Coastal Marine Systems Research Articles

Existence and Uniqueness of the Initial-Boundary Value Problem Solution of Multicomponent Sediments Transport in Coastal Marine Systems

Introduction. This work is devoted to the study of a non-stationary two-dimensional model of sediment transport in coastal marine systems. The model takes into account the complex multi-fractional composition of sediments, the gravity effect and tangential stress caused by the impact of waves, turbulent exchange, dynamically changing bottom topography, and other factors. The aim of the work was to carry out an analytical study of the conditions for the initialboundary value problem existence and uniqueness corresponding to the specified model.Materials and Methods. Linearization of the initial-boundary value problem is performed on a temporary uniform grid. The nonlinear coefficients of a quasilinear parabolic equation are taken with a “delay” by one grid step. Thus, a chain of correlated by initial conditions is the final solutions of problems is built. The study of the existence and uniqueness of the problems included in this chain, and therefore the original problem as a whole, is carried out involving the methods of mathematical and functional analysis, as well as methods for solving differential equations.Results. Earlier, the authors investigated the existence and uniqueness of the initial-boundary value problem of the transport of sediments of a single-component composition. In the present work, the result obtained is extended to the case of multi-fractional sediments.Discussion and Conclusions. The non-linear spatial two-dimensional model of sediment transport was previously investigated by the team of authors in the case of bottom sediments consisting of particles having the same characteristic dimensions and density (single-component composition) based on the analysis of the existing results of mathematical modeling of hydrodynamic processes. In this paper, the previous results of the study are extended to the case of sediments of a multicomponent composition, namely, the conditions for the existence and uniqueness of the solution of the initial-boundary value problem corresponding to the considered model are determined.

Mercury accumulation, biomagnification, and relationships to δ13C, δ15N and δ34S of fishes and marine mammals in a coastal Arctic marine food web

Combining mercury and stable isotope data sets of consumers facilitates the quantification of whether contaminant variation in predators is due to diet, habitat use and/or environmental factors. We investigated inter-species variation in total Hg (THg) concentrations, trophic magnification slope between δ15N and THg, and relationships of THg with δ13C and δ34S in 15 fish and four marine mammal species (249 individuals in total) in coastal Arctic waters. Median THg concentration in muscle varied between species ranging from 0.08 ± 0.04 μg g−1 dw in capelin to 3.10 ± 0.80 μg g−1 dw in beluga whales. Both δ15N (r2 = 0.26) and δ34S (r2 = 0.19) best explained variation in log-THg across consumers. Higher THg concentrations occurred in higher trophic level species that consumed more pelagic-associated prey than consumers that rely on the benthic microbial-based food web. Our study illustrates the importance of using a multi-isotopic approach that includes δ34S when investigating trophic Hg dynamics in coastal marine systems.

A CHEMTAX‐derived phytoplankton community structure during 12‐year observations in the Gulf of Naples (LTER‐MC)

AbstractThe rapid response of phytoplankton communities to environmental changes makes this compartment one of the most important biological variable to consider in dealing with ecology and trophodynamic of coastal areas, especially in relation with ongoing climate changes and increased human pressures. In the last 30 years, the use of chemotaxonomy has improved the capability to detect phytoplankton community composition in terms of chemofunctional groups, especially for small size species requiring specific expertise and techniques, as well as time‐consuming observation with light microscope. In this study, the temporal variability of chemotaxonomic functional groups has been investigated in surface waters of a LTER station in the Gulf of Naples over 12‐year weekly sampling activities (2003–2015). Data reveal increasing trends in the percentage contribution of diatoms, prasinophytes, cryptophytes to the total phytoplankton biomass, while other groups show a decreasing trend. Nevertheless, strong differences in the intervals of periodicity for each chemofunctional group have emerged, both in terms of timescale and strength of periodicity over time, implying that temporal dynamics of groups were not stationary over the time and that they have different relationships with environmental variability. Our results contribute to enrich scientific knowledge on the ecology of this LTER site and underline the importance of chemotaxonomy as a monitoring tool in coastal marine systems.

COVID-19 Lockdown Effects on a Highly Contaminated Coastal Site: The Mar Piccolo Basin of Taranto

The COVID-19 pandemic has had a dramatic socio-economic impact on mankind; however, the COVID-19 lockdown brought a drastic reduction of anthropic impacts on the environment worldwide, including the marine–coastal system. This study is concentrated on the Mar Piccolo basin of Taranto, a complex marine ecosystem model that is important in terms of ecological, social, and economic activities. Although many numerical studies have been conducted to investigate the features of the water fluxes in the Mar Piccolo basin, this is the first study conducted in order to link meteo-oceanographic conditions, water quality, and potential reduction of anthropic inputs. In particular, we used the model results in order to study the response of the Mar Piccolo basin to a drastic reduction in the leakage of heavy metal IPAs from industrial discharges during the two months of the mandated nationwide lockdown. The results show the different behavior of the two sub-basins of Mar Piccolo, showing the different times necessary for a reduction in the concentrations of heavy metals even after a total stop in the leakage of heavy metal IPAs. The results highlight the high sensitivity of the basin to environmental problems and the different times necessary for the renewal of the water in both sub-basins.

An integrated conceptual model to characterize the effects of offshore wind farms on ecosystem services

Offshore wind farm development has become a key measure of energy transition in recent years. Coastal territories are particularly favorable to the development of offshore wind farms due to their high energy potential. However, these areas are also hotspots of biodiversity, provide attractive landscapes and are under strong anthropogenic pressures. Preserving and sharing the natural and cultural resources of coastal territories while intensifying renewable marine energies, represents one of the most important challenges for future management of coastal environments. Consequently, systemic models that consider all the effects of offshore wind farms on ecosystems and society are essential. Here, we propose a conceptual model for studying these effects, by mobilizing the concept of ecosystem service in a systemic and integrated assessment approach. To that aim, we reviewed the literature and compiled experts’ knowledge in order to characterize the effects of offshore wind farms on food webs during the construction and operation phases. Then, we analyzed the contribution of trophic compartments on ecosystem functions, ecosystem services and beneficiaries, and how offshore wind farms modify the relationships between these compartments of the marine coastal social-ecological systems. Our approach helps identify the causal chains that generate the most important modifications in this system. This information could then be used to predict impacts of offshore wind farms on ecosystem services, and to suggest management trade-offs. This study reveals the need for further studies relating marine biodiversity to ecosystem services, and developing systemic approaches at different scales. The analysis of the effects of offshore wind farms on ecosystem services is crucial since it is linked to strong ecological, socio-economic and political issues.

Protected areas of Brazil’s coastal- marine system: spatial modeling and conservation planning on biomes – ocean interface

The limits of the six biomes of the Brazilian territory (i.g. Amazon, Atlantic Forest, Cerrado, Caatinga, Pampa and Pantanal) were recently revised,1 and a new territorial section of the ocean-continent interface, called Marine Coastal System (CMS) was presented. However, despite being a central theme for conservation planning, the spatial relationship between federal conservation units of Brazil (FCU) and CMS remained without integration. In this work we investigate ecological and territorial representativeness of FCU on Brazil's four geopolitical regions with biomes and ocean interface by developing spatial modeling (five models) encompassing a broad biogeographic context. The objective was to determine the spatial relationship between CMS and FCU, through the application of a set of topological and algebraic rules. Maps of spatial distribution of the FCU in the 5 biomes and in the 4 geopolitical regions shows overlapping CMS. The results indicate that among the 63 FCU found by the M_5 model, 51 FCU present a territorial sharing area with 5 biomes: Amazon, Pampa, Atlantic Forest, Caatinga and Cerrado. In the Amazon and Pampa biomes occur the largest area of overlap with the CMS, but the highest concentration of FCU occurs in the Atlantic Forest biome. The CMS area in the Northeastern region presented the highest environmental heterogeneity, and overlaps four biomes, encompassed most of the FCU of the ocean-continent interface, and also evidenced that the lack of integration of both legal concepts and government databases might cause differences on ecological and territorial representativeness of FCU on Brazil's four geopolitical regions with biomes-ocean interface.

A socio-ecological assessment of land-based contamination and pollution: The Magdalena delta, Colombia

River mouth systems, such as estuaries and deltas are important earth system transitional zones linking the land and coastal marine systems. They funnel anthropogenic contaminants and pollutants from the activities in the river catchment into the marine environment. The present study is focused on the Magdalena River-mouth at Bocas de Ceniza where land-based contamination and pollution are important issues. These were subsequently analysed using an expanded DPSIR framework (Drivers Pressures, State, Impacts Responses). Based on export coefficients and secondary information, the loads of BOD, TSS, Nutrients and solid waste from different sources were identified and compared to prioritize their management within the study area. Findings suggest that contaminants generated in the study area may be insignificant compared to the inputs from the Magdalena River, but they can have a significant impact on the state of local ecosystems. Of all the sources analysed, agriculture and livestock are theoretically the largest contributors of nitrogen (i.e., 14.84 t d-1 and 48.99 t d-1) and phosphorus (i.e., 5.90 t d-1 and 19.46 t d-1) in the basin ‘Direct to the Caribbean’ and ‘Cienaga de Mallorquín’ (that altogether are identified as DtC+) and the ‘Western bank of the lower Magdalena’ (DtM-LM), respectively. In the case of BOD, domestic and industrial wastewaters contribute about 5.10 t d-1 and 98.43 t d-1 in the same basins. Contributions of faecal coliforms were more than 4 orders of magnitude higher in untreated wastewater, being 4.86 x1016 NMP d-1 and 1.78 x1016 NMP d-1 in the lower Magdalena and Caribbean catchments, respectively. Inadequately managed waste and plastic represent a serious problem for the Caribbean Basin. Solid waste generated within the study area and coming from the Magdalena basin and the Caribbean Sea, reaches the coast and deteriorates its visual quality, affects mangrove ecosystems, and generates impacts on coastal populations. By basin, the DtM-LM is where the greatest pollutant loads are generated. However, in terms of impact on human well-being, it is the DtC+ that bears the brunt where pressures are translated in impacts such as increased maintenance and cleaning cost of beaches, reduction or loss of tourism revenue, adverse health effects to vulnerable groups, reduce protection against natural hazards, increased living costs and loss of cultural values.

Effects of upwelling and runoff on water mass mixing and nutrient supply induced by typhoons: Insight from dual water isotopes tracing

AbstractThe issue of whether the increase in nutrients is supplied by increasing runoff or by enhancing upwelling in coastal marine ecosystems after a typhoon is considered controversial. This is because it is relatively difficult to quantify water mixing using traditional methods. Dual water isotopes in the northwestern South China Sea during Typhoon Wipha (July–August 2019) were investigated to address this issue. Weak mixing among different water masses was observed before the typhoon because of strong thermal stratification. After the typhoon, temperature and salinity dropped in the water column, particularly in the upper layer (<20 m), due to strengthened mixing. Mixing in the upper layer predominantly originated from coastal diluted water (36%) in the nearshore, whereas it changed to upwelling (51%) offshore. Upwelling was stronger on the right of the typhoon path (50%) than on the left (36%). Nutrients predominantly originated from the coastal diluted water input (50%) in the upper nearshore layer, while upwelling occurred (53%) offshore. The nutrient supply from upwelling on the right of the typhoon path (43%) was also more considerable than that on the left (25%). This study suggests that typhoon‐induced nutrient supply to the coastal upper water layers from the upwelling water (38%) was more substantial than that from the runoff input (30%), providing new insight into the biogeochemical and ecological responses of coastal marine systems to typhoons.

Abundance and composition of marine litter on the coasts of the Dardanelles (Canakkale Strait, Turkey).

The amount of human-origin litter in sea surface water, sediment, and beaches has been increasing for decades. Initially described in marine coastal systems in the 1960s, marine litter (ML) is nowadays commonly observed in all marine systems. There is even a gigantic island consisting of garbage in the gyre area of the Atlantic Ocean. In relation to this significant problem, ML was collected from seven stations on beaches along the Dardanelles for the first time in the period May 2017-May 2018 and was seasonally and regionally analyzed in terms of densities and weights. ML was categorized by material type (plastic, rubber, paper, etc.) and field of use (mixed packaging wastes, personal use products, fishing wastes, etc.). Total numbers and weights of ML during the study were 5751 items and 115.7kg in an area of 15,980 m2, respectively. Density and weight of ML ranged from 0.050 to 1.182 items/m2 and from 0.446 to 78.46g/m2, respectively. The main ML component was plastic items in terms of both density (90.95%) and weight (53.76%) according to material type. Additionally, mixed packaging wastes (MPW) were the most common ML items in terms of density (82.14%) and weight (49.38%) according to usage. According to the clean-coast index, while Kilya (St.2) and Kepez (St.5) beaches were dirty, Seddulbahir (St.1) beach was clean. The beaches in other stations were neither dirty nor clean (medium) according to the index. At the end of the study, suggestions for a regional strategy were made.

Presence of microplastics in six bivalve species (Mollusca, Bivalvia) commercially exploited at the Pacific coast of Costa Rica, Central America.

Microplastic pollution represents a serious threat to coastal marine systems. We evaluated the presence of microplastics (MPs) in 168 specimens of six commercially exploited bivalve species in the Golfo de Nicoya, Costa Rica. MPs were present in 100 % of the specimens of Leukoma asperrima and L. ecuadoriana, 74 % of Mytella strigata, 82 % of M. guyanensis, 84 % of Asthenometis asthenodon, and 82 % of Tagelus affinis. When considering all specimens, we found on average 4.8 ± 8.0 pieces per individual and 2.1 ± 3.3 items g-1 of wet tissue. There were significant differences between species with L. asperrima and L. ecuadoriana containing the highest number of pieces. Fibers and particles comprised 92 % and 8 %, respectively. This is the first study from the Central America's Pacific region showing the presence of MPs in bivalve species.

How much city is too much city? Biodiversity and ecosystem functioning along an urban gradient at the interface of land and sea

A huge proportion of the world’s population resides in urban areas along the coast. As cities expand, the ability of coastal ecosystems to provide the benefits people derive from nature, ranging from food from fisheries to coastal defense to maritime transportation and beyond, is in question. While it is well understood that coastal development changes ecosystems, quantitative insights about how terrestrial urbanization fundamentally alters ecosystem structure and function in adjacent freshwater and downstream coastal marine habitats remain rare, though a general expectation is that impacts of terrestrial urbanization will attenuate from land to freshwater to coastal marine habitats. Empirical assessments of these phenomena are especially important for species that rely on freshwater and coastal marine habitats at multiple points in their life cycles, including endangered and threatened Pacific salmon (Oncorhynchus spp.). We investigated associations between landscape-scale urbanization and ecosystem structure (biodiversity of epibenthic invertebrate taxa) and function (benthic net primary productivity and decomposition) in freshwater and coastal marine habitats across six pairs of more and less urbanized, coastal watersheds in Puget Sound, WA, USA, using principal components analysis, analysis of covariance, and Mantel tests. Greater upland urbanization was associated with greater reductions in freshwater biodiversity, measured as the density and evenness of epibenthic invertebrate families. In contrast and surprisingly, however, coastal marine biodiversity (measured as the density and evenness of epibenthic invertebrate families) tended to be higher at more urbanized sites, suggesting the potential role of low to moderate levels of urbanization-related disturbance in determining coastal marine biodiversity patterns. We found no statistical association between urbanization and freshwater and coastal marine ecosystem functions, estimated from changes in accumulated algal biomass on tiles (benthic net primary productivity) and loss of biomass from litter bags (decomposition). In addition, there was no evidence that changes in ecosystem structure and function with urbanization were more severe in freshwater than coastal marine habitats, as might be expected if the land-sea boundary diminished effects of landscape-scale urbanization. Our results suggest that the effects of urbanization can be complex and that attention to terrestrial, freshwater, and coastal marine systems in concert will produce more effective, ecosystem-based management.

Connectivity modelling informs metapopulation structure and conservation priorities for a reef‐building species

AbstractAimIn coastal marine systems, biogenic reef‐building species have great importance for conservation as they provide habitat for a wide range of species, promoting biodiversity, ecosystem functioning and services. Biogenic reef persistence and recovery from perturbations depend on recolonization by new recruits. Characterizing larval dispersal among distant reefs is key to understanding how connectivity shapes metapopulation structure and determines network coherence; all of which are of critical importance for effective conservation.LocationNortheast Atlantic coast and western English Channel, France.MethodsWe used a biophysical transport model to simulate larval dispersal of the reef‐building polychaete Sabellaria alveolata. We combined dispersal modelling and network analysis into a framework aiming to identify key reef areas and critical dispersal pathways, whose presence in the network is vital to its overall coherence. We evaluated changes in dispersal pathways constrained by different connectivity thresholds, i.e., minimum dispersal rate for the presence of a connection. We tested scenarios of sequential loss of reefs: randomly, by habitat quality (a score for reef status and occupancy in an area) or by betweenness centrality metric (BC; quantifying the proportion of shortest paths connecting all areas that are passing through any given area).ResultsWe found that the network of S. alveolata reefs forms two main regional clusters, the Atlantic coast and the English Channel, which are connected only through weak sporadic dispersal events. Within each cluster, the network is characterized by relatively high connectivity among neighbouring areas with reefs, maintained even under higher connectivity thresholds. Simulating scenarios of sequential loss of reefs further identified high centrality reefs, those with highest BC values, key to network coherence.Main conclusionsEffective conservation of this important reef habitat requires a network of protected areas designed to sustain a combination of locally important source reefs, and those that act as stepping stones connecting distant reefs.

The influence of salinity on the toxicity of chemical UV-filters to sperms of the free-spawning mussel Mytilus galloprovincialis (Lamark, 1819)

Marine-coastal systems have been increasingly exposed to multiple stressors, including anthropogenic pollution and variations of Climate Change (CC) related factors, whose coexistence could create associated environmental and ecotoxicological risks. Among emergent stressors, 4-methylbenzylidenecamphor (4-MBC) and benzophenone-3 (BP-3) UV-filters are compounds widely used in increasing consumer products, resulting in their ubiquity in aquatic environments and possible pressing challenges on gamete susceptibility. Since most marine invertebrates reproduce by external fertilization, after spawning, gametes may be exposed to several pressures, affecting reproductive success and outcome. The present study focuses on the spermiotoxicity of the environmentally relevant UV-filters 4-MBC and BP-3 combined with salinity shifts, as potential modulators of their harmful effects. For this, Mytilus galloprovincialis male gametes were exposed in vitro to environmentally relevant and slightly higher concentrations (1, 10 and 100 µg/L) of 4-MBC or BP-3 under three different salinities (S 20, 30 and 40). Sperm quality endpoints associated with oxidative status, viability, motility, kinetics, and genotoxicity were evaluated. Similarities and differences in sperm responses among all conditions were highlighted by principal coordinates analysis (PCO). Results showed that salinity acting alone posed greater sperms impairments at the lowest (20) and highest (40) tested levels. When salinity acts as a co-varying stressor, salinity-dominant interactive effects resulted evident, especially for 4-MBC at S 40 and BP-3 at S 20. These findings were pointed out as the worst exposure conditions for M. galloprovincialis sperms, since caused major toxicological effects in terms of: (I) oxidative stress, sperm structural impairments, motility and kinetic alterations in 4-MBC-exposed sperms; (II) DNA damage, compromised mitochondrial activity and hyperactivation in BP-3-exposed ones. Overall, it stands out that salinity influences UV-filter toxicological pathways and, thereby, the potential environmental risk of these contaminants on M. galloprovincialis male gametes, especially in an expected salinity stress scenario.

Multi-channel feeding by migratory sharks in a fluvial-dominated estuary

Rivers can transport a substantial amount of allochthonous nutrients into coastal marine ecosystems. These nutrients are a significant contributor to estuarine productivity, resulting in increased fishery production. However, for migratory marine predators, the importance of nutrients from fluvial-dominated estuaries is unclear. We used carbon (δ 13C) and sulfur (δ 34S) stable isotope mixing models to identify the contribution of prey sources in fluvial-dominated estuarine habitat relative to nearby seagrass and offshore reef habitats to five species of migratory shark: finetooth shark Carcharhinus isodon, blacktip shark Carcharhinus limbatus, bull shark Carcharhinus leucas, Atlantic sharpnose shark Rhizoprionodon terraenovae, and bonnethead shark Sphyrna tiburo. We explored how the contribution of these sources varied as a function of shark length. Sharks generally exhibited a strong reliance on prey from fluvial-estuarine energy channels, with the youngest individuals displaying the highest reliance relative to larger individuals. Models suggested that sharks rely increasingly on nutrient sources from nearby seagrass or offshore reef habitats with age, potentially acting as vectors of nutrient transport across systems. These findings illustrate the importance of a fluvial-dominated estuarine system to migratory marine predators and suggest that these individuals may connect inshore and offshore food-webs. Estuarine systems with high fluvial-influence offer important nutrient subsidies for migratory species, which can transport that energy to adjacent, nutrient-limited systems. Changes to river-flow regimes could disrupt the channeling of nutrients to coastal marine systems, affecting migratory predator populations and their role in transporting these nutrients across the seascape.

Disentangling the components of coastal fish biodiversity in southern Brittany by applying an environmental DNA approach

AbstractThe global biodiversity crisis from anthropogenic activities significantly weakens the functioning of marine ecosystems and jeopardizes their ecosystem services. Increasing monitoring of marine ecosystems is crucial to understand the breadth of the changes in biodiversity, ecosystem functioning and propose more effective conservation strategies. Such strategies should not only focus on maximizing the number of species (i.e., taxonomic diversity) but also the diversity of phylogenetic histories and ecological functions within communities. To support future conservation decisions, multicomponent biodiversity monitoring can be combined with high‐throughput species assemblage detection methods such as environmental DNA (eDNA) metabarcoding. Here, we used eDNA to assess fish biodiversity along the coast of southern Brittany (France, Iroise Sea). We filtered surface marine water from 17 sampling stations and applied an eDNA metabarcoding approach targeting Actinopterygii and Elasmobranchii taxa. We documented three complementary biodiversity components—taxonomic, phylogenetic, and functional diversity—and three diversity facets—richness, divergence and regularity. We identified a north/south contrast with higher diversity for the three facets of the biodiversity components in the northern part of the study area. The northern communities showed higher species richness, stronger phylogenetic overdispersion and lower functional clustering compared to the ones in the southern part, due to the higher diversity of habitats (reefs, rocky shores) and restricted access for fishing. Moreover, we also detected a higher level of taxonomic, phylogenetic, and functional uniqueness in many offshore stations compared to more coastal ones, with the presence of species typically living at greater depths (> 300 m), which suggests an influence of hydrodynamic structures and currents on eDNA dispersion and hence sample composition. eDNA metabarcoding can, therefore, be used as an efficient sampling method to reveal fine‐scale community compositions and in combination with functional and phylogenetic information to document multicomponent biodiversity gradients in coastal marine systems.

A century of warming on Caribbean reefs

The world’s oceans are warming at an unprecedented rate, causing dramatic changes to coastal marine systems, especially coral reefs. We used three complementary ocean temperature databases (HadISST, Pathfinder, and OISST) to quantify change in thermal characteristics of Caribbean coral reefs over the last 150 years (1871–2020). These sea surface temperature (SST) databases included in situ and satellite-derived measurements at multiple spatial resolutions. We also compiled a Caribbean coral reef database identifying 5,326 unique reefs across the region. We found that Caribbean reefs have been warming for at least a century. Regionally reef warming began in 1915, and for four of the eight Caribbean ecoregions we assessed, significant warming was detected for the latter half of the nineteenth century. Following the global mid-twentieth century stasis, warming resumed on Caribbean reefs in the early 1980s in some ecoregions and in the 1990s for others. On average, Caribbean reefs warmed by 0.18°C per decade during this period, ranging from 0.17°C per decade on Bahamian reefs (since 1988) to 0.26°C per decade on reefs within the Southern and Eastern Caribbean ecoregions (since 1981 and 1984, respectively). If this linear rate of warming continues, these already threatened ecosystems would warm by an additional ~1.5°C on average by 2100. We also found that marine heatwave (MHW) events are increasing in both frequency and duration across the Caribbean. Caribbean coral reefs now experience on average 5 MHW events annually, compared to 1 per year in the early 1980s, with recent events lasting on average 14 days. These changes in the thermal environment, in addition to other stressors including fishing and pollution, have caused a dramatic shift in the composition and functioning of Caribbean coral reef ecosystems.

Effects of spatial scale on assessments of suspension bivalve aquaculture for productivity and environmental impacts

Proper evaluations of productivity and environmental impacts of bivalve aquaculture are necessary to achieve sustainable operations in coastal marine systems. Estimation of organic matter budgets using completely mixed one-box models provides an easy approach to help stakeholders of environmental management and aquaculture fisheries obtain an overview of the interactions between aquaculture and the environment. However, estimations and interpretations are highly dependent on the spatial scale of assessments because the distributions of aquaculture facilities and ecosystem structures are spatially heterogeneous. The objective of the present study was to examine how the spatial scale of assessments for the budgets of particulate organic matter (POM) affects the interpretation of the site-specific food supply for suspension oyster aquaculture and impacts of oyster biodeposition on local bottom environments. Based on the actual distribution of oyster farms in a temperate bay on the northeast coast of Japan, we estimated [food supply]/[food demand] (S/D) for oysters as well as the relative contribution of oyster biodeposition to the total deposition of POM (Brel) in the bay along a gradient of spatial scales l from 0.5 m to 4000 m. Although food limitation for aquaculture oysters has been reported in the study bay, S/D was greater than 1 (ranging from 16 to 154) over the spatial scale gradient. S/D tended to be relatively high and overestimated for l < 200 m and l > 1400 m due to the nature of completely mixed one-box models, but relatively lower at intermediate scales. Brel was higher in assessments at farms or smaller scales (e.g., l < 100 m) and was relatively lower at larger scales (e.g., <0.2 at the scale of >500 m). Based on our model-based calculations, the patterns of variation in S/D along the spatial scale gradient are considered to be universal; however, the scale at which S/D values are relatively low varies depending on site-specific conditions, including primary productivity and current velocity. Our findings suggest that estimated budgets of POM need to be carefully interpreted, accounting for model assumptions as well as the influence of the spatial scale of assessments.

An integrated multiple driver mesocosm experiment reveals the effect of global change on planktonic food web structure

Global change puts coastal marine systems under pressure, affecting community structure and functioning. Here, we conducted a mesocosm experiment with an integrated multiple driver design to assess the impact of future global change scenarios on plankton, a key component of marine food webs. The experimental treatments were based on the RCP 6.0 and 8.5 scenarios developed by the IPCC, which were Extended (ERCP) to integrate the future predicted changing nutrient inputs into coastal waters. We show that simultaneous influence of warming, acidification, and increased N:P ratios alter plankton dynamics, favours smaller phytoplankton species, benefits microzooplankton, and impairs mesozooplankton. We observed that future environmental conditions may lead to the rise of Emiliania huxleyi and demise of Noctiluca scintillans, key species for coastal planktonic food webs. In this study, we identified a tipping point between ERCP 6.0 and ERCP 8.5 scenarios, beyond which alterations of food web structure and dynamics are substantial.

Dissolved Nitrous Oxide and Hydroxylamine in the South Yellow Sea and the East China Sea During Early Spring: Distribution, Production, and Emissions

Coastal marine systems are active regions for the production and emission of nitrous oxide (N2O), a potent greenhouse gas. Due to the inherently high variability in different coastal biogeochemical cycles, the factors and mechanisms regulating coastal N2O cycling remain poorly understood. Hydroxylamine (NH2OH), a potential precursor of N2O, has received less attention than other compounds in the coastal areas. Here, we present the spatial distribution of N2O and the first reported NH2OH distribution in the South Yellow Sea (SYS) and the East China Sea (ECS) between March and April 2017. The surface N2O concentrations in the SYS and the ECS varied from 5.9 to 11.3 nmol L–1 (average of 8.4 ± 1.4 nmol L–1) and were characterized by offshore and north–south decreasing gradients. NH2OH showed patchy characteristics and was highly variable, fluctuating between undetectable to 16.4 nmol L–1. We found no apparent covariation between N2O and NH2OH, suggesting the NH2OH pathway, i.e., nitrification (ammonium oxidation), was not the only process affecting N2O production here. The high NH2OH values co-occurred with the greatest chlorophyll-a and oxygen levels in the nearshore region, along with the relationships between NO2–, NO3–, and NH2OH, indicating that a “fresh” nitrifying system, favoring the production and accumulation of NH2OH, was established during the phytoplankton bloom. The high N2O concentrations were not observed in the nearshore. Based on the correlations of the excess N2O (ΔN2O) and apparent oxygen utilization, as well as ΔN2O vs. NO3–, we concluded that the N2O on the continental shelf was mainly derived from nitrification and nitrifier denitrification. Sea-to-air fluxes of N2O varied from −12.4 to 6.6 μmol m–2 d–1 (−3.8 ± 3.7 μmol m–2 d–1) using the Nightingale et al. (2000) formula and −13.3 to 6.9 μmol m–2 d–1 (−3.9 ± 3.9 μmol m–2 d–1) using the Wanninkhof (2014) formula, which corresponds to 75–112% in saturation, suggesting that the SYS and the ECS acted overall as a sink of atmospheric N2O in early spring, with the strength weakening. Our results reveal the factors and potential mechanisms controlling the production and accumulation of NH2OH and N2O in the SYS and the ECS during early spring.

Two-Dimensional-One-Dimensional Alternating Direction Schemes for Coastal Systems Convection-Diffusion Problems

The initial boundary value problem for the 3D convection-diffusion equation corresponding to the mathematical model of suspended matter transport in coastal marine systems and extended shallow water bodies is considered. Convective and diffusive transport operators in horizontal and vertical directions for this type of problem have significantly different physical and spectral properties. In connection with the above, a two-dimensional–one-dimensional splitting scheme has been built—a three-dimensional analog of the Peaceman–Rachford alternating direction scheme, which is suitable for the operational suspension spread prediction in coastal systems. The paper has proved the theorem of stability solution with respect to the initial data and functions of the right side, in the case of time-independent operators in special energy norms determined by one of the splitting scheme operators. The accuracy has been investigated, which, as in the case of the Peaceman–Rachford scheme, with the special definition of boundary conditions on a fractional time step, is the value of the second order in dependency of time and spatial steps. The use of this approach makes it possible to obtain parallel algorithms for solving grid convection-diffusion equations which are economical in the sense of total time of problem solution on multiprocessor systems, which includes time for arithmetic operations realization and the one required to carry of information exchange between processors.