Differential response of Bay of Bengal during deficit and normal monsoons.

Present study explains the disparity in biological production (primary and secondary) with respect to two distinct monsoonal regimes in the western Bay of Bengal, viz., deficit monsoon (DM) and normal monsoon (NM). A combination of in situ and satellite data during the years 2002 (DM) and 2003 (NM) was used to address the physico-chemical and biological responses. The basin was relatively warm (ΔSST = 0.55 °C) and fresh (ΔSSS = -0.55) during DM than NM. Physical processes such as coastal upwelling and cyclonic eddy were prominent during NM. Variations of hydrography between DM and NM were reflected in the biological production as well. Chlorophyll a concentration (0.05 to 5.2 mg m-2) was almost similar during both the periods; however, column production showed higher values during DM. Mesozooplankton standing stock was relatively less during DM than NM. Composition of zooplankton also showed pronounced variation between the periods. This can be attributed to the variability in biological response of the region to the varying environmental condition. Relatively high chlorophyll a and primary productivity observed during DM may be due to the increased light availability (less cloud cover) and extended euphotic depth. In addition, the low mesozooplankton standing stock (low grazing) observed during the period also might have helped in maintaining a relatively high rate of production. The seasonal production of the basin is influenced by duration and intensity of various atmospheric as well as oceanic processes.

Role of mesoscale eddies in the sustenance of high biological productivity in North Eastern Arabian Sea during the winter-spring transition period.

Convective mixing, mesoscale eddies and regenerated production sustain an above-average biological productivity in the North East Arabian Sea (NEAS) during the winter-spring transition period. Satellite-derived long-term data sets on Chlorophyll-a (Chl-a), Sea Surface Height Anomaly (SSHA), Sea Surface Temperature (SST) and Okubo-Weiss parameterization show existence of number of mesoscale eddies, propagating and non-propagating, that contribute to the regional production. The dominance of Eddy Kinetic Energy (EKE) over the Available Potential Energy (APE) in the core depth and the diameter (120km) of the observed eddy being wider than the Rossby Radius of Deformation (RRD, 55 km), it is suggested that the baroclinic instability is a possible mechanism for the eddy formation. Spatial variation in APE and its influences on the regional dynamics, including chemical and biological response are explained. In the non-eddy areas, where convective mixing is active, diatoms (96.74%) dominated than dinoflagellates (3.14%), and the Chl-a in the Cold Core Eddy (CCE) were two to three folds higher to non-eddy regions. The abundance increased from core (58,152 cells L-1) to periphery (5.95 × 105 cells L-1) where the water column is less dynamic. Extensive blooms of the dinoflagellate green Noctiluca (N. scintillans) contribute to the very high cell density in the periphery of the CCE, where the currents were comparatively weak, and water column was more stable. Active mixing is associated with diatom dominance, followed by Noctiluca when the mixing slackens, making use of the available nutrients and supported by regenerated production. The bloom dynamics is explained for pre-bloom, bloom and post-bloom conditions with measurements on nutrients and plankton assemblages. The Noctiluca bloom (mid-March) is succeeded by Trichodesmium (April-May), in the stratified nutrient depleted, abundant light environment and propagated southwards. Observed increasing trends in the SSHA over the period indicate strengthening of stratification and hence altered production patterns in the NEAS.

Response of macrozoobenthic communities to summer monsoon upwelling and related hypoxia in the south eastern Arabian Sea shelf.

Coastal upwelling in the south eastern Arabian Sea (SEAS) leads to oxygen depletion over the continental shelf during the summer monsoon season (June-September), with latitudinal gradients in intensity. Based on two surveys in the onset (June) and peak (August) phases of the summer monsoon, the present study evaluates the response of macrozoobenthic communities (size >500 µm) to upwelling and consequent hypoxia (dissolved oxygen <0.2 ml/l) in the central sector of the SEAS shelf (10-12°N, 30-200 m). From the onset to the peak monsoon, macrozoobenthic density increased five-fold in the mid-shelf (50 m water depth), and nearly doubled in the outer shelf (100 m water depth) and shelf edge (200 m water depth). This was found to be a direct consequence of recruitment and proliferation of opportunistic polychaetes, particularly the spionid Paraprionospio pinnata, which was the single dominant species (52-78%) at all depths during the peak monsoon. With the establishment of the monsoon, the shelf communities (particularly 50-100 m depth sites) are thus transformed from relatively diverse assemblages to dense, single-species dominated ones. The shelf-edge communities (150-200 m depths), which are impacted with the perennial Arabian Sea oxygen minimum zone, and therefore harbour opportunist-dominated communities year-round. It is postulated that larvae of hypoxia-tolerant taxa are transported from the shelf edge by the process of upwelling onto the shelf. The settlement and survival of these larvae are regulated by the nature of shelf sediments and by the prevailing hypoxia. Thus, substantial recruitment of opportunists occurred in the outer and mid-shelf (50-100 m), but not in the inner shelf (30 m), where sedimentation from river discharge hindered settlement and survival of juveniles.

Description of a new species of deep-water snake eel, Ophichthus mccoskeri (Ophichthidae: Ophichthinae) from Andaman Sea, India.

A deep-sea species of snake eel (family Ophichthidae, subfamily Ophichthinae) Ophichthus mccoskeri sp. nov. is described based on 6 specimens (331-447 mm total length) trawled at 314-363 m depth in Andaman waters, India. This species is differentiated from its deep-water congeners by a combination of characters such as its large eyes, dorsal-fin origin a short distance behind pectoral-fin tip, anal fin black posteriorly, three preopercular pores, maxillary and mandibular teeth ending as triserial, and in a vertebral formula of 20/55/153.

A new species of white-spotted moray eel, Gymnothorax smithi (Muraenidae: Muraeninae) from deep waters of Arabian Sea, India.

A new species of white-spotted moray eel Gymnothorax smithi sp. nov. is described based on three specimens collected from the southeastern Arabian Sea, India. This is the first deep water report of a moray eel from Indian waters from 200 m depth. This new species is distinguishable from its congeners by the following combination of characters: greyish brown body overlain with white spots of irregular shape, dorsal-fin origin anterior to gill opening, anus positioned slightly behind the mid-point of the body, serrated teeth and a unique vertebral count 3-5 /57/130-132. [Zoobank URL: urn:lsid:zoobank.org:act:9554CE07-E9E7-4B4F-95CD-54F2BB26FF28].

Redescription and sexual dimorphism of Andaman leg-skate Cruriraja andamanica (Chondrichthyes: Rajiformes) with comments on the zoogeography of the genus Cruriraja.

This paper redescribes sexually dimorphic Cruriraja andamanica based on five juvenile (four males, one female) and four adult specimens (three males, one female) collected from Andaman waters. Morphometric comparison of the present specimens with a female specimen collected off the coast of Tanzania reveals considerable dissimilarities between them. These findings, along with the wide geographical distance between collection locations, support a need for revision of the Tanzanian specimen, which, in all probability, represents a new species in the genus. The paper also addresses zoogeography of genus Cruriraja across the world's oceans and provides a revised key to the species.

Response of micro- and mesozooplankton in the southwestern Bay of Bengal to a cyclonic eddy during the winter monsoon, 2005.

A cyclonic eddy (CE) in the southwestern Bay of Bengal (SWBoB; 10-15° N; 81-87° E) during winter monsoon 2005 and associated changes in the open ocean hydrography and productivity patterns were studied using satellite observations and in situ measurements. Analysis of the satellite-derived sea surface height anomaly (SSHA) indicated the existence of a large eddy (10-15° N; 81-87° E) from November to January, with its core centered at 13° N and 82° E. The large positive wind stress curl (~1.8 × 10(-7) N m(-2)) and resultant Ekman pumping (~3 × 10(-2) cm s(-1)) were identified as the prominent forcing mechanisms. In addition, the cyclonic storms and depressions experienced in the region during the study period seem to have served to maintain the strength of the CE through associated Ekman pumping. The cold (~26.6 °C), nutrient-enriched (NO3 > 2 µM, PO4 > 0.73 µM and SiO4 > 3 µM) upwelled waters in the upper layers of the CE enhanced the biological production (chl. a > 0.56 mg m(-3)). Dissolved oxygen in the surface waters was > 200 µM. The phytoplankton and zooplankton biomass recorded during the season was comparable or perhaps higher than the peak values reported from the northeastern Arabian Sea (chlorophyll a concentrations of 0.2 to 0.4 mg m(-3) and zooplankton biovolume 0.6 ml m(-3)) during winter. Occurrence of a higher mesozooplankton biovolume (0.8 ml m(-3)) and relatively low abundance of microzooplankton indicates the prevalence of a short food chain. In conclusion, high biological production, both at primary as well as secondary level, suggests the prevalence of an efficient food web as a result of physical forcing and subsequent ecological interactions evident up to tertiary level in an oligotrophic basin like BoB.

Characteristics of a cyclonic eddy and its influence on mesozooplankton community in the northern Bay of Bengal during early winter monsoon.

Characteristics of a cold-core eddy and its influence on the mesozooplankton community were studied along the central (87° E) Bay of Bengal during winter monsoon (November 2008) based on in situ data. The thermo-haline structure and the satellite-derived sea level anomaly maps showed the presence of a cyclonic eddy between 16° N and 20° N. The nutrient enhancement due to the eddy pumping in the euphotic column (∼ 50 m) had resulted in high chlorophyll a concentration, a factor of 8 times higher than that outside the eddy, which led to higher mesozooplankton biovolume (0.35 ± 0.36 ml m(-3)) and abundance (276 ± 184 ind m(-3)). The northern cyclonic eddy (NCE) seems to exist for approximately 6 months between July and January. During summer, the NCE is forced by local wind stress curl and the resultant Ekman pumping, whereas during fall and early phase of the winter, it is sustained by westward propagating semi-annual Rossby waves. The longer existence of NCE in the study region, which originated 6 months prior to the present observation, provides a favourable environment for the mesozooplankton community to grow and reproduce, resulting in noticeable increase in the biovolume. Hence, the persistent and longer existence of NCE significantly influences the biological production of the generally oligotrophic BoB, making it locally biologically 'active'.

Species identification of mixed algal bloom in the Northern Arabian Sea using remote sensing techniques.

Oceanic waters of the Northern Arabian Sea experience massive algal blooms during winter-spring (mid Feb-end Mar), which prevail for at least for 3 months covering the entire northern half of the basin from east to west. Ship cruises were conducted during winter-spring of 2001-2012 covering different stages of the bloom to study the biogeochemistry of the region. Phytoplankton analysis indicated the presence of green tides of dinoflagellate, Noctiluca scintillans (=N. miliaris), in the oceanic waters. Our observations indicated that diatoms are coupled and often co-exist with N. scintillans, making it a mixed-species ecosystem. In this paper, we describe an approach for detection of bloom-forming algae N. scintillans and its discrimination from diatoms using Moderate Resolution Imaging Spectroradiometer (MODIS)-Aqua data in a mixed-species environment. In situ remote sensing reflectance spectra were generated using Satlantic™ hyperspectral radiometer for the bloom and non-bloom waters. Spectral shapes of the reflectance spectra for different water types were distinct, and the same were used for species identification. Scatter of points representing different phytoplankton classes on a derivative plot revealed four diverse clusters, viz. N. scintillans, diatoms, non-bloom oceanic, and non-bloom coastal waters. The criteria developed for species discrimination were implemented on MODIS data and validated using inputs from a recent ship cruise conducted in March 2013.

A Novel Isoform of the Hepatic Antimicrobial Peptide, Hepcidin (Hepc-CB1), from a Deep-Sea Fish, the Spinyjaw Greeneye Chlorophthalmus bicornis (Norman, 1939): Molecular Characterisation and Phylogeny.

Hepcidin is cysteine-rich short peptide of innate immune system of fishes, equipped to perform prevention and proliferation of invading pathogens like bacteria and viruses by limiting iron availability and activating intracellular cascades. Hepcidins are diverse in teleost fishes, due to the varied aquatic environments including exposure to pathogens, oxygenation and iron concentration. In the present study, we report a 87-amino acid (aa) preprohepcidin (Hepc-CB1) with a signal peptide of 24 aa, a prodomain of 39 aa and a bioactive mature peptide of 24 aa from the gill mRNA transcripts of the deep-sea fish spinyjaw greeneye, Chlorophthalmus bicornis. Molecular characterisation and phylogenetic analysis categorised the peptide to HAMP2-like group with a mature peptide of 2.53 kDa; a net positive charge (+3) and capacity to form ß-hairpin-like structure configured by 8 conserved cysteines. The present work provides new insight into the mass gene duplication events and adaptive evolution of hepcidin isoforms with respect to environmental influences and positive Darwinian selection. This work reports a novel hepcidin isoform under the group HAMP2 from a non-acanthopterygian deep-sea fish, C. bicornis.

Characterization of Histone H2A Derived Antimicrobial Peptides, Harriottins, from Sicklefin Chimaera Neoharriotta pinnata (Schnakenbeck, 1931) and Its Evolutionary Divergence with respect to CO1 and Histone H2A.

Antimicrobial peptides (AMPs) are humoral innate immune components of fishes that provide protection against pathogenic infections. Histone derived antimicrobial peptides are reported to actively participate in the immune defenses of fishes. Present study deals with identification of putative antimicrobial sequences from the histone H2A of sicklefin chimaera, Neoharriotta pinnata. A 52 amino acid residue termed Harriottin-1, a 40 amino acid Harriottin-2, and a 21 mer Harriottin-3 were identified to possess antimicrobial sequence motif. Physicochemical properties and molecular structure of Harriottins are in agreement with the characteristic features of antimicrobial peptides, indicating its potential role in innate immunity of sicklefin chimaera. The histone H2A sequence of sicklefin chimera was found to differ from previously reported histone H2A sequences. Phylogenetic analysis based on histone H2A and cytochrome oxidase subunit-1 (CO1) gene revealed N. pinnata to occupy an intermediate position with respect to invertebrates and vertebrates.

Hydrographic characterization of southeast Arabian Sea during the wane of southwest monsoon and spring intermonsoon.

Seasonal variation of the hydrography along the southeast Arabian Sea is described using data collected onboard FORV Sagar Sampada in September--October 2003 (later phase of Southwest monsoon, SWM) and March--April 2004 (Spring inter monsoon, SIM). During the later phase of the SWM, upwelling was in the withdrawal phase and the frontal structure was clearer in the northern sections (13 and 15 degrees N lat) indicating strong upwelling in the area. The driving force of upwelling is identified as the combination of alongshore wind stress and remote forcing with a latitudinal variability. Although a more prominent upwelling was found in the north, a maximum surface Chlorophyll-a was found in the south (10 degrees N). During the SIM, the area was characterized by oligotrophic water with relatively high Sea Surface Temperature (>29 degrees C) and low salinity (33.8 to 35.4). During March, the surface hydrography was found to be controlled mainly by the intrusion of low-saline waters from the south, while during September by the high saline water from the north. The presence of various water masses [Arabian Sea High Salinity Water (ASHSW), Persian Gulf Water (PGW), Red Sea Water (RSW)] and their seasonal variations in the region is discussed and their decreasing influence towards the south is noted during both periods of observation. During the SWM, the dynamic topography showed the equator-ward flow of the West India Coastal Current (WICC) at the surface and a pole-ward coastal under current at sub-thermocline depth. During the SIM, surface circulation revealed the WICC flowing pole-ward north of 13 degrees N, but equator-ward flow in the south, with a clockwise circulation around the Lakshadweep High.