Macrofaunal Abundance Research Articles

The Role of Cajanus cajan in Enhancing Soil Fertility and Macrofauna Populations in Intensively Cultivated Systems in Korhogo (Northern Côte d’ivoire)

In the Korhogo department, it is almost impossible to practice fallowing. The aim of this study is to determine how the Cajanus fallow impact the soil the biological and physical soil fertility. Macrofauna and soil samples were taken in different cropping systems (Cajan + maize, Cajanus + groundnut, Cajanus + maize + groundnut, Cajanus) and compared with the control (soil that did not contain any legume). The population density and abundance of the different macrofauna sampled were calculated and compared by analysis of variance ANOVA at the threshold of 0.05. The results show that the cropping system based on Cajanus cajan favoured the repopulation of the soil with Termicidae, Lumbricidae and Formicidae to the control. These values varied from 90 to 340 individuals/m2 for Lumbricidae in the system based on Cajanus. compared to the control values lower than 5 individuals/m2. The comparison of the population density according to the type of tillage also shows that flat plowing systems stimulate increase Lumbricidae populations more than ridged soils (325; 275; 125 individuals/m2 on plowing. against 230; 100 individuals /m2 on ridge) respectively on Cajanus+ groundnut, Cajanus + groundnut+ maize and pure Cajanus. On the other hand, the intercropping which increased the number of Lumbricidae, Termicidae and Formicidae, whatever the type of tillage, are, respectively, Cajanus + groundnut, Cajanus + groundnut + maize, Cajanus + maize and pure Cajanus.The introduction of Cajanus into intercropping systems leads to an improvement in the physical and biological fertility of the soil.

Seagrass space occupation efficiency is key for their role as ecosystem engineers and ecological indicators

Studies for the preservation of seagrass beds biotopes have met difficulties in establishing appropriate methods assessing their health. We tested the efficiency of space occupation by seagrasses scattered worldwide (dgrass index), which proved to be dependent on clonal growth form and morphometric plasticity. dgrass correlated with the above-ground to below-ground biomass ratio. However, the latter was misleading when high ratios resulted from low below-ground biomass. Nutrient Posphate-limitations were revealed in situations of theoretical Nitrogen-limitation. Enhanced nutrient supply benefitted seagrasses only up to a threshold after which it became detrimental. Better nurtured, healthier meadows with denser canopies increased the organic matter in the sediment and had associated greater abundances of benthic macrofauna. Hence, seagrass biotopes could benefit from moderate anthropogenic nutrient additions. However, organic matter above ≈6% and/or reduced riverine discharges (dams upstream and climate-change-related droughts) were detrimental to healthy meadows, jeopardizing ecosystem services such as macrofauna abundances and carbon sinks.

Assessing the diversity and species composition in macroinvertebrate assemblages thriving in shallow water macroalgal habitats: Structural complexity is not always better

The assemblages of motile and sessile macroinvertebrates [mainly arthropods (peracarids), mollusks and annelids] were studied in three shallow macroalgal habitats from the NW Mediterranean Sea. Habitats were respectively dominated by three macroalgae: Ericaria mediterranea, a canopy-forming fucoid with repeatedly ramified cylindrical branches and spine-like projections; Cystoseira compressa, a canopy-forming fucoid with occasionally ramified compressed branches; and Ellisolandia elongata, a turf-forming, repeatedly branched, geniculate calcified alga. A total of 175,800 macroinvertebrate specimens, belonging to 228 taxa were collected. Macroinvertebrate assemblages in E. mediterranea habitat showed the highest abundances and number of taxa (104,412 specimens and 184 taxa), followed by those from C. compressa (49,128 specimens and 157 taxa) and E. elongata habitats (22,260 specimens and 144 taxa). Annelids were the most diverse group (43% of taxa) and amphipods the most abundant (78% of individuals). Macroinvertebrate abundances, alpha-diversity and species composition significantly differed among habitats and/or sites, while the number of taxa did not show significant differences neither among sites nor among habitats. Despite the simpler morphology of E. elongata respect to fucoid species, E. elongata habitat registered the lowest macrofauna abundance values but the highest alpha-diversity. Amphipods were the most abundant group in fucoid algae habitats (82–85%), while bivalves dominated in E. elongata one. Annelid polychaetes were the third more abundant group. Macroinvertebrate assemblages thriving in E. elongata habitat were always different to those found in fucoid algae habitats. Amphipods Protohyale schmidtii, Jassa herdmani, Jassa morinoi and Stenothoe gallensis were the most abundant species in fucoid algae habitats, while several species of Mytilidae, together with Caprella liparotensis, S. gallensis and nematodes dominated in E. elongata turfs. Differences observed are explained according to differences in algal morphological complexity and natural variability.

Conservation agriculture compared to conventional tillage improves the trade-off between ground-dwelling arthropod trophic groups for natural pest regulation in cotton cropping systems

Conservation agriculture is an innovative approach based on minimal soil disturbance, soil cover with crop residues, and crop rotation, which increases the biodiversity of soil macrofauna thus contributing to nutrient cycling and soil aggregation. In addition, macrofaunal abundance may play a role at regulating insect pest populations. The study aims to predict the effects of soil management practices (conventional tillage and conservation agriculture) on the abundance of soil macrofauna and herbivore predation in cotton (Gossypium hirsutum L.) based cropping systems. We conducted a field experiment with a randomized complete block comprising two treatments, Conventional Tillage (CT) and Conservation Agriculture (CA), and six replications in a cotton-maize rotation system from 2020 to 2023. Soil monoliths and pitfall traps were installed in both treatments to collect ground-dwelling arthropods, to analyse the influence of soil management practices on their abundance, their trophic groups, and the rate of pest predation by generalist predators. Pest predation rates were assessed using artificial caterpillars made from plasticine. The results showed significant positive effects of soil management practices on herbivory rate, herbivore abundance, predator abundance, omnivore-predator abundance and pest predation rate. The average herbivory rate was 9.8 % in the conservation agriculture plots and 11.6 % in the conventional tillage plots. Overall, the predation rate was 58.9 % in the conservation agriculture plots and 21.8 % in the conventional tillage plots. The abundance of predators and of omnivore-predators were significantly higher in conservation agriculture than in conventional tillage. These findings suggest that conservation agriculture practices improve soil macrofauna and pest regulation, with potential benefits on soil quality and sustainability in cotton cropping systems.

Effects of experimental in situ seabed disturbance on deep-sea macrofaunal communities of Chatham Rise, Southwest Pacific

ABSTRACT With the possibility of deep-sea mining of mineral resources occurring, it is necessary to understand potential impacts on benthic communities. Previous simulated mining experiments revealed direct benthic impacts; however, indirect impacts of sedimentation are not well understood. A disturbance experiment was conducted on Chatham Rise, New Zealand, to assess the resilience of benthic communities to sedimentation that could result from future deep-sea phosphorite mining. Macrofaunal and sediment samples were collected before, immediately after, and one year after a disturbance in areas directly physically disturbed and subjected to induced sedimentation (DI), and undisturbed or subjected to sedimentation only (UI). Macrofaunal abundance significantly decreased in DI areas but not in UI areas. However, abundance-based community structure changed in both areas; in DI areas this was mostly driven by decreases in dominant fauna, but in UI areas by changes in more sensitive fauna. One year after disturbance, abundance-based community structure had recovered in both areas and was correlated most strongly with variations in sediment C:N molar ratios. Biomass-based community structure in DI areas differed one-year post disturbance from communities sampled at the two earlier periods. These results are useful for informing the management of impacts from offshore industries where sedimentation is an issue.

Efficient and reliable methods for estimating the abundance of keystone coastal macrofauna over large spatial scales.

Coastal bivalves are important ecosystem engineers, and identifying critical habitats can enhance conservation outcomes for threated keystone species as well as determining hotspots for invasive species. As early action is more efficient in both conservation and mitigation of species invasions, efficient and reliable tools for mapping and monitoring species over large scales are essential. We assessed the reliability and efficiency of towed video and quadrat sampling for estimating the abundance of three keystone macrofaunal bivalve species. To assess reliability, we compared the measured density based on each of the two methods to the "true" density estimated by manually surveying an entire transect. We found that both the video and quadrat method caused underestimation of the density of bivalves, but that the amount of underestimation was comparable, and further that both methods took substantially less time than surveying an entire transect manually. The video method underestimated the abundance of Pacific oysters (Magallana gigas), European flat oysters (Ostrea edulis), and blue mussels (Mytilus spp.) by 23%, 24%, and 16%, respectively. The causes of underestimation for the two oyster species were bivalves grouped in clusters, large amounts of small individuals, and generally higher abundances. While Mytilus spp. were underestimated overall, here observer experience was important, with inexperienced observers overestimating and experienced observers underestimating. Our study found both methods to be reliable and efficient for estimating the abundance of three keystone macrofaunal species, suggesting their potential applicability to other sessile or slow-moving species. We propose that these methods, due to their efficiency, can advance scientific knowledge and enhance conservation outcomes by establishing population baselines, assessing trends over time, and identifying and protecting critical habitats.

Seasonal Variability in the Influence of Coastal Aquaculture Operation on Benthic–Pelagic Coupling Processes in Shallow Aquatic Ecosystems

Coastal shellfish aquaculture can influence benthic–pelagic-coupled systems because cultured species consume phytoplankton in the water column and return the captured organic matter and nutrients to the environment as biodeposits, which fall to the seafloor, affecting local sediment characteristics and the benthic community. In 2023, we conducted monthly field surveys to characterize the relationships between shellfish aquaculture and the surrounding environment by examining a range of physical and biological variables along the benthic–pelagic gradient at multiple sampling locations in relation to their distances from the aquaculture facilities in Onagawa Bay, Japan. The abundances of benthic macrofauna were dominated by polychaetes (86.3%), followed by gastropods (4.7%), malacostracans (2.7%), ophiuroids (2.1%), and bivalves (1.5%). Both benthic biomass and biodiversity were markedly higher, but the chlorophyll-a concentration of the water column and the sediment organic matter content were significantly lower at the closest proximity to the aquaculture facilities. Although the physical presence of shellfish aquaculture may effectively enhance pelagic–benthic energy fluxes, such processes may also pose a new challenge under the influence of recent global warming, causing widespread hypoxic conditions due to increased stratification in the water column accompanied by excess organic inputs from the aquaculture.

Soil–Plant–Pollinator Relationships in Urban Grass and Meadow Habitats: Competing Benefits and Demands of Tall Flowering Plants on Soil and Pollinator Diversity

Urban green spaces can be important habitats for soil, plant, and pollinator diversity and the complementary ecosystem functions they confer. Most studies tend to investigate the relationships between plant diversity with either soil or pollinator diversity, but establishing their relationship across habitat types could be important for optimising ecosystem service provision via alternative management (for instance, urban meadows in place of short amenity grass). Here, we investigate soil–plant–pollinator relationships across urban grass and meadow habitats through a range of measured biodiversity (soil mesofauna and macrofauna, plants, aboveground invertebrates, and pollinators) and edaphic variables. We found significant effects of habitat type on available nutrients (plant and soil C:N ratios) but less clear relationships were observed between habitat type and diversity metrics. Soil–plant–pollinator interactions across habitat types and sites showed an interconnection, whereby flowering plant abundance increased alongside soil macrofauna abundance. Site characteristics that showed strong effects on plant and invertebrate diversity metrics were C:N ratios (plant and soil) and soil pH, suggesting a potential role of nutrient availability on soil–plant–pollinator associations. Our results suggest that a combination of short-mown grass, tall grass, and sown flowers can provide greater benefits for soil and pollination services as each habitat type benefits different taxa due to differing sensitivities to management practices. For example, pollinators benefit from sown flowers but soil fauna are sensitive to annual sowing. Our results also indicate that sown flowers may not optimise overall biodiversity as expected due to disturbance and the depleting role of tall, flowering plants on soil nutrient availability. Future research across a greater range of sites in urban landscapes would resolve the potential role of nutrient availability in modulating soil–plant–pollinator interactions in urban green spaces.

Diversity and Abundance of Soil Macrofauna in Wheat Fields with Low and High Input of Fertilizers

Diversity and Abundance of Soil Macrofauna in Wheat Fields with Low and High Input of Fertilizers

Quantifying direct and indirect linkages between seagrasses, environment and associated macrofauna in a temperate lagoon

AbstractSeagrass ecosystems play a vital role in marine environments, providing essential services, including physical habitat that supports a species diversity critical to robust trophic structures. However, seagrass loss due to various influences raises concerns about the persistence of these ecosystems. Seagrass‐associated macrofauna serve as indicators of environmental health, noting change or stability. This study investigated the structural and environmental drivers influencing macrofaunal communities associated with seagrass (Zostera capensis) in a temperate lagoon. Variation in macrofaunal community structure across phenotypically distinct seagrass populations found large‐leaved morphotypes in deeper intertidal stands to support higher species diversity and richness. Conversely, small‐leaved populations in higher shore positions had a greater abundance of desiccation‐resistant gastropods. Seasonal differences were significant, with higher abundances generally observed during spring and summer, while diversity and richness peaked in autumn and winter. Structural equation modelling revealed shoot densities and leaf width to have positive direct effects on macrofaunal abundance, while temperature and tidal exposure produced significant indirect effects. Temperature had a direct effect on seagrass structure and significantly influenced five out of six seagrass metrics measured. Observations of seagrass distribution in the lagoon indicate significant declines in large‐leaved populations with likely adverse consequences for associated macrofauna and related trophic levels.

The abundance of soil mesofauna and macrofauna at different altitudes in Mount Gede Pangrango National Park

Soil fauna is important in the breakdown of organic matter for soil fertility. Various environmental factors, including edaphic, climatic factors, and overlying vegetation, influence the abundance of soil fauna. This study aims to analyze the abundance of soil fauna at different altitudes and the influence of the environment on it. The research was conducted at three different altitudes, namely 1,550 m asl, 1,650 m asl, 1,750 m asl, and in open land (1,200 m asl). The LSD test results showed that the abundance of soil fauna significantly differed between the altitude of 1,650 m asl and open land. In comparison, the abundance of soil fauna at the 1,550 m asl and 1,750 m asl was not significantly different at the 95% confidence interval. The results of the correlation analysis show that the climatic factors of light intensity and air temperature are negatively correlated. In contrast, air humidity positively correlates with the abundance of soil fauna. Factors strongly correlated with abundance are litter wet weight and soil pH.

The interplay of co-occurring ecosystem engineers shapes the structure of benthic communities – a mesocosm experiment

IntroductionEcosystem engineers play a pivotal role in shaping habitats through their activities and presence. In shallow Baltic waters, seagrasses, patch-forming mussels, and infaunal clams modify soft bottom habitats, impacting benthic community structure. While the individual effects of these ecosystem engineers are well studied, interactions among co-occurring engineers are poorly understood. MethodsWe conducted a mesocosm experiment to assess the independent and combined impacts of seagrass (Zostera marina), epifaunal mussels (Mytilus spp.), and infaunal clams (Macoma balthica) on invertebrate colonization in soft sediments. ResultsOur findings reveal significant engineer-driven alterations in macrofaunal community structure. Combined engineer effects diverged from individual impacts, indicating potential synergies or antagonisms in sediment (re)colonization. Notably, a higher number of engineer species positively affected the diversity of settled macrofauna, with the lowest macrofaunal abundance and biomass but the highest Shannon diversity found in the presence of all three engineers. DiscussionResults suggest that seagrass, mussels, and clams influence benthos through larval settlement and sediment biogeochemistry, providing insights into the distinct roles of habitat-forming organisms in shaping the benthic communities in coastal ecosystems of the Baltic Sea.

Assessing sandy beach macrofaunal assemblages across geographically diverse morphodynamic environments

While the physical characteristics of sandy beaches play a significant role in shaping the macrofaunal community features through morphodynamics, regional environmental factors may also account for deviations from the expected patterns. Here, we assess the concurrent effects of local morphodynamic factors and regional variables, such as sea surface temperature (SST), salinity, and chlorophyll-a (chl-a), on species richness and abundance of intertidal macrofaunal assemblages in four sandy beaches located along the estuarine gradient generated by the Río de la Plata (RdlP) in the southwestern Atlantic Ocean. Species richness was higher in dissipative beaches compared to intermediate ones, consistent with the predictions of the Swash Exclusion Hypothesis. However, this trend was not observed for total abundance, which significantly increased with chl-a. Both local and regional-scale environmental factors, such as salinity and chl-a, proved to be significant predictors in the arrangement of these communities. These results further support previous findings that highlight the critical role of the estuarine gradient of the RdlP in shaping life-history traits, population structure, and abundance of the resident intertidal macrofauna at both local and regional scales. The study underscores the importance of integrating environmental factors operating at different spatial scales to decipher community patterns in these physically-controlled environments.

Biological soil health indicators are sensitive to shade tree management in a young cacao (Theobroma cacao L.) production system

Cacao agroforestry systems can offer important benefits, such as greenhouse gas mitigation, microclimate regulation and improved soil health. The selection of tree species for cacao agroforestry systems is a critical step impacting cacao yields, as well as the environmental and economic sustainability of the production system. However, the effects of different tree species on soil processes and functions have been poorly studied. We assessed a series of soil health indicators in a five-year-old agroforestry trial located in the Ecuadorian Amazon. The following treatments: “control” (cacao monoculture), “timber” (cacao with Cedrelinga cateniformis Ducke; a leguminous tree), “fruit” (cacao with Bactris gasipaes), “N-fix” (cacao with Erythrina velutina Wild) and “mixed” (cacao with C. cateniformis + E. velutina) were replicated 3 times in randomized blocks. The experiment was managed organically with low levels of external inputs. We collected soil, litter and leaf samples of cacao trees at two different distances (∼2 m and ∼ 6 m) from the shade tree. Biological (potential soil respiration, and macrofauna abundance, richness and Shannon diversity), chemical (pH, CEC, total C and N, macro and micronutrients and Cd), and physical (bulk density and water holding capacity) soil health indicators were measured. Additionally, we analysed nutrients and Cd in cacao leaves and litter. Results showed positive effects of the “timber” and “mixed” treatments on biological soil health indicators, primarily earthworm abundance and potential respiration, as compared to cacao monocultures. Treatment effects on potential respiration showed different trends in litter versus soil, indicating that effects of shade trees on litter respiration do not transfer directly to soil respiration. Physical and chemical soil indicators, including available Cd which is irrelevant in the context of food safety regulations, did not show any differences among the treatments. Five years after establishment, no significant differences in yields were found among the control and any of the shade tree treatments.

Denitrification, anammox, and DNRA in oligotrophic continental shelf sediments

AbstractContinental shelf sediments are considered hotspots for nitrogen (N) removal. While most investigations have quantified denitrification in shelves receiving large amounts of anthropogenic nutrient supply, we lack insight into the key drivers of N removal on oligotrophic shelves. Here, we measured rates of N removal through denitrification and anammox by the revised‐isotope pairing technique (r‐IPT) along the Northeastern New Zealand shelf. Denitrification dominated total N2 production at depths between 30 and 128 m with average rates (± SE) ranging from 65 ± 28 to 284 ± 72 μmol N m−2 d−1. N2 production by anammox ranged from 3 ± 1 to 28 ± 11 μmol N m−2 d−1 and accounted for 2–19% of total N2 production. DNRA was negligible in these oligotrophic settings. Parallel microbial community analysis showed that both Proteobacteria and Planctomycetota were key taxa driving denitrification. Denitrification displayed a negative correlation with oxygen penetration depth, and a positive correlation with macrofauna abundance. Our denitrification rates were comparable to oligotrophic shelves from the Arctic, but were lower than those from nutrient‐rich Pacific and Atlantic shelves. Based on our results and existing IPT measurements, the global shelf denitrification rate was reassessed to be 53.5 ± 8.1 Tg N yr−1, equivalent to 20 ± 2% of marine N removal. We suggest that previous estimates of global shelf N loss might have been overestimated due to sampling bias toward areas with high N loads in the Northern Hemisphere.

Kelimpahan Fauna Tanah dan Hubungannya dengan Karakteristik Tapak pada Vegetasi Submontana di Taman Nasional Gunung Gede Pangrango

Soil fauna is a biotic soil component that can be used as fertility bio-indicators. This altitude difference is thought to affect the soil fauna. This research aims to identify differences in the abundance of soil mesofauna and macrofauna at the study site and to analyze the relationship between climatic and edaphic factors. Sampling measuring 20 m x 20 m was placed by purposive sampling at 1.250, 1.350, 1.450 m asl, and open area (1.200 m asl) for vegetation analysis and subplots were carried out by purposive sampling on three sample subplots measuring (1 m x 1 m) for soil samples and environmental factors. The highest soil fauna was found at an altitude of 1.350 m asl (265 individual / m2) and the lowest was in the open area (11 individual / m2). The different test results showed that the altitude of 1.250 and 1.450 m asl was not significantly different, while the altitude of 1.350 m asl and in open area showed a significant difference. The relationship between the population of soil fauna and climatic factors such as ambient temperature and sunlight intensity has a negative correlation value, while humidity shows a positive correlation value. Edaphic factors such as pH, and cation exchange capacity, have negative correlation, while litter weight, respiration, and soil porosity show positive correlation values.
 Keywords: climatic, edaphic, population, soil fauna, submontane

Influences of conservation tillage on soil macrofaunal biodiversity and trophic structure in the Mollisol region of Northeast China

Tillage regimes directly impact soil disturbance and crop residue levels in the field, subsequently affecting soil macrofauna abundance and diversity, crucial for maintaining soil health and ecosystem functionality. The present study aimed to investigate the effects of different tillage regimes (no-tillage (NT), conventional tillage (CT) and reduced-tillage (RT)) on soil properties and macrofaunal communities in a typical black soil region of Northeast China. Our study revealed that, in comparison to CT and RT, NT significantly enhanced soil macrofauna biodiversity and brought about modification in the community composition. Additionally, it reduced changes in the soil physical–chemical properties. Furthermore, the choice of tillage regimes impacted the trophic structure of soil macrofauna, manifesting in great density and species richness of herbivores and predators in NT plots with crop residue retention when compared to those managed with tillage. Overall, soil organic carbon (SOC) and pH played pivotal roles in regulating the soil macrofaunal community. The alternations observed in the soil macrofaunal community represented a comprehensive response to tillage practices and residue return, which in turn influenced soil properties and microenvironments, including food resources and microhabitats. Therefore, our findings indicated that conservation tillage exerted a notable influence on the soil macrofaunal community. This underscores the significance of soil environments and properties in molding the structure and composition of the soil macrofaunal community. The study will enhance comprehension of soil management practices and advocate for diversity within soil macrofaunal communities.

Soil Macrofauna Abundance in the Intercropping of Mangifera Indica with Aromatic Plants

Soil macrofauna such as earthworms, beetles, ants, and centipedes are an important aspect of soil health as they help in the breakdown of plant residue to provide natural resources such as carbon, nitrogen, and phosphorous into the soil. Monocropping practice uses heavy machinery, pesticides, and herbicides to maintain farm productivity, which negatively impacts soil macrofauna abundance. Thus, intercropping is a sustainable practice for farmers to maintain soil health with the minimal use of external input, which can do more harm to the soil ecosystem over a long period of time. The objective of the study is to evaluate the effect of intercropping mango with pandan and lemongrass on soil macrofauna density compared to mango monocrop. The field experiment consisted of mango, mango-pandan intercrops, and mango-lemongrass intercrops. Soil macrofauna was assessed using the tropical soil biology and fertility (TSBF) monolith method. The result showed that intercropping of mango-lemongrass and mango-pandan had higher soil macrofauna density compared with mango monocrop due to the presence of intercrops providing more natural resources and a better soil environment for soil macrofauna to grow and reproduce. However, further long-term research is needed to reinforce these findings.

Dynamics of nitrous oxide and methane in the southeastern Arabian Sea

This study examined the factors controlling the intra- and inter-seasonal variations of dissolved methane (CH4) and nitrous oxide (N2O) in the southeastern Arabian Sea (SEAS). Time-series measurements of CH4, N2O and allied biogeochemical parameters were carried out during the monthly campaigns in the coastal waters and a seasonal campaign in the shelf waters of the SEAS. The southwest monsoon period (SWM) brought drastic changes in the regional hydrography through the incursion of hypoxic waters due to coastal upwelling, which increased N2O concentrations substantially but reduced CH4 levels. The ranges of N2O and CH4 during the upwelling period were 8–89 nM and 9–165 nM, respectively, and the non-upwelling period was 2–27 nM and 5–271 nM, respectively. The significant positive correlations of N2O with apparent oxygen utilisation (AOU), the sum of dissolved nitrate and nitrite (NO2− + NO3−) and excess N2O (ΔN2O), as well as a negative correlation with dissolved oxygen indicates that nitrification is the major process in this region during the non-upwelling period. In contrast, during SWM, N2O did not correlate with NO2− + NO3−; however, it exhibited a significant negative correlation with dissolved nitrite (under hypoxia), suggesting the possibility of nitrifier-denitrification as an active process during hypoxia. The high (low) levels of CH4 recorded during the oxic spring inter-monsoon (hypoxic during the SWM) period showed a direct dependency on the changes in the benthic community. The high abundance of the adult macrofauna and active bioturbation resulted in high sedimentary CH4 release, which led to enhanced water column CH4 concentrations (17–271 nM) during the spring inter-monsoon period. In addition, the breakdown of methylated organic compounds under nutrient-limited conditions may also support the elevated CH4 levels in surface waters. A low macrofaunal abundance and reduced bioturbation led to a considerable reduction of subsurface CH4 concentrations during hypoxia. Overall, the SEAS is found to be a net source of CH4 and N2O to the atmosphere, with its sea-to-air fluxes ranging from 1.7 to 85.8 μM m−2 d−1 (19.88 ± 22.20 μM m−2 d−1) for N2O and 4–756 μM m−2 d−1(133 ± 158 μM m−2 d−1) for CH4.

Deep-sea macrofauna community recovery in Kaikōura canyon following an earthquake-triggered turbidity flow

Sediment density flows can transport massive amounts of sediment across large distances and can have dramatic, long-lasting impacts on deep-sea benthic communities. A canyon-flushing event in Kaikōura Canyon, New Zealand, triggered by the 2016 Mw 7.8 Kaikōura Earthquake, which included significant submarine mass wasting, debris and turbidity flows, provides an excellent opportunity to investigate the effects of this type of large-scale natural disturbance on benthic communities. The macrofauna community in the canyon was well characterised before the disturbance and the canyon described as a deep-sea benthic biomass hotspot. Macrofauna community structure before and after the event was analysed in a time series of sediment cores from 8 sites (∼400–1300 m water depth) collected 10 years and 6 years before, and 10 weeks, 10 months, and 4 years after the disturbance. The benthic community structure showed significant variability at all time points, but immediately after the 2016 disturbance abundances of all macrofauna dramatically decreased. Four years after the disturbance the benthic community was similar to, but not yet comparable to the pre-event community. The average abundances of most macrofauna increased over the 4 years post-earthquake, with polychaetes and bivalves being key taxa in the recovery process, especially 10 months and 4 years after the disturbance. Infauna abundances >5 cm below the seabed, remained low even 4 years after the event but the overall pattern of vertical faunal distribution was trending towards a pre-disturbance state. Community recovery was investigated in relation to changes in the physical characteristics of the habitat caused by the disturbance, using variables derived from sediment cores (e.g., sediment texture, organic matter, and pigment content). While the environmental variables explained relatively little of the overall variability in macrofauna community structure, key variables identified were related to particle size structure and food availability and quality. The minimum threshold time for the macrofauna community to fully recover, based on within-community similarity, was estimated to be between 5.6 and 6.7 years, although recovery was predicted to take up to 9 years if higher recovery thresholds were used. The management implications of this study are considered in comparison to the few studies of large-scale disturbances in the deep sea, in terms of their relevance to the efficacy of the marine reserve that encompasses Kaikōura Canyon, and potential implications for our understanding of the impacts of anthropogenic disturbances such as seabed mining.