Showing papers by "National Institute of Oceanography, India published in 2000"
TL;DR: It is suggested that a global expansion of hypoxic zones may lead to an increase in marine production and emission of N2O, which, as a potent greenhouse gas, could contribute significantly to the accumulation of radiatively active trace gases in the atmosphere.
Abstract: Eutrophication of surface waters and hypoxia in bottom waters has been increasing in many coastal areas1,2,3,4, leading to very large depletions of marine life in the affected regions4. These areas of high surface productivity and low bottom-water oxygen concentration are caused by increasing runoff of nutrients from land. Although the local ecological and socio-economic effects have received much attention2,3,4, the potential contribution of increasing hypoxia to global-change phenomena is unknown. Here we report the intensification of one of the largest low-oxygen zones in the ocean, which develops naturally over the western Indian continental shelf during late summer and autumn. We also report the highest accumulations yet observed of hydrogen sulphide (H2S) and nitrous oxide (N2O) in open coastal waters. Increased N2O production is probably caused by the addition of anthropogenic nitrate and its subsequent denitrification, which is favoured by hypoxic conditions. We suggest that a global expansion of hypoxic zones may lead to an increase in marine production and emission of N2O, which, as a potent greenhouse gas, could contribute significantly to the accumulation of radiatively active trace gases in the atmosphere5.
514 citations
TL;DR: The rate of biotic invasions has increased in recent decades, and they collectively have significant ecological and economic impacts in the Mediterranean Sea.
Abstract: Exotic macrophytes, invertebrates and fish are found in most coastal habitats in the Mediterranean Sea. The Mediterranean Sea has been subjected to introductions of non-indigenous species by ship traffic since the opening of interoceanic maritime routes five centuries ago. The Sea, a hub of shipping, is exceptionally susceptible to invaders that arrive in fouling communities or ballast. The Suez Canal has been the largest pathway for the entry of these species: more than 300 Erythrean species – principally molluscs, fish, decapod crustaceans, polychaetes and algae – have become established in the eastern Mediterranean, primarily along the Levantine coasts. Mariculture of nonindigenous shellfish predominates in the northern Mediterranean lagoonar environments. Unrestricted transport of commercially important exotic shellfish has resulted in numerous unintentional introductions of pathogens, parasites and pest species. Some invaders have outcompeted or replaced native species locally, severely reducing biodiversity; some other invaders are so abundant they are exploited commercially. The rate of these biotic invasions has increased in recent decades, and they collectively have significant ecological and economic impacts in the Mediterranean Sea.
294 citations
01 Mar 2000
TL;DR: In this article, the seasonality of phytoplankton in the western and northern Bay of Bengal using shipboard data collected during three seasons as well as ocean colour imagery from OCTS and SeaWiFS was examined.
Abstract: We have examined the seasonality of phytoplankton in the western and northern Bay of Bengal using shipboard data collected during three seasons as well as ocean colour imagery from OCTS and SeaWiFS. Seasonal changes in the hydrography of the bay observed during these seasons gave rise to striking differences in biomass and primary productivity. Heavy fresh water influx from rivers and the resulting vertical stratification impeded vertical transfer of nutrients. Although such a nutrient regime resulted in an oligotrophic environment, chlorophyll a and primary production were substantially enhanced by physical processes that could erode the strong halocline. In March–April (pre-southwest monsoon), the poleward flowing East India Coastal Current brought to the surface, nutrient laden cooler waters that enriched the coastal region, but highest biomass (Chl a, 53 mg m−2) and productivity (4.5 g C m−2 d−1) were in the region of an eddylike structure along the coast and in the region between 13° and 16°N lat. Its appearance in satellite images of two consecutive years suggests the structure to be an annual feature. Wind driven coastal upwelling and increased river runoff during the following season, the southwest monsoon (July–August), increased phytoplankton biomass dramatically (92 mg m−2) but productivity averaged only 0.3 g C m−2 d−1 suggesting light limitation due to intense cloud cover. With a reduction in cloud cover and enhanced irradiance during the following season, the northeast monsoon (January–February), primary production increased especially in the northern part of the bay where phytoplankton appeared to benefit from both improved light conditions and nutrient inputs from estuarine mechanisms and river runoff.
249 citations
148 citations
TL;DR: In this paper, the authors used the chemical index of alteration (CIA) to quantify the degree of weathering in the upper continental crust (UCC) of the United States and found that the UCC-normalized patterns are strikingly similar for all the three sediment types, probably because of efficient mixing of sedimentary material during weathering, transport and deposition.
Abstract: Geochemical studies, comprising twelve major elements and twenty-four trace elements, including the rare earth elements (REE), have been carried out on the Concentrations normalized to the average upper continental crust (UCC) show that the sediments studied are depleted in Rb, K, Ba, Ta, Hf, Na, and Ca and enriched in Cs, U, Th, REEs, Sc, Fe, Co, and Cr. UCC-normalized patterns are strikingly similar for all the three sediment types, probably because of efficient mixing of sedimentary material during weathering, transport, and deposition. The depletion of Na, K, Ca, and Ba in sediments relative to UCC could be attributed to their mobility during weathering. The depletion of Ta and Hf and enrichment of Th, REE, and Sc are probably related to provenance characteristics, and enrichment of U is attributed to oxidation-reduction processes. Shale-normalized REE values reveal steep HREE patterns [(Tbsample/Tbshale)/(Ybsample/Ybshale)] >> [(Lasample/Lashale)/(Smsample /Smshale)] and flat LREE patterns. The shale-normalized patterns for all the three types of sediments are remarkably similar, with variations in the magnitude of LREE enrichment (Lan/Ybn varies between 1.72 to 2.57 times that of PAAS). LREE enrichment and steep HREE patterns are attributed to felsic source-rock characteristics. Other geochemical characteristics such as high La/Th and low La/Sc and Th/Sc ratios compared to UCC also support a felsic provenance. Eu/Eu* values for all the three types are little more than 1, which is also a characteristic feature of Archean crust. Furthermore, data plotted on discrimination diagrams of La/Th vs. Hf and La-Th-Sc cluster closer to granite and away from basalt and komatiite and are consistent with source-rock geology. Geochemical data have also helped in ascertaining the weathering trends. The chemical index of alteration (CIA) has been used to quantify the degree of weathering. CIA values range between 81 and 94 on a scale of 40-100, indicating a high degree of alteration (fluvial sediments seem to be more altered). On an A-CN-K diagram, the data fall closer to the compositional fields of highly weathered minerals kaolinite, gibbsite, and chlorite. A high degree of weathering is also indicated by other plots such as K2O-Fe2O3-Al2O3 and log K vs. log Rb. The geochemical data are consistent with the studies on clay mineralogy (higher kaolinite) carried out by other authors on the sediments of the same area. Secondary processes seem to affect other geochemical discriminants such as Co, Cr, Ni, and U, as revealed by plots of (1) La/Sc vs. Co/Th and (2) Th-Hf-Co and Co/Th, Cr/Th ratios and makes them unsuitable for determining provenance and tectonic setting.
146 citations
TL;DR: In this paper, the authors show that the biological productivity of the Arabian Sea is tightly coupled to the physical forcing mediated through nutrient availability, and that inter-annual variability in physical forcing during winter resulted in one-and-a-half times higher production in 1997 than in 1995.
Abstract: Usingin situ data collected during 1992–1997, under the Indian programme of Joint Global Ocean Flux Study (JGOFS), we show that the biological productivity of the Arabian Sea is tightly coupled to the physical forcing mediated through nutrient availability. The Arabian Sea becomes productive in summer not only along the coastal regions of Somalia, Arabia and southern parts of the west coast of India due to coastal upwelling but also in the open waters of the central region. The open waters in the north are fertilized by a combination of divergence driven by cyclonic wind stress curl to the north of the Findlater Jet and lateral advection of nutrient-rich upwelled waters from Arabia. Productivity in the southern part of the central Arabian Sea, on the other hand, is driven by advection from the Somalia upwelling. Surface cooling and convection resulting from reduced solar radiation and increased evaporation make the northern region productive in winter. During both spring and fall inter-monsoons, this sea remains warm and stratified with low production as surface waters are oligotrophic. Inter-annual variability in physical forcing during winter resulted in one-and-a-half times higher production in 1997 than in 1995.
103 citations
TL;DR: Evaluation of the potentiality for restoration use of different types of small fragments subcloned from the Red Sea coral species Stylophora pistillata revealed high survivorship and small, isolated branches revealedhigh survivorship, showing that small-sized branches are suitable for restoration purposes.
Abstract: “Gardening” of denuded coral reef habitats is a novel restoration approach in which sexual and asexual recruits are used. The present study aimed at the evaluation of the potentiality for restoration use of different types of small fragments subcloned from the Red Sea coral species Stylophora pistillata. In situ short-term (24 h, 45Ca method) and long-term (1 year, alizarin Red S vital staining) experiments revealed high variation (up to 70%) in growth rates between up-growing branches of a specific genet, and that tip ratios in dichotomous branches (n = 880) differ significantly between newly formed and older branches, further emphasizing the within-colony genetic background for spatial configuration. Small, isolated branches (<4 cm) revealed high survivorship (up to 90%, 1 year) and up to 20–30% (1 year, single- vs. dichotomous-tip branches, respectively) growth, showing that small-sized branches are suitable for restoration purposes. Results differed significantly between genets. Total length added for dichotomous-tip branches was in general at least twice that recorded for single tips of a specific genet. Restoration protocols may be applied either by sacrificing whole large colonies via pruning high numbers of small fragments or, by pruning only a few small branches from each one of many genets. An in situ “nursery period” of approximately 8 years is predicted for S. pistillata small fragments.
102 citations
TL;DR: In this article, a field of presently inactive mud diapirs with elevations up to 65'm was discovered in the abyssal plain seawards of the deformation front.
Abstract: The Makran accretionary complex shows a distinct bottom-simulating reflector, indicating a thick gas-hydrate-bearing horizon between the deformational front and about 1350 m water depth which seals off the upward flow of gas-charged fluids. A field of presently inactive mud diapirs with elevations up to 65 m was discovered in the abyssal plain seawards of the deformation front, suggesting that in the past conditions were favorable for periodic but localized vigorous mud diapirism. Regional destabilization of the gas hydrate leading to focused flow was observed where deep-penetrating, active faults reach the base of the gas-hydrate layer, as in a deeply incised submarine canyon (2100–2500 m water depth). At this location we discovered seeps of methane and H2S-rich fluids associated with chemoautotrophic vent faunas (e.g., Calyptogena sp.). Driven by the accretionary wedge dynamics, the landward part of the gas-hydrate layer below the Makran margin is being progressively uplifted. Due to reduced hydrostatic pressure and rising ocean bottom-water temperatures, gas hydrates are progressively destabilized and dissociated into hydrate water, methane and H2S. Sediment temperatures lie outside the methane stability field wherever water depth is less than 800 m. Above this depth, upward migration of fluids to the seafloor is unimpeded, thus explaining the abundance of randomly distributed gas seeps observed at water depths of 350 to 800 m.
97 citations
TL;DR: The results of a sequence of twelve research cruises over a two-year period, from June 1996 through May 1998, examined the seasonal variations in the nutrient (NO3, PO43, and Si(OH)4) and in the chlorophyll a (Chl a) concentrations at two permanent stations across the SE Mediterranean continental shelf and slope (120 and 400m water depth off the Israeli coast) as mentioned in this paper.
95 citations
TL;DR: In this article, the authors show that if changes in T-N relationships resulting from phytoplankton (chlorophyll a) are taken into account, remote sensing can be exploited to provide high resolution maps of sea surface nitrate (SSN).
Abstract: The highly variable nature of T-N relationships in oceanic waters has restricted nitrate (N) measurements from remotely sensed sea surface temperature (SST) to small time and space domains. Here we show that if changes in T-N relationships resulting from phytoplankton (chlorophyll a) are taken into account, remote sensing can be exploited to provide high resolution maps of sea surface nitrate (SSN) that are valid over much larger scales than has been previously possible. We illustrate the potential of the method for monitoring basin scale, interannual variations in SSN in the north Pacific Ocean using co-registered imagery of SST and chl a and demonstrate the usefulness of such data for estimating basin scale annual new production.
94 citations
TL;DR: In this paper, the average rainwater salinity, mainly contributed by non-sea-salt fraction (NSSF), varies by more than one order of magnitude from south to north.
TL;DR: The acute effects of lycopene (LYC‐O‐MATOTM) on airway hyperreactivity were assessed in patients with exercise‐induced asthma (EIA) in order to assess the beneficial effect of antioxidants on asthma.
Abstract: Background: Lycopene has previously been shown to have high antioxidative activity. In view of the controversy regarding the beneficial effect of antioxidants on asthma, the acute effects of lycopene (LYC-O-MATOTM) on airway hyperreactivity were assessed in patients with exercise-induced asthma (EIA).
Methods: Twenty patients with EIA participated in our study to verify the antioxidative effects. The test was based on the following sequence: measurement of baseline pulmonary function, 7-min exercise session on a motorized treadmill, 8-min rest and again measurement of pulmonary function, 1-week, oral, randomly administered, double-blind supplementation of placebo or 30 mg/day of lycopene (LYC-O-MATO), measurement of pulmonary function at rest, 7-min exercise session, and 8-min rest and again measurement of pulmonary function. A 4-week washout interval was allowed between each protocol.
Results: All patients given placebo showed significant postexercise reduction of more than 15% in their forced expiratory volume in 1 s (FEV1). After receiving a daily dose of 30 mg of lycopene for 1 week, 11 (55%) patients were significantly protected against EIA. Serum analyses of the patients by high-pressure liquid chromatography detected in the lycopene-supplemented patients an elevated level of lycopene compared to the placebo group, with no change in retinol, tocopherols, or in the other carotenoids.
Conclusions: Our results indicate that a daily dose of lycopene exerts a protective effect against EIA in some patients, most probably through an in vivo antioxidative effect.
TL;DR: Avoidance of the use of chemical dispersion in cases of oil spills near or within coral reef habitats is suggested, as dispersants and WAFs treatments caused larval morphology deformations, loss of normal swimming behaviour and rapid tissue degeneration.
TL;DR: The hypersensitive response of G. conferta after contact with oligoagars is thus a true defense response, because it enables the plant to protect itself efficiently from enzymatic attacks on its cell wall.
Abstract: Elicitation of Gracilaria conferta (Schousboe ex Montagne) J. ct G. Feldmann with oligoagars resulted in a defense response that was strong enough to kill epiphytic bacteria associated with the alga. Up to 60% of the resident bacterial flora of healthy plants was eliminated within 60 min after addition of neoagarohexaose to the algal medium. Single isolates of agar-degrading bacteria that had been isolated previously from healthy or decaying algal tissues proved to be more sensitive, Some of them were generally unable to survive on healthy G, conferta. Others survived on unelicited plants. Approximately 90% of these more resistant agar degraders were eliminated within 15 min after elicitation. The bacterial degradation of dead tissue of G, conferta resulted in a release of elicitors. The elicitors accumulated in the medium and reached high enough concentrations within 24 h to induce a hypersensitive response in healthy algae, The eliciting agent could be destroyed with beta -agarase and was thus probably oligoagar, Application of antibiotics prevented the accumulation of the elicitor, which indicated that bacteria were responsible for its release from the algal biomass, The hypersensitive response of G. conferta after contact with oligoagars is thus a true defense response, because it enables the plant to protect itself efficiently from enzymatic attacks on its cell wall.
TL;DR: Local expression and production of IGFs and their receptors in fish gonads support a role for the IGF system inFish gonadal physiology.
Abstract: Expression of insulin-like growth factor (IGF)-I, IGF-II, and IGF type I receptor (IGF-1R) genes was studied in gonads at different developmental stages of the protandrous hermaphroditic species the gilthead seabream (Sparus aurata) by reverse transcription-polymerase chain reaction and Northern blot analysis. Both IGF-I and IGF-II mRNA levels were highest in bisexual gonads and decreased during gonadal development. Regardless of the stage of gametogenesis, IGF-II mRNA levels exceeded those of IGF-I. Transcripts for IGF-1R RNA were detected in gonads at all stages studied. A major transcript of 11 kb was found in gonads and in gill arch and brain, but it was not found in liver and muscle. Distribution of the two types of IGF-1R and IGF-I in gonads was studied by immunohistochemistry. Immunoreactive IGF-I was found in the granulosa and theca cells of follicles at different vitellogenic stages and in oocytes at the chromatin-nucleolus and perinucleolus stage. In the testis, immunoreactive IGF-I was found in somatic cells of the cyst wall, interstitial cells, and spermatogonia A. In addition, IGF-1R was detected in the membrane of previtellogenic oocytes and in the theca and granulosa cells of vitellogenic and late vitellogenic follicles. In the testis, a positive reaction was identified in spermatogonia A and spermatids for the germ cells and in somatic cells of the cyst walls and interstitial cells. Local expression and production of IGFs and their receptors in fish gonads support a role for the IGF system in fish gonadal physiology.
TL;DR: The chemical nature and production of antibacterial compounds produced by sponge or its associated bacteria appears to be governed by the environment, and an inverse relationship was observed between the epibacterial abundance over the sponge surface in nature and the antibacterial activity displayed by the sponge extracts in laboratory bioassays.
Abstract: Variations in the antibacterial activity of the sponge Ircinia ramosa were evaluated during two collection periods (January and May) against vicinity fouling bacteria (VFB) and sponge surface-associated bacteria (SAB). The density of fouling bacteria in the water column, as well as epibacterial abundance on the sponge surface, was enumerated during both collections, and both increased in the warmer month of May. The extracts obtained from SAB were also tested for their role in antibacterial activity of the host. Sponge-associated bacteria are capable of producing antibacterial metabolites. The antibacterial activity that originated from polar fractions in the cooler month of January shifted towards the nonpolar fractions in May. Nonpolar fractions were more useful for the sponge when threatened with increased bacterial density. Thus, the chemical nature and production of antibacterial compounds produced by sponge or its associated bacteria appears to be governed by the environment. An inverse relationship was observed between the epibacterial abundance over the sponge surface in nature and the antibacterial activity displayed by the sponge extracts in laboratory bioassays. This investigation reveals the importance of collection period as well as the role of associated bacteria in the evaluation of antibacterial activity.
TL;DR: In this paper, the authors measured chlorophyll pigment concentrations from the Coastal Zone Color Scanner (CZCS) to estimate biological heating rate and investigate the biological modulation of the sea surface temperature in a bulk mixed layer model, embedded in the ocean isopycnal general circulation model (OPYC).
Abstract: Remotely sensed chlorophyll pigment concentrations from the Coastal Zone Color Scanner (CZCS) are used to estimate biological heating rate and investigate the biological modulation of the sea surface temperature (SST) in a bulk mixed layer model, embedded in the ocean isopycnal general circulation model (OPYC). A higher abundance of chlorophyll in October than in April in the Arabian Sea increases absorption of solar irradiance and heating rate in the upper ocean, resulting in decreasing the mixed layer thickness and lowering temperatures in the layers below the mixed layer than they would be under clear water condition. These changes in the model mixed layer were consistent with Joint Global Ocean Flux Study (JGOFS) observations during the 1994–1995 Arabian Sea experiment.
TL;DR: In this paper, the authors synthesize the work done on decolourization of bleach plant effluent and synthetic dyes using fungi from marine habitats and obtain up to 95% decoloration of pulp paper mill effluent.
TL;DR: The relation between climatic parameters (relative air humidity) and the water activity of the Dead Sea water determines the possible maximum evaporation of the lake using the Pitzer thermodynamic approach as discussed by the authors.
TL;DR: The growth performance, biochemical composition and nutritive value of the mixed culture of Isochrysis galbana and Chaetoceros calcitrans, grown in batch cultures under laboratory conditions was compared with those in monoculture conditions.
TL;DR: In this paper, the authors focused on clay fraction deposition along the inner (∼40-1000m water depth) shelf of Israel in order to substantiate and quantify its different sources.
TL;DR: Sequence analysis of four variants found revealed that the variation in length is due to differences in the number of repeat monomers (17-mer or 15-mer) as well as minor changes in their length.
Abstract: The growth hormone (GH) gene of the gilthead seabream (Sparus aurata) (saGH) has been cloned, sequenced, and characterized The saGH gene spans approximately 43 kb and consists of six exons and five introns, as found for all cloned teleost GH genes with the exception of carps and catfish The first and third introns contain long stretches of repetitive tandem repeats The second intron, which is unusually long compared with that in other teleosts (and other vertebrates) spans 1747 nucleotides (nt) and contains several inverted repeats Intron-targeted polymerase chain reaction (PCR) analysis identified length polymorphism of the first intron Sequence analysis of four variants (405, 424, 636, and 720 nt) out of many variants found revealed that the variation in length is due to differences in the number of repeat monomers (17-mer or 15-mer) as well as minor changes in their length This repeat unit contains the consensus half-site motif of the thyroid hormone response element (TRE) and estrogen response
TL;DR: In this article, the authors measured the differences in biofouling and bio-ouling adhesion strength on three known silicone formulations and an epoxy control at seven static immersion sites located in California, Florida, Hawaii, Hong Kong, India, Italy and Singapore.
Abstract: Little is known about the performance of fouling‐release coatings at different geographical locations. An investigation was designed to measure the differences in biofouling and biofouling adhesion strength on three known silicone formulations and an epoxy control at seven static immersion sites located in California, Florida, Hawaii, Hong Kong, India, Italy and Singapore. The study found that whilst the relative performance of the coatings was similar at each site, there were statistically significant differences in the type and intensity of fouling that developed on the coatings and in barnacle adhesion strength among sites. The results emphasize the importance of evaluating potential coatings at more than one static immersion site.
TL;DR: The pigment caulerpin hitherto known to be a constituent of green algae of genus Caulerpa is being reported here for the first time from a red alga.
TL;DR: It is concluded that the chaperone HSP90 might become a suitable biomarker to monitor environmental stress on corals.
TL;DR: While VTG mRNA was induced by E(2) treatment, transthyretin mRNA levels were reduced and these data provide the first demonstration that estrogen exhibits contrasting effect on VTG and on TTR gene expression in teleosts.
TL;DR: In this paper, the authors present a study based on X-ray chronologies and the stable isotopic composition of fossil Porites spp. corals from the northern Gulf of Aqaba (Red Sea) covering the mid-Holocene period from 5750 to 4450 14C years BP (before present).
Abstract: We present a study based on X-ray chronologies and the stable isotopic composition of fossil Porites spp. corals from the northern Gulf of Aqaba (Red Sea) covering the mid-Holocene period from 5750 to 4450 14C years BP (before present). The stable oxygen and carbon isotopic compositions of five specimens reveal regular annual periodicities. Compared with modern Porites spp. from the same environment, the average seasonal δ18O amplitude of the fossil corals is higher (by ca. 0.35–0.60‰), whereas annual growth rates are lower (by ca. 3.5 to 2 mm/year). This suggests stronger seasonality of sea surface temperatures and increased variability of the oxygen isotopic composition of the sea water due to changes in the precipitation and evaporation regime during the mid-Holocene. Most likely, summer monsoon rains reached the northern end of the Red Sea at that time. Average annual coral growth rates are diminished probably due to an increased input and resuspension of terrestrial debris to the shallow marine environment during more humid conditions. Our results corroborate published reports of paleodata and model simulations suggesting a northward migration of the African monsoon giving rise to increased seasonalities during the mid-Holocene over northeastern Africa and Arabia.
TL;DR: Differences in the epibiotic community present on horseshoe crabs, according to gender, were evaluated, and the macro-epibiont population from different regions of the carapace was mapped.
Abstract: Horseshoe crabs act as moving substrata for simple to complex communities of small marine organisms. Amplexed adult pairs migrate for breeding once every 2 weeks from deep waters towards nearshore waters during highest high tide. Female horseshoe crabs bury themselves to the level of the lateral eyes to deposit eggs while the male crabs fertilize them. Subsequently eggs are buried by the female. Tachypleus gigas (Muller) is the most abundant horseshoe crab species above available along the Orissa coast (India). Adults reach terminal anecdysis once sexually mature and live with their carapace for 4 to 9 years. In spite of this, epibiosis is limited. In the current investigation, differences in the epibiotic community (diatoms and macro-epibionts) present on horseshoe crabs, according to gender, were evaluated, and the macro-epibiont population from different regions of the carapace was mapped. In general, female horseshoe crabs harbored fewer epibionts than the males. Among the diatoms, Navicula spp., Nitzschia spp. and Skeletonema sp. were dominant in both sexes. However, the abundance and diversity of diatoms was greater on the carapaces of male crabs. Among the macro-epibionts, the acorn barnacle (Balanus amphitrite Darwin) and encrusting bryozoan (Membranipora sp.) were the most dominant forms. Barnacles and bryozoans were greater in abundance in the “rough” zone (cardiopthalmic region and anterior region of the opisthosoma). Mapping of the macro-epibionts from different regions of the carapace revealed differential distribution in males and females. Such differentiated distribution of the macro-epibionts can be related to factors such as changing habitat by the horseshoe crabs during breeding, mechanical abrasion and surface availability during mating and nesting periods, requirements of epizootic larvae and surface properties of the carapace (wettability and roughness). In the case of females, mechanical abrasion and surface availability played an important role in the epibiotic community structure and distribution patterns. The surface wettability measurements indicated male carapace to be slightly more hydrophobic than the female carapace. Scanning electron microscopy revealed that the male carapace was comparatively rough compared to the smooth carapace of females. A comparison of surface properties of the carapace indicated that the male carapace is more conducive for epibiosis.
01 May 2000
TL;DR: A two-gyre circulation system consisting of an anticyclonic gyre (ACG) in the northwestern Bay of Bengal and a cyclonic gyres (CG) west of the Andaman Islands is shown by the hydrographic data collected during May-June, prior to the southwest monsoon of 1996 as mentioned in this paper.
Abstract: A two-gyre circulation system consisting of an anticyclonic gyre (ACG) in the northwestern Bay of Bengal and a cyclonic gyre (CG) west of the Andaman Islands is shown by the hydrographic data collected during May–June, prior to the southwest monsoon of 1996. This circulation system leads to an intense southwestward flow in the central Bay. The circulation pattern characterizes the transition from the pre-monsoon (spring season) ACG to the southwest monsoon CG. A deep chlorophyll maximum (DCM) is found in the depth range 30–50 m in the coastal region and 50–100 m in the open sea. The DCM is located below the surface mixed layer, in the oxycline and nutricline, and above the seasonal thermocline/pycnocline, which coincides with the deep stability maximum (DSM). In the ACG, the DCM is located at 100 m when DSM is at 140 m deep, whereas in the CG, the DCM and DSM rise to 50 and 80 m, respectively. The magnitude of the chlorophyll maximum (CMAX) is nearly twice as high in the CG zone as in the ACG zone. The depths of both DCM and DSM, however, are twice as large in the ACG zone as in the CG zone. This shows that the meso-scale circulation patterns affect the spatial distribution of chlorophyll a (both DCM and CMAX) in the Bay of Bengal.
TL;DR: In this paper, the authors measured the relationship between TEP, the most labile particulate organic carbon, and bacteria and found that bacterial metabolism is fueled by availability of TEP in the Arabian Sea.
Abstract: Bacterial abundance and production, numbers, sizes and concentrations of transparent exopolymer particles (TEP) and total organic carbon (TOC) were measured during the 1996 summer monsoon to understand the relationship between TEP, the most labile particulate organic carbon, and bacteria. While high regional variability in the vertical distribution of TOC was discernible, TEP concentrations were high in surface waters at 18–20°N along 64°E with concentrations well over 25 mg alginic acid equivalents I−1 due to upwelling induced productivity. Their concentrations decreased with depth and were lower between 200 and 500 m. Bacterial concentrations were up to 1.99 × 108 I–1 in the surface waters and decreased by an order of magnitude or more at depths below 500 m. A better relationship has been found between bacterial abundance and concentrations of TEP than between bacteria and TOC, indicating that bacterial metabolism is fueled by availability of TEP in the Arabian Sea. Assuming a carbon assimilation of 33%, bacterial carbon demand (BCD) is estimated to be 1.017 to 4.035 g C m–2 d–1 in the surface waters. The observed TEP concentrations appear to be sufficient in meeting the surface and subsurface BCD in the northern Arabian Sea.