An integrated buoy-satellite based coastal water quality nowcasting system: India's pioneering efforts towards addressing UN ocean decade challenges

The Indian coastal waters are stressed due to a multitude of factors, such as the discharge of industrial effluents, urbanization (municipal sewage), agricultural runoff, and river discharge. The coastal waters along the eastern and western seaboard of India exhibit contrasting characteristics in terms of seasonality, the magnitude of river influx, circulation pattern, and degree of anthropogenic activity. Therefore, understanding these processes and forecasting their occurrence is highly necessary to secure the health of coastal waters, habitats, marine resources, and the safety of tourists. This article introduces an integrated buoy-satellite based Water Quality Nowcasting System (WQNS) to address the unique challenges of water quality monitoring in Indian coastal waters and to boost the regional blue economy. The Indian National Centre for Ocean Information Services (INCOIS) has launched a first-of-its-kind WQNS, and positioned the buoys at two important locations along the east (Visakhapatnam) and west (Kochi) coast of India, covering a range of environmental conditions and tourist-intensive zones. These buoys are equipped with different physical-biogeochemical sensors, data telemetry systems, and integration with satellite-based observations for real-time data transmission to land. The sensors onboard these buoys continuously measure 22 water quality parameters, including surface current (speed and direction), salinity, temperature, pH, dissolved oxygen, phycocyanin, phycoerythrin, Coloured Dissolved Organic Matter, chlorophyll-a, turbidity, dissolved methane, hydrocarbon (crude and refined), scattering, pCO2 (water and air), and inorganic macronutrients (nitrite, nitrate, ammonium, phosphate, silicate). This real-time data is transmitted to a central processing facility at INCOIS, and after necessary quality control, the data is disseminated through the INCOIS website. Preliminary results from the WQNS show promising outcomes, including the short-term changes in the water column oxic and hypoxic regimes within a day in coastal waters off Kochi during the monsoon period, whereas effluxing of high levels of CO2 into the atmosphere associated with the mixing of water, driven by local depression in the coastal waters off Visakhapatnam. The system has demonstrated its ability to detect changes in the water column properties due to episodic events and mesoscale processes. Additionally, it offers valuable data for research, management, and policy development related to coastal water quality.

Winter phytoplankton size classes in the Northeastern Arabian Sea based on in-situ and remote sensing methods

Phytoplankton size classes (PSCs) are important in marine ecosystems because they organise the food chain and trophic pathways, which determine the overall biological environment. Based on three FORV Sagar Sampada cruises, the current study provides changes in PSCs in the Northeastern Arabian Sea (NEAS; north of 18 N) during different phases of the Northeast Monsoon [NEM (November-February)]. During all three phases of NEM such as early (November), peak (December), and late (February), in-situ chlorophyll-a fractionation data revealed that nanoplankton (2-20 μm) predominated, followed by microplankton (>20 μm) and picoplankton (0.2-2.0 μm). This was primarily because winter convective mixing in the NEAS maintains only a moderate level of nutrients in the surface mixed layer, which is more conducive to the dominance of nanoplankton. Brewin et al. (2012) and Sahay et al. (2017) have satellite-based PSC estimation algorithms; the former was developed for the entire Indian Ocean, while the latter is a modification of the former for the Noctiluca bloom-infested NEAS, with a claim that such blooms are typical of the NEM. When current in-situ PSCs data were compared to algorithm-based NEM data, Brewin et al. (2012) revealed a more realistic PSCs contribution pattern, especially in oceanic waters, with nanoplankton predominating except during early NEM. But the PSCs data from Sahay et al. (2017) showed a high degree of variation from the in-situ data, demonstrating the dominance of pico- and microplankton and a notably small contribution from the nano phytoplankton. The current study showed that Sahay et al. (2017) is inferior to Brewin et al. (2012) at quantifying PSCs in the NEAS without Noctiluca blooms, and provided evidence to show that Noctiluca blooms are not a typical feature of the region during the NEM.

Trait-based and taxonomic macrofauna community patterns in the upwelling ecosystem of the southeastern Arabian sea

Coastal upwelling that occurs in the eastern Arabian Sea (EAS) drive the complex dynamics of the food chain. Macrofauna plays a key role in the functioning of coastal ecosystems, but few studies explored the taxonomic and functional patterns of macrofaunal communities under the influence of upwelling. These patterns have been investigated in this study by sampling macrofauna and environmental variables during March-December 2012 across six depths (13-100 m) over the continental shelf off Kochi, south EAS. Upwelling, set over outer shelf prior to March, occupies the entire shelf by May, peaked during June-July and withdrew rapidly by September. A total of 203 macrofaunal taxa were collected in this study. Multivariate analysis revealed that the macrofaunal composition showed a spatiotemporal variation. Taxonomic diversity increases from nearshore to mid shelf whereas abundance and biomass decreased. Macrobenthic functioning, assessed through Biological Trait Analyses, displayed similar trait modalities between depths and seasons but abundance driven differences in trait expression revealed important habitat filtering. Increase in organic matter and decrease in dissolved oxygen influenced by upwelling and the spatial variation in sediment texture were the strongest drivers of the macrofaunal taxonomic pattern. We suggest that taxonomic and biological trait information needs to be considered in ecological studies as it provides a better understanding of how biodiversity responds to and interacts with environmental changes.

Ciguatera in the Indian Ocean with Special Insights on the Arabian Sea and Adjacent Gulf and Seas: A Review

The dinoflagellates of the genus Gambierdiscus are found in almost all oceans and seas between the coordinates 35° N and 35° S. Gambierdiscus and Fukuyoa are producers of ciguatoxins (CTXs), which are known to cause foodborne disease associated with contaminated seafood. The occurrence and effects of CTXs are well described in the Pacific and the Caribbean. However, historically, their properties and presence have been poorly documented in the Indian Ocean (including the Bay of Bengal, Andaman Sea, and the Gulf). A higher occurrence of these microorganisms will proportionately increase the likelihood of CTXs entering the food chain, posing a severe threat to human seafood consumers. Therefore, comprehensive research strategies are critically important for developing effective monitoring and risk assessments of this emerging threat in the Indian Ocean. This review presents the available literature on ciguatera occurrence in the region and its adjacent marginal waters: aiming to identify the data gaps and vectors.

Coccolithophores: an environmentally significant and understudied phytoplankton group in the Indian Ocean

Coccolithophores are unique primary producers in the ocean with the ability to calcify. They are known to produce calcareous scales, which form the significant part of calcite oozes or chalk deposits on the seafloor. Coccolithophores are very noteworthy and they are explored to a great extent as nannofossils to reconstruct the past climate. Calcite plates in coccolithophores make them a vital tool in global climate change studies specifically with ocean acidification. These microscopic plants are the major contributor of the carbonate rain that controls the inorganic carbon pump in the ocean, which in turn influences both carbon and carbonate cycles. The emergence of advanced techniques enables us to study the biological aspects of this pelagic calcifier with improved precision. But still, they are understudied world over compared to any other phytoplankton groups. The northern Indian Ocean, being landlocked in three sides and vulnerable to climate change and ocean acidification, severely lacks focused studies on coccolithophores, though the US JGOFS in the 1990s have outlined the ecological significance of coccolithophores in the Arabian Sea. This paper reviews and outlines our understanding of coccolithophores as well as the nix in the northern Indian Ocean.

Variation in phytoplankton community and its implication to dimethylsulphide production at a coastal station off Goa, India

Seasonal hypoxia/suboxia (at times anoxia) towards the end of Southwest monsoon (SWM; June to September) at the coastal time series site off Goa, West coast of India was found to influence the dynamics of phytoplankton biomass, community structure and production of climatically active gas, dimethylsulphide (DMS). In this diatom dominated study region, high DMS production in the subsurface waters during late SWM might possible be attributed to the stress experienced by micro- and macro-algae from the prevailing low oxygen subsurface waters through different pathways specifically believed to be via methylation pathway (see Schafer et al., 2010). Based on laboratory experiments, we hypothesize presence of floating seaweeds mostly Sargassum species washed from the shore to the study site to contribute sizably to DMS production in the water column as they sink and degrade during the senescence phase. However, we are yet to address its loss/emission processes across the oxic-hypoxic boundary of seasonal (and permanent) oxygen minimum zone of the northern Indian Ocean, which is important from the viewpoint of global climate change.

Continental outflow of anthropogenic aerosols over Arabian Sea and Indian Ocean during wintertime: ICARB-2018 campaign

Chemical characterisation of atmospheric aerosols over Arabian Sea (AS) and Indian Ocean (IO) have been carried out during the winter period (January to February 2018) as part of the Integrated Campaign for Aerosols, gases and Radiation Budget (ICARB-2018). Mass concentrations of organic carbon (OC), elemental carbon (EC), water soluble and insoluble OC (WSOC, WIOC), primary and secondary OC (POC, SOC), water-soluble inorganic ions and trace metals have been estimated with a view to identify and quantify the major anthropogenic pollutants affecting the oceanic environments. Aerosol mass loading was found to exhibit strong spatial heterogeneity (varying from 13 to 84 μg m^-3), significantly modulated by the origin of air-mass trajectories. Chemical analysis of aerosols revealed the presence of an intense pollution plume over south-eastern coastal Arabian Sea, near to south-west Indian peninsula (extending from ~ 12°N to 0° at 75°E) with a strong latitudinal gradient (~3 μg m^-3/deg. from north to south) dominated by anthropogenic species contributing as high as 73% (38% nss-SO₄^2-, 24.2% carbonaceous aerosols (21% Organic Matter, 3.2% EC) and 10% NH₄⁺). Anthropogenic signature over oceanic environment was also evident from the dominance and high enrichment of elements like Zn, Cu, Mn and Pb in trace metals. Long-range transport of air-masses originating from Indo Gangetic Plains and its outflow regions in Bay of Bengal, has been seen over Arabian Sea during winter, that imparted such strong anthropogenic signatures over this oceanic environment. Comparison with previous cruise studies conducted nearly two decades ago shows a more than two-fold increase in the concentration of nss-SO₄^2-, over the continental outflow region in Arabian Sea.

Impacts of Zn and Cu enrichment under ocean acidification scenario on a phytoplankton community from tropical upwelling system

Increasing dissolution of CO₂ in the surface ocean is rapidly decreasing its pH and changing carbon chemistry which is further affecting marine biota in several ways. Phytoplankton response studies under the combination of elevated CO₂ and trace metals are rare. We have conducted two consecutive onboard incubation experiments (R. V. Sindhu Sadhana; August 2017) in the eastern Arabian Sea (SW coast of India) during an upwelling event. A nutrient enriched diatom bloom was initiated onboard and grown under ambient (≈400 μatm, A-CO₂) and high CO₂ levels (≈1000 μatm; H-CO₂) with different zinc (Zn; 1 nM) and copper (Cu) concentrations (1 nM, 2 nM and 8 nM). Phytoplankton community composition and the dominant genera were different during these two experiments. CO₂ enrichment alone did not show any significant growth stimulating impact on the experimental community except enhanced cell density in the first experiment. Addition of Zn at A-CO₂ level revealed no noticeable responses; whereas, the same treatment under H-CO₂ level significantly reduced cell number. Considerably high protein content under H-CO₂+Zn treatment was possibly counteracting Zn toxicity which also caused slower growth rate. Cu addition did not show any noticeable impact on growth and biomass production except increased protein content as well as decreased carbohydrate: protein ratio. This can be attributed to relatively higher protein synthesis than carbohydrate to alleviate oxidative stress generated by Cu. The centric diatom Chaetoceros and toxin producing pennate diatom Pseudo-nitzschia showed no significant response to either CO₂ or Zn enrichment. Large centric diatom Leptocylindrus and Skeletonema responded positively to Zn addition in both CO₂ levels. The former species showed the most sensitive response at the highest Cu and H-CO₂ treatment; whereas, the pennate diatoms Nitzschia and Pseudo-nitzschia (toxigenic diatom) showed higher resilience under elevated CO₂ and Cu levels. This observation indicated that in future ocean, increasing CO₂ concentrations and trace metal pollution may potentially alter phytoplankton community structure and may facilitate toxigenic diatom bloom in the coastal waters.

Metagenomic data on bacterial diversity profiling of Arabian sea sediment by amplicon sequencing

This data is about the microbial community genome analysis of Arabian sea sediment by Illumina sequencing by targeting the hypervariable region V3 of 16S rRNA gene. The data analysis revealed the existence of numerous unknown sequences, indicating a large unexploited bacterial diversity in the area. The raw sequence data used for analysis is available in NCBI under the Sequence Read Archive (SRA) with the BioProject No. PRJNA397165 and SRA accession number SRP125840.

Characterization of oceanic Noctiluca blooms not associated with hypoxia in the Northeastern Arabian Sea

Intense blooms of the heterotrophic dinoflagellate, green Noctiluca scintillans, have been reported annually in the Northern Arabian Sea since the early 2000s. Although not known to produce organic toxins, these blooms are still categorized as a harmful due to their association with massive fish mortalities. Recent work has attributed these blooms to the vertical expansion of the oxygen minimum zone, driven by cultural eutrophication from major coastal cities in western India. As diatoms are preferred prey of green Noctiluca scintillans, more frequent blooms of this mixotroph will likely impact the productivity of important fisheries in the region. The present study uses a satellite algorithm to determine the distribution of both diatom and green Noctiluca blooms in the Northeastern Arabian Sea from 2009 to 2016. The results from shipboard microscopy of phytoplankton community composition were used to validate the satellite estimates. The satellite algorithm showed 76% accuracy for detection of green Noctiluca and 92% for diatoms. Shipboard measurements and data from biogeochemical-Argo floats were used to assess the relationship between oxygen concentrations and green Noctiluca blooms in the Northeastern Arabian Sea. Regardless of the presence of a Noctiluca bloom, the dissolved oxygen in the photic zone was always >70% saturated, with an average oxygen saturation >90%. The variability in the relative abundance of diatoms and green Noctiluca is not correlated with changes in oxygen concentration. These findings provide no evidence that cultural eutrophication has contributed to the decadal scale shifts in plankton composition in the Northeastern Arabian Sea oceanic waters. Conversely, the climatic warming of surface waters would have intensified stratification, thereby reducing net nutrient flux to the photic zone and decreasing silicate to nitrate ratios (Si:N); both factors that could increase the competitive advantage of the mixotroph, green Noctiluca, over diatoms. If so, the decadal-scale trajectory of phytoplankton community composition in the Northeastern Arabian Sea may be a harbinger of future climate-driven change in other productive oceanic systems.

Community composition of ammonia-oxidizing archaea from surface and anoxic depths of oceanic oxygen minimum zones

Ammonia-oxidizing archaea (AOA) have been reported at high abundance in much of the global ocean, even in environments, such as pelagic oxygen minimum zones (OMZs), where conditions seem unlikely to support aerobic ammonium oxidation. Due to the lack of information on any potential alternative metabolism of AOA, the AOA community composition might be expected to differ between oxic and anoxic environments. This hypothesis was tested by evaluating AOA community composition using a functional gene microarray that targets the ammonia monooxygenase gene subunit A (amoA). The relationship between environmental parameters and the biogeography of the Arabian Sea and the Eastern Tropical South Pacific (ETSP) AOA assemblages was investigated using principal component analysis (PCA) and redundancy analysis (RDA). In both the Arabian Sea and the ETSP, AOA communities within the core of the OMZ were not significantly different from those inhabiting the oxygenated surface waters above the OMZ. The AOA communities in the Arabian Sea were significantly different from those in the ETSP. In both oceans, the abundance of archaeal amoA gene in the core of the OMZ was higher than that in the surface waters. Our results indicate that AOA communities are distinguished by their geographic origin. RDA suggested that temperature (higher in the Arabian Sea than in the ETSP) was the main factor that correlated with the differences between the AOA communities. Physicochemical properties that characterized the different environments of the OMZ and surface waters played a less important role, than did geography, in shaping the AOA community composition.