Subsurface Deposit Feeders Research Articles

What has Changed in 20 Years? Structure and Function of Soft-sediment Macrofauna in a Subarctic Embayment, Newfoundland (Canada)

Understanding how natural and anthropogenic disturbances affect the structure and functioning of marine ecosystems is central to predicting future dynamics. Placentia Bay is an Ecologically and Biologically Significant Area (EBSA) in the North Atlantic exposed to multiple stressors (e.g., rising sea surface temperatures, tanker traffic, and aquaculture). To investigate changes in the community and functional structure of soft-sediment macrofauna as well as environmental drivers of observed variation, we compared contemporary (2019–2020) and historical (1998) samples at eight stations (n = 77) collected 21 years apart. Although community and functional structure differed between these time points, functional traits were maintained (i.e., no loss of 36 trait modalities). Overall, 37% of species/taxa were only observed in either the historical or contemporary community, and the contemporary community exhibited lower macrofaunal density but had similar richness, resulting in higher evenness and diversity. Highly tolerant subsurface deposit feeders having small body sizes (< 10 mm) and direct development dominated the historical community. The contemporary community had nearly equal proportions of surface and subsurface deposit feeders with small to medium body sizes (< 10–50 mm) with pelagic larvae, and the proportion of highly tolerant species/taxa was reduced. These changes likely reflect the reduction in polychaetes (91 vs. 58%) and increased bivalves (4 vs. 25%) relative to the historical time point. Community variation was driven by changes in the sedimentary habitat. Contemporary versus historical sediments were ~ 4.5x coarser (possibly due to storms) with higher levels of sedimentary organic matter. This work contributes to advancing the understanding of relationships between benthic macrofauna, functional traits, and the sedimentary habitat in coastal environments.

Salmon farming alters the structure and functioning of Norwegian maerl bed communities

Abstract 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.

The Impact of Sea Ice Loss on Benthic Communities of the Makarov Strait (Northeastern Barents Sea).

The continental shelf of the northeastern Barents Sea is presently experiencing a weak influx of Atlantic water from the west. In recent times, warming in Arctic regions has led to an increase in extended ice-free periods in this area, instead of significantly elevating water temperatures. The implications of this phenomenon on the structure and functioning of benthic communities were investigated during the autumn of 2019 within the Makarov Strait, located in the southwestern part of the St. Anna Trough. The macrozoobenthic communities exhibited a clear connection with the duration of ice-free periods. This variable influenced a vertical carbon flux, which subsequently served as the primary predictor for faunal abundance and diversity, as demonstrated by redundancy and correlation analyses. Two faunal groups were identified, corresponding to short and long open-water periods. Both groups had similar alpha diversity (65 ± 6 and 61 ± 9 species per station) and biomasses (39 ± 13 and 47 ± 13 g m-2) but displayed differing abundances (1140 ± 100 vs. 4070 ± 790 ind. m-2) and other diversity indices. We observed a decline in the proportion of polychaetes, accompanied by an increase in the proportion and diversity of bivalves, as well as a rise in the abundance of infaunal species, sub-surface deposit feeders, and mobile suspension feeders, in response to the increasing vertical carbon flux. The potential increase in anthropogenic pressures related to oil development in the northeastern Barents Sea highlights the importance of our study for conservation and monitoring efforts in the region.

Opportunistic consumption of marine pelagic, terrestrial, and chemosynthetic organic matter by macrofauna on the Arctic shelf: a stable isotope approach.

Macrofauna can contribute substantially to the organic matter cycling on the seafloor, yet the role of terrestrial and chemosynthetic organic matter in the diets of microphagous (deposit and suspension) feeders is poorly understood. In the present study, we used stable isotopes of carbon and nitrogen to test the hypothesis that the terrestrial organic matter supplied with river runoff and local chemosynthetic production at methane seeps might be important organic matter sources for macrofaunal consumers on the Laptev Sea shelf. We sampled locations from three habitats with the presumed differences in organic matter supply: "Delta" with terrestrial inputs from the Lena River, "Background" on the northern part of the shelf with pelagic production as the main organic matter source, and "Seep" in the areas with detected methane seepage, where chemosynthetic production might be available. Macrobenthic communities inhabiting each of the habitats were characterized by a distinct isotopic niche, mostly in terms of δ13C values, directly reflecting differences in the origin of organic matter supply, while δ15N values mostly reflected the feeding group (surface deposit/suspension feeders, subsurface deposit feeders, and carnivores). We conclude that both terrestrial and chemosynthetic organic matter sources might be substitutes for pelagic primary production in the benthic food webs on the largely oligotrophic Laptev Sea shelf. Furthermore, species-specific differences in the isotopic niches of species belonging to the same feeding group are discussed, as well as the isotopic niches of the symbiotrophic tubeworm Oligobrachia sp. and the rissoid gastropod Frigidoalvania sp., which are exclusively associated with methane seeps.

Shallow-Water Benthic Communities on Soft Bottoms of a Sub-Arctic Fjord (Southern Barents Sea, Russia) along a Gradient of Ecological Factors

Kola Bay is the most developed coastal area in the Russian part of the Barents Sea, but despite a long history of research, information about the local shallow-water benthic communities is lacking. For this reason, in this fjord area, we investigated the soft-bottom zoobenthos to determine its distribution and the factors influencing its abundance, biomass, and diversity. An analysis of 24 samples collected by divers at eight stations located at 7–8 and 10–15 m depths revealed 127 benthic taxa with an average abundance and biomass of 12,190 ± 4740 ind. m−2 and 30 ± 8 g m−2, respectively. The most severe abiotic conditions (high rates of sedimentation and eutrophication) were found at the head of the bay while the highest densities of predator red king crabs were registered in the middle part. The total benthic abundance and biomass, as well as the abundances of infauna, mobile taxa, subsurface deposit feeders, and surface deposit feeders, decreased towards the central part of the bay, reflecting gradients in the environmental conditions. In the inner part of the bay, we registered two communities: Cossura pygodactylata + Ciliatocardium ciliatum and Arctica islandica + Laonice cirrata, while the benthos of the middle part was less structured. Redundancy analysis indicated that the faunal abundances were influenced mainly by predator density (negative association) and the organic matter content (positive association). The total benthic biomass was negatively linked to water temperature due to the predominance of cold-water species in the area and a close positive association of this factor with crab abundance. In contrast, the highest diversity was registered at the warmer sites, which may have been a reflection of the borealization process in the Arctic. Our results contribute towards the proper management and conservation of the local benthic ecosystem and provide reference data for future monitoring programs and coastal management guidelines.

Trait-based assessment of polychaete assemblages distinguishes macrofaunal community structure among four distinct benthic eco-regions on a shallow arctic shelf

In a rapidly changing Arctic, effects of taxonomic and functional composition of infaunal benthic communities on ecosystem function are poorly characterized for many areas of the continental shelf environment. Infaunal macrobenthos perform essential ecosystem services in soft-sediment habitats, including sediment oxygenation, organic-matter burial, and nutrient regeneration. Changes in the distribution and composition of infauna are likely to impact these important processes. We investigated spatial patterns in macrofauna on the northern Bering and southern Chukchi Sea continental shelves in conjunction with a suite of environmental variables as part of the Arctic Shelf Growth, Advection, Respiration, and Deposition (ASGARD) project. Depth-stratified macrofauna samples (>500 μm) were collected from multi-cores in June 2017 and 2018. Abundance and biomass were recorded for broad taxonomic categories (phylum or class). Polychaetes were identified to family to capture well-described functional-trait information. Functional guilds were assigned to polychaete families, reflecting feeding mode, motility, and feeding structures. Macrofauna exhibited no significant spatial patterns when examined at higher taxonomic levels; however, analysis of polychaete families yielded three distinct station groups, and polychaete functional guilds yielded four distinct groups. These groups were aligned with variations in key habitat characteristics and suggest variation in ecosystem function across the study area. At sandy stations, tube-dwelling, particle-selective suspension and surface deposit feeders were relatively abundant, reflecting an advective system with moderate current speeds and low deposition. Sites with gravelly substrate and moderate levels of organic matter in deeper sediment layers likely experience sporadic organic-matter deposition and disturbance from scouring and were inhabited by larger-bodied species, including bivalves and subsurface deposit-feeding or carnivorous polychaetes. Muddy, offshore stations in the southern Chukchi Sea also contained large bivalves and large carnivorous polychaetes, with evidence of high bioturbation. At more coastal Chukchi Sea stations, macrofauna were dominated by small, motile polychaetes concentrated in the 1-cm surface layer, with indications of anaerobic conditions below. Overall, polychaete functional traits and vertical distribution reflected the quality and quantity of organic matter input and the depositional environment inferred from grain size and current speed, with implications for biogeochemical cycling in sediments.

Spatial and temporal distribution of macrobenthos communities and their relationship with secondary front in Hangzhou Bay

Water quality in Hangzhou Bay is inferior (grade 5) because of discharged from Yangtze River and Qiantang River, and from factories around the bay. This study analyzed relationships between the environment and macrobenthic communities at 44 stations throughout Hangzhou Bay, based on samples collected in 2006, from 2016–2018, and in 2021. Long-term spatial and temporal changed in macrobenthos, and the influence of secondary water fronts on community composition, were discussed. Macrobenthos in Qiantang River Estuary was numerically, primarily dominated by crustaceans, and elsewhere by polychaetes. Species that differ most in abundance between four identified regions in the bay were the amphipod Corophium sinensis, clam Potamocorbula laevis, and polychaete Amaeana occidentalis. The abundance and biomass of macrobenthos in different regions differs significantly. Taxa were allocated to six feeding guilds: filter feeders and omnivores predominate in Qiantang River Estuary and south of Hangzhou Bay, while surface and subsurface deposit feeders predominate in sediments north of Hangzhou Bay and in the bay mouth area. Negative correlations were apparent between the abundances of polychaetes Nephtys polybranchia, Magelona japonica, Heterospio sinica, Sabella sp. and A. occidentalis and salinity and pH, while positive correlations were apparent between those of Sternaspis chinensis and Capitellidae indet. Fine-grained fraction (silt and clay) and mid-salinity were more suitable for macrobenthos. The numbers and biomasses of macrobenthic species in the Hangzhou Bay frontal area increased significantly relative to values in adjacent areas. The difference of each area near the front was more than 94%, and the main difference species were polychaetes and mollusks. Our baseline data for this region might ultimately contribute towards improved conservation of regional macrobenthos, and a better understanding of ecosystem health in this highly polluted bay.

Effect of cyclonic storm Vardah on the community structure and ecosystem functioning of macrobenthic fauna in the intertidal region of South Andaman Islands

An investigation was carried out to understand the effect of a cyclone Vardah on the functioning of macrobenthos. The assessment was accomplished by comparing before cyclone (BC) and after cyclone (AC) data of macrobenthos. Additionally, temporal changes in the faunal assemblages were evident through multivariate techniques. Five distinguished assemblages could be noticed through the Bray–Curtis similarity representing different phases of the cyclone. The cyclonic effect also resulted in the recruitment of some macrobenthic species and the loss of a few during the study period. Biological trait analysis identified subsurface deposit feeders, upward and downward conveyers, Ecological Group IV, mid-mobile macrobenthos and size class of 2–4 cm as the important groups that dominated the functioning of the macrobenthic community immediately after the cyclone. The resilience and recruitment of macrobenthos were explained using functional redundancy.

MACROZOOBENTHOS DIVERSITY AND FUNCTIONAL FEEDING GROUP (FFG) IN BEREMBANG RIVER OF WEST KALIMANTAN

This study analyzes macrozoobenthos diversity and functional feeding group in Berembang River, Kubu Raya Regency, West Kalimantan. The obtained macrozoobenthos were identified to the genus level, and their functional feeding group was determined through a literature study. Data on diversity, evenness, and dominance were analyzed descriptively. Diversity (H') and Evenness (E) of macrozoobenthos in Berembang River were low (H'=0.73 and E=0.15) while Dominance (C) was high (C=0.81) as evidenced by a large number of genera Corbicula and Gammarus. Macrozoobenthos functional feeding groups found at both stations can be divided into six categories, namely shredders, gathering collectors, deposit feeders, sub-surface deposit feeders, filtering collectors, and scrapers.

Can no-bubble methane seeps affect biological traits of benthic macroinvertebrates in coastal systems?

Methane seep studies often target sites where methane gas is actively bubbling from the sea floor to the water column. However, gas bubbles often remain trapped in surficial seabed sediments, especially in coastal systems; notably few ecological studies exist for these systems. These environments form patches on the seafloor in the Bahia Blanca estuary that, based on taxonomic analysis, represent a distinct benthic habitat. Here we examine whether taxonomic changes in benthic communities associated with trapped methane gas bubbles are related to functional changes. We found significant differences in biological traits of macroinvertebrates weighted by abundance and by species between two sites differing in gas presence and between spring and winter seasons. Compared with the control (no gas) site, the gas site had subsurface-deposit feeders and large sessile animals partially calcified with suspension-feeding mode. In contrast, at the control site the small and non-calcified animals are discretely motile, building burrows and tubes and feeding on surface deposit material. Trapped methane gas, detected with seismic methods, changes biological traits in benthic fauna and can lead to alteration of some ecosystem functions. This suggests the utility of high-resolution seismic methods for detect these benthic habitats with high spatial accuracy, and a need to further understanding of ecosystem processes associated with gas presence in the context of both direct anthropogenic and climate-change pressures.

Biological traits of benthic macrofauna show sizebased differences in response to bottom trawling intensity

Bottom trawling results in widespread impacts to the structure and composition of benthic communities. Although an ecosystem approach to fisheries management aims to conserve marine biodiversity and ecosystem function, there remains a lack of empirical evidence regarding the effects of trawling on benthic functional properties. Here, we examined the sensitivity of benthic macrofauna communities to trawling using their biological traits, and compared trait responses across size-categories and survey types. We collected 84 benthic soft-sediment samples by Van Veen grab (0.1 m2) in the Kattegat in 2016, and complemented with 827 Haps cores (0.0143 m2) gathered over a long-term monitoring programme between 2006 and 2013. By analysing trait response in 3 size categories (small: 1-4 mm fraction; large: ≥4 mm fraction; full community: all individuals combined), we demonstrate a size-dependent effect of trawling on benthic trait composition, where the traits of large-bodied fauna (≥4 mm) were more sensitive. Specifically, larger sessile, deep-living, suspension-feeding, tube-dwelling, subsurface deposit-feeding, burrow-dwelling, and long-lived (≥10 yr) individuals were among the most affected. Our results based on large fauna were largely in agreement with trait responses observed in the multi-year monitoring data, suggesting that trait data gathered from a targeted one-time sampling event can convey information on both acute (short-term) and chronic (long-term) trawling impacts. Given that most trawling impact assessments do not consider size-based effects, we outline how size-separating the community can be used to improve the detectability of trawling impacts, and provide new insights into the functional impacts of fishing on the seabed.

Historical Shifts in Benthic Infaunal Diversity in the Northern Gulf of Mexico since the Appearance of Seasonally Severe Hypoxia

Severe and persistent bottom-water hypoxia (≤2 mg O2 L−1) occurs on the Louisiana/Texas continental shelf from mid-May through mid-September over a large area (up to 23,000 km2 in mid-summer). Benthic infauna are less mobile than demersal organisms and become stressed by the low dissolved oxygen; benthic community composition, abundance, diversity, and biomass become altered. From the 1950s to the early 1970s, when sediment core indicators identified the initiation and subsequent worsening of dissolved oxygen conditions, there were no hydrographic data or benthic infaunal studies within the current area of frequent bottom-water hypoxia. This study highlights the impacts of severe hypoxia on benthic macroinfaunal communities and how they may have changed from less-hypoxic periods. Polychaetes were and are the dominant taxa in the available studies, but polychaete species richness in summer is now curtailed severely beginning with our 1985–1986 data. Species richness of polychaetes in summer hypoxia (1985–1986 and 1990–1991) was about 60% less than comparable taxa in 1972–1973. Abundance of polychaetes was much less in summer than spring, and recent infaunal biomass in summer was only 15% of what was found in spring. The result is less prey for demersal penaeid shrimp and fishes. Over the period of our comparison, infaunal feeding modes shifted from subsurface deposit feeders and surface deposit feeders to primarily surface deposit feeders (i.e., 95.5% of all polychaetes). Most were opportunistic, hypoxia tolerant, and recruited in high numbers following hypoxia abatement, some in fall and winter but most in spring. As benthic communities succumb to the stress of severe and continued seasonal low oxygen, they occupy the few upper centimeters of the sediment profile above the redox discontinuity layer with negative feedbacks to the water column by way of altered biogeochemical processes.

Structural and functional response of coastal macrofaunal community to terrigenous input from the Po River (northern Adriatic Sea)

To assess the influence of river-derived material on the benthic ecosystem in the Po River prodelta area, we investigated the structural and functional features of macrofaunal invertebrates in 14 sites. Biodiversity, species composition, response and effect traits of the community were determined and related to the main sediment physical-chemical and nutritional features (biopolymeric carbon, BPC; protein to carbohydrate ratio, Prt/Cho ratio; phaeopigment to chlorophyll-a ratio, Phaeo/Chl-a), as well as contaminants. We found significant spatial differences in community structure and its functional expression between northern and southern stations, and between nearshore and offshore ones. The shallower stations located nearby the main river mouth displayed higher densities, diversity and functional redundancy compared to southern stations. The main discriminating factors for the community were the higher percentage of sand and Prt/Cho nearby the river mouth, and fine grain-size and high Phaeo/Chl-a at the southernmost and deeper stations. Contaminant concentrations did not seem to severely affect the macrofaunal community. Changes in community structure were due to the dominance of few species, which occurrence varied according to grain-size and organic matter quality that in turn were linked to the different magnitude of depositional loads in the investigated area.Focusing on response traits, we observed a clear influence of high loads nearby the main river mouth, through the dominance of sessile and tube-builder trait-categories at stations with a higher sand content. In contrast, we detected a major expression of burrowers and interface crawlers, and swimmers at southern and principally offshore muddy stations. Effect traits revealed that in the northern part of the prodelta prevailed suspension, surface deposit feeders and conveyor invertebrates that are, respectively, fundamental players in the benthic-pelagic coupling and elemental cycling within benthos. In the southern part, subsurface deposit feeder and biodiffuser organisms dominated. The latter are able to rework huge amounts of sediments also in the deepest layers, amplifying the elemental cycling and decomposition. In highly dynamic systems, as delta areas, the presence of invertebrates able to exploit different resources through bioturbation activities may enhance the functions of riverine costal ecosystems.

Macrofaunal bioturbation attributes in relation to riverine influence: What can we learn from the Po River lagoonal system (Adriatic Sea)?

Delta areas are highly dynamic transitional areas, important for burial and decomposition of terrestrial and marine organic matter (OM). In these environments, macrofaunal organisms are influenced by fluctuations of fresh OM inputs that modify several aspects of their growth, reproduction and behaviour. Macrofaunal bioturbation activities are significant processes performed by individuals, which directly influence the biogeochemical cycling and thus the ecosystem functioning. To assess the influence of terrigenous/freshwater OM on bioturbation attributes of macrofauna in a lagoonal system, we integrated the bioturbation and irrigation potential (BPc and IPc) community indices and functional traits linked to reworking and ventilation of sediments (using Biological Traits Analysis-BTA). The macrofaunal community was investigated in four lagoons (Caleri, Marinetta-Vallona, Canarin and Scardovari) of the Po River Delta in Italy (northern Adriatic Sea). We examined the macrofaunal biodiversity and bioturbation attributes in relation to grain-size distribution, carbon and nitrogen ratio (C:N), carbon and nitrogen stable isotopes (δ13C and δ15N), and the radionuclides 137Cs and 7Be. The latter were used as proxies of the age of terrigenous/riverine-derived OM. The lowest values of BPc and IPc that corresponded to minimum values of benthic biodiversity were observed at the inner sampling stations of Scardovari. Here, low diversity values were likely ascribed to recent hypoxic/anoxic conditions exacerbated by the low water renewal that characterizes this lagoon, influencing the bioturbation processes. Grain-size fractions were significant drivers of the differences in BPc and IPc, and the major number of taxa in coarse sediments contributed to the highest values of bioturbation indices. A significant difference in IPc between sandy and muddy stations was due to the presence of subsurface deposit feeders with high burrowing depths and blind-ended burrows that enhanced the bio-irrigation in coarse sediments. We observed diverse spatial patterns of trait-categories belonging to sediment reworking activity at stations differently influenced by freshwater OM. Semi-motile and conveyor invertebrates, that are able to move sediment particles through their gut by ingestion and secretion, were dominant nearby the lagoon mouths where OM of freshwater origin was present. High occurrence of motile and biodiffuser invertebrates, that can randomly mix sediments layers, were found at stations characterized by old OM. Macrofaunal sediment reworking and ventilation processes are of paramount importance in the framework of an efficient management and sustainable use of lagoons, often exposed to anoxic and dystrophic events, that are strongly exploited for aquaculture.

Macrobenthos functional trait responses to heavy metal pollution gradients in a temperate lagoon

Biological traits analysis (BTA) can help identify the effect of various contaminants on functional trait composition of macrobenthos. However, the effects of bioavailable heavy metals on functional traits of macrobenthos communities remain to be examined. We sampled macrobenthos communities and assessed environmental variables over gradients of heavy metal pollution in Swan Lagoon, China. The RLQ and fourth-corner approaches were used to investigate the response of functional traits to heavy metal pollution. Our findings suggested that macrobenthic functional traits can be used to distinguish the effects of heavy metals and other environmental variables and isolate the corresponding species associated with heavy metal contamination. The macrobenthos at highly contaminated sites comprised taxa of sub-surface deposit-feeders, second-order opportunistic species, and tube-builders, mainly represented by the polychaeta Cirriformia tentaculata and Cirratulus chrysoderma. At less contaminated sites, indifferent species, species attached to seagrass, and crawlers were observed. The results confirm that BTA can provide new insights into the response of macrobenthic functional traits to heavy metal pollution in coastal lagoons.

Spatio-temporal variability in macrobenthic communities and trophic structure of a tropical estuary and its adjacent coastal waters.

Spatio-temporal distribution of the macrobenthic community (> 500μm) and the trophic ecology of polychaetes were studied for a year in the Cochin estuary (CE) and its adjacent coastal waters. A profound influence of the southwest monsoon (SWM) was evident in the CE, a tropical monsoonal estuary, during the present study. The sediment texture and macrobenthic density exhibited a pronounced spatial variation in the estuary, while in the coastal waters temporal changes were more prominent. Polychaetes formed the dominant taxa in terms of density and diversity in the estuary (53 species belonging to 25 families) as well as in the adjacent coastal waters (39 species belonging to 20 families). The polychaete species Diopatra neapolitana dominated during nonmonsoonal periods was found to be replaced by the higher abundance of Pisione sp. in the CE during the monsoon period. On the other hand, in the coastal waters, Cossura coasta, the dominant species during the pre-monsoon period, was replaced by the surface deposit feeder Paraprionospio pinnata during the monsoon and post-monsoon periods. The study evidenced the combined influence of sediment texture, salinity, and food availability in determining the distribution and abundance of the macrobenthic fauna in the CE and adjacent coastal waters. Feeding guild analysis and trophic importance index showed that carnivores and surface and subsurface deposit feeders were the dominant and trophically important feeding guilds in the study area. Redundancy analysis showed that the sandy substratum supported a diversified functional composition in the estuary and its adjacent coastal waters, and motile, discretely motile polychaetes and filter feeders were more associated with the sandy substratum. Results of the present study revealed that the seasonally fluctuating polychaete community structure in the study area was predominantly controlled by their diversified feeding habits and the ecological descriptors of the polychaete feeding guilds were linked primarily to the substratum type and food availability.

The current status of the macrozoobenthos around the Atlantic walrus haul-outs in the Pechora Sea (SE Barents Sea)

Although benthic fauna in the Pechora Sea (SE Barents Sea) is generally well-studied, information on the bottom communities in the shallows near islands and the mainland is still sparse. Shallow marine areas in the Pechora Sea serve as important feeding grounds for numerous benthophagous fish, waterfowl and marine mammals, including the Atlantic walrus (Odobenus rosmarus rosmarus). To study the patterns of macrozoobenthic distribution in the shallows and evaluate the ecological state of the zoobenthic populations close to walrus haul-outs, sampling was performed in 2014 and 2016 around an archipelago in the Pechora Sea. In 2014, the average biomass, the Shannon's Diversity Index and the predominance of filter feeders in benthic communities were, in general, similar to the respective characteristics in neighboring deeper areas studied in the 1990s. In 2016, significant differences in species number and in biomass were recorded compared to 2014. An increase was observed in Atlantic boreo-Arctic species. Analysis of the trophic structure showed a slight decrease in the proportion of filter feeders and a significant increase in the proportion of subsurface deposit feeders. However, the Shannon's Diversity and Ecological Stress Indices indicated that the macrozoobenthos in the study area was in a state of equilibrium. Changes in the zoobenthos may result from several factors, such as an increase in water temperature, sediment re-deposition under wind-induced waves and the plowing of bottom sediments by walruses during their foraging.

Macrobenthic functional feeding groups in a microtidal monsoonal estuary (Kodungallur–Azhikode estuary, India)

The functional feeding groups of macrobenthos in the Kodungallur–Azhikode estuary were studied on a monthly basis for a two year period (2009–2011). The main aim of the study was to understand the distribution pattern of macrobenthic functional feeding groups and their relationship to environmental drivers in the estuary. Malacostracan crustaceans dominated the system (60%) by numerical density, while molluscs contributed significantly to macrobenthic biomass (63%). Many species exploit the same class of resources within an assemblage of macrofaunal groups. The suspension feeding corophiid amphipod Americorophium triaeonyx was the most represented macrofaunal species. Other dominant macrofaunal feeding groups were the suspension feeding hydroid colonies of Obelia bidentata, surface deposit feeding polychaetes Prionospio cirrifera, suspension feeding mussels Arcuatula senhousia, carnivorous isopods Cirolana fluviatilis and sub-surface deposit feeding polychaetes Capitella sp. The sampling stations were compared using taxonomic distinctness (AvTD), and variations in taxonomic distinctness (VarTD), the values of AvTD and VarTD for all stations during the entire monthly survey fell within the confidence intervals of probability funnel (95%, p<0.05). However, a significant variation was noticed in the values between stations (AvTD: F (6,161) = 3.105, p=0.007; VarTD: F (6,161) = 2.489, p=0.025). The abundance biomass curves were plotted separately for each site as well as combined for the entire estuary. The relatively high negative trend was observed in the station 5 (W=−0.139) which indicates potential for the relatively high disturbance among all other stations. However, the W-value for the entire estuary was -0.079, which depicted moderate disturbance.

Do high Arctic coastal food webs rely on a terrestrial carbon subsidy?

Lagoons are a prominent feature of Arctic coastlines, support diverse benthic food webs, and provide vital feeding grounds for fish, migratory birds, and marine mammals. Across the Arctic, loading of terrestrial/freshwater-derived organic carbon (CT) from watershed runoff and coastal erosion is predicted to increase with global warming, and may subsidize marine organic carbon as an energy source. To assess the importance of CT, we analyzed the trophic links and carbon assimilation pathways of twenty genera in five trophic guilds (suspension and filter feeders (Su/FF), surface and subsurface deposit feeders (Ss/De), epibenthic omnivorous invertebrates (Ep/Om), omnivorous fishes (Fish), and mammalian carnivores (Mam/Carn) as well as end-member organic matter (OM) sources. Because end-members had distinct carbon and nitrogen isotopic ratios, we employed a Bayesian stable isotope mixing model (simmr) to determine the contributions of CT, shelf OM, and marine microphytobenthos, to the diets of resident fauna. Ss/De and Ep/Om mainly assimilated marine-derived OM end-members. Su/FF, Fish, and beluga whales derived large portions of their diet from CT (>40%). We conclude that (1) coastal food webs are characterized by a high degree of omnivory and plasticity, (2) CT is an important OM subsidy to food webs, and (3) omnivorous fish transfer CT from lower to upper trophic levels.

Fatty acid composition as an indicator of the trophic position of abyssal megabenthic deposit feeders in the Kuril Basin of the Sea of Okhotsk

This study examines the fatty acid (FA) composition in eight species of deposit feeders, including holothurians, echiurans, sipunculan, polychaete and bivalve mollusc from the Kuril Basin of the Sea of Okhotsk. Most of the FAs in the species studied have been described previously for abyssal deposit feeders, but 20:2(n-12), 22:4(n-8), and 22:5(n-5) were new among megabenthic invertebrates. Principal component analysis indicated sample separation of the deposit feeders into three groups. The first group included subsurface deposit feeders, and the other two consisted of surface deposit feeders. All groups differed in the ratio of 20:5(n-3) to 20:4(n-6). This ratio was 0.2–0.4 in the subsurface deposit feeder Molpadia musculus Risso, 1826 (group I) and 0.6–0.9 in the surface deposit feeding echiuran Pseudoikedella achaeta (Zenkevitch, 1958) and the elasipodid holothurian Psychropotes raripes Ludwig, 1893 (group II). In the second group of surface deposit feeders (group III), this ratio was a little larger in the polychaete Travisia sp. (1.3) and was much larger (2.1–2.5) in the echiuran Alomasoma nordpacificum Zenkevitch, 1958, the sipunculan Golfingia margaritacea (Sars, 1851), and the holothurian Peniagone dubia (D′yakonov and Savel'eva in D′yakonov et al., 1958). Unlike previous data, we found that the most abundant megabenthos species in the basin are subsurface deposit feeders and two groups of surface deposit feeders.