Structure Of Macrobenthic Assemblages Research Articles

Effects of habitat homogenisation on assemblages associated with mussel clumps.

Biodiversity loss is considered one of the main threats to marine ecosystems. In this framework of biodiversity decline, organisms that provide biogenic habitat play a relevant role by their capacity to structure assemblages and influence ecological processes. The Mediterranean mussel Mytilus galloprovincialis is considered an ecosystem engineer because it alters local environmental conditions maintaining habitat suitability for other organisms, and enhancing local biodiversity. Although it is widely recognized that mussel beds increase diversity, the drivers shaping these assemblages are poorly explored. We investigate whether mussel size homogenisation shapes the abundance, richness and structure of macrobenthic assemblages associated with mussel beds in two shores of the Galician coast (NW Spain). At each shore, two sites, 10 m apart, were selected and at each site, faunal assemblages were compared between mussel clumps showing shells of various sizes (control), and mussel clumps with closely similar-sized mussels, considered as homogenised. Homogenised clumps showed, in general, higher values in total number of individuals and species than control clumps. Regarding the effect of mussel size homogenisation on the multivariate structure of the assemblages, significant differences between control and homogenised clumps were found in three out of the four sites. Most relevant associated species usually reached higher abundances in homogenised clumps than control ones. Therefore, mussel size homogenisation influenced the structure of the macrofaunal assemblages associated with mussel beds but, its effect was context dependent (i.e., varied with sites). Information about the species contribution to dissimilarities among homogenised and control clumps was provided and the potential influence of sediment and algae on mussel clumps was discussed.

Community Structure of Macrobenthic Assemblages on Soft Bottom around Heuksan Island, Korea

다도해해상국립공원의 흑산도 주변해역 연성기질 조하대에 서식하는 대형저서동물 군집의 구조와 공간적인 분포양상을 파악하기 위하여 2012년 8월부터 2013년 5월까지 계절별로 현장조사를 실시하였다. 연구해역에서 출현한 대형저서동물은 221종/8㎡과 2,718개체/㎡ 이었고, 환형동물의 다모류는 105종(47.51%)과 2,713개체(79.97%)가 출현하여 가장 우점하였다. 연구해역에서 출현한 대형저서동물의 개체수 자료를 기초로 군집구조 분석을 실시한 결과, 대형저서동물 군집은 크게 3개의 그룹과 1개의 정점(하계의 정점 6)으로 구분되었다. 이 가운데 그룹 1은 다모류의 Aonides oxycephala, Prionospio membranacea, 투구갯지렁이(Sigambra tentaculata)와 등각류의 Symmius caudatus로 대표되는 모든 조사시기의 정점 1과 2가 포함되었다. 그룹 2는 다모류의 긴자락송곳갯지렁이(Lumbrineris longifolia), 꼬리대나무갯지렁이(Praxillea affinis), Tharyx sp.1, Chaetozone sp.와 이매패류의 아기반투명조개(Theora fragilis)가 특징적으로 출현한 모든 조사 시기의 정점 9와 10으로 구성되었다. 마지막으로 그룹 3은 다모류의 Heterospio sinica와 이매패류의 쇄개량조개(Raetellops pulchella)로 대표되는 정점 4, 5, 6, 7과 8이었다. 연구해역에 서식하는 대형저서동물 군집은 공간적으로 어류양식어장 입지해역, 예리항 내부해역과 흑산도 주변해역으로 구분됨을 알 수 있었다. 연구해역에 서식하는 대형저서동물 군집은 인위적인 활동(양식장 운영과 지형적 조건)과 기질 특성에 의해 영향을 받는 것으로 파악할 수 있었다.

Composition, uniqueness and connectivity across tropical coastal lagoon habitats in the Red Sea

BackgroundTropical habitats and their associated environmental characteristics play a critical role in shaping macroinvertebrate communities. Assessing patterns of diversity over space and time and investigating the factors that control and generate those patterns is critical for conservation efforts. However, these factors are still poorly understood in sub-tropical and tropical regions. The present study applied a combination of uni- and multivariate techniques to test whether patterns of biodiversity, composition, and structure of macrobenthic assemblages change across different lagoon habitats (two mangrove sites; two seagrass meadows with varying levels of vegetation cover; and an unvegetated subtidal area) and between seasons and years.ResultsIn total, 4771 invertebrates were identified belonging to 272 operational taxonomic units (OTUs). We observed that macrobenthic lagoon assemblages are diverse, heterogeneous and that the most evident biological pattern was spatial rather than temporal. To investigate whether macrofaunal patterns within the lagoon habitats (mangrove, seagrass, unvegetated area) changed through the time, we analysed each habitat separately. The results showed high seasonal and inter-annual variability in the macrofaunal patterns. However, the seagrass beds that are characterized by variable vegetation cover, through time, showed comparatively higher stability (with the lowest values of inter-annual variability and a high number of resident taxa). These results support the theory that seagrass habitat complexity promotes diversity and density of macrobenthic assemblages. Despite the structural and functional importance of seagrass beds documented in this study, the results also highlighted the small-scale heterogeneity of tropical habitats that may serve as biodiversity repositories.ConclusionsComprehensive approaches at the “seascape” level are required for improved ecosystem management and to maintain connectivity patterns amongst habitats. This is particularly true along the Saudi Arabian coast of the Red Sea, which is currently experiencing rapid coastal development. Also, considering the high temporal variability (seasonal and inter-annual) of tropical shallow-water habitats, monitoring and management plans must include temporal scales.

Longitudinal and temporal assemblage patterns of benthic macroinvertebrates in snow melt stream waters of the Jhelum River Basin of Kashmir Himalaya (India)

AbstractThis article tries to understand the dynamics involving benthic macroinvertebrate studies over 18 watersheds for a period of 2 years in the Jhelum River Basin (JRB) of Kashmir Himalaya, India. We aimed to understand this by recognizing spatio‐temporal patterns of macroinvertebrates and their relation to some environmental factors across the whole JRB. A total of 93 taxa pertaining to 3 phyla, 7 classes and 55 families were observed. Our observations revealed that taxa richness, Shannon diversity, total density and percentage of Ephemeroptera, Plecoptera and Trichoptera (EPT) metrics considerably declined towards downstream regions. Summer and spring seasons have higher influence on richness, diversity and abundance of most percentage indices. Macrobenthic assemblage structure reflected significant variability with space and time having clear segregation of the downstream sites from upper and midstream reaches in canonical ordination plots. Variation partitioning models [distance‐based redundancy analysis (dbRDA)] showed water discharge and temperature as the main drivers of variation in community structure during summer, whereas fine substrate composition (% sand) and pH were revealed to define the variability in the biology of streams during other seasonal times. Pertinently, much of the variability in benthic faunal assemblages could not be deciphered by environmental drivers and therefore may be linked to other hydrochemical variables (like alkalinity, hardness, chloride and dissolved organic matter) and nutrients (nitrogen and phosphorus). Given the apprehension of future climatic changes, understanding spatial and seasonal influences on the macroinvertebrate assemblage structure remains highlighted here, which is crucial for baseline information as well as management of lotic Himalayan systems spanning longitudinal gradients and climatic variability.

Macrobenthic assemblage structure and distribution at the Boojagh Marine National Park, Southern Caspian Sea, Iran.

Although macrobenthic assemblages are considered as major players in many ecosystems around the world, the ecology of Caspian Sea macrobenthos is currently understudied. This study describes the species composition and quantitative distribution of macrobenthos in the southern Caspian Sea and relates the distribution to seasonal changes at three depths (1, 5 and 10 meters) on the Boojagh Marine National Park (BMNP) coast in the southern Caspian Sea between the summers of 2015 and 2016. To investigate the distribution of macrobenthos in BMNP, the data of 450 samples were analyzed. In this study sixteen species were identified: Cerastoderma glaucum, Mytilaster lineatus, Pyrgula grimmi, Anisus kolesnikovi, Stenogammarus carausui, Paraniphargoides motasi, Onisimus caspius, Pterocuma pectinatum, Pterocuma sowinskyi, Pseudocuma (Stenocuma) gracile, Nais sp., Hypania invalida, Manayunkia caspica, Streblospio gynobranchiata, Hediste diversicolor, Amphibalanus improvisus. Among them, the non-indigenous C. glaucum was the dominant species, accounting for 27% of the total abundance and in descending order P. grimmi with 14.4%, A. improvisus with 8.7%, M. lineatus with 7.9%, Nais sp. with 7.5%, N. carausui with 5.2%, P. motasi with 5%, S. gynobranchiata with 4.5%, H. invalida with 5%, M. Caspica with 3.1%, P. sowinskyi with 2.5%, O. caspius with 2.4%, A. kolesnikovi and H. diversicolor with 1.8%, S. gracilis with 1.6% and P. pectinatum with 1.5% were in the next rank. Significant differences in abundance across the sixteen species were observed among depths and seasons. This study highlights the potential consequences of established non-indigenous species in the southern Caspian Sea.

Environmental and Benthic Community Patterns of the Shallow Hydrothermal Area of Secca Delle Fumose (Baia, Naples, Italy)

The occurrence of hydrothermal vent ecosystems at Secca delle Fumose, Pozzuoli Bay (Gulf of Naples), represented an opportunity to study the benthic assemblages under the thermal stress of hydrothermal emissions in a very shallow environment (9 – 14 m water depth). In autumn 2016, the macrobenthic community was sampled by scuba divers at four sites located in the Baia Underwater Archaeological Park. Two sites were characterized by vent emissions (one with white bacterial mat scattered on the bottom and one with a yellow substrate around a geyser opening) and two at about 100 m away, used as control. Sediment and interstitial water environmental variables were measured to determine their influence on the structure of macrobenthic assemblages. A total of 1,954 macrofaunal individuals was found, characterized by great differences in abundance and species richness among sites. This pattern was correlated to the dominance of a particular set of variables that drastically change in a very small spatial scale, from one site to another. The control sites, characterized by the highest percentage of gravel in the sediments (19.67±2.6%) and normal level of major ions such as Ca2+, K+ and Mg2+ in the interstitial waters, showed the highest values of sinecological indices. The “white” hydrothermal site exhibited the lowest species richness, abundance and species diversity, influenced by low pH values (~7.6), high temperatures (~37.53°C) and by the highest total organic carbon content (TOC 34.78%) in the sediment. The “yellow” hydrothermal site, with sediment TOC equal to 30.03% and interstitial sulphide ions measuring 130.58 ppm, showed higher values of sinecological indices than those recorded at the “white” site. Therefore, taxonomic analysis revealed a high turnover between control and vents sites. This highlights the preference for hydrothermal vents by a few resistant species, such as the gastropod Tritia cuvierii and the polychaete Capitella capitata, confirming the role of the latter species as opportunistic in extreme environments like Secca delle Fumose.

Macrofaunal spatial distribution and community structure in a lagoon without a river discharge (the Oualidia lagoon, NW Morocco)

AbstractThe assemblage structure and spatial distribution patterns of macrobenthic communities according to environmental conditions were analysed through five samplings carried out at 14 intertidal soft sediment stations in the Oualidia lagoon (NW Morocco). A total of 89 macrobenthic taxa were collected, amounting to 55.188 specimens. Molluscs, polychaetes and arthropods were the most species‐rich groups. The snail Peringia ulvae was the most dominant species, especially abundant in the mid‐ and upper lagoon sections (nearly 64% of the total specimens gathered), followed by the mollusc Scrobicularia plana (10%). Diversity values were generally low (<3 bit) pointing out the high dominance by few species. Multivariate analyses clearly distinguished three distinct macrobenthic assemblages, successively distributed from lagoon inlets towards inner parts. Nevertheless, each assemblage was found in particular habitat types and had a specific species composition in response to different environmental characteristics. (a) The Scolelepis fuliginosa community occupied sandy substrates at the lower section of the lagoon with stronger marine influence and, (b) the P. ulvae community lived in sandy‐muddy substrates, including two sub‐communities dominated, respectively, by Cerastoderma edule, S. plana and Tritia pfeffeiri inhabiting the middle section and S. plana the upper section. The combination of salinity, temperature, pH and silt content was identified as the major environmental variable subset with the highest correlation with the observed macrofaunal patterns and silt fraction as the single best correlated variable. The results demonstrated significant spatial differences in macrobenthic assemblage structure and composition along environmental gradients in spite of the absence of direct freshwater river inflow.

The comparison of distribution patterns of macrobenthic assemblages adjacent floating net cage areas at Karang Lebar Island, Jakarta: a multivariate approach

Water and sediment ecosystems are often influenced by fish farming activities especially organic matter that lead to organic enrichment. The macrobenthic community is one of the benthic organisms that can be used as bioindicator to detect disturbances in aquatic environments. The purpose of this study was to compare the distribution patterns of macrobenthic assemblages adjacent to floating net cages situated at Karang Lebar Island, Jakarta using a multivariate approach. Three sampling locations were assessed, each with three stations and three replicates. Each location consisted of a floating net cage of monoculture, a floating net cage of IMTA (Integrated Multi-Trophic Aquaculture), and a reference site at Karang Lebar Island, Kepulauan Seribu, DKI Jakarta. All data concerning macrobenthic presence was expressed using diversity (H’), evenness (e) and dominance (C) indices.Further analysis done using multivariate analysis was presented as 2D-ordination by Nonmetric Multi-Dimensional Scaling (NMDS). The composition of macrobenthic assemblages was dominated by gastropods (18 species), bivalves (9 species) and Polychaeta (7 species). Based on NMDS ordination, there was a tendency of grouping stations by sampling time. It is particularly so between sampling times II and III, and between sampling times I and III. However, this grouping did not occur between sampling times I and II. It may indicate that the macrobenthic assemblages were influenced by certain annual seasons.Meanwhile, depending on sampling locations, the assemblages were influenced by environmental variability. The stations were grouped by the aquacultural areas and reference area on the ordination with some overlapping stations positioned among them. However, the tendency of grouping the stations between IMTA and monocultural sites did not occur, implying both farming practices have a relatively similar impact on the structure of macrobenthic assemblages.

Structure of Macrobenthic Assemblages and Its Relationship with Environmental Variables in the East China Sea of Xiangshan

Structure of Macrobenthic Assemblages and Its Relationship with Environmental Variables in the East China Sea of Xiangshan

Macrobenthic assemblage characteristics under stressed waters and ecological health assessment using AMBI and M-AMBI: a case study at the Xin’an River Estuary, Yantai, China

To understand the ecological status and macrobenthic assemblages of the Xin’an River Estuary and its adjacent waters, a survey was conducted for environmental variables and macrobenthic assemblage structure in September 2012 (Yantai, China). Several methods are adopted in the data analysis process: dominance index, diversity indices, cluster analysis, non-metric multi-dimentional scaling ordination, AMBI and M-AMBI. The dissolved inorganic nitrogen and soluble reactive phosphorus of six out of eight sampling stations were in a good condition with low concentration. The average value of DO ((2.89±0.60) mg/L) and pH (4.28±0.43) indicated that the research area faced with the risk of ocean acidification and underlying hypoxia. A total of 62 species were identified, of which the dominant species group was polychaetes. The average abundance and biomass was 577.50 ind./m2 and 6.01 g/m2, respectively. Compared with historical data, the macrobenthic assemblage structure at waters around the Xin’an River Estuary was in a relatively stable status from 2009 to 2012. Contaminant indicator species Capitella capitata appeared at Sta. Y1, indicating the animals here suffered from hypoxia and acidification. AMBI and M-AMBI results showed that most sampling stations were slightly disturbed, which were coincided with the abiotic measurement on evaluating the health conditions. Macrobenthic communities suffered pressures from ocean acidification and hypoxia at the research waters, particularly those at Stas Y1, Y2 and Y5, which displays negative results in benthic health evaluation.

Linking chemical and physical parameters of a coastal water ecosystem with macrobenthic assemblages to assess environmental disturbance

Environmental disturbance, whether natural or anthropogenic, may change the structure of macrobenthic assemblages (across various spatial and temporal scales) in terms of taxa richness, animal abundance, and animal biomass. Such changes may be used as an indicator and can provide a quantitative basis when assessing the levels of disturbance. This study is aimed to assess environmental disturbance caused by fish farming by linking chemical and physical parameters to differences in the structure of macrobenthic communities. The study sites comprised coastal water ecosystems in the Awerange Gulf, South Sulawesi, Indonesia. The study compared macrobenthic communities associated with polyculture and monoculture farming against reference sites. The tendency of reduction in their abundance occurred at polyculture and monoculture sites, compared to the reference site, i.e. 5882 ind.m-2, 3531 ind.m-2, 2112.5 ind.m-2, respectively. The results from multivariate and graphical methods using NMDS plots, k-dominance curve, and ABC curves, tend to be in accordance with the results from index values, thus both methods may be used as a apart of rapid assessment of level of environmental disturbance in coastal water ecosystem. Carbon and nitrogen contents in sediment and dissolved oxygen (DO) were the most chemical and physical parameters influencing structure of macrobenthos (r=0.457; BIO-ENV).

Effects of hydrocarbon pollution in the structure of macrobenthic assemblages from two large estuaries in Brazil

Changes in the structure of benthic macrofauna and its relationship with hydrocarbon contamination were determined at different spatial scales in sublittoral sediments of two large estuaries in Brazil. Guanabara Bay (GB) is a heavily polluted estuary due to the presence of a large industrial complex and high demographic density. Laranjeiras Bay (LB) lies in an Environmental Protection Area and can still be considered as preserved from human activities. Despite some spatial differences within each bay, the PAHs concentrations were significantly and consistently higher in GB, with values generally above the threshold effect levels. No signs of hydrocarbon contamination were observed in LB. Macrofauna abundance, diversity and overall assemblage structure were largely different between bays. Canonical analysis of principal coordinates (CAP), used to model the relationship between macrofauna and PAHs levels, indicated that this class of hydrocarbons is the main structuring factor of soft-bottom assemblages in both bays.

Relationship between structure of macrobenthic assemblages and environmental variables in shallow sublittoral soft bottoms

We establish baseline knowledge of abundance, diversity and multivariate structure of macrobenthos from shallow sublitoral soft bottoms in the North Portuguese coast and elucidate main environmental factors that shape their spatial patterns. In this area distribution of soft bottoms is patchy, surrounded by boulders and rocky substrates. This particular landscape and the lack of significant anthropogenic disturbances are values for the conservation of this habitat. Sediment and physicochemical properties of the water column were studied to provide models for each studied macrobenthic variable. Our models highlighted that most of variation (59%–72%) in macrobenthic spatial patterns was explained by the studied environmental variables. Sedimentary variables were more relevant that those of the water column. Therefore, disturbances affecting sedimentary environment could cause dramatic changes in macrobenthic assemblages because of the limited availability of soft bottoms in the area. In this way, results are useful to adopt right management and conservation strategies.

Macrobenthic assemblage structure associated with a Caulerpa prolifera meadow in the eastern Mediterranean Sea (Elounda Bay, Crete Island)

The present study investigates the structure and intra-annual variation of the benthic macrofaunal community associated with a monospecific C. prolifera meadow in a shallow semi-enclosed coastal marine ecosystem of the eastern Mediterranean Sea (Elounda Bay, Crete Island). The samples were collected on five occasions (May, September and November 2006, February and April 2007) by using an epibenthic sledge (0.5 mm mesh size). The analysis of the macrofauna revealed 319 taxa with densities ranging from 71 to 410 individuals m−2. The most diversified animal groups were polychaetes, gastropods and amphipods. Crustaceans were by far the most abundant group with densities exceeding 50% of the total macrofauna during the study period. The dominant species were the amphipods Caprella acanthifera acanthifera, C. rapax and Microdeutopus stationis, the gastropod Pusillina lineolata, the tanaid Leptochelia sp. and the bivalve Abra alba. The results of the present study revealed a relatively high diversified and abundant benthic macrofauna, which is supported by the presence of the dense and continuous canopy of C. prolifera in this shallow wave-sheltered area characterized by high organic matter input.

The Community Structure of Macrobenthic Assemblages in the Taehwa River Estuary, Ulsan, Korea

The Community Structure of Macrobenthic Assemblages in the Taehwa River Estuary, Ulsan, Korea

Structuring factors of the spatio-temporal variability of macrozoobenthos assemblages in a southern Mediterranean lagoon: How useful for bioindication is a multi-biotic indices approach?

The authors investigated the impact of the extension of the El Kantra Channel on the composition and structure of macrobenthic assemblages in Boughrara Lagoon (Gulf of Gabes, Tunisia along with the use of 4 biotic indices (AMBI, BENTIX, M-AMBI and TUBI). Thirteen stations were sampled seasonally in 2012–2013. Forty-one species were found in 2012–2013 not recorded in 2009–2010, including 20 species of polychaetes belonging to the trophic groups of deposit-feeders and carnivores which are expected to increase in areas disturbed by organic pollution. During the survey, we recorded a high fish mortality, essentially caused by the development of harmful algal blooms (HAB) which increased organic matter deposition, thus inducing polychaete development. This seems to weaken the bio-indicating power of biotic indices used here which, paradoxically, classified all sampled stations at a high ecological status. A review of these indices and their applicability to all marine environments is recommended.

Impacts of shrimp farming cultivation cycles on macrobenthic assemblages and chemistry of sediments

AbstractThe aim of this study was to evaluate the influence of a shrimp farm cultivation cycle in the composition of sediments and on the structure of macrobenthic assemblages. Concentrations of nutrients, Zn and Cu were significantly higher in impact than control areas. In general, the level of contaminants was highest during the harvesting period and in sites closest to the discharge of effluents. Abundances and number of taxa of benthic invertebrates were at least one order of magnitude smaller in impacted areas than in controls. The structure of the benthic assemblages was significantly different at these two treatments. The combined use of biological and chemical data showed to be efficient to provide precise answers regarding the extent of impacts caused by shrimp cultivation. The results provide the basis for a better understanding of impacts of this activity and can subsidize the development of better management practices for coastal areas.

Intertidal benthic macrofaunal assemblages: changes in structure along entire tropical estuarine salinity gradients

Spatial variation in the structure of macrobenthic assemblages on intertidal flats is known to be related to different environmental variables. Most of the studies have observed that along the estuarine gradient, salinity is the most important variable driving the patterns of the macrobenthic assemblages. However, the great majority of studies have been done on single estuarine systems in temperate regions. We investigated the relationship between the macrobenthic assemblages in intertidal habitats and the environmental variables along three tropical estuaries. From lower to upper estuarine regions we sampled benthic macrofauna, salinity and sediments. The structure of the benthic assemblages was primarily related to salinity. There was a decrease in the number of taxa from the upper to the lower estuarine regions, indicating important deviation from Remane's model of estuarine diversity. There were important similarities of taxa abundance along different estuarine salinity gradients which can be properly tested in other tropical and temperate regions. We advocate that in order to adopt general and robust management practices it is essential to identify broad patterns and general rules governing estuarine systems.

Spatial variability of macrobenthic zonation on exposed sandy beaches

We analysed the consistence of vertical patterns of distribution (i.e. zonation) for macrofauna at different spatial scales on four intermediate exposed beaches in the North of Portugal. We tested the hypothesis that biological zonation on exposed sandy beaches would vary at the studied spatial scales. For this aim, abundance, diversity and structure of macrobenthic assemblages were examined at the scales of transect and beach. Moreover, the main environmental factors that could potentially drive zonation patterns were investigated. Univariate and multivariate analyses revealed that the number of biological zones ranged from two to three depending on the beach and from indistinct zonation to three zones at the scale of transect. Therefore, results support our working hypothesis because zonation patterns were not consistent at the studied spatial scales. The median particle size, sorting coefficient and water content were significantly correlated with zonation patterns of macrobenthic assemblages. However, a high degree of correlation was not reached when the total structure of the assemblage was considered.

Macrobenthic assemblage structure and organismal stoichiometry control faunal processing of particulate organic carbon and nitrogen in oxygen minimum zone sediments

Abstract. The Arabian Sea oxygen minimum zone (OMZ) impinges on the western Indian continental margin between 150 and 1500 m, causing gradients in oxygen availability and sediment geochemistry at the sea floor. Oxygen availability and sediment geochemistry are important factors structuring macrofaunal assemblages in marine sediments. However, relationships between macrofaunal assemblage structure and sea-floor carbon and nitrogen cycling are poorly understood. We conducted in situ 13C:15N tracer experiments in the OMZ core (540 m [O2] = 0.35 μmol l–1) and lower OMZ boundary (800–1100 m, [O2] = 2.2–15.0 μmol l–1) to investigate how macrofaunal assemblage structure, affected by different oxygen levels, and C:N coupling influence the fate of particulate organic matter. No macrofauna were present in the OMZ core. Within the OMZ boundary, relatively high abundance and biomass resulted in the highest macrofaunal assimilation of particulate organic carbon (POC) and nitrogen (PON) at the lower oxygen 800 m stations ([O2] = 2.2–2.36 μmol l–1). At these stations the numerically dominant cirratulid polychaetes exhibited greatest POC and PON uptake. By contrast, at the higher oxygen 1100 m station ([O2] = 15.0 μmol l–1) macrofaunal C and N assimilation was lower, with POC assimilation dominated by one large solitary ascidian. Macrofaunal POC and PON assimilation were influenced by changes in oxygen availability, and significantly correlated to differences in macrofaunal assemblage structure between stations. However, macrofaunal feeding responses were ultimately characterised by preferential organic nitrogen assimilation, relative to their internal C:N budgets.