Marine Sites Research Articles

Deep marine records of Deccan Trap volcanism before the Cretaceous–Paleogene (K–Pg) mass extinction

The Cretaceous−Paleogene boundary is marked by a large impact and coeval mass extinction event that occurred 66 m.y. ago. Contemporaneous emplacement of the volcanic Deccan Traps also affected global climate before, during, and after the mass extinction. Many questions remain about the timing and eruption rates of Deccan volcanism, its precise forcing of climatic changes, and its signature in the marine geochemical sedimentary proxy record. Here, we compile new and existing mercury (Hg) concentration and osmium isotope (187Os/188Os) records for various stratigraphic sections worldwide. Both geochemical proxies have been suggested to reflect past variations in Deccan volcanic activity. New data from deep marine pelagic carbonate records are compared to contemporaneous records from shallower marine sites correlated through high-resolution cyclostratigraphic age models. The robustness of the proxy records is evaluated on a common timeline and compared to two different Deccan eruption history scenarios. Results show that the global 187Os/188Os signal is clearly reproducible, while the global Hg record does not form a consistent pattern. Moreover, the deep marine sections investigated do not record clear variations in the Hg cycle, particularly in the latest Cretaceous, prior to the extinction event. A detailed reevaluation of the precise depth of the redistribution of impactor-sourced platinum group elements does not exclude the possibility of a minor drop in 187Os/188Os corresponding with a pulse of Deccan volcanism ∼50,000 years before the Cretaceous−Paleogene boundary. Simple Os isotope mass balance modeling indicates that the latest Cretaceous was marked by significant levels of basalt weathering. CO2 sequestration during this weathering likely overwhelmed the emission of Deccan volatiles, thereby contributing to the end of the late Maastrichtian warming.

Assessment of Essential Trace Elements Cu, Zn, Mn, and Ni in Mediterranean Mussels (Mytilus galloprovincialis) from the Algerian Coast.

The aim of this study was to determine the levels of essential trace elements copper, zinc, manganese, and nickel in two size groups of mussels, Mytilus galloprovincialis, sampled from three sites along the Algerian coast with different levels of pollution. The results of this work are very interesting for determining the effect of mussel size on the variation of contaminant levels in environmental monitoring studies. Thirty individuals from 2 size groups, less than 4-cm and more than 4-cm shell length, were collected over 4 seasons at each site studied. The samples were dissected, and copper, zinc, manganese, and nickel were measured in the whole soft tissues by inductively coupled plasma mass spectrometry (ICP-MS). The maximum concentrations of copper, zinc, manganese, and nickel expressed in mg/kg dry weight at the three sites were 54.01, 146.25, 20.69, and 8.85, respectively. A clear distribution pattern of the studied elements was observed in the two size classes. In fact, significantly higher concentrations (P < 0.05) were found in individuals with a shell length of less than 4 cm. Significantly, higher concentrations (P < 0.05) were found in individuals with a shell length of less than 4 cm due to their high filtration and low excretion activities compared to long individuals. In addition, metal pollution index (MPI) values were higher in small bivalve individuals. The trace element contents found in the mussel samples of the present study showed large spatial and temporal variations among the different sites studied, highlighting the typical exposure of marine sites to different marine pollutants. Notably, elevated concentrations of copper were observed in the port of Zemmouri, likely due to port activities. Conversely, the highest levels of manganese and nickel were recorded at Boudouaou El Bahri, potentially attributable to the use of fertilisers by agricultural activities. Some shellfish samples had exceeded the permissible concentration levels of copper and manganese, thereby posing a danger to bivalve consumers.

Behavioural response of Australian fur seals (Arctocephalus pusillus doriferus) to vessel noise during peak and off-peak human visitation

Vessel traffic is the greatest contributor to marine anthropogenic noise pollution, and particularly affects species utilising coastal areas. Seal Rocks (Victoria), the largest Australian fur seal breeding colony, has a relatively small vessel exclusion zone during the pupping and breeding season, when vessel traffic is at its peak. It is necessary to understand the impacts of visitation at sensitive marine sites to ensure they are adequately protected from human disturbance. This study assessed the behavioural response of hauled-out Australian fur seals at Seal Rocks to controlled vessel noise exposure during peak and off-peak vessel visitation periods. High level noise exposure (76–80 dB) resulted in increased vigilance and interruption to vital behaviours in both peak and off-peak periods. These behavioural responses were limited to the period of noise exposure but are nevertheless indicative of disturbance. It is important to ensure regulations intended to protect sensitive sites are up-to-date and evidence based.

Statistically Resolved Planetary Boundary Layer Height Diurnal Variability Using Spaceborne Lidar Data

The Planetary Boundary Layer Height (PBLH) significantly impacts weather, climate, and air quality. Understanding the global diurnal variation of the PBLH is particularly challenging due to the necessity of extensive observations and suitable retrieval algorithms that can adapt to diverse thermodynamic and dynamic conditions. This study utilized data from the Cloud-Aerosol Transport System (CATS) to analyze the diurnal variation of PBLH in both continental and marine regions. By leveraging CATS data and a modified version of the Different Thermo-Dynamics Stability (DTDS) algorithm, along with machine learning denoising, the study determined the diurnal variation of the PBLH in continental mid-latitude and marine regions. The CATS DTDS-PBLH closely matches ground-based lidar and radiosonde measurements at the continental sites, with correlation coefficients above 0.6 and well-aligned diurnal variability, although slightly overestimated at nighttime. In contrast, PBLH at the marine site was consistently overestimated due to the viewing geometry of CATS and complex cloud structures. The study emphasizes the importance of integrating meteorological data with lidar signals for accurate and robust PBLH estimations, which are essential for effective boundary layer assessment from satellite observations.

Spatial and temporal patterns of floating litter in shallow habitats: Insights from high-tourism tropical areas in Northeastern Brazil

We investigated the composition, quantity, distribution and potential sources of floating litter in the subtidal zones of tropical beaches. Marine sampling sites were selected based on the presence (protected/sheltered) or absence (non-protected) of reefs. Plastic was the most abundant material, and the presence of floating litter from land-based sources was confirmed, which was likely associated with domestic and tourism-related activities, owing to irregular waste disposal. Marine debris was more abundant during the rainy season, and marine beaches had more floating litter than estuarine beaches. Coastal reefs served as a barrier, impeding the transport of marine litter by coastal currents, explaining the greater abundance of floating litter on protected/sheltered marine beaches. Thus, three mechanisms seemed to drive the amount of floating litter in the subtidal zone of the tropical beaches: 1) the availability of floating litter in the water, 2) coastal hydrodynamics favoring the accumulation of floating litter, and 3) a beach’s capacity to retain floating litter. Our study demonstrates that marine litter is an important pollution source in sensitive areas that play a key role as nurseries for marine life, especially in beaches close to reef formations.

A multi-pronged approach to assessing antimicrobial resistance risks in coastal waters and aquaculture systems

Antimicrobial resistance (AMR) is a global challenge that has impacted aquaculture and surrounding marine environments. In this study, a year-long monitoring program was implemented to evaluate AMR in two different aquaculture settings (i.e., open cage farming, recirculating aquaculture system (RAS)) and surrounding marine environment within a tropical coastal region. The objectives of this study are to (i) investigate the prevalence and co-occurrence of antibiotic-resistant bacteria (ARB), antibiotic resistance genes (ARGs), antibiotics (AB) and various associated chemical compounds at these study sites; (ii) explore the contributing factors to development and propagation of AMR in the coastal environment; and (iii) assess the AMR risks from different perspectives based on the three AMR determinants (i.e., ARB, ARGs and AB). Key findings revealed a distinct pattern of AMR across the different aquaculture settings, notably a higher prevalence of antibiotic-resistant Vibrio at RAS outfalls, suggesting a potential accumulation of microorganisms within the treatment system. Despite the relative uniform distribution of ARGs across marine sites, specific genes such as qepA, blaCTX−M and bacA, were found to be abundant in fish samples, especially from the RAS. Variations in chemical contaminant prevalence across sites highlighted possible anthropogenic impacts. Moreover, environmental and seasonal variations were found to significantly influence the distribution of ARGs and chemical compounds in the coastal waters. Hierarchical cluster analysis that was based on ARGs, chemical compounds and environmental data, categorized the sites into three distinct clusters which reflected strong association with location, seasonality and aquaculture activities. The observed weak correlations between ARGs and chemical compounds imply that low environmental concentrations may be insufficient for resistance selection. A comprehensive risk assessment using methodologies such as the multiple antibiotic resistance (MAR) index, comparative AMR risk index (CAMRI) and Risk quotient (RQ) underscored the complexity of AMR risks. This research significantly contributes to the understanding of AMR dynamics in natural aquatic systems and provides valuable insights for managing and mitigating AMR risks in coastal environments.

Utilising the Ipzo parameter for more reliable estimates of undrained shear strength directly from CPTU data in saturated natural clay-like soils

Ramsey and Tho illustrated the ability of the Ipzo parameter to estimate plasticity index in a wide range of saturated natural soils and highlighted the potential of the Ipzo parameter for improving the reliability of estimations of other soil properties affected by plasticity index. In this note, an improved method is proposed for estimating undrained shear strength in clay-like soils using CPTU data, where clay-like is defined as Ipzo ≥ 12%. The improved method is validated using a geographically and geologically diverse “Nkt1-database” comprising 54 anisotropically consolidated undrained triaxial compression tests, with complementary CPTU measurements from 36 geological units at 18 globally distributed marine sites.

Seismic response characteristics of offshore sites in the Sagami Bay, Japan—Part I: Comparison of spectral inversion and ratio under weak motions

Understanding offshore site amplification (AF) characteristics is crucial for marine engineering. Thus far, the spectral ratio (SR) has been widely used to analyze offshore AF characteristics, despite its reliability not yet being fully investigated. In this study, we used 826 ground-motion data recorded at 6 offshore and 19 onshore stations in the Sagami Bay region to reveal the source, path, and AF characteristics using the generalized inversion technique (GIT). The average stress drops for the shallow crustal, subduction interface, and subduction slab earthquakes were 3.55, 6.59, and 7.07 MPa, respectively. The offshore sites were categorized into flat and steep stations based on the local slope gradient (LSG), and systematic AF characteristics were observed. We found that the topography had a negligible influence on the flat free-field station KNG205. AFs obtained using the GIT and SR were analyzed and compared, revealing two main differences: (1) SR-obtained AF values were significantly larger than GIT-obtained AF values above 0.5 Hz and 5 Hz at the flat and steep sites, respectively; (2) resonant frequencies estimated using the SR drifted to lower and higher frequencies for flat and steep sites, respectively. The ineffectiveness of the SR for flat and steep stations was attributed to the effects of topography and seawater pressure on low- and high-frequency vertical ground-motions, respectively. These results suggest that the SR is only reliable for estimating AF curves at marine free-field sites and low-frequency AFs at steep sites. The LSG may play an important role in offshore ground-motion studies.

Influence of offshore wind turbine size in levelised cost of energy

Offshore wind energy is developing rapidly in recent years. Within the offshore wind energy industry, the main advance that has occurred has been the wind turbine growth. In fact, the offshore turbines have changed from small turbines adapted to the marine environment to turbines that currently range between 16~18 MW. This increase has been done in order to cut down costs and get longer production of wind energy, consequently, reducing the levelized cost of energy. The current mechanisms for assigning marine sites are based on successive auctions organized by government agencies. In some countries, these auctions are carried out through reverse bidding, that is, they are awarded to the promoters who present the lowest sales price for the energy generated or, in the case of other countries, that price marked in the auction has a partial weight of 60%~80% in the final ranking. Other countries organize a second type of reverse auction to award subsidies, which, being limited, are awarded to the promoters who present the lowest energy sales price. In this article, a comparative study developed for evaluation of the value of levelized cost of energy, as a result of bigger nameplate capacity of the offshore wind turbines. The results show that the bigger turbine capacity, the lower the levelized cost of energy is obtained.

Local scour effects on seismic behavior of pile-group foundations in cohesionless soils: Insights from quasi-static tests

Local scour has been reported as a common phenomenon for pile-group foundations in marine, coastal, and riverine sites, while its effects on the seismic behavior of pile-group foundations are yet to be well documented. This paper reported a pair of quasi-static cyclic loading tests on 2 × 3 scoured pile-group foundation specimens, one in global scour and the other in local scour, to understand the influence of local scour on the seismic behavior, particularly in terms of soil-pile interaction features and failure mechanisms. Test results indicate a flexural failure mode for both specimens. Local scour does not change the order of limit states but postpones the occurrence of concrete cover cracking and rebar yielding due to the reduced lateral stiffness of the locally scoured piles. Moreover, local scour rarely changes the aboveground damage regions at the top of outer piles (one time the side length of squared pile section, D), but significantly aggravates and deepens the underground damage regions at outer piles (from 4 ∼ 5D for global scour to 3.7 ∼ 6D for local scour). Besides, local scour reduces the displacement ductility factor from 2.50 to 1.25 for the Easy-to-Repair limit state, resulting in adverse impacts on pile-group foundations in general.

Integrated record of the Late Lutetian Thermal Maximum at IODP site U1508, Tasman Sea: The deep-sea response

The Late Lutetian Thermal Maximum (LLTM) was a transient and brief global warming event recorded in the middle Eocene, at 41.52 Ma. The biotic response to the LLTM has been documented at only a few marine sites so far. Here, we present the first record of deep-sea benthic foraminiferal assemblage changes during the LLTM in the southwest Pacific at International Ocean Discovery Program Hole U1508C (1609 m water depth) in the Tasman Sea. The LLTM coincides with a negative excursion in bulk sediment δ13C (0.47‰) and benthic foraminifera δ13C (0.36‰), with changes in the relative abundance of benthic foraminiferal species and in the deep-water organic geochemistry. The decrease in diversity of the assemblages indicates environmental stress during the event, potentially linked to oxygen deficiency, as evidenced by the occurrence of dysoxic taxa (e.g. Lenticulina spp., Turrillina brevispira). Although calcareous taxa dominate, the presence of corrosion-resistant species and poorly preserved foraminiferal tests suggest slightly CaCO3-corrosive bottom waters, but no dissolution was evident. We suggest the shallowing of the thermocline and enhanced water column stratification at this site during the LLTM.

Heterogeneous marine response during the Toarcian Oceanic Anoxic Event (TOAE): The potential role of storminess

The Toarcian Oceanic Anoxic Event (TOAE; ∼183 Ma) represents an important hyperthermal and deoxygenation event in the Early Jurassic. However, TOAE marine records are spatially heterogeneous with regard to nutrient levels, primary productivity, redox conditions and organic enrichment. This non-uniform response to global hyperwarming is not readily accounted for by local variations in paleogeography, climate, or water depth. Largely overlooked to date is the intensified storm activity that characterized the TOAE, and the role that this may have played in controlling marine responses to that event. A review of TOAE studies from multiple marine environments suggests that storm intensity covaried with paleoceanographic conditions, such as nutrient availability, primary productivity, redox conditions, and organic-rich sedimentation. At mid-paleolatitude sites, relatively weak storm activity during the TOAE induced short-term watermass oxygenation, and marine settings were mainly characterized by enhanced anoxia (even euxinia), water-column stratification, increased primary productivity (fueled by terrestrial runoff and P regeneration in euxinic settings), and organic-rich sedimentation. At low-paleolatitude sites, TOAE storm activity was relatively strong, and contributed to marine environments characterized by oxic to suboxic conditions, reduced water-column stratification, decreased primary productivity (possibly due to limited P regeneration and upwelling), low sedimentary organic content, and locally high oolite abundance. TOAE marine sites at all paleolatitudes exhibit: i) sea-level rise and enhanced continental weathering fluxes linked to an intensified hydrological cycle; ii) reduced dinoflagellate and increased cyanobacterial activity; and iii) low δ15N values (mainly −1‰ to +3‰) linked to enhanced diazotrophic nitrogen fixation. The spatial heterogeneity of the response of TOAE marine systems is difficult to reconcile with scenarios linking increased terrestrial flux to marine eutrophication, primary productivity increase and organic-rich sedimentation. Consequently, we hypothesize that the intensity of storm activity influenced TOAE marine systems, and that this factor can, at least partially, account for heterogeneous patterns of environmental changes at middle versus low paleolatitudes and open versus restricted marine settings. Importantly, increased storm activity can induce pycnocline deepening via vertical water-column mixing, thereby promoting: i) enhanced aerobic degradation of organic matter (low sediment organic matter content) due to a reduced oxygen-minimum zone; ii) less nutrient upwelling from deep waters into the photic zone (nutrient-depleted upper ocean), and iii) blooms of nitrogen-fixing cyanobacteria (low δ15N) and calcification (ooid formation). Thus, the interaction between storminess and pycnocline depth is a potentially important factor affecting marine environmental changes during TOAE. These findings have implications for modern oceans now experiencing climatic warming and intensified tropical storm activity.

Laboratory test study on deterioration process of cement soil piles in radial direction in marine soft soil foundation

The deep mixing method is a commonly used foundation treatment technology for marine soft soil sites. Due to the long-term corrosion of seawater ions, the deterioration of cement soil pile in-site is inevitable. Revealing and predicting the development trend of cement soil can provide data support for the durability evaluation of marine engineering. The existing research on the deterioration development trend of cement soil neglects the influence of different stress states along the length direction of the pile on the deterioration. This study developed a tester that can simulate the deterioration of solidified soil in the stress state of natural foundations. A rapid prediction method for the deterioration depth of cement soil considering the influence of seawater pressure is established. The research concept has certain reference significance for research on the prediction of the deterioration depth for solidified soil in similar corrosive environments.

Snapshots of Coastal Ecology Using Multiproxy Analysis Reveals Insights Into the Preservation of Swamp and Marsh Environments Since the Late Pleistocene

AbstractThe southeastern United States Coastal Plain ecosystem contains baldcypress (Taxodium distichum) swamps and grass‐dominated marshes. These ecosystems also occurred on the exposed continental shelf during lower sea levels but are rarely preserved due to the mechanically erosive nature of transgression and regression. Two presently marine sites on the northeastern Gulf of Mexico's continental shelf contain well‐preserved woody terrestrial sediments that were the subject of previous studies. This study continues the investigation using geochemical (δ13C, δ15N, δ34S) and palynological characteristics of these formerly terrestrial sediments to determine if swamps and/or marshes existed at the time of deposition. The first site is located ∼20 km southeast of Horn Island, Mississippi (MS) and the core has terrestrial sediments radiocarbon dated to 11,066–10,228 (2σ) calibrated years BP (early Holocene). The second site is the “Alabama Underwater Forest” located ∼13 km south of Gulf Shores, Alabama (AL) and the cores have terrestrial sediments optically stimulated luminescence dated to 63 ka (±10 ka, 2σ) to 72 ka (±16 ka, 2σ) (late Pleistocene). Geochemical results for the MS sediments indicate a swamp‐to‐freshwater marsh transitional series, whereas the AL sediments indicate a swamp‐to‐saltwater marsh transitional series, both supported by palynological results. Further exploration of the geochemical results using linear discriminant analysis, trained with published geochemical data, supports the swamp and marsh interpretations. We conclude that the near‐pristine preservation of these woody deposits is not solely due to physical mechanisms, such as rapid burial, but is also coupled with anoxia‐ and euxinia‐driven biogeochemical reactions promoting wood and woody debris preservation in swamp and marsh environments.

Probability and severity of climate change threats to natural world heritage sites vary across site specifics and over time

This study contributes a first comparison of current and potential threats to Natural World Heritage Sites from climate change, as assessed by experts, when site and location characteristics (size, year of inscription to the World Heritage list, continent, climate zone and kind of site) are controlled for. The probability of a threat as well as its intensity is analysed. Another novelty lies in the use of data from the IUCN Conservation Outlook Assessment, covering all 245 Natural and Mixed World Heritage Sites across the world for three points in time: 2014, 2017 and 2020. The threat of climate change is broadly defined and includes temperature extremes, rising temperatures, disappearing glaciers, coral bleaching, droughts, desertification, and rising sea levels. Results based on a simultaneous Probit model with random effects show that the probability of actual and potential climate change threats increases over time, but with differences for size, kind of site and location. The probability that a threat is identified is highest for marine and coastal sites, and for those in Latin America, while it is significantly lower for sites on the African continent. Larger sites have a higher probability of being assessed as at risk and the severity of threats is found to be lower for recently inscribed sites. The rate at which the likelihood of a threat assessment increases is consistent for both current and future situations, while the probability of the most severe threat is larger for the current than the future period. A serious threat from climate change is assessed as highest for locations in the tropical monsoon (current period) or the tropical savannah climate (future period). Estimations also show that pure descriptive statistics or bivariate correlations may not correctly identify the risk or the dignity of a threat.

Quantification of heavy metals in wild gravid female mud crab (Scylla olivacea) collected from different rivers of Sundarbans mangrove region

Heavy metals pollution is one of our major problems in Sundarbans mangrove zone as we all their surrounding rivers. The presence of industrial development in the nearby areas of coastal and marine aquacultures sites are the cause of heavy metals pollution. The aim of the research was to quantify heavy metals in gravid female mud crabs (Scylla olivacea) in three different rivers of Sundarbans region. Mud crabs and their surrounding water and soil sediments were collected from Mongla, Kholpetua, and Kopotakkho rivers. Analysis of river water was conducted in the laboratory of Shiva Analyticals (India) Private Limited, India, whereas live mud crabs and sediment samples were analyzed from Quality Control Laboratory (QCL), Khulna, Bangladesh for the quantification of heavy metals. The results showed that the heavy metals As, Cr, Cd, Hg and Pb were detected in mud crabs and their surrounding river water and sediments, but the concentration of heavy metals in mud crabs was remains below the limit of human’s consumptions except the heavy metal Chromium (Cr). Maximum concentration of heavy metals was detected Kopotakkho river followed by Mongla and Kholpetua river. The concentration of heavy metals was highest in soil sediments followed by mud crabs and river waters. Mud crabs were contaminated by heavy metals that bioaccumulated from their surrounding sediments and water sources. The hierarchy of mean concentrations (mg/kg) of the heavy metals were Pb>As>Cr>Pb>Hg. Heavy metals are carcinogenic for human consumption when exceeded their permissible levels. It is urgent to stop pollution in Sundarbans mangrove zone and led to serve healthy foods for the nations.

Actinobacteria diversity associated with marine sediments and a wetland system, Agulhas-South Africa

BackgroundSouth Africa is known for its great biodiversity. The Agulhas Plain represents one such unique environment where low-gradient topography has resulted in extensive wetland formation. It is fed by two major river systems, bringing in brackish, alkaline water. It has been exposed to major marine transgression and regression events, and harbours great Fynbos diversity as well as a Mediterranean-type climate, thereby creating unique ecosystems. It is therefore surprising that little is known about the bacterial diversity associated with the Agulhas Plain and associated marine ecosystems.MethodsIn this study, we focused on the actinobacterial diversity (Phylum Actinomycetota) associated with an emerging peatland on the Agulhas Plain (SF; Areas 1–3) and a marine site (ANP; Ocean, Rocky, Dry) located 10 km away from SF. A combined metataxanomics and isolation approach was taken to evaluate the actinobacterial diversity of the sampling sites and to determine the effect of environmental physicochemical parameters on these populations. Various genome analyses were performed on an Sva0096 marine bin to gain insight into its ecological role.ResultsMetataxanomics showed that the two sites shared defined major taxa, including Blastococcus, Geodermatophilus, Microbacterium, Mycobacterium, Nocardioides, Streptomyces, and the Sva0996 marine group. Analysis of the biosynthetic potential of an Sva0996 marine bin134 (obtained from GenBank) provided insights into the potential ecological role of this group of bacteria in both the marine and terrestrial environments. Higher actinobacterial diversity (Shannon index > 5) was observed for Areas 2 and 3 (SF), as well as the ANP Dry samples. The actinobacterial population composition was found to be driven by salinity, pH, Mn, and Ca, with certain areas of SF exhibiting similar (and even higher) salinity (SF: 70–100 Ω vs. ANP: 100–160 Ω) and lower pH levels (SF: 6.3-8.0 vs. ANP: 8.6–8.9) to that of the marine environment.ConclusionThis snapshot study has provided some insights into the actinobacterial diversity of the two sites studied. Analysis of an Sva0096 marine bin134 provided further insights into the potential ability of the Sva0096 marine group to survive in a unique terrestrial environment that is periodically exposed to environmental pressures that mimic the marine environment.

Responses of zooplankton assemblages to environmental variability among brackish coastal ponds, New Zealand

Coastal brackish waters, including estuaries, lagoons and coastal ponds, experience fluctuations in physicochemical properties, particularly in salinity, due to the differential forcing of marine and freshwater inflows. Most research concerning brackish waters is skewed towards lagoons and estuaries, while relatively little exists on small coastal ponds. This study examined variability in zooplankton community composition relative to environmental conditions among brackish coastal ponds in Auckland, New Zealand. Eight coastal stormwater ponds, four freshwater ponds, and four marine sites were selected to represent a wide salinity gradient and sampled for zooplankton and environmental variables. Marked spatial and temporal variability in environmental conditions was observed among the coastal ponds. Salinity of the ponds was, on average, lower in winter, influenced by higher rainfall, while in summer reduced rainfall led to significantly lower freshwater inputs. Zooplankton communities within the coastal ponds were a mix of those in freshwater and marine sites, along with unique species not observed in each of the adjoining ecosystems. Salinity was the most important factor driving zooplankton community composition among sites, as widely reported for estuaries and lagoons. The degree of temporal change in salinity within ponds also affected community composition, with euryhaline copepods such as Sulcanus conflictus and Mesochra parva most abundant at sites with larger seasonal salinity changes. Salinity increases due to sea-level rises may lead to the disappearance of species that are less tolerant to salinity, with a move to dominance by euryhaline species.

Vertical-Axis Tidal Turbines: Model Development and Farm Layout Design

In this paper, we propose a new 3D model for vertical-axis tidal turbines (VATTs) embedded in the shallow-water code SHYFEM. The turbine model is based on the Blade-Element∖Momentum (BEM) theory and, therefore, is able to predict turbine performance based on the local flow conditions and the geometric characteristics of the turbine. It is particularly suitable for studying turbine arrays, as it can capture the interactions between the turbines. For this reason, the model is used to test a tidal farm of 21 devices with fluid dynamic simulations. In particular, we deploy the farm at Portland Bill, which is a marine site characterised by a wide spread in the direction of the tidal currents during a flood-ebb tide cycle. We optimised the lateral and longitudinal spacing of the turbines in a fence using computational fluid dynamics simulations and then performed a sensitivity analysis by changing the distance between the fences. The results show that the greater the distance between the fences, the higher the power output. The increase in power generation is around 16%, but this implies a huge increase in the horizontal extent of the farm. Further assessments should be carried out, as the expansion of a marine area dedicated to energy exploitation may conflict with other stakeholder interests.

Global survey of hgcA-carrying genomes in marine and freshwater sediments: Insights into mercury methylation processes

Mercury (Hg) methylation is a microbially mediated process that produces methylmercury (MeHg), a bioaccumulative neurotoxin. A highly conserved gene pair, hgcAB, is required for Hg methylation, which provides a basis for identifying Hg methylators and evaluating their genomic composition. In this study, we conducted a large-scale omics analysis in which 281 metagenomic freshwater and marine sediment samples from 46 geographic locations across the globe were queried. Specific objectives were to examine the prevalence of Hg methylators, to identify horizontal gene transfer (HGT) events involving hgcAB within Hg methylator communities, and to identify associations between hgcAB and microbial biochemical functions/genes. Hg methylators from the phyla Desulfobacterota and Bacteroidota were dominant in both freshwater and marine sediments while Firmicutes and methanogens belonging to Euryarchaeota were identified only in freshwater sediments. Novel Hg methylators were found in the Phycisphaerae and Planctomycetia classes within the phylum Planctomycetota, including potential hgcA-carrying anammox metagenome-assembled genomes (MAGs) from Candidatus Brocadiia. HGT of hgcA and hgcB were identified in both freshwater and marine methylator communities. Spearman's correlation analysis of methylator genomes suggested that in addition to sulfide, thiosulfate, sulfite, and ammonia may be important parameters for Hg methylation processes in sediments. Overall, our results indicated that the biochemical drivers of Hg methylation vary between marine and freshwater sites, lending insight into the influence of environmental perturbances, such as a changing climate, on Hg methylation processes.