Abundance and relationship of bacteria with transparent exopolymer particles during the 1996 summer monsoon in the Arabian Sea

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 gCm-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

Meta-analysis cum machine learning approaches address the structure and biogeochemical potential of marine copepod associated bacteriobiomes

Copepods are the dominant members of the zooplankton community and the most abundant form of life. It is imperative to obtain insights into the copepod-associated bacteriobiomes (CAB) in order to identify specific bacterial taxa associated within a copepod, and to understand how they vary between different copepods. Analysing the potential genes within the CAB may reveal their intrinsic role in biogeochemical cycles. For this, machine-learning models and PICRUSt2 analysis were deployed to analyse 16S rDNA gene sequences (approximately 16 million reads) of CAB belonging to five different copepod genera viz., Acartia spp., Calanus spp., Centropages sp., Pleuromamma spp., and Temora spp.. Overall, we predict 50 sub-OTUs (s-OTUs) (gradient boosting classifiers) to be important in five copepod genera. Among these, 15 s-OTUs were predicted to be important in Calanus spp. and 20 s-OTUs as important in Pleuromamma spp.. Four bacterial s-OTUs Acinetobacter johnsonii, Phaeobacter, Vibrio shilonii and Piscirickettsiaceae were identified as important s-OTUs in Calanus spp., and the s-OTUs Marinobacter, Alteromonas, Desulfovibrio, Limnobacter, Sphingomonas, Methyloversatilis, Enhydrobacter and Coriobacteriaceae were predicted as important s-OTUs in Pleuromamma spp., for the first time. Our meta-analysis revealed that the CAB of Pleuromamma spp. had a high proportion of potential genes responsible for methanogenesis and nitrogen fixation, whereas the CAB of Temora spp. had a high proportion of potential genes involved in assimilatory sulphate reduction, and cyanocobalamin synthesis. The CAB of Pleuromamma spp. and Temora spp. have potential genes accountable for iron transport

Physical control of primary productivity on a seasonal scale in central and eastern Arabian Sea

Using in 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

Seasonal occurrence of anoxygenic photosynthesis in Tillari and Selaulim reservoirs, Western India

© The Author(s), 2012. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Biogeosciences 9 (2012): 2485-2495, doi:10.5194/bg-9-2485-2012.Phytoplankton and bacterial pigment compositions were determined by high performance liquid chromatography (HPLC) and liquid chromatography-mass spectrometry (LC-MS) in two freshwater reservoirs (Tillari Dam and Selaulim Dam), which are located at the foothills of the Western Ghats in India. These reservoirs experience anoxia in the hypolimnion during summer. Water samples were collected from both reservoirs during anoxic periods while one of them (Tillari Reservoir) was also sampled in winter, when convective mixing results in well-oxygenated conditions throughout the water column. During the period of anoxia (summer), bacteriochlorophyll (BChl) e isomers and isorenieratene, characteristic of brown sulfur bacteria, were dominant in the anoxic (sulfidic) layer of the Tillari Reservoir under low light intensities. The winter observations showed the dominance of small cells of Chlorophyll b-containing green algae and cyanobacteria, with minor presence of fucoxanthin-containing diatoms and peridinin-containing dinoflagellates. Using total BChl e concentration observed in June, the standing stock of brown sulfur bacteria carbon in the anoxic compartment of Tillari Reservoir was estimated to be 2.27 gC m−2, which is much higher than the similar estimate for carbon derived from oxygenic photosynthesis (0.82 gC m−2. The Selaulim Reservoir also displayed similar characteristics with the presence of BChl e isomers and isorenieratene in the anoxic hypolimnion during summer. Although sulfidic conditions prevailed in the water column below the thermocline, the occurrence of photo-autotrophic bacteria was restricted only to mid-depths (maximal concentration of BChl e isomers was detected at 0.2% of the surface incident light). This shows that the vertical distribution of photo-autotrophic sulfur bacteria is primarily controlled by light penetration in the water column where the presence of H2S provides a suitable biogeochemical environment for them to flourish.Financial support for this work was provided by the Council of Scientific & Industrial Research (CSIR) and Ministry of Earth Sciences (MoES). S. Kurian acknowledges POGO-SCOR for financial support to visit WHOI. R. Roy, G. Narvenkar and A. Sarkar received fellowship support from CSIR. D. Repeta acknowledges support from US National Science Foundation Center Award EF0424599 to the Center for Microbial Oceanography: Research and Education (C-MORE)

High biological productivity in the central Arabian Sea during the summer monsoon driven by Ekman pumping and lateral advection

Open oceans are generally oligotrophic and support less biological production. Results from the central Arabian Sea show that it may be an exception to this. We provide the observational evidence of fairly high biological production (up to 1700 mg C m-2 d-1) in the central Arabian Sea, along 64oE, during the summer monsoons of 1995 and 1996. The reasons for the observed high biological production, comparable to that from the traditionally well-known Somali upwelling region, were examined in light of the physical forcing and prevailing chemical fields. In the northern part of the central Arabian Sea, north of the axis of the Findlater Jet, upward Ekman pumping and entrainment driven by basin-wide winds along with advection of upwelled waters from the coastal region of Arabia supply nutrients to the upper layers. In the southern part, production is supported by nutrients advected from the Somali upwelling regio

The Arabian Sea as a high-nutrient, low-chlorophyll region during the late Southwest Monsoon

© The Authors, 2010. This article is distributed under the terms of the Creative Commons Attribution 3.0 License. The definitive version was published in Biogeosciences 7 (2010): 2091-2100, doi:10.5194/bg-7-2091-2010.Extensive observations were made during the late Southwest Monsoon of 2004 over the Indian and Omani shelves, and along a transect that extended from the southern coast of Oman to the central west coast of India, tracking the southern leg of the US JGOFS expedition (1994–1995) in the west. The data are used, in conjunction with satellite-derived data, to investigate long-term trends in chlorophyll and sea surface temperature, indicators of upwelling intensity, and to understand factors that control primary production (PP) in the Arabian Sea, focussing on the role of iron. Our results do not support an intensification of upwelling in the western Arabian Sea, reported to have been caused by the decline in the winter/spring Eurasian snow cover since 1997. We also noticed, for the first time, an unexpected development of high-nutrient, low-chlorophyll condition off the southern Omani coast. This feature, coupled with other characteristics of the system, such as a narrow shelf and relatively low iron concentrations in surface waters, suggest a close similarity between the Omani upwelling system and the Peruvian and California upwelling systems, where PP is limited by iron. Iron limitation of PP may complicate simple relationship between upwelling and PP assumed by previous workers, and contribute to the anomalous offshore occurrence of the most severe oxygen (O2) depletion in the region. Over the much wider Indian shelf, which experiences large-scale bottom water O2-depletion in summer, adequate iron supply from reducing bottom-waters and sediments seems to support moderately high PP; however, such production is restricted to the thin, oxygenated surface layer, probably because of the unsuitability of the O2-depleted environment for the growth of oxygenic photosynthesizers.Financial support was provided by CSIR through the Network Project CMM0009 to SWAN and by NSF through OCE-0327227S to JWM

A first report on a bloom of the marine prymnesiophycean, Phaeocystis globosa from the Arabian Sea

A thick bloom of the marine prymnesiophycean, Phaeocystis globosa was observed in the central Arabian Sea during the summer monsoon period (July-August, 1996). The cells were mostly in colonial form, embedded in gelatinous matrices. The cell diameter was approximately 7 mu m and showed a distinct double feature form. The intensity of the bloom was as high as 3750 x 10(6) cells m(-2) and the carbon content ranged between 33 and 550 mu g L(-1). Almost 90% of the phytoplankton population was composed of P. globosa in the bloom area. Other common forms were chain-forming diatoms like Rhizosolenia spp., Nitzschia spp. and Chaetoreros spp. The photosynthetic pigment chlorophyll a, however did not show any concomitant rise with the bloom intensity probably because the bloom was sampled during a senescent phase. The carbon chlorophyll ratio varied between 112 and 810. This is the first report on the occurrence of Phaeocystis from the Arabian Sea. It seems pertinent to ask whether this is a result of the genus being introduced and adapted to new environments due to human influence and whether it will influence food chains in the future.Une floraison importante de la prymnésiophycée marine Phaeocystis globosa est observée au centre de la mer d’Arabie pendant la mousson d’été, en juillet–août 1996. Les cellules forment en général une colonie incluse dans une gangue gélatineuse. D’un diamétre d’environ 7 μm, les cellules ont une forme caractéristique double. L’intensité de la floraison est de 3 750×106 cellules par m2, avec une teneur en carbone comprise entre 33 et 550 μg L−1. La population phytoplanctonique est composée, pour près de 90 % de P.globosa; les autres formes communes sont des chaı̂nes de diatomées telles que Rhizosolenia spp., Nitzschia spp. et Chaetoceros spp. La teneur en chlorophylle a ne présente cependant pas d’augmentation concomitante à la poussée de la floraison, probablement parce que celle-ci a été échantillonnée dans une phase de sénéscence. Le rapport chlorophylle/carbone varie entre 112 et 810. Cette première observation de Phaeocystis en mer d’Arabie pose des questions: provient-elle d’un genre introduit par l’homme et qui se serait adapté à de nouveaux environnements ? Quel sera son effet éventuel sur les chaı̂nes alimentaires

A quantitative analysis of fine scale distribution of intertidal meiofauna In response to food resources

259-263Fine scale vertical and spatial distribution of meiofauna in relation to food abundance was studied in the intertidal sediment at Dias beach. The major abiotic factors showed significant changes and progressive fine scale decrease in vertical distribution, with increasing depth in the sediments. Meiofauna were concentrated more in the 4-6 mm and decreased progressively in the deeper layer. The density of meiofauna was high at mid tide level. Nematodes, turbillarians and harpacticoids were the taxa recorded. Spatially, meiofauna showed patchy dispersion, related to the availability of food and predation

The Arabian Sea: Physical environment, zooplankton and myctophid abundance

138-145The Arabian Sea is one of the most productive regions of the world oceans. This productivity mainly results from coastal and open ocean upwelling in summer and cooling effects during winter. Earlier and more recent studies showed that there are considerable spatial and temporal variations in the area in primary productivity. Nonetheless, contrary to, earlier thinking, it would seem that the mesozooplankton abundance in the Arabian Sea is fairly high in the mixed layer all through the year. This paradox of the Arabian Sea could be partly resolved by explaining the microbial loop and a fresh set of data is presented here in support. This is because most of the herbivorous forms are either small filter feeders like copepods or larger mucous filter feeders like tunicates which are able to feed on very small particles. It would seem that the Arabian Sea sustains a large biomass of mesopelagic fishes (about 100 million tonnes), mainly myctophids. They mostly live in the core of oxygen minimum layer and ascend to the surface layers during night to feed on the abundant zooplankton