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Effluents resulting from fish farming activities can alter the structure and functioning of benthic ecosystems. In Norway, recent technological advances within the salmon industry have facilitated the expansion of aquaculture into shallower locations, leading to additional pressures upon coastal habitats.Maerl/rhodolith beds are important bioengineers in coastal waters—supporting highly diverse associated macrofaunal communities—and are likely to be particularly at risk.This study aims to investigate the environmental changes induced by fish farms in their vicinity and their impact on the structure and functioning of maerl bed macrofaunal communities.High dissolved nutrients and organic enrichment levels were observed close to the cages, associated with lower live maerl cover.Overall, the most substantial impact of salmon farms on macrofaunal communities was observed within 100 m from the cages. Nevertheless, changes in the structure and functioning of assemblages were evidenced up to 300 m.In the vicinity of the cages, communities were characterized by the dominance of endobenthic subsurface deposit feeders and opportunistic species, notably the polychaetes Chaetozone sp., Capitella sp. and Scoloplos armiger. Conversely, sites situated farther away from the cages exhibited higher abundances of epibenthic taxa, including crawlers, grazers and species sensitive to organic enrichment.Sites unaffected by the presence of fish farms were described by high abundances of the ophiuroid Ophiura robusta, the polychaete Proclea graffi and ostracods, reflecting more favourable environmental conditions.Such changes in macrofaunal communities highlight the vulnerability of maerl beds to the impacts of aquaculture, thus emphasizing the importance of rigorous site selection when establishing new fish farming facilities. [ABSTRACT FROM AUTHOR]

To identify the distribution pattern of macrofaunal assemblages of the Dafeng intertidal flats in response to hydrodynamic and sediment dynamic processes in the northern Jiangsu coast, East China, macrofauna sampling and hydrodynamic observations were carried out simultaneously across the mud flat, mixed mud-sand flat, and silt-sand flat of the intertidal zone in June 2018. Results show that there was a clear zonal distribution pattern of the macrofaunal communities, as is controlled by local hydrological and sedimentary environments. Principal component analysis (PCA) revealed three types of intertidal area in terms of hydrological and surficial sediment parameters. Similarly, three distinct groups of the macrofaunal communities, i.e., mud flat, mix mud-sand, and silt-sand groups, were recognized at similarity level of 24% based on the CLUSTER analysis in similarity profile (SIMPROF) test. Correlation analysis upon best variables stepwise search (BVSTEP) indicated the importance of the hydrodynamics (e.g., water temperature and salinity, tidal duration, flow speed, suspended sediment concentration, and wave height) in the differentiation of macrofaunal communities with different taxonomic classes over the intertidal zone. Therefore, macrofaunal assemblages, similar to hydrology and surficial sediment, have a unique zonation pattern. Small-sized deposit feeders adapt better to low energy environments, thus dominated the upper part of the intertidal flat, whilst the heavy and large-sized filter feeders and deposit feeders were dominant over the middle and lower parts. The hydrodynamic and sediment processes cause biota-niche separation, which affected the biological processes across the intertidal flat. [ABSTRACT FROM AUTHOR]

In 2012, Hurricane Sandy created a new tidal inlet at Fire Island National Seashore (FIIS) in New York, USA, consequently altering environmental conditions within Great South Bay. This event presented a unique opportunity to establish new ecological baselines, assess resulting ecological change, and explore management implications. This study focuses on benthic mapping within the bayside of FIIS using acoustic, grab sample, and imagery data. Biotope (habitat) maps were developed describing relationships between macrofaunal communities and their environment. Additionally, biotopes were prioritized by "ecological value" based on user-defined criteria (presence of seagrass and potential for higher trophic level interactions) to guide management. While there are limited pre-Sandy data for comparison, findings from this study suggest the inlet has been a positive ecological influence on the nearby area. Dense concentrations of mature blue mussels (Mytilus edulis) documented near the inlet are considered ecologically beneficial and represent a post-Sandy distinction in ecosystem structure; M. edulis was last common when the inlet was previously open (early 1800s). The inlet is also likely responsible for seagrass expansion near the inlet but decline in other areas. This study advances the utility of the Coastal and Marine Ecological Classification Standard (CMECS) by including CMECS-defined data in analyses and expanding the definition of "dominance." CMECS played a key role in developing map units, interpreting biotopes, and establishing statistically significant and ecologically meaningful biotic–abiotic relationships. This study also highlights the value and management applications of benthic mapping specific to FIIS and more broadly and advocates for similar studies elsewhere. [ABSTRACT FROM AUTHOR]

Seagrass habitats are important natural carbon sinks, with an average of ~14 kg C m−2 buried in their sediments. The fate of this carbon following seagrass removal or damage has major environmental implications but is poorly understood. Using a removal experiment lasting 18 months at Gazi Bay, Kenya, we investigated the impacts of seagrass loss on sediment topography, hydrodynamics, faunal community structure and carbon dynamics. Sediment pins were used to monitor surface elevation. The effects of seagrass removal on water velocity was investigated using Plaster of Paris dissolution. Sediment carbon concentration was measured at the surface and down to 50 cm. Rates of litter decay at three depths in harvested and control treatments were measured using litter bags. Drop samples, cores, and visual counts of faunal mounds and burrows were used to monitor the impact of seagrass removal on the epifaunal and infaunal communities. Whilst control plots showed sediment elevation, harvested plots were eroded (7.6 ± 0.4 and −15.8 ± 0.5 mm yr−1 respectively, mean ± 95% CI). Carbon concentration in the surface sediments was significantly reduced with a mean carbon loss of 2.21 Mg C ha−1 in the top 5 cm. Because sediment was lost from harvested plots, with a mean difference in elevation of 3 cm, an additional carbon loss of up to 2.54 Mg C ha−1 may have occurred over the 18 months. Seagrass removal had rapid and dramatic impacts on infauna and epifauna. There was a loss of diversity in harvested plots and a shift toward larger bodied, bioturbating species, with a significant increase in mounds and burrows. Buried seagrass litter decomposed significantly faster in the harvested compared with the control plots. Loss of seagrass therefore led to rapid changes in sediment dynamics and chemistry driven in part by significant alterations in the faunal community.

Comprehending the mechanisms and circumstances responsible for the dynamics of biological communities is a fundamental step for predicting responses to environmental changes as well as efficient conservation and management efforts. Macrofaunal assemblages support a wide range of ecosystem services, serving as integral components of the biogeochemical cycle. Here, we examine the structure of the subtidal macrofaunal community in a semi-enclosed bay system located in the Northeast Atlantic. Employing a functional approach, our aim is to understand the interplay between water depth, geographical position, colonisation development and the communities. Our findings did not reveal the influence of water depth (range of 4 m–12 m) on the functional structures of the communities. Instead, only significant differences were demonstrated for 'time of colonisation' and 'site'. The community with 1 month of colonisation presented limited functional diversity lacking overall ecological resilience. It was mainly characterised by 'small-sized', 'short-lived', 'mobile', and 'deposit-feed' organisms indicating an incipient state of development. Communities Site 2 and Site 3 revealed significant differences in the functional structure of the communities. They exhibited similar levels of functional diversity, yet significant differences emerged in the Biological Trait Analysis. Community Site 2 was characterised by 'sessile', 'long-lived', 'large-sized' 'suspension feed' while community Site 3 was characterised by 'herbivore/grazer', 'tubicolous', and 'medium-lived' organisms. Site 2 focuses on the transport of elements from pelagos to the benthos and from benthos to pelagos while Site 3 focus on the transport of elements within the benthos and from benthos to pelagos, and effectively contributes to decomposition and resuspension processes. Moreover, they differ in their sensitivity to disturbance, which suggests that their location in the Ría influences the functional composition of the communities. Understanding these patterns within this environment of significant ecological and economic importance holds profound implications for the effective preservation of ecosystem services. • Functional analysis on the structure of the macrofaunal communities in a semi-enclosed bay system of the Northeast Atlantic. • Standard methodology wherein artificial substrates mimic a 3D complex habitat, avoid destructive sampling effectively. • Biological traits analysis reveals distinct trait patterns as it explores community relations and environmental conditions. • Traits offer distinct details into macrofaunal communities' dynamics, which traditional community analysis fails to uncover. [ABSTRACT FROM AUTHOR]

During three cruises to the Bay of Gdansk, Baltic Sea, the fauna, porewater and bottom water were sampled at stations parallel to the shore and along a transect offshore. Diffusive porewater fluxes were calculated and related to the total net fluxes (TNF) of nutrients. The TNF comprise all nutrients that reach the bottom water from the sediment including diffusive nutrient efflux, discharge from macrozoobenthos and microbial activity. They were determined during in situ incubations using a benthic chamber lander, which is rarely done in coastal research. The lander restricts the physical influence of currents and waves on the sediments and only allows nutrient fluxes due to bioturbation by natural communities. Strong benthic-pelagic coupling in the shallow coastal zone suggested a crucial filter function for the bioturbated coastal sediments, which are separated from muddy deep sediments with little or no fauna at a depth of 50 m; in between is a small intermediate zone. While diffusive fluxes were highest at intermediate and offshore stations, TNF were highest at sandy coastal stations, where reservoirs of dissolved nutrients were small and sediments almost devoid of organic material. The greatest impact of macrofauna on sedimentary fluxes was found at stations whose communities were dominated by deep-burrowing polychaetes. The largest TNF were measured directly at the mouth of the Vistula River, where riverine food and nutrients supplies were highest. Macrofauna communities and sediment variables can thus serve as descriptive indicator to estimate the extent of the coastal filter. Finally, based on the total areal size of the different sediment types, annual efflux for the complete coastal zone of the Gdansk Bay was estimated to be 6.9 kt N, 19 kt Si, and 0.9 kt P. Compared to the muddy offshore area, which is twice as large, these amounts were similar for P and threefold higher for N and Si.

Methane-rich fluids arising from organic matter diagenesis in deep sediment layers sustain chemosynthesis-based ecosystems along continental margins. This type of cold seep develops on pockmarks along the Congo margin, where fluids migrate from deep-buried paleo-channels of the Congo River, acting as reservoirs. Similar ecosystems based on shallow methane production occur in the terminal lobes of the present-day Congo deep-sea fan, which is supplied by huge quantities of primarily terrestrial material carried by turbiditic currents along the 800 km channel, and deposited at depths of up to nearly 5000 m. In this paper, we explore the effect of this carbon enrichment of deep-sea sediments on benthic macrofauna, along the prograding lobes fed by the current active channel, and on older lobes receiving less turbiditic inputs. Macrofaunal communities were sampled using either USNEL cores on the channel levees, or ROV blade cores in the chemosynthesis-based habitats patchily distributed in the active lobe complex. The exceptionally high organic content of the surface sediment in the active lobe complex was correlated with unusual densities of macrofauna for this depth, enhanced by a factor 7–8, compared with those of the older, abandoned lobe, whose sediment carbon content is still higher than in Angola Basin at same depth. Macrofaunal communities, dominated by cossurid polychaetes and tanaids were also more closely related to those colonizing low-flow cold seeps than those of typical deep-sea sediment. In reduced sediments, microbial mats and vesicomyid bivalve beds displayed macrofaunal community patterns that were similar to their cold-seep counterparts, with high densities, low diversity and dominance of sulfide-tolerant polychaetes and gastropods in the most sulfidic habitats. In addition, diversity was higher in vesicomyid bivalve beds, which appeared to bio-irrigate the upper sediment layers. High beta-diversity is underscored by the variability of geochemical gradients in vesicomyid assemblages, and by the vesicomyid population characteristics that vary in density, size and composition. By modifying the sediment geochemistry differently according to their morphology and physiology, the different vesicomyid species play an important role structuring macrofauna composition and vertical distribution. Dynamics of turbiditic deposits at a longer temporal scale (thousands of years) and their spatial distribution in the lobe area also resulted in high heterogeneity of the “cold-seep-like communities”. Dynamics of chemosynthetic habitats and associated macrofauna in the active lobe area resembled those previously observed at the Regab pockmark along the Congo margin and rapid succession is expected to cope with high physical disturbance by frequent turbiditic events and huge sedimentation rates. Finally, we propose a model of the temporal evolution of these peculiar habitats and communities on longer timescales in response to changes in distributary channels within the lobe complex. [ABSTRACT FROM AUTHOR]

In this study, "artificial reef" (AR) impacts of offshore windfarms (OWFs) on the surrounding soft-sediments were investigated. Benthic grab samples were collected at nearby (37.5 m) and distant (500 or 350 m) positions from turbines of two Belgian OWFs (Belwind: monopiles and C-Power: jackets). Higher macrobenthos abundance and species richness were found nearby jacket foundations of C-Power compared to distant positions and differences were most pronounced within deeper sediments (i.e., gullies between sandbanks) at intermediate levels of fine sand fractions (10–20%) and total organic matter (0.5–0.9%). Strong benthic enrichment (>1000 ind. m−2, >20 spp. sample−1) was also linked with higher fine sand fractions (>20%) near the jackets. Moreover, nearby sediments showed higher occurrences of coastal species and habitat diversification was promoted by Mytilus edulis shell debris and alive organisms ("biofouling drop-offs"). The lack of similar results around monopiles (Belwind) confirms that the extent of detectable AR-effects depends on site- and turbine specific factors. • "Artificial reef" (AR) effects influence soft-sediment benthic communities nearby (37.5 m) jacket turbines. • Nearby sediments contained more abundant, richer and compositionally different communities compared to distant sediments. • Strongest benthic enrichment was observed in deeper sediments (i.e., sandbank gullies) and was linked with sediment fining. • Mytilus edulis - associated biofouling drop-off products enhanced habitat diversification nearby the jackets. • The detectability and extent of AR-effects strongly depends on site - and turbine specific factors. [ABSTRACT FROM AUTHOR]

Spatial and seasonal changes in benthic fluxes of dissolved silica (DSi) across the coastal zones were investigated in the southern Baltic Sea. Measurements were performed using ex situ incubations of sediment cores with natural benthic assemblages. Obtained benthic fluxes ranged from the uptake of −1.11 mmol m−2 d−1 in summer to a release of 6.79 mmol m−2 d−1 in autumn, while in situ concentrations in the bottom water were the lowest in autumn (1 μmol L−1) and the highest in winter (up to 58 μmol L−1). Sediments with high mud content had the highest fluxes in autumn, intermediate in spring, and the lowest in winter whereas no clear seasonal patterns were detected for sandy sediments. Generalized Linear Models indicated that in shallow enclosed areas biological factors, particularly presence of Chironomidae larvae, explained DSi fluxes variation while in open areas the environmental factors, such as organic matter quantity and quality, were key explanatory variables. In all studied environments (enclosed lagoon, open bay, and open coastal zone) DSi benthic fluxes represent an important component of the marine Si cycle. Further, the total yearly load of DSi from two major rivers (Vistula and Oder) and from the sediments, to the southern Baltic Sea reaches 258 kt y−1 of which benthic fluxes may constitute up to 34%. [Display omitted] • Spatial and seasonal changes in dissolved silica benthic fluxes were investigated. • There were significant differences in fluxes rates between sands and sandy muds. • Biological factors controlled benthic fluxes in the shallow enclosed areas. • Environmental factors mainly explained flux variation in the open-sea areas. • Benthic fluxes constitute a significant part of silica budget in the coastal areas. [ABSTRACT FROM AUTHOR]