reduction in FAA pool size was considerably larger in the growing tip than further down the stalk. Soluble protein concentration remained unchanged during both exposure and recovery. The data are consistent with the interpretation that turbidity not only causes a decrease in photosynthetic rate and the synthesis of small molecules, but also causes a large increase in the utilization of stored organic molecules for such metabolically costly processes as mucus production and sediment removal.

Chapter 16 Effects of Drilling Mud on Seven Species of Reef-Building Corals as Measured in the Field and Laboratory*

Publisher Summary This chapter discusses the effects of drilling mud on seven species of reef-building corals. A 10 3 : 1 dilution of the drilling mud tested caused significant mortality within 65 hours in three species of coral examined. Four species suffered no mortality at any dilution tested. A 10 4 :1 dilution of the drilling fluid tested caused a statistically significant increase in polyp retraction for five of the seven species tested, whereas 3160 : 1 dilution is required to elicit significant polyp retraction in Porites divaricata, and no statistically significant polyp retraction is detected for Dichocoenia stokesii at any dilution. Dilutions greater than 10 4 : 1 are not studied.

Growth of Mercenaria mercenaria and Mercenaria mercenaria texana seed clams planted in two Texas bays

Abstract Survival and growth of Mercenaria mercenaria imported from Massachusetts, and M. mercenaria texana, the Texas subspecies, were studied in two Texas bays. Mesh-covered trays were used to limit predation. Survival was high in protected trays; unprotected trays reached 100% mortality within 6 months. In Christmas Bay, M. mercenaria growth averaged 1.8 mm/month. Most growth occurred during the summer months. Periods of no significant growth corresponded to periods when salinities under 20‰ were recorded. In Redfish Bay, growth was significantly different between stations, being fastest at a station located along the Aransas ship channel, where circulation was the highest of all sample sites (2.8 mm/month vs. 0.9–1.5 mm/month in the grass flats of the bay). Significant differences in growth between bays or between sample sites during some seasons were not correlated with either temperature or salinity regimes. Native clams, M. mercenaria texana, grew faster than imported clams in both the field and the laboratory. It is possible that differences in circulation and circulation-related parameters (e.g., food supply and waste flushing rates) account for much of the variation in growth in the bays and that periods of no growth may be determined by limiting salinities, and less frequently, temperature. Measurements made during and after this study suggest that a 2- to 3-year growout period may produce market-size clams.

Chapter 6 Reconnaissance of Reefs and Fishing Banks of the Texas Continental Shelf

Publisher Summary This chapter discusses the investigation study of reefs and fishing banks of the Texas continental shelf. Biotic assemblages of reefs and hard-banks of the Texas–Louisiana outer continental shelf can be distinctly grouped according to their natures into four categories: (1) the sparse Claypile Bank biota (35–55 m) of predominantly low-growing filamentous and leafy algae and sponges with occasional “meadows” of high-standing leafy algae occupied by numerous fish, (2) the more diverse Stetson bank and Three Hickey rock biota (28–56 m) dominated by the hydrozoan fire coral Millepol alcicornis and sponges, (3) the highly diverse and abundant flower gardens/twenty-eight Fathom bank biota with coral reefs (22–49 m), algal nodule and sand-covered platforms (45–76 m), and drowned reefs from 76 to 100+ m, bearing an assemblage of organisms directly comparable to the deep-water biota of category 3, and (4) the deep-water biota of the South Texas fishing banks (56–78 m) and fishnet bank (61–82 m) are characterized by the presence of antipatharian whips, deep-water alcyonarian fans, comatulid crinoids, certain species of deep-dwelling fishes, and sparse populations of encrusting coralline algae. This chapter discusses about the coral reef at West Flower Garden Bank. It also presents some findings on antipatharian zone.

Chapter 10 Environmental Effects of a Natural Brine Seep at the East Flower Garden Bank, Northwestern Gulf of Mexico

Publisher Summary This chapter describes anoxic sulfide-rich brine of nearly ambient temperature, which percolates from the sea floor, forming a small, shallow lake of dense water in a depression at the eastern margin of the East Flower Garden (EFG) bank. Residence time for the brine in the lake is less than one day. Brine overflows the lake and is substantially mixed with seawater in the axis of a 60 m long canyon extending from the lake to the bank edge, where dilutions are greater. The chemical composition of the brine indicates that it is a product of dissolution of the salt by seawater percolating through cracks, faults or permeable strata. Sulfide-oxidizing bacteria are abundant at the brine seawater interface and on the canyon floor where mixing brine and entrained seawater flow in a recognizable stream along the bottom. The EFG seep provides an example of a possible management technique for brine discharges.

Chapter 5 The Role of Submersibles in a University

Publisher Summary This chapter describes the DIAPHUS submersible, operated by the Department of Oceanography at Texas A&M University. DIAPHUS has provided a major methodological breakthrough for some of the biological and geological oceanographers on the Texas A&M faculty. Its unique advantages are the opportunities to (1) view the substrata and biota directly, (2) to photograph, (3) describe, (4) record them on audio and video tape, and (5) selectively sample them at a more or less leisurely pace down to depths at which divers are not effective. In pursuit of these objectives, the instruments most used have been (1) a portable black-and-white video recording system, (2) various audiocassette recorders, (3) various standard cameras, (4) hydraulic manipulator arm, and (5) sample basket. In addition to the usual safety precautions found on a submersible for returning it to the surface in an emergency, the life-support system for DIAPHUS has been expanded to provide for a maximum of 96 hours. A back-up communication system with the support ship is also available. Diving plans similar to aircraft flight plans are filed with the proper branch of the United States coast guard, well in advance of the actual operations, and a constant plot is maintained aboard the support vessel of movements of DIAPHUS, while submerged.