Benthic Boundary Layer Research Articles

Tracking hydrothermal particles from the ridge axis to the sediment column along the Endeavour segment of the Juan de Fuca Ridge

Elemental fluxes associated with mid-ocean ridge hydrothermal systems are thought to be important in the ocean budgets of many elements but quantitative models of these fluxes, and how they vary in space and time due to different boundary conditions, are in their infancy. This is especially true for non-conservative elements that can be involved in multiple processes transforming them between the dissolved and particulate phases both in the water column and after sedimentation. To help develop a more robust database for parameterizing the processes operating, we undertook a coupled sediment trap and sediment core study of hydrothermal sediments on the west flank of the Endeavour segment of the Juan de Fuca Ridge. Sediment traps deployed in the Main Endeavour Field (MEF) and 3 and 9 km southwest of this field, along the mean flow direction of the hydrothermal plume, show that the rate of change of the concentration of sulfide-associated elements (Cu, Zn, Cd, Pb, Ag, As, Mo) in sediment settling from the plume differs between elements. We interpret this as indicating both different dissolution rates of phases containing these elements and different rates of scavenging of these elements from seawater. Scavenging is most readily tracked using elements for which the scavenged fraction is large relative to the hydrothermally derived fraction. For such elements, the relative efficiency of scavenging from seawater (REE > Cr > Ni > V > P > U) matches that previously reported from the TAG system on the Mid-Atlantic ridge despite different vent fluid and seawater chemistries that are expected to lead to both differing roles of Fe-sulfide and Fe-oxyhydroxides and different Fe oxidation rates. In the sediment trap samples collected 9 km off-axis, but not in those collected 3 km off-axis, the Mn and Ti concentrations correlate strongly despite these samples having much higher Mn concentrations than background sediment. Since Ti is sourced almost entirely from background terrigenous material such a correlation was not expected. The most reasonable explanation for this is that aggregation of hydrothermally derived particles with terrigenous material settling through the water column controls removal of hydrothermally derived particles from the water column. Changes in sediment composition with depth in the off-axis sediment core, along with differences between the composition of material from the sediment core and the off-axis sediment traps, are interpreted as indicating large post-deposition changes in sediment composition. For example, much or all of the Mn, P, As and Mo carried to the sediments with hydrothermally derived particles is released back into the water column during diagenesis. In contrast, V and REE concentrations in the sediment core are higher than those in the off-axis sediment trap samples, which may be due to continued scavenging in a benthic boundary layer post-deposition. Overall these data are interpreted as indicating that the net loss of many elements from the non-buoyant plume may not be a proxy for loss from the ocean, and a better understanding of post-depositional processes in hydrothermal settings may be important in understanding cycling of the aforementioned elements, and likely others, in seawater.

Distribution and co-occurrence of microplastics and co-existing pollutants in bottom water and sediment of the East China Sea

Microplastics (MPs) contamination in marine environment has been an emerging issue worldwide, notably due to the potential ecological risks of MPs with co-existing environmental contaminants and released toxic plastic additives. To verify the co-occurrence characteristics of MPs and co-existing pollutants in the benthic boundary layer (BBL), the distribution characteristics of MPs, and selected heavy metals (HMs) and halogenated flame retardants (Polybrominated diphenyl ethers, PBDEs, and Dechlorane Plus) in the bottom water and sediment were comprehensively investigated in the East China Sea (ECS). The sampling sites were selected along the coast of ECS, where might be significantly affected by terrigenous inputs and anthropogenic sources. MPs were abundant in the bottom water (62.8–480.2 items/L) and sediment (80.1–1346.7 items/kg d.w.) with polyester, polyethylene, and polypropylene being as the most abundant types and characterized as fiber/line, particle size 200–500 μm, and transparent/white. The abundance and characteristics of MPs demonstrated strong correlations within the bottom water and sediment, which might be due to the frequent exchange of materials. In addition, the abundance of MPs was significantly positively correlated with HMs (Cd, Cr, Pb) in the bottom water and PBDEs in sediment, respectively. According to the scanning electron microscopy/energy dispersive X-ray spectrometry analysis, MPs might act as carriers to transport and co-sediment the co-existing pollutants in water, and physically adsorb or chemically bind with pollutants in sediment. These results could help to elucidate the sources, migration, and fate, and verify the occurrence and potential risks of MPs and their co-existing pollutants in BBL, thus realize the management and control of MPs contamination in marine.

Quantification of Mixing Depth Using the Gradient Richardson Number in Submerged Aquatic Vegetation Meadows

AbstractUpper layer thickness (mixing depth) is an essential parameter for estimating the dissolved inorganic carbon and carbon flux at the water surface based on their association with the vertical flux of dissolved inorganic carbon. Previous studies quantified the mixing depth without SAV meadow or penetration depth in the SAV meadow without stratification and wind stress. However, mixing depth related to interaction with submerged aquatic vegetations (SAVs), stratification, and wind stress has yet to be quantified in the previous studies. Our study is the first to quantify the theoretical mixing depth with SAVs according to wind stress, SAV height, and drag coefficient. Theoretical mixing depth was quantified from modeled vertical temperature profile, vertical profile of horizontal velocity, and gradient Richardson number (Rig,veg). We found that mixing depth at a Rig,veg of 100 demonstrated good agreement with numerical results on average, with the mixing depth estimated in this study (hU,this study) showing high applicability to observations at Komuke Lagoon. Moreover, hU,this study increased with the increasing wind stress and decreasing drag coefficient and SAV height. Further, we found that SAV meadows with stratification and wind stress could be divided into four hydrodynamic regimes: non‐vegetated layers, upper vegetated layers, thermoclines, and benthic boundary layers. Our findings help us estimate mixing depth or vertical flux without complicated numerical simulation and understand flow interaction with SAV, wind stress, and stratification.

Light Intensity of Phosphorescent-Netting Pots and Determining Their Visibility to Snow Crab (Chionoecetes opilio) Using Visual Modeling Techniques

This study explores the visibility of phosphorescent-netting pots to snow crab (Chionoecetes opilio) using visual modeling techniques. Light emitted from such pots increases catch per unit effort, yet little is understood about the factors driving these higher catch rates. In this study, we measure pot light emission and snow crab visual acuity. Combining these data with estimates obtained in the literature for other biotic and abiotic factors, we model snow crab vision in relation to the pots. Utilizing these factors and environmental conditions, we derive a contrast ratio between the pot light and the ambient light. Findings reveal that the visibility of pot lights at 200-m depth depends primarily on solar angle (time of day) and time elapsed post-deployment. Additional factors influencing the vision of the pots include water column quality and benthic boundary layer turbidity. This study is the first to model the visual ecology of snow crab and the first to estimate snow crab visual acuity. These insights into snow crab visual ecology can potentially enhance fishing techniques, promote catch efficiency and sustainability, and help provide a path forward for visual ecology research in the fisheries science field.

The Vertical Metabolic Activity and Community Structure of Prokaryotes along Different Water Depths in the Kermadec and Diamantina Trenches.

Prokaryotes play a key role in particulate organic matter's decomposition and remineralization processes in the vertical scale of seawater, and prokaryotes contribute to more than 70% of the estimated remineralization. However, little is known about the microbial community and metabolic activity of the vertical distribution in the trenches. The composition and distribution of prokaryotes in the water columns and benthic boundary layers of the Kermadec Trench and the Diamantina Trench were investigated using high-throughput sequencing and quantitative PCR, together with the Biolog EcoplateTM microplates culture to analyze the microbial metabolic activity. Microbial communities in both trenches were dominated by Nitrososphaera and Halobacteria in archaea, and by Alphaproteobacteria and Gammaproteobacteria in bacteria, and the microbial community structure was significantly different between the water column and the benthic boundary layer. At the surface water, amino acids and polymers were used preferentially; at the benthic boundary layers, amino acids and amines were used preferentially. Cooperative relationships among different microbial groups and their carbon utilization capabilities could help to make better use of various carbon sources along the water depths, reflected by the predominantly positive relationships based on the co-occurrence network analysis. In addition, the distinct microbial metabolic activity detected at 800 m, which was the lower boundary of the twilight zone, had the lowest salinity and might have had higher proportions of refractory carbon sources than the shallower water depths and benthic boundary layers. This study reflected the initial preference of the carbon source by the natural microbes in the vertical scale of different trenches and should be complemented with stable isotopic tracing experiments in future studies to enhance the understanding of the complex carbon utilization pathways along the vertical scale by prokaryotes among different trenches.

The impact of topography and rotation in shaping the basin-scale circulation in Lough Corrib, Ireland, under homogenous conditions

Abstract: The impact of the Earth's rotation on circulation patterns in homogenous basins has been well studied using numerical models. This contribution addresses the need for supporting observational studies. Bottom mounted acoustic doppler current (ADCP) velocity profiles are analysed alongside drifter tracks and numerical solutions in order to demonstrate how rotation modifies circulation patterns and horizontal velocity profiles in Lough Corrib, Ireland. The wind driven circulation in Lough Corrib forms a system of topographic gyres, shaped by the complex bathymetry of the basin. Surface and benthic frictional boundary layers are demonstrated to be closely described by classical Ekman theory, despite the system being constrained by shallow water depths (mean depth = 8.4m) and small horizontal dimensions (∼10km). Observed velocity profiles can be derived theoretically by summing the two driving forces of the flow (the barotropic pressure gradient force and the surface wind stress force) and their opposing forces (internal friction and Coriolis acceleration). Rotation introduces a significant cross-wind component to the flow, which is thus described as being quasi-geostrophic. The barotropic pressure gradient force is empirically quantified as a function of wind stress by relating surface set-up to the surface water shear velocity. The vertical eddy viscosity profile, derived from ADCP data, increases approximately linearly with increasing depth and is largest at the upper interface of the benthic boundary layer.

The role of seasonal hypoxia and benthic boundary layer exchange on iron redox cycling on the Oregon shelf

AbstractWidespread hypoxia occurs seasonally across the Oregon continental shelf, and the duration, intensity, and frequency of hypoxic events have increased in recent years. In hypoxic regions, iron reduction can liberate dissolved Fe(II) from continental shelf sediments. Fe(II) was measured in the water column across the continental shelf and slope on the Oregon coast during summer 2022 using both a trace metal clean rosette and a high‐resolution benthic gradient sampler. In the summer, Fe(II) concentrations were exceptionally high (40–60 nM) within bottom waters and ubiquitous across the Oregon shelf, reflecting the low oxygen condition (40–70 μM) at that time. The observed inverse correlation between Fe(II) and bottom water oxygen concentrations is in agreement with expectations based on previous work that demonstrates oxygen is a major determinant of benthic Fe fluxes. Rapid attenuation of Fe(II) from the benthic boundary layer (within 1 m of the seafloor) probably reflects efficient cross‐shelf advection. One region, centered around Heceta Bank (~ 44°N) acts a hotspot for Fe release on the Oregon continental shelf, likely due to its semi‐retentive nature and high percent mud content in sediment. The results suggest that hypoxia is an important determinant of the inventory of iron is Oregon shelf waters and thus ultimately controls the importance of continental margin‐derived iron to the interior of the North Pacific Basin.

The Impact of Topography and Rotation in Shaping the Basin-Scale Circulation in Lough Corrib, Ireland, Under Homogenous Conditions

The impact of the Earth’s rotation on circulation patterns in homogenous basins has been well studied using numerical models. This contribution addresses the need for supporting observational studies. Bottom mounted acoustic doppler current (ADCP) velocity profiles are analysed alongside drifter tracks and numerical solutions in order to demonstrate how rotation modifies circulation patterns and horizontal velocity profiles in Lough Corrib, Ireland. The wind driven circulation in Lough Corrib forms a system of topographic gyres, shaped by the complex bathymetry of the basin. Surface and benthic frictional boundary layers are demonstrated to be closely described by classical Ekman theory, despite the system being constrained by shallow water depths (mean depth = 8.4m) and small horizontal dimensions (~10km). Observed velocity profiles can be derived theoretically by summing the two driving forces of the flow (the barotropic pressure gradient force and the surface wind stress force) and their opposing forces (internal friction and Coriolis acceleration). Rotation introduces a significant cross-wind component to the flow, which is thus described as being quasi-geostrophic. The barotropic pressure gradient force is empirically quantified as a function of wind stress by relating surface set-up to the surface water shear velocity. The vertical eddy viscosity profile, derived from ADCP data, increases approximately linearly with increasing depth and is largest at the upper interface of the benthic boundary layer.

Iron Limitation and Biogeochemical Effects in Southern California Current Coastal Upwelling Filaments

AbstractIn the spring and summer, high rates of primary production occur in the California Current Ecosystem (CCE) when nutrients are supplied to the euphotic zone. During periods of intense coastal upwelling, a flux of the micronutrient iron comes from nearshore sedimentary sources. In this upwelling region, mesoscale filament features distribute iron laterally, leading to distinct iron‐influenced ecological zones. This study is the first to focus on the biogeochemical links between iron, the macronutrients, and particulates in coastal upwelling filaments. Broad spatial patterns of iron and biogenic silica concentrations, and proxies of iron‐stress of diatoms, support results from microcosm amendment studies conducted during CCE Long Term Ecological Research process cruises in the summers of 2017 and 2019. We found that the benthic boundary layer and shoreward filament endmember supply dissolved and total dissolvable iron to this feature, but rapid assimilation and sinking by biogenic particles (e.g., diatoms) depletes the surface concentrations. Subsequently, diatom blooms which form in recently upwelled water masses become iron limited over time, thereby affecting the ratios of surface macronutrient reservoirs and biogeochemical advective fluxes. The development of Fe‐limitation during lateral advection may lead to efficient carbon export downstream and offshore of the region with the highest phytoplankton growth rates and productivity.

Significant benthic fluxes of bioavailable dissolved amino acids to the ocean: Results from the East/Japan Sea

AbstractWe measured dissolved organic carbon (DOC) and total dissolved amino acid (TDAA) in seawater and sediment porewater of the Ulleung Basin in the East/Japan Sea. The DOC and TDAA concentrations were 1.1‐ and 1.4‐fold higher in the euphotic zone, and 11‐ and 43‐fold higher in sediment porewater, respectively, than those in the deep ocean. Consequently, in the deep ocean, TDAA and DOC input fluxes from porewater were 2‐ and 0.4‐fold of those from the euphotic zone, respectively. This larger contribution of benthic flux for TDAA and its shorter residence time in the benthic boundary layer (BBL) (1.3 ± 0.9 yr) seem to result in steep TDAA increases in the BBL, although DOC concentrations remained relatively uniform throughout the entire deep ocean. AA‐derived indices also show enhanced bioavailability of dissolved organic matter in the BBL. Benthic inputs seem to supply a significant amount of bioavailable TDAA to the deep ocean, fueling microbial activity.

Turbulence and fine sediment dynamics in a benthic boundary layer in Fujian Coastal Sea, SE China

A short-term (∼ 25 h) intensive field observation focused on flow, turbulence, suspended sediment concentration, and floc/particle size distributions was conducted in a coastal benthic boundary layer to understand flocculation and erosion/deposition processes of fine sediment. Observations showed suspended particles were mainly flocculated into the size range of microflocs (50-200 μm). Macroflocs (> 230 μm) occurred at slack tides and SPM (suspended particulate matter) concentrations decreased as they settled faster. Twofold intra-tidal variations in floc size and settling velocity were observed with a larger medium floc size of 140 μm and a settling velocity of 1.3 mm/s occurring at slack tides than peak flood/ebb tides with their corresponding values of 70 μm and 0.7 mm/s. This variability can be ascribed to the turbulence modulation in that low turbulence enhances aggregation to form large flocs but they turn to break down by high turbulence. The inverse relationship was found between floc size and turbulence shear rate, SPM concentration, and their product. SPM concentration covaried with bed stress and the low critical erosion stress (∼ 0.02 Pa) indicates that the cohesive bed was primarily eroded as aggregates which formed a fluff layer above the consolidated bed. The fine sediment dynamics behave as a loop from resuspension, through to breakup and re-aggregation, and to settling in response to intro-tidal turbulence variability. This looped behavior is vital for understanding the sequestration of organic carbon and pollutants in fine sediments, awaiting more detailed and longer-term field observations and the assemblage into numerical models.

Benthic sediment disturbances by episodic human-controlled discharge in an altered estuary

In the Geum River, a representative altered estuary, in-situ mooring and erosion experiments were conducted to reveal the effects of human-controlled discharge on benthic sediment disturbances. The strong discharge through the estuarine dam increased the current velocities within the benthic boundary layer (BBL) up to 79% and 153% during spring and neap tides, respectively. During the discharge period, the suspended sediment concentration in BBL was five times higher than that during the non-discharge period. During the flood phase, a critical shear stress for erosion (τce) was in the range of 0.1278 to 0.1391 Pa. Immediately after the ebb phase with strong discharge, τce increased to 0.1848 Pa, and the erosion rate (E) decreased from 33.73 to 14.81 mg m−2 s−1. The repetition of human-controlled discharge removed the erodible sediments within BBL, exposing the underlying consolidated sediment bed with low E and high τce. The results suggest that an altered estuary is vulnerable to benthic sediment erosion under combined natural and anthropogenic forcings.

THE NUMERICAL ANALYSIS OF MIXING DEPTH AND THE THICKNESS OF BBL CONSIDERING THE SUBMERGED AQUATIC VEGETATION AND WIND STRESS

Mangrove forests, salt marshes, and seagrass meadows have a vital role in mitigating global warming (Duarte et al.,2013). They contribute about 50 percent of carbon burial in ocean sediments (Duarte et al., 2013). On the other hand, submerged aquatic vegetations (SAVs) significantly affect the mixing depth (the thickness of the upper layer), resulting in a change in carbon flux with the atmosphere. According to the numerical simulations in the previous studies, mixing depth becomes larger with increasing SAV's density and decreasing SAV’s height (Herb et al., 2005, Vilas et al., 2017). On the other hand, Coates et al. (2009) indicated that wind stress was not crucial for mixing depth in SAV’s meadow since it did not change the vertical turbulent kinetic energy (TKE) profile, except in the thin surface layer, thus mixing depth became similar even though wind speed varied under the effect of SAVs (Coates et al., 2009). In addition, it is crucial to estimate the thickness of the benthic boundary layer (BBL) because dissolved inorganic carbon elucidates from bottom sediments, affecting carbon flux. Therefore, we aim to clarify how wind stress impacts the mixing depth and thickness of BBL with SAVs.

Insights into the prokaryotic communities of the abyssal-hadal benthic-boundary layer of the Kuril Kamchatka Trench

BackgroundThe Kuril–Kamchatka Trench (maximum depth 9604 m), located in the NW Pacific Ocean, is among the top seven deepest hadal trenches. The work aimed to investigate the unexplored abyssal-hadal prokaryotic communities of this fascinating, but underrated environment.ResultsAs for the bacterial communities, we found that Proteobacteria (56.1–74.5%), Bacteroidetes (6.5–19.1%), and Actinobacteria (0.9–16.1%) were the most represented bacterial phyla over all samples. Thaumarchaeota (52.9–91.1%) was the most abundant phylum in the archaeal communities. The archaeal diversity was highly represented by the ammonia-oxidizing Nitrosopumilus, and the potential hydrocarbon-degrading bacteria Acinetobacter, Zhongshania, and Colwellia were the main bacterial genera. The α-diversity analysis evidenced that both prokaryotic communities were characterized by low evenness, as indicated by the high Gini index values (> 0.9). The β-diversity analysis (Redundancy Analysis) indicated that, as expected, the depth significantly affected the structure of the prokaryotic communities. The co-occurrence network revealed seven prokaryotic groups that covaried across the abyssal-hadal zone of the Kuril–Kamchatka Trench. Among them, the main group included the most abundant archaeal and bacterial OTUs (Nitrosopumilus OTU A2 and OTU A1; Acinetobacter OTU B1), which were ubiquitous across the trench.ConclusionsThis manuscript represents the first attempt to characterize the prokaryotic communities of the KKT abyssal-hadal zone. Our results reveal that the most abundant prokaryotes harbored by the abyssal-hadal zone of Kuril–Kamchatka Trench were chemolithotrophic archaea and heterotrophic bacteria, which did not show a distinctive pattern distribution according to depth. In particular, Acinetobacter, Zhongshania, and Colwellia (potential hydrocarbon degraders) were the main bacterial genera, and Nitrosopumilus (ammonia oxidizer) was the dominant representative of the archaeal diversity.

The nocturnal distribution of deep-pelagic fish on the continental slope of the Bay of Biscay

The biomass of deep-sea pelagic fishes could represent more than 90% of the total fish biomass on earth, which represents an important potential for exploitation. However, this community plays multiple key ecological roles in biogeochemical cycles and food webs. Information on their ecology and function is needed to plan effective sustainable conservation measures. In particular, the distribution of deep-sea pelagic fish biomass and the environmental factors that control it remain poorly understood on slope areas at the interface of coastal and oceanic habitats. The combined use of biological data collected by pelagic trawling between 20 and 2000 m depth at night and 16 environmental variables allowed us to study the distribution of this community on the continental slope of the Bay of Biscay, NE Atlantic. Multivariate regression tree analysis suggested that immersion depth was the most important variable structuring this community by night, defining four depth assemblages with different indicator species (i.e. organisms whose presence, absence, or biomass reflects specific environmental conditions): the epipelagic (20–175 m), the upper mesopelagic (175–700 m), the lower mesopelagic (700–1000 m) and the bathypelagic assemblage (1000–2000 m). The use of generalized additive models indicated a positive relationship between bottom proximity and biomass for three of the four assemblages. This contrasts with the paradigm in open ocean areas where the biomass of meso- and bathypelagic fishes decreases with depth. The echograms also showed low acoustic detection at the surface at night, which differs from the open ocean models where nocturnal migration results in a high density of mesopelagic organisms in the epipelagic layer. Different mechanisms could explain this relationship, such as the concentration of food resources in the benthic boundary layer, an ontogenetic change of some species, active horizontal migration, or a demersal spawning behavior. This specific distribution on the continental slope may influence the transition of carbon and energy flows within this ecosystem located in a Special Area of Conservation (SAC).

Development and application of a 6000-meter double decelerating lander

The deep-sea lander is an important equipment for in-situ detection and monitoring. It is of great significance to understand the benthic boundary layer’s physical, chemical, and ecological environment. A 6000-meter double decelerating lander was created to meet the deployment requirements of underwater detection and monitoring, allowing for long-term in-situ monitoring of several benthic boundary layer components. Protection of the installed ocean bottom seismometer (OBS) is required due to the lander’s and OBS’s different impact resistances. The double decelerating unit enables the OBS to avoid colliding with the seabed when the lander lands and then collides with the seabed at a slow speed rather than the speed at which the lander falls, which is intended to safeguard OBS from damage. To ensure a safe deployment, the lander’s static analysis and simulation were performed using ANSYS, and the motion characteristics of the application process were derived. Numerous data have been obtained after the lander’s successful application in the South China Sea. The lander provides an investigation approach for marine science and geochemistry, complementing a technical approach to marine environmental investigations.

Elemental Composition of Particulate Matter in the Euphotic and Benthic Boundary Layers of the Barents and Norwegian Seas

The increasing influence of Atlantic inflows in the Arctic Ocean in recent decades has had a potential impact on regional biogeochemical cycles of major and trace elements. The warm and salty Atlantic water, entering the Eurasian Basin through the Norwegian Sea margin and the Barents Sea, affects particle transport, sink, phyto-, and zooplankton community structure and could have far-reaching consequences for the marine ecosystems. This study discusses the elemental composition of suspended particulate matter and fluffy-layer suspended matter derived from samples collected in the Barents Sea and northern Norwegian Sea in August 2017. The mosaic distribution of SPM elemental composition is mainly determined by two factors: (i) The essential spatial variability of biological processes (primary production, abundance, and phytoplankton composition) and (ii) differences in the input of terrigenous sedimentary matter to the sea area from drainage sources (weak river runoff, melting of archipelago glaciers, etc.). The distribution of lithogenic, bioessential, and redox-sensitive groups of elements in the particulate matter was studied at full-depth profiles. Marine cycling of strontium in the Barents Sea is shown to be significantly affected by increasing coccolithophorid bloom, which is associated with Atlantic water. Mn, Cu, Cd, and Ba significantly enrich the suspended particulate matter of the benthic nepheloid layer relative to the fluffy layer particulate matter within the benthic boundary layer.

Temporal dynamics of the deep-sea pink urchin Strongylocentrotus fragilis on the Northeast Pacific continental margin

The Northeast Pacific continental margin is characterized by strong seasonal upwelling, which drives high primary productivity, and supports high diversity and biomass of benthic megafauna. The recent occurrence of a marine heat wave (“The Blob”, sensu Kintisch, 2015) in 2013–2016 resulted in changes to phytoplankton community composition and loss of coastal kelp abundance and diversity, reducing gross primary productivity in the region. However, cumulative effects of marine heat waves and ongoing basin-scale deoxygenation in deep-sea ecosystems remain poorly understood. Here, we use a 7-year time series of physicochemical and video imagery data from Ocean Networks Canada's NEPTUNE observatory to investigate temporal dynamics of the deep-sea pink urchin Strongylocentrotus fragilis in relation to multi-year environmental variability. Using generalized additive models, we show that local S. fragilis density at Barkley Upper Slope (420 m) fluctuated over time and was partially explained by changes in dissolved oxygen concentration and suspended particulate matter in the benthic boundary layer (ADCP backscatter), with high urchin density corresponding to high oxygen and low backscatter. Seafloor dissolved oxygen ranged from 0.80 to 1.89 mL/L and varied seasonally, exhibiting a clear negative correlation with sea surface primary productivity (MODIS satellite Chl-a data), corresponding with the onset of yearly upwelling conditions. However, during the anomalously warm years affected by ‘The Blob’, dampened upwelling maintained higher dissolved oxygen conditions near the seafloor. S. fragilis density declined during ‘Blob’ conditions, likely in response to reduced kelp and phytodetritus subsidies from coastal waters. We propose a foraging-respiration trade-off hypothesis, whereby S. fragilis forages in deeper water during weak upwelling and migrates to shallower habitats during low oxygen conditions. S. fragilis is an important bioturbator and detritivore; changes in the density and distribution of this species may directly affect sediment turnover rates and nutrient cycling on the continental margin, with consequences for surface and coastal productivity.https://github.com/rjcommand/.

Deep-sea fishes in a sauna: Viperfishes dominate a submarine caldera

Barbeled dragonfishes (family Stomiidae) are considered rare, solitary deep-sea predators. We document the fish fauna of the Kurose Hole, a submarine caldera within Japanese waters. The area has been surveyed on three occasions: twice in 2000 during the RV ‘Natsushima’ cruise and once in 2020 during the RV ‘Kaimei’ cruise. Within the span of twenty years, the base of the caldera warmed from 11.1 °C to 17.8 °C at 790 m. No dragonfishes were observed during the 2000 ‘Natsushima’ expedition while over 1500 viperfishes (genus Chauliodus) were observed during a five and a half hour period in the 2020 ‘Kaimei’ expedition. Viperfishes have never been seen at such high densities, accounting for 61.4% of fish observations with 6.7 viperfish per 100 m3 within the benthic boundary layer. All captured dragonfishes were juveniles, suggesting that this population arose from larvae becoming trapped within the caldera as they developed.

What Inspiring Elements from Natural Services of Water Quality Regulation Could Be Applied to Water Management?

Theoretical and functional ecology is a source of useful knowledge for ecological engineering. The better understanding of the natural service of water quality regulation is now inspiring for optimization of water resource management, restoration and bioremediation practices. This transfer with a biomimicry approach applies particularly well in the urban, rural and agricultural areas, but is yet underexplored for water quality purposes. This natural service intensely involves the benthic boundary layer as a biogeochemical hot spot with living communities. A selection of processes related to the bioturbation phenomena is explored because of their influence on properties of the aquatic environment. The applications are valuable in a range of fields, from water treatment technology to management of ecosystems such as constructed and natural wetlands, streams, rivers, lagoons and coastal ecosystems. This paper gathers the more obvious cases of potential applications of bioturbation research findings on the biomimicry of natural services to water practices. These include pollution pumping by bioturbated sediment, water column oxygen saving during early diagenesis of deposits under conveyors transport and conservation of macroporous as well as fine sediment. Some applications for constructed devices are also emerging, including infiltration optimization and sewage reduction based on cross-biological community involvement.