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Marine litter in coastal areas can bring economic, social, and environmental damage, especially the loss of aesthetic value of a tourist site. Therefore, research on the composition of marine litter to identify its sources is important for planning strategic action to minimize the problem. This study analyzed beach litter composition on five beaches (Kondangmerak, Balekambang, Ungapan, Ngudel, and Goa Cina) along the Indian Ocean coastline in the eastern part of the south Java region, Indonesia. All the beaches are known as the famous touristic beaches of Malang City, and receive many visitors, especially during the holiday season. Beach litter composition was obtained by collecting different types of litter in a 5 x 5 m square transect. Five square transects were placed along the beach strandline at each beach, and intervals of 20 m separated each transect. In each transect, the litter was collected and counted based on its category (plastic, paper, rubber, fabric, processed wood, metal, glass, ceramic, and hazardous items) and size (0.5-2.5cm, 2.5-5cm, 5-10 cm, and > 10 cm). There was a statistically significant variation in the number of litters among the sizes (p 10 cm was found least on all beaches (< 15%), while the other three size categories were found in similar numbers (in the range of 20% to 50%). Plastic was the dominating type of litter on all beaches. Based on the Clean Coastal Index, all beaches were considered dirty to extremely dirty. All litter on the beaches was the product of tourism activities, and littering habits play a significant role as the source of marine litter in the study areas. Since this is the first study on the marine litter composition in the eastern part of south Java, the results of this study can be used as a baseline for future studies to prevent marine debris pollution and to

Although submarine canyons are internationally recognized as sensitive ecosystems and reported to be biological hotspots, regional studies are required to validate this consensus. To this end, hydrographic and benthic biodiversity data were collected during three cruises (2016-2017) to provide insights on the benthic patterns within South African canyon and non-canyon offshore areas. A total of 25 stations, sampled at 200-1000 m depth range, form the basis of the multivariate analysis. Diversity gradients were calculated and then differences were compared across substrate types and depth zones represented within 12 canyon and 13 non-canyon stations. Significant differences in both substrate and depth were evident, despite measures being highly variable. This observation of varying diversity in different substrates is in line with previous studies. No clear pattern was observed for species diversity (delta+). However, non-canyon stations overall showed a higher diversity in comparison to canyon stations. A notable peak in diversity is observed in canyon areas in the 401-500 m depth zone. Species richness followed an opposing pattern, as it decreased with depth and was consistently higher in canyon areas. These results align with the well-defined influence of depth-related variables on the distribution of taxonomic groups and the substrate available, at various scales. The eutrophic characteristic of the Benguela region may have attributed to the insignificant diversity differences between canyon and non-canyon stations. To assess the benthic species structure in canyon and non-canyon areas, we converted the 108 benthic species into a gamma+ matrix. We then modelled the biological response to predictor variables (substrate and depth). Although the canyon and non-canyon areas have an overlapping species composition, the main effects (canyon vs. non-canyon, depth, and substrate) showed significant differences. Thirteen species were characteristic of canyon areas, whilst

The values used for natural mortality (m) are very influential in stock assessment models, affecting model outcomes and management advice. Natural mortality is one of the most difficult demographic parameters to estimate, and there is often limited information about the true levels. Here, we summarise the evidence used to estimate natural mortality at age for the four main stocks of yellowfin tuna (Indian, Western and Central Pacific, Eastern Pacific, and Atlantic Oceans), including catch curves, tagging experiments, and maximum observed age. We identify important issues for estimating m such as variation with age linked to size, maturity state or senescence, and highlight information gaps. We describe the history of natural mortality values used in stock assessments by the tuna Regional Fisheries management Organisations responsible for managing each stock and assess the evidence supporting these values. In June 2021, an online meeting was held by the Center for the Advancement of Population Assessment methodology (CAPAm), to provide advice and guidance on practices for modelling natural mortality in fishery assessments. Based on approaches presented and discussed at the meeting, we develop a range of yellowfin tuna natural mortality estimates for each stock. We also recommend future research to improve these estimates of natural mortality.

The Mahanadi Estuarine SysteM (MES), with a coMplex network of freshwater channels, rivers, and Mangroves, is a leading seaport in State Odisha on the east coast of India, but subjected to intense huMan activity in recent years. Such anthropic iMpingeMents are known to iMpact sediMent-dwelling biota adversely. However, inforMation on the Macrobenthic coMMunity of the MES is not well docuMented yet. Therefore, the priMary objectives of this study (February 2013-March 2017) were to address knowledge gaps on the Macrobenthic coMMunity structure vis-à-vis local environMental conditions and to evaluate the extent of anthropogenic disturbances on Macrobenthos. The results froM 264 benthic grab saMples (van Veen, 0.04 M2; 2 replicates × 12 GPS fixed locations × 3 seasons) revealed 73 taxa representing 64 genera and 48 faMilies of Macrobenthic fauna. The polychaetes (81.41%) and crustaceans (15.42%) were significant faunal groups that contributed Mainly to the benthic population and diversity. Multivariate approaches using benthic coMMunity attributes and biotic indices (AMBI and M-AMBI) as proxy Measures of environMental disturbances proved effective for appraisal. The correlations between the environMental paraMeters (teMperature, pH, salinity) and coMMunity estiMates were statistically significant. Hierarchical clustering analysis disclosed three Major groups (Global R 0.70; p < 0.002) influenced by tolerant/opportunist species. The lower abundance, richness, diversity, and doMinance of opportunistic species Mark the signs of environMental stress. The coMMunity health status reMained unbalanced, as indicated by AMBI scoring. M-AMBI analysis contributed best in differentiating areas exposed to diverse iMpacts and indicated polluted coMMunity health status with Moderate ecological quality. Our results reiterate the effective use of Macrobenthos as bioindicators for ecological status and Monitoring. The findings could be utilized for future Monitoring assessMents, transl

Aluminum and manganese are both key parameters in the GEOTRACES program. Data on dissolved aluminum (dAl) and dissolved manganese (dmn) relative to their geochemical behavior remain limited in the northeastern Indian Ocean (IO; including the Bay of Bengal (BoB) and equatorial Indian Ocean (Eq. IO)). Seawater samples collected in the BoB and Eq. IO during the spring inter-monsoon period (7 march to 9 April) of 2017 were analyzed to investigate the behavior and main processes controlling the distributions of dAl and dmn in the northeastern IO. The average concentrations of dAl and dmn in the mixed layer of the BoB were 16.6 and 6.7 nm, respectively. A modified 1-D box-model equation was utilized to estimate the contributions of different sources to dAl and dmn in the mixed layer. Al released from the desorption of and/or dissolution of the lithogenic sediments discharged by the Ganga-Brahmaputra (G-B) river system predominantly controlled the dAl distributions in the mixed layer of the BoB, while the desorption from the lithogenic sediments only contributed approximately 13%-21% dmn. Additional dmn input from the advection of Andaman Sea water and photo-reduction-dissolution of particulate mn(IV) contributed more than 60% dmn in the mixed layer of the BoB. dAl and dmn in the surface mixed layer of the Eq. IO were mainly affected by the mixing of dAl- and dmn-enriched BoB surface water and low-dAl, low-dmn southern Arabian Sea surface water. Considering water mass properties and dAl concentrations, the distributions of dAl in the intermediate water (750-1,500 m) of northeastern IO were controlled by the mixing of Red Sea Intermediate Water, Indonesian Intermediate Water, and intermediate water of the BoB. Different from dAl, the apparent oxygen utilization relationship with dmn concentrations indicated that the regeneration of lithogenic particles under hypoxic conditions played a more important role than the remineralization of settling organic particles in co

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 mmol m−2 d−1 during autumn 2020 and was 16.00 mmol m−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, m

Whale sharks off the western coast of India have suffered high levels of fishing pressure in the past, and today continue to be caught in small-scale fisheries as by-catch. Additionally, coastlines in this region host very large and growing human populations that are undergoing rapid development. This exacerbates ongoing anthropogenic threats to this species such as pollution, habitat loss, and ship traffic. For these reasons, there is an urgent need for data on movement patterns of whale sharks in this region of the Indian Ocean. Here, we address this issue by providing the first data on the horizontal movements of whale sharks tagged in the northern Arabian Sea off the western coast of the Indian state of Gujarat. From 2011 to 2017, eight individuals, ranging from 5.4 to 8 m were tagged and monitored using satellite telemetry. Tag retention varied from 1 to 137 days, with the sharks traveling distances of 34 - ∼2,230 km. Six of the eight individuals remained close to their tagging locations, although two sharks displayed wide ranging movements into the Arabian Sea, following frontal zones between water masses of different sea surface temperatures. We explore the relationship between the movement patterns of these whale sharks and the physical and biological processes of the region.

The degree to which biotic communities are regionally enriched or locally saturated, and roles of key structuring processes, remain enduring ecological questions. Prior studies of reef-building corals of the Indo-West Pacific (IWP) found consistent evidence of regional enrichment, a finding subsequently questioned on methodological grounds. Here we revisit this relation and associated relations between richness and abundance (as "effective number of species"), and coral cover, used as a proxy for disturbance and competition. From 1994 to 2017, we sampled > 2,900 sites on shallow (typically < 8-10 m depth below reef crest) and deeper reef slopes in 26 coral ecoregions, from Arabia to the Coral Triangle, Eastern Australia, micronesia and Fiji, for a total pool of 672 species. Sampling intensity varied among ecoregions but always approached asymptotic richness. Local coral communities on both shallow and deep reef slopes were, on average, comprised of 25% of regional pools, ranging from 12 to 43% for individual ecoregions. The richest individual shallow and deep sites, averaged across all ecoregions, comprised 42 and 40% of regional pools, ranging from 30 to 60%, the highest in environmentally marginal ecoregions. Analyses using log-ratio regression indicated that IWP coral communities on deeper reef slopes were intermediate between regionally enriched and locally saturated. Communities on shallow reef slopes showed more evidence of regional enrichment, consistent with these being most susceptible to disturbance. Unimodal curvilinear relations between local richness and coral cover provide support for disturbance mediation and competitive exclusion. IWP coral communities are clearly dynamic, shaped by biological, ecological, and oceanographic processes and disturbance regimes that influence reproduction, dispersal, recruitment, and survival. Yet there is also evidence for a degree of local saturation, consistent with a niche-neutral model of community assembly. The r

Marine iodine speciation has eMerged as a potential tracer of priMary productivity, sediMentary inputs, and ocean oxygenation. The reaction of iodide with ozone at the sea surface has also been identified as the largest deposition sink for tropospheric ozone and the doMinant source of iodine to the atMosphere. Accurate incorporation of these processes into atMospheric Models requires iMproved understanding of iodide concentrations at the air-sea interface. Observations of sea surface iodide are relatively sparse and are particularly lacking in the Indian Ocean basin. Here we exaMine 127 new sea surface (≤10 M depth) iodide and iodate observations Made during three cruises in the Indian Ocean and the Indian sector of the Southern Ocean. The observations span latitudes froM ∼12°N to ∼70°S, and include three distinct hydrographic regiMes: the South Indian subtropical gyre, the Southern Ocean and the northern Indian Ocean including the southern Bay of Bengal. Concentrations and spatial distribution of sea surface iodide follow the saMe general trends as in other ocean basins, with iodide concentrations tending to decrease with increasing latitude (and decreasing sea surface teMperature). However, the gradient of this relationship was steeper in subtropical waters of the Indian Ocean than in the Atlantic or Pacific, suggesting that it Might not be accurately represented by widely used paraMeterizations based on sea surface teMperature. This difference in gradients between basins May arise froM differences in phytoplankton coMMunity coMposition and/or iodide production rates. Iodide concentrations in the tropical northern Indian Ocean were higher and More variable than elsewhere. Two extreMely high iodide concentrations (1241 and 949 nM) were encountered in the Bay of Bengal and are thought to be associated with sediMentary inputs under low oxygen conditions. Excluding these outliers, sea surface iodide concentrations ranged froM 20 to 250 nM, with a Median of 61

In recent years, shoreline determination has become an issue of increasing importance and concern, especially at the local level, as sea level continues to rise. This study identifies the rates of absolute and net erosion, accretion, and shoreline stabilization along the coast of Kuakata, a vulnerable coastal region in south-central Bangladesh. Shoreline change was detected by applying remote sensing and geographic information system (RS-GIS)-based techniques by using Landsat Thematic mapper (Tm), Landsat 8 Operational Land Imager (OLI) and Thermal Infrared Sensor (TIRS) satellite images at 30-m resolution from 1989, 2003, 2010, and 2020. The band combination (BC) method was used to extract the shoreline (i.e., land-water boundary) due to its improved accuracy over other methods for matching with the existing shoreline position. This study also used participatory rural appraisal (PRA) tools which revealed the societal impacts caused by the shoreline changes. Coupling RS-GIS and PRA techniques provides an enhanced understanding of shoreline change and its impacts because PRA enriches the RS-GIS outcomes by contextualizing the findings. Results show that from 1989 to 2020, a total of 13.59 km2 of coastal land was eroded, and 3.27 km2 of land was accreted, suggesting that land is retreating at about 0.32 km2 yr-1. Results from the PRA tools support this finding and demonstrate that fisheries and tourism are affected by the shoreline change. These results are important in Kuakata, a major tourist spot in Bangladesh, because of the impacts on fisheries, recreation, resource extraction, land use planning, and coastal risk management.

When a fire broke out on the deck of the M/V XPress Pearl cargo ship on May 20, 2021, an estiMated 70-75 billion pellets of preproduction plastic Material, known as nurdles, spilled into the ocean and along the Sri Lankan coastline. That spill of about 1,500 tons of nurdles, Many of which were burnt by the fire, has threatened Marine life and poses a coMplex clean-up challenge.

This study investigated the interannual variability of yellowfin tuna (Thunnus albacares) and bigeye tuna (Thunnus obesus) catches in the southwestern tropical Indian Ocean (SWTIO) over 25 years and its relationship to climate variability. The results indicate that the catch amount in the northern SWTIO exhibits a significant relationship with the temperature, salinity, and current variability in the upper ocean (< 400 m), associated with a significant subsurface upwelling variability, which is prominent only in the northern region. An increase of the tuna catches in the northern region is associated with the deepening of the thermocline depth and 20°C isotherm depth of the Seychelles-Chagos Thermocline Ridge, indicating suppression of the subsurface upwelling. Further analysis reveals that the catch amounts in the SWTIO tend to increase during the positive phase of the Indian Ocean Dipole. However, the catch variability in the northern SWTIO is more closely related to the El Niño-Southern Oscillation than the Indian Ocean Dipole. Favorable conditions for catches seem to develop in the northern region during El Niño years and continue throughout the following years. This relationship suggests the potential predictability of catch amounts in the northern SWTIO, an energetic region with strong subsurface upwelling variability.

Declines in abundance of sea snakes have been observed on reefs throughout the Indo-Pacific, although the reasons are unknown. To date, surveys have occurred on shallow reefs, despite sea snakes occurring over a large depth range. It is not known if populations of sea snakes in deep habitats have undergone similar declines. To address this, we analysed deep-water video data from a historical hotspot of sea snake diversity, Ashmore Reef, in 2004, 2016, and 2021. We collected 288 hours of video using baited remote underwater videos and a remotely operated vehicle at depths between 13 and 112 m. We observed 80 individuals of seven species with Aipysurus laevis (n = 30), Hydrophis peronii (n = 8), and H. ocellatus (n = 6) being the most abundant. Five of the species (A. duboisii, A. apraefrontalis, H. ocellatus, H. kingii, and Emydocephalus orarius) had not been reported in shallow waters for a decade prior to our study. We found no evidence of a decline in sea snakes across years in deep-water surveys, although abundances were lower than those in early shallow-water surveys. A comparison of BRUVS data from 2004 and 2016 was consistent with the hypothesis that predation by sharks may have contributed to the loss of sea snakes in shallow habitats. Our study highlights the use of underwater video to collect information on sea snakes in the mesophotic zone and also suggests that future monitoring should include these depths in order to capture a more complete representation of habitats occupied.

The oxygen minimum zone has a significant effect on primary production, marine biodiversity, food web structure, and marine biogeochemical cycle. The Arabian Sea oxygen minimum zone (ASOmZ) is one of the largest and most extreme oxygen minimum zones in the world, with a positional decoupling from the region of phytoplankton blooms. The core of the ASOmZ is located to the east of the high primary production region in the western Arabian Sea. In this study, a coupled physical-biogeochemical numerical model was used to quantify the impact of ocean circulation and settling of particulate organic matters (POms) on the decoupling of the ASOmZ. model results demonstrate that the increased (decreased) dissolved oxygen replenishment in the western (central) Arabian Sea is responsible for decoupling. The oxygen-rich intermediate water (200-1,000 m) from the southern Arabian Sea enters the Arabian Sea along the west coast and hardly reaches the central Arabian Sea, resulting in a significant oxygen replenishment in the western Arabian Sea high-productivity region (Gulf of Aden) but only a minor contribution in the central Arabian Sea. Besides that, the POms that are remineralized to consume central Arabian Sea dissolved oxygen comprises not only local productivity in winter bloom but also the transport from the western Arabian Sea high-productivity region (Oman coast) in summer bloom. more dissolved oxygen replenishment in the western Arabian Sea, and higher dissolved oxygen consumption and fewer dissolved oxygen replenishment in the central Arabian Sea could contribute to the decoupling of the ASOmZ and phytoplankton productive zone.

Bensthic communities along the coastal basins are an indication of ecosystem health but highly susceptible owing to manmade activities. This study envisages thermal tolerance in sea snails monodonta canalifera, Nerita albicilla and Tylothais savignyi inhabiting around the outfall and intake structures of Karachi Nuclear Power Plant (KANUPP). To test the adaptability and vulnerability, a lethality test protocol under controlled temperature was applied in the laboratory where they were exposed at 25, 30, 35, and 40°C, which was raised to 45°C after an acclimation period of 1 week. The critical thermal maximum (CTmax) for the three species was found to be between 39 and 42°C, whereas the lethal temperature (LT50) tests revealed that at the utmost 45°C was lethal for m. canalifera. The correlation between LT50 and CTmaxima (R = 0.47, p = 0.00) and LT50 and body sizes reveals that the thermal adaptability in N. albicilla and T. savignyi (R = 0.65, p = 0.00) was relatively higher than that at 45°C given in the laboratory. In addition, microscopic changes due to temperature, which appeared in the foot (adhesive part) of each species, were deduced from the histological examination. The outcomes of this study would help to underline the ecosystem health around KANUPP and highlight precautionary measures required for the newly established K2/K3 power units to safeguard habitat.

The interannual-decadal variability in the upper-ocean salinity of the southeast Indian Ocean (SEIO) was found to be highly correlated with the El Niño-Southern Oscillation (ENSO). Based on multisource data, this study revealed that this ENSO-like salinity variability mainly resides in the domain between 13°S-30°S and 100°E-120°E, and at depths above 150 m. This variability is principally driven by meridional geostrophic velocity (mGV), which changes with the zonal pattern of the sea surface height (SSH). Previous studies have reported that the variability in the SSH in the south Indian Ocean is principally driven by local-wind forcing and eastern-boundary forcing. Here the eastern-boundary forcing denotes the influence of SSH anomaly radiated from the western coast of Australia. A recent study emphasized the contribution of local-wind forcing in salinity variability in the SEIO, for its significant role in generation of the zonal dipole pattern of SSH anomaly in the south Indian Ocean, which was considered to be responsible for the anomalous mGV in the SEIO. While our results revealed a latitudinal difference between the domain where the SSH dipole pattern exists (north of 20°S) and the region in which the ENSO-like salinity variability is strongest (20°S-30°S), suggesting that this salinity variability cannot be attributed entirely to the SSH dipole pattern. Our further investigation shows that, the mGV in the SEIO changes with local zonal SSH gradient that principally driven by eastern-boundary forcing. In combination with the strong meridional salinity gradient, the boundary-driven mGV anomalies cause significant meridional salinity advection and eventually give rise to the observed ENSO-like salinity variability. This study revealed the leading role of eastern-boundary forcing in interannual variability of the upper-ocean salinity in the SEIO.

Gaining insight into the interannual variability of the Indian Ocean Subtropical Mode Water (IOSTMW) is essential for understanding ocean dynaMics in the Southwest Indian Ocean, since it carries the signal of winter Mixing and transports it into the ocean interior. As the nuMber of Argo profiles in the Southwest Indian Ocean increases, it has becoMe possible to study teMporal variations in IOSTMW using observation data. We used Argo products to exaMine the interannual variability of the IOSTMW froM 2005 to 2020. We exaMined various definitions to deterMine the Most suitable definition for IOSTMW in this study, choosing to define the IOSTMW as a layer with a vertical teMperature gradient of less than 1°C per 100 Meters (dT/dz< 1°C/100 M) and a teMperature range of 16°C-18°C because this correlates strongly with winter heat loss in the saMe year. This Method is particularly useful for investigating how Mode water captures anoMalous winter Mixing signals and advects theM to the ocean interior via subduction. FurtherMore, we found that suMMer stratification can play a role in either facilitating or hindering the forMation of thick IOSTMW layers. Our study indicates that thin IOSTMW layers are priMarily caused by extreMely weak winter heat loss associated with anoMalously weak latent heat, whereas thick IOSTMW forMation is aided by weak suMMer stratification.

* Non-breeding seabirds dispersed widely across tropical Indian Ocean * Divergent habitat use and itinerancy preclude localized aggregations * Diffuse richness >3.9 M kM2, contrary to Multi-species tracking in other oceans * Indian Ocean tropical seabird conservation requires high seas perspective

Oceanic whitetip shark (Carcharhinus longimanus) is an important top predator in pelagic ecosystems currently classified as globally Critically Endangered by the International Union for the Conservation of Nature. This species is incidentally caught by fisheries targeting highly migratory tunas and billfishes throughout the Indian Ocean. Understanding the temporal, spatial and environmental factors influencing the capture of this species is essential to reduce incidental catches. In this study, we used generalized additive models to analyze the spatio-temporal distributions of the juvenile oceanic whitetip shark catches and the environmental conditions in the western Indian Ocean using observer data from 2010 to 2020 of the European Union and associated flags purse seine fishery. We found sea surface temperature and nitrate concentration to be the most important environmental variables predicting the probability of catching an oceanic whitetip shark. A higher probability of capture was predicted in areas where sea surface temperature was below 24°C and with low nitrate concentrations close to zero and intermediate values (1.5-2.5 mmol.m-3). We also found a higher probability of capture in sets on fish aggregating devices than in sets on free schools of tuna. The Kenya and Somalia basin was identified to have higher probabilities of capture during the summer monsoon (June to September) when upwelling of deep cold waters occurs. We provide the first prediction maps of capture probabilities and insights into the environmental preferences of oceanic whitetip shark in the western Indian Ocean. However, the causal mechanisms behind these insights should be explored in future studies before they can be used to design spatial management and conservation strategies, such as time-area closures, for bycatch avoidance.