Tropical Coastal Waters Research Articles

Byssus of Green-Lipped Mussel Perna viridis as a Biomonitoring Biopolymer for Zinc Pollution in Coastal Waters.

The present study aimed to confirm the use of the byssus (BYS) of the green-lipped mussel Perna viridis as a biomonitoring biopolymer for zinc (Zn) by comparing it to copper (Cu) and cadmium (Cd) pollution in coastal waters under experimental field conditions, based on the transplantation of caged mussels between polluted and unpolluted sites in the Straits of Johore (SOJ). Four important evidential points were found in the present study. First, the 34 field-collected populations with BYS/total soft tissue (TST) ratios > 1 indicated that the BYS was a more sensitive, concentrative, and accumulative biopolymer for the three metals than TST. Significant (p < 0.05) and positive correlations between BYS and TST in terms of the levels of the three metals were observed. Second, the data obtained in the present study were well-supported by the interspecific comparison, which indicated that the BYS of P. viridis was a significantly better biomonitoring biopolymer for the identification of coastal areas exposed to Zn, Cd, and Cu pollution and played the role of an excretion route of metal wastes. Third, the higher positive correlation coefficients for the metals between the BYS sedimentary geochemical fractions than the TST sedimentary geochemical fractions indicated that the BYS was more reflective of metal bioavailability and contamination in coastal waters. Fourth, and most importantly, the field-based cage transplantation study clearly indicated the accumulation and elimination of the three metals by the BYS in both polluted and unpolluted sites in the Straits of Johore. In sum, the BYS of P. viridis was confirmed as a better biopolymer than TST for Zn, as well as Cd and Cu, bioavailability and contamination in tropical coastal waters.

Sentinel-2 mapping of a turbid intertidal seagrass meadow in Southern Vietnam

Seagrass ecosystems are crucial to the carbon cycle, biodiversity, fisheries, and erosion prevention. However, there are gaps in mapping seagrass in tropical coastal waters due to turbidity and constantly changing tidal dynamics. To tackle such issues, tidal heights and reflectance of 33 Sentinel-2 images were used to calculate a multitemporal composite of Sentinel-2 images, which was classified using the Random Forest classifier. UAV images classified with Object-based image analysis provided ground truth for training and validation. The effectiveness of water column correction and using the multitemporal composite was evaluated by comparing overall classification accuracy. As a result, applying water column correction improved classification accuracy from 80.4% to 80.6%, while using the multi-temporal composite improved accuracy to 88.6%, among the highest accuracy achieved for seagrass classification in turbid waters. The combined protocol could lead to advances in quantifying seagrass distribution in the tropical coastal waters and their carbon sequestration capacity, resolving significant uncertainties in blue carbon estimation.

Risk of Gastroenteritis from Swimming at a Wastewater-Impacted Tropical Beach Varies across Localized Scales.

Population growth and changing climate are expected to increase human exposure to pathogens in tropical coastal waters. We examined microbiological water quality in three rivers within 2.3 km of each other that impact a Costa Rican beach and in the ocean outside their plumes during the rainy and dry seasons. We performed quantitative microbial risk assessment (QMRA) to predict the risk of gastroenteritis associated with swimming and the amount of pathogen reduction needed to achieve safe conditions. Recreational water quality criteria based on enterococci were exceeded in >90% of river samples but in only 13% of ocean samples. Multivariate analysis grouped microbial observations by subwatershed and season in river samples but only by subwatershed in the ocean. The modeled median risk from all pathogens in river samples was between 0.345 and 0.577, 10-fold above the U.S. Environmental Protection Agency (U.S. EPA) benchmark of 0.036 (36 illnesses/1,000 swimmers). Norovirus genogroup I (NoVGI) contributed most to risk, but adenoviruses raised risk above the threshold in the two most urban subwatersheds. The risk was greater in the dry compared to the rainy season, due largely to the greater frequency of NoVGI detection (100% versus 41%). Viral log10 reduction needed to ensure safe swimming conditions varied by subwatershed and season and was greatest in the dry season (3.8 to 4.1 dry; 2.7 to 3.2 rainy). QMRA that accounts for seasonal and local variability of water quality contributes to understanding the complex influences of hydrology, land use, and environment on human health risk in tropical coastal areas and can contribute to improved beach management. IMPORTANCE This holistic investigation of sanitary water quality at a Costa Rican beach assessed microbial source tracking (MST) marker genes, pathogens, and indicators of sewage. Such studies are still rare in tropical climates. Quantitative microbial risk assessment (QMRA) found that rivers impacting the beach consistently exceeded the U.S. EPA risk threshold for gastroenteritis of 36/1,000 swimmers. The study improves upon many QMRA studies by measuring specific pathogens, rather than relying on surrogates (indicator organisms or MST markers) or estimating pathogen concentrations from the literature. By analyzing microbial levels and estimating the risk of gastrointestinal illness in each river, we were able to discern differences in pathogen levels and human health risks even though all rivers were highly polluted by wastewater and were located less than 2.5 km from one another. This variability on a localized scale has not, to our knowledge, previously been demonstrated.

Gymnodinium catenatum Paralytic Shellfish Toxin Production and Photobiological Responses under Marine Heat Waves

Marine heatwaves (MHWs) have doubled in frequency since the 1980s and are projected to be exacerbated during this century. MHWs have been shown to trigger harmful algal blooms (HABs), with severe consequences to marine life and human populations. Within this context, this study aims to understand, for the first time, how MHWs impact key biological and toxicological parameters of the paralytic shellfish toxin (PST) producer Gymnodinium catenatum, a dinoflagellate inhabiting temperate and tropical coastal waters. Two MHW were simulated-category I (i.e., peak: 19.9 °C) and category IV (i.e., peak: 24.1 °C)-relative to the estimated baseline in the western coast of Portugal (18.5 °C). No significant changes in abundance, size, and photosynthetic efficiency were observed among treatments. On the other hand, chain-formation was significantly reduced under category IV MHW, as was PSP toxicity and production of some PST compounds. Overall, this suggests that G. catenatum may have a high tolerance to MHWs. Nevertheless, some sublethal effects may have occurred since chain-formation was affected, suggesting that these growth conditions may be sub-optimal for this population. Our study suggests that the increase in frequency, intensity, and duration of MHWs may lead to reduced severity of G. catenatum blooms.

Sounds of snapping shrimp (Alpheidae) as important input to the soundscape in the southeast China coastal sea

As a biological sound source widely distributed in temperate and tropical coastal waters, snapping shrimp produce strong pulses which can serve as honest signals to indicate habitat-specific soundscape. The past decade has witnessed the growing interest in investigating the acoustical activity of snapping shrimp across many shallow waters including the coastal line of the west Pacific Ocean. It was extended to the Southeast China coastal area where snapping sounds and the associated soundscape were recorded at four sites. Customized codes incorporating bandwidth and amplitude threshold operations were developed to detect snaps from the ambient noise to estimate snap rate and extract snaps individually. The subsequent analysis suggested that snaps recorded at different sites were unanimously stronger than background noise. Sound pressure level of the snaps ranged from 150 dB to 190 dB (re 1 μPa). The characteristics of snaps, including sound pressure level, duration, peak frequency, -3dB bandwidth from different sites are examined to evaluate the variability across the sites. Though snapping pulses had peak frequencies and the -3 dB bandwidth consistently below 10 kHz, snaps had considerable energy extending to the high frequency range over 200 kHz. The analysis of the acoustic data received for 7 consecutive days at one site indicated that the snap rate corresponded to tidal level periodicity. A high tide was accompanied with a local high snap rate regardless of light but this local snap rate peak was much higher at night. The mean rate fluctuated between 2000 and 4000 snaps per minute and more snaps were recorded after sunset suggesting that snapping shrimp living in the area snapped in response to light. These data may indicate that snaps are important communication means in light-limited condition and deepen our understanding on the correlation of snapping behavior and ecological environments.

Viral dynamics in tropical coastal waters: effects of warming and nutrient enrichment

Context We studied the virus component in the microbial food-web in the tropical coastal Sunda Shelf waters. Aims We investigated viral processes, including the lysogenic to lytic shift dynamics with seawater warming and nutrient enrichment. Methods We sampled nearshore and offshore waters of Peninsular Malaysia to provide a natural trophic gradient for correlational analyses. We also conducted laboratory experiments to investigate the changes in virus production rates and lysogeny, when temperature (range: 25–37°C) and nutrient concentrations (range: 0.1–1.0× marine-broth concentration) were manipulated. Key results Observations showed site-dependent differences in dissolved inorganic nutrient concentration, Chl-a (0.21–3.54 μg L−1) and bacterial abundance (4.09 × 105−9.41 × 105 cells mL−1), but not in viral abundance (measured as virus-like particles or VLP) (1.04 × 106−2.39 × 106 VLP mL−1) and virus production rates (0.59 × 105−4.55 × 105 VLP mL−1 h−1). From laboratory experiments, both warming and nutrient enrichment increased virus production (R2 &gt; 0.651), decreased lysogeny (R2 &gt; 0.743), and resulted in an increase of the viral lysis:bacterial production ratio, and a stronger viral control on bacterial production. Conclusions Although both seawater warming and nutrient enrichment increased virus production and reduced lysogeny, nutrient enrichment was a more important factor. Implications The increasing nutrient concentrations in these waters will increase virus production and virus top-down control of bacteria, and drive the ecosystem towards heterotrophy.

Northernmost record of the Chilean torpedo Tetronarce tremens from tropical coastal waters of the Mexican Pacific

Abstract The Chilean torpedo Tetronarce tremens is recorded for the first time in the Mexican Pacific. A single male specimen was captured by artisanal fishermen using a bottom-set gillnet off San Agustinillo, Oaxaca. The specimen identification was based on morphology and confirmed by DNA barcoding of the cytochrome oxidase subunit I gene and its comparison with sequences available in online repositories. A phylogenetic analysis of Tetronarce resulted in the clustering of three species that inhabit the Pacific Ocean: Tetronarce tremens, Tetronarce californica and Tetronarce tokionis. This study provides the northernmost record of Tetronarce tremens in the Eastern Pacific Ocean, an atypical sighting beyond its native distribution range in tropical and temperate waters off South America.

Structural complexity of seagrass and environmental variables as a determinant of fish larvae assemblages in tropical coastal waters: Implications for seagrass management and conservation

Anthropogenic activities including climate change affect the development of structural complexity in seagrass and the state of environmental variables. It remains unclear whether these variables, alone or in combination, have an important influence on fish larvae assemblages. This study examined the influence of the structural complexity of seagrass meadows and various environmental variables on fish larvae assemblages in tropical coastal waters of Tanga, Tanzania. The study was conducted in four Thalassia hemprichii dominated seagrass meadows from June 2019 to January 2021. Multiple regression analysis indicated that the structural complexity of seagrass (canopy height, seagrass cover, and shoot density) and environmental variables (dissolved oxygen, temperature and salinity) were the foremost predictors for fish larvae assemblages; abundance and richness (R2 = 0.75, p = 0.0185, R2 = 0.54, p = 0.0396, respectively). Based on these findings, the structural complexity of seagrass and environmental variables are both important determinants of fish larvae assemblages in tropical coastal waters. The findings suggest that reducing anthropogenic activities that affect the development of structural complexity of seagrass and negatively impact environmental variables in seagrass meadows through more effective governance would result in increased production of fish larvae in meadows and, as a result, increased fish recruitment in tropical coastal waters.

Heterotrophic Bacteria Respond Differently to Increasing Temperature and Dissolved Organic Carbon Sources in Two Tropical Coastal Systems

AbstractTemperature and substrate availability are important variables controlling marine heterotrophic bacterial activity. However, particularly in tropical regions it remains to be determined how these variables jointly affect bacterial activity. In this study we show how bacterial carbon cycling in two tropical coastal ecosystems (the Great Barrier Reef [GBR, Australia] and the Red Sea [Saudi Arabia]) are influenced by changing temperature (using a 6°C gradient) and the addition of dissolved organic carbon (DOC) from different sources (addition of mangroves and seagrass leachates, plus natural seawater). Our study demonstrates that elevated temperatures in the GBR increased bacterial organic carbon processing, while in the Red Sea no clear effects were found. More of the added DOC was degraded in the Red Sea but this additional carbon did not increase the biomass production, due to low bacterial growth efficiencies in all treatments. In addition, increasing temperatures in the GBR resulted in lower bacterial growth efficiencies, while no clear impact were found in the Red Sea. In conclusion, this study suggests that site‐specific ecosystem differences (e.g., different microbial and macrophyte community composition) may override general responses to temperature and substrate in tropical coastal waters.

Heterotrophic Bacterioplankton Growth and Physiological Properties in Red Sea Tropical Shallow Ecosystems With Different Dissolved Organic Matter Sources.

Despite the key role of heterotrophic bacterioplankton in the biogeochemistry of tropical coastal waters, their dynamics have been poorly investigated in relation to the different dissolved organic matter (DOM) pools usually available. In this study we conducted four seasonal incubations of unfiltered and predator-free seawater (Community and Filtered treatment, respectively) at three Red Sea coastal sites characterized by different dominant DOM sources: Seagrass, Mangrove, and Phytoplankton. Bacterial abundance, growth and physiological status were assessed by flow cytometry and community composition by 16S rRNA gene amplicons. The Seagrass site showed the highest initial abundances (6.93 ± 0.30 × 105 cells mL–1), coincident with maximum DOC concentrations (>100 μmol C L–1), while growth rates peaked at the Mangrove site (1.11 ± 0.09 d–1) and were consistently higher in the Filtered treatment. The ratio between the Filtered and Community maximum bacterial abundance (a proxy for top-down control by protistan grazers) showed minimum values at the Seagrass site (1.05 ± 0.05) and maximum at the Phytoplankton site (1.24 ± 0.30), suggesting protistan grazing was higher in open waters, especially in the first half of the year. Since the Mangrove and Seagrass sites shared a similar bacterial diversity, the unexpected lack of bacterial response to predators removal at the latter site should be explained by differences in DOM characteristics. Nitrogen-rich DOM and fluorescent protein-like components were significantly associated with enhanced specific growth rates along the inshore-offshore gradient. Our study confirms the hypotheses that top–down factors control bacterial standing stocks while specific growth rates are bottom-up controlled in representative Red Sea shallow, oligotrophic ecosystems.

The estimation of total suspended matter from satellite imagery of tropical coastal water Berau Estuary, Indonesia

Water in coastal and estuary areas needs to be investigated as human activities is allegedly decrease their quality. This has led to optical remote sensing for mapping optical water quality using empirical and semi-analytical approaches. Therefore, this study aims to estimate the Total Suspended Matter (TSM) concentration from Medium Resolution Imaging Spectrometer (MERIS) data using a spectral unmixing approach combined with a radiative transfer model. This approach was implemented in the equatorial tropical coastal water, the Berau estuary, Indonesia, by generating a look-up table (LUT) of top-of-atmosphere radiance spectra through the coupled forward models, and the endmembers were selected from the LUT. The spectral unmixing algorithm was employed to the MERIS data for decomposing the image into haze and sediment components. The data were then transformed into images of a constant haze level corresponding to 50 km visibility, and the atmospheric correction was applied. Furthermore, the TMS concentration was retrieved using the inverse semi-analytical Kubelka-Munk model. The result gave overestimated TSM concentration values on clear waters. However, in turbid waters, a lower RMSE was obtained, and the coefficient of determination was higher than in clear waters.

Puffer proliferation in tropical coastal waters: influence of indiscriminate trawling

Intensive mechanized fishing has induced marked alterations in coastal marine ecosystems resulting in proliferation of low-value, nuisance species in marine fish catches. Assessment of 75 shrimp trawl catches taken in the near-shore waters off Goa, west coast of India during active fishing periods from 2006 – 2008 revealed that the demersal pufferfish, Lagocephalus spadiceus constituted ≈ 27 % by weight of the trawl catch during January – March, and its catch was inversely related to prey and predator species. Sub-tidal rock reefs and submerged rocky patches in the study area offer suitable substrates for spawning, and the predominance of adults during these months suggesting spawning migration. Comparison of the present data with published literature indicates a significant reduction in puffer predators (catfishes). Excessive removal of high-value predators favours the proliferation of pufferfish and its establishment as a meso-predator, probably triggering a potential trophic cascade. The paper discusses the role of removal of High Trophic Level (HTL) species in the proliferation of a meso-predator and its impact on ecosystem function.

Mangrove microbiome reveals importance of sulfur metabolism in tropical coastal waters

Mangroves under macro-tidal regimes are global carbon sequestration hotspots but the microbial drivers of biogeochemical cycles remain poorly understood. Here, we investigate the drivers of mangrove microbial community composition across a porewater-creek-estuary-ocean continuum. Observations were performed on the Amazon region in one of the largest mangrove systems worldwide with effective sequestration of organic carbon buried in soils and dissolved carbon via outwelling to the ocean. The potential export to the adjacent oceanic region ranged from 57 to 380 kg of dissolved and particulate organic carbon per second (up to 33 thousand tons C per day). Macro tides modulated microbial communities and their metabolic processes, e.g., anoxygenic phototrophy, sulfur, and nitrogen cycling. Respiration, sulfur metabolism and dissolved organic carbon (DOC) levels were linked to functional groups and microbial cell counts. Total microbial counts decreased and cyanobacteria counts peaked in the spring tide. The microbial groups driving carbon, nitrogen, sulfur and methane cycles were consistent across all spatial scales. Taxonomic groups engaged in sulfur cycling (Allochromatium, Desulfovibrio, and Thibacillus) within mangroves were abundant at all scales. Tidally-driven porewater exchange within mangroves drove a progressive increase of sulfur cycle taxonomic groups and their functional genes both temporally (tidal cycles) and spatially (from mangrove porewater to continental shelf). Overall, we revealed a unified and consistent response of microbiomes at different spatial and temporal scales to tidally-driven mangrove porewater exchange.

Diversity and health risk potentials of the Enterococcus population in tropical coastal water impacted by Hurricane Lane.

Hurricane-caused stormwater runoffs transport diverse terrestrial pollutants, adversely impact microbiological water quality, and introduce fecal and other pathogens to coastal water environments. This study investigated the genotypic diversity, phylogenetic composition, antibiotic resistance patterns, and virulence gene repertoire of the Enterococcus population in the Hilo Bay coastal water after the immediate impact of Hurricane Lane. DNA fingerprinting of Enterococcus isolates exhibited large genotypic diversity, while 16S rRNA gene sequencing identified four major species, including E. faecalis (34.7%), E. faecium (22.4%), E. hirae (22.4%), and E. durans (18.4%). Four common enterococcal virulence genes (cylA, esp, asa1, and gelE) were detected in the Enterococcus population, with significant portions of E. durans (33.3%), E. faecalis (41.2%), E. faecium (36.4%), and E. hirae (27.3%) isolates possessing two or more virulence genes. Considerable antibiotic resistance to rifampin, erythromycin, tetracycline, and nitrofurantoin was detected in the Enterococcus population, with one E. durans isolate showing vancomycin resistance. The results indicate considerable health implications associated with Enterococcus spp. in the hurricane-impacted tropical coastal water, illustrating the needs for more comprehensive understanding of the microbiological risks associated with storm-impacted coastal water.

Persisting antibiotic resistance gene pollution and its association with human sewage sources in tropical marine beach waters.

Antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs) are pollutants of worldwide concern that threaten human health and ecosystems. Anthropogenic activities and wastewater could be ARB and ARG pollution sources; however, research on ARG abundance and microbial source tracking (MST) of contamination in tropical marine waters is limited. This study examined spatiotemporal variations of six ARGs (blaNDM, blaTEM, blaVIM, mcr-1, sul1, and tetQ) against the widely used antibiotic groups and a class 1 integron-integrase gene (intI1) at two Thai tropical recreational beaches (n=41). Correlations between ARGs and sewage-specific MST markers (i.e., crAssphage and human polyomaviruses [HPyVs]) and fecal indicator bacteria (i.e., total coliforms, fecal coliforms, and enterococci) were also investigated. BlaTEM, intI1, sul1, and tetQ were ubiquitous at both beaches (85.4-100% detection rate); intI1 was the most abundant (3-6 orders in log10 copies/100mL), followed by blaTEM (2-4 orders), sul1 (2-3 orders), and tetQ (2-4 orders). BlaNDM was found in 7.3% (up to 4 orders), and no mcr-1 was detected. Interestingly, blaVIM was prevalent at one beach (2-5 orders; n=17), but found in only one sample at the other (4 orders). Temporal, but not spatial, differences were noticed; blaTEM was at higher levels in the wet season. IntI1 correlated with sul1 and tetQ (Spearman's rho=0.47-0.97), suggesting potential horizontal gene transfer. CrAssphage, but not HPyVs, correlated with intI1, sul1, and tetQ (Spearman's rho=0.50-0.74). Higher numbers of ARGs tended to co-occur in samples with higher crAssphage concentrations, implying sewage contribution to the marine water, with a persisting ARG background. This study provides insight into the ARG pollution status of tropical coastal waters and suggests crAssphage as a proxy for ARG pollution, which could facilitate effective management policies to minimize ARG dissemination in marine environments.

Demographics and reproductive biology of Hydrophis schistosus may make it more resilient to bycatch effects than other sea snakes

Mortality in fisheries bycatch is a threat to marine taxa globally. True sea snakes are viviparous marine reptiles found throughout tropical coastal waters, with varying reproductive strategies that differ from their terrestrial counterparts. Hydrophis schistosus and H. curtus are both caught frequently in large numbers as bycatch in gillnets, shore seines and trawlers on the west coast of India. In this study, we aimed to describe the population of H. curtus and H. schistosus in bycatch in terms of developmental stages; compare mortality rates across developmental stages and sexes; and discuss their breeding cycle and reproductive strategies in the context of fisheries threats. We sampled fishing nets for sea snakes from 2016 to 2019. The population structure of H. schistosus consisted primarily of breeding adults and did not change in the four years of sampling. However, the proportion of breeding adults of H. curtus in bycatch declined steadily. Gravid female H. schistosus appear to carry young from November to May, giving birth in April. We did not encounter any gravid H. curtus during our sampling. While the number of eggs increased with female snout to vent length in H. schsitosus, the overall reproductive effort remained the same and investment per embryo reduced. Bycatch - induced mortality of H. curtus was significantly higher than H. schistosus. Adult H. curtus were most vulnerable to bycatch mortality of all demographic groups in both species. Reproductive strategies along with other ecological and life history differences may give H. schistosus an advantage compared to other taxa in the face of anthropogenic threats.

The impact of eutrophication towards selected bacterial process rates in tropical coastal waters

The dissolved organic nutrient conditions and bacterial process rates at two tropical coastal sites in Peninsular Malaysia (Port Klang and Port Dickson) were initially studied in 2004–2005 period and later revisited in 2010–2011. We observed that dissolved organic nitrogen (DON) increased about two- and ten-fold at Port Klang and Port Dickson, respectively and resulted in a significant change in DOC:DON ratio (t ≥ 2.077, p < 0.05). Among the bacterial processes measured, bacterial respiration (BR) was lower in the 2010–2011 period at both stations (t ≥ 3.390, p < 0.01). BR also correlated to the DOC:DON ratio (R2 ≥ 0.259, p < 0.01). The increase in substrate quality enabled the bacteria to respire less in the dissolved organic matter degradation. As a result, the average bacterial growth efficiency increased slightly in the 2010–2011 period.

Temperate and tropical coastal waters share relatively similar microbial biofilm communities while free‐living or particle‐attached communities are distinct

Free-living (FL) marine microbial communities differ from those attached to particles (PA). Likewise, biofilms (B) colonizing artificial surfaces, including plastics or ship hulls, hardly resemble their planktonic surroundings. However, few studies have examined the effect of the environment on these lifestyles and on the source of organisms colonizing marine surfaces. Using 16S rRNA gene metabarcoding, we identified specificities of marine prokaryotic community lifestyles (FL, PA or B) sampled in three coastal polluted locations with dissimilar environmental conditions: the North-Western Mediterranean Sea and the Atlantic and Indian Oceans. Biofilms developed over polyvinyl chloride (PVC) were found to be significantly different from FL or PA collected during the immersions. Alpha-diversity increased from FL to PA and to B, illustrating the integrative aspect of the latter, with little proportion of operational taxonomic units shared with the first two. Beta-diversity clustered first the lifestyles and then the sites. FL and PA were more affected by water quality, especially by trace metal contamination, whereas B were as sensitive to trace metals as to nutrients. Although biofilms should be supplied by the planktonic (ultra) rare biosphere, source tracking could only detect small contributions of FL or PA taxa to B communities.

Coral Skeletal Luminescence Records Changes in Terrestrial Chromophoric Dissolved Organic Matter in Tropical Coastal Waters

AbstractTerrigenous dissolved organic matter (tDOM) carried by rivers represents an important carbon flux to the coastal ocean, which is thought to be increasing globally. Because tDOM is rich in light‐absorbent chromophoric dissolved organic matter (CDOM), it may also reduce the amount of sunlight available in coastal ecosystems. Despite its biogeochemical and ecological significance, there are few long‐term records of tDOM, hindering our understanding of its drivers and dynamics. Corals incorporate terrestrial humic acids, an important constituent of CDOM, resulting in luminescent bands that have been previously linked to rainfall and run‐off. We show that luminescence green‐to‐blue (G/B) ratios in a coral core growing in waters affected by peatland run‐off correlate strongly with remote sensing‐derived CDOM absorption. The 24‐year monthly resolution reconstructed record shows that rainfall controls land‐to‐ocean tDOM flux from this protected peatland catchment, and suggests an additional impact by solar radiation, which degrades tDOM at sea.

A case study of coastal currents in relation with tides and winds in a tropical coastal waters of Vengurla, West Coast of India

Coastal currents consist of wind-driven, tidal, surface wave and geostrophic flows. These currents have a major role for nearshore sediment transport, but the measured data availability on coastal currents for the Indian coast is relatively less. This study analyze the variability of coastal currents along with the tides at nearshore and offshore waters during two different seasons (fag end of summer monsoon and initial stage of pre-monsoon) at Vengurla, west coast of India. Results of this study exhibited that the tides at Vengurla are mixed semi-diurnal dominated by solar constituent during summer monsoon (September to October); whereas the lunar constituents dominates during pre-monsoon (February to March). The nearshore current was dominated by the westward flow (sluggish current) during monsoon and south eastward flow during pre-monsoon, whereas the offshore flow (strong current) showed seasonality. At offshore, southerly current dominated during summer monsoon, whereas the northerly current played a major role during pre-monsoon. The current profile analysis at offshore revealed that the gradation of strong current at the surface to the sluggish nature of currents at the bottom and were comparatively higher during summer monsoon than pre-monsoon periods. This study revealed a complex pattern among winds, tides and currents at offshore.