Macrofaunal Communities Research Articles

Land use conversion to agriculture impacts biodiversity, erosion control, and key soil properties in an Andean watershed

AbstractThe conversion of natural vegetation to agricultural land uses in mountainous Andean landscapes threatens an array of key ecological processes and ecosystem services (ES). In protected areas and buffer regions that provide water to cities, it is critical to understand how interactions between plants and soil communities sustain a range of ecosystem functions associated with nutrient recycling, soil structure, and erosion control. We sought to examine how land use conversion within a mountainous tropical forest landscape influences the diversity of vegetation and soil macrofauna communities, soil physicochemical properties, and hydrological regulation services. Biodiversity and a suite of key soil‐based ES were compared in five major land uses of the Cali River watershed: (1) annual cropping systems, (2) coffee plantations, (3) pastures, (4) abandoned shrubland, and (5) secondary forests. The diversity of woody and herbaceous vegetation, as well as soil macrofauna, was assessed in each land use. Soil chemical fertility and aggregate morphology were assessed via laboratory analyses and visual separation of soil aggregates based on their origin. Infiltration, runoff, and sediment production were measured using a portable rainfall simulator. We found a decrease in the diversity of woody vegetation across land uses to be associated with lower diversity of soil macrofauna. At the same time, agricultural management, annual crops in particular, supports the largest earthworm populations, likely due to increased organic inputs and low impact tillage, which appears not to diminish soil fertility and water infiltration. In contrast, the low soil fertility in pastures was associated with the lowest values of soil C, poor aggregation, and high bulk density and likely reflects overgrazing, with negative implications for water infiltration and erosion. Associations between the different sets of variables, evaluated with co‐inertia analysis, highlight the hierarchical relevance of plant cover and woody diversity on ES. The biological complexity associated with intact forest cover appears to generate “bundles” of co‐occurring ES, with this land use demonstrating the highest infiltration, and low runoff and sediment losses. Our findings demonstrate that forests and tree‐based agricultural systems may better contribute to the provision of multiple ES, including biodiversity conservation and hydrologic regulation.

Characteristics of Soil Macrofauna and Its Coupling Relationship with Environmental Factors in the Loess Area of Northern Shaanxi

Even with the in-depth implementation of forestry ecological projects, such as restoring farmland to forest (grass) in the loess area of northern Shaanxi, the characteristics of soil macrofauna communities and their coupling relationship with environmental factors after vegetation restoration in the study area are yet obscure. However, the soil macrofauna community characteristics are of great significance for evaluating the effectiveness of vegetation restoration in the study area. Therefore, the study aims to reveal the characteristics of the soil macrofauna community and their coupling relationships with the environment in the loess area of northern Shaanxi. In this study, all organisms of the five typical vegetation types in the study area were collected by manual sorting (Armeniaca sibirica and Populus simonii mixed forest (M), Robinia pseudoacacia (P), Populus simonii (S), Populus hopeiensis (H) and Hippophae rhamnoides (R)), and the adjacent abandoned grassland (G) was used as a control group. The group number and the individual number of soil macrofauna of different vegetation types in the study area and their coupling relationships with environmental factors are studied, and the following conclusions were drawn. (1) The study shows that there are certain differences in the environmental factors of different vegetation types in the study area, which include the significant differences in the alkaline nitrogen content of various vegetation types (p < 0.05). (2) The effects of different vegetation on soil macrofauna community were different. There were no significant differences in the soil macrofauna community structure between Armeniaca sibirica and Populus simonii mixed forest, Robinia pseudoacacia, Populus simonii and Populus hopeiensis, but there was a large difference from that of the abandoned grasslands. The community density of soil macrofauna in Armeniaca sibirica and Populus simonii mixed forest and Populus simonii were significantly higher than that in the abandoned grassland (p < 0.05), but the other indexes showed no significant differences. The Shannon–Wiener index of Robinia pseudoacacia and Populus hopeiensis were much lower than that of the abandoned grassland (p < 0.05). (3) The diversity of soil macrofauna communities was mainly affected by pH, alkaline nitrogen, potassium available, vegetation coverage and litter production. (4) Different groups of soil macrofauna were closely related and reacted differently to environmental factors, and vegetation coverage, litter production and alkaline nitrogen content were the key factors affecting the composition of soil macrofauna communities.

Benthos response to nutrient enrichment and functional consequences in coastal ecosystems

As land use intensifies, many coastal waters are becoming enriched with otherwise limiting nutrients, leading to eutrophication. While the extreme effects of eutrophication on benthic communities are well documented, there is still a lack of knowledge about how nutrient enrichment alters biogeochemical interactions occurring at the sediment-water interface. Using ex-situ experiments, this study explores the consequences of nutrient enrichment on sediment characteristics, macrofauna community and benthic fluxes. The quantity of sedimentary organic matter and porewater concentration of NH4+, NOx and PO43− increased in enriched treatments. These changes did not affect the macrobenthic community structure. However, macroinfauna buried less deep and increased their ventilation activity. As consequences, nutrient efflux increased, thereby favouring eutrophication processes. These effects were reduced in presence of seagrass, thus illustrating the buffering capacity of seagrass in the context of environmental changes, and particularly, of eutrophication. Overall, this study highlights that the functional consequences of nutrient enrichment involve interconnected processes that are variable in space and time.

Soil macrofaunal communities develop a habitat-specific trophic structure dependent on the degree of degradation of alpine wetlands

The alpine wetlands in the Qinghai-Tibetan Plateau have degraded in recent decades. However, the response of the soil food web to the degradation is still unclear. Four habitats including a wet meadow (WM), a grassland meadow (GM), a moderately degraded meadow (MDM) and a severely degraded meadow (SDM) (sandy meadows) were selected along the degrees of degradation. The soil macrofaunal biomass and the environmental factors of vegetation and soil were investigated. The soil macrofaunal community biomass increased significantly from WM to MDM and decreased to a very small amount in SDM, with most taxa disappearing. The biomass of the trophic groups of detritivores, herbivores and predators exhibited similar responses to soil macrofaunal communities. The relative biomass of detritivores increased from WM to MDM, but herbivores responded in an opposite manner, resulting in the dominant trophic group and trophic structure varying progressively from WM to GM to MDM. Soil properties but not vegetation determined the changes in trophic groups and trophic structure. The results implied that the higher trophic levels (carnivores or omnivores) responded more sensitively than the lower trophic levels (herbivores) to alpine wetland degradation. Our results also suggested that soil macrofauna have a habitat-specific characteristic trophic structure and can be used as indicators of soil health conditions.

Sea pens as indicators of macrofaunal communities in deep-sea sediments: Evidence from the Laurentian Channel Marine Protected Area

Pennatulacean octocorals (sea pens), one of the primary conservation targets of the Laurentian Channel Marine Protected Area (MPA) in eastern Canada, occur at high densities in some deep-sea sedimentary habitats. Considered important habitat-forming organisms for many megafaunal organisms, the effect of sea pens on nearby sedimentary macrofaunal communities remains unexplored. During two cruises in September 2017 and July 2018, we sampled 9 stations within the MPA (336-445 m depth), including sea pen fields and bare sedimentary habitats, targeting individual sea pens in a subset of the cores to assess small-scale effects. We evaluated macrofaunal density, taxonomic diversity, vertical distribution, community composition, and biological trait expression, and investigated variation between sea pen fields and other (bare) sedimentary habitats, as well as between cores with and without sea pen specimens. Using multivariate analyses, we identified abiotic and biotic drivers of macrofaunal community composition and biological trait expression. Enhancement of macrofaunal density and taxonomic diversity and higher percentages of organisms in the upper sediment layers characterized sea pen fields in autumn, with more variable results in summer. Community composition and biological trait expression consistently differed in sea pen fields compared to bare sedimentary habitats, with Pennatula sea pen density as one of the primary drivers of variation especially for community composition, along with other environmental drivers (depth, grain size, and organic matter quantity and quality). We also detected small-scale enhancement of macrofaunal diversity in cores containing sea pens at stations characterized by predominantly bare sediments. Our results indicate that macrofaunal communities within sea pen fields differ from those in bare sediments and we propose sea pens play a role in influencing those patterns by increasing food availability, stability, and small-scale heterogeneity in sedimentary habitats, acknowledging that other environmental factors might also play a role in determining the observed patterns. Characteristics of macrofaunal communities within sea pen fields also suggested potentially higher sensitivity to disturbance, which amplifies the need for protection of sea pen fields in deep-sea sedimentary environments.

Relationship between beach morphodynamics and body traits in a sand-dwelling wolf spider

Sandy beach macrofaunal communities are mainly structured by the independent response of species to the harsh physical environment. The theoretical framework for sandy beach ecology has been mainly developed on the basis of the outstanding role of morphodynamic factors on resident fauna in this narrow land-sea interface. In the case of supralittoral species, the habitat safety hypothesis (HSH) predicts an increase in body size and weight (among several individual and population attributes) from dissipative beaches (fine sand, gentle slope) to reflective beaches (coarse sand, steep slope). Spiders are relevant components of coastal ecosystems due to their strict dependence on prey availability and their carnivore condition; however, the HSH has never before been tested in this taxonomic group. We studied the relationship between beach morphodynamics and body size, weight and body condition of the wolf spider Allocosa marindia. We performed simultaneous collections of adults of A. marindia in two contiguous estuarine beaches with contrasting morphodynamics. As males were scarce, we measured and weighed only females. In agreement with predictions of the HSH, individuals were larger and heavier at the reflective beach. Individual size, weight and body condition were higher at the beginning of the reproductive period. Reflective beaches would act as more benign environments, providing secure microhabitats for the individuals and their potential prey, while affecting positively body traits during development. Our results provide the first formal testing of the HSH in a sand-dwelling spider on beaches with contrasting morphodynamics.

Macrofauna communities and their relationship with soil structural quality in different land use systems

Context Soil structural quality (Sq) influences soil water dynamics, greenhouse gas emissions and plant productivity in natural and agricultural environments. Hence, assessing soil structural quality using simple methods is crucial to identifying potential impacts of different land uses. Aims Identify correlations between Sq and macroinvertebrate communities in seven land use systems (LUS). Methods Seven LUS were studied: native mixed ombrophylous forest (NF), native grassland (NG), native grass pasture (NP), Eucalyptus sp. plantation (EP, 20-years-old), no-tillage annual cropping (NT), integrated crop–livestock (ICL) and crop–livestock–forestry (ICLF). Each LUS had three plots and Sq and macrofauna community were evaluated. Sq was assessed through visual evaluation of soil structure (VESS) – a Sq score was assigned to each identified layer. Soil macrofauna were hand-sorted from each of these layers. Soil samples were taken in each LUS to describe selected chemical and physical attributes related to soil quality. Results All LUS had non-degraded soil structure quality (Sq ≤ 3); however, with differences in Sq among LUS mainly in deeper layers. The VESS showed better Sq in NF (1.53) and NP (1.85) compared to the other LUS, with highest Sq scores for ICL and NG. The NP had the largest macrofauna communities (12 183 ind. m−2), comprising mainly termites and earthworms, with taxa richness highest in NF. Conclusions Correlations between soil macrofauna (i.e. total density, termites and other groups) and Sq were observed, demonstrating that larger macrofauna populations were associated with better soil structural quality. Implications Biological indicators, like soil macrofauna, can be easily measured at low cost and linked to visual Sq, facilitating simultaneous assessment of soil physical and biological health.

Sea-ice-related environmental drivers affect meiofauna and macrofauna communities differently at large scales (Southern Ocean, Antarctic)

The structure and drivers of Southern Ocean meiofauna and macrofauna were investigated together in one extensive study. From the tip of the Antarctic Peninsula to the southeastern Weddell Sea, we classified the investigated stations into 5 categories according to their summer sea-ice cover: (I) none (Drake Passage), (II) irregular (Bransfield Strait), (III) seasonal (northwestern Weddell Sea), (IV) high (South Filchner Trough), and (V) constant (North Filchner Trough). The categories differed significantly in primary-production-related characteristics in the water column and food availability at the seafloor. Almost all ice-cover categories differed significantly in meiofauna communities (32-500 µm, 20 taxa, 585 825 individuals). Fewer regions differed significantly in macrofauna (>500 µm, 19 taxa, 3974 individuals) or the combined meiofauna and macrofauna communities. Environmental drivers explained >66% of the variation among different communities and differed for the faunal size classes: for meiofauna (84.2%), sea-ice cover (1 yr) and availability of fresh food (chlorophyll a [chl a]) were most important, whereas 1 yr ice cover, chl a, and total organic carbon were decisive drivers for macrofauna (66.6%). Grain size, water depth, water-column chl a, long-term ice cover, seafloor temperature, and the carbon/nitrogen ratio influenced communities to a lesser extent. We demonstrated a stronger relationship with sea-ice cover in meiofauna communities than in macrofauna communities, and we recommend including meiofauna in future assessments of the influence of environmental changes on Southern Ocean ecosystems.

A history of Pistacia lentiscus and Pinus brutia trees and their ecological changes in the Güllük Bay (Muğla, SW Turkey) during the last 400 years

In this study, we present pollen records together with a multiproxy analysis from a sediment core collected from the Güllük Bay (Bargilya Cove, Muğla, SW Turkey), covering the last 400 years. Pistachio shrubland was occupying around the Güllük Bay between 1613 and 1741 AD. However, after 1741 AD, the vegetation canopy suddenly changed and Turkish pine (Pinus brutia) was established. This supports that the main factor affecting the expansion of Pistacia lentiscus was precipitation rather than temperature after 1741 AD. This change is also indicated by high Sr-Ca values, reflecting arid conditions. Two anthropogenic phases developed in the region. The first phase is marked by Olea europeae between 1613 and 1789 AD. The second is characterized by Plantago, Caryophyllaceae, Cerelia, Rumex, and Sanguisorba minor type suggesting pastoralism and agricultural activities between 1789 and 1964 AD. Macrofaunal communities are also indicative of environmental changes. Abra ovata, Cerastoderma glaucum, Bittium reticulatum, and Skenea catenoides were first settlers between 1572 and 1643 AD. The prominent presence of lagoonal species Abra ovata and Hydrobia ventrosa indicates a lagoonal depositional environment in 1799-1948 AD.

Effects of Oil and Diesel on Macrofaunal Communities in Marine Sediments: A Five Year Field Experiment in Antarctica

Effects of Oil and Diesel on Macrofaunal Communities in Marine Sediments: A Five Year Field Experiment in Antarctica

Assessing Shellfish Farming-Mediated Benthic Impacts Based on Organic Carbon Flux Simulation and Composition of Macrofaunal Community

Assessing Shellfish Farming-Mediated Benthic Impacts Based on Organic Carbon Flux Simulation and Composition of Macrofaunal Community

A tale of two key species in a subtropical mudflat: four-fold density increases produce minimal ecological response in macrofauna

Context Understanding how ecosystems function to deliver services is essential if we are to limit the impacts off human activities. Aim We hypothesised that increased densities of whelk, Pyrazus ebeninus, and crab, Macrophthalmus setosus, up to four times (given their large body-size and ecological roles, e.g. consuming deposits and disturbing sediments) would affect the macrofaunal community and how it functions in a south-eastern Queensland mudflat. Method The biota and physical environment of the field-deployed cages (three density treatments, caged and control plots) were sampled up to 90 days. Results After 90 days, the redox discontinuity layer was deeper and sediment organic matter was higher in all density treatments. This is consistent with enhanced burrowing, surface disturbance, mucus and pellet production. However, no significant changes in the taxonomic composition of the unmanipulated portion of the macrofaunal resident assemblage were observed. Conclusion Whereas some communities change structurally when perturbated and then revert, this community remained in the new manipulated configuration for at least 90 days. Implications Limited understanding of the ecological relationships in these systems, such as the processes operating to support this large increase in deposit-feeding biomass constrains evidence-based management. These systems may be able to, at least temporally, support enhanced biomasses and levels of ecosystem services.

Influence of different Eucalyptus hybrids on soil macrofauna.

The present work aimed to evaluate the influence of different eucalyptus hybrids on the edaphic macrofauna community. It is hypothesized that the density and diversity of edaphic fauna are influenced by the quantity and quality of the litter deposited by the different hybrids on the soil surface. The study area is in the city of Vitória da Conquista (BA) and consists of seven eucalyptus hybrids, one from sexual reproduction (seminal) and six from asexual (clonal) reproduction. Sampling of the soil macrofauna was performed by the Tropical Soil Biology and Fertility method. All visible invertebrates were collected and identified at the level of large taxonomic groups. The relative density, group richness, and diversity index were calculated. Hybrids did not influence the total density and richness of the soil macrofauna. However, it was possible to observe changes in litter accumulation and composition, and as a result in the diversity indexes and in the presence or absence of macrofauna groups. Among the studied hybrids, those from Eucalyptus urophylla (seminal, 1335 and 1249) promote greater macrofauna diversity and favor the occurrence of detritivores organisms, suggesting the occurrence of better quality and more palatable litter for the edaphic fauna.

Ecomorphic Structure Transformation of Soil Macrofauna Amid Recreational Impact

The level of reacreation load on the components of urban green areas is increasing, so identifying the effective management tools in these ecosystems is becoming crucial for ensuring the maintenance of soil biota habitats. The purpose of this study is to reveal a pattern of structuring community of soil macrofauna under a recreational impact based on an ecomorphic approach. The article assesses the level of recreational transformation of the soil macrofauna of public green spaces in the city of Melitopol on the territory of Novooleksandrivskyi Park. For research purposes, a testing site was allocated in an area with a high level of recreational load, with samples taken within this site. To collect soil macrofauna and assess soil properties at each point of the testing site, soil and zoological tests were carried out and the following soil indicators were measured: temperature, electrical conductivity, humidity and soil penetration resistance, litter depth and grass stand height. The community ordination was performed using two approaches: OMI and RLQ analysis. The study found that the ecological niches of soil macrofauna in recreational conditions are spatially structured. The main factors for structuring the ecological niche of soil macrofauna within the study area are soil penetration resistance in the range of the entire measured layer, soil moisture, and distance to trees. As for the number of species, the basis of the coenomorphic structure of soil macrofauna are silvants (45.5%) and pratants (24.2%). As for the species abundance, the basis of the coenomorphic structure of macrofauna comprises pratants (64.5%), slightly less stepants (19.1%) and silvants (16.1%), and sporadic occurrence of paludants (0.2%). Such coenomorphic structure can be considered as ecologically labile. Zoophages, hemiaerophobes, and megatrophs are tolerant to a high level of recreational load. The area corresponding to the highest level of recreational load is vacant. This indicates factual absence of soil macrofauna species that could exist amid intense recreational exposure

How Biodiversity-Friendly Is Regenerative Grazing?

Regenerative grazing management (ReGM) seeks to mimic natural grazing dynamics to restore degraded soils and the ecological processes underpinning sustainable livestock production while enhancing biodiversity. Regenerative grazing, including holistic planned grazing and related methods, is an adaptive, rotational stocking approach in which dense livestock herds are rotated rapidly through multiple paddocks in short bouts of grazing to defoliate plants evenly and infrequently, interspersed with long recovery periods to boost regrowth. The concentrated “hoof action” of herds in ReGM is regarded vital for regenerating soils and ecosystem services. Evidence (from 58 studies) that ReGM benefits biodiversity is reviewed. Soils enriched by ReGM have increased microbial bioactivity, higher fungal:bacteria biomass, greater functional diversity, and richer microarthropods and macrofauna communities. Vegetation responds inconsistently, with increased, neutral, or decreased total plant diversity, richness of forage grasses and invasive species under ReGM: grasses tend to be favored but shrubs and forbs can be depleted by the mechanical action of hooves. Trampling also reduces numerous arthropods by altering vegetation structure, but creates favorable habitat and food for a few taxa, such as dung beetles. Similarly, grazing-induced structural changes benefit some birds (for foraging, nest sites) while heavy stocking during winter and droughts reduces food for seedeaters and songbirds. With herding and no fences, wildlife (herbivores and predators) thrives on nutritious regrowth while having access to large undisturbed areas. It is concluded that ReGM does not universally promote biodiversity but can be adapted to provide greater landscape habitat heterogeneity suitable to a wider range of biota.

Material type weakly affects algal colonisation but not macrofaunal community in an artificial intertidal habitat

The urbanisation and hardening of shorelines is likely to continue in response to coastal population growth and climate change. To mitigate associated ecological impacts, ecological engineering is being increasingly applied to enhance local biodiversity. This includes retrofitting topographically complex tiles or units onto intertidal artificial structures to mimic features of the natural hard-bottom habitats that were lost. However, the effect of material (different rock types) on the biotic colonisation of these habitat enhancements has rarely been investigated. We constructed complex tiles using a range of materials (concrete, granite, limestone, pink sandstone, violet sandstone, and a composite of the natural stones) to test their effects on the colonisation and establishment of intertidal algae and macrofaunal communities on seawalls in Singapore. We found no significant differences in macrofaunal species richness, total abundance, and community composition among treatments. There were only minor differences in algal community composition, total algal cover, and algal succession patterns among tile types. For both macrofaunal and algal communities, site-specific differences significantly affected colonisation. Our study suggests that material does not substantially influence biotic colonisation on habitat enhancement units and, therefore, other factors such as the associated environmental impacts of potential fabrication materials could be weighted more heavily when planning ecological engineering solutions for hardened shorelines.

Anthropogenic effects on the marine environment adjacent to Palmer Station, Antarctica

AbstractLocalized contamination from research-related activities and its effects on macrofauna communities in the marine environment were investigated at Palmer Station, a medium-sized Antarctic research station. Relatively low concentrations of polycyclic aromatic hydrocarbons (PAHs; 32–302 ng g-1) and total petroleum hydrocarbons (TPHs; 0.9–8.9 μg g-1) were detected in sediments adjacent to the sewage outfall and pier, where most human activities were expected to have occurred, and at even lower concentrations at two seemingly reference areas (PAHs 6–30 ng g-1, TPHs 0.03–5.1 μg g-1). Elevated concentrations of PAHs in one sample taken in one reference area (816 ng g-1) and polychlorinated biphenyls (353 ng g-1) and dichloro-diphenyl-trichloroethane (3.2 and 25.3 ng g-1) in two samples taken adjacent to the sewage outfall indicate spatial heterogeneity of localized sediment contamination. Limpet (Nacella concinna) tissues collected adjacent to Palmer Station had high concentrations of PAHs, copper, lead, zinc and several other metals relative to outlying islands. Sediment and limpet tissue contaminant concentrations have decreased since the early 1990s following theBahía Paraísospill. Natural sediment characteristics affected macrofaunal community composition more than contamination adjacent to Palmer Station, presumably because of the low overall contamination levels.

Determination of functional structure of soft-bottom marine macrobenthic communities of the Samsun Shelf Area using biological traits analysis

Abstract Biological Traits Analysis (BTA) was used to investigate the functional structure of marine macrobenthic communities along the Samsun Shelf Area (SSA). Benthic samples were collected seasonally from five different locations and at four different depths using a Van Veen grab sampler. Macrofaunal communities distributed in the SSA were assessed using 10 biological traits to identify characteristic traits for each depth and location. It was found that variability of benthic ecosystem functions in the SSA was driven by biological traits such as maximum size, living habit, sediment position, feeding mode and type of reproductive behavior. Bivalves, polychaetes and crustaceans of small to medium size, biodepositing, burying themselves in the sediment (burrowers) and feeding in suspension were relatively more abundant at depths of 0–60 m. However, the biomass of Amphiura, Abra, Papillicardium and some polychaetes characterized by medium to large sizes, diffusive mixing, free living and feeding on deposit and subsurface deposit showed higher values at depths below 60 m. In general, it is concluded that the functional structure of the benthic infauna in the SSA has adapted to physical disturbance, and communities distributed in this area consist mainly of taxa resistant to mechanical pressure.

Evaluation of phenolic content of wrack debris on estuarine beaches: The effect on upper beach macrofauna

AbstractWrack supply represents the main organic input in sandy beaches ecosystems and is a common feature of beaches around the world. The chemical composition of the wrack is important in determining the extent and rate of the decay; in particular, phenolic compounds may affect consumption rates by wrack‐associated macrofauna and, consequently, modify the nutrient processing and recycling in sandy beaches. The aim of this research was to investigate the possible links between phenolic content of wrack supplies and the macrofaunal community inhabiting them. To achieve this, patches of wrack in three beaches of the NW coast of Spain were analysed and the phenolic contents and macrofaunal distribution, both at spatial and temporal scales, were assessed. Wrack and macrofaunal samples were collected along two shore‐parallel transects, coinciding with the wrack lines of previous tidal deposition. The results showed a general spatial distribution in the phenolic content of the beach‐cast according to their tidal position on the beach. Thus, two distinct zones were identified: the “spring‐tide deposited” zone located in the upper beach close to the base of the dunes and composed by wrack material with the lowest phenolic concentrations; and a “freshly deposited” zone with wrack deposits containing the highest concentrations of deterrent compounds. Nevertheless, only supratidal grazers, mostly linked to fresh deposits, have shown a slightly negative association between their abundance and the increasing phenolic contents of the stranded macroalgae. The lack of a consistent pattern in macrofaunal occupation of fresh and decayed drift lines detected suggests the species could be selecting habitats for reasons other than phenolic content.

Sedimentary Organic Matter Shapes Macrofaunal Communities but Not Benthic Nutrient Fluxes in Contrasting Habitats Along the Northwest Atlantic Continental Margin

The heterogeneous topography of continental margins can influence patterns of resource availability and biodiversity in deep-sea sediments, potentially altering ecosystem functioning (e.g., organic matter remineralization). Noting a lack of studies that address the latter, we contrasted spatial patterns and drivers of benthic nutrient fluxes and multiple characteristics of macrofaunal communities in shelf, slope, canyon and inter-canyon sedimentary habitats along the Northwest Atlantic continental margin. Replicate sediment push cores were collected from 10 stations (229–996 m depth), incubated for ∼48 h to estimate fluxes of nitrate, nitrite, ammonium, phosphate, and silicate (as a measure of organic matter remineralization) and subsequently analyzed to characterize macrofaunal communities. We also considered various environmental factors, including sedimentary organic matter quantity and quality, and assessed their influence on fluxes and macrofauna. Comparatively high macrofaunal density and distinct community composition and trait expression characterized Georges Canyon, where elevated sedimentary organic matter suggested important lateral transport mechanisms along this canyon axis, with deposition of organic matter strongly affecting biological communities but not benthic nutrient fluxes. Lower penetration of macrofauna into the sediments, distinct community composition, biological traits, and higher nutrient flux rates characterized inter-canyon habitats compared to slope habitats at similar depths. Within inter-canyons, intermediate to low organic matter suggested hydrodynamic forces inhibiting organic matter deposition, affecting biological and functional processes. The input of fresh phytodetritus to the seafloor was the best predictor of macrofaunal density and diversity and contributed to variation in macrofaunal community composition and biological trait expression, together with latitude, depth, and other measures of organic matter quantity and quality. Benthic nutrient fluxes revealed complex variation, with disproportionate effects of few key macrofaunal taxa, together with bottom water oxygen concentration, and sediment granulometry. Our results suggest a relationship between resource availability and macrofaunal density, diversity, and taxonomic and trait composition, whereas organic matter remineralization exhibited a more complex response, which we suggest reflected variation in hydrodynamics and/or physical disturbance in heterogeneous continental margin habitats.