Showing papers by "National Institute of Oceanography, India published in 2004"

Are eddies nature's trigger to enhance biological productivity in the Bay of Bengal?

Abstract: [1] The Bay of Bengal is traditionally considered to be a less productive basin compared to the Arabian Sea. Despite the contrasting chlorophyll and primary productivity pattern, sediment trap data shows that annual fluxes of organic carbon reach comparable rates in both the basins. The traditional mechanisms of nutrient supply to the upper ocean waters cannot account for this. We propose eddy pumping as a possible mechanism of vertical transfer of nutrients across the halocline to the oligotrophic euphotic zone during summer monsoon when upper ocean is highly stratified. This would induce rapid biological uptake and in turn significantly increase biological production. In the northern Bay, riverine input acts as an additional source of nutrients and augments the subsurface nutrient injection to the euphotic zone by eddy pumping. Notwithstanding this, the lower than expected primary production in the north suggests the possible role of riverine sediment in limiting the sunlight for photosynthesis.

Intrusion of the Bay of Bengal water into the Arabian Sea during winter monsoon and associated chemical and biological response

Abstract: This work was supported by the Department of Ocean development under the program Marine Research-Living Resources (MR-LR). Jayu Narvekar acknowledges the financial support from CSIR.

Impact of temperature inversions on SST evolution in the South-Eastern Arabian Sea during the pre-summer monsoon season

Abstract: Temperature inversions are known to occur in the near-surface ocean regime where salinity stratification is large enough to influence the density field. However, they have not been known as features that alter near-surface processes significantly to influence the sea surface temperature (SST). From the analysis of new observed datasets as well as of state-of-the-art numerical model outputs, this paper shows that heat trapped within a temperature inversion makes significant contribution to warming of the SST in the South-Eastern Arabian Sea during the pre-southwest monsoon season.

Buried in time: culturable fungi in a deep-sea sediment core from the Chagos Trench, Indian Ocean

Abstract: The recovery of culturable microorganisms from ancient materials, ranging from a few thousand to several million years old, has generated interest in the long-term survival capabilities of micrororganisms. We report the occurrence of such paleobes for the first time from a deep-sea sediment core obtained from a depth of 5904 m from the Chagos trench in the Indian Ocean. Culturable fungi, direct counts of bacteria, age of the sediments based on the radiolarian assemblage, total organic carbon, Eh and CaCO 3 were determined in these sediments. Culturable fungi were obtained from subsections up to 370 cm depth. The age of the sediments from which fungi were isolated was estimated to range from>0.18 to 0.43 million years (Ma), being the oldest recorded age for recovery of culturable fungi. Colony forming units of fungi ranged from 69 to 2493 g −1 dry weight sediment with a maximum abundance recorded at 160 cm depth of the core, corresponding to ∼0.18 Ma. Bacterial numbers in the core showed oscillations corresponding to cycles of approximately 100 ka (kilo years). The fungi comprised non-sporulating forms and a sporulating form identified to be Aspergillus sydowii . Germination of spores of A. sydowii at 100, 300 and 500 bar hydrostatic pressures at 5 °C confirmed its barotolerance and its nativity to deep-sea sediments. We propose that deep-sea sediments are a source of paleobes, which could be useful in studies on palaeoclimate, long-term microbial survival and biotechnology.

Use of cottonseed meal supplemented with iron for detoxification of gossypol as a total replacement of fish meal in Nile tilapia, Oreochromis niloticus (L.) diets

Abstract: The objective of this study was to determine the effect of total replacement of fish meal by cottonseed meal (CSM) supplemented with various levels of iron in practical diets on growth performance, feed utilization, body composition and some biological and haematological parameters of Nile tilapia, Oreochromis niloticus (L.). Juvenile fish (average weight 3.78±0.1 g) were stocked in 18 glass aquariums (80 L each) at 25 fish per aquarium. Fish meal (50% of the diet) was used as the sole source of animal protein in the control diet 1. Diets 2–6 had 100% CSM (0.145% free gossypol) protein with various levels of supplemented iron (86, 486, 972, 1458 and 1944 mg Fe kg diet−1) in diets 2–6 respectively. Diets were fed to fish twice daily at a rate of 3% of body weight during the first 12 weeks then 2% of the total fish biomass daily until the end of the experiment (30 weeks). The results of this study revealed that, groups of fish fed diets 1, 4, 5 and 6 had significantly (P≤0.01) the higher average body weight and specific growth rate than those of fish fed diet 2 (100% CSM without iron supplementation) and diet 3 (100% CSM plus 486 mg Fe kg diet−1). The best values for feed conversion ratio, protein efficiency ratio and condition factor (K) were recorded with groups of fish fed diet 4 (100% CSM plus 972 mg Fe kg diet−1). Red blood cell count, haematocrit and haemoglobin were increased with increasing levels of iron and significantly affected by dietary iron. Hepatosomatic index for diets 3–6 were not significantly different (P>0.05) and superior to that of diet 1 control [100% fish meal (FM)]. The gonadosomatic index of males of Nile tilapia was not influenced by CSM diets with or without iron, while females of Nile tilapia were significantly influenced with iron and the lowest values were recorded with groups of fish fed diet 2 (100% CSM without iron supplementation). Apparent digestibility coefficients of protein, fat dry matter and energy were relatively high for most diets supplemented with iron and increased by increasing iron supplementation. There were no significant differences between groups of fish fed diet 1 (100% FM) and diets 5 and 6 which contained 100% CSM with additional 1458 and 1944 mg Fe kg diet supplemental iron−1 respectively. Proximate composition of whole body was not influenced by diet. Adding 972 mg Fe kg diet−1 from ferrous sulphate to the CSM-based diets that contained 972 mg free gossypol (1:1 iron to free gossypol ratio) for Nile tilapia reduce the negative effects of gossypol and improved growth performance, feed utilization and blood parameters and can totally replace fish meal in tilapia diets.

Xylanases of marine fungi of potential use for biobleaching of paper pulp

Abstract: Microbial xylanases that are thermostable, active at alkaline pH and cellulase-free are generally preferred for biobleaching of paper pulp. We screened obligate and facultative marine fungi for xylanase activity with these desirable traits. Several fungal isolates obtained from marine habitats showed alkaline xylanase activity. The crude enzyme from NIOCC isolate 3 (Aspergillus niger), with high xylanase activity, cellulase-free and unique properties containing 580 U l−1 xylanase, could bring about bleaching of sugarcane bagasse pulp by a 60 min treatment at 55°C, resulting in a decrease of ten kappa numbers and a 30% reduction in consumption of chlorine during bleaching. The culture filtrate showed peaks of xylanase activity at pH 3.5 and pH 8.5. When assayed at pH 3.5, optimum activity was detected at 50°C, with a second peak of activity at 90°C. When assayed at pH 8.5, optimum activity was seen at 80°C. The crude enzyme was thermostable at 55°C for at least 4 h and retained about 60% activity. Gel filtration of the 50–80% ammonium sulphate-precipitated fraction of the crude culture filtrate separated into two peaks of xylanase with specific activities of 393 and 2,457 U (mg protein)−1. The two peaks showing xylanase activity had molecular masses of 13 and 18 kDa. Zymogram analysis of xylanase of crude culture filtrate as well as the 50–80% ammonium sulphate-precipitated fraction showed two distinct xylanase activity bands on native PAGE. The crude culture filtrate also showed moderate activities of β-xylosidase and α-l-arabinofuranosidase, which could act synergistically with xylanase in attacking xylan. This is the first report showing the potential application of crude culture filtrate of a marine fungal isolate possessing thermostable, cellulase-free alkaline xylanase activity in biobleaching of paper pulp.

Heavy Metals Monitoring using Bivalves from Mediterranean Sea and Red Sea

Abstract: The concentrations of heavy metals (Cd, Co, Cu, Fe, Mn, Ni, Pd and Zn) were measured in the Bivalves (Modiolus auriculatus and Donax trunculus) collected from the Egyptian coasts of Mediterranean Sea and Brachiodonates sp. from the Egyptian coasts of Red Sea. The average concentrations of the heavy metals analyzed exhibited the following decreasing order: Fe > Zn > Cu > Mn > Ni > Co > Pb > Cd for both Mediterranean Sea and Red Sea. The analyses of Cd, Co, Ni, Pb, and Zn showed higher average concentrations for samples collected from Red Sea than that collected from Mediterranean Sea, while Fe, Cu and Mn showed the reverse results. Fe was used as a normalizing agent for all studied metals and exhibited presence of two locations from each of Mediterranean Sea and Red Sea have anthropogenic inputs of heavy metals. These results suggest that the coastal area in both Mediterranean Sea and Red Sea of Egypt might be considered relatively unpolluted with heavy metal.

Vertical migratory rhythms of benthic diatoms in a tropical intertidal sand flat: influence of irradiance and tides

Abstract: Vertical migratory behavior of benthic diatoms is one of the adaptive strategies employed for a life in intertidal habitats. Irradiance and tides are considered to be the key factors governing vertical migration. Experiments were carried out to determine the influence of these factors in a tropical intertidal sand flat. Rising to the sediment surface for fulfilment of their light requirements for photosynthesis was the first priority. If not fulfilled during the low-tide exposure, diatoms could withstand the tidal effects and stay up at the surface even during the high-tide coverage. In the laboratory experiments, where the effects of tides were removed, the endogenous clock continued to operate in a similar fashion to that in the field when under 12-h light:12-h dark conditions, whereas continuous darkness induced a tidal rhythm. In continuous light, diatoms preferred to stay up longer than was observed in field. The above-mentioned observations reveal that irradiance has a stronger effect than tides in controlling/regulating microscale migrations in benthic diatoms. In addition, temporal differences in the irradiance and the resulting changes in diatom migration can have implications for littoral primary productivity.

High new production in the Bay of Bengal: Possible causes and implications

Abstract: [1] We report the first measurements of new production (15N tracer technique), the component of primary production that sustains on extraneous nutrient inputs to the euphotic zone, in the Bay of Bengal. Experiments done in two different seasons consistently show high new production (averaging around 4 mmol N m−2 d−1 during post monsoon and 5.4 mmol N m−2 d−1 during pre monsoon), validating the earlier conjecture of high new production, based on pCO2 measurements, in the Bay. Averaged over annual time scales, higher new production could cause higher rate of removal of organic carbon. This could also be one of the reasons for comparable organic carbon fluxes observed in the sediment traps of the Bay of Bengal and the eastern Arabian Sea. Thus, oceanic regions like Bay of Bengal may play a more significant role in removing the excess CO2 from the atmosphere than hitherto believed.

Remote forcing annihilates barrier layer in southeastern Arabian Sea

Abstract: [1] Time-series measurements of temperature and salinity profiles were made every two hours at 74°30′E, 9°13′N in the southeastern Arabian Sea (SEAS) during 22-March–7-April and 23-May–7-June 2003 as part of the Arabian Sea Monsoon Experiment (ARMEX). The observations show that a 20 m thick barrier layer (BL) exists during March–April owing to a surface layer of low-salinity waters advected earlier during December–January from the Bay of Bengal. The BL is almost annihilated by 7 April owing to upwelling. The relic BL that survives is annihilated later in May by upwelling, and by the inflow of high-salinity waters from the north and by mixing due to stronger winds, which deepen the mixed layer. We present evidence from satellite data and arguments based on existing theories to show that both the upwelling and the advection of high-salinity waters are remotely forced.

A biweekly mode in the equatorial Indian Ocean

Abstract: [1] The National Institute of Oceanography, Goa, deployed moorings with several subsurface current meters at 0°, 93°E (in February 2000) and 0°, 83°E (in December 2000) in the eastern Indian Ocean. Observed meridional current at all depths has a 10- to 20-day (or biweekly) variability that is distinct from longer period (20- to 60-day) subseasonal variability. Lags between different instruments suggest the presence of groups of westward and vertically propagating biweekly waves with zonal wavelength in the range 2100 to 6100 km. We use an ocean model forced by high-resolution scatterometer wind stress to show that the observed biweekly variability is due to equatorially trapped mixed Rossby-gravity waves generated by subseasonal variability of winds. We demonstrate that quasi-biweekly fluctuations of surface meridional wind stress resonantly excite ocean waves with westward and upward phase propagation, with a typical period of 14 days and zonal wavelength of 3000–4500 km. The biweekly wave is associated with fluctuating upwelling/downwelling in the equatorial Indian Ocean, with amplitude of 2–3 m per day located 2–3 away from the equator. Possible reasons for eastward intensification of biweekly energy are discussed.

Observational evidence for westward propagation of temperature inversions in the southeastern Arabian Sea

Abstract: [1] A warm pool forms in the southeastern Arabian Sea (SEAS) prior to the onset of the summer monsoon over India in early June; the core of this warm pool is in the Lakshadweep Sea (LS). XBT and surface salinity data collected in the LS during May-2002–April-2003 show that temperature inversions occur off the southwest coast of India in early December with the arrival of low-salinity waters from the Bay of Bengal. The low-salinity waters and the inversions propagate westward along with the downwelling Rossby waves that constitute the Lakshadweep sea-level high; inversions occur in the western LS (∼73°E) about 40 days after they occur near the coast in the eastern LS (∼75.5°E). They disappear in April, when the Tropical Convergence Zone moves over the SEAS and the warm pool engulfs the region. Ocean dynamics and air-sea fluxes are together responsible for the formation and westward propagation of the inversions.

Trace Metals in the Water Columns of the Red Sea and the Gulf of Aqaba, Egypt

Abstract: Seawater samples were collected from the northern Red Sea and the Gulf of Aqaba at different depths during February 1999 and analyzed for iron, zinc, manganese, nickel, copper, cadmium, cobalt and lead to determine the existing concentration of these metals, their distribution patterns and where contamination has occurred. The concentrations of Fe, Zn, Mn, Ni, Cu, Cd, Co, Pb were scatteredin the ranges: (0.56–4.44; mean 1.67±0.9 μg L-1), (0.13–1.17; mean 0.24±0.12 μg L-1), (0.06–0.21; mean 0.13±0.03 μg L-1), (0.05–0.52; mean 0.16±0.06 μg L-1), (0.07–0.29; mean 0.14±0.06 μg L-1), (0.02–0.78; mean 0.49±0.14 μg L-1), (0.06–0.29; mean 0.15±0.04 μg L-1), and (0.02–0.68; mean 0.31±0.13 μg L-1), respectively. The results revealed a small range of variation and regional irregularities. It also indicated significant higher concentrations for Fe, Cd and Pb compared to other metals. Compared to the northern Red Sea, significant higher concentrations for Ni and Cd are measured at the Gulf of Aqaba. Other metals, i.e. Fe, Zn, Mn, Cu, Co, and Pb are not significantly different in both areas indicating no distinct concentration gradients. Except for Pb, the distribution patterns indicated significantly lower concentrations at surface layer in both regions, then increasing to their maximum values at the sub-surface layers which followed by a decrease in deep water. The study indicated also that the mean concentrations of trace metals examined here are much lower than those reported for the Mediterranean Sea and typical of open ocean water.

The limit of the sea: the bathyal fauna of the Levantine Sea*

Abstract: SUMMARY: In the present study, the fish, molluscs, crustaceans and echinoderms collected at depths between 734 and 1558 m during a series of cruises conducted between 1988 and 1999 off the coast of Israel, supplemented by a photographic survey carried out southwest of Cyprus at a depth of 2900 m, were analysed. The main objectives were to determine the faunal composition of the bathybenthic assemblages in the southeastern Levantine Sea, and to compare them with the western Mediterranean assemblages in order to elucidate whether general trends in their bathymetric distribution and population density may be related to environmental/geographic factors. Considering the sampling effort, the diverse gear used and the extended period of sampling, we may assume that the low number of species and specimens recorded actually reflects a lowdiversity, low-density deep water fauna. The faunal scarcity may cause a different parcelling of the populations which is reflected in bathymetric distributions that in many cases extend to greater depths than in the Western Mediterranean. The Levantine bathybenthos is composed of autochthonous, self-sustaining populations of opportunistic, eurybathic species that have settled there following the last sapropelic event.

Primitive immune systems: are your ways my ways?

Abstract: Summary: Although vertebrate immune systems have been commonly conceived as exquisitely developed to combat pervasiveness by pathogens, they are not infallible. The enigmatic expression of histocompatibility in vertebrates, the manifestation of natural chimerism, autoimmunity, malignancy, and other puzzling outcomes hint that immunity did not arise in evolution to fight infections and that this capacity is a late evolutionary appendage, owing its appearance to the redeployment of a system developed for other reasons. Allorecognition in the colonial tunicate Botryllus schlosseri serves here as a platform for a contending paradigm, advocating that immunity has developed as a surveillance machinery against and for purging of nascent selfish cells (stemmed from a kin organism or from transformed cells within the organism of origin). Defense against pathogens (always representing xenogeneic aliens) appeared later, revealing the multiplicity of newly developed phenomena. Allorecognition events characteristic of the Botryllus primitive immune system, such as fusion versus rejection, the morphological resorption with its expressed hierarchy, and the somatic/germ-cell parasitic outcomes, provide clues to the evolutionary basis of allorecognition. Recent work on Botryllus immunity that highlights the cost of littering individuality by somatic variants/allogeneic cells is discussed.