Benthic System Research Articles

Chronic effects of irregular and fibril microplastics on Artemia franciscana in a benthic environment: Size and shape-dependent toxicity

Marine ecosystems are contaminated by plastic products, particularly microplastics (MPs), which settle on the seafloor and affect benthic organisms. This study explores the toxicity of irregular fibril-shaped MPs of various sizes and lengths on Artemia franciscana. We exposed juvenile A. franciscana to irregular-shaped MPs of three sizes, small (<20 μm), medium (40–70 μm), and large (>120 μm), and MP fibers of two length categories, short (200–300 μm) and long (3 mm), in a sand-layered benthic system. The concentrations of the MPs were maintained at 0.05–20 mg/L, and the study was conducted over a 28-d of chronic period. Among all the MPs considered in this study, the small and short MPs exerted the most severe effects (causing mortality, growth inhibition, gut damage, alterations in movement, and a decrease in positive phototaxis). Our study highlights the importance of considering the morphological characteristics of MPs for analyzing their toxicity to aquatic eco-receptors.

Spatiotemporal distribution of sedimentary chloropigments and organic carbon in a shelf sea ecosystem, with a focus on the cold water mass

The Yellow Sea is one of the most thoroughly studied shelf seas in the northwestern Pacific. However, many aspects of the northern Yellow Sea sediments remain poorly understood. Sedimentary chloropigments and total organic carbon (TOC) are crucial components that indicate benthic primary productivity and ecosystem functioning in the marginal sea system. The present study investigated the temporal and spatial variations of sediment chloroplastic pigments (Chl-a and Pha-a) and TOC contents in relation to seasons and the northern Yellow Sea Cold Water Mass (NYSCWM). Decadal trends were also examined using linear regression on time-series data from 12 cruises conducted over a nine-year period (2006–2014). The correlations between sedimentary Chorophy-a (Chl-a), Pheophorbide-a (Pha-a), TOC, and their ratios with other abiotic and biotic factors were analyzed to detect any effects of the NYSCWM on the spatiotemporal distribution of sediment Chl-a, Pha-a, TOC contents, as well as the ecological relevance of their ratios as indicators of food quality (freshness) in the benthic system. The NYSCWM substantially influences the spatial and seasonal distribution of sedimentary Chl-a, Pha-a, and TOC contents. High values of Pha-a, TOC, and the ratios of Pha-a/(Chl-a + Pha-a) and TOC/Chl-a were often observed in the central region of the NYSCWM, where Chl-a showed clear seasonal fluctuations while Pha-a and TOC remained relatively constant. While sedimentary TOC appears to negatively mirror the spatial pattern of primary productivity in the water column, the spatial pattern of sedimentary Chl-a in relation to NYSCWM is less evident. However, the contents of Pha-a and TOC in the central NYSCWM sediments were higher than those at surrounding NYSCWM stations. Surface sediment Pha-a/(Chl-a + Pha-a) ratio was negatively correlated with meiofauna abundance and biomass and positively correlated with nematode/copepod ratio. This finding indicates that the quality of sediment organic matter is important to meiofauna. Conversely, the lower organic degradation rate at the lower bottom temperature of the NYSCWM may explain the observed higher Pha-a and TOC contents in its central area. Time-series data collected over nine years at the NYSCWM stations showed a decreasing trend for Chl-a, while TOC and the ratio of Pha-a/(Chl-a + Pha-a) exhibited increasing tendencies. This trend may imply a reduced quality of food supply to the benthic food web in the shelf sea system, along with degraded ecosystem functioning and service under the impacts of global change and anthropogenic disturbances.

Do stingray feeding pits enhance intertidal macrobenthic biodiversity?

Little is known of the macrobenthos supported within stingray feeding pits. Compared to adjacent unpitted areas during low tide, macrobenthic abundance and biodiversity within the stingray pits might be expected to be (i) greater, the water-retaining pits functioning like rock pools; (ii) no different, since macrofaunal recolonisation can occur very rapidly; or (iii) less, consequent on the substratum changes that typify depressions in soft sediments. In both (i) and (iii) differences in composition of the supported assemblages would be expected, though not in (ii). To differentiate between these alternative hypotheses, faunal characteristics within intertidal stingray pits were compared to those in the adjacent background sandflat in Moreton Bay, Queensland, where the prey of the rays are the decapod crustaceans Trypaea and Mictyris that otherwise structure the benthic system. Results generally (though not totally) support hypothesis (ii), it being consistently found that feeding pits supported less macrobenthic abundance than the surrounding sandflat but subequal taxon density, evenness and patchiness of their faunas, and their taxonomic compositions were very similar. Such feeding pits undoubtedly structure many intertidal sandflats and increase both their topographical complexity and their habitat diversity, but this is not reflected in increased macrobenthic biodiversity.

Biomass-based stochastic model for the transfer of polychlorinated biphenyls in a marine food web

Clarifying the state of marine pollution is important for evaluating the health risk to predators in the marine food web such as fishes and mammals. Although previous studies have generally modeled marine pollution targeting a single organism, this study focused on the transfer of marine pollution in terms of ecological network. In this study, a biomass-based stochastic model was constructed for the transfer of 2,2′,4,4′,5,5′-hexachlorobiphenyl (PCB153) in a coupled pelagic–benthic system targeting populations of species. Incorporating the populations of species allows for discussions on predation pressure and anthropogenic activities such as fishing. The biomass parameters representing populations of species were set by using published data on the ecosystem in Tokyo Bay, Japan and were represented by probability density distributions to reflect population uncertainty. The PCB153 concentrations computed by the model were then compared with observations for validation. The results showed that the probability density distributions of PCB153 concentrations in marine species had a long tail to the right, which indicated the occurrence probabilities of individual organisms having considerably high contamination levels. A theoretical analysis was performed to quantify the response of species (e.g., fish, plankton, and benthos) to PCB153 accumulation accounting for population uncertainty, which indicated that a reduction in the population of predator species may contribute to the occurrence of high PCB153 concentrations in individual organisms in other species. The obtained probability density distributions were then used to compare the PCB153 human intake through ingesting seafood with the human's acceptable daily intake. The model can quantitatively demonstrate the probability distributions of PCB153 concentrations in marine species and PCB153 intake by humans through seafood, to which more attention should be paid.

Revealing zooplankton diversity in the midnight zone

Zooplankton diversity in the deep “midnight zone” (&amp;gt;1000 m), where sunlight does not reach, remains largely unknown. Uncovering such diversity has been challenging because of the major difficulties in sampling deep pelagic fauna and identifying many (unknown) species that belong to these complex swimmer assemblages. In this study, we evaluated zooplankton diversity using two taxonomic marker genes: mitochondrial cytochrome oxidase subunit 1 (COI) and nuclear 18S ribosomal RNA (18S). We collected samples from plankton net tows, ranging from the surface to a depth of 5000 m above the Atacama Trench in the Southeast Pacific. Our study aimed to assess the zooplankton diversity among layers from the upper 1000 m to the ultra-deep abyssopelagic zone to test the hypothesis of decreasing diversity with depth resulting from limited carbon sources. The results showed unique, highly vertically structured communities within the five depth strata sampled, with maximal species richness observed in the upper bathypelagic layer (1000–2000 m). The high species richness of zooplankton (&amp;gt;750 OTUS) at these depths was higher than that found in the upper 1000 m. The vertical diversity trend exhibited a pattern similar to the well-known vertical pattern described for the benthic system. However, a large part of this diversity was either unknown (&amp;gt;50%) or could not be assigned to any known species in current genetic diversity databases. DNA analysis showed that the Calanoid copepods, mostly represented by Subeucalanus monachus, the Euphausiacea, Euphausia mucronata, and the halocypridade, Paraconchoecia dasyophthalma, dominated the community. Water column temperature, dissolved oxygen, particulate carbon, and nitrogen appeared to be related to the observed vertical diversity pattern. Our findings revealed rich and little-known zooplankton diversity in the deep sea, emphasizing the importance of further exploration of this ecosystem to conserve and protect its unique biota.

Lack of strong seasonality in macrobenthic communities from the northern Barents Sea shelf and Nansen Basin

The Barents Sea has been coined ‘the Arctic hotspot’ of climate change due to the rapidity with which environmental changes are taking place. This transitional domain from Atlantic to Arctic waters is home to highly productive benthic communities. This system strongly fluctuates on a seasonal basis in its sympagic-pelagic-benthic coupling interactions, with potential effects on benthic standing stocks and production. Recent discoveries have questioned the marked seasonality for several high Arctic seafloor communities in coastal waters of Svalbard. Still, the seasonal variability of benthic process in the extensive Barents Sea open shelf remains poorly understood. Therefore, we studied the seasonality of macrofauna communities along a transect in the northwestern Barents Sea comprising two hydrographic domains (Arctic vs. Atlantic Water, across the Polar Front) and three geomorphological settings (shelf, continental slope and abyssal plain). Overall, we did not find strong signs of seasonal variation in taxonomic community structure and functional diversity. However, we found some weak signs of seasonality when examining each station separately, especially at a station close to the Polar Front, with high seasonal fluctuations in abiotic drivers indicating a stronger pelagic-benthic coupling. The lack of seasonality found both at the shelf stations south and north of the Polar Front could be related to organic matter stored in the sediments, reflected in constant levels of total organic carbon in surface sediment across time for all stations. We did observe, as expected, highly spatially structured environmental regimes and macrofauna communities associated to them from shelf to slope and basin locations. Understanding the underlying spatio-temporal mechanisms by which soft-bottom benthic communities are structured along environmental gradients is necessary to predict future impacts of climate change in this area. Our results indicate that short-term climate driven changes in the phenology of pelagic ecosystem components might not be directly reflected in the Arctic benthic system, as seafloor processes seem to be partially decoupled from those in the overlying water.

Functional redundancy as an indicator for evaluating functional diversity of macrobenthos under the mussel raft farm near Gouqi Island

Biological traits analysis (BTA) helps to evaluate the effects of different environmental variables on the traits-based functional composition of macrobenthos. However, research on functional traits of macrobenthos under mussel farming is limited. We investigated the spatial and temporal response of the benthic system in terms of taxonomic and functional diversity to environmental variables of farming and natural stressors resulting from suspended mussel farming near Gouqi Island of eastern China Sea. The functional traits of macrobenthic assemblages under mussel farming were characterized by “medium adult body size”, “vermiform body form”, “high flexibility”, “infauna”, “semi-motile”, “gonochoristic”, “surface deposit-feeders”, “carnivores”, “semi-motile burrowers”, and “tube-dwellers”. Functional redundancy was stable in response to mussel farming stresses among seasons, whereas species diversity showed efficient to evaluate natural variables. Functional diversity was significantly affected by farming stressors rather than natural variables, Further analysis using multivariate methods together with continuous monitoring were highlighted to evaluate the impacts of mussel farming. Our results reinforce the importance of macrobenthic species and functional traits analysis to evaluate human stresses driven impacts in offshore ecosystems. By analysing the environmental variables with different sources, independently, we concluded the main effects of human pressures on macrobenthic community. Such distinction could be particularly effective to isolate variable environmental descriptors and evaluate their effects on functional diversity, making the current approach promising for the evaluation of ecological effects of anthropogenic stressors in aquaculture areas.

Nematode community structures in the presence of wastewater treatment plant discharge.

Wastewater treatment plants (WWTPs) represent major point sources of pollution in coastal systems, affecting benthic ecosystems. In the present study, we assessed the potential role that WWTPs have in shaping nematode communities and established baseline knowledge of free-living nematode community structures in St. Andrew Bay, Florida. Sediment samples were collected from four sites representing areas of WWTP outflow and areas with no apparent outflow, during the winter and summer. Nematode communities across sites were significantly different, and the differences were strongly associated with the distance to the nearest WWTP. While the communities were not different along transects at each site, nor across seasons, community dissimilarity across sites was high, implying strong contrasts throughout the bay system. Dominance of tolerant, opportunistic genera and Ecological Quality Status assessments suggest that the system is stressed by organic enrichment, possibly linked to the WWTPs. Our results suggest that knowledge on the life-history of dominant genera is imperative to assess the ecological quality of a benthic system, in addition to taxonomic and functional metrics. Considering the value of marine nematodes as bioindicators, more work should be done to monitor temporal variability in nematode communities in this system as future infrastructure changes alter its dynamics.

Multi-benthic size approach to unveil different environmental conditions in a Mediterranean harbor area (Ancona, Adriatic Sea, Italy).

Harbors are hubs of human activity and are subject to the continuous discharge and release of industrial, agricultural, and municipal waste and contaminants. Benthic organisms are largely known to reflect environmental conditions they live in. Despite meio- and macrofauna interacting within the benthic system, they are ecologically distinct components of the benthos and as such may not necessarily respond to environmental conditions and/or disturbances in the same way. However, in a few field studies the spatial patterns of meio- and macrofauna have been simultaneously compared. In the present study, we assess the response and patterns in the abundance, diversity, and distribution of the two benthic size classes to the different environmental conditions they live in (i.e., sediment concentrations of selected trace metals and polycyclic aromatic hydrocarbons (PAHs); organic matter contents and grain size) characterizing the Ancona Harbor (Adriatic Sea). Meio- and macrofauna provided partially similar types of information depending on the indices used (univariate measures or community structure/species composition) and the different 'response-to-stress'. The community structure (i.e., taxa composition) of both benthic size components clearly showed differences among sampling stations located from inside to outside the harbor, reflecting the marked environmental heterogeneity and disturbance typically characterizing these systems. Notwithstanding, the univariate measures (i.e., meio- and macrofauna total abundance, diversity indices and equitability) didn't show similar spatial patterns. Meiofauna were likely to be more sensitive to the effects of environmental features and contaminants than macrofauna. Overall, trace metals and PAHs affected the community composition of the two benthic components, but only the meiofauna abundance and diversity were related to the environmental variables considered (i.e., quantity and quality of organic matter). Our results pinpoint the importance of studying both meio- and macrofauna communities, which could provide greater insight into the processes affecting the investigated area and reveal different aspects of the benthic ecosystems in response to harbor conditions.

Integrated Multi-Trophic Aquaculture (IMTA): Strategic model for sustainable mariculture in Samanco Bay, Peru

The development of industrial mariculture in Peruvian coasts will continue to grow according to global trends; however, it is characterized by being mostly monospecific, resulting in ecosystemic impacts due to organic matter, which deteriorate the benthic system and encourage eutrophication, negatively affecting biodiversity and fishery resources, which in a long term could turn the activity into an unsustainable practice. Therefore, it is imperative to adopt new production models, focused on the sustainability principle, such as Integrated Multi-Trophic Aquaculture (IMTA), that allow for greater efficiency, competitiveness, and profitability, while guaranteeing environmental balance. In this context, the present study has addressed the problem of Argopecten purpuratus cultivation in Samanco Bay, in which, based on a diagnosis of the bay's conditions, details of the cultivation, and a thorough analysis of the IMTA concept, a strategic model for mariculture is proposed in order to be adopted by private companies, after a validation process. These concepts can be transferred for their adaptation to other scenarios. Furthermore, it is expected that the academic sector, private companies, and the competent authority will be able to intervene synergistically in this process.

Community dynamics of microbial eukaryotes in intertidal mudflats in the hypertidal Bay of Fundy

Protists (microbial eukaryotes) are a critically important but understudied group of microorganisms. They are ubiquitous, represent most of the genetic and functional diversity among eukaryotes, and play essential roles in nutrient and energy cycling. Yet, protists remain a black box in marine sedimentary ecosystems like the intertidal mudflats in the Bay of Fundy. The harsh conditions of the intertidal zone and high energy nature of tides in the Bay of Fundy provide an ideal system for gaining insights into the major food web players, diversity patterns and potential structuring influences of protist communities. Our 18S rDNA metabarcoding study quantified seasonal variations and vertical stratification of protist communities in Bay of Fundy mudflat sediments. Three ‘SAR’ lineages were consistently dominant (in terms of abundance, richness, and prevalence), drove overall community dynamics and formed the core microbiome in sediments. They are Cercozoa (specifically thecate, benthic gliding forms), Bacillariophyta (mainly cosmopolitan, typically planktonic diatoms), and Dinophyceae (dominated by a toxigenic, bloom-forming species). Consumers were the dominant trophic functional group and were comprised mostly of eukaryvorous and bacterivorous Cercozoa, and omnivorous Ciliophora, while phototrophs were dominated by Bacillariophyta. The codominance of Apicomplexa (invertebrate parasites) and Syndiniales (protist parasites) in parasite assemblages, coupled with broader diversity patterns, highlighted the combined marine and terrestrial influences on microbial communities inhabiting intertidal sediments. Our findings, the most comprehensive in a hypertidal benthic system, suggest that synergistic interactions of both local and regional processes (notably benthic-pelagic coupling) may drive heterogenous microbial distribution in high-energy coastal systems.

High capacity for a dietary specialist consumer population to cope with increasing cyanobacterial blooms

We present a common-garden experiment to examine the amphipod Monoporeia affinis, a key deposit-feeder in the Baltic Sea, a low diversity system offering a good model for studying local adaptations. In the northern part of this system, the seasonal development of phytoplankton is characterized by a single diatom bloom (high nutritional quality), whereas in the south, the diatom bloom is followed by a cyanobacteria bloom (low nutritional quality) during summer. Therefore, the nutrient input to the benthic system differs between the sea basins. Accordingly, the amphipod populations were expected to be dietary specialists in the north and generalists in the south. We tested this hypothesis using a combination of stable isotope tracers, trophic niche analyses, and various endpoints of growth and health status. We found that when mixed with diatomes, the toxin-producing cyanobacteria, were efficiently incorporated and used for growth by both populations. However, contrary to expectations, the feeding plasticity was more pronounced in the northern population, indicating genetically-based divergence and suggesting that these animals can develop ecological adaptations to the climate-induced northward cyanobacteria expansion in this system. These findings improve our understanding regarding possible adaptations of the deposit-feeders to increasing cyanobacteria under global warming world in both limnic and marine ecosystems. It is possible that the observed effects apply to other consumers facing altered food quality due to environmental changes.

Biogeochemical buffers in a eutrophic coastal lagoon along an oxic-hypoxic transition

The effects of bottom water oxic-hypoxic transition on estuarine benthic ecosystems have been extensively studied as oxygen (O2) depletion leads to the accumulation of toxic sulphides impacting sediment biogeochemical functioning. The role of benthic macrofauna in modulating such effects is understudied. Macrofauna may increase the resilience of sediments to critical O2 transitions via direct and indirect mechanisms acting upon organic matter (OM) and solid-phase metal pools that represent internal geochemical buffers for sediments. In this study we analysed whether and how the macrofaunal community may facilitate sediment resilience against short-term hypoxic events. Thus, net fluxes of reduced metals and inorganic nutrients were measured under oxic conditions and induced hypoxia in intact cores representing most of the sedimentary environments of the eutrophic Curonian Lagoon. Afterwards, distance-based linear models (distLM) were applied to explore the relationship between the dominant macrofauna taxa, sediment properties and the net fluxes. The results show a mosaic of sedimentary environments including OM poor (0.3%) sandy areas, OM rich (23%) muddy areas and variable combinations of these extremes. The variability of the macrofauna community was comparatively much lower, with oligochaetes and chironomids representing the most abundant taxa at most sampling sites. Along with the induced oxic-hypoxic transition metal fluxes tended to increase, together with dissolved inorganic phosphorus release, whereas dissolved inorganic nitrogen and silica tended to decrease. The distLM model evidenced that sediment properties accounted for 84.2% of the total flux variability whereas Chironomidae, Gammaridae and Gastropoda cumulatively accounted for 15.8% of the total explained variation in fluxes under oxic conditions. Under hypoxic conditions macrofauna explained a measurable but minor fraction of flux variability whereas OM and granulometry were best predictors. In the Curonian Lagoon macrofauna has a minor role in regulating fluxes and in providing biogeochemical services as compared to sediment features. As such, the benthic system appears vulnerable to short-term events of O2 shortage.

Magnetic proxies of continental shelf sediments and their implication for the benthic zone and shrimp fishing activities

The San Jorge Gulf is an ecosystem of great economic importance in the southern hemisphere. It is a breeding and spawning area for various fish and crustacean species. In particular, the Pleoticus muelleri shrimp in different stages of its life cycle and the benthic system are linked. Therefore, in recent decades, it has been of interest for this shrimp resource to carry out interdisciplinary studies focused on the properties of the marine substrate. The concentration of single domain + multidomain magnetite, paramagnetic minerals, and organic matter of seabed sediments vary widely within a study area of about 60400 km2. Values of specific magnetic susceptibility (χ), anhysteretic ratio (χARM/χ), total organic carbon (TOC), and total nitrogen (TN) range between 18.3–323.1 × 10−8m3kg−1, 1.5–13.2, 0.14–1.58%, and 0.02–0.19%, respectively. The spatial correlations between TOC and TN with χ (ρK = −0.72 and −0.59, respectively) and χARM/χ (ρK = 0.90 and 0.71) for these seabed sediments provide good magnetic proxies, which can be determined readily and with low cost. The spatial distribution of geochemical variables and magnetic proxies shows well-delimited areas concerning coastal, inner gulf, eastern, and northeastern zones, which could benefit the management of shrimp resource.

Benthic silicon cycling in the Arctic Barents Sea: a reaction–transport model study

Abstract. Over recent decades the highest rates of water column warming and sea ice loss across the Arctic Ocean have been observed in the Barents Sea. These physical changes have resulted in rapid ecosystem adjustments, manifesting as a northward migration of temperate phytoplankton species at the expense of silica-based diatoms. These changes will potentially alter the composition of phytodetritus deposited at the seafloor, which acts as a biogeochemical reactor and is pivotal in the recycling of key nutrients, such as silicon (Si). To appreciate the sensitivity of the Barents Sea benthic system to the observed changes in surface primary production, there is a need to better understand this benthic–pelagic coupling. Stable Si isotopic compositions of sediment pore waters and the solid phase from three stations in the Barents Sea reveal a coupling of the iron (Fe) and Si cycles, the contemporaneous dissolution of lithogenic silicate minerals (LSi) alongside biogenic silica (BSi), and the potential for the reprecipitation of dissolved silicic acid (DSi) as authigenic clay minerals (AuSi). However, as reaction rates cannot be quantified from observational data alone, a mechanistic understanding of which factors control these processes is missing. Here, we employ reaction–transport modelling together with observational data to disentangle the reaction pathways controlling the cycling of Si within the seafloor. Processes such as the dissolution of BSi are active on multiple timescales, ranging from weeks to hundreds of years, which we are able to examine through steady state and transient model runs. Steady state simulations show that 60 % to 98 % of the sediment pore water DSi pool may be sourced from the dissolution of LSi, while the isotopic composition is also strongly influenced by the desorption of Si from metal oxides, most likely Fe (oxyhydr)oxides (FeSi), as they reductively dissolve. Further, our model simulations indicate that between 2.9 % and 37 % of the DSi released into sediment pore waters is subsequently removed by a process that has a fractionation factor of approximately −2 ‰, most likely representing reprecipitation as AuSi. These observations are significant as the dissolution of LSi represents a source of new Si to the ocean DSi pool and precipitation of AuSi an additional sink, which could address imbalances in the current regional ocean Si budget. Lastly, transient modelling suggests that at least one-third of the total annual benthic DSi flux could be sourced from the dissolution of more reactive, diatom-derived BSi deposited after the surface water bloom at the marginal ice zone. This benthic–pelagic coupling will be subject to change with the continued northward migration of Atlantic phytoplankton species, the northward retreat of the marginal ice zone and the observed decline in the DSi inventory of the subpolar North Atlantic Ocean over the last 3 decades.

Benthic-Pelagic Coupling of Marine Primary Producers Under Different Natural and Human-Induced Pressures’ Regimes

Marine primary producers are highly sensitive to environmental deterioration caused by natural and human-induced stressors. Following the Water Framework Directive and the Marine Strategy Framework Directive requirements, the importance of using the different primary producers of the coastal marine ecosystem (pelagic: phytoplankton and benthic: macroalgae and angiosperms) as appropriate tools for an integrated assessment of the ecological status of the coastal environment has been recognized. However, the processes by which water column characteristics and phytobenthic indicators are linked have not been systematically studied. Based on a large dataset from three Mediterranean sub-basins (Adriatic, Ionian and Aegean Seas) with different trophic conditions, this study aims to explore the coupled responses of benthic and pelagic primary producers to eutrophication pressures on a large scale, focusing on the structural and functional traits of benthic macroalgal and angiosperm communities, and to investigate the key drivers among the different eutrophication-related pelagic indicators (such as nutrient and Chl-a concentrations, water transparency, etc.) that can force the benthic system indicators to low ecological quality levels. In addition to the effects of high nutrient loading on phytoplankton biomass, our results also show that increased nutrient concentrations in seawater have a similar effect on macroalgal communities. Indeed, increasing nutrient concentrations lead to increased coverage of opportunistic macroalgal species at the expense of canopy-forming species. Most structural traits ofPosidonia oceanica(expressed either as individual metrics: shoot density, lower limit depth and lower limit type, or in the context of PREI index) show opposite trends to increasing levels of pressure indicators such as ammonium, nitrate, phosphate, Chl-a and light attenuation. Furthermore, our results highlight the regulating effect of light availability on the ecological status of seagrass meadows (Posidonia oceanicaandCymodocea nodosa). Increasing leaf length values ofC. nodosaare closely associated with higher turbidity values linked to higher phytoplankton biomass (expressed as Chl-a). Overall, the coupling of pelagic and benthic primary producers showed consistent patterns across trophic gradients at the subregional scale.

Benthic–Pelagic Coupling in the Oligotrophic Eastern Mediterranean: A Synthesis of the HYPOXIA Project Results

Benthic–pelagic coupling studies have shown that the response of the benthic system to eutrophication is subject to complex nonlinear dynamics with specific thresholds beyond which abrupt changes in the response of the ecosystem occur and time lags between inputs and responses. The “HYPOXIA: Benthic–pelagic coupling and regime shifts” project aimed to investigate how nutrient input in the water column results in ecological processes of eutrophication, which may lead to significant, irreversible changes in the eastern Mediterranean marine ecosystems within a short period of time. The project included analysis of historical water and benthic data, field sampling, and mesocosm experiments. From the project results, it can be concluded that nutrient inputs are quickly capitalized by small phytoplankton species in the water column resulting in the bloom of specific species with high nutrient uptake capabilities. When Eutrophic Index values (calculated using nutrient and chlorophyll-a concentrations) cross the moderate-to-poor threshold, the precipitating organic matter can cause observable effects on the benthic system. Depending on eutrophication intensity and persistence, the effects can start from microbenthos, meiofauna, and macrofauna increase in abundance and biomass to significant changes in the community structure. The latter includes the proliferation of macrofaunal opportunistic species, an increase in deposit feeders, and the high risk of ecosystem quality degradation. However, contrary to other regions of the world, no water hypoxia or benthic dead zones were observed as chlorophyll-a and O2 concentrations showed a positive correlation. This is caused by the high photosynthetic activity of the phytoplankton and microphytobenthos, the increased bioturbation of macrofauna, and the increased abundance of sediment deposit-feeding species, which quickly consume the excess organic matter. Eastern Mediterranean coastal ecosystems show high resilience to the adverse effects of eutrophication, preventing hypoxia and azoic conditions when eutrophication is the only source of environmental disturbance.

Improved the in-situ remediation effect of benthic microbial electrochemical system by optimizing the anode structure.

Six 60-L benthic microbial electrochemical systems (BMESs) were built for the bioremediation of river sediment. Carbon mesh anodes with honeycomb-structure supports were compared with horizontal anodes, and the system was tested using different cover depths and anode densities. The pollutant removal, electricity generation, and electrochemistry of the six BMES with different anodes was examined using the Ashi River (Harbin, China) as a case study. Total organic carbon and total nitrogen removal from sediments in BMES with Honeycomb-structure anodes were 20-30% and 20-33% higher for the other reactors. The maximum power densities of 43.2 mW m-2 was obtained in BMES. The maximum power densities in BMES with honeycomb-structure anodes were 10-40% higher than that of BMESs with horizontal anode reactors.

Impact of plastic bags on the benthic system of a tropical estuary: An experimental study

Plastic bags are among the most discarded waste items as they are generally only used once and are often improperly eliminated and transported by rivers and estuaries to the ocean. We developed an experimental design to mimic the effect of plastic bag deposition in a tropical estuary and investigated its short-term impact on benthic community structure. We observed a significant influence of the presence of plastic bags on the abundance, richness and diversity of benthic fauna after an eight-week exposure period. Plastic bags acted as a barrier and interfered in processes that occur at the water-sediment interface, such as organic matter and silt-clay deposition. Our results indicate that plastic bags, in addition to directly affecting benthic fauna, may alter processes such as carbon burying, known as “blue carbon”, thus making its storage in the sediment more difficult.

A coral reef benthic system with grazing intensity and immigrated macroalgae in deterministic and stochastic environments

&lt;abstract&gt;&lt;p&gt;As the most diverse, productive but vulnerable marine habitats in the world, coral reefs are easily affected by the ubiquitous environmental fluctuations, which could change the population dynamics and induce phase shifts of the ecosystem. In this paper, we consider a coral reef benthic system, where macroalgae, corals and algal turfs compete for the available space on a given region of the seabed with grazing intensity and immigrated macroalgae in both deterministic and stochastic environments. For the deterministic system, we analyze the existence and stability of equilibria, as well as the existence of bifurcations. For the stochastic system, sufficient conditions for the existence of the unique ergodic stationary distribution as well as the extinction of corals are obtained, by choosing suitable Lyapunov functions. Moreover, for the scenario that the system exhibits bistability between a macroalgal-coral coexistence equilibrium and a coral-free equilibrium in the absence of environmental fluctuation, we further investigate the irreversible noise-induced transition from macroalgal-coral coexistence to coral extirpation, and numerically estimate the critical values of noise intensity for the occurrence of such transition with the aids of the technique of stochastic sensitivity functions.&lt;/p&gt;&lt;/abstract&gt;