Tropical Marine Environments Research Articles

Study of chloride diffusion as a corrosive agent in reinforced concrete for a tropical marine environment

Diffusion of chloride ions through 7.5 cm × 15.0 cm concrete cylinders was studied. The cylinders were immersed for 30 days in a tank containing distilled water and a sodium chloride solution. Five water/cement (w/c) ratios and three curing times ( t c) were tested. It is suggested that coarse aggregate is a barrier which blocks chloride ion diffusion. A model considering a homogeneous and porous concrete was used to describe the influence of high w/c ratios and t c. A dependence between t c and the chloride concentration at the concrete surface ( C 0) for high w/c ratios was found. Dispersion in the results was minimized by using a large number of specimens.

Paleoecology of Upper Eifelian and Lower Givetian coral limestones in the northwestern Sauerland (Devonian; Rhenish Massif)

The prevailing sandy/silty lower part of the Middle Devonian in the northwestern Sauerland includes two coral limestone horizons, which contain a rich fauna of corals, stromatoporoids, and calcareous algae. The Ihmert-Formation is subdvided into three parts. The older coral limestone horizon is the Grunewiese-Member of the Ihmert-Formation (uppermost Eifelian), the younger is in the Bredenbruch-Member of the Unterhonsel-Formation (lower Lower Givetian). Conclusions about the environmental constraints are drawn from the sedimentology and the fossil content of the coral limestones. Predominant biostromes are built between storm wave base and normal wave base. Only the few bioherms grew above the normal wave base. These coral limestones were deposited in a tropical or subtropical normal marine environment in the shallow euphotic zone. Among the reef-builders epoecism is very frequent, and until now this phenomenon has not been investigated in detail. Fragile rugose and tabulate corals lived as commensals with stromatoporoids. Some other aspects of paleoecology are concisely presented.

Aryl isoprenoids and diaromatic carotenoids in Paleozoic source rocks and oils from the Western Canada and Williston Basins

Aryl isoprenoids in the range C 13–C 31 have been identified in source rock bitumens and oils from several Paleozoic-age petroleum systems in the Western Canada and Williston Basins. The principal compounds possess the 2-alkyl-1,3,4-trimethyl substitution pattern characteristic of diaromatic carotenoids found in the Chlorobiaceae family of photosynthetic sulfur bacteria. Two C 40 perhydrodiaromatic carotenoids which are structurally related to the presumed precursors of the aryl isoprenoids have also been identified in oils and source rock bitumens of the Duvernay (Late Devonian) petroleum system. Pyrolysis/gas chromatograms of kerogens isolated from several Paleozoic source rocks show an unusual abundance of 1,2,3,4-tetramethylbenzene. It is proposed that this compound arises from β-cleavage of diaromatic carotenoid moieties which have been incorporated into the kerogen structure. With increasing maturation, concentrations of the aryl isoprenoids in Duvernay source rock bitumens increase to a point, whereas the C 40 perhydrodiaromatic carotenoids decrease steadily. Previous studies have suggested that aryl isoprenoids may be indicators of enhanced-salinity environments. This is not supported by the present work, which shows high concentrations in source rocks associated with presumed normal marine salinities. There is, however, a general association with intervals of condensed clastic or mixed clastic/carbonate sedimentation within carbonate depositional systems. From the association found and from parallels to modern habitats of photosynthetic bacteria, it can be inferred that these biomarkers indicate prolific bacterial growth in a stratified water column at and below the oxic-anoxic boundary layer in sub-tropical to tropical marine environments.

Chloride ingress measurements and corrosion potential mapping study of a 24-year-old reinforced concrete jetty structure in a tropical marine environment

A corrosion survey was made of a 24-year-old reinforced concrete jetty structure in Woodlands, in the northern part of Singapore. This particular jetty structure was selected for the field survey since it was already showing signs of reinforcement corrosion and deterioration. Two piles which were located near the stairs (and were easily accessible) were surveyed in detail. The survey covered the mean tidal zone, the upper tidal zone at 0·8 m above the mean tide level, and the splash zone at 1·3m above the mean tide level. The principal test methods used in the survey were chloride profile analysis and corrosion potential mapping. A general visual and de lamination survey was also carried out. The chloride content in the concrete increased with height above the mean tide level. Chloride diffusion coefficient values, which were calculated from the chloride profile measurmounts, ranged from 2·13 × 10-8 cm2/s athe mean tidal zone to 5·50 × 10 8 cm2/s at the splash zone. The upper tidal and splash zones, i.e. those with the highest chloride content, were found to be most susceptible to corrosion. The corrosion potential measurement was reasonably consistent and reliable method for monitoring and assessing the level of rebar corrosion.

Persistent organophosphorus pesticides in tropical marine environments

‘New generation’ organophosphorus insecticides are extensively used in tropical agriculture. Investigations into the distribution of a selection of these highly toxic compounds in coastal areas of Central America and Mexico have revealed that some are sufficiently heavily used and persistent to potentially impact sensitive tropical marine ecosystems. In sediments from the areas chosen for study, chlorpyrifos was found to be the most widely distributed compound. Traces of parathion and methyl-chlorpyrifos were, however, also encountered. Concentrations of the other major organophosphorus agrochemicals applied in these regions (including methyl-parathion, malathion, monocrotofos, and fenitrothion) were generally found to be below the limits of detection of the analytical techniques employed (typically <0.1 ng g −1 dry wt).

The global Frasnian-Famennian »Kellwasser Event«

During the UppermostP. gigas conodont zone (P. linguiformis zone) the stepwise Frasnian extinction culminates in the global transgressive-regressive Frasnian-Famennian »Kellwasser event«. Most pelagic organisms of the tropical marine environment are more or less affected by this mass extinction. During the early Upper Devonian extinction rates are clearly related to the deposition of black shales and the storage of a great amount of organic carbon in the (shelf) sediments. Contemporaneous positive excursions of the δ13C recorded from pelagic limestones of Europe and Australia prove a worldwide change in the CO2 content of the oceans surface water which is in balance with the atmosphere. If the climate is controlled by the CO2 content of the atmosphere, a cyclic operation process might have developed with the succession: transgression — high organic production — deposition of organic carbon — lowering of CO2 in the atmosphere — icehouse effect — polar glaciation — regression — erosion of organic carbon and re-supply of CO2 to the ocean and atmosphere — greenhouse effect — deglaciation — transgression. During the change from a greenhouse to an icehouse effect an overturn of the anoxic oceans probably was one of the causes for the mass killing of low latitude marine organisms.

Nitrogenase activity of Microcoleus lyngbyaceus mat communities in a eutrophic, tropical marine environment

Floating and attached cyanobacterial mats consisting primarily of Microcoleus lyngbyaceus, a nonheterocystous, filamentous cyanobacterium, are a permanent feature of the nearshore marine environment at La Parguera, Puerto Rico. Nitrogenase activity in these mat communities, as determined by acetylene reduction, exhibited a diel cycle with daytime inhibition and enhanced nocturnal activity. Contrary to reports regarding benthic cyanobacterial mats adapted to oligotrophic conditions, nitrogenase activity in M. lyngbyaceus mats is closely regulated by concentrations of NH4+ and NO3− within the range of values common to their environment. The opportunistic strategy of N utilization used by M. lyngbyaceus, whereby molecular N is primarily consumed only in the absence of significant concentrations of alternate inorganic N sources, assures the success of these cyanobacterial mat communities.

Seasonal changes in serum gonadal steroids associated with migration, mating, and nesting in the loggerhead sea turtle ( Caretta caretta)

Adult male loggerhead sea turtles, Caretta caretta, exhibited a “prenuptial” spermatogenic cycle that was coincident with increased concentrations of serum testosterone (T). Serum T was high during the months when migration and mating have been recorded for males. In contrast to females, males appear to be annual breeders. Nine reproductively active female C. caretta (as verified through laparoscopy) were tagged with sonic transmitters and were repeatedly bled prior to migration. Four months prior to the nesting season, the ovaries of reproductively active females had hundreds of vitellogenic follicles of approximately 1.5 cm in diameter (i.e., half the size of ovulatory follicles). Approximately 4–6 weeks prior to migration from feeding grounds to mating and nesting areas, serum estradiol-17β (E 2) concentrations increased significantly and remained high for approximately 4 weeks, suggesting a period of increased vitellogenesis. During a 1- to 2-week period prior to migration, serum E 2 decreased significantly, while serum T concentrations increased (at least) until the time of migration. Serum T, E 2, and progesterone (PRO) were elevated during nesting if a turtle was going to nest again during that nesting season. During the last nesting of a season, turtles had low serum concentrations of T, E 2, and Pro. The prenuptial pattern of gonadal recrudescence and gonadal steroid production in both male and female C. caretta contrasts with those of many temperate freshwater turtles, and this type of reproductive pattern may have been facilitated by adaptation to a tropical marine environment.

Comparison of the in situ survival and activity ofKlebsiella pneumoniae andEscherichia coli in tropical marine environments

A near-shore coastal mangrove island receiving untreated sewage and a coastal cove receiving rum distillery effluent in Puerto Rico were examined for their ability to support survival and activity ofKlebsiella pneumoniae andEscherichia coli. Pure cultures of both bacteria were monitored for 96 hours in situ at both locations using membrane diffusion chambers.K. pneumoniae survived at all sites as measured by AODC and Coulter Counter direct counts. However, at the mangrove island less than 20% of theK. pneumoniae population was active (AODC) after the first 3 hours and less than 10% of this population was respiring (INT). In contrast, the coastal area which was receiving rum distillery effluent was able to maintain 40% of theK. pneumoniae population in an active state with 90% respiring. TheE. coli population declined by two orders of magnitude at the mangrove island, but remained unchanged at the rum distillery outfall. TheE. coli population had a higher proportion of active cells and respiring cells thanK. pneumoniae at all sites. At the rum distillery site, theE. coli population was remarkable in that 95% remained active and 99% were respiring. This study suggests that, when sufficient organic loading exists,E. coli, a "nonsurvivor," can overcome the bactericidal effects of tropical marine waters.K. pneumoniae, a "survivor," could survive under all conditions but could not maintain the activity or respiration that theE. coli population could, even when high organic loads were present. Morphological changes related to nutrient stress in the tropical marine environment were apparent inE. coli, but not inK. pneumoniae. Based on physiological activityE. coli is just as much a "survivor" asK. pneumoniae in tropical marine waters.

Compartmental models of nitrogen cycling in tropical and temperate marine environments

Time-course measurements of 15N tracer kinetics in particulate organic and in N+4 pools from tropical and temperate regions were used to test several compartmental models describing the exchange of I5N tracer in microplankton communities. Several lines of evidence suggested the involvement of a third, dissolved pool, arbitrarily labelled dissolved organic nitrogen (DON). Although the kinetic patterns of tracer movement were different between the tropical statlons and the temperate one, the same 3-compartmental model in which PON and DON can exchange material only through the intermediate of NH: gave the best fit. Only the transfer coefficients were modified. Results show that compartmental analysis is useful for the estimation of compartmental transfer rates and for testing the assumptions implicit in any given model.

Background levels of heavy metals in nine tropical seagrass species in Indonesia

Tropical marine environments are increasingly threatened by heavy metal pollution and yet very little is known about the effects of these trace elements upon coral reefs and adjoining seagrass beds. Natural background levels for Cd, Cu, Pb and Zn were estimated in 9 tropical seagrass species ( Cymodocea rotundata, C. serrulata, Thalassia hemprichii, Syringodium isoetifolium, Enhalus acoroides, Halodule uninervis, H. pinifolia, Thalassodendron ciliatum, Halophila ovalis) from pristine coastal localities in the Flores Sea, Indonesia. Above- and below-ground plant parts were analysed separately and showed extremely low metal values for most seagrass species compared to its literature data. Natural accumulation of heavy metals may occur in certain seagrass species. It is suggested that seagrasses may be used as indicator organisms for heavy metal contamination and bioavailability at the start of the food chain in marine habitats.

Seabird Patchiness in Tropical Oceanic Waters: The Influence of Sargassum “Reefs”

Abstract The relationships of seabirds to the holopelagic macroalga Sargassum were studied during a 2-yr survey in the South Atlantic Bight off the southeastern United States. Seabirds were significantly more abundant in waters with large (&gt;5 m2) patches of the alga, and mean avian density was 32-43 times greater in waters where Sargassum was present than in adjacent waters without the alga. Seabirds aggregate at Sargassum patches formed by Langmuir circulation, convergence fronts, Gulf Stream eddies, and Gulf Stream warm core rings. Twenty-three seabird species foraged at Sargassum. Significantly more than 50% of White-tailed Tropicbirds (Phaethon lepturus), Masked Boobies (Sula dactylatra), and Bridled Terns (Sterna anaethetus) were observed at algal patches. Species that use aerial-dipping and plunge-diving foraging behaviors displayed the greatest affinity for Sargassum. Large-bodied seabirds (large shearwaters, tropicbirds, and boobies) generally were found at large patches, while small-bodied species (phalaropes and Puffinus lherminieri) occurred at smaller patches. The seasonal abundance of the pelagic Bridled Tern corresponded to seasonal variation in Sargassum abundance. Most seabirds associated with Sargassum for foraging, but Bridled and Black terns (Chlidonias niger) also used large algal mats for roost sites. The highly localized biomass of the pelagic Sargassum community and its associated motile macrofauna (zooplankton and fish) may allow seabirds to forage efficiently for prey in the oligotrophic surface waters of tropical marine environments. The patchy occurrence of Sargassum "reefs" may explain part of the local and mesoscale variation in seabird distribution and abundance in portions of the western North Atlantic Ocean.

Distribution, behavior and fate of PCBs in the marine environment

I am extremely grateful and honored for being awarded the Okada Prize (1985) for my study. The present article reviews my research on the distribution, behavior and fate of PCBs in the marine environment. The outline of this study is summarized as follows: 1. Polychlorinated biphenyls (PCBs) were detectable in the wide range of environmental media and biota of the Seto-Inland Sea, Japan, in which much high concentrations were found in sediment and biological samples due to their hydrophobic, lipophilic and less biodegradable properties as well as their extensive production and use in estuarine and coastal regions. 2. PCBs extend the boundaries of their distribution all over the global environment, being evidenced by their occurrence in open ocean atmosphere, hydrosphere and biosphere, even in Antarctica. The global contamination of PCBs is much more prominent in northern hemisphere than in southern hemisphere. 3. The sinking rate of PCBs from surface to deeper layers in open ocean water column is relatively slower in tropical waters than in high latitude ones. This implies the possible prolonged contamination of persistent synthetic organic chemicals in the tropical marine environment. 4. The bioaccumulation processes in marine ecosystems can be explained by the physicochemical and biochemical properties of PCBs and the metabolic capacity of organisms. In higher animals, additional factors such as parturition and lactation are also related to this process. 5. Total PCB load in global environment was estimated to be about 370 thousand tons. Of this, most amounts were in coastal sediment and open ocean water. Presently, about 780 thousand tons of PCBs are still in use mainly in electrical equipments. In order to reduce the PCB levels in marine environment, pertinent measures to prevent the further discharge and safe disposal of PCBs are required.

Environmental Behavior and Fate of Persistent Organochlorines (Recent Evidences on Dynamics in Environment and Toxicity of Organochlorine Compounds) (Proceedings of the 11 th Symposium on Environmental Pollutants and Toxicology)

The persistent organochlorines such as PCBs, DDT compounds and HCH (BHC) isomers were detectable all over the environmental media and biota, in which much higher levels were found in agricultural soil, coastal sediment and biological samples due to their hydrophobic, lipophilic and less biodegradable properties. These pollutants extend the boundaries of distribution over the global environment, being evidenced by their occurrence in Antarctic atmosphere, hydrosphere and biosphere. In open ocean environment, organochlorine contamination is much more prominent in northern hemisphere than in southern hemisphere. The open ocean water serves as a vast reservoir and final sink of these persistent organochlorines. The clearance rate of these chemicals from surface to deeper layer in open ocean water columns is relatively slower in tropical waters than in high latitude ones. This implies the possible prolonged contamination of persistent organochlorines in the tropical marine environment, even if their uses would be stopped in the future. The bioaccumulation processes in marine organisms depend primarily on the physicochemical and biochemical properties of organochlorines and the metabolic capacity and life-span of organisms. The species-specific drug metabolizing enzymes might be related to the differencial ecotoxicity of xenobiotics in wild animals. Of these organochlorines, PCBs are most noticeable chemicals in view of the future trend of environmental contamination. About two thirds of cummulative production of PCBs are still in use mainly for electrical equipments. The pertinent measures to prevent the further discharge of PCBs are required to reduce the present status of contamination in abiotic and biotic environment.

Favositid Tabulates: Evidence for Poriferan Affinity

Calcitic pseudomorphs of desma-like siliceous spicules found in the calcareous skeleton of a Devonian thamnoporid support the proposal of poriferan origin of at least some favositid Tabulata. These favositids arose from a group of Ordovician lithistid demosponges that adapted to toxic calcium excess in shallow, tropical marine environments by developing calicoblasts within the pinacoderm, supplementing their primary siliceous spicular skeletons with basally secreted calcium carbonate. They are tentatively recognized as an order of the subclass Sclerospongiae (class Demospongiae).

Standing-stock and potential of phytoplankton production in the bay of Santos, Brazil

Phytoplankton primary production and the maximum photo synthetic index (Pbm) from the region of Bay of Santos were measured every two months during 1976 by simulated incubations using 14C method and incandescent lamps (737 µE.m-2 .s-140 klux) . The results obtained for production rates (maximum of 204.6 mgC.m-3.hr-1 in winter and 488.3 mgC m-3.hr-1 in summer) are among the highest recorded for tropical marine environments. A high capability of light adaptation under high temperatures was also verified. The photo synthetic indexes obtained were also very high and seems to be due to the high nutrient level of the region. The eutrophic state is supported by the high nutrient and chlorophyll-a concentrations and by the phytoplankton cells number.

A review of some problems of tropical marine conservation with particular reference to the Tanzanian coast

Abstract The productivity, diversity and susceptibility to stress of tropical marine communities are compared with those of temperate marine communities. The question of the i importance of conservation is raised. The applicability of island biogeographical theories in relation to the design of marine reserves is briefly reviewed. It is suggested that the contention that conservation areas should always consist of the largest possible single area is not necessarily correct for the tropical marine environment. Conservation problems of particular habitats within Tanzanian coastal waters are detailed with special reference to the following: coral reefs, rocky intertidal platforms, cliffs, sandy beaches, sandy-muddy tidal flats, seagrass beds, mangroves, estuaries and small islands. The plight of some endangered species is discussed. Conclusions are drawn regarding the present status of marine conservation in Tanzania.

Hydrogen production by marine photosynthetic bacteria: Effect of environmental factors and substrate specificity on the growth of a hydrogen-producing marine photosynthetic bacterium, Chromatium sp. Miami PBS 1071

The growth potential of the marine Chromatium sp. Miami PBS 1071, a strain of photosynthetic bacteria exhibiting high hydrogen-production capabilities, was studied. This strain, isolated by our laboratory from the subtropical marine environment, grows well at high light intensities (light saturation: 140 μEinstein m −2s −1), high temperatures (optimum: 34°C), salinities normally found in marine environments (optimum: 30‰) and slightly basic pHs (optimum: 7.4–8.1). This strain grows in sulfide concentrations of 0.5–2.5 mM, and oxygen less than 4%. The growth rate in terms of doubling time was 1.75 h, which is one of the fastest rates observed for marine photosynthetic bacteria. Thus, the strain would be well suited for application to a saltwater-based tropical or subtropical outdoor mass-culturing system linked to bio-solar hydrogen-production technologies. This strain cannot utilize carbohydrates for growth but can employ various other carbon and nitrogen compounds. Besides the subject of utilization, the contribution of this work to the study of primary productivity and ecology in tropical and subtropical marine environments is discussed.

Evolutionary replacement of ecological equivalents in Late Devonian benthic marine communities

Temporal changes in taxonomic diversity, dominance structure, trophic structure, niche structure, and community composition are examined in equivalent nearshore and offshore Late Devonian benthic marine communities of New York and the central Applachians. The study interval spans an approximately 5-m.y. record of Frasnian tropical marine environments. Community structures remain relatively constant during the five million year interval, though offshore communities appear to be more unstable than nearshore communities. Considerable change in community composition occurs, however, with the total replacement of dominant spiriferacean brachiopods in the early Frasnian by their ecological equivalents in the late Frasnian. Ecological replacement of dominant species affected both offshore and nearshore communities, and does not appear to be a function of spatial environmental gradients.

Investigation of Corrosion and Weathering Phenomena in Tropical Marine Environment

Investigation of Corrosion and Weathering Phenomena in Tropical Marine Environment