Trophic Diversity Index Research Articles

Unveiling the meiobenthic community structure of Prydz Bay, Antarctica during austral summer

Meiobenthos are bottom-dwelling aquatic invertebrates having a size range of 63–500 μm. They play a pivotal role in ecosystem functioning, biogeochemical and trophic nutrient cycling. Due to the presence of Antarctic Circumpolar Current and steep gradient in nutrients and temperature, many taxa of the Southern Ocean (SO) show diverse biodiversity patterns in comparison to other deep sea areas of the world. Over the years, several Indian SO Expeditions have been carried out in the Indian sector of SO (ISSO), but this is a pioneer attempt to unveil the meiobenthic community structure and their functional diversity pattern from Prydz Bay (Indian sector of Southern Ocean), Antarctica. Meiobenthic community structures were investigated in eight different sampling sites along with their vertical profiling from the Prydz Bay during the austral summer 2020. Total meiofaunal abundance ranged from 24 to 521 indv. 10 cm-2, with the highest abundance recorded at station 23 and the lowest at station 9. A total of 9 meiobenthic taxa were found from this eco-region, with the highest percentage being the free-living marine nematodes as metazoan taxa. A total of 86 free-living nematode species were identified, where Sabatieria was the most common genus and represented by eleven species. Several univariate and multivariate analyses deciphered a distinct spatial variation in the meiobenthic community structure. Sediment texture and depth were the most significant environmental variables in shaping nematode assemblages. Biological Trait Analysis was performed using a total of 24 traits in 5 categories to unravel the functional diversity of free-living marine nematodes. The most dominant morphotypes were slender body shape, conical tail shape, dotted cuticle pattern, and non-selective deposit feeders with colonizing abilities of 2 (c–p score 2, in a scale from 1 to 5). Maturity Index (MI) and Index of Trophic Diversity (ITD) were highest in stations 15 and 32, respectively. RLQ approach with fourth-corner analysis was used to decipher the relationship between traits and environmental parameters. The RLQ analysis revealed the positive association of non-selective deposit feeder and slender body-shaped nematodes with higher water depth. The characterization of meiobenthic (especially nematode) communities in the context of taxonomic and functional attributes could help to evaluate the ecological status of ISSO. Further long term monitoring is also needed to get a comprehensive idea about their role in benthic ecosystem functioning in the milieu of global climate change.

An Insight into the Feeding Ecology of Serranus scriba, a Shallow Water Mesopredator in the Northern Adriatic Sea, with a Non-Destructive Method

Serranus scriba is a common member of the coastal fish community in the Adriatic Sea, but knowledge about its feeding ecology is scarce. The aim of this paper is to present new evidence about its food preferences and feeding habits. An innovative non-destructive method of fecal pellet analysis was used for this study. This method does not require sacrificing specimens and the fish can be released back into the sea alive after the laboratory work. The results demonstrated that S. scriba mainly preys on decapods, followed by polychaetes, isopods, fish, mollusks and swarming shrimps. The calculated index of trophic diversity (ITD) value of 0.89 indicates that it is an opportunistic feeder that feeds on a wide range of different prey. According to the calculated trophic level of 3.43, which is higher than that of other members of the community, S. scriba is also an important piscivorous predator. With age, S. scriba undergoes an ontogenetic shift. The proportion of crustaceans, gastropods and polychaetes decreases with age and body size, while the proportion of fish increases.

TROPHIC DIVERSITY OF LITTER NEMATODE COMMUNITIES OF FORESTS IN THE MEZIN NATIONAL NATURE PARK

Introduction. Nematodes are one of the most abundant groups of the soil and litter fauna in forest ecosystems. The faunal composition may mirror the activity of decomposition pathways and give indications of nutrient status and fertility of soil. Nematodes play an important role in regulating microbial communities and affect the speed and direction of mineralization and humification of plant precipitation.
 Aim. Trophic structure of nematode communities from litter in forests of the Mezin National Nature Park was studied.
 Materials and methods. Samples litter were collected from June to July 2010 and 2014 in 21 forest ecosystems. Nematodes were extracted by a modified Baermann’s method from the 5-g sample. The exposition time was 48 h. Extracted nematodes were fixed in the triethanolamine–formalin (TAF, 2 % triethanolamine, 7 % formaldehyde solution, 91% water), and mounted on the temporary hydroglyceric slides. Nematode abundance was expressed as specimens per 100 g of dry substrate.
 Results. The 46 identified nematode species were divided into five trophic groups: saprobionts, mycohelminths, omnivores, predators and phytohelminths. Saprobionts were both the most diverse and the most numerous. 26 species (56,52% of all species collected) belonged to the this trophic group, proportion in the community was 63,97%. Plectus cirratus, Plectus parietinus, Panagrolaimus rigidus were the most numerous (proportion in the community 24,13%, 9,65% and 8,18% of the total, respectively). P. rigidus occurred in 95,2% of all samples. Aphelenchoides composticola dominated among 10 species of mycohelminths (frequency was 85,7%, proportion in the community 8,99%). Mesodorylaimus bastiani was common аmong the three species of omnivorous nematodes (frequency was 90,48%, proportion in the community 13,74%). Predatory nematodes (5 species) were in 57,1% of samples, proportion in the community together was 3,17%. Only two species phytohelminths (Gracilacus audriellus, Paratylenchus nanus) were found in the analyzed litter samples. They were rare; their frequency was 9,52% and 4,76% respectively. Moreover they were not very abundant (0,12% and 0,08% of total number respectively).
 Conclusions. The mycohelminths and saprobionts make an important component of the litter decomposer community of all forest ecosystems in the Mezin National Nature Park. The ratio of mycohelminths to saprobionts (М/S) shows a constant preponderance of saprobionts and was 0,27. Twenty five species (54,35% of all species collected) were high colonization ability, high reproduction rate and high tolerance to disturbances. The trophic diversity index was 2,16. The maturity index was 2,27. These indexes show stability of habitat in the forest litter.

Free-living nematodes of Mediterranean ports: A mandatory contribution for their use in ecological quality assessment

Free-living nematodes were investigated in three Mediterranean commercial ports (Ancona and Trieste, Italy; Koper, Slovenia) in terms of abundance, diversity and functionality. Results indicated that r-strategist genera were dominant in all ports and that a more diverse assemblage characterized Trieste, despite the high contamination levels, suggesting a potential adaptation to long-standing contamination. The main environmental factor that shaped the assemblage in all ports were Total Polycyclic Aromatic Hydrocarbons, while Total Organic Carbon and the grain-size were less relevant. A co-occurrence analysis was applied for identifying which genera cohesively respond to site-specific environmental conditions in order to recalibrate and implement the sets of bioindicator genera in relation to their different opportunistic behaviour. Finally, we provided some suggestions for a proper application of the nematode indices (Maturity Index, Index of Trophic Diversity, Shannon diversity) in order to encourage the use of free-living nematodes for the environmental quality assessment of commercial ports.

The soil nematode community indicates the soil ecological restoration of the Pinus massoniana plantation gap replanted with Cinnamomum longipaniculatum

Interactions between aboveground and belowground ecosystems components modulate ecosystem functions. However, few studies have focused on the response of soil nematodes to plantation reconstruction. In this study, Cinnamomum longipaniculatum was planted in the gap of a Pinus massoniana plantation. Based on the size, center and edge of C. longipaniculatum patches, the characteristics of the soil nematode community were studied after 8 years of plantation reconstruction. The effect of the C. longipaniculatum plantation on the soil nematode community was related to patch size. The soil nematode community did not change significantly with increasing patch size above 30 m × 30 m. The soil recovered better in the patch center than at the edge, but the edge increased the diversity of soil nematodes with low C-P values. The experimental treatment increased the dominance of soil plant parasite nematodes and bacterivores, decreased the trophic diversity index, and increased the channel ratio, maturity index, enrichment index and structure index of soil nematodes, indicating that soil nutrient cycling improved and the diversity of the soil food web increased. After P. massoniana plantation gaps were replanted with C. longipaniculatum, the main soil properties that affected the soil nematode community were organic carbon, pH, water content and soil aggregate degree. In the soil nematode community, fungal nematodes had the strongest influence on omnivorous-predatory nematodes. Our study showed that the soil environment changed with vegetation and affected soil nematode groups, and soil nematodes effectively reflected soil ecological restoration after P. massoniana plantation gaps were replanted with C. longipaniculatum.

浙江南部近海前肛鳗营养生态位变化研究——基于稳定同位素技术

PDF HTML阅读 XML下载 导出引用 引用提醒 浙江南部近海前肛鳗营养生态位变化研究——基于稳定同位素技术 DOI: 10.5846/stxb202112073477 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金（31902372，41906074）；上海海洋大学青年教师科研启动基金（210021）；温台渔业资源专项调查项目（158053） Change of trophic niche of Dysomma anguillare in the offshore waters of southern Zhejiang by stable isotope analysis Author: Affiliation: Fund Project: National Natural Science Foundation of China；National Natural Science Foundation of China 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:基于2016年和2020年浙江南部近海收集的71尾前肛鳗样品，通过测定碳氮稳定同位素比值计算其营养生态位指标，对比分析前肛鳗不同发育过程、不同季节及不同年份营养生态位的差异，探究营养生态位的变动规律及对资源的利用情况。结果表明：（1）2016年和2020年前肛鳗平均δ13C值分别为（-15.19±0.31）‰、（-15.90±0.45）‰；平均δ15N值分别为（12.42±0.45）‰、（12.92±0.25）‰；（2）单因素方差分析表明，2016年前肛鳗不同发育过程δ13C值差异不显著（P>0.05），δ15N值差异显著（P<0.05），不同季节间δ13C值和δ15N值均存在显著差异（P<0.05），而2020年前肛鳗不同发育过程δ13C值和δ15N值差异均不显著（P>0.05），不同季节间δ13C值存在显著差异（P<0.05），δ15N值差异不显著（P>0.05）；（3）从个体发育来看，2016年前肛鳗有向高营养级饵料生物摄食的趋势，而2020年前肛鳗摄食特化现象不明显，但均随个体发育过程生态位宽幅逐渐减小，表明个体发育过程营养生态位会出现资源竞争共存分化现象；（4）种群营养多样性指标结果显示前肛鳗在秋、冬两季食物来源较春、夏两季更广泛，春季营养多元化程度与秋季相似，夏季营养多元化程度与冬季相似，各季节间营养生态位重叠较小，存在明显的时间分化现象；（5）2020年前肛鳗种群营养结构多样性指标相比2016年均出现不同程度的降低，两年的SEAc未发生重叠现象。由于种内种间的竞争压力，研究发现前肛鳗在个体发育过程及不同时间段都出现了营养生态位分化现象，从而达到维持物种共存、保持食物网结构稳态的目的。 Abstract:Based on 71 Dysomma anguillare samples collected in the offshore waters of southern Zhejiang in 2016 and 2020, the trophic niche indexes were calculated by carbon and nitrogen stable isotope ratio. The trophic niche in different development processes, seasons and years were compared to explore the variation pattern of trophic niche and the utilization of resources. The results showed that:(1) the average δ13C values of D. anguillare in 2016 and 2020 were (-15.19±0.31)‰ and (-15.90±0.45)‰, respectively; The average δ15N values were (12.42±0.45)‰ and (12.92±0.25)‰, respectively; The results of one-way ANOVA showed that there was no significant difference in δ13C value (P>0.05) and δ15N value (P<0.05) at different development processes of D. anguillare in 2016. There were significant differences in δ13C value and δ15N value between different seasons (P<0.05); In 2020, there was no significant difference in δ13C value and δ15N value at different development processes of D. anguillare (P>0.05), there was significant difference in δ13C value between different seasons (P<0.05), and there was no significant difference in δ15N value (P>0.05). (2) From the perspective of ontogeny, the D. anguillare had a tendency to feed on highly trophic level prey food in 2016, while the feeding specialization of D. anguillare was not obvious in 2020, but the niche width decreased gradually with ontogeny, indicating that there would be interspecific resource competition and differentiation in the ontogeny stage. (3) The results of population trophic diversity index showed that the food sources of D. anguillare in autumn and winter were more extensive than those in spring and summer. The degree of trophic diversity in spring was similar to that in autumn, and that in summer was similar to that in winter. The overlap of trophic niche among seasons was small, and there was an obvious phenomenon of time differentiation. (4) Compared with 2016, the diversity index of trophic structure of D. anguillare population in 2020 decreased to varying degrees, and there was no overlap in corrected standard ellipse area (SEAc) in the two years. Due to the pressure of intraspecific and interspecific competition, it was found that there was a phenomenon of nutritional niche differentiation in the process of ontogeny and different time periods, so as to maintain species coexistence and maintain the stability of food web structure. Exploring the adaptive ability of species to the utilization of bait resources and the ecological environment has scientific significance for investigating the structural pattern and stability mechanism of marine food web. 参考文献 相似文献 引证文献

Coexistence strategies of invaded gobies in the Dianchi Lake, Yunnan, China

Gobiids are widespread invasive species, with many species from this group usually invade into the same ecosystem simultaneously. Understanding the mechanisms underlying the coexi-stence of different gobiid species in the sympatric habitats is a key issue in fish invasion ecology. Incorporating morphological analyses, spatial distribution survey, and trophic analyses, we examined the coexistence strategy of Mugilogobius myxodermus and related species (the earlier invaders) in Dianchi Lake, Yunnan, China. Our results showed significant differences in morphology and spatial distribution among the four invasive gobies species (i.e., M. myxodermus, Micropercops swinhonis, Rhinogobius giurinus and Rhinogobius cliffordpopei). The spatial niche index of M. myxodermus was the highest. Food composition between M. myxodermus and other gobies was significantly different, with the former mainly feeding on Chydorus ovalis and Cypris sp. The trophic diversity index of M. myxodermus was the highest. Overall, we found that morphological differences, spatial niche diffe-rentiation, and trophic niche differentiation contributed to the coexistence of the gobies in Dianchi Lake, which could help M. myxodermus reduce interspecific competition. Importantly, the feeding strategy is the key factor determining population size and habitas of M. myxodermus during their competition with the other gobies, and finally contributing to the dominant position in the study area.

Are free-living nematodes effective environmental quality indicators? Insights from Bohai Bay, China

Free-living marine nematodes are sensitive biological indicators of environmental quality in marine sediments. This study investigated nematode communities in coastal waters in Bohai Bay, China. Nematode community taxonomic structure, colonizer–persister classes, maturity index (MI), index of trophic diversity (ITD), Shannon–Wiener diversity index (H′), together with the Hakanson’s Ecological Risk Index, were applied to assess the environmental quality of the investigated stations. The taxonomic structure, MI, ITD, and H′ varied among the study stations. In addition to the stochastic causes, variability in environmental variables together with metal concentrations explained, to a certain extent, the observed variations in nematode features. The differentiation in nematode species’ composition was attributed to changes in water depth, temperature, salinity, dissolved oxygen concentration, sediment medium diameter, organic matter, chlorophyll-a and pheophytin-a concentrations, and concentrations of manganese (Mn) and cobalt (Co). Mn was the most influential metal in explaining nematode diversity. MI appeared to be affected more by metals than by other environmental variables. According to the nematode features, the environmental quality ranged from bad to good at the majority of stations, although the rankings varied among different indices. Taxonomic structure, life strategy traits, ITD, and H′ were all effective in highlighting the areas subjected to severe metal contamination in the bay, and could provide more comprehensive assessments when used in combination. These indices suggested a more severe pollution status than the results obtained from the Hakanson’s Ecological Risk Index method, and may be more sensitive to ecological quality deterioration. However, their effectiveness requires further testing over larger spatial ranges and with more data.

Toxicity of hydroxychloroquine, a potential treatment for COVID-19, on free-living marine nematodes

On March 2020, hydroxychloroquine (HCQ) was recommended as a treatment for COVID-19 high risk patients. Following the massive and widespread use of HCQ worldwide, a discernible high quantity is anticipated to end-up through the sewage systems in marine coastal areas. A closed microcosm study was undertaken herein for 30 days where meiobenthic nematodes were exposed to a range of HCQ concentrations (3.162, 31.62 and 63.24 μg.ml−1). After one month of exposure in HCQ, the total abundances and Shannon-Wiener index of the assemblages decreased, whereas the individual mass and the Trophic Diversity Index increased at the highest concentrations. Overall, a numerical negative impact was observed for the epistrate feeders and non-selective deposit feeders, however, this benefited to the omnivores-carnivores, and particularly to the Oncholaimids. Such responses of the nematodes 2B and the corresponding taxa are bioindicative of current- or post-COVID-19 crisis risks in relation with the bioaccumulation of HCQ in seafood.

Next-generation sequencing of the soil nematode community enables the sustainability of banana plantations to be monitored

Uganda faces a considerable challenge to match its food production to an annual population growth rate of 3%. Cooking bananas are the country's most produced staple crop but the annual national harvest is not increasing. The crop grows on infertile soils that are normally fertilised organically and often susceptible to erosion. Soil nematodes are well-established as bioindicators of soil quality that can support environmental monitoring and assessment of the sustainability of agricultural systems. These invertebrates are a highly ranked indicator of biodiversity with molecular approaches available. Consequently, we have applied next-generation DNA sequencing of soil nematodes to evaluate soil quality of Ugandan banana plantations. The aim is to establish a method for constructing an aspect of an environmental biosafety dossier with the future aim of assessing the impact of transgenic crops and improving current cropping systems. The soil samples did not differ significantly in any of the measured soil chemistry factors, soil texture or percentage of organic matter. Thirty taxons of soil nematodes other than the plant parasites were recovered from soil supporting nine banana plantations plus three each from coffee and banana-coffee interplants from East and West Uganda. Cluster analysis correctly allocated each plantation to the crop/intercrop being grown when based on the abundance of taxa rather than taxa presence or absence. This indicates that the host has considerable effects on the abundance of specific nematode species within the soil. Overall, nematodes were more abundant in soil from coffee plantations than from banana-coffee interplants with the lowest values being from fields supporting just banana. Only the basal and trophic diversity indices and the percentage of nematodes that are rapid colonisers varied between the three plantation types. The soil of all fifteen plantations can be classified as having a mature soil web condition with low physical disturbance, limited chemical stressors, moderately high nutrient enrichment and balanced decomposition channels.

Comparison of benthic nematode assemblages in native mangrove forest and exotic mangrove plantations (Sonneratia apetala Buch-Ham) along the South China Coast

The exotic mangrove species Sonneratia apetala has been planted widely in China since 1985. As an exotic mangrove species, it is important to understand the influence of Sonneratia plantations on marine nematode assemblages. We studied the Zhanjiang and Xiatanwei mangrove wetlands on the South China Coast during the four seasons of 2010 and 2019. The results showed that S. apetala plantations increased the number of genera, Shannon-Wiener diversity, richness, evenness, maturity index (MI) and decreased the index of trophic diversity (ITD) values for nematodes compared to those in mudflats, but did not change significantly compared to those of native mangrove forests. In addition, Sonneratia plantations did not significantly change nematode assemblages compared to those of native mangroves, though they did change significantly compared to those in mudflats. Thus, interplanting S. apetala into native mangrove forests may be an effective substitute for using native mangroves in mangrove plantation.

What makes a better indicator? Taxonomic vs functional response of nematodes to estuarine gradient

Efficient implementation of nematodes-based indices for ecological quality assessment requires fundamental knowledge on their biodiversity and functional patterns along with the drivers that generate these patterns. Though, it is still unclear if nematodes taxonomical attributes are driven by the same environmental drivers as their functional (biological traits) counterparts, or if their taxonomical diversity is also enhanced by their functional diversity. To fill this knowledge gap, we investigated taxonomical (based on nematode genera abundances dataset) and functional attributes: trophic groups (TG) and life history strategies (LHS) of benthic nematodes collected from 35 sampling stations along the Sado Estuary, SW Portugal. Along with biological samples we measured environmental variables in the water and sediments as well as sediment grain size.Our results demonstrated that taxonomy-based assemblages were mainly structured by the salinity gradient and further by the interplay of granulometry and organic matter content. Contrastingly, trait-based distribution patterns were largely driven by the variations in the above sediment dissolved oxygen concentration. This finding largely draw attention to the role that above sediment dissolved oxygen concentration exerts on nematode assemblages and their functional distribution patterns. Consequently, our results demonstrate that biological traits introduce a new dimensionality in multivariate data that otherwise could not be detected using solely taxonomical information, thereby enhancing our knowledge on ecological gradients existing within an estuary.Additionally, we found a strong correlation between functional richness (based on the combination of TG and LHS traits) and diversity taxonomic metrics (species richness, Simpson and Shannon diversity), although no correlation was found between taxonomic diversity indices and single nematode ecological indices (ITD index of trophic diversity and MI Maturity Index). Therefore, the combined use of functional traits and its derived metrics was demonstrated to effectively reflect taxonomical diversity presenting reliable and highly complementary information for the assessment and monitoring of marine coastal sediments using benthic nematodes.

Does vertical distribution of meiobenthic community structure differ among various mangrove habitats of Sundarban Estuarine System?

Mangroves are the most productive environments that play significant ecological and socioeconomic roles. For the first time we investigated vertical stratification of meiofaunal community and nematode species composition from the sediments of five mangroves (Aegiceras corniculatum, Bruguiera gymnorrhiza, Avicennia alba, Rhizophora mangle and Sonneratia caseolaris) at Bali Island in the worlds’ largest mangrove ecosystem of Sundarbans, India. Among different mangrove species, S.caseolaris had the highest density of meiofauna with the lowest in B. gymnorrhiza. A total of eight taxa were recorded from the sediment of different mangrove habitats. In terms of percentage composition, free-living nematodes dominated followed by harpacticoid copepods, kinorhynch, ostracods, foraminifera, polychaete, halacarid mite and bivalve juvenile. The vertical profile of meiofaunal composition suggested upper 3–4 cm harboured 90% of total meiofauna, although they were present up to 15 cm depth. Environmental variables explained meiofaunal community structure. Availability of food sources such as phaeopigments, Chlorophyll a, organic carbon and sediment texture controlled meiofaunal distribution. The nematode fauna consisted of 52 species belonging to 39 genera and 20 families. The trophic structure of nematode taxa revealed a community dominated by epistrate feeders (2A) followed by selective deposit feeders (1A). Moreover, marine nematode genera were used to test Maturity Index (MI), life strategy or biological traits (i.e. c–p classes) and Index of Trophic Diversity (ITD) for assessing ecological health. Higher MI among different mangrove vegetation indicated a stable environment; moreover, biological trait analysis showed that mangrove sediments were dominated by r-strategists. Lower values of ITD index revealed a proportionate occurrence of trophic diversity in nematode communities among different vegetation. In the current context of habitat destruction and anthropogenic perturbations, investigation of ecological interactions between mangroves and meiofauna would be imperative for ecosystem monitoring and sustainable development in future.

Community analysis of soil nematodes in vegetable growing areas of Dhading District, a high hill of Nepal

A nematological survey was carried out in the year 2014 from vegetable crops of Dhading district; a high hill of Nepal located at latitude 2752'0.120"N, longitude 8455'0.120"E and altitude 1518m. The entire district covers mainly temperate zone with annual average precipitation and temperature 1683.9 mm and 11.8 – 22.4°C respectively. Thirty soil samples were collected randomly from ten vegetable crops during their flowering time. A total of 23 genera of soil inhabiting nematodes belonging to 7 orders and 14 families were encountered. Of the total population, herbivores were 33%, bacteriovores 35%, fungivores 12%, predators 14% and omnivores 6%. In terms of number of genera varied from 8 to 14 and in terms of abundance the number varied from 64 to 308 per 100cc of soil. Rhabditis was the most abundant genus among bacteriovores, Aphelenchoides among fungivores, Mononchus among predators and Helicotylenchus among herbivores. Meloidogyne sp was the most dominant plant parasitic nematode in terms of both frequency and density occurring in many vegetable crops. The trophic diversity index (TDI) in the sample was 1.07 – 1.30 (1.16 ± 0.06), maturity index (MI) 1.66 – 2.65 (2.22 ± 0.25), plant parasitic index (PPI) 2.49 – 3.0 (2.95 ± 0.11) and channel index (CI) 0.21 – 1.48 (0.82 ± 0.35).

Interannual patterns of the large free-living nematode assemblages in the Mexican Exclusive Economic Zone, NW Gulf of Mexico after the Deepwater Horizon oil spill

The presence and abundance of particular nematode genera in marine sediments are bioindicators of environmental disturbance. They can even reveal the existence of specific toxicants, such as trace-metals and hydrocarbons derived from fossil fuels. We studied this important infaunal component during a three-year monitoring program in Mexico’s Exclusive Economic Zone (EEZ) in the aftermath of a major oil spill in the northern Gulf of Mexico caused by the sinking of the Deepwater Horizon platform (DWH) in April of 2010. A closer look at the nematode composition and density values throughout and after the DWH oil spill revealed considerable changes. Continental shelf and upper slope sediments sampled in the summer of 2010 included 48 genera and a density of 44.45 ind/10cm−2. Eight months later in the winter of 2011, there was a critical decrement in genera number (23) and density (25.22 ind/10cm−2). However, in 2012, the nematode community showed signs of recovery: genus diversity was 58 with a density of 91.45 ind/10cm−2. Significant differences were recorded between the first and the last sampling periods, driven by a remarkable turn-over in genera composition, and by an increase in density of the genera Sabatieria, Dorylaimopsis, and Cheironchus. Similarly, significant spatial differences between the nematofauna of the inner-middle shelf and the deepest zone (>2000m) were detected. Correlation analyses confirmed the tolerant behavior of the above genera to Ni and Co, and their proliferation when hydrocarbon compounds presumably derived from the DWH oil spill increased throughout the study. The Maturity Index (MI) estimated for each survey ranged from 2.35 to 2.6. Environmental Quality Status conditions in the summer of 2010 were good while in the winter of 2011 were poor, and moderate towards the winter of 2012. Index of Trophic Diversity (ITD) values for each survey were high: 0.70, 0.68, and 0.74, respectively. A high predominance of feeding guilds 1B and 2B was recorded throughout the study.The estimated Index of Trophic Diversity (ITD) values resulted high (Table 5). These values apparently indicated that the four feeding types were proportionally distributed in the nematode assemblage. This fact was better reflected during the winter of 2012. Nonetheless, these results are not congruent with the high predominance of feeding guilds 1B and 2B observed throughout the study.

Seasonality and trophic diversity in molluscan assemblages from the Bay of Tunis (southern Mediterranean Sea)

Soft bottom molluscan assemblages from the Bay of Tunis have been studied in order to analyse their seasonality and trophic diversity in relation to environmental variables. A total of 147 species of molluscs was identified, with gastropods displaying the highest species richness and bivalves the highest abundances, and including five non-indigenous species such as the dominant ectoparasite Polycerella emertoni. Carnivorous and scavenger gastropods were among the most frequent species, reflecting a diverse benthic community. Seasonal changes were significant, being more acute at 3-4 m than at 10-15 m depth, and were driven mainly by seawater temperature and percentage of organic matter in the sediment. The high affluence of tourists in summer was coincident with high decreases in species richness and abundance of molluscs, together with a strong siltation of the sediment. Nevertheless, most trophic groups remained and the trophic diversity was relatively high. Significant relationships were found between the index of trophic diversity and Shannon-Wiener diversity and evenness indices, suggesting that the identity of the species with its particular trophic trait, together with the good distribution of the individuals among the species (density) would be the drivers for the maintenance of the molluscan food web under environmental stress. The abundance of P. emertoni altered the trophic structure of the molluscan assemblage, with the ectoparasite trophic group reaching an unusual punctual higher dominance. Soft bottom molluscan assemblages of the Bay of Tunis should be taken into account in monitoring programs for anthropogenic impacts and non-indigenous species trends throughout the Mediterranean basin.

Influence of returning corn straw to soil on soil nematode communities in winter wheat

This study used pot microcosms to investigate the influence of returning different amounts of corn straw on soil nematode communities in winter wheat with five treatments: no corn straw (CS-1), 3000 kg/hm2 (CS-2), 6000 kg/hm2 (CS-3), 9000 kg/hm2 (CS-4), and 12,000 kg/hm2 of added corn straw (CS-5). The microcosms were sampled at winter wheat jointing stage, booting stage and harvest stage, and the growth and fertility of soil nematode community dynamics were observed. A total of 37 nematode genera were identified. The genus richness and abundance of soil nematodes were significantly different (P < 0.01) at the different growing stages. The trophic group composition of the nematodes was also significantly different between different treatments (P < 0.01) but the differences in total abundance were not. The abundance and genus richness achieved a maximum at booting stage, and both were significantly higher with the addition of corn straw. The genus richness maximum was in treatment CS-2, and decreased when the addition of corn straw was increased. The maximum number of individuals was in treatment CS-4. The relative abundance of soil nematode trophic groups changed significantly throughout the growth of winter wheat. The relative abundance of bacterivorous nematodes gradually increased and the relative abundance of omnivorous nematodes gradually decreased. Plant parasites had the largest relative abundance at booting stage, and were higher in treatment CS-4 and CS-5. The Shannon–Weaver diversity index, trophic diversity index and maturity index were significantly different at booting stage in the different treatments. The values of these ecological indices significantly increased by the addition of corn straw, but decreased with increasing application. Factor analysis revealed that the first effect factors on soil nematode community composition were the above and belowground biomass of winter wheat and soil N content. The second effect factors were the soil available P and K and soil bacteria content. Returning a small quantity of corn straw positively impacted the nematode community composition and changed the soil nematode taxa of common and rare nematode genera. The growth and development of winter wheat had a significant impact on the abundance and genus richness of the soil nematode community. Corn straw addition at 3000 kg/hm2 could maintain a higher diversity of soil nematode but 6000–9000 kg/hm2 could increase crop productivity.

Status of soil nematode communities during natural regeneration of a subtropical forest in southwestern China

Forest recovery has been extensively evaluated using plant communities but fewer studies have been conducted on soil fauna. This study reports the status of soil nematode communities during natural re-establishment after deforestation in a subtropical forest in southwestern China. Soil nematode communities of two secondary succession stages, shrub-grassland and secondary forest, were compared with those of virgin forest. Shrub-grassland had higher herbivore relative abundance but lower fungivore and bacterivore relative abundance than forests. Between secondary and virgin forest, the latter had higher abundance of bacterivores. Shrub-grassland had lower nematode diversity, generic richness, maturity index and trophic diversity index than virgin forest, whereas there were no differences in these indices between secondary forest and virgin forest. The small differences in nematode community structures between secondary forest and virgin forest suggest that soil nematode communities recovered to a level close to that of the undisturbed forest after up to 50 years of natural succession.

Do nematode and macrofauna assemblages provide similar ecological assessment information?

Do nematode and macrofauna assemblages provide similar ecological assessment information? To answer this question, in the summer of 2006, subtidal soft-bottom assemblages were sampled and environmental parameters were measured at seven stations covering the entire salinity gradient of the Mondego estuary. Principal components analysis (PCA) was performed on the environmental parameters, thus establishing different estuarine stretches. The ecological status of each community was determined by applying the Maturity Index and the Index of Trophic Diversity to the nematode data and the Benthic Assessment Tool to the macrofaunal data. Overall, the results indicated that the answer to the initial question is not straightforward. The fact that nematode and macrofauna have provided different responses regarding environmental status may be partially explained by local differentiation in microhabitat conditions, given by distinct sampling locations within each estuarine stretch and by different response-to-stress times of each benthic community. Therefore, our study suggests that both assemblages should be used in marine pollution monitoring programs.

The use of nematodes in assessing ecological quality status in the Mediterranean coastal ecosystems

The use of nematodes as biological indicators of environmental quality was evaluated in sediments of the Mediterranean Sea. The Shannon-Diversity Index (H′), the Maturity Index, the c-p%, the Index of Trophic Diversity (ITD) and the presence of sensitive/tolerant genera were applied at a Mediterranean scale to 12 different coastal sites and used to identify the five classes of ecological quality status assessed according to the Water Framework Directive. The results revealed that nematodes represent a highly informative assemblage. In particular, the presence/absence of specific genera indicators, followed by c-p% composition and H′, can be used to evaluate the ecological quality status efficiently.