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Highlights: • Higher representation of picophytoplankton in land-terminating glacier fjord. • Smaller phytoplankton cells associated with glacial retreat. • Intermediate baroclinic circulation influences phytoplankton distribution. • Glacial retreat likely to have major implications for summer productivity. Abstract: Along Greenland's coastline, the magnitude and timing of primary production in fjords is influenced by meltwater release from marine-terminating glaciers. How local ecosystems will adapt as these glaciers retreat onto land, forcing fundamental changes in hydrography, remains an open question. To further our understanding of this transition, we examine how marine- and land-terminating glaciers respectively influence fjord bloom phenology. Between spring and autumn 2019, we conducted along-fjord transects of hydrographic variables, biogeochemical properties and pico- and nanophytoplankton counts to illustrate the contrasting seasonal bloom dynamics in the fjords Nuup Kangerlua and Ameralik. These fjords are in the same climatic region of west Greenland but influenced by different glacial structures. Nuup Kangerlua, a predominantly marine-terminating system, was differentiated by its sustained second summer bloom and high Chl a fluorescence in summer and autumn. In Ameralik, influenced by a land-terminating glacier, we found higher abundances of pico- and nanophytoplankton, and high cyanobacteria growth in autumn. The summer bloom in Nuup Kangerlua is known to be coincident with subglacial freshwater discharge sustaining renewed nutrient supply to the fjord. We observe here that the intermediate baroclinic circulation, which creates an inflow at subsurface depths, also plays an important role in increasing nutrient availability at shallower depths and potentially explains the distribution of primary producers. Our observations suggest that the retreat of marine-terminating glaciers onto land, with consequent increases in surface water temperature and strat

Intertidal biodiversity is being severely disrupted as a result of increased anthropogenic activity. However, our knowledge about how natural gradients, human induced disturbance and biotic interactions affect biodiversity is limited. So, we investigated how three facets of alpha diversity and community composition of benthic ciliates responded to environmental and biological gradients in the intertidal zone of Zhejiang, China. The key determinants and their relative effects on ciliate communities were identified using structural equation modeling, distance-based redundancy analysis and variation partitioning analysis. Our results revealed that sediment grain size was the most important factor affecting alpha diversity and community composition. Human induced eutrophication had significant effects on phylogenetic alpha diversity and community composition. However, the effects of biotic interactions on ciliate communities were relatively small. Moreover, we found community composition was more sensitive to human disturbance than alpha diversity, thus, more suitable for indicating human-induced eutrophication.

Estuarine intertidal sediments are important centres for organic matter remineralization and nutrients recycling. Nevertheless, there is limited understanding regarding how these processes occur along the salinity gradient and their seasonality. Here, we report on the seasonal biogeochemical cycles from three types of intertidal sedimentary habitats (freshwater, brackish and marine) located in the Western Scheldt estuary (The Netherlands and Belgium). A full year of solute fluxes, porewater nutrient and sediment pigment concentrations at a monthly resolution revealed clear differences in the biogeochemistry of the three sites, indicating that environmental conditions determined the local nutrient dynamics. Temperature controlled sediment oxygen consumption rates and nutrient fluxes, but also affected pore water nutrient concentrations up to 14 cm deep. Fresh and brackish sediments had a net influx of dissolved inorganic nitrogen (DIN) (−1.62 mmol m−2 d−1 and -2.84 mmol m−2 d−1, respectively), while only the freshwater sediments showed a net influx of phosphate (−0.07 mmol m−2 d−1). We estimated that intertidal sediments remineralized a total of 10,000 t C y−1, with 97% of mineralization occurring in the brackish and marine parts. Overall, sediments removed 11% (1500 t N y−1) and 15% (∼200 t P y−1) of the total nitrogen and phosphorus entering the estuary from riverine input. Moreover, observations revealed the historical improvement of water quality resulting from water treatment policies. This spatiotemporal study of OM remineralization and early diagenesis in estuarine systems highlights the importance of intertidal sediments for estuarine systems. Our observations can be used in models to predict estuarine biogeochemistry or assess climate change scenarios.

Coastal areas are subjected to several anthropogenic stressors with much of the world's intertidal areas receding due to human activities, coastal erosion and sea level rise. The Dutch Eastern Scheldt (ES) has been predicted to lose around 35% of intertidal areas by 2060. This study investigates differences between biogeochemical fluxes of intertidal and subtidal sediments of the ES and assesses how ongoing erosion may modify the sedimentary ecosystem functioning of this coastal bay in the coming decades. Monthly fluxes and porewater concentrations of dissolved inorganicnitrogen (DIN), phosphorous (DIP), silica (DSi), carbon (DIC) and oxygen (O 2) as well as organic matter (OM) characteristics were measured from intertidal and subtidal sediments from June 2016–December 2017. Compared to subtidal stations, OM was significantly more reactive in intertidal samples and exhibited 37% higher O2 fluxes, suggesting a strong influence from microphytobenthos. Subtidal sedimentsexhibited an average efflux of nitrates (0.28 mmol m−2 d −1) and phosphates (0.09 mmol m−2 d−1) into the water column, while intertidal areas displayed average influxes (nitrates = −1.2 mmol m−2 d−1, phosphates = −0.03 mmol m−2 d−1) directed into the sediment. The calculated removal of total DIN and DIP from the water column was 34–38% higher in intertidal compared to subtidal samples suggesting stronger denitrification and phosphorus adsorption to solid particles from intertidal sediments. As an upscaling exercise, we estimate potential erosion induced changes if the ES stations are representative for the system. With this assumption, we estimate 11% and 8% reductions for respective nitrogen and phosphorus removal in the entire ES by 2060. Given the global observations of eroding intertidal areas and rising sea levels, we suggest that the predicted habitat loss may cause significant changes

The Eastern Scheldt estuary in the Netherlands has been anthropogenically changed by the construction of a storm surge barrier about 30 years ago, affecting abiotic conditions as well as phytoplankton and zooplankton (ZP). As ZP communities have not been sampled in the last decades, it is unclear to what extent they have changed during the last 30 years. We analyzed the micro- and mesoZP composition and background parameters at eight stations in the Eastern Scheldt in spring, summer, and autumn 2018. Additionally, we conducted dilution experiments to estimate phytoplankton growth and microZP grazing rates. Seasonal variability of ZP was higher than spatial variability, but there were differences between stations. In agreement with data from the 1980s, we identified salinity and chlorophyll a as the most important factors in explaining the ZP community. Suspended particulate matter and water retention time were additionally identified for mesoZP, as well as dissolved inorganic nitrogen and phosphate concentration for microZP. We observed some changes in ZP composition with respect to the 1980s, most of which could be explained by the changes induced by the barrier construction. However, increased abundances of the cyclopoid copepod Oithona sp. were likely related to changes in phytoplankton composition due to large-scale bivalve cultivation in the estuary. Phytoplankton growth and microZP grazing rates were variable between seasons, which could be explained by changes in the phytoplankton community during the annual plankton succession. Overall, the observed alterations in the ZP community due to changed background parameters and intense bivalve filtration could affect the microbial loop as well as consumers of mesoZP and thus the functioning of the pelagic food web.

Blue mussels (Mytilus edulis) are an abundant and economically important species across the North Sea. Partly because of their potent filter feeding and associated shell biofilm, they are able to influence and alter the surrounding marine ecosystem. As a result of proliferating offshore wind farms (OWFs), whose turbine foundations are rapidly colonised by suspension feeding artificial hard substrate communities dominated by M. edulis, as well as planned co-location strategies of these OWFs with mussel mariculture, their numbers will only increase towards the future. On top of these local stressors, global climate change is exerting additional pressure on the marine environment. This study focusses on the link between M. edulis, its microbial shell biofilm and the local nitrogen cycling by quantifying the magnitude and underlying pathways of mussel-associated nitrous oxide (N2O) production. A set of closed-core incubations established nitrifier denitrification as the main chemical pathway of M. edulis related N2O production, although ammonium, nitrite and nitrate all acted as possible precursors. Additional future-climate experiments revealed that blue mussel’s total N2O production, as well as its metabolic activity and the relative contribution of its shell biofilm, were affected by warming (+ 3°C), acidification (- 0.3 pH units), or the combination of both. Because the effects of temperature and acidity were often of an antagonistic nature, the results suggest a relatively small net effect on local N2O production in future-climate marine environments. However, N2O production rates were several orders of magnitude lower than other measured N species (NH+4, NO−2 and NO−3), making substantial mussel-associated N2 production likely. This would greatly affect the local eutrophication levels or even bioavailable n

Spatial variability in the Wadden Sea fish food-web structure was studied by comparing stomach content and bulk stable isotopes of fish species caught simultaneously in the Ems and Marsdiep basins during 2012-2014. Almost all 31 fish species caught were generalist feeders. In both basins, similar predator-prey relationships were found in which a few key prey species fuelled the fish food web. Copepods and brown shrimp were the most important prey species in both basins, mysid shrimp were more important as prey in the Ems basin, while shore crab and herring were more important prey species in the Marsdiep basin. The observed spatial variability in prey preferences was most likely the result of local differences in predator and prey abundances. Published absolute trophic positions based on compound-specific stable isotopes were available for some fish species and indicated low variability between the basins. Estimated absolute trophic positions based on stomach content and on bulk stable isotopes could not be used for the analysis of spatial variability due to sensitivity to sampling procedure (stomach content) and sampling size and baseline (bulk stable isotopes). Although estimates based on bulk stable isotopes underestimated absolute trophic levels in both basins, they can be used for the analysis of relative trophic positions of fish species. Relative trophic positions showed a significant correlation for most fish between the Ems and Marsdiep basins, also indicating a large spatial similarity in trophic structure.

Nutrient import into eutrophic estuarine-coastal zones is modulated by river discharge and anthropogenic activities (agriculture, industry, sewage, etc.). Comparing anthropogenic vs. hydrological influences on nutrient loading is important for ecosystem managers but has been a long-standing challenge. As an attempt to fill this gap, a retrospective study was conducted using multiyear (2012–2022) data in one of the most eutrophic coastal seas in China, the Jiangsu coastal waters. Of the two main pollutants on the Jiangsu coast, dissolved inorganic nitrogen (DIN) is extremely overloaded relative to phosphate (PO4). Their spatial distribution shows clear terrestrial sources as concentrations decrease offshore. Although in each survey DIN and PO4 are enriched in low-salinity waters, their spatially averaged concentrations are out of phase with river discharge on the seasonal and interannual scales. A box model was applied to decompose contributions of river discharge and nutrient import by anthropogenic activities. Results show that the human impacts on the interannual nutrient variability exceed those of hydrological factors on the Jiangsu coast. Anthropogenic nutrient loading decreases during 2012–2020, paralleled with the reduced fertilizer use and other nonpoint sources. Sporadic nutrient fluxes from point sources are likely responsible for the aseasonal nutrient-rich patches. Our study demonstrates that water quality in the Jiangsu coastal waters is highly affected by anthropogenic activities. Findings in this study have broad implications for local monitoring strategies and restoration efforts and provide insight into assessing human stress from field data in global eutrophic ecosystems.

The marine benthos has been largely studied through the use of response traits that characterise species vulnerability to disturbance. More limited has been the specific use of effect traits that represent other species descriptors and that express ecosystem functions. On the sea floor, the benthos is a key ecosystem-engineering component for which functions can be relevantly derived from effect traits. This study provides a typology of sea floor functions based on an extensive data compilation of effect traits. We classified 812 benthic invertebrate species from the northeast Atlantic by 15 effect traits expressing substratum alteration and habitat creation. Cluster analysis identified 15 species groups that represented various epi- or endobenthic functions. Beyond function-habitat specificity, we show that soft sediment species exhibited broader functional niches in the trait space that increase multi-functionality, and were endowed with rare combinations of traits that expanded the functional extent of the species assemblage. As a consequence, soft sediments can host a higher functional diversity than hard substrata because a wider range of above- and below-substratum activities are possible in soft bottoms. Based on response traits documented for the same species and used to express vulnerability to natural or human-induced disturbance, we then show that vulnerability within sea floor functions can be considerably variable. This can be a consequence of the independence between the evolutionary nature of response traits and the contingent engineering abilities of benthic species through effect traits. The paper provides theoretical and utilitarian clarifications on this trait dichotomy.

Kelp cultivation receives increasing interest for its high-value products and ecological services, especially in Europe and North America. Before industrial kelp farming in marine ecosystems continue to scale up, evaluation of the site-wide production relative to ecological carrying capacity (CC) of the identified system is essential. For this purpose, a mechanistic kelp model was developed and applied for hypothetical numerical experiments of expanding the farming area in a Dutch coastal bay (the Eastern Scheldt), where cultivation of Saccharina latissima (sugar kelp) is emerging. The kelp model was implemented within a three-dimensional hydrodynamic–biogeochemical model to account for the environmental interactions. The model captured the seasonal growth dynamics of S. latissima, as well as its carbon and nitrogen contents measured at the Eastern Scheldt pilot sites. The model results suggest that expanding the kelp farming area to ∼1–30% of the bay (representing ∼3.4–75 kt harvest dry weight in the 350-km2 bay) had the potential to weaken the spring bloom, and thereby affected the coexisting shellfish culture in the bay. Competition between S. latissima and phytoplankton mostly occurred in late spring for nutrients (dissolved inorganic nitrogen). The ecological CC should be weighed according to these negative impacts. However, the production CC was not reached even when farming ∼30% of the Eastern Scheldt, i.e. harvesting totally 75 kt dry mass, given that the simulated overall S. latissima production kept increasing with the farming activity. Our modelling approach can be applied to other systems for S. latissima cultivation and assist in assessing CC and environmental impacts.

Cold-water corals (CWCs) are important ecosystem engineers in the deep sea that provide habitat for numerous species and can form large coral mounds. These mounds influence surrounding currents and induce distinct hydrodynamic features, such as internal waves and episodic downwelling events that accelerate transport of organic matter towards the mounds, supplying the corals with food. To date, research on organic matter distribution at coral mounds has focussed either on seasonal timescales or has provided single point snapshots. Data on food distribution at the timescale of a diurnal tidal cycle is currently limited. Here, we integrate physical, biogeochemical, and biological data throughout the water column and along a transect on the south-eastern slope of Rockall Bank, Northeast Atlantic Ocean. This transect consisted of 24-hour sampling stations at four locations: Bank, Upper slope, Lower slope, and the Oreo coral mound. We investigated how the organic matter distribution in the water column along the transect is affected by tidal activity. Repeated CTD casts indicated that the water column above Oreo mound was more dynamic than above other stations in multiple ways. First, the bottom water showed high variability in physical parameters and nutrient concentrations, possibly due to the interaction of the tide with the mound topography. Second, in the surface water a diurnal tidal wave replenished nutrients in the photic zone, supporting new primary production. Third, above the coral mound an internal wave (200 m amplitude) was recorded at 400 m depth after the turning of the barotropic tide. After this wave passed, high quality organic matter was recorded in bottom waters on the mound coinciding with shallow water physical characteristics such as high oxygen concentration and high temperature. Trophic markers in the benthic community suggest feeding on a variety of food sources, including phytodetritus and zooplankton. We suggest that there are three transport m

Cultivation of Saccharina latissima, a brown macroalga, is fast developing in Europe and North America for the sustainable production of food and biorefinery materials and important ecosystem services. Prior studies have demonstrated large spatial variability in the yield and chemical composition of the cultivated S. latissima, even within a small coastal bay. Using a validated hydrodynamic-biogeochemical-kelpmodel, this study examined main drivers of the spatial variability in S. latissima growth dynamics in 40 hypothetical farms throughout a Dutch coastal bay, the Eastern Scheldt. Results indicate that temperatureplays a primary role in driving the spatial variability. For example, S. latissima yield in the deeper and better flushed western part is more than double that in the eastern part, mainly due to its 2–3°C warmer seawater in winter. It is also found that S. latissima benefits from co-cultivation with shellfish, since nutrients excreted by shellfish replenish its nitrogen reserve, which fuels a relatively high growth rate in the nitrogen-depleted late spring. The model assessment offers insight into optimal potential locations of S. latissima farms in the Eastern Scheldt. Applicability of our modelling approach to other coastal ecosystems and possible further improvements for assisting in seaweed farming practice are discussed.

The amount of suspended fines in the southern North Sea strongly depends on their exchange with the sandy seabed. This exchange is governed by resuspension of fines during storms, followed by burial in the week thereafter. Despite its importance for fine sediment dynamics, the burial of fines into a sandy seabed is currently not well understood. This paper presents a mechanistic conceptual model, explaining how the interaction of migrating small ripples and larger megaripples can bury fine sediment in a sandy seabed shortly after storms. The burial process consists of four phases forming a dynamic cycle. A storm stirs up the bed, remobilising fines, while forming megaripples. After the storm, fines can settle again depositing atop the sandy seabed. Interaction between bedforms of different scales is then crucial to bury fines 1–2 dm within the seabed. Megaripples formed during storms gradually adjust to calmer conditions in the waning of storms. During this adjustment period, fines are buried by current-induced ripples in the troughs of the former megaripples. Field measurements collected in 2017 corroborate this conceptual model, showing fines in distinct patches, both horizontally and vertically. Furthermore, fines are found up to 10–15 cm in the seabed shortly after storms. The data further reveal how fine sediment occurrences on and within the seabed vary strongly over multiple length scales. They both vary on the mega-scale (kilometres) and on the micro-scale (metres-centimetres). As the micro-scale is multiple orders of magnitude smaller than the scale on which hydro-morphological models operate, parameterisations are required to aggregate the effect of burial in numerical models., Environmental Fluid Mechanics, Coastal Engineering, Hydraulic Engineering