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In contrast to the Pacific and Atlantic Oceans, the Indian Ocean has lacked in-situ observations of wind profiles over open sea areas for decades. In 2021, a shipborne coherent Doppler lidar (CDL) was used to observe in-situ wind profiles in the eastern tropical Indian Ocean. This equipment successfully captured low-level jets (LLJs) in the region, and their characteristics were thoroughly analyzed. Results reveal that the observed wind speed of LLJs in the eastern Indian Ocean ranges from 6 ms−1 to 10 ms−1 during the boreal winter and spring seasons, showing a height range of 0.6 to 1 km and two peak times at 0800 and 2000 UTC. This wind shear is weaker than that in land or offshore areas, ranging from 0s−1 to 0.006s−1. Moreover, the accuracy of the CDL data is compared to that of ERA5 data in the study area. The results indicate that the zonal wind from ERA5 data significantly deviated from the CDL measurement data, and the overall ERA5 data are substantially weaker than the in-situ observations. Notably, ERA5 underestimates northwestward LLJs. [ABSTRACT FROM AUTHOR]

China is significantly impacted by torrential rainfall induced by tropical cyclone (TC) activity particularly in South China (SC) and East China (EC). This study delineates the distinct TC activities associated with these regions over the western North Pacific (WNP). Our analysis reveals that in SC, positive TC rainfall is largely attributed to a significant increase in TC genesis within the South China Sea (SCS), along with predominantly westward TC tracks. In EC, rainfall patterns are influenced by a northward extension of both TC genesis and tracks, notably affecting areas such as the Yangtze River delta and Shandong Province. This study further explores the modulation effects of preceding sea surface temperature (SST) anomalies in the eastern Indian Ocean (EIO) and the eastern Pacific on summer TC rainfall in SC and EC. We find that autumn warming in the EIO enhances subsequent summer TC rainfall in SC by modulating cyclonic anomalies along with favorable conditions for TC genesis and convection over the SC coast, while simultaneously diminishing convections over EC. Meanwhile, La Niña events lead to increased TC rainfall in EC during the subsequent summer by modifying the large-scale background circulation. This modification promotes TC formation at higher latitudes and facilitates more TCs moving northwestward directly toward EC. This research provides valuable insights into the distinct underlying mechanisms driving regional TC rainfall variation, highlighting the importance of region-specific analyses in understanding and forecasting TC impacts in China. [ABSTRACT FROM AUTHOR]

The Eastern Indian Ocean (EIO) is an ideal region to explore the variability and controlling mechanisms of the seawater carbonate system and their potential influence on global climate change due to the distinctive environmental features, while studies in the EIO is far from sufficient. The spatiotemporal distributions of pH, dissolved inorganic carbon (DIC), alkalinity (Alk), and partial pressure of carbon dioxide (pCO2) were investigated in the EIO during autumn 2020 and spring 2021. The respective quantitative contributions of different controlling processes to DIC were further delineated. Significant seasonal variations were observed in the study area. Overall, the surface pH was lower and DIC, Alk, and pCO2 were higher during spring 2021 than during autumn 2020. The pH generally decreased from east to west during autumn 2020, whereas it decreased from north to south during spring 2021. The low values of DIC and Alk that were detected in the Bay of Bengal in these two seasons were mainly attributed to the influence of river inputs. Coastal upwelling during monsoon periods led to higher pCO2 and DIC values near Sumatra and Sri Lanka during spring 2021. The relationships of carbonate system parameters with different types of nutrients and different sized chlorophyll-a in the two seasons indicated the shifts of nutrients utilized by the phytoplankton, and phytoplankton species dominated the carbonate system variabilities. In vertical profiles, carbonate system parameters showed strong correlations with other physical and biogeochemical parameters, and these correlations were more robust during spring 2021 than during autumn 2020. The average sea-air flux of CO2 was 10.00 mmolm-2 d-1 during autumn 2020 andwas 16.00 mmolm-2 d-1 during spring 2021, which revealed that the EIO served as a CO2 source during the study period. In addition, the separation of different controlling processes of DIC indicated stronger mixing processes, less CaCO3 precipitation, more intensive sea-air exchange, and weaker photosynthesis during spring 2021 than during autumn 2020. [ABSTRACT FROM AUTHOR]

Mixed Layer Depth (MLD) plays an important role in various aspects of oceanography. MLD has a characteristic parameter value that is uniform with depth. MLD has an important role for local, regional, and global phenomena. Indonesia, which is surrounded by the East Indian Ocean, will be directly influenced by the dynamics of MLD. This study aimed to analyze seasonal variability and MLD between years. Mixed layer depth data from the ARMOR3D Dataset Copernicus-Marine Environment Monitoring Service was used for MLD analysis with a threshold of 0.2°C for temperature. Wavelet analysis showed that MLD variability in the eastern Indian Ocean spans from intra-seasonal to interannual scales. Time series analysis showed a complex relationship between MLD and SST in the annual and interannual periods which indicates a different process. The MLD monthly climatology at point 90E, 0 showed the depth of mixed layers is deeper during the east monsoon (JJA-SON) ranging from 50-65 m compared to the west monsoon (DJF-MAM) which has a range of 20-40 m. Spatially the MLD in the south of the equator is deeper than in the north. Interannually, MLD is heavily influenced by the Indian Ocean Dipole. MLD depth is deeper in nIOD with a maximum depth in the range of 100 m compared to pIOD. MLD with maximum depth in the strong nIOD phase is around the equator and the pIOD phase is south of the equator. The study also showed that inter-annual variability in regions around the mainland showed a stronger response. [ABSTRACT FROM AUTHOR]

As the only low‐latitude connection along the return branch of the Great Conveyor Belt, the Indonesian Throughflow (ITF) plays an important role in the large‐scale ocean–atmosphere interaction in the tropical region. However, the heat transport processes of the ITF along the outflow pathway in the eastern Indian Ocean over the recent geologic period is still debated. In this study, by using Mg/Ca ratios of the surface‐dwelling and thermocline‐dwelling planktonic foraminifera Globigerinoides ruber and Pulleniatina obliquiloculata, we reconstruct sea surface temperature and thermocline water temperature (TWT), and thermocline structure at two sites in the main outflow path of the ITF in the eastern Indian Ocean for the last 160 Kyr, and compare these new data with those from two cores in the central Indo‐Pacific Warm Pool. Our results show that, on the orbital time scale, the thermocline structure changes above the equatorial 90°E Ridge mimic those of the eastern Timor Sea, indicating that the ITF vertical structure remained unchanged during its penetration into the Indian Ocean. The TWT in the equatorial western Pacific and eastern Indian Ocean presents similar change trend, suggesting that the ITF is likely to be an important route for thermocline water transport into the Indian Ocean. However, the vertical structure of the ITF varied through time, reflecting the effects of sea level and orbitally‐driven monsoonal activity. This impacted heat transport processes, resulting in changes in the surface water temperature along the outflow pathway in the eastern Indian Ocean. Key Points: Sea surface and thermocline water temperatures and vertical structure of the Indonesian Throughflow (ITF) outflow for the last 160 Kyr were reconstructedVertical structure of the ITF remained unchanged during its penetration into the Indian OceanVariation of the ITF through time impacted the heat transport processes along the outflow pathway in the eastern Indian Ocean [ABSTRACT FROM AUTHOR]

The widespread distribution of Prochlorococcus can be attributed to the extensive genetic diversity that allows them to adapt to various oligotrophic environments. We investigated the adaptation of Prochlorococcus to nutrient environments in the surface eastern Indian Ocean (EIO, 16.5°N to 20°S, 88°E) in November 2018. The growth rate of the Prochlorococcus population and its response to macronutrient enrichments (NH4+andPO43− ${{\text{NH}}_{4}}^{+}\,\text{and}\,{{\text{PO}}_{4}}^{3-}$) and the abundance of functional gene modules related to nutrient utilization were examined by on‐deck incubation experiments and metagenomic analysis, respectively. Although the dissolved inorganic nitrogen was depleted (∼58 nM) and the Prochlorococcus populations were dominated by the high‐light‐adapted II ecotype, Prochlorococcus populations showed distinct physiological patterns, especially the response to macronutrient enrichments, indicating their adaptation to local nutrient environments. At the northernmost station in the Bay of Bengal, the significant increase in growth rate with macronutrient enrichments and the highest abundance of the phosphate starvation response two‐component regulatory system module indicated adaptation to phosphorus‐limited environments. In the southern EIO, the insignificant increase in growth rate with macronutrient enrichment and higher abundance of the iron complex transport system module suggested adaptation to iron‐limited environments. However, genomic characteristics are not always associated with physiological characteristics. The abundance of the nitrate/nitrite transport system module was higher in the southern EIO, where the growth of Prochlorococcus relied on regenerated nitrogen sources as revealed by incubation experiments. These results reflected the complexity of Prochlorococcus adaptation especially in chronically oligotrophic environments, which was better revealed by combining physiological and genomic analyses. Plain Language Summary: Prochlorococcus are the smallest but most abundant photosynthetic organisms on Earth. Their widespread distribution (40°N to 40°S) and dominance in global subtropical and tropical phytoplankton communities could be attributed to the extensive genetic diversity that allows them to adapt to various environments. Although the adaptation of Prochlorococcus to nutrient environments could be reflected by variation in the genome, this method sometimes masks the complexity of Prochlorococcus adaptation. In this study, we combined incubation experiments with metagenomic analysis to better understand Prochlorococcus adaptation in the eastern Indian Ocean, which is consistently nutrient‐depleted but has subtle variations in nutrient environments. The results showed that the Prochlorococcus population had three distinct physiological patterns in the study area. In particular, the distinct response to the additional nutrients in incubation experiments indicated their specific adaptations to local nutrient environments. Furthermore, by considering the physiological characteristics with the spatially varied abundance of functional genes related to nutrient acquisition, it was revealed that Prochlorococcus growth was limited by different nutrients (nitrogen, phosphorus or iron) across the study area. Our results suggested the complexity of Prochlorococcus adaptation to oligotrophic environments, which can be elucidated by considering both physiological and genomic characteristics. Key Points: Prochlorococcus had varied physiological and genomic characteristics as adaptations to nutrient environments in the eastern Indian OceanProchlorococcus adapted to phosphorus‐ and iron‐limited environments in the Bay of Bengal and southern eastern Indian Ocean, respectivelyThe adaptation of Prochlorococcus could be complex and better revealed by conducting both the physiological and genomic analyses [ABSTRACT FROM AUTHOR]

The Eastern Indian Ocean is a tectonically and geodynamically active region that has experienced deformations due to rifting, uplifting, and plume activity. The earlier Rayleigh wave studies in the East Indian Ocean were mainly focused on the structure of the Bay of Bengal, Ninety East Ridge, and Broken Ridge. The structure of other region of the East Indian Ocean is not much explored. In the present study, Rayleigh wave dispersion analysis is performed to observe the signatures of upper mantle deformation in terms of shear wave velocity of the East Indian Ocean using global search method. The fundamental mode Rayleigh wave group velocities are estimated between 15 and 100 s using the multiple filter technique. The group velocities of the raypaths that traverse the same region are clustered (E1–E8) to get an average dispersion curve. Using a genetic algorithm, each cluster's group velocities are inverted for shear velocity structure. The observed dispersion curve of E6, E7, and E8 indicates the lower group velocities between 35 and 100 s relative to E1, E2, E3, E4, and E5, with an average variation of about 0.07–0.18 km/s. The crustal thickness obtained in the study region is ~ 26 km and is due to the increased thickness of the lower crust (9.1–12.4 km) having Vs 3.95–4.04 km/s. The theoretical Vs have been calculated for serpentinite rock at uppermost lithospheric conditions and found to be similar to the Vs of the lower crust in the present study. Hence, it is assumed that unusual crustal thickness is due to the progressive development of the upper lithosphere formation (Ultramafic rock) into material (serpentinite rock) with crustal-like shear velocity or moderately lower than sub-Moho shears velocity. The undeformed lithosphere is evidenced by the high-velocity (Vs 4.62–4.77 km/s) layer beneath the Moho, whose thickness ranges from 41.3 to 51.6 km. The high-velocity lithosphere is followed by a low-velocity zone that extends up to 160 km; however, the variation in Vs (4.57–4.31 km/s) indicates that the low-velocity zone is deformed. [ABSTRACT FROM AUTHOR]

The Argo Abyssal Plain (AAP), south of Java and northwest of Australia in the tropical eastern Indian Ocean, is an oligotrophic region (low in chlorophyll and nutrients), downstream of the Indonesian throughflow. The processes that supply nitrogen to the AAP and support ecosystem production are unknown. Here we quantified lateral advection of particulate organic matter (POM) and the role of this advected POM in supplying new nitrogen (i.e., allochthonous nitrogen supply) to the mixed layer of the AAP using 14 yr of remotely sensed data, combined with sampling undertaken on a research cruise in February 2022. Our results indicate that the average net primary productivity of phytoplankton in this offshore oligotrophic region is 98.5 Gg C d−1 and that lateral advection transports 1.21 Gg C d−1 of particulate organic carbon (POC) into the region. We find that lateral advection of POM within the mixed layer supplies an annual average of 12% (95% C.I. = 5.2%–49%) of allochthonous "new" nitrogen supporting phytoplankton productivity, if regenerated to nutrients through microbial processes. Accounting for lateral transport in the deep euphotic zone, lateral transport supplies an average of 32% (10%–>100%) of new nitrogen, although this calculation is less certain due to inability to constrain subsurface POM fields. Our data suggest that lateral advection is a quantitatively important but not dominant source of nitrogen supporting new production. Overall, approximately half of the lateral transport is driven by transient eddies (mostly during winter) highlighting the importance of mesoscale circulation. Plain Language Summary: In most ocean regions, phytoplankton (microscopic algae that form the base of the ecosystem) are nitrogen limited. Nitrogen can enter the ecosystem through upwelling of deep waters, nitrogen fixation, or through lateral transport of particulate or dissolved organic matter which can be recycled through microbial processes. The Argo Abyssal Plain, between Indonesia and Australia, is an interesting low‐nutrient study site because it is downstream of the only tropical connection between the Pacific and Indian Oceans and is also the only known spawning site for southern bluefin tuna. In this study, we combine shipboard sampling with satellite remote sensing to investigate primary production and lateral organic matter transport in the Abyssal Argo Plain. We show that lateral transport (i.e., horizontal currents that transport matter from coastal regions) is an important source, though likely not a dominant source of nitrogen, for this deepwater basin. We also show that approximately half of this lateral nitrogen supply is derived from transient eddies (i.e., rotating currents that are basically storms in the ocean that can persist for weeks or months). Substantial uncertainty remains and ascertaining how the region will respond to climatic forcing will likely require multidisciplinary programs combining shipboard sampling with synthetic modeling tools. Key Points: Particulate organic carbon concentrations and net primary productivity in the Argo Abyssal Plain peak during Austral winterLateral advection is quantitatively important, but not the dominant source of nitrogen supporting phytoplankton new productionRemote‐sensing results suggest that most of the laterally advected organic matter in this region is eddy‐driven [ABSTRACT FROM AUTHOR]

Carbon monoxide (CO) is an indirect greenhouse gas and a crucial component of the global carbon cycle. The ocean is an important source of atmospheric CO, but the factors controlling the sources and sinks of CO in the marine environment remain uncertain. For the first time, the spatial distribution, production, and removal pathways of seawater CO (including photoproduction, dark production, microbial consumption, and sea‐to‐air exchange) were systematically investigated in the Eastern Indian Ocean. The abundance and component source of chromophoric dissolved organic matter (CDOM) dominated the photoproduction and dark production rates of CO, and the net CO production rate was 2.19 ± 0.71 nmol L−1 d−1 (mean ± SD). The ratio of CO photoproduction efficiencies (normalized by solar radiation) for ultraviolet B radiation (UVB): ultraviolet A radiation (UVA): photosynthetically active radiation (PAR) was 854: 39: 1, while UVA was the most significant contributor to surface CO photoproduction due to the stronger radiation intensity. In the mixed layer, UVB, UVA, and PAR were estimated to contribute 12% ± 5%, 38% ± 8%, and 50% ± 8% (mean ± SD) to CO photoproduction, respectively. The total removal of CO by microbial consumption (96%) and sea‐to‐air exchange (1%) accounted for 97% of the total production. Overall, the sources and sinks of CO kept a dynamic balance in the mixed layer. Our comprehensive approach provides in‐detail insights into the understanding of CO cycling processes in the Eastern Indian Ocean, which is scientifically important for understanding the bio‐geochemical cycling and climate effects of CO in the Eastern Indian Ocean, and also provides additional data support for the CO global cycle modeling studies. Plain Language Summary: The Eastern Indian Ocean is one of the world's most active monsoonal regions and an essential component of the Indian Ocean warm pool. In addition, there is an extensive oxygen minimum zone in the Eastern Indian Ocean. Despite the potential impact of this region on the global CO cycle, only a few studies have been carried out. Here, we explored the controlling factors leading to the heterogeneous distribution of CO in the surface seawater of the Eastern Indian Ocean by studying sources and sinks. We also simulated CO photoproduction in the mixed layer, where light attenuation affects wavebands differently, and evaluated the corresponding CO budget. This study provides in‐detail insights into the CO cycling processes in the Eastern Indian Ocean. Key Points: Ultraviolet A radiation and photosynthetically effective radiation were the primary drivers of CO photoproduction in the mixed layerDark production accounted for about 20% of the total CO production in the mixed layerMicrobial consumption could remove 99% of the seawater CO before it released into the atmosphere [ABSTRACT FROM AUTHOR]

The consequences of climate change may directly or indirectly impact the marine biosphere. Although ocean stratification has been recognized as one of the crucial consequences of ocean warming, its impacts on several critical aspects of marine microbes remain largely unknown in the Indian Ocean. Here, we investigate the effects of water stratification, in both surface and subsurface layers, on hydrogeographic parameters and bacterioplankton diversity within the equatorial eastern Indian Ocean (EIO). Strong stratification in the upper 200 m of equatorial EIO was detected with evidential low primary productivity. The vertical bacterioplankton diversity of the whole water columns displayed noticeable variation, with lower diversity occurring in the surface layer than in the subsurface layers. Horizontal heterogeneity of bacterioplankton communities was also in the well-mixed layer among different stations. SAR11 and Prochlorococcus displayed uncharacteristic low abundance in the surface water. Some amplicon sequence variants (ASVs) were identified as potential biomarkers for their specific depths in strongly-stratified water columns. Thus, barriers resulting from stratification are proposed to function as an 'ASV filter' to regulate the vertical bacterioplankton community diversity along the water columns. Overall, our results suggest that the effects of stratification on the structure and diversity of bacterioplankton can extend up to the bathypelagic zone in the strongly-stratified waters of the equatorial EIO. This study provides the first insight into the effect of stratification on the subsurface microbial communities in the equatorial eastern Indian Ocean. [ABSTRACT FROM AUTHOR]

Uropterygius cyamommatus, new species, is described based on nine specimens from limestone anchialine caves in Christmas Island and Panglao Island. This species is a small-sized, elongated moray eel belonging to the uniform brown-coloured species group of the genus. It differs from all congeners of Uropterygius in having very small eyes (3.0-4.6% of head length), a relatively long tail (56.3-61.1% of total length), and a comparatively large number of vertebrae (total vertebrae 141-149). The new species represents the first-recorded moray eel that inhabits anchialine caves. [ABSTRACT FROM AUTHOR]

Genus Echinorhinus is a very poorly known group of deep-water sharks with widespread but patchy distribution in all major oceans. Echinorhinid sharks consist of two valid species, Echinorhinus brucus is reported more commonly in the Indian Ocean region than its congeneric species, E. cookei. Regular data collections in major shark landing sites in Indonesia have documented additional records of both E. brucus and E. cookei from the Indonesian waters, with updated information on their distributions in the Indian Ocean. [ABSTRACT FROM AUTHOR]

The eastern Indian Ocean (EIO) is characterized by oligotrophic surface water with abundant dust supply, and thus, this environment is considered to provide a favorable niche for cyanobacterial diazotrophs. However, direct measurements have reported low nitrogen fixation with the dominance of heterotrophic diazotrophs, suggesting that the EIO has unique geophysical features and nutrient supplies controlling diazotrophy, in contrast to those in the Atlantic and Pacific Oceans. In this study, we investigated the activity and community of diazotrophs across the EIO from the Bay of Bengal to the west of Australia. Low nitrogen fixation was observed broadly in the EIO (26.1–75.6 μmol N m−2 d−1), except in the west of Australia (82–286 μmol N m−2 d−1). Although the surface nitrate concentration was low in the EIO, the upward nitrate flux was higher because of the shallower nitracline than that in other oligotrophic oceans. This created widespread conditions with low aeFe:N (supply ratio of aerosol iron to nitrogen), resulting in low nitrogen fixation rates. NifH amplicon sequencing demonstrated the dominance of heterotrophic diazotrophs widely in the EIO, with spatial segregation from cyanobacterial diazotrophs (Trichodesmium, UCYN‐A1). In general, cyanobacterial diazotrophs were abundant in the surface waters of the Bay of Bengal and west of Australia with a high aeFe:N supply, whereas heterotrophic diazotrophs were dominant in other broad regions. This finding demonstrates that the shallow nitracline and associated high upward nitrate supply are key factors for the unique diazotrophy in the EIO. Plain Language Summary: Biological nitrogen fixation is a major source of bioavailable nitrogen in the ocean. The eastern Indian Ocean (EIO) has nitrate‐poor surface waters with a replete dust supply from the continents. Thus, it has been considered to provide a niche preferable for cyanobacterial diazotrophs. However, previous direct measurements have shown low nitrogen fixation and dominance of heterotrophic diazotrophs, suggesting the distinct regulation of diazotrophy in the EIO from that in the Atlantic and Pacific Oceans. Here, we examined the activity and community of diazotrophs in the EIO from the Bay of Bengal to the west of Australia. Nitrogen fixation was generally low in the study area, except in the west of Australia. Low nitrogen fixation was related to shallow nitracline and associated low supply ratio of aerosol iron to nitrogen. We also found the spatial segregations of diazotroph communities in response to regional differences in biogeochemical factors such as temperature and nutrient availability. Our results suggest that the high upward nitrate flux due to the shallow nitracline is an important factor for the unique diazotrophy in the Indian Ocean. Key Points: We broadly found low nitrogen fixation rates and dominance of heterotrophic diazotrophs across the eastern Indian OceanConsistently low nitrogen fixation was attributed to the high upward nitrate flux due to the shallow nitraclineCyanobacterial diazotrophs dominate locally with higher activities in regions with elevated aerosol iron supply against nitrate supply [ABSTRACT FROM AUTHOR]

Microplastics have been found in the marine environment worldwide. Due to their very small size, it could be ingested by marine organisms from small size plankton to big size fish. The aim of this study is to assess the variability of microplastics in three different organs (gills, gastrointestinal tracts, and muscles) of commercial fishes in five different fishing ports in East Java Province, Indonesia. A total of 137 fish samples from 14 species were extracted to identify the types of microplastics. The microplastics found in the fish samples were mostly dominated by fiber, fragments, and a little quantity of film. In most species, the gills accumulated more microplastics compared to the gastrointestinal tracts and muscles. Gill is the organ that is highly exposed to the environmental conditions, therefore, it is more susceptible to the microplastic contamination. The results showed that there was an inverse relationship between the size of the fish and the occurrence of microplastics (P<0.05). Small size Sardinella lemuru contained more microplastics than bigger size fish such as Katsuwonus pelamis. The variability of microplastics found in this study showed important factors such as habitat, fish size, feeding behavior, and organ function which influenced the ingestion process of microplastic. This study also revealed the presence of microplastics were not only in the gills and gastrointestinal tracts of fish, but also in its muscles. Since this study targeted commercial fishes, further research is needed to know the possible impact on human consumption of fish containing microplastics. [ABSTRACT FROM AUTHOR]

Distribution and carbon biomass of planktonic foraminifera were investigated from the euphotic zone of the Eastern Indian Ocean during a two-month cruise, 'Shiyan I' (10 April–13 May 2014). Foraminifera species were collected through plankton net sampling at 44 locations (80.00°–96.10° E, 10.08° N–6.00° S). The temperature (°C) ranged between 12.82 and 31.8 °C, the salinity ranged between 32.5 and 35.5, and chlorophyll-a concentrations ranged between 0.005 µg/L and 0.89 µg/L. A total of 20 taxa were identified based on the spherical chamber shell, spines, and a final whorl which were examined under light microscopy and scanning electron microscopy. Dominant species that were characterized by the high dominant index Y > 0.14–0.46 were Globigerina bulloides, Globigerinoides ruber white, Globigerinella siphonifera, Turborotalita quinqueloba, and Globigerinella calida, contributing to the community up to 86%. The shell size of collected taxa was from 51 to 508 μm and the total carbon biomass was estimated to be between 0.062 µg C m–3 and 26.52 µg C m–3. The high carbon biomass was recorded at two stations in the equator zone. Due to its large size, Globorotalia menardii had total carbon biomass of 3.9 µg C m–3, followed by G. calida 0.68 µg C m−3, Trilobatus sacculifer 0.38 µg C m–3, Orbulina universa 0.56 µg C m–3, and G. ruber white 0.22 µg C m–3, respectively. The Pearson correlation analysis showed that the temperature and chlorophyll-a were two explanatory environmental variables that were found to be highly significant (p < 0.05) and that triggered the distribution and abundance of dominant foraminifera species in the study region. Overall, high abundances and carbon biomass were derived from the euphotic zone and equatorial region of the Eastern Indian Ocean. [ABSTRACT FROM AUTHOR]

The phytoplankton sinking rate in the eastern Indian Ocean was measured during spring 2017 based on the SETCOL method. The range of phytoplankton sinking rates was −0.291 to 2.188 md−1, with an average of 0.420 ± 0.646 md−1. The phytoplankton sinking rate in the Equator (EQ) and the eastern boundary of the Indian Ocean near Sumatra (EB) was lower than that in the Bay of Bengal (BOB). The sinking rate above 100 m was low and increased rapidly below 100 m in all the three regions. The phytoplankton community composition had an important impact on the phytoplankton sinking rate in the east Indian Ocean. The strong stratification in BOB resulted in Trichodesmium spp. bloom and a lower phytoplankton diversity and evenness in BOB, while the phytoplankton in the deep layer are senescent cells that sink down from the upper layer and cannot actively regulate the state of the cells, resulting in a higher sinking rate. Depth and temperature have a great impact on the physiological state of phytoplankton. The sinking rate of phytoplankton depend on the dominant groups composing the phytoplankton community. For the eastern Indian Ocean, seawater stratification caused by temperature changes the distribution of nutrients in the upper layer, and phytoplankton are affected by temperature and nutrients, resulting in changes in community structure, and finally showing different subsidence characteristics. [ABSTRACT FROM AUTHOR]

Water‐soluble organic carbon (WSOC) is a substantial component of carbonaceous aerosols in South/East Asia. However, the poorly constrained sources, molecular compositions, and light absorption properties of WSOC over South/East Asian marine regions lead to large uncertainty in climate effects. Herein, we collected marine aerosol samples from South China Sea to the eastern Indian Ocean to investigate the sources, molecular compositions, and light absorption properties of WSOC. The δ13C of Marine‐influenced WSOC (−20.6 ± 1.4‰) was higher than those in Continent‐influenced (South Asia‐influenced: −24.4 ± 1.1‰ and Southeast Asia‐influenced: −22.7 ± 1.0‰, p < 0.01) regions. Additionally, combining with 5‐day back trajectories and the relationships of δ13C‐WSOC with chemical tracers (Cl−/Na+ and nonsea salt K+/K+), we found that the Marine‐influenced WSOC was mostly related to oceanic emissions, which was more enriched in saturated primary marine biological compounds with lower oxidation level. In contrast, the Continent‐influenced WSOC was significantly affected by C3 biomass burning and secondary organic aerosols formation, and it has a higher fraction of aromatic and highly oxidized compounds. Moreover, the high aromatic level of Continental‐influenced WSOC may result in high mass absorption efficiency at 365 nm (MAE365) but low absorption Ångström exponent (AAE) values. Taken together with previous WSOC light absorption properties studies, we found that the MAE365 of WSOC in urban, rural and background, and marine regions correlated well with AAE. However, the response and correlation coefficients of MAE365 to AAE were highest in urban regions, followed by rural and background and marine regions, which is likely associated with different aromatic compound contents. Therefore, in the future, more attention should be paid to the sources and atmospheric processes of condensed aromatic compounds. Key Points: The Continent‐influenced and Marine‐influenced WSOC were significantly affected by anthropogenic and oceanic emissions, respectivelyThe Continental‐influenced WSOC was more enriched in aromatic compounds, with stronger light absorption capacity than Marine‐influenced WSOCDifference in response and correlation coefficients of MAE365 to AAE in different regions may be related to varied aromatic compound contents [ABSTRACT FROM AUTHOR]

Picophytoplankton (pico) in the eastern Indian Ocean (EIO) were investigated during the inter-monsoon periods. They were found to typically comprise Prochlorococcus (Pro), Synechococcus (Syn), and Picoeukaryotes (PEuks). In the survey area, the pico showed two different vertical distribution patterns in different regions, whereby the Syn abundance decreased with depth, whereas those of Pro and PEuks increased and then decreased with depth, with the maximum depths ranging from 50 to 100 m. The cell abundance and community structure of the pico were similar at the equator (EQ) and the eastern boundary of the Indian Ocean near Sumatra (EB), but the pico cell abundance was significantly lower in the Bay of Bengal (BOB). Pro dominated most regions of the entire EIO and were approximately one-to-two orders of magnitude more abundant than Syn and PEuks. The distributions of Syn and PEuks showed little difference across various regions. Influenced by the physicochemistry of circulation and water masses, there were many different environmental factors in the different regions. The abundance of pico domination by Pro showed a strong positive correlation with the nutrients and salinity in the survey area, indicating increasing nutrient availability, particularly in the oligotrophic EIO. Generalized additive models (GAMs) analysis showed the differences in their responses to environmental variability. Pro and PEuks both increased strongly with warming up to below 26 °C, and Pro and PEuks were more responsive to chemical (nutrient) variability. Syn showed a broader tolerance of low-salinity conditions. In a certain range, an increase in nitrite and nitric acid can improve the cell abundance of Pro. As a significant contributor to primary productivity in oligotrophic waters, this study provides essential information for studying pico communities in the EIO and its adjacent marine ecosystems. [ABSTRACT FROM AUTHOR]

Ocean acidification (OA) and global warming-induced water column stratification can significantly alter phytoplankton-related biological activity in the marine ecosystem. Yet how these changes may play out in the tropical Indian Ocean remains unclear. This study investigated the ecological and metabolic responses of the different phytoplankton functional groups to elevated CO2 partial pressure and nitrate deficiency in two different environments of the eastern Indian Ocean (EIO). It is revealed that phytoplankton growth and metabolic rates are more sensitive to inorganic nutrients rather than CO2. The combined interactive effects of OA and N-limitation on phytoplankton populations are functional group-specific. In particular, the abundance and calcification rate of calcifying coccolithophores are expected to be enhanced in the future EIO. The underlying mechanisms for this enhancement may be ascribed to coccolithophore's lower carbon concentrating mechanisms (CCMs) efficiency and OA-induced [HCO3−] increase. In comparison, the abundance of non-calcifying microphytoplankton (e.g., diatoms and dinoflagellates) and primary productivity would be inhibited under those conditions. Different from previous laboratory experiments, interspecific competition for resources would be an important consideration in the natural phytoplankton populations. These combined factors would roughly determine calcifying coccolithophores as "winners" and non-calcifying microphytoplankton as "losers" in the future ocean scenario. Due to the large species-specific differences in phytoplankton sensitivity to OA, comprehensive investigations on oceanic phytoplankton communities are essential to precisely predict phytoplankton ecophysiological response to ocean acidification. [ABSTRACT FROM AUTHOR]

The present study reveals the first documented distribution record of Desmodema polystictum (Ogilby, 1898) from the Andaman coast, eastern Indian Ocean. The species is rare in nature and the knowledge regarding the taxonomy, ecology and distribution is still limited. Only few records have been come from the Indian Ocean. The study is based on a single specimen (34 cm total length) collected from the northeastern region of Andaman Islands, India. The present record of D. polystictum from Andaman waters provides greater latitude and depth distribution than previously acknowledged from the Indian Exclusive Economic zone. Along with the comparative morphometric and meristic data from previous reports, description of present specimen as well as distributional information are also provided and discussed. [ABSTRACT FROM AUTHOR]

Marine picocyanobacteria Synechococcus exhibit highly diverse pigment types (PTs) and hence possess great advantage to utilize different spectrum of light effectively and to occupy a wide range of light niches. In this study, we explored the diversity of Synechococcus PTs in the eastern Indian Ocean (EIO), surface water of Strait of Malacca (SSM), and coastal waters of Sri Lanka (SSL). All the detected PTs were phycourobilin (PUB) containing PT 3 and showed distinct distribution patterns. Low PUB PT 3a and partial chromatic acclimater PT 3eA dominated in coastal and shallow waters (SSM and SSL). In contrast, high PUB and chromatic acclimaters PT 3dA and PT 3c/3dB were mainly distributed in open ocean (EIO). PT 3dA and PT 3c/3dB occurred at similar depths of the lower euphotic layers but showed distinct distribution pattern that are partially exclusive, indicating that they compete with each other for the same light niche. Interestingly, the newly described PT 3f was detected with high relative abundances at all stations and particularly dominated in the upper euphotic layer in EIO, which was confirmed with PT-specific quantitative polymerase chain reaction (qPCR). The relative abundance of PT 3f was negatively correlated with nutrient level, implying that PT 3f is adapted to oligotrophic waters. Pronounced niche partition of different PTs was observed in the upper and lower layers of euphotic zone in EIO and SSM/SSL. Light, nutrients, and strong stratification may play important roles in the niche partition of different PTs. Further analysis about ecologically significant taxonomic units revealed high diversity within each PT at different locations, which provided insights for understanding specific PT with wide range of niches. [ABSTRACT FROM AUTHOR]

The present study involves the first measurements of size-fractionated biogenic silica (bSi) standing stocks and production rates in the oligotrophic Eastern Indian Ocean. The 150-m integrated bSi standing stocks in the pico- and nanosized fractions averaged 49% and 39%, respectively, of the total; the contributions of pico- and nanoplankton to total bSi production rates were 43% and 38%, respectively, together suggesting that these smaller plankton contributed a significant proportion of both the total bSi standing stock and its rate of production. The total bSi variability appeared to be driven by smaller-plankton dynamics. Also, our results suggest that the detrital bSi stocks were potentially sustained by the pico- and nanosized siliceous organisms (for example, Minidiscus and Synechococcus) instead of broken fragments of large diatoms or other siliceous microplankton. In particular, the atomically dense structure from Synechococcus cell lysis was enriched in Si element compared with intact cells. The factors controlling size-fractionated bSi standing stocks may be biological rather than physical processes, and the clear correlation between picoeukaryotes and the < 2 μm bSi further confirmed the possibility of Si accumulation by other smaller plankton. [ABSTRACT FROM AUTHOR]

Microbial communities are composed of many rare species and a few abundant species. Considering the disproportionate importance of rare species for ecosystem functioning, it is important to understand the mechanisms structuring the rare and abundant components of a diverse community in response to environmental changes. Here, we used a 16S ribosomal RNA gene sequencing approach to investigate the bacterial community diversity in the Eastern Indian Ocean (EIO) during the monsoon and intermonsoon. We employed a phylogenetic null model and network analysis to evaluate the assembly processes and co-occurrence pattern of the microbial community. We found that higher bacterial diversity was detected in the intermonsoon with high temperature and low Chlorophyll a concentrations and N/P ratios. The balance between ecological deterministic processes and stochastic processes varied with seasons in the EIO. Meanwhile, conditionally rare taxa (CRT) were more likely modulated by variable selection processes than always rare taxa (ART) and abundant taxa (AT) (CRT > ART > AT). By linking assembly process and species co-occurrence, we demonstrated that the microbial co-occurrence associations tended to be higher when deterministic processes (mainly variable selection) were weaker. This negative trend was observed in rare species rather than abundant species. The linkage could enhance our understanding of the underlying mechanisms underpinning the generation and maintenance of microbial community diversity. [ABSTRACT FROM AUTHOR]

Reliable catch information is scarce for most sharks and rays worldwide, with almost half of the stocks considered to be Data Deficient due to limited species-specific catch statistics. Western Australia (WA) hosts a diverse number of shark and ray species, some of which are considered to be threatened with extinction at a global level. Commercial catch statistics only account for shark and ray landings. The present study used the best available information to reconstruct unaccounted and unreported catches for 47 shark and ray taxa to better understand the impact of fishing. For some species, there was good agreement between reconstructed catches and reported landings, but overall reconstructed catches were 57% higher than those derived from official statistics alone, underestimating the actual extraction level for many species. The reconstructed catch time series provide the basis for the assessment of all species of sharks and rays captured in WA, including protected species that interact with commercial and recreational fisheries. [ABSTRACT FROM AUTHOR]

The detailed transparent exopolymer particles (TEP) distribution, sinking behavior and the potential mechanisms behind that were revealed in the upper 200 m water column of the eastern Indian Ocean (EIO). The biological process and nutrient limitation have proved to be non‐negligible, both of which possessed potential functions in controlling the TEP pool. TEP production and fate presented significant subregional variations in the study area. The vertical distributions of TEP displayed coherent declined patterns with depth between the marginal sea and pelagic ecosystems, but the concentration of TEP horizontally decreased from marginal sea to open ocean. Dissimilarly, variable distribution patterns and magnitudes were distinguished between stratified and active current zones with the conclusion that the stratified condition was in favor of downward remove of TEP pool but turbulence facilitated the accumulation of TEP especially in the deep chlorophyll maximum (DCM) layer. Distinct sinking regimes of TEP in the stratified zone were distinguishable between layers, with the regulatory mechanisms in the upper, DCM and lower layer of water column being physical diffusion of denser seawater and solutes, aggregation by biotic and abiotic processes and buoyancy effect by entrained lighter fluid, respectively. By comparing the theoretical and measured sinking rates of TEP‐formed aggregates and considering the complicated and uncontrollable situations in non‐culture scenarios, the coupling effects of physical and biological variables on TEP dynamics were elucidated, thus providing a compelling theory for predicting the downward fate of carbon flux in the field environments. Plain Language Summary: Transparent exopolymer particles (TEP) have been brought into focus owing to their close relation with carbon cycle. However, the inconstant nature of TEP limits our understanding of TEP dynamic process, especially in situ. In this study, we measured TEP sinking rates onboard in the eastern Indian Ocean by recording the concentration variations between layers in the settling column after a given time. The fundamental purpose of this work was to expound the transport pattern of TEP above the 200 m‐depth water column ​in complicated field environment. We constructed a simplified model to emphatically discuss the functional mechanisms of physical diffusion and aggregation in the stratified environment. We also compared the measured sinking rates with the theatrical values by considering the varied properties of seawater and particles. The used measuring method for TEP sinking rates turned out to be receivable on one hand, and the model results helped explain the observed phenomena on the other hand. The changes of ambient variables as well as physical attributes of TEP were taken into account to draw a more integrated conclusion, which would provide a potential novel approach to figure out the carbon budget driven by TEP pool. Key Points: Transparent exopolymer particles (TEP) distribution and sinking dynamic were uncovered in non‐culture fields based on the model and statistical analysis methodsThe coupling of physical and biological factor has proved to be defining in controlling the production and fate of TEPThe coordinated variation of TEP physical attributes tend to determine the ratio between the upward and downward flux of particulate organic carbon (POC) [ABSTRACT FROM AUTHOR]

The Eocene Epoch corresponds to the runup toward the Greenhouse to Icehouse Cenozoic transition. To fully appreciate this climate evolution, detailed and accurate age‐depth models are required. While much progress has been made recently in the field of Eocene astrochronology, the construction of unambiguous Eocene astronomical timescales (ATS) is hampered by lithologically undetected hiatuses, the scarcity of carbonate‐rich marine successions, and conflicting cyclostratigraphies. In this study, we present an orbital‐scale cyclostratigraphy for Ocean Drilling Program (ODP) Hole 762C, and we reconstruct Eastern Indian Ocean dynamics. This reconstruction is based on two ocean‐drilling Eocene sequences: ODP Hole 762C and International Ocean Discovery Program (IODP) Site U1514. Our eccentricity‐based cyclostratigraphy for Hole 762C is integrated with existing bio and magnetostratigraphies and constitutes the most precise available chronology for this legacy site. The Hole 762C stratigraphy is combined with the existing Site U1514 age‐depth model to obtain a high‐resolution Eocene ATS for the Eastern Indian Ocean. We apply sedimentary noise modeling to obtain new insights in benthic turbulence at both sites. Despite the significant difference in paleo‐waterdepth, noise levels at both sites carry a 1.2‐Myr obliquity amplitude imprint. We interpret the sedimentary noise at Hole 762C, on a submarine plateau, in terms of sea‐level change. The sedimentary noise at U1514, by contrary, is interpreted to be modulated by bottom current intensity as this site represents a deep‐sea basinal environment. We conclude that, despite very similar astronomical signatures, the mechanistic pathways between astronomical forcing and sedimentary response were radically different at these two sites. Key Points: Cyclostratigraphy applied to two Eocene Indian Ocean scientific drilling records reveals the fingerprint of orbital eccentricitySedimentary noise at both sites contains a 1.2‐Myr obliquity imprint, albeit in antiphase: Mechanisms causing noise are thus differentWhile sea‐level change causes noise at shallower sites, bottom current intensity might introduce sedimentary noise at deep‐ocean sites [ABSTRACT FROM AUTHOR]

Coccolithophores are calcifying protists that have a significant role in marine biological pump through calcite production (CP). We determined the biological calcification rate and ecologically key species (e.g., Gephyrocapsa oceanica) contribution to total calcite stocks in the eastern Indian Ocean (EIO) during spring intermonsoon; this region was quite undersampled compared to other oceanic regions. Our results indicated that the numerically dominant species are of great importance to cell calcite even with low cellular calcite. CP rate in EIO ranged from 0.148 to 85.017 μmol C·m−3·day−1 in the entire data set, which was lower than those in the global ocean. Coccolithophores contributed 8.5% of total phytoplankton carbon fixation. CP acted as a function of light irradiance in the euphotic zone, while a decoupling between CP and primary productivity was found in most of the bottom of euphotic zone. To some degree, this decoupling indicated calcification was more nitrate dependent and less light dependent than photosynthesis. CP/primary productivity ratios were highly variable in our database and were possibly influenced by photoacclimation across various coccolithophore species. As roughly estimated, the turnover rate of coccolith calcite took values around 0.02–0.05 day−1. The association between particulate organic carbon and calcite stocks implied a potential increasing ballast as depth increase. The current profiles of calcification and associated biogeochemical elements obtained from this field study helps our understanding about characteristics of biological pump in the EIO and are valuable for estimating calcification rate in the region using satellite data and numerical modeling. Key Points: Numerically abundant species characterized by small nannoliths were major contributors of total coccolith calcite stocksCoccolithophores contributed 8.5% of total phytoplankton carbon fixation in eastern Indian OceanParticulate organic carbon (POC) and calcite stocks implied a potential increasing ballast effect with depth [ABSTRACT FROM AUTHOR]

Remotely sensed data and habitat model approach were employed to evaluate the present of oceanographic aspect in the Bigeye tuna's potential fishing zone (PFZ) at a profundity of 155 m. Vessel monitoring system was employed to acquire the angling vessels for Bigeye tuna from January through December, 2015-2016. Daily data of sub-surface temperature (Sub_ST), sub-surface chlorophyll-a (Sub_SC), and sub-surface salinity (Sub_SS) were downloaded from INDESO Project website. Vessel monitoring system and environmental data were employed for maximum entropy (maxent) model development. The model predictive achievement was then estimated applying the area under the curve (AUC) value. Maxent model results (AUC>0.745) exhibited its probable to understand the Bigeye tuna's spatial dispersion on the specific sub-surface. In addition, the results also showed Sub_ST (43,1%) was the most affective aspect in the Bigeye tuna dispersion, pursued by Sub_SC (35,2%) and Sub_SS (21,6%). [ABSTRACT FROM AUTHOR]

Picophytoplankton were investigated during spring 2015 and 2016 extending from near‐shore coastal waters to oligotrophic open waters in the eastern Indian Ocean (EIO). They were typically composed of Prochlorococcus (Pro), Synechococcus (Syn), and picoeukaryotes (PEuks). Pro dominated most regions of the entire EIO and were approximately 1–2 orders of magnitude more abundant than Syn and PEuks. Under the influence of physicochemical conditions induced by annual variations of circulations and water masses, no coherent abundance and horizontal distributions of picophytoplankton were observed between spring 2015 and 2016. Although previous studies reported the limited effects of nutrients and heavy metals around coastal waters or upwelling zones could constrain Pro growth, Pro abundance showed strong positive correlation with nutrients, indicating the increase in nutrient availability particularly in the oligotrophic EIO could appreciably elevate their abundance. The exceptional appearance of picophytoplankton with high abundance along the equator appeared to be associated with the advection processes supported by the Wyrtki jets. For vertical patterns of picophytoplankton, a simple conceptual model was built based upon physicochemical parameters. However, Pro and PEuks simultaneously formed a subsurface maximum, while Syn generally restricted to the upper waters, significantly correlating with the combined effects of temperature, light, and nutrient availability. The average chlorophyll a concentrations (Chl a) of picophytoplankton accounted for above 49.6% and 44.9% of the total Chl a during both years, respectively, suggesting that picophytoplankton contributed a significant proportion of the phytoplankton community in the whole EIO. [ABSTRACT FROM AUTHOR]

This document is an erratum for an article titled "Diversity and community structure of microzooplankton in the eastern Indian Ocean during the inter-monsoon period." The erratum corrects an error in the listing of the editor's name and affiliation. The original version of the article has been updated to reflect this correction. The document also includes information about the publication date, citation, and copyright information. [Extracted from the article]

Length‐weight relationship parameter was estimated for eight coral reef‐associated finfish species from the Gulf of Mannar and Palk Bay, Eastern Indian Ocean. Fish samples were collected from the landings of trawlers with a cod‐end mesh size of 25–35 mm, operated at a depth ranging from 50–70 m off Tuticorin, Rameswaram and Thondi coasts on monthly basis between June‐2018 and July‐2019. Fish specimens were sampled by measuring total length (TL) and total weight (TW) with precision to 0.1 cm and 0.1 g respectively. A new maximum total length was recorded for Canthigaster solandri, Centriscus scutatus and Halichoeres stigmaticus from this study. [ABSTRACT FROM AUTHOR]

A new species of the deep-sea porter crab genus, Gordonopsis Guinot & Richer de Forges, 1995 (Homolidae), is described from the Andaman Sea in the eastern Indian Ocean. Gordonopsis has previously been represented by G. profundorum (Alcock & Anderson, 1899) from the western Indian Ocean and G. pacifica Takeda & Suyama, 2019 from Japan. Gordonopsis robusta, new species, differs markedly from G. profundorum and G. pacifica in its more globose carapace, more tomentose body, and proportionately shorter ambulatory meri, notably that of the last pair of legs which just reach the gastric groove on the carapace. [ABSTRACT FROM AUTHOR]

Epipont peritrich ciliates are one of the most sessilie protists that attached to the substrate of zooplankton communities especially copepods and crustaceans. Peritrich ciliates can be solitary or colonial form found from the coastal zones and embayment around the world. Present research report is the first snapshot study of the peritrich ciliates and the horizontal distribution in open waters from surface to 200 m depth in the eastern Indian Ocean. Recently, five peritrich ciliates, e.g., Vorticella oceanica, Zoothamnium alternans, Z. alrasheidi, Z. pelagicum, and Z. marinum were collected from plankton net tow samples during the cruise from April 10 to May 13, 2014. The characteristics of the peritrich ciliate were determined according to the shape of the zooids, the ciliary structure and the stalks. The morphometric shape, sizes and characters also explained by examination under light/scanning electron microscopy. Vorticella oceanica and Z. pelagicum showed their association with host such as diatom (i.e, Chaetoceros coarctatus) and copepod (Oithona brevicornis) including some individuals around the dinoflagellate species (Ceraitum tripose). The distribution of these sessilid ciliates was dominated by the V. oceanica, Z. pelagicum and Z. marinum at the southeast zone while the large colonies of Z. alrasheidi observed at the Bay of Bengal. This distribution can be influenced by substrate availability like diatom (Ch. coarctatus) and copepods (O. brevicornis). [ABSTRACT FROM AUTHOR]

A brief morphometric study of the recent planktonic foraminifera in the eastern Indian Ocean was provided with the taxonomic key to species, synonyms, SEM microphotographs of shells and chamber arrays. By recent classification, currently 20 species representing 13 genera and 6 families (Canderinidae, Heterohelicoidae, Hedbergellidae, Higerigerinoidae, Globigerinoidae, and Globorotaloidae) identified from the planktonic material of the eastern Indian Ocean up to a depth of 200 m. Their distribution in water (0-200 m) also reports on the new range of expansion in the eastern Indian Ocean, with Dentigloborotalia anfracta, Hastigerina pelagica, Streptochilus globigerus, Globigerinella calida, Globigerinella adamsi, Orcadia reidelii, Tenuitella parkerae, Tenuitella compressa, reported for the first time in this study area. In general, only around 50 planktonic species are valid worldwide, more specifically the species, e.g., H. pelagica, G. calida, G. adamsi, S. globigerus, O. riedeli, T. parkerae, T. compressa, which occur in the eastern Indian Ocean to fill the the paucity of the recent regional taxonomic literature and the problematic identification from the eastern Indian Ocean. This work aims to bridge this gap and help scientists, managers, educators and students to identify plankton foraminifers by using species notes and images. [ABSTRACT FROM AUTHOR]

Specimens of Pontella sinica Chen & Zhang, 1965, that were collected for the first time from the eastern Indian Ocean, are described, and a revised synonymy of the species is presented, including an amendment of P. sewelli Heinrich, 1987 as a junior synonym of P. sinica. The present specimens agree with most of the previous descriptions except for the frontal, rostral, and/or ventral eye lenses, which have been described as present in some previous studies, but proved to be all absent in the present examination. In addition, an analysis applying mitochondrial cytochrome c oxidase subunit I (mt COI) as a genetic marker confirmed matching of the female and male that were morphologically described by previous workers. [ABSTRACT FROM AUTHOR]

Ammonia-oxidizing Archaea (AOA) and ammonia-oxidizing Bacteria (AOB) oxidize ammonia to nitrite, and therefore play essential roles in nitrification and global nitrogen cycling. To better understand the population structure and the distribution of AOA and AOB in the deep Eastern Indian Ocean (EIO), nine surface sediment samples (>3,300m depth) were collected during the inter-monsoon Spring 2013. One sediment sample from the South China Sea (SCS; 2,510 m) was also included for comparison. The community composition, species richness, and diversity were characterized by clone libraries (total 1,238 clones), and higher diversity of archaeal amoA genes than bacterial amoA genes was observed in all analyzed samples. Real time qPCR analysis also demonstrated higher abundances (gene copy numbers) of archaeal amoA genes than bacterial amoA genes, and the ratios of AOA/AOB ranged from 1.42 to 8.49 among sites. In addition, unique and distinct clades were found in both reconstructed AOA and AOB phylogeny, suggesting the presence of niche-specific ammonia-oxidizingmicroorganisms in the EIO. The distribution pattern of both archaeal and bacterial amoA genes revealed by NMDS (non-metric multidimensional scaling) showed a distinct geographic separation of the sample from the SCS and most of the samples from the EIO following nitrogen gradients. Higher abundance and diversity of archaeal amoA genes indicated that AOA may play a more important role than AOB in the deep Indian Ocean. Environmental parameters shaping the distribution pattern of AOA were different fromthat of AOB, indicating distinct metabolic characteristics and/or adaptation mechanisms between AOA and AOB in the EIO, especially in deep-sea environments. [ABSTRACT FROM AUTHOR]

The present study reports Nettastoma solitarium Castle & Smith, 1981 based on a single specimen collected from the Andaman Sea (12°49.60′N, 93°12.78′E) at a depth range of 400-441 m. This eel was previously reported from the Western Pacific and Western Indian Oceans. The present observation done in the centre of the known biogeographic distribution area confirms the presence of this species in the Eastern Indian Ocean. Notable morphological features of the species are discussed. [ABSTRACT FROM AUTHOR]

This study assessed the biodiversity of sponges within the Integrated Marine and Coastal Regionalisation for Australia (IMCRA) bioregions of the Pilbara using datasets amalgamated from the Western Australian Museum and the Atlas of Living Australia. The Pilbara accounts for a total of 1164 Linnean and morphospecies. A high level of "apparent endemism" was recorded with 78% of species found in only one of six bioregions, with less than 10% confirmed as widely distributed. The Ningaloo, Pilbara Nearshore and Pilbara Offshore bioregions are biodiversity hotspots (>250 species) and are recognised as having the highest conservation value, followed by North West Shelf containing 232 species. Species compositions differed between bioregions, with those that are less spatially separated sharing more species. Notably, the NorthWest Province bioregion (110 species) exhibited the most distinct species composition, highlighting it as a unique habitat within the Pilbara. While sponge biodiversity is apparently high, incomplete sampling effort for the region was identified, with only two sampling events recorded for the Central West Transition bioregion. Furthermore, only 15% of records in the dataset are presently described (Linnean) species, highlighting the continuing need for taxonomic expertise for the conservation and management of marine biodiversity resources. [ABSTRACT FROM AUTHOR]

Besides being critical components of marine food web, microorganisms play vital roles in biogeochemical cycling of nutrients and elements in the ocean. Currently little is known about microbial population structure and their distributions in the eastern Indian Ocean. In this study, we applied molecular approaches including polymerase chain reaction-denaturant gradient gel electrophoresis (PCR-DGGE) and High-Throughput next generation sequencing to investigate bacterial 16S rRNA genes from the equatorial regions and the adjacent Bay of Bengal in the eastern Indian Ocean. In general, Bacteroidetes, Proteobacteria (mainly Alpha, and Gamma), Actinobacteria, Cyanobacteria and Planctomycetes dominated the microbial communities. Horizontally distinct spatial distribution of major microbial groups was observed from PCR-DGGE gel image analyses. However, further detailed characterization of community structures by pyrosequencing suggested a more pronounced stratified distribution pattern: Cyanobacteria and Actinobacteria were more predominant at surface water (25 m); Bacteroidetes dominated at 25 m and 150 m while Proteobacteria (mainly Alphaproteobacteria) occurred more frequently at 75 m water depth. With increasing water depth, the bacterial communities from different locations tended to share high similarity, indicating a niche partitioning for minor groups of bacteria recovered with high throughput sequencing approaches. This study provided the first 'snapshot' on biodiversity and spatial distribution of Bacteria in water columns in the eastern Indian Ocean, and the findings further emphasized the potential functional roles of these microbes in energy and resource cycling in the eastern Indian Ocean. [ABSTRACT FROM AUTHOR]

A systematic salinity variation in the upper ocean may have an impact on air-sea interactions through a change in ocean stratification and hence on the oceanic response to atmospheric forcing. In this study, we evaluate the possible role of salinity variation in the oceanic response to intraseasonal atmospheric forcing, by investigating the ocean temperature and salinity variation in the eastern Indian Ocean. We primarily used data from three moored buoys located in an area with a large salinity gradient in the eastern equatorial Indian Ocean. Observed upper-layer salinity variation shows significant spectral peaks at intraseasonal time scales. Analysis indicates that surface zonal currents mainly produce the intraseasonal salinity variation through zonal advection with these currents induced by the Madden-Julian Oscillation (MJO). Composite analyses focusing on 35 significant MJO events during 2002-2012 confirmed that intraseasonal atmospheric forcing resulted in variations of net surface heat flux, mixed layer temperature and salinity, and mixed layer depth. We also found that a large salinity change could increase the amplitude of mixed layer temperature variation by changing the mixed layer depth. A possible process by which intraseasonal salinity variation could affect sea surface temperature is discussed. [ABSTRACT FROM AUTHOR]

Eight porcellanid species are reported from Christmas Island and the Cocos (Keeling) Islands in the southeastern Indian Ocean, based on specimens collected by three expeditions to the islands from 2010 to 2012. Of them, five species are new local records: Petrolisthes asiaticus (Leach, 1820), P. bispinosus Borradaile, 1900, P. fimbriatus Borradaile, 1898, P. pubescens Stimpson, 1858, and P. scabriculus (Dana, 1852). Petrolisthes bispinosus and P. fimbriatus are reported for the first time from the Indian Ocean. [ABSTRACT FROM AUTHOR]

Background The Indo-Pacific region has the largest number of seagrass species worldwide and this region is considered as the origin of the Hydrocharitaceae. Halophila ovalis and its closely-related species belonging to the Hydrocharitaceae are well-known as a complex taxonomic challenge mainly due to their high morphological plasticity. The relationship of genetic differentiation and geographic barriers of H. ovalis radiation was not much studied in this region. Are there misidentifications between H. ovalis and its closely related species? Does any taxonomic uncertainty among different populations of H. ovalis persist? Is there any genetic differentiation among populations in the Western Pacific and the Eastern Indian Ocean, which are separated by the Thai-Malay peninsula? Genetic markers can be used to characterize and identify individuals or species and will be used to answer these questions. Results Phylogenetic analyses of the nuclear ribosomal internal transcribed spacer region based on materials collected from 17 populations in the Western Pacific and the Eastern Indian Ocean showed that some specimens identified as H. ovalis belonged to the H. major clade, also supported by morphological data. Evolutionary divergence between the two clades is between 0.033 and 0.038, much higher than the evolutionary divergence among H. ovalis populations. Eight haplotypes were found; none of the haplotypes from the Western Pacific is found in India and vice versa. Analysis of genetic diversity based on microsatellite analysis revealed that the genetic diversity in the Western Pacific is higher than in the Eastern Indian Ocean. The unrooted neighbor-joining tree among 14 populations from the Western Pacific and the Eastern Indian Ocean showed six groups. The Mantel test results revealed a significant correlation between genetic and geographic distances among populations. Results from band-based and allele frequency-based approaches from Amplified Fragment Length Polymorphism showed that all samples collected from both sides of the Thai-Malay peninsula were clustered into two clades: Gulf of Thailand and Andaman Sea. Conclusions Our study documented the new records of H. major for Malaysia and Myanmar. The study also revealed that the Thai-Malay peninsula is a geographic barrier between H. ovalis populations in the Western Pacific and the Eastern Indian Ocean. [ABSTRACT FROM AUTHOR]

In May 2006 (Austral autumn) the distribution and abundance of the cyanobacteria Synechococcus spp. and Prochlorococcus spp. were examined to assess the connectivity of a forming warm-core mesoscale eddy with the Leeuwin Current and shelf waters off south-west Western Australia. Distributions of the cyanobacteria resulted in two broad categories of samples, those dominated by Prochlorococcus spp. from subtropical and Leeuwin Current waters and those with mixed populations from shelf and eddy waters. Water temperature (21.45°C), salinity (35.46) and nitrate (0.33 µM) contributed to these groupings. Synechococcus spp. reached an integrated abundance of 3.3 x 10[sup 8] cells cm[sup -2] in warm shelf waters, with 60% of cells in G2 phase in the mid-afternoon (~16:00 hours). Cooler, nitrate-poor oceanic waters were almost exclusively inhabited by Prochlorococcus spp., with the highest abundance of 4.2 x 10[sup 8] cells cm[sup -2] in cool deep waters off the Capes in the south with 40% of cells in G2 phase in the evening (~19:00 hours). The eddy perimeter represented a clear boundary for both species, but showed connectivity between the shelf and eddy centre as both locations had a mixed community, dominated by Synechococcus spp. Eddies of the Leeuwin Current advect shelf waters, and their assemblages and productivity offshore. Marine cyanobacteria are among the most abundant organisms and make a significant contribution to productivity. Examination of the influence of the Indian Ocean eastern boundary current on the distribution of Synechococcus spp. and Prochlorococcus spp. identified that mesoscale eddies strongly modified their distribution. The importance of eddies in the redistribution of cyanobacteria and plankton determines regional scale dynamics in productivity. [ABSTRACT FROM AUTHOR]

To study the effect of hydrographic factors on the spatial distributions of chlorophyll a (Chl a), an investigation was carried out in the tropical eastern Indian Ocean (80°-100°E along 7°S, and 7°-18°S along 80°E) in December 2010. The fluorescent method was used to obtain total Chl a and size-fractioned Chl a at the 26 stations. The results show that surface Chl a concentration averaged at (0.168±0.095) mg/m s.d. (range: 0.034-0.475 mg/m), concentrations appeared to be higher in the west for longitudinal variations, and higher in the north for latitudinal variations. Furthermore, the surface Chl a concentration was lower (0.034-0.066 mg/m) in the region to the south of 16°S. There was a strong subsurface Chl a maximum layer at all stations and the depth of the Chl a maximum increased towards to the east and south along with the respective nitracline. The spatial variation of Chl a was significant: correlation and regression analysis suggests that it was primarily affected by PO, N(NO-N+NO-N) and temperature. Size-fractionated Chl a concentration clearly showed that the study area was a typical oligotrophic open ocean, in which picophytoplankton dominated, accounting for approximately 67.8% of total Chl a, followed by nanophytoplankton (24.5%) and microphytoplankton (7.6%). The two larger fractions were sensitive to the limitation of P, while picophytoplankton was primarily affected by temperature. [ABSTRACT FROM AUTHOR]

Sharks and rays are a global conservation concern with an increasing number of species considered at risk of extinction, mostly due to overfishing. Although the recreational harvest of sharks and rays is poorly documented and generally minimal, it can be comparable to the commercial harvest. In this study, we quantified the recreational harvest of sharks and rays in Western Australia, a region with a marine coastline greater than 20,000 km. A total of 33 species/taxonomic groups were identified, with the harvest dominated by dusky and bronze whalers, blacktip reef sharks, gummy sharks, Port Jackson sharks, wobbegongs, and rays and skates. Eighty-five percent of individuals were released with an unknown status (alive or dead). We found a latitudinal gradient of species composition, with tropical and subtropical species of the genus Carcharhinus dominating in the north and temperate species from a range of families dominating in the south. Overall, our findings showed that the recreational harvest was negligible when compared with commercial landings. [ABSTRACT FROM AUTHOR]

Simple Summary: Marine microbes are regarded as the most diverse organisms in the biosphere and drive biogeochemical cycles through their metabolism. It is essential to understand the structure and metabolic function of microbial communities. The Indian Ocean is the third largest ocean in the world, and it possesses unique hydrographical properties. So far, assessments of microbial diversity and metabolism need to be improved in the Indian Ocean. Therefore, we carried out a series of investigations in the equatorial eastern Indian Ocean in order to clarify the local microbial communities and detect the genetic potential for microbial functions. The obtained results suggested Cyanobacteria was the dominant microbial group, and predicted the Calvin cycle and the assimilatory nitrate and nitrite reduction played important role in the pathway of carbon fixation and nitrogen metabolism respectively. This study provides insights into microbial community structures as well as the metabolic potential that may be active in the local environment, and lays the groundwork for understanding the roles of microbes in energy and resource cycling in this habitat. Currently, there is scant information about the biodiversity and functional diversity of microbes in the eastern Indian Ocean (EIO). Here, we used a combination of high-throughput sequencing of 16S rRNA genes and a metagenomic approach to investigate the microbial population structure and its metabolic function in the equatorial EIO. Our results show that Cyanobacterial Prochlorococcus made up the majority of the population. Interestingly, there were fewer contributions from clades SAR11 (Alphaproteobacteria) and SAR86 (Gammaproteobacteria) to microbial communities than contributions from Prochlorococcus. Based on functional gene analysis, functional genes rbcL, narB, and nasA were relatively abundant among the relevant genes. The abundance of Prochlorococcus implies its typically ecological adaptation in the local ecosystem. The microbial metabolic potential shows that in addition to the main carbon fixation pathway Calvin cycle, the rTCA cycle and the 3-HP/4-HB cycle have potential alternative carbon fixation contributions to local ecosystems. For the nitrogen cycle, the assimilatory nitrate and nitrite reduction pathway is potentially the crucial form of nitrogen utilization; unexpectedly, nitrogen fixation activity was relatively weak. This study extends our knowledge of the roles of microbes in energy and resource cycling in the EIO and provides a foundation for revealing profound biogeochemical processes driven by the microbial community in the ocean. [ABSTRACT FROM AUTHOR]