Macrofaunal Communities Research Articles

Spatio-temporal comparison of intertidal macrofaunal communities along anthropogenically influenced Mandvi coast, Gulf of Kachchh, India

Spatio-temporal comparison of intertidal macrofaunal communities along anthropogenically influenced Mandvi coast, Gulf of Kachchh, India

Benthic oxygen dynamics and implication for the maintenance of chronic hypoxia and ecosystem degradation in the Berre lagoon (France)

Chronic hypoxia and anoxia have strong impacts on coastal ecosystems worldwide. In shallow coastal ecosystems, such situations are essentially driven by high benthic oxygen (O2) demand resulting from organic matter mineralization in surface sediment and amplified by a low mixing of the water column. However, the benthic O2 demand may greatly vary according to the O2 availability, sediment biogeochemical properties, and bioturbation by macrobenthic fauna. Here we examined how the sediment O2 demand varies in response to seasonal and long-lasting (pluri-decadal) hypoxia in the Berre lagoon, a coastal ecosystem impacted by chronic hypoxia events since 60 years. Oxygen penetration depth, diffusive and total O2 fluxes were measured in situ using a microelectrode autonomous profiler and benthic chamber deployments at three sites impacted by quite-permanent (PA), seasonal (PI) and occasional (PO) hypoxia in August 2016. They were seasonally repeated at site PI between August 2015 and August 2016. Additional physical and chemical characteristics were also measured in surface sediment. Sediment profile images and characteristics of benthic macrofauna communities enabled to estimate the quality of the benthic ecosystem. The highest benthic O2 demand was observed after seasonal anoxia in relation to the important accumulation of reduced chemical species in surface sediment. Interestingly, both pluri-decadal hypoxia and normoxia produced relatively high benthic O2 demand related to a higher accumulation of organic matter and to the presence of reduced chemical species at site dominated by hypoxia, and to the presence of fresher organic matter and active bioturbating macrofaunal communities in normoxic site. The low benthic O2 demand at site seasonally impacted by hypoxia likely resulted from the degraded state of the macrofaunal community and from the lower accumulation of reduced chemical species. The occurrence of hypoxia and anoxia situations in the Berre lagoon was predicted from the competition between kinetics of benthic O2 demand and water column reoxygenation events induced by strong wind. The good agreement between the measured and predicted hypoxia/anoxia occurrence clearly indicates that the chronic deoxygenation events in the Berre lagoon, and the resulting degraded ecological state of the benthic ecosystem are driven both by the benthic O2 demand and by the intensity and duration of the water column stratification.

Winter cover crops and no-till promote soil macrofauna communities in irrigated, Mediterranean cropland in California, USA

Cover crops and reduced tillage are two elements of conservation agriculture with potential to support larger and more diverse soil biological communities. Soil macrofauna can be indicators of soil quality and can regulate multiple soil functions, but their response to cover crop adoption in temperate regions is not well studied. We evaluated soil macrofauna communities and related soil quality metrics in response to a 16-year winter cover crop and tillage trial located in the San Joaquin Valley of California, USA. The most abundant taxa were Coleoptera (beetles) and Lumbricidae (earthworms), with average densities ranging between 5 and 318 beetles m−2 and 65–480 earthworms m−2 depending on sample date and treatments. Overall macrofauna abundance increased by 93% with the addition of cover crops in rotation, and 50% with the elimination of tillage. Taxonomic richness increased by 48% with cover crops in treatments managed without tillage, though there was no effect of cover crops under standard tillage. Macrofauna abundance was positively related to total soil carbon, water infiltration, and soil aggregate stability. Macrofauna community composition was best explained by soil carbon, water stable aggregate fraction, and cover crop usage. Agricultural management practices that foster soil biological communities may support biodiversity and improve environmental outcomes critical for sustainable food production.

Responses of a soil mollusk community to an extreme cold event

Soil communities are impacted by increasingly frequent and intense climate extremes. To accurately predict the effects of these events on soil communities and effectively design recovery and management programs for soil biodiversity, it is necessary to understand the spatiotemporal patterns and mechanisms underlying the soil community responses. Here, we investigated a mangrove soil macrofaunal (mollusk) community before and after an extreme cold event (ECE) to determine the effects of the ECE on the spatial pattern, temporal succession, and deterministic and stochastic processes affecting the soil metacommunity. We used distance-decay and time-decay analyses to characterize the spatial pattern and temporal succession of soil mollusk community dissimilarity (e.g., species identity, abundance, and biomass) across a reginal scale (~350 km scale). We used null models to compare the relative importance of deterministic and stochastic processes in shaping the regional soil mollusk community assembly. The ECE resulted in a reorganization of the soil mollusk metacommunity reflected by the mortality and extinction of several original species, colonization by new opportunistic species, and a significant reduction in mollusk abundance and biomass. The ECE increased divergent temporal succession but decreased spatial segregation in the soil mollusks, consistent with changes in the community dissimilarity of species abundance, richness, and biomass. The ECE increased the numbers of non-random segregated and random structures of soil mollusks while decreased the number of non-random aggregated communities. Notably, non-random segregated communities were the most strongly affected. Thus, the response of the soil mollusk metacommunity to the ECE was mediated by an increase in limiting similarity processes and stochastic processes and a decrease in limiting dissimilarity processes. The dominant limiting similarity processes involved species competition and/or dispersal limitation. More broadly, our study indicated that alterations in the spatiotemporal dynamics of soil fauna in response to climate change should be studied at the metacommunity scale. These spatiotemporal dynamics should be further tested in an ecological processes framework to reliably evaluate soil community responses to climate change and to devise management strategies for global soils.

Relative importance of tree species richness, tree functional type, and microenvironment for soil macrofauna communities in European forests.

Soil fauna communities are major drivers of many forest ecosystem processes. Tree species diversity and composition shape soil fauna communities, but their relationships are poorly understood, notably whether or not soil fauna diversity depends on tree species diversity. Here, we characterized soil macrofauna communities from forests composed of either one or three tree species, located in four different climate zones and growing on different soil types. Using multivariate analysis and model averaging we investigated the relative importance of tree species richness, tree functional type (deciduous vs. evergreen), litter quality, microhabitat and microclimatic characteristics as drivers of soil macrofauna community composition and structure. We found that macrofauna communities in mixed forest stands were represented by a higher number of broad taxonomic groups that were more diverse and more evenly represented. We also observed a switch from earthworm-dominated to predator-dominated communities with increasing evergreen proportion in forest stands, which we interpreted as a result of a lower litter quality and a higher forest floor mass. Finally, canopy openness was positively related to detritivore abundance and biomass, leading to higher predator species richness and diversity probably through trophic cascade effects. Interestingly, considering different levels of taxonomic resolution in the analyses highlighted different facets of macrofauna response to tree species richness, likely a result of both different ecological niche range and methodological constraints. Overall, our study supports the positive effects of tree species richness on macrofauna diversity and abundance through multiple changes in resource quality and availability, microhabitat, and microclimate modifications.

Small‐scale macrobenthic community structure along asymmetrical sand waves in an underwater seascape

AbstractSand waves are dynamic and regular bedforms that are ubiquitous in sandy shelf seas. However, information about the ecological characteristics (e.g., benthic community structure) and their spatial variability within these habitats is very limited. To address this knowledge gap, we undertook a field campaign in summer 2017 to investigate the macrofaunal community composition of a sand wave area off Texel (Dutch part of the North Sea). Sand waves in this area were asymmetrical, with longer gentle slopes that were approximately double in length to the shorter steep slopes. The benthic distribution along the different parts of these sand waves was assessed by collecting a large number of box cores within a transect line (~1 km). We show considerable variability in the individual, biomass and taxon densities, which were all significantly higher on the steeper slopes of the sand waves. These results are consistent with the trends observed in both the abiotic parameters and video analysis that were measured in two recent studies at the same study area. Our results provide valuable insight into the small‐scale patterns of variability in asymmetrical dynamic bedform environments, where gentle slopes seem to be primarily controlled by physical forces, while steep slopes are more under biotic control.

Benthic Community Responses to the Filling of a Hurricane-Induced Barrier Island Inlet

Rodil, I.F.; Long, Z.T.; Fegley, S.R.; Rodriguez, A.B., and Peterson, C.H., 2021. Benthic community responses to the filling of a hurricane-induced barrier island inlet. Journal of Coastal Research, 37(3), 601–610. Coconut Creek (Florida), ISSN 0749-0208.In September 2003, Hurricane Isabel created a new tidal inlet through Hatteras Island, a barrier island of North Carolina (U.S.A.). Within two months, the breach was filled with sand dredged from nearby areas. Subsequent ecological response of the benthic macroinvertebrate communities to the filling differed on shores on opposite sides of the island. Thus, the filled area on the high-energy sandy beach exhibited convergence in community composition and abundance with a nearby reference area within 30 months, whereas the filled area on the lower-energy sound shoreline still possessed a depauperate benthos. The high volume of long-shore sediment transport documented along the ocean beaches of Hatteras Island probably acted quickly to transport benthic macrofauna to the fill along with natural beach sediments, and thereby activating a rapid ecological response of the beach community. The beach community was dominated by annual macroinvertebrate species, which could account for mixing from nearby areas in the rapid macrofauna community response. In contrast, the Pamlico Sound shoreline experiences only local wind-driven waves and modest long-shore currents likely insufficient to import macrobenthos readily. Infrequent passive transport of macrobenthos and persistence of defaunated sediment habitats nearby probably slowed the macrofauna community response on the sound-shore side. Management intervention through habitat restoration would be recommended in the less dynamic sound shore environment compared to the high-energy ocean beach where ecological responses of the invertebrate community occurred rapidly.

Macrofauna edáfica asociada al cultivo de maíz (Zea maíz)

Macrofauna is a biological indicator of soils, in this sense, the objective of this research was to determine the edaphic macrofauna community and its physicochemical properties of the soil, by means of its abundance and richness of groups during the growing season and post-harvest of corn. Three monoliths 25 x 25 cm wide by 30 cm deep were established. Soil samples were taken in each plot, then the organic matter (OM) content, hydrogen potential (pH), electrical conductivity (EC) and nitrogen (N) content were determined. The results show differences between atmos-pheric temperatures during the development period (25 °C) and the post-harvest period (41.4 °C). Physicochemical parameters such as pH ranged between 8.5 and 8.3. The maximum Shannon index was 0.48 (growing season) and 0.13 (post-harvest season). The greatest number of individuals was ants (111) and was identified during the postharvest period. In this sense, the biological diversity was lower in the growing season of corn, and during the post-harvest period a greater number of ant organisms was determined, which was associated with the resistance to high temperatures.

Spatial Patterns of Macrozoobenthos Assemblages in a Sentinel Coastal Lagoon: Biodiversity and Environmental Drivers

This study presents an assessment of the diversity and spatial distribution of benthic macrofauna communities along the Moulay Bousselham lagoon and discusses the environmental factors contributing to observed patterns. In the autumn of 2018, 68 stations were sampled with three replicates per station in subtidal and intertidal areas. Environmental conditions showed that the range of water temperature was from 25.0 °C to 12.3 °C, the salinity varied between 38.7 and 3.7, while the average of pH values fluctuated between 7.3 and 8.0. In vegetated habitats, biomass values of the seagrass Zostera noltei Hornemann ranged between 31.7 gDW/m² and 170.2 gDW/m² while the biomass of the seagrass Ruppia cirrhosa (Petagna) Grande between 54.2 gDW/m² and 84.7 gDW/m². Sediment analyses showed that the lagoon is mainly composed of sandy and silty sediments. We recorded 37,165 individuals of macrofauna distributed in 63 taxa belonging to 50 families, with a mean abundance value of 4582.8 ind/m² and biomass average of 22.2 g/m². Distance-based linear modeling analysis (DISTLM) identified sediment characteristics, water parameters and habitat type (biomass of Z. noltei) as the major environmental drivers influencing macrozoobenthos patterns. Our results clearly revealed that the hydrographic regime (marine and terrestrial freshwater), sediment distribution and characteristics and the type of habitat (vegetated vs. unvegetated substrate) are the key factors determining the species composition and patterns of macrozoobenthos assemblages.

Polycyclic Aromatic Hydrocarbons Have Adverse Effects on Benthic Communities in the Baltic Sea: Implications for Environmental Status Assessment

Changes in benthic macrofaunal communities are indicative of environmental stressors, including eutrophication and hypoxia. However, some species are sensitive not only to hypoxia but also to various environmental contaminants. We tested which of the environmental predictors (sediment organic carbon, sediment concentrations of metals and polyaromatic hydrocarbons [PAHs], bottom water oxygen, salinity, temperature, and surface chlorophyll-a concentration) that best explained the following response variables: (1) macrofauna community composition, (2) abundance of a benthic sentinel species, the amphipod Monoporeia affinis; and (3) the Benthic Quality Index (BQI). All data originated from 29 reference monitoring stations in the Baltic Sea and the statistical tests included both uni- and multivariate analyses. The community composition and BQI were best explained by the same combination of salinity, depth, temperature and PAH concentrations. The abundance of M. affinis, which is sensitive to hypoxia and chemical exposure, was best explained by PAHs as a single predictor. Our findings suggest that benthic communities in the Baltic Sea are influenced by anthropogenic contaminants, which should be taken into account when benthos is used for eutrophication status assessment.

Variable contributions of seafloor communities to ecosystem metabolism across a gradient of habitat-forming species

The contributions of habitat-forming species to the biodiversity and ecosystem processes of marine and terrestrial ecosystems are widely recognized. Aquatic plants are considered foundation species in shallow ecosystems, as they maintain biodiversity and sustain many ecosystem functions such as primary production and respiration. Despite the increasing amount of biodiversity-ecosystem functioning experiments in seagrass habitats, the effects of benthic variability on ecosystem functioning are rarely investigated across spatially variable aquatic plant habitats. Here, we quantitatively link seasonal variability in seafloor metabolism (i.e. gross primary production and community respiration) with major benthic community components (i.e. microphytobenthos, aquatic plants and macrofauna) across a structural complexity gradient of habitat-forming species (in terms of shoot density and biomass), ranging from bare sand, to a sparse mixture of plants to a dense monospecific seagrass meadow. The increasing complexity gradient enhanced the magnitude of the relationships between benthic community and seafloor metabolism. The daily average seafloor metabolism per season at the bare site was similar to the sparse site, highlighting the role of microphytobenthos for seafloor metabolism in shallow unvegetated sediments. The contribution of the associated macrofauna to the seafloor respiration was similar to the aquatic plant community contribution. Infauna was the main macrofaunal component significantly explaining the seasonal variability of seafloor respiration. However, benthic community-metabolism relationships were stronger within the plant community than within the macrofauna community (i.e. steepest slopes and lowest p-values). Understanding these relationships are a priority since climate change and biodiversity loss are reducing habitat complexity around the world, jeopardizing valuable ecosystem functions and services.

EDNA reveals estuarine benthic community response to nutrient enrichment – evidence from an in-situ experiment

Nutrient loading is a major threat to estuaries and coastal environments worldwide, therefore, it is critical that we have good monitoring tools to detect early signs of degradation in these ecologically important and vulnerable ecosystems. We carried out a seven-month manipulative experiment in two estuaries to assess the effects of nutrient loading on benthic communities. Environmental DNA metabarcoding was used to examine the response of eukaryotic (18S rRNA), diatom (rbcL), and bacterial (16S rRNA) communities to two levels of nutrient enrichment (150 and 600 g N m-2). Multivariate analyses demonstrated consistent changes in eukaryotic, diatom, and bacterial communities in response to enrichment, despite differing environmental conditions between sites (Fig. 1). These patterns aligned with changes in macrofaunal communities identified using traditional morphological techniques, confirming concordance between disturbance indicators detected by eDNA and current monitoring approaches. Clear shifts in eukaryotic and bacterial indicator taxa were seen in response to nutrient loading while changes in diatom communities were more subtle. Community changes were discernable between nutrient levels, suggesting that estuary health assessment tools could be developed to detect early signs of degradation. Existing eDNA-based biotic indices (microgAMBI and mtMBI) were able to detect these community shifts, suggesting transferability of these indices to other regions and systems. This work represents a first step towards the development of molecular-based estuary monitoring tools, which could provide a more holistic and sensitive approach to ecosystem health assessment with faster turn-around times and lower costs.

Ecogeochemistry and Denitrification in Non-eutrophic Coastal Sediments

Coastal nutrient pollution is an ever-present threat to estuaries worldwide. Benthic denitrification has been identified as a crucial ecosystem service to help mitigate increasing N loads to the coast. However, the controls on denitrification in low-nutrient systems are not well constrained and are likely different to those in more widely studied eutrophic systems. This study aims to identify the specific controls on denitrification in low-nutrient estuaries, including the contribution of the macrofaunal community to denitrification rates, and to understand how this important service fits into the network of ecogeochemical processes in these systems. Results show that porewater ammonium concentrations and mud content are good predictors of net N2 flux in the dark. Additionally, models predict N2 flux rates much more effectively in the dark than in the light, but the macrofaunal community data, specifically species richness, is a key factor in both increasing the explanatory power of both models by nearly 20%. Additionally, interaction networks reveal that increasing mud content results in a shift in the macrofaunal community and a reduction in the N removal capacity of these intertidal systems.

Dynamic of organic matter and meiofaunal community on a river-dominated shelf (Rhône prodelta, NW Mediterranean Sea): Responses to river regime

In the oligotrophic context of the Mediterranean Sea, riverine inputs of particulate organic matter represent an important source of food for benthic communities. However, since most of these inputs are delivered during short, but intense flood events, communities living in the vicinity of river mouths are also exposed to strong and frequent physical disturbances. A very tight and complex relationship links river dynamic and macrofaunal communities in Mediterranean deltas, but less is known on the response of meiobenthic communities to river regime. In 2010, sediments cores were collected in the Rhône River prodelta in winter and spring before the flooding of the Rhône River tributaries in June, and then twice in the early and late summer. The hypothesis was that increased runoff and export of terrigenous material would induce major changes in the sediment biochemistry, which would in turn trigger modifications in abundances and vertical distribution of the meiofauna. The origin and quality (lability, degradation state) of the different pools of organic matter preserved in these recent sediments were determined using bulk geochemical and molecular analyses (fatty acids, amino acids). Vertical profiles of descriptors for organic matter origin and quality revealed major changes in the nature of the inputs occurring at monthly time scales. Inputs of plant detritus from autumnal and winter flood events were still visible in the cores collected in February and April. A few days after the June 2010 high-discharge event, a newly deposit (~7 cm) containing soil organic matter has recovered the prodeltaic sediments and the resident meiofaunal community, but at the end of August only 2 cm of this deposit remained. Multivariate analyses furthermore highlighted that the meiofaunal community was driven by both the trophic conditions and the deposition of a new sediment layer driven by the hydrological regime of the Rhône River. In April, increased abundances of meiofauna were observed in response to the sedimentation of labile organic matter after the spring bloom. The June high-discharge event affected the meiofauna with a reduction of its abundance and the burial of the resident meiobenthic community. However, the meiofauna recovered in less than two months after this disturbance, showing the strong resilience of this component of the benthic ecosystem in this high energy environment.

Patterns of structural and functional diversity of macrofaunal communities in a subtropical mangrove ecosystem

Biological trait analysis has been successfully used to describe ecological functions in marine benthic ecosystems. However, it has rarely been applied to mangrove habitats. This study analyzes taxonomic and functional diversity and the components thereof in two mangrove habitats in the Hara Biosphere Reserve, Persian Gulf: a vegetated area with both mangrove trees and pneumatophores, and an adjacent mudflat. Species diversity and functional diversity were higher in vegetated habitats and slightly increased in summer. Our study demonstrates the importance of mangrove structural complexity for the structure and functioning of invertebrate communities. The macrofaunal communities were characterized by low diversity and a high dominance of just a few species, such as crab Opusia indica which are specifically adapted to this stressed environment. Burrowers, surface deposit feeders, free-living, and large sized organisms were dominant trait modalities that essentially shape the functional composition of arid mangrove ecosystem of the Persian Gulf. The low functional redundancy among species implies that small changes in species diversity may have marked impacts on the system functional diversity.

The role of habitat heterogeneity and canyon processes in structuring sediment macrofaunal communities associated with hard substrate habitats in Norfolk Canyon, USA

Topographic and hydrodynamic complexity in submarine canyons promotes steep gradients in food availability and geophysical parameters which affect ecological assemblages and beta diversity. While habitat heterogeneity in submarine canyons is known to support diverse and abundant megafaunal communities, due to difficulty in sampling little is known about infaunal communities adjacent to hard substrate habitats, their contribution to canyon assemblages, and overall deep-sea diversity. Sediments were collected in three distinct habitat types: within Norfolk Canyon (western Atlantic) adjacent to hard substrate habitats including canyon walls and large boulders, along the main axis of the canyon, and on the adjacent continental slope to quantify macrofaunal (>300 μm) density, diversity and community composition, and sediment geochemical parameters including grain size, organic content, and stable isotope composition. While macrofaunal densities were similar among habitats sampled at comparable depths, diversity was higher near the hard substrate environments. Discrete communities were present in each habitat type, while annelid functional composition was similar between hard substrate adjacent and canyon axis habitats. Although diversity and abundance of hard substrate adjacent sediment communities did not change with depth, communities were driven by sediments with low organic matter content, whereas canyon and slope community assemblages were best explained by depth and higher organic content. Beta diversity among hard substrate adjacent sediments and canyon axis communities was high, with 27% of canyon taxa and 10% of regional taxa only occurring in hard substrate habitats. Given the thousands of submarine canyons worldwide, our results highlight the overall importance of substrate habitat heterogeneity within canyons in supporting deep-sea benthic diversity and suggest that both within-canyon and regional diversity are underestimated.

Immediate effects of the 2019 oil spill on the macrobenthic fauna associated with macroalgae on the tropical coast of Brazil

The 2019–2020 Brazil oil spill disaster affected several ecosystems and species-rich areas. The shallow-water reefs of Paiva beach are among the best-preserved coastal environments in the State of Pernambuco (NE Brazil), but were severely affected by oil arrival at the end of 2019. The reefs are densely covered by macroalgae as important biogenic substrates for benthic fauna. Based on that, herein, we provide a baseline assessment of the immediate impacts of the oil spill on the structure of epifaunal communities associated with the algae Jania capillacea and Penicillus capitatus. The benthic communities in both algae simplified (reduction of species richness and abundance) soon after oil arrival, while opportunistic taxa increased. After two months, the macrofaunal communities restructured to almost pre-disaster levels. However, polychaeta diversity remained low. Despite the apparently fast recovery of reef macrobenthos, a more detailed, long-term monitoring is necessary to evaluate the chronic effects.

Abundance and diversity of soil invertebrate macro-fauna in different land uses at Shenkolla watershed, South Central Ethiopia

BackgroundLand use can exert a strong influence on the abundance, diversity, and community composition of soil macro-fauna. This study was conducted to evaluate the effects of four land use types on the abundance and diversity of soil invertebrate macro-fauna communities. These land uses include forest land, grazing land, crop cultivated outfields, and homestead garden fields present at Shenkolla watershed, south central Ethiopia. Monolith sampling of soil macro-fauna was done according to the standard of Tropical Soils Biology and Fertility Institute (TSBF) procedure. Five sampling points were chosen in each land use type and small monolith (25 × 25 × 30 cm) was dug out at 5-m interval along a transect with randomly positioned starting point, but perpendiculars to the slope. A total of 20 monoliths (4 treatments × 5 replications) were taken across all the land use types. Sampling of SIMF was carried out in April 2019 where soil macro-faunas are known to be more active. To evaluate the SIMF community eight parameters were measured: Shannon-Wiener index, Simpson diversity index, Pielou’s measure of evenness, Margalef’s diversity index, the Number of Occurrence Index, Relative abundance, Density (individuals per square meter) of each taxon and density of all SIMF and Bray-Curtis similarity index. The data were further analyzed using ANOVA and a general linear model to determine the variation and the influence of land use type, respectively.ResultsIn general, 332 individuals, 10 orders, 12 families, and 15 species were identified, from the collected samples. There were significant differences (p < 0.05) among the four land use types for SIMF except wireworm, spiders, and millipedes. Overall abundance and diversity were lowest in the crop cultivated outfields and highest in homestead garden fields and forest land. Bray-Curtis’ similarity was highest between the sampled sites s16 and s19 with in the forest land, and lowest (2%) between sites s1 (crop cultivated out fields) and s14 (homestead garden fields).ConclusionThe results revealed that the diversity of SIMF was positively influenced by forest land and homestead garden fields and negatively influenced in grazing land and cultivated outfields. Therefore, maintenance of a continuous litter cover at the surface and application of a wide range of organic fertilizers (farmyard manure, household refuse, and compost) is very much critical to prevent the decrease in diversity of SIMF.

Macrofauna community patterns in a Chiloe Island channel used intensely for aquaculture: the ecological status of its benthic environment

BackgroundIt is known that aquaculture may produce negative environmental effects on marine ecosystems. Southern Chile is one of the most important salmon and mussel-producing areas in the world. Here we assess the ecological status of benthic communities near farming centers in Caucahue Channel, Chiloe, which has been used intensely for salmon and mussel production for 30 years.MethodsThe macrofauna, sediments and water column were characterized at distances of 5 to 100 m from three salmon and three mussel-producing centers. Information was also obtained from reference sites 500 to 3000 m from these aquaculture farms. The macrofauna and environmental conditions during winter were analyzed using uni- and multivariate analysis and the AZTI Marine Biotic Index (AMBI) as an indicator of benthic community condition.Results(i) There is a high degree of spatial dissimilarity in macrofauna and environmental variables among sampling sites and types of environments (far from or near farming centers) and between the northern and southern areas of the channel; (ii) sediment structure (mean grain size and percentage of total organic matter) correlated with the observed dissimilarities in macrofauna communities; and (iii) the level of perturbation according to AMBI was heterogeneous, with sites in the undisturbed/normal range to moderately disturbed/polluted.ConclusionsWe found a high spatial dissimilarity in benthic macrofauna and environmental variables among sampling sites, environmental types and between the northern and southern areas of the channel. AMBI and multivariate community-environment analysis are useful tools to define the level of perturbation of a geographic area at different spatial scales, using all the ecological information from each sample and replicates.

Functional changes in benthic macrofaunal communities along a natural gradient of hypoxia in an upwelling system

Increasing global concern has been raised about the expansion of hypoxia in coastal waters and its potential to impact benthic ecosystems. Upwelling areas offer opportunities to study the effects of hypoxia on benthic communities under natural conditions. We used a biological trait-based approach and estimated functional diversity indices to assess macrobenthic community functioning along a depth gradient associated with naturally increasing hypoxia and concentrations of organic matter in the upwelling zone of northern Chile (South-East Pacific) over two years. Our results highlighted the increasing dominance of opportunistic biological traits associated with hypoxia and high organic matter content. Habitat filtering was the main process affecting the studied communities. Functional diversity patterns were persistent overtime despite the occurrence of a pulse of oxygenation. This study contributes to our understanding of how natural hypoxia impacts macrobenthic communities, providing useful information in the context of increasing eutrophication due to human influence on coastal areas.