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The response of phytoplankton community to the co-existing events of coastal upwelling and mud banks in the nearshore waters of Alappuzha (15 m depth), located in the southwest coast of India from April to November 2016, is described based on size-fractionated phytoplankton biomass (chlorophyll a), primary production and community composition. The study region exhibited well-distinct spatio-temporal hydrological changes because of the influence of wind-driven coastal upwelling, prevalent during the southwest monsoon (SWM) period. However, the formation of mud banks, in addition to coastal upwelling, was observed at station M2, which facilitated the substantial increase of water column turbidity and inorganic nutrients (ammonium, phosphate, and silicate) during and after the peak SWM period compared to the non-mud bank reference stations (M1 and M3). The prevailing hydrological changes were complemented the corresponding phytoplankton productivity patterns, in which profound domination of nanophytoplankton (2–20 µm) chlorophyll a and primary production was observed throughout the study region, irrespective of seasons. The SIMPER analysis, based on phytoplankton (mostly >20 µm) species composition data (microscopy), revealed the formation of certain characterizing species, mainly comprised of diatoms and dinoflagellates. The consistent predominance of the nanophytoplankton, established under variable hydrological scenarios, showed that the inorganic nutrient (specifically ammonium) availability was instrumental in defining the widespread growth of nanophytoplankton community compared to the prevailing light levels. The present study thus revealed that even the small-sized phytoplankton community could survive in the nutrient-enriched coastal waters, characterised by the co-existing upwelling and mud banks.

A conspicuous bioluminescence during nighttime was reported in an aquaculture farm in the Cochin estuary due to Gonyaulax spinifera bloom on March 20, 2020. In situ measurements on bioluminescence was carried out during nighttime to quantify the response of G. spinifera to various mechanical stimuli. The bioluminescence intensity (BI) was measured using Glowtracka, an advanced single channel sensor, attached to a Conductivity–Temperature–Depth Profiler. In steady environment, without any external stimuli, the bioluminescence generated due to the movement of fishes and shrimps in the water column was not detected by the sensor. However, stimuli such as a hand splash, oar and swimming movements, and a mixer could generate measurable bioluminescence responses. An abundance of ~ 2.7 × 106 cells L−1 of G. spinifera with exceptionally high chlorophyll a of 25 mg m−3 was recorded. The BI in response to hand splash was recorded as high as 1.6 × 1011 photons cm−2 s−1. Similarly, BI of ~ 1–6 × 1010 photons cm−2 s−1 with a cumulative bioluminescence of ~ 2.51 × 1012 photons cm−2 (for 35 s) was recorded when there is a mixer with a constant force of 494 N/800 rpm min−1. The response of G. spinifera was spontaneous with no time lapse between application of stimuli and the bioluminescence response. Interestingly, in natural environment, application of stimulus for longer time periods (10 min) does not lower the bioluminescence intensity due to the replenishment of water thrusted in by the mixer from surrounding areas. We also demonstrated that the bioluminescence intensity decreases with increase in distance from the source of stimuli (mixer) (av. 1.84 × 1010 photons cm−2 s−1 at 0.2 m to av. 0.05 × 1010 photons cm−2 s−1 at 1 m). The BI was highest in the periphery of the turbulent wake generated by the stimuli (av. 3.1 × 1010 photons cm−2 s−1) compared to the center (av. 1.8 × 1010 photons cm−2 s−1). When the stimuli was applied vertically down, the BI decreased from 0.2 m (0.3 × 1010 photons cm−2 s−1) to 0.5 m (0.10 × 1010 photons cm−2 s−1). Our study demonstrates that the BI of G. spinifera increases with increase in mechanical stimuli and decreases with increase in distance from the stimuli.

Hydrographic conditions such as water level, velocity, adequate water circulation and stratifications have a strong influence on the management of fish cage culture in the estuarine environment. In this study, a 3D hydrodynamic model was used to identify the areas of the mixed and stratified water column and to use this in conjunction with particle tracking models for appropriate site selection for cage culture. A Lagrangian method was used to simulate the instantaneous release of "particles" emulating discharge from fish cages to show the behaviour of waste in terms of water circulation and water exchange. Model simulation at Pizhala cage farm revealed that desirable water exchange is experienced in the monsoon and pre-monsoon period. There have existed strong spring-neap variability in the water level with an average range of 0.7 m with a speed of < 0.12 m/s in pre-monsoon and < 0.24 m/s in monsoon. This consistent flow patterns in the Pizhala region helps in the replenishment of oxygenated water and removal of waste produced beneath the cages, and it is corroborated by the Lagrangian particle transport model experiment coupled with Finite Volume Community Ocean Model (FVCOM) in the study.

The changes in the hydro-chemical properties of a near shore waters of Alappuzha, southwest coast of India, where the mud banks and coastal upwelling are co-existent, are presented based on two time-series measurements taken during 2014 and 2016. The meteorological data show that the wind speed was significantly high during 2014 as compared to that during 2016 (p

The time-dependent plume front fluctuation concerning different tidal phases and its dynamics coupled with seasonal river efflux in the shelf off Kochi, south west coast of India, were investigated using Finite Volume Community Ocean Model (FVCOM). The region is linked with a monsoonal estuary, featured by mixed semi-diurnal tide (1 m) and exhibited a highly complicated plume pattern. The rivalry between river efflux with tidal phases create plume fronts in the shelf, whose gradients fortified or weakened by mixing dynamics. Eventhough the incessant river efflux in the summer monsoon impart significant momentum in the shelf, the range of frontal fluctuation was curtailed to 2 km by strong monsoon currents. During transient phase of the season (fall inter-monsoon), the tidal forcings on plume positioning overwhelm the shelf currents, such that the plume front fluctuate between 6-17 km (range increased to ~11 km) from the inlet. In low tides, the region near to the inlets was almost homogenized (Rdd>1). The location of frontal zones suitable for the propagation of nonlinear waves (F≤1)will change in respect to the competition between river efflux and tide-topography interaction. The strong stratified plume front regions with increased Brunt Vaisala Frequency (BVF) in summer monsoon behave as active zones of non linear wave propagation only when the plume front decelerates from supercritical to subcritical. During dry season, the F≤1 was satisfied at limited locations, but the absence of BVFmax zone (frequency >0.3 s-1) revealed that the amplitude of such nonlinear waves would be considerably small. The study divulge that tidally pulsating plume front fluctuates between 3-18 km from inlet and also highlights that the propagation of nonlinear waves with considerable amplitude will depend on both the plume front velocity and the Brunt Vaisala Frequency of the water column.

The present study reports the influence of upwelling on the abundance and community structure of archaea and bacteria in a mud bank formed along the coastal waters of Alappuzha, the southwest coast of India. The signatures of upwelling were observed with the onset of southwest monsoon, characterized by a decrease in sea surface temperature and dissolved oxygen in bottom waters and increase in salinity. Nitrite, nitrate, and phosphate showed a significant increase during upwelling compared to pre-upwelling conditions. There were no significant differences in the abundance of archaea across seasons (pre- and during upwelling conditions) and regions (Station S1, inside and Station S2, outside the mud bank), while the bacterial abundance showed a six-fold increase for S1 and four-fold increase for S2 during upwelling. The PCR–DGGE results show the existence of a transient population of archaea and bacteria in the mud bank region during upwelling. The step up multiple regression models could explain 66.5% and 56.3% of the temporal variations in archaeal and 96.5% and 53.63% in bacterial distribution inside and outside of mud bank respectively, at pre-upwelling conditions. About 67% of the temporal variations in the distribution of archaea and 41.4% in bacteria inside and 49.9% in bacteria outside of mud bank during upwelling conditions could be explained by the same model. The temporal variation in the distribution of archaea outside mud bank during upwelling conditions could not be explained by the present regression model. Our studies indicate that the upwelling induces changes in the abundance and community structure of bacteria in the mudbank, which are modulated by the interactive effects of hydrographic variables. Further studies to unravel the interactive effect of hydrographic variables on the biogeochemical activities of microorganisms would be appreciated.

Mud bank formation during the southwest monsoon along the southwest coast of India remains an enigma to the researchers and coastal community in spite of several earlier studies. The present study attempts to unravel the mystery through a high-frequency, season-long time-series observation at Alappuzha, located at the southern part of the west coast of India, a region of frequent occurrence of mud bank. Using 7-month-long weekly time-series observation, we identified strong winds and high waves associated with onset of the southwest monsoon and subsequent three episodic atmospheric low-pressure events (LPEs).With the help of in situ time-series data, we show that the strong winds and high waves associated with southwest monsoon pre-conditions the near shore bottom sediment to bring it into suspension. The high amplitude waves associated with the southwest monsoon, while propagating from the deep water to shallow water region, interact with the bottom initiating bottom-sediment movement and its suspension due to wave refraction and shoaling. The sporadic occurrence of the atmospheric LPEs enhances the process of suspension of bottom sediment in the near shore region leading to the formation of fluid mud. Simulations with a cohesive sediment transport model yielded realistic estimates of sediment transport, in the presence of an onshore current, a pre-requisite for transporting the fluid mud toward the coast. The prevailing onshore upwelling current during the southwest monsoon provides the favorable pre-requisite conditions for transporting the fluid mud through depression channel network towards the coast. Once sufficient quantity and thickness of fluid mud is accumulated in the near shore region, it acts as a wave damper for subsequent high monsoon waves, as indicated by the time-series wave data, leading to the formation of tranquil mud bank region. Depression channel networks extending from the shelf to the coast off Alappuzha, Kochi, Ponnani, Beypore, and Ullal were found in the bathymetric charts, thus explaining why mud banks occur only at few locations in spite of the prevalence of similar monsoon conditions.

Trichodesmium is a bloom-forming, diazotrophic, non-heterocystous cyanobacteria widely distributed in the warmer oceans, and their bloom is considered a ‘biological indication’ of stratification and nitrogen limitation in the ocean surface layer. In the first part of this paper, based on the retrospective analyses of the ocean surface mesoscale features associated with 59 Trichodesmium bloom incidences recorded in the past, 32 from the Arabian Sea and the Bay of Bengal, and 27 from the rest of the world, we have showed that warm-core features have an inducing effect on bloom formation. In the second part, we have considered the environmental preferences of Trichodesmium bloom based on laboratory and field studies across the globe, and proposed a view about how warm-core features could provide an inducing pre-requisite condition for the bloom formation in the Arabian Sea and the Bay of Bengal. Proposed that the subsurface waters of warm-core features maintain more likely chances for the conducive nutrient and light conditions required for the triggering of the blooms.

Coastal upwelling and mud banks are two oceanographic processes concurrently operating along certain stretches of the southwest (Kerala) coast of India during the Southwest Monsoon period (June–September), facilitating significant enhancement in plankton biomass. Mud banks have scientific and societal attention from time immemorial, predominantly due to the large fisheries associated with them. In this paper, for the first time, the specific biophysical roles of these oceanographic processes have been discriminated, based on a focused 18 weekly/fortnightly time-series study (April to September 2014) in a mud bank-upwelling area (off Alappuzha, southwest coast of India). In conjunction with standard hydrographical and satellite remote sensing data, we utilised a FlowCAM to track the biophysical linkage in terms of plankton composition abundance and size structure at three locations (M1, M2 and M3) in the study area. During the Pre-Southwest Monsoon (April–May), the entire study area was warmer with low nitrate concentration in the surface waters, which caused lower biomass of autotrophs compared to the Southwest Monsoon (June–September). By the onset of the Southwest Monsoon (June), drastic hydrographical transformations took place in the study domain due to the Coastal upwelling, reflected as the surfacing of significantly cool, high nutrient and hypoxic waters. Concurrently, mud bank formed at location M2 due to the presence of relatively high-suspended sediments in the region, creating a localised calm environment conducive for fishing activities. In response to the hydrographical transformations in the entire study area during the Southwest Monsoon, the autotrophic plankton biomass and size structure experienced significant change. The micro-autotrophs biomass that was low during the Pre-Southwest Monsoon (av. 0.33 ± 0.2 mgC L− 1 at surface and av. 0.07 ± 0.04 mgC L− 1 at subsurface) noticeably increased during the Southwest Monsoon (av. 1.6 ± 0.4 mgC L− 1 at surface and av. 1.3 ± 0.2 mgC L− 1 at subsurface). The seasonal mean bio-volume of micro-autotrophs followed the same pattern in all three locations with the dominance of smaller individuals during the Pre-Southwest Monsoon (av. 55 ± 4.4 × 103 μm3 individual− 1 at surface and av. 67.1 ± 38.4 × 103 μm3 individual− 1 at subsurface). Relatively large phytoplankton dominated during the Southwest Monsoon (av. 77.3 ± 5.5 × 103 μm3 individual− 1 at surface and av. 90.3 ± 4.9 × 103 μm3 individual− 1 at subsurface). Similar spatial change in the plankton composition, biomass and size structure in all three locations suggested the dominant role of coastal upwelling, and not the mud bank, in shaping the dominant autotrophic plankton in the study domain. The nutrient enrichment in the region associated with the coastal upwelling facilitated the predominance of a classical short food chain capable of supporting large fish stocks. In addition to relatively calm mud bank, the hypoxic, cool upwelled waters that existed in the subsurface induce the fish stock to concentrate in the surface waters, making the relatively calm mud bank and adjoining areas a rich fishing ground for the native fishers.

The results of the first time-series measurements spanning 18-weeks (22 April to 20 September 2014) from a coastal environment (Alappuzha, southwest India), where two process of upwelling and mud banks are concurrent during summer monsoon are presented. The upwelling signals were evident from the 2nd week of May onwards and the intensity varied widely from 1st week of June to 3rd week of September. The formation of mud banks was observed during the peak upwelling period (14th June) and once formed, they were persistent till the end of monsoon season (September 2014). The time-series evolution of dissolved oxygen levels showed the incursion of hypoxic waters well in to the mud banks during peak upwelling period. The considerable reduction in the dissolved methane levels (300 to

Alappuzha mud bank draws special attention among the twenty-mud bank locations reported along the Kerala coast by its remoteness from riverine sources. Among several hypotheses proposed for the formation of mud bank, the subterranean hypothesis was most accepted because of the occurrence of low salinity in the bottom layers. The present study provides evidence to show that occurrence of low salinity waters near the bottom in the mud bank region is an artifact of measuring technique employed for the measurement of salinity. The usual technique of conductivity based salinity determination completely fails in the presence of water laden with high amount of suspended sediment. Laboratory experiments were conducted to determine the response of electrode and conductivity cell sensor types to determine the salinity using a range of suspended sediment in the water column. Actual sediment samples from the mud bank region were utilized for the above studies. Based on field observations and experiments, we conclude that the low salinity was the manifestation of the presence highly turbid fluid mud formation in the mud bank region rather than the influence of fresh water.

Estuaries with poor flushing and longer residence time retain effluents and pollutants, ultimately resulting in eutrophication, a decline in biodiversity and, finally, deterioration of water quality. Cochin Estuary (CE), southwest coast of India, is under the threat of nutrient enrichment by the anthropogenic interventions and terrestrial inputs through land runoff. The present study used the FVCOM hydrodynamic model coupled with the Lagrangian particle module (passive) to estimate the residence time and to delineate site-specific transport pathways in the CE. The back and forth movements and residence time of particles was elucidated by using metrics such as path length, net displacement and tortuosity. Spatio-temporal patterns of the particle distribution in the CE showed a similar trend during monsoon and post-monsoon with an average residence time of 25 and 30 days, respectively. During the low river discharge period (pre-monsoon), flood-ebb velocities resulted in a minimum net transport of the water and longer residence time of 90 days compared to that of the high discharge period (monsoon). During the pre-monsoon, particle released at the southern upstream (station 15) traversed a path length of 350 km in 90 days before being flushed out through the Fortkochi inlet, where the axial distance was only 35 km. This indicates that the retention capacity of pollutants within the system is very high and can adversely affect the water quality of the ecosystem. However, path length (120 km) and residence time (7.5 days) of CE were considerably reduced during the high discharge period. Thus the reduced path length and the lower residence time can effectively transport the pollutants reaching the system, which will ultimately restore the healthy ecosystem. This is a pioneer attempt to estimate the flushing characteristics and residence time of the CE by integrating the hydrodynamics and Lagrangian particle tracking module of FVCOM. This information is vital for the sustainable management of sensitive ecosystems.

We investigated the seasonal spreading and transport of buoyant plume in the shelf off Kochi using Finite Volume Community Ocean Model (FVCOM). The modelled river plume typically consisted of an offshore bulge and a coastal current. The spreading of the bulge extended up to a distance of 19 km from inlet during the summer monsoon to

Oceans are vast, dynamic, and complex ecosystems characterized by fluctuations in environmental parameters like sea surface temperature (SST), salinity, oxygen availability, and productivity. Environmental variability acts as the driver of organismal evolution and speciation as organisms strive to cope with the challenges. We investigated the evolutionary consequences of heterogeneous environmental conditions on the mitogenome of a widely distributed small pelagic fish of Indian ocean, Indian oil sardine, Sardinella longiceps. Sardines were collected from different eco-regions of the Indian Ocean and selection patterns analyzed in coding and non-coding regions. Signals of diversifying selection were observed in key functional regions involved in OXPHOS indicating OXPHOS gene regulation as the critical factor to meet enhanced energetic demands. A characteristic control region with 38–40 bp tandem repeat units under strong selective pressure as evidenced by sequence conservation and low free energy values was also observed. These changes were prevalent in fishes from the South Eastern Arabian Sea (SEAS) followed by the Northern Arabian Sea (NAS) and rare in Bay of Bengal (BoB) populations. Fishes belonging to SEAS exhibited accelerated substitution rate mainly due to the selective pressures to survive in a highly variable oceanic environment characterized by seasonal hypoxia, variable SST, and food availability.

The influence of oil and gas exploration activities on the macrobenthic community of an offshore oil and gas drilling site was investigated along the Krishna-Godavari basin (KG), Western Bay of Bengal. In the oil well sites, the enrichment factor of most of the metals (Cu, Zn, Pb, Cr) showed relatively higher values (EF > 10), indicating their anthropogenic origin. The macrobenthic community exhibited a conspicuous reduction in biomass (av. 33.5%), density (av. 20.9%) and diversity (av. 6.7%) in and around the oil well platforms. Polychaetes abundance increased towards the oil well platforms and decreased away from the wells, whereas cumaceans dominated at the coastal stations. The lower density of Ampelisca sp. in the oil well platforms and higher density at the locations away from the oil wells indicates the adverse effects of exploration activities. Along with the environmental variables such as depth, sediment texture and composition, trace metal concentration also had a prominent influence on the macrobenthic fauna. The biotic indices (H’ index and AMBI) exhibiting slightly disturbed condition at the oil well sites; and M-AMBI exhibiting moderate-good–high condition, reveals the distinct distribution pattern of benthic communities in the region. Slightly disturbed conditions at a distance of 1–1.5 km from the oil wells compared to the undisturbed conditions at regions 3–4 km away from the platforms reveals the impacts of oil and gas exploration activities on the benthic habitat quality.

The short-term changes in hydrochemical and phytoplankton characteristics occurring in the Alappuzha mud bank (AMB) region, located on the southwest coast of India, were monitored in association with a red-tide event caused by an autotrophic dinoflagellate, Prorocentrum shikokuense Hada. Dark-brownish waters detected in the AMB region on 7 September 2016, exhibited substantially high levels of chlorophyll a (68.29 mg m−3) and peridinin (53.61 mg m−3). The dominance of large-sized phytoplankton (> 20 μ m ), mostly of diatoms along with a moderate amount of fucoxanthin (>2.5 mg m−3), was detected in the study region during the pre-bloom period (10 and 28 August). The post-bloom period was characterised by the abundance of diatoms and dinoflagellates on 23 September, and cyanobacteria and diatoms on 14 October. The prevalence of cold (

Flow dynamics are a key part of the physical processes that drive the sediment transport in an aquatic system, affecting depositional processes and leading to landform evolution. The current asymmetry (CA) noted in Vembanad Lake (VL), India, have a particularly strong influence on the sediment budget and thus shape its geomorphology. In the present study the Coastal Ocean Model - Finite Volume Coastal Ocean Model (FVCOM) was used to compute the lateral current asymmetries and their implications for the long-term morphological changes in VL during different tidal phases. Model results were utilised to calculate the CA using two criteria: (1) Peak flood/ebb velocities with duration, and (2) Asymmetry Index (AIDV). AIDV values suggest the prevalence of ebb dominance over the entire system except at Cherai and Vallarpadam. However, several isolated pockets were noted on the right/eastern bank (shallow depth) of the system where the peak flood velocity exceeded the ebb, favouring accretion. Contrary to the concept of ebb asymmetry, mean velocity and duration asymmetries were prevalent in the asymmetry index (AIDV); hence we adopted peak flood/ebb velocity and its duration asymmetries to improve our understanding of the sediment transport dynamics. Typical flood asymmetry was identified on the right bank and at many of the lateral stations in VL, which switched to the modified ebb asymmetry during substantial river discharge. Analysis of CA enables understanding of the process that influences selective morphological changes, as explained by the model results. This conclusion was well corroborated by results obtained over the past three decades (1973–2008) from analysis of Landsat satellite imagery. Flood/ebb dominance in VL is explicitly substantiated with regions of accretion/erosion derived from satellite imageries. A holistic approach encompassing modelling, observations, remote sensing, and GIS techniques were used to address the erosion-accretion process in VL.

Presence of multiple antibiotic resistant microorganisms in marine systems is increasingly a focus of concern as they pose potential health risk to humans and animals. The present study reports the distribution, diversity, antibiotic resistance profile and pathogenicity of Vibrio spp. in the water column of Palk Bay (PB) extending from Uchipuli along the southeast Indian coast to Thalaimannar in the northwest of Sri Lanka. Our analysis has confirmed the presence of five Vibrio spp ( V. cholerae, V. hollisae, V. furnissi, V. alginolyticus and V. aestuarianus ) in the region with the dominance of V. cholerae , which accounted for more than 50% of the total number of isolates. V. cholerae isolates showed resistance against β -lactam, vancomycin, nitrofurantoin, gentamicin, azithromycin, oxytetracycline, tetracycline and chloramphenicol antibiotics. High levels of Escherichia coli in PB indicate the possible anthropogenic input to the prevalence of multiple antibiotic resistance. On a positive note is the absence of blaNDM-1 gene, which confers microorganism with resistance against third generation carbapenem antibiotics. Among toxicity genes tested, toxR gene was found present and ctxA absent in all the isolates. The step up multiple regression model confirmed the interaction effect, more of environmental parameters than their individual influence on the distribution of E. coli and Vibrio spp. In conclusion, the present study reports the widespread distribution of multiple antibiotic resistant Vibrio spp. in the water column of PB. Further studies are in progress to assess the level of antibiotic pollution in PB, and antibiotic resistance among microorganisms associated with fauna and flora of PB.

Long-term variability of Sea Surface Temperature (SST) in the Arabian Sea (AS) and Bay of Bengal (BoB) during 1880–2010 is examined using all the available data sets of monthly SST, wind speed, incoming solar radiation, cloud cover, long wave radiation, latent heat flux, net surface heat flux and surface currents. SST time series reveal an upward (increasing) trend (warming) after 1940 in both the basins. Wavelet analyses of the SST time series reveal that AS SST is controlled by semi-annual and annual forcing while the BoB SST is influenced predominantly by annual forcing. The SST responses in both the basins are in phase to the climatic events such as El Nino, La Nina and Indian Ocean Dipole, but a stronger impact is noticed in the AS SST. The climatic events affected the seasonal peaks of SST warming (April–May) and cooling (August–September) in both the basins. Time series of SST anomaly also showed in phase responses to the climatic events and an upward trend from 1960 to 2010 in both the basins. Long-term decreasing trends observed in surface wind speed, latent heat flux and advective process via the weakened surface currents, together with the long-term increasing trend in P − E (Precipitation, P minus Evaporation, E) contributed to the SST warming trend in both the basins. In association with the upward trend in P − E, the Simple Ocean Data Assimilation (SODA) Reanalysis Sea Surface Salinity time series exhibited freshening (a decreasing trend) and enhanced the salinity stratification in the BoB, thus modulated the BoB SST warming. These cumulative processes led to the warmer SSTs in the BoB compared to that in AS.

L-moments are expectations of linear combinations of order statistics, their use in reliability analysis has been established. In the present paper we study L-moments in relation to income inequality measures. Models characterized by functional relationships between L-moments and income inequality measures are studied. Finally, we define the ordering based on L-moments and study its implications on other existing orderings.

Vinita, J.; Shivaprasad, A.; Revichandran, C.; Manoj, N.T.; Muraleedharan, K.R., and Binzy, J., 2015. Salinity response to seasonal runoff in a complex estuarine system (Cochin estuary, west coast of India). The hydrographic conditions in Cochin estuary are investigated using longitudinal measurements of salinity profiles during a 1-year period. The estuary transformed from salt wedge conditions during the wet season to a partially or well-mixed state during the dry season. During high runoff months (June–September) and moderate runoff months (October–December and May), the salinity structure is a strong function of variations in river runoff, and the estuary responds coherently to episodic inputs of freshwater. However, during the period from January to April, the dependence of the salinity field on runoff was weakened by axial diffusivity. The salt transport was a balance between seaward flux induced by river runoff and tidally induced diffusive landward flux. The latter dominated in almost all...

Though microbial processes in the oxygen minimum zones (OMZs) of the Arabian Sea (AS) are well documented, prokaryote-virus interactions are less known. The present study was carried out to determine the potential physico-chemical factors influencing viral abundances and their life strategies (lytic and lysogenic) along the vertical gradient in the OMZ of the AS (southwest coast of India). Water samples were collected during the southwest monsoon (SWM) season in two consecutive years (2015 and 2016) from different depths, namely, the surface layer, secondary chlorophyll a maxima (~30&ndash, 40 m), oxycline (~70&ndash, 80 m), and hypoxic/suboxic layers (~200&ndash, 350 m). The high viral abundances observed in oxygenated surface waters (mean &plusmn, SD = 6.1 &plusmn, 3.4 &times, 106 viral-like particles (VLPs) mL&minus, 1), drastically decreased with depth in the oxycline region (1.2 &plusmn, 0.5 &times, 106 VLPs mL&minus, 1) and hypoxic/suboxic waters (0.3 &plusmn, 0.3 &times, 1). Virus to prokaryote ratio fluctuated in the mixed layer (~10) and declined significantly (p &lt, 0.001) to 1 in the hypoxic layer. Viral production (VP) and frequency of virus infected cells (FIC) were maximum in the surface and minimum in the oxycline layer, whereas the viral lysis was undetectable in the suboxic/hypoxic layer. The detection of a high percentage of lysogeny in suboxic (48%) and oxycline zones (9&ndash, 24%), accompanied by undetectable rates of lytic viral infection support the hypothesis that lysogeny may represent the major survival strategy for viruses in unproductive or harsh nutrient/host conditions in deoxygenated waters.

The southwest coast of India is known to experience two concurrent processes during the southwest monsoon, namely coastal upwelling and mud banks at selected stretches such as that off Alappuzha. The mud bank sediments were found to contain very high concentrations of phosphorus (ave. 2255 ± 278 μ g/g), and the present study measured changes in concentration of elements such as carbon, phosphorus, iron, and manganese within the Alappuzha mud banks, to understand the influence of upwelling on the cycling of these elements. The results showed that coastal upwelling led to hypoxic conditions within the mud bank region during the peak southwest monsoon, which induced significant changes in the phosphorus fractions in the sediments. There was an enrichment of iron, caused by the efflux of reactive Fe from the subsurface sediment layers and depletion of manganese, due to reductive dissolution of Mn oxides and subsequent release of Mn. The low molar ratios of total organic carbon to total nitrogen (9 ± 1) and total organic carbon to organic phosphorus (118 ± 57) generally indicated that the organic matter was relatively fresh and derived from marine plankton. Sedimentary phosphorus also exhibited wide fluctuations in its geochemical forms during hypoxia. Five geochemical forms of P such as exchangeable P (Ex-P), Fe and Mn bound P (Fe-P), P from Al oxides, non-reducible Fe bound P and organic P (Non Red-P), calcium bound P (Ca-P) and refractory organic P (ROP) were extracted, adopting sequential extraction procedure. The percentage contribution of various P forms were 2%–11% Ex-P, 4%–25% Fe-P, 4%–10% Non Red-P, 60%–78% Ca-P and 4%–12% ROP. The fractionation study revealed that precipitation of apatite and vivianite are the significant pathways of phosphorus enrichment in mud bank sediments. The study indicates that the enrichment of labile P fractions could be mediating the enhancement in biological production in the Alappuzha mud banks during the southwest monsoon.

The viral dynamics have rarely been investigated in estuarine environments of India. The present study brings out a first hand information on the distribution of virus and bacteria in an eutrophic estuary (Cochin, India). Thirteen stations were selected for monthly monitoring of bacterial abundance (BA), total viable bacterial count (TVC), viral abundance (VA), chlorophyll a (Chl a) and other water quality parameters (temperature, salinity, pH, dissolved oxygen and inorganic nutrients such as NO3–N, NH4–N, PO4–P and SiO4–Si) for 1 year. There was significant variations in the VA [0.59–4.48 × 107viral like particles (VLPs) mL−1] and BA (0.49–8.12 × 106 cells mL−1) in the estuary. The variation in the viral to bacterial ratio (3–22) indicated marked seasonality. Statistical analysis showed bacteria as a major factor controlling the distribution of viruses (60 % variability) in Cochin estuary (CE). The viruses also showed positive correlations with Chl a, pH and salinity. The distribution of virus followed a distinct pattern of three different zones in the estuary controlled by salinity in zone I, Chl a in zone II and salinity, Chl a in zone III. The zonal distribution suggests that the factors that control the viral-host systems vary in different areas due to the complex hydrography of the estuary and environmental changes are very sensitive to the viral population in CE.

Kumar, P.K.D.; Gopinath, G.; Murali, R.M., and Muraleedharan, K.R., 2014. Geospatial analysis of long-term morphological changes in Cochin estuary, SW coast of India. The Cochin estuary along the SW coast of India has undergone tremendous environmental changes due to continuous alterations. Geospatial information available since 1967 has been compiled to evaluate the long-term morphological changes. Quantification of geomorphological changes that occurred over the decades was made to have an integrated profile to ascertain the changes in the extent. Toposheet maps (1967) and satellite imageries for 2004 and 2011 have been interpreted. Quantitative comparison of inner island segments showed significant changes in island widths through time. It was found that the areas covered by the islands within the estuary during 1967, 2004, and 2011 were 81.62, 89.26, and 89.52 km2, respectively, and those covered by the water body were 130.68, 121.3, and 118.01 km2, respectively. The shrinking rate of the est...

In this article, we look into the properties and characterizations of the New Zenga curve. The relationship of the curve with other measures of inequality as well as some reliability concepts are examined. Classification of lifetime distributions using the Zenga curve and an illustration for the behaviour of the curve using a survival data are also provided.

The study addresses the coupled spatial scales in the physico-chemical variables and chaetognaths in the upwelling system of the eastern Arabian Sea during the 2005 summer monsoon. We studied the taxon between 0 and 1,000 m depth along seven zonal sections between 8° and 19° N and especially observed the vertical stratification of the animals. In the upwelling regions, higher chaetognath abundance was observed resulted by the local population growth and advection of the upwelling preferred epipelagic species. Abundance weight (Aw) value further helped to understand the mode of distribution of the chaetognath community around the upwelling locations. The variation in the depth-weighted average values of different species between the upwelling and non-upwelling sites helped to identify the dissimilarity in their coupling with the abiotic components. As this eastern boundary current region further draws research interest as one of the major natural oxygen deficient system in the global ocean, the role of this hypoxia was shelved separately from the influence of upwelling in the heterogeneity of distribution of chaetognaths. In our study, two mesopelagic species Eukrohnia fowleri and E. minuta were identified as the indicator species of this upwelling process. Our observation suggests that the temporal physical event (upwelling) plays a decisive role in the heterogeneity of the spatial abundance, community composition and diversity of chaetognaths in this least studied eastern boundary current system.

The cumulative residual entropy (CRE), introduced by Rao et al. (2004) [23] , is viewed as a dynamic measure of uncertainty. Recently Asadi and Zohrevand (2007) [2] proposed a dynamic form of CRE, namely dynamic cumulative residual entropy (DCRE), and discussed some of its properties. The present paper addresses the question of extending the definition of DCRE to bivariate setup and study its properties. We also look into the problem of characterising certain bivariate models using the functional form of the DCRE. Further, we define new classes of life distributions based on this measure.

Recently, Nair and Rajesh (2000) proposed a measure to describe the failure pattern of components/devices in terms of the geometric mean of the residual life. This measure find applications in modeling life time data. In the present work we provide a nonparametric kernel-type estimator for the geometric vitality function, both in the case of complete and censored samples. The properties of the estimator, under certain regularity conditions, are studied. The performance of the estimator is compared with the empirical estimator using a real data set and simulation studies are carried out using the Monte Carlo method.

The Generalized Cumulative Entropy for residual life time (GCRE), introduced by Kumar and Taneja (Statist Probab Lett 81:1072–1077, 2011), is viewed as a dynamic measure of uncertainty. The present paper addresses the question of extending this measure to higher dimensions and study its properties. It is shown that the proposed measure uniquely determines the distribution. We use this measure to characterize some bivariate lifetime models. Further, we define a new classes of life distributions using this measure and various properties of these classes are also studied.

The Gulf of Mannar and the Palk Bay, located between India and Sri Lanka, are the two least studied marine environments in the northern Indian Ocean. We hypothesis, perceptible physical barriers that exist between the deep Gulf of Mannar and shallow Palk Bay, and seasonally reversing surface circulation patterns in the region have a concerted effect on the ecology of these oceanographically important areas. In the present study, data collected from 30 locations in the Gulf of Mannar and the Palk Bay in March 2010 (Spring Intermonsoon), September 2010 (Southwest Monsoon) and January 2011 (Northeast Monsoon) were used to investigate the role of ocean currents in molding mesozooplankton community characteristics in these, geographically closer and ecologically important transitional zones. Spatial difference in salinity was evident in the area with consistently higher values in the Gulf of Mannar as compared to the Palk Bay. The surface salinity was maximal during the Southwest Monsoon followed by the Spring Intermonsoon, and the Northeast Monsoon. These variations in salinity were closely linked with the seasonally reversing ocean currents as revealed in MIKE 21 flow model results. The mesozooplankton community dominated by copepods showed significant difference in species richness between the Gulf of Mannar (81 species) and the Palk Bay (63 species). Non-metric Multidimensional Scaling (NMDS) and Agglomerative Hierarchical Cluster Analysis (AHCA) on Bray–Curtis copepod similarity clearly estranged the Gulf of Mannar and the Palk Bay waters during the Spring Intermonsoon, and the Northeast Monsoon, attributable to the truancy of durable mixing typical of these seasons. In contrast, aided by strong currents, the increased mixing resulted in a homogenous copepod population in the Gulf of Mannar and the Palk Bay during the Southwest Monsoon. Furthermore, the indicator and dominant species analysis for copepods divulged the spatial heterogeneity in species composition during the Spring Intermonsoon and the Northeast Monsoon periods. Multivariate Redundancy Analyses showed salinity as the most important variable accountable for the observed variance in copepod distribution. In general, the copepod community in the Gulf of Mannar was composed both of coastal and offshore species whereas, coastal species largely inhabited the Palk Bay. This kind of a study depicting zooplankton community organization as governed by seasonally reversing monsoon circulation patterns forms the first record from the Indian coastal waters. The findings attain absolute significance considering its ecological implications on oceanographically transitional systems like the Gulf of Mannar, and the Palk Bay.

In the present paper, we propose nonparametric estimators for the Renyi’s information measure for the residual lifetime distribution based on complete and censored data. This measure plays important roles in reliability and survival analysis in connection with modeling and analysis of life time data. Asymptotic properties of the estimators are established under suitable regularity conditions. Monte-Carlo simulation studies are carried out to compare the performance of the estimators using the mean-squared error. The methods are illustrated using real data sets.

The Gulf of Mannar (GoM) and the Palk Bay (PB) are two least studied marine environments located between India and Sri Lanka. The environmental and smaller plankton (0.2–20 μm) data from 30 locations in the GoM and PB during the northeast monsoon (November–February) are presented in this paper. Coastal currents during the study period was from the east to west and as a result, the PB had Bay of Bengal (BoB) waters, which was low saline (av. 28.98 ± 1.34) as compared to the GoM (av. 31.96 ± 0.58). The BoB waters caused significantly higher turbidity in the PB (av. 7.84 ± 13.59 NTU) as compared to the GoM (av. 1.76 ± 1.38 NTU). Multivariate analyses of hydrographical parameters demarcated two separate clusters in the study area clearly segregating the GoM and PB. This was mainly due to the physical barriers (Rameswaram Island, Ramsethu and Mannar Island) that inhibit the mixing of waters between the GoM and PB. The fluorescence microscopy and flow cytometry data showed a high abundance of picoeukaryotes, heterotrophic bacteria and autotrophic nanoplankton in the GoM whereas, Synechococcus and heterotrophic nanoplankton were higher in the PB. The picoplankton and nanoplankton carbon biomass was higher in the GoM (av. 62.2 mgC m − 3 ) as compared to the PB (av. 47.6 mgC m − 3 ). The carbon biomass in the GoM and PB was mainly contributed by nanoplankton (> 70%) signifying their trophic preference in the study area. The carbon contribution of different plankton components in the GoM was autotrophic nanoplankton > heterotrophic bacteria > heterotrophic nanoplankton > Synechococcus > picoeukaryotes. On the other hand, heterotrophic nanoplankton was the second most dominant component in the PB followed by heterotrophic bacteria, Synechococcus and picoeukaryotes. The redundancy analysis (RDA) showed that picoeukaryotes, heterotrophic bacteria and autotrophic nanoplankton are positively correlated with salinity and nitrate, whereas Synechococcus and heterotrophic nanoplankton are positively correlated with turbidity, phosphate and dissolved oxygen. The data presented in this paper forms the first information on the relative trophic preference of various fractions of smaller plankton in Indian coastal waters.

Hydrography of the eastern Arabian Sea and associated chemical and biological responses were studied during the withdrawal phase of summer monsoon 2003. The shelf region off the southwest coast of India (10°N–15°N) continued to exhibit upwelling of colder ( 2.0 μM, phosphate >0.8 μM, silicate >4.0 μM) and relatively low oxygenated waters (~180 μM). The vertical advection of nutrients, coupled with anthropogenic terrestrial inputs, enhanced the levels of chlorophyll and primary productivity near the coastal margin off Cochin. The influence of both natural and anthropogenic nutrient loadings on the coastal system of the western continental shelf of India leads to eutrophication and hypoxia with negative impacts on the environment in general and fisheries in particular.

Phytoplankton studies in early 1970s have shown the annual dominance of diatoms and a seasonal abundance of Trichodesmium in the lower reaches of the Cochin backwaters (CBW) and adjacent coastal Arabian Sea during the pre-summer monsoon period (February to May). Surprisingly, more recent literature shows a complete absence of Trichodesmium in the CBW after 1975 even though their seasonal occurrence in the adjacent coastal Arabian Sea continued without much change. In order to understand this important ecological feature, we analyzed the long-term water quality data (1965-2005) from the lower reaches of the CBW. The analyses have shown that salinity did not undergo any major change in the lower reaches over the years and values remained30 throughout the period. In contrast, a tremendous increase was well marked in levels of nitrate (NO(3)) and phosphate (PO(4)) in the CBW after 1975 (av. 15 and 3.5 μM, respectively) compared with the period before (av. 2 and 0.9 μM, respectively). Monthly time series data collected in 2004-2005 period from the lower reaches of the CBW and coastal Arabian Sea have clearly shown that the physical characteristics like salinity, temperature, water column stability, and transparency in both regions are very similar during the pre-summer monsoon period. In contrast, the nutrient level in the CBW is several folds higher (NO(3), 8(;) PO(4), 4; SiO(4), 10; and NH(4), 19 μM) than the adjacent coastal Arabian Sea (NO(3), 0.7; PO(4), 0.5; SiO(4), 0.9; and NH(4), 0.6 μM). The historic and fresh time series data evidences a close coupling between enriched levels of nutrients and the absence of Trichodesmium in the Cochin backwaters.