Stocking Island Research Articles

DNA as a solar dosimeter in the ocean.

Stratospheric ozone depletion may result in increased solar UV-B radiation to the ocean's upper layers and may cause deleterious effects on marine organisms. The primary UV-B damage induced in biological systems is to DNA. While physical measurements of solar UV-B penetration into the sea have been made, the effective depth and magnitude of actual DNA damage have not been determined. In the experiments reported here, UV-B-induced photoproducts (cyclobutane pyrimidine dimers) have been quantified in DNA molecules exposed to solar UV at the surface and at various depths in clear, tropical marine waters off Lee Stocking Island (23 degrees 45' N, 76 degrees 0.7' W), Exuma Cays, Bahamas. (14C)thymidine-labeled DNA or unlabeled bacteriophage phi X174 DNA was placed in specially designed quartz tubes at various depths for up to five days. Following exposure, DNA samples were removed to the laboratory where UV-B-induced pyrimidine dimers were quantified using a radiochromatographic assay, and bacteriophage DNA inactivation by solar UV-B was assayed by plaque formation in spheroplasts of Escherichia coli. Pyrimidine dimer induction was linear with time but the accumulation of dimers in DNA with time varied greatly with depth. Attenuation of dimer formation with depth of water was exponential. DNA at 3 m depth had only 17% of the pyrimidine dimers found at the surface. Bacteriophage phi X174 DNA, while reduced 96% in plaque-forming ability by a one day exposure to solar UV at the surface of the water, showed no effect on plaque formation after a similar exposure at 3 m. The data collected at the water's surface showed a "surface-enhanced dose" in that DNA damages at the real surface were greater than at the imaginary surface, which was obtained by extrapolating the data at depth to the surface. These results show the sensitivity of both the biochemical (dimers) and biological (phage plaques) DNA dosimeters. DNA dosimeters offer a sensitive, convenient and relatively inexpensive monitoring system, having both biochemical and biological endpoints for monitoring the biologically effective UV-B flux in the marine environment. Unlike physical dosimeters, DNA dosimeters do not have to be adjusted for biological effectiveness since they are sensitive only to DNA-mediated biologically effective UV-B radiation. Results of pyrimidine dimer induction in DNA by solar UV accurately predicted UV doses to the phage DNA.

Hatchery production of Florida red tilapia seed in brackishwater tanks under natural-mouthbrooding and clutch-removal methods

Hatchery production of Florida red tilapia seed (eggs, sacfry and fry) in brackishwater (12 ppt) tanks was studied on Lee Stocking Island (Exuma Cays, Bahamas) under two methods of broodstock management. Six above-ground tanks (34.2 m 2) were each stocked with 240 year-class 1 breeders (avg. wt. = 143 g) at a ratio of 3 females to 1 male. Seed production was monitored either under the natural-mouthbrooding method by collecting free-swimming (i.e., post-yolksac stage) fry from tanks every 8–16 days, or under the clutch-removal method by removing free-swimming fry from tanks, and eggs and sacfry from the mouths of brooding females every 15–16 days, and assessing the numbers of each. Seed production over a 3-month period under the natural-mouthbrooding method (3.3 seed m −2 day −1) was significantly lower ( P < 0.001) than that obtained under the clutch-removal method (91.7 seed m −2 day −1) which is among the highest reported for tilapia hatcheries. Poor seed production under the natural-mouthbrooding method was attributable to cannibalism of eggs and fry by adults. Hatching success of eggs in upwelling incubators averaged 64.8% with effects of densities of 462, 923, 1385 and 1846/1 not differing significantly ( P > 0.05). Fry obtained from artificial incubation were significantly ( P < 0.05) larger (9.9 mg vs. 7.5 mg) and more viable than those obtained through natural mouthbrooding as evidenced by higher survival (73.9% vs. 49.7%) during a 29-day sex-reversal period. The results suggest that the clutch-removal method, while more labor intensive, yields markedly higher numbers of viable fry for growout.

Bahamian giant stromatolites: microbial composition of surface mats

AbstractSubtidal columnar stromatolites up to 2.5 m high near Lee Stocking Island in the Exuma Cays, Bahamas, have surface mats approximately equally composed of algae and cyanobacteria. The stromatolites are composed of fine–medium oöid and peloid sand. This sediment is supplied to the growing stromatolite surfaces by strong tidal currents which lift grains into suspension and sweep migrating dunes over the columns. The algae include an unidentified filamentous chlorophyte, and numerous diatom species mostly belonging to Mastogloia, Nitzschia and Navicula. The dominant cyanobacteria are two oscillatoriacean species, both probably belonging to Schizothrix. Trapping of sediment is mainly effected by the unidentified chlorophyte which is veneered by epiphytic diatoms. Grains are bound into a mucilaginous mat composed of diatoms and cyanobacteria. Cyanobacteria alone would not be able to trap and bind coarse sediment so effectively in this environment. In being coarse-grained and having a significant eualgal component to their mats, these stromatolites are similar to subtidal columnar stromatolites at Shark Bay, Western Australia. The Lee Stocking stromatolites are physically stressed by high velocity tidal currents and mobile sediment. The Shark Bay stromatolites are stressed by hypersalinity. In both cases stress deters grazers, encrusters and bioeroders. These coarse-grained eualgal stromatolites contrast with micritic and predominantly prokaryotic stromatolites of most Recent marine environments, and are not analogues for most pre-Phanerozoic stromatolites. They appear to be a response to changing stromatolitic mat components in the Cenozoic.

Oolite stromatolites and thrombolites, Miocene, Spain: analogues of Recent giant Bahamian examples

At El Joyazo in Almeria, southeast Spain, closely packed thrombolite and stromatolite domes of Messinian age form a bioherm 12 m thick surrounded by oolite. Individual domes, up to 1.5 m high and 4 m across, are typically composite, with distinct stromatolitic and thrombolitic parts which are sharply juxtaposed. Both parts are composed of ooid and peloid fine-medium sand. Stromatolitic parts show good lamination and often contain small finger-like columns. Thrombolite is more abundant than stromatolite and has a distinct clotted fabric produced by irregular fenestrae. In size, general shape, internal structure, depositional environment (ooid shoal), grain size (fine-medium sand), and grain composition (ooids, peloids) the stromatolitic parts of the domes are closely comparable with Recent “giant” subtidal columnar stromatolites at Lee Stocking Island, Bahamas, and we regard them as analogues of these Recent examples. At present no modern analogues are known for the thrombolites. Previously, large Messinian stromatolites elsewhere in southeast Spain have been attributed to hypersalinity caused by the Mediterranean “salinity crisis”. The El Joyazo examples formed in current-swept ooid shoal environment, probably of normal marine salinity. We suggest that mobile sands, rather than hypersaline conditions, provided the stress to inhibit predators and competitors. These “giant” Messinian coarse-grained domes, like the Lee Stocking Island stromatolites, may have formed because of the presence of algae, such as chlorophytes and diatoms, capable of trapping large grains.

Hatchery production of Florida red tilapia seed in brackishwater tanks: the influence of broodstock age

Abstract. Production of Florida red tilapia seed (eggs, sacfry and fry) in 34-m2 above-ground tanks using recirculated brackishwater (12 ppt) was studied over a 5-month period on Lee Stocking Island (Exuma Cays, Bahamas). Four tanks were stocked with year class 1 (YCI) breeders, while 2 tanks were stocked with year class 2 (YCII) breeders at densities of 200 and 240/tank (5·9 and 7·1/m2), respectively, and at a sex ratio of 3 females to 1 male, beginning in November 1988. Seed production was measured by removing free-swimming fry from tanks and eggs and sacfry from the mouths of brooding females, and assessing the number of each at 15 to 16-day intervals from February to June 1989. Average seed production (seed/m2/day) was significantly higher in YCI (52·3) than in YCII (36·0) broodstock, indicating the advantages of replacing broodstock with yearling breeders each year.

Commercial‐Scale Production of Florida Red Tilapia Seed in Low‐ and Brackish‐Salinity Tanks

AbstractCommercial‐scale production of Florida red tilapia (Oreochromis sp.) seed (eggs, sacfry, and fry) under methods that minimized freshwater usage was studied on Lee Stocking Island, Bahamas. Comparisons of seed production by broodstock held in low‐salinity (LS = 5 ppt; mixed rain and ground water) and brackish‐salinity (BS = 18 ppt; mixed ground and sea water) tanks (34 m2) showed that seed production over an 8 month period was significantly greater in LS (77.7 seed/m2/ day) than in BS tanks (47.4 seed/m2/day), with average proportion of brooding females and number of seed per clutch being greater in LS (26.9% and 763) than in BS tanks (19.8% and 643). While LS seed production was among the highest reported values for tilapias, BS production was within reported ranges for fresh and low‐salinity tilapia hatcheries. Seed production per unit of low‐salinity water (i.e., rain and/or groundwater) consumed in both LS (7,262 seed/m3) and BS (5,337 seed/ m3) tanks exceeded reported values. The results support the feasibility of commercial‐scale production of Florida red tilapia seed under intensive methods and of salinities as high as 18 ppt in regions where fresh or low‐salinity water resources are limited.

Intertidal stromatolites in a fringing Holocene reef complex, Bahamas

Intertidal stromatolites are major components of a fringing Holocene reef complex at Stocking Island, Exuma Cays, Bahamas. Trapping and binding of fine-grained carbonate sand by microorganisms, primarily filamentous cyanobacteria and diatoms, and differential lithification of sediment have produced layered structures with up to 0.5 m of relief. Formation of these stromatolites in an environment of normal marine salinity is attributed to reduced competition from crustose red algae, availability of a stable substrate, and rapid cementation. Destruction of lamination in Stocking Island stromatolites by molluscs, sponges, and worms suggests that boring invertebrates play a key role in stromatolite preservation.

Cement Fabrics of the Bahamian Platform and Its Margin Near Lee Stocking Island

Consolidated to firable carbonate rock samples were collected on and around Lee Stocking Island to determine the distribution, fabric, and mineralogy of their cements. The rocks include: (1) beachrock rimming the islands, (2) shallow-water hardgrounds, (3) reef rock, (4) channel stromatolites, and (5) Pleistocene bedrock. Analyses by SEM, microprobe, X-ray diffraction, and petrographic microscope have revealed ten different cement fabrics. Five of these cements are varieties of fibers, all of which are aragonitic except the whisker' fibers that form coarse networks of intertwining high-Mg calcite in a Pleistocene cave sample. Acicular fan-druse and square-tipped coarse fibers cement the beachrock, while an isopachous, needle-fiber rim is found only in the hardgrounds. A radial fibrous cement occurs in several ooids and biogenic grains, representing a replacement fabric of aragonite that has inverted to high-Mg calcite. Two types of blades are present: a stubby variety with a length:width ratio of 2:1 and an elongated 5:1 variety, both of which are high-Mg calcite. While the 2:1 variety is rather common, the 5:1 variety only occurred in one sample. Aragonitic micrite envelopes often surround grains in beachrock and hardgrounds, but only in association with fibrous cement. An aragonitic lime mud matrix cements the crusted mudmore » beds and low-Mg calcite equant spar cements the Pleistocene samples and occurs as void-fill in beachrock and hardgrounds. The most common marine cementation is associated with the aragonitic fibers found in the discontinuous hardgrounds and beachrocks. The more widespread cements are the low Mg-calcite spar associated with meteoric diagenesis and cementation of the Pleistocene surface.« less

Origin and Accumulation of Lime Mud in Ooid Tidal Channels, Bahamas

ABSTRACT Mud layers have been found within the ooid sands of Joulters Cays and Lee Stocking Island, Bahamas. A 1.3-m vibracore extracted from 4 m water depth in the Lee Stocking tidal channel contains a lower unit of dark brown muddy sand (skeletal rich) overlain by two layers of ooid sands intercalated with two layers of creamy, white mud. The two upper mud layers are aragonite-rich, sometimes pelleted, and contain very few skeletal grains. The contacts between the ooid sands and mud layers are commonly sharp, but some contacts show evidence of burrowing and mud clast formation. A mud layer with similar textural, mineralogic and petrographic characteristics was recovered from a 16-cm core from a tidal channel on Joulters Cays, Bahamas. This mud layer was also enclosed within ooid sands. Mud in the Lee Stocking ooid tidal channel is apparently of two origins. Mud in the lower unit of the core contains a more equal distribution of aragonite and calcite (50% each) and abundant skeletal grains of normal marine origin, indicating that the lower unit is lagoonal. Mud that is interlayered with ooid sands in the same core is dominated by aragonite (80%) and contains little sand-sized material, suggesting that it is not a typical lagoon mud. SEM examination also confirms that this mud is quite different from the lagoonal mud found at the base of the core. C-14 dating of the mud from the lagoonal unit shows that this sediment was deposited in water depths of 2 to 3 m approximately 5000 years ago when sea level was 3 m lower than present. C-14 dating coupled with knowledge of Holocene sea level indicates that both the ooid sands and the mud layers were also deposited as subtidal sediments. The mechanism by which the mud layers are accumulated with ooid sands is problematic. Suspension by storms and transport to tidal channels is one possibility; however, evaluation of the data suggests an alternative explanation. The post-lagoon history of deposition of the tidal channel may include nearly continuous restriction during which mud layers were deposited. The restriction was possibly caused by the formation and maintenance of ooid sand barri rs. Ooid sand deposition and burial of these layers may have accompanied barrier destruction.

Stable Oxygen and Carbon Isotope Study of Recent Sediments and Cements, Lee Stocking Island, Bahamas: Organic vs. Inorganic Precipitation: ABSTRACT

Stable isotope analyses of modern carbonates from the tidal inlet along the north end of Lee Stocking Island indicate a strong correlation of both carbon and oxygen isotope values with grain size. Carbonate samples used in this study include the soft, recently formed outer surface of several large columnar stromatolites, bedded muds from within the tidal channel, and marine hardgrounds from the shallow shoals adjacent to the channel. All samples are predominantly aragonite and were divided into mud-, silt-, and sand-size particles and bleached of organics prior to isotopic analysis. The range in isotopic values for all carbonate samples is 3.3 to 4.6 {per thousand} for {delta}{sup 13}C and {minus}0.3 to {minus}1.4{per thousand} for {delta}{sup 18}O. The {delta}{sup 18}O and {delta}{sup 13}C values of the mud-size aragonite from all of these samples are depleted relative to the silt- and sand-size ooids and peloids and have isotope values lighter than 1.4{per thousand} for {delta}{sup 13}C and 0.8{per thousand} for {delta}{sup 18}O. The {delta}{sup 13}C values for green calcerous algae from the restricted platform behind Lee Stocking are similar to values for the stromatolite mud. {delta}{sup 13}C values for the hardground and channel-based muds are intermediate between the {delta}{sup 13}C values formore » the calcareous algae, and coarse-grained sediment. These data suggest that the green calcareous algae which fluorish in the restricted platform, are a significant source of aragonite mud in and around the channel but are not the only source.« less

Food Habits of Florida Red Tilapia Fry in Manured Seawater Pools in the Bahamas

Abstract Florida red tilapia fry (hybrids of Oreochromis urolepis ♀ × O. mossambicus ♂) were grown on Lee Stocking Island, Exuma Cays, Bahamas, in two seawater pools that were intensively enriched with chicken manure (105 kg/hectare daily). Despite identical management during the conditioning period, the pools developed substantially different food resources. Diets of red tilapias were monitored for 20 d. In a pool where primary production was dominated by macroalgae, the diet consisted largely of macroalgae. In the other pool, where phytoplankton was dominant, phytoplankton and particulate organic matter made up the bulk of the diet. A comparison of diet with available zooplankton indicated that copepods were selectively ingested in both pools, and rotifers were nearly randomly ingested in one pool.

Growth of Tilapia aurea in Seawater Cages

AbstractFingerling Tilapia aurea were reared for 90 days in three 1.0 m3 floating cages in seawater (36 ppt) at Lee Stocking Island, Bahamas. Fish stocking density (100, 200 and 400 fish/m3) apparently did not affect growth rate but it appears salinity inhibited growth. Daily weight gain and specific growth rate (G) averaged 0.34 g/day and l.08%/day, respectively, for Tilapia aurea fingerlings. Infection of the Tilapia aurea by Bacillus sp. was associated with a significant number of mortalities. The relatively low growth rate and the high incidence of disease and mortality of Tilapita aures in seawater indicate that it may not be a good candidate for cage culture in full‐strength seawater.