Bioaccumulation and risk assessment of radiocesium in the Northwest Pacific Ocean from Fukushima Dai-ichi Nuclear Power Plant accident.

To understand which biota are more exposed to radionuclides, the bioaccumulation and risk assessment of radiocesium (137Cs and 134Cs) release from FDNPP in the Northwest Pacific Ocean were analyzed using ERICA tools. The activity level was determined by the Japanese Nuclear Regulatory Authority (RNA) in 2013. The data were used as input to the ERICA Tool modeling software to evaluate the accumulation and dose of marine organisms. The highest and lowest accumulate concentration rate were observed in birds (4.78E+02 Bq kg-1/Bq L-1) and the Vascular plant (1.04E+01 Bq kg-1/Bq L-1), respectively. The total dose rate range for the 137Cs and 134Cs ranged between 7.39E-04 and 2.65E+00 µGy h-1 and 4.24E-05 and 2.91E-01 µGy h-1, respectively. There is no considerable risk to the marine biota in the research region since the cumulative dose rates of radiocesium to the chosen species were all less than 10 µGy h-1.

A risk assessment on Zostera chilensis, the last relict of marine angiosperms in the South-East Pacific Ocean, due to the development of the desalination industry in Chile.

Seagrasses, which are considered among the most ecologically valuable and endangered coastal ecosystems, have a narrowly limited distribution in the south-east Pacific, where Zostera chilensis is the only remaining relict. Due to water scarcity, desalination industry has grown in the last decades in the central-north coasts of Chile, which may be relevant to address in terms of potential impacts on benthic communities due to their associated high-salinity brine discharges to subtidal ecosystems. In this work, we assessed ecophysiological and cellular responses to desalination-extrapolable hypersalinity conditions on Z. chilensis. Mesocosms experiments were performed for 10 days, where plants were exposed to 3 different salinity treatments: 34 psu (control), 37 psu and 40 psu. Photosynthetic performance, H2O2 accumulation, and ascorbate content (reduced and oxidized) were measured, as well as relative gene expression of enzymes related to osmotic regulation and oxidative stress; these, at 1, 3, 6 and 10 days. Z. chilensis showed a decrease in photosynthetic parameters such as electron transport rate (ETRmax) and saturation irradiance (EkETR) under hypersalinity treatments, while non-photochemical quenching (NPQmax) presented an initial increment and a subsequent decline at 40 psu. H2O2 levels increased with hypersalinity, while ascorbate and dehydroascorbate only increased under 37 psu, although decreased along the experimental period. Increased salinities also triggered the expression of genes related to ion transport and osmolyte syntheses, but salinity-dependent up-regulated genes were mostly those related to the reactive oxygen species metabolism. The relict seagrass Z. chilensis has shown to withstand increased salinities that may be extrapolable to desalination effects in the short-term. As the latter is not fully clear in the long-term, and considering the restricted distribution and ecological importance, direct brine discharges to Z. chilensis meadows may not be recommended.

Settlement dynamics, subsistence economies and climate change during the late Holocene at Nunura Bay (Sechura Desert, Peru): A multiproxy approach.

Long considered on the margins, far from the major cultural traditions, the Sechura Desert is situated at the crossroads between the cultures of southern Ecuador and those of the northern Peruvian coast and preserves a large number of varied archaeological sites. Despite this evidence, little is known about the societies that inhabited this region during the Holocene. Exposed to natural hazards, including El Niño events, and to major climatic changes, they were able to adapt and exploit the scarce resources that this extreme environment offered them. Because of this rich history, we have been conducting archaeological research in this region since 2012 in order to clarify the dynamics of human occupation and their links with climate oscillations and environmental changes. This paper present the results of a multidisciplinary study of Huaca Grande, a mound located on Nunura Bay, 300 m from the Pacific Ocean. The nature of the human occupations at Huaca Grande was varied, and several adjustments occurred over time. The subsistence economy was based mainly on local marine resources and a continual use of terrestrial vegetal resources. However, a major change occurred in the more recent occupations, with the apparition of non-local resources (maize and cotton) indicating that Huaca Grande was connected to trade networks. The results show two main phases of occupation separated by a long abandonment (mid-5th century CE to mid-7th century CE and mid-13th century to mid-15th century CE). The occupation of the site appears to have been influenced by changes in the local climate and by extreme El Niño events. Our results highlight the great adaptability of these human groups over the span of a millennium and their capacity to react to the climatic changes and hazards that characterise this region.

Assessment of global habitat suitability and risk of ocean green tides.

Green tides, which are widespread problems, are harmful issues that affect the protection of ocean ecosystems and natural resources. Scientific assessment and prevention of the green tides are essential for sustainable planning and the utilization of maritime traffic, tourism, and industry. However, the suitable or risk habitats and their dominant factors of green tides from global perspective are unknown. Here, this study proposed a novel framework to show the habitat suitability and risk of ocean green tides by considering marine environmental factors (i.e., sea surface temperature, sea surface salinity, solar irradiance, chlorophyll-a concentration, and sea surface wind). Through global remote sensing images and marine environmental factor data, this study found that (1) suitable and at-risk green tides areas are located in the north and south temperate zones; (2) marine physical factors are expected to weaken the green tide risk globally and enhance the green tide risk in coastal areas; (3) the green tides in the North Atlantic Ocean and the West Pacific Ocean are dominated by environmental factors and physical factors, respectively; and (4) when reducing carbon to promote sustainability, more potentially suitable green tide areas may appear at high latitudes. The results demonstrate the at-risk location and future trend of green tides, which are helpful for sustainable planning of ocean ecosystems.

Microplastic contamination and risk assessment in blue shark (Prionace glauca) from the eastern tropical Pacific Ocean.

We quantified the abundance and characteristics of microplastics in the blue shark, Prionace glauca, found in the eastern tropical Pacific Ocean and investigated the potential microplastic pollution risks. Microplastics (MPs) were detected in 39.1 % of specimens, up to 0.15 ± 0.38 items/g wet weight of the posterior part of the pylorus, and were sized 45.87 to 3220.12 µm. The majority were fibrous in shape (83.3 %) and blue in color (72.2 %). Both sexes of sharks had similar MP abundance and characteristics, except for polymers, with polyethylene terephthalate and polypropylene representing the dominant type in males and females, respectively. Most individuals experienced low pollution, but one male P. glauca exhibited a high ecological risk level owing to the high MP abundance and detection of polyvinyl chloride. This study provides an important baseline for the ingestion of microplastics by pelagic shark species and is a preliminary quantitative measure that could be used in future studies of the risk of MPs.

A first assessment of the distribution and abundance of large pelagic species at Cocos Ridge seamounts (Eastern Tropical Pacific) using drifting pelagic baited remote cameras.

Understanding the link between seamounts and large pelagic species (LPS) may provide important insights for the conservation of these species in open water ecosystems. The seamounts along the Cocos Ridge in the Eastern Tropical Pacific (ETP) ocean are thought to be ecologically important aggregation sites for LPS when moving between Cocos Island (Costa Rica) and Galapagos Islands (Ecuador). However, to date, research efforts to quantify the abundance and distribution patterns of LPS beyond the borders of these two oceanic Marine Protected Areas (MPAs) have been limited. This study used drifting-pelagic baited remote underwater video stations (BRUVS) to investigate the distribution and relative abundance of LPS at Cocos Ridge seamounts. Our drifting-pelagic BRUVS recorded a total of 21 species including elasmobranchs, small and large teleosts, dolphins and one sea turtle; of which four species are currently threatened. Depth of seamount summit was the most significant driver for LPS richness and abundance which were significantly higher at shallow seamounts (< 400 m) compared to deeper ones (> 400m). Distance to nearest MPA was also a significant predictor for LPS abundance, which increased at increasing distances from the nearest MPA. Our results suggest that the Cocos Ridge seamounts, specifically Paramount and West Cocos which had the highest LPS richness and abundance, are important aggregation sites for LPS in the ETP. However, further research is still needed to demonstrate a positive association between LPS and Cocos Ridge seamounts. Our findings showed that drifting pelagic BRUVS are an effective tool to survey LPS in fully pelagic ecosystems of the ETP. This study represents the first step towards the standardization of this technique throughout the region.

Baseline assessment of ocean ambient noise in the western Clarion Clipperton Zone, Pacific Ocean.

Ocean noise in the western Clarion Clipperton Zone, Pacific Ocean was recorded for 5 min every hour during 2017 and 2018, at a depth of 300 m. The monthly and hourly mean spectrum levels in the 20-1000 Hz band were calculated, along with their skewness, kurtosis, percentile distributions, and spectral probability densities. The high noise levels at low frequencies generated from distant shipping and vocalizations of whales were found to range between 70 and 100 dB (<100 Hz) and 64-93 dB (100-200 Hz), respectively. The noise levels at high frequencies (>200 Hz), which are typically dominated by wind, were found to be low, ranging from 53 to 75 dB. At frequencies above 200 Hz, noise levels in winter were approximately 5 dB higher than those in summer, consistent with the seasonal variations in wind speed. Fin whales, blue whales, and fishes also potentially contributed to variations in the baseline of ambient noise.

Fishing trip cost modeling using generalized linear model and machine learning methods - A case study with longline fisheries in the Pacific and an application in Regulatory Impact Analysis.

Fishing trip cost is an important element in evaluating economic performance of fisheries, assessing economic effects from fisheries management alternatives, and serving as input for ecosystem and bioeconomic modeling. However, many fisheries have limited trip-level data due to low observer coverage. This article introduces a generalized linear model (GLM) utilizing machine learning (ML) techniques to develop a modeling approach to estimate the functional forms and predict the fishing trip costs of unsampled trips. GLM with Lasso regularization and ML cross-validation of model are done simultaneously for predictor selection and evaluation of the predictive power of a model. This modeling approach is applied to estimate the trip-level fishing costs using the empirical sampled trip costs and the associated trip-level fishing operational data and vessel characteristics in the Hawaii and American Samoa longline fisheries. Using this approach to build models is particularly important when there is no strong theoretical guideline on predictor selection. Also, the modeling approach addresses the issue of skewed trip cost data and provides predictive power measurement, compared with the previous modeling efforts in trip cost estimation for the Hawaii longline fishery. As a result, fishing trip costs for all trips in the fishery can be estimated. Lastly, this study applies the estimated trip cost model to conduct an empirical analysis to evaluate the impacts on trip costs due to spatial regulations in the Hawaii longline fishery. The results show that closing the Western and Central Pacific Ocean (WCPO) could induce an average 14% increase in fishing trip costs, while the trip cost impacts of the Eastern Pacific Ocean (EPO) closures could be lower.

Assessment of the effect of thinning on the resistance of Pinus thunbergii Parlat. trees in mature coastal forests to tsunami fluid forces.

The Great East Japan Tsunami, triggered by the earthquake that occurred on March 11, 2011 in the Pacific Ocean, caused significant fatalities and socioeconomic damage. As recovery of a disaster area requires significant time, all possible mitigation measures must be prepared in advance for future events. As a tsunami countermeasure, coastal forests have been acknowledged to considerably reduce tsunami energy and decrease tsunami-related damage. In the Great East Japan tsunami, many trees of coastal forests were damaged by trunk breakage and overturning. This led to further infrastructural damage as the debris were transported landward and seaward by floodwaters. To better protect coastal areas from the secondary effects of tsunamis and reduce tsunami energy, coastal forests must exhibit higher resistance. This research investigated the effect of forestry management by applying different levels of thinning of trees as a means of resistance to tree damage under tsunami events. In October of 1999, study plots were established with different thinning intensities in a mature coastal forest of Pinus thunbergii trees. As a useful indicator of the resistance of coastal forests to tsunamis, the threshold tsunami velocities at which trees in these study plots begin to be destroyed were calculated using a mechanistic model. The results revealed that trunk diameter is the most important parameter for increasing resistance to tsunamis. An analysis of the generalized linear model for diameter growth showed that heavy thinning best enhanced the diameter growth. Therefore, heavy thinning is the most effective approach to increasing the resistance of trees to tsunamis. Considering the relationship between resistance to tsunami and inundation depth, the resistance to tsunami decreased rapidly with increasing inundation depth in all plots. Differences in the resistance to the tsunami were not observed across all plots when the inundation depth exceeded the mean tree height.

Natural and Anthropogenic Drivers of Acidification in Large Estuaries.

Oceanic uptake of anthropogenic carbon dioxide (CO2) from the atmosphere has changed ocean biogeochemistry and threatened the health of organisms through a process known as ocean acidification (OA). Such large-scale changes affect ecosystem functions and can have impacts on societal uses, fisheries resources, and economies. In many large estuaries, anthropogenic CO2-induced acidification is enhanced by strong stratification, long water residence times, eutrophication, and a weak acid-base buffer capacity. In this article, we review how a variety of processes influence aquatic acid-base properties in estuarine waters, including coastal upwelling, river-ocean mixing, air-water gas exchange, biological production and subsequent aerobic and anaerobic respiration, calcium carbonate (CaCO3) dissolution, and benthic inputs. We emphasize the spatial and temporal dynamics of partial pressure of CO2 (pCO2), pH, and calcium carbonate mineral saturation states. Examples from three large estuaries-Chesapeake Bay, the Salish Sea, and Prince William Sound-are used to illustrate how natural and anthropogenic processes and climate change may manifest differently across estuaries, as well as the biological implications of OA on coastal calcifiers.

Profile and consumption risk assessment of trace elements in megamouth sharks (Megachasma pelagios) captured from the Pacific Ocean to the east of Taiwan.

Focusing on 27 rare filter-feeding megamouth sharks (Megachasma pelagios) captured as a by-catch of drift gillnet fishery in the Pacific Ocean to the east of Taiwan, this study analyzes the concentrations of 24 elements in their muscle, discusses the bioaccumulation of each element and the correlation between different elements, and assesses the potential health risks of consuming megamouth shark muscle. Among the 24 elements, mean concentrations of Ga, Ag, Li, Bi, Hg, Co, and Cd were relatively low ranging from 10-3 to 10-1 mg/kg, those of Pb, Ba, Mn, Ni, As, Cr, B, Sr, Cu, and Zn ranged from 10-1-101 mg/kg, and those of Fe, Ca, Al, K, Mg, Ti, and Na were relatively high ranging from 101 to 103 mg/kg. The toxic element content index was most significantly correlated with the concentration of Cu. Hence, this study recommends that the concentration of Cu could be used as an indicator of metal accumulation in megamouth shark muscle. The log bioconcentration factor (BCF) ranged from less than 0 to 7.85 in shark muscle. For elements with a concentration of less than 100 µg/L in seawater, the log BCF was inversely proportional to their concentration in seawater. According to the correlation analysis, the accumulation of elements in muscle of megamouth sharks is primarily affected by the concentrations of dissolved elements in seawater, except that the accumulation of Hg, As, Cu, Ti, Al, and Fe appears to be mainly affected by feeding behaviors. The assessment of the health risk of consuming megamouth shark muscle showed that its total hazard index was greater than 1. This suggests that the long-term or high-frequency consumption of megamouth shark muscle may cause health hazards due to the accumulation of trace elements, particularly those with a large contribution of health risk, including As, Hg, and Cu.

Integrated assessment of the acclimation capacity of the marine bivalve Crenomytilus grayanus under naturally highly contaminated conditions: Subcellular distribution of trace metals and structural alterations of nephrocytes.

The aim of our work was to assess whether the cellular processes in the nephrocytes of the long-lived mussel Crenomytilus grayanus tend to acclimation or destruction under trace metal contamination. Mussels were collected from three sites in the north-western Pacific Ocean: reference site, upwelling site, and a site highly contaminated with trace metals. Concentration, subcellular distribution of trace metals (Cd, Cu, Zn, and Pb) in the mussel kidneys, and ultrastructural alterations of the nephrocytes were studied. To assess the total load of accumulated trace metals, the total concentration coefficient (∑СС) was determined. In the kidneys of the reference C. grayanus, trace metals were eliminated from cell metabolism mainly by lysosomal granules or residue bodies. Under high levels of contamination, the defense mechanisms of C. grayanus are practically suppressed (no metallothionein-like protein peak, decreased content of granules) by the total effect of accumulated pollutants that leads to the destruction of cellular structures. Under natural conditions (upwelling site), increased accumulation of trace metals in the mussel kidneys did not lead to an increase in the number or size of lysosomal granules. However, abnormal high Cd accumulation in the kidneys caused the synthesis of high levels of metallothionein-like proteins that sequester most of the studied trace metals. To quickly lower the metal levels in nephrocytes under these conditions, a unique long-term acclimatory response - apocrine-like secretion in nephrocytes, which provides rapid elimination of me-MTLP complexes from the cell arose. Thus, our integrated study of the subcellular distribution of trace metals and ultrastructural alterations in nephrocytes allowed us to characterize the features of the structural and functional alterations in mussel cells under the field conditions tested.

Hydrogeochemical baseline in a human-altered landscape of the central Pacific coast of Costa Rica.

Groundwater pollution in tropical and human-altered coastal landscapes is receiving novel attention due to decreasing in annual recharge as a consequence of recurrent droughts and overexploitation, whereby saline intrusion, point and diffuse source contamination, and water conflicts are common denominators. This study presents a detailed groundwater evaluation in a coastal aquifer within the central Pacific coast of Costa Rica. Three sampling campaigns including major ions, heavy metals, and fecal coliform analyses were conducted between July 2013 and March 2014 across 17 wells within the alluvial and fissured units of the Jacó aquifer. The groundwater system is classified as mixed HCO3--Ca2+-Mg2+ type. Coliforms presence was found in two wells, nearby Mona Creek headwaters and near the coastal line. Heavy metal concentrations were below quantification limits in most of the wells; however, chromium concentrations up to 6.56 µg/L were quantified within the coastal line and central portion of the alluvial aquifer in 20 out of the 48 samples. The spatial distribution of major ions (K+, Na+, Ca2+, Mg2+, Cl-, SO42-, and HCO3-) exhibited an increasing trend towards the central portion of the alluvial aquifer, which may be potentially associated with the large unregulated urban expansion, invoking a need of a continuous water quality monitoring program in this touristic hot spot. This study provides useful information for other similar coastal aquifers in Central America, whereby increasing population growth and unregulated touristic, industrial, and agricultural activities are posing a truly challenge to ensure water security and sustainability parallel to the economic development in a changing climate.

Two new species of Acanthocotyle Monticelli, 1888 (Monogenea: Acanthocotylidae), parasites of two deep-sea skates (Elasmobranchii: Rajiformes) in the South-East Pacific.

BACKGROUND: Parasites of deep-sea fishes from the South-East Pacific (SPO) are poorly known. Of c.1030 species of fish found in this area, 100-150 inhabit the deep-sea (deeper than 200 m). Only six articles concerning metazoan parasites of fish from deep-waters of SOP are known, and nine monogenean species have been reported. Currently, ten species are known in Acanthocotyle Monticelli, 1888 (Monogenea) and when stated, all of them are found in shallow waters (10-100 m). Acanthocotyle gurgesiella Ñacari, Sepulveda, Escribano & Oliva, 2018 is the only known species parasitizing deep-sea skates (350-450 m) in the SPO. The aim of this study was the description of two new species of Acanthocotyle from two Rajiformes. METHODS: In September 2017, we examined specimens of two species of deep-sea skates (Rajiformes), Amblyraja frerichsi (Krefft) and Bathyraja peruana McEachran & Myyake, caught at c.1500 m depth off Tocopilla, northern Chile, as a by-catch of the Patagonian tooth fish Dissostichus eleginoides Smitt fishery. Specimens of Acanthocotyle were collected from the skin of the skates. Morphometric (including multivariate analysis of proportional measurements, standardized by total length), morphological and molecular analyses (LSU rRNA and cox1 genes) were performed in order to identify the collected specimens. RESULTS: The three approaches used in this study strongly suggest the presence of two new species in the genus Acanthocotyle: Acanthocotyle imo n. sp. and Acanthocotyle atacamensis n. sp. parasitizing the skin of the thickbody skate Amblyraja frerichsi and the Peruvian skate Bathyraja peruana, respectively. The main morphological differences from the closely related species Acanthocotyle verrilli Goto, 1899 include the number of radial rows of sclerites, the non-discrete vitelline follicles and the number of testes. CONCLUSIONS: The two species of monogeneans described here are the only recorded parasites from their respective host species in the SPO. Assessing host specificity for members of Acanthocotyle requires clarifying the systematics of Rajiformes.

Assessment of genetic diversity and population structure in cultured Australian Pacific oysters.

The recent development of Pacific oyster (Crassostrea gigas) SNP genotyping arrays has allowed detailed characterisation of genetic diversity and population structure within and between oyster populations. It also raises the potential of harnessing genomic selection for genetic improvement in oyster breeding programmes. The aim of this study was to characterise a breeding population of Australian oysters through genotyping and analysis of 18 027 SNPs, followed by comparison with genotypes of oyster sampled from Europe and Asia. This revealed that the Australian populations had similar population diversity (HE ) to oysters from New Zealand, the British Isles, France and Japan. Population divergence was assessed using PCA of genetic distance and revealed that Australian oysters were distinct from all other populations tested. Australian Pacific oysters originate from planned introductions sourced from three Japanese populations. Approximately 95% of these introductions were from geographically, and potentially genetically, distinct populations from the Nagasaki oysters assessed in this study. Finally, in preparation for the application of genomic selection in oyster breeding programmes, the strength of LD was evaluated and subsets of loci were tested for their ability to accurately infer relationships. Weak LD was observed on average; however, SNP subsets were shown to accurately reconstitute a genomic relationship matrix constructed using all loci. This suggests that low-density SNP panels may have utility in the Australian population tested, and the findings represent an important first step towards the design and implementation of genomic approaches for applied breeding in Pacific oysters.

Climate vulnerability assessment for Pacific salmon and steelhead in the California Current Large Marine Ecosystem.

Major ecological realignments are already occurring in response to climate change. To be successful, conservation strategies now need to account for geographical patterns in traits sensitive to climate change, as well as climate threats to species-level diversity. As part of an effort to provide such information, we conducted a climate vulnerability assessment that included all anadromous Pacific salmon and steelhead (Oncorhynchus spp.) population units listed under the U.S. Endangered Species Act. Using an expert-based scoring system, we ranked 20 attributes for the 28 listed units and 5 additional units. Attributes captured biological sensitivity, or the strength of linkages between each listing unit and the present climate; climate exposure, or the magnitude of projected change in local environmental conditions; and adaptive capacity, or the ability to modify phenotypes to cope with new climatic conditions. Each listing unit was then assigned one of four vulnerability categories. Units ranked most vulnerable overall were Chinook (O. tshawytscha) in the California Central Valley, coho (O. kisutch) in California and southern Oregon, sockeye (O. nerka) in the Snake River Basin, and spring-run Chinook in the interior Columbia and Willamette River Basins. We identified units with similar vulnerability profiles using a hierarchical cluster analysis. Life history characteristics, especially freshwater and estuary residence times, interplayed with gradations in exposure from south to north and from coastal to interior regions to generate landscape-level patterns within each species. Nearly all listing units faced high exposures to projected increases in stream temperature, sea surface temperature, and ocean acidification, but other aspects of exposure peaked in particular regions. Anthropogenic factors, especially migration barriers, habitat degradation, and hatchery influence, have reduced the adaptive capacity of most steelhead and salmon populations. Enhancing adaptive capacity is essential to mitigate for the increasing threat of climate change. Collectively, these results provide a framework to support recovery planning that considers climate impacts on the majority of West Coast anadromous salmonids.

Toxicity assessment of pollutants sorbed on environmental microplastics collected on beaches: Part II-adverse effects on Japanese medaka early life stages.

While microplastics are present in great abundance across all seas and oceans, little is known about their effects on marine life. In the aquatic environment, they can accumulate a variety of chemicals and can be ingested by many marine organisms including fish, with chronic physical and chemical effects. The purpose of this paper is to evaluate the toxic effects of pollutants sorbed at the surface of environmental microplastics (MPs), collected on various beaches from three islands of the Pacific Ocean. Developmental toxicity of virgin MPs or artificially coated with B[a]P and environmental MPs from Easter Island, Guam and Hawaii was evaluated on embryos and prolarvae of Japanese medaka. Mortality, hatching success, biometry, malformations, EROD activity and DNA damage were analyzed after exposure to DMSO extracts. No toxicity was observed for extracts of virgin MPs whatever the endpoint considered. Extracts of virgin MPs coated with 250 µg.g-1 of B(a)P induced lethal effects with high embryo mortality (+81%) and low hatching rate (-28%) and sublethal effects including biometry and swimming behavior changes, increase of EROD activity (+94%) and DNA damage (+60%). Environmental MPs collected on the three selected islands exhibited different polymer, pollutant and toxicity patterns. The highest toxicity was detected for MPs extract from Hawaï with head/body length and swimming speed decreases and induction of EROD activity and DNA stand breaks. This study reports the possible sublethal toxicity of organic pollutants sorbed on MPs to fish early life stages.

Lag effect of climatic variables on dengue burden in India.

Dengue is a widespread vector-borne disease believed to affect between 100 and 390 million people every year. The interaction between vector, host and pathogen is influenced by various climatic factors and the relationship between dengue and climatic conditions has been poorly explored in India. This study explores the relationship between El Niño Southern Oscillation (ENSO), the Indian Ocean Dipole (IOD) and dengue cases in India. Additionally, distributed lag non-linear model was used to assess the delayed effects of climatic factors on dengue cases. The weekly dengue cases reported by the Integrated Disease Surveillance Program (IDSP) over India during the period 2010-2017 were analysed. The study shows that dengue cases usually follow a seasonal pattern, with most cases reported in August and September. Both temperature and rainfall were positively associated with the number of dengue cases. The precipitation shows the higher transmission risk of dengue was observed between 8 and 15 weeks of lag. The highest relative risk (RR) of dengue was observed at 60 mm rainfall with a 12-week lag period when compared with 40 and 80 mm rainfall. The RR of dengue tends to increase with increasing mean temperature above 24 °C. The largest transmission risk of dengue was observed at 30 °C with a 0-3 weeks of lag. Similarly, the transmission risk increases more than twofold when the minimum temperature reaches 26 °C with a 2-week lag period. The dengue cases and El Niño were positively correlated with a 3-6 months lag period. The significant correlation observed between the IOD and dengue cases was shown for a 0-2 months lag period.