Epizooic metazoan meiobenthos associated with tubeworm and mussel aggregations from cold seeps of the northern Gulf of Mexico

The abundance and higher taxonomic composition of epizooic metazoan meiobenthic communities associated with mussel and tubeworm aggregations of hydrocarbon seeps at Green Canyon, Atwater Valley, and Alaminos Canyon in depths between 1400 and 2800?m were studied and compared to the infaunal community of non-seep sediments nearby. Epizooic meiofaunal abundances of associated meiobenthos living in tubeworm bushes and mussel beds at seeps were extremely low (usually <100?ind. 10?cm(-2)), similar to epizooic meiofauna at deep-sea hydrothermal vents, and the communities were composed primarily of nematodes, copepods, ostracods, and halacarids. In contrast, epizooic meiobenthic abundance is lower than previous studies have reported for infauna from seep sediments. Interestingly, non-seep sediments contained higher abundances and higher taxonomic diversity than epizooic seep communities, although in situ primary production is restricted to seeps.     

Deep-sea habitat heterogeneity influence on meiofaunal communities in the Gulf of Guinea

To estimate the degree of spatial heterogeneity of benthic deep-sea communities, we carried out a multiple-scale (from m's to 200 km) investigation in the Congo-Angola margins (Equatorial West African margin, 3150–4800 m) in which we examined the metazoan meiofauna at a variety of habitats along the Congo Channel system and in the associated cold seep. We investigate the structure, density, vertical distribution patterns in the sediment and biomass of meiofaunal communities in the Gulf of Guinea and how they are controlled by hydrologic and biogeochemical processes. The meiofaunal communities in the Gulf of Guinea were shaped by heterogeneous conditions on the margin, and reflect the multiple-scale spatial variability that corresponds with the different identified habitats. The two control sites, located at >100 km away from the canyon, were inhabited by very dense and the most diverse meiobenthic communities. Similar meiobenthic communities inhabited the transition zone between the canyon and the cold seep. Sites located along the Congo Channel were obviously affected by the local high-velocity bottom currents and unstable sedimentary conditions in this active submarine system. Extremely low meiobenthic densities and very low proportions in the most surficial sediment layers provided evidence for recently highly disturbed sediments at these sites. The remote operated vehicle (ROV) Victor 6000 provided images of the cold seep, showing a patchy distribution of several types of patchy distributed megafaunal communities dominated by three key symbiotic taxa (Mytilidae, Vesicomyidae and Siboglinidae). These cold seep sediments were colonised by a unique meiobenthic community, characterised by a high small-scale (m's) patchiness, low species richness and the prominent dominance of two large-sized nematode species: Sabatieria mortenseni, which is a cosmopolitan nematode known from littoral habitats, and an undescribed Desmodora species. The high individual body weight of S. mortenseni and its dominance at the cold seep site resulted in a significantly higher nematode biomass at the seep compared to the surrounding sites. In addition, the vertical nematode profiles, with maximum proportions in subsurficial layers, points to a chemosynthesis-based meiobenthic community in this cold seep, in contrast to the phytodetritus-based communities at the control sites and at the transition zone.     

Meiofauna distributions at the oxygen minimum zone in Changjiang (Yangtze) River Estuary waters

1 IntroductionOxygen minimum zone (OMZ) is a midwaterregion in the open ocean where dissolved oxygen con-centrations fall below 0.5 ml/L (0.714 mg/dm3,Kamykowski and Zentara, 1990; Levin et al.,1991). It results from the biological oxygen demandand is wel…     

Metazoan meiofaunal communities at cold seeps along the Norwegian margin: Influence of habitat heterogeneity and evidence for connection with shallow-water habitats

Cold-seep environments and their associated symbiont-bearing megafaunal communities create islands of primary production for macro- and meiofauna in the otherwise monotonous and nutrient-poor deep-sea environment. To examine the spatial variation and distribution patterns of metazoan meiobenthos in different seepage-related habitats, samples were collected in two regions off Norway: several pockmarks associated with the Storegga Slide including the Nyegga pockmark area (730 m; 64°N), and the active, methane-venting Håkon Mosby Mud Volcano (HMMV) west of the Barents Sea (1280 m; 72°N). Based on sediment geochemistry and associated epifauna, three different habitat types were distinguished across the two regions: (1) reduced sediment with suboxic conditions, sometimes covered by bacterial mats, (2) sediment colonised by chemosynthetic, siboglinid tubeworms, and (3) sediment outside the influence of seepage and without a large chemosynthetic fauna. Meiofaunal communities varied strongly in terms of generic diversity and dominance among the different habitat types. Control sites and Siboglinidae polychaete fields both supported high nematode genus richness similar to normal deep-sea sediments, whereas the reduced sediments yielded a genus-poor nematode community dominated by one or two successful species. Meiofaunal densities in the different habitats were negatively correlated with macrobenthic densities. An extremely dense (>11,000 ind. 10 cm^–2), mono-specific nematode population appeared to be restricted to the bacterial mats at HMMV. It consisted of a new cryptic species of the Halomonhystera disjuncta complex, which has been described from intertidal habitats in the North Sea. The reduced seep sediments at Nyegga did not yield H. disjuncta but were dominated by Terschellingia longicaudata, another cosmopolitan nematode species known to be abundant in organic-rich, oxygen-poor, shallow-water environments. These observations point to a past or recent connection between margins and shallow-water habitats.     

The effect of the dominant polychaete Scolelepis squamata on nematode colonisation in sandy beach sediments: An experimental approach

The effect of an abundant sandy beach polychaete, Scolelepis squamata, on the colonisation of defaunated sediments by marine nematodes indicates that sandy beach fauna can be partially controlled by biological interactions within and across size groups. Experimental cores, equipped with windows allowing infaunal colonisation, were filled with defaunated sandy beach sediment containing two different treatments with and without S. squamata. These cores were inserted into microcosms filled with sediment with indigenous meiofauna collected from the field. The treatments were incubated in the laboratory at ambient temperature and salinity for 2, 7, 14 and 21 days, in order to follow the colonisation process of the defaunated sediments by the indigenous nematode fauna over time. Nematodes initially colonised both treatments, with abundances of up to 10% of the densities in the control; after 2 weeks, nematode densities in the cores without S. squamata surpassed the control densities. Nematode assemblages in both treatments were not species rich, and also differed in composition from the natural assemblages. The most successful colonising species, Enoplolaimus litoralis, was rare in the surrounding sediment, suggesting that colonisation was determined by species-specific characteristics such as body size, motility and feeding strategy. Initially the presence of macrofauna did not affect the nematode community composition, but after 2 weeks of the experiment, the presence of the polychaete seemed to facilitate the earlier establishment of non-opportunistic species.     

The impact of Melinna palmata grube, a tube-building polychaete, on meiofaunal community structure in a soft-bottom subtidal habitat

Field investigations were performed in a low-energy subtidal muddy sediment in Loch Creran, a sea-loch on the west coast of Scotland where the impact of Melinna palmata, a tube-building polychaete, on the meiofaunal community structure was assessed. This polychaete was found in high densities and forms prominent faecal casts on the sediment surface. Samples were retrieved from the casts, the feeding area of the polychaete and from an unaffected control area. The number of nematodes, the dominant taxon, did not vary significantly between areas. Of the five most abundant nematode species one was significantly more abundant in the cast area. Diversity and trophic structure of the nematode component of the meiofauna was very similar in all three areas. Copepods were more than twice as abundant in background sediments as in faecal mounds and feeding areas; however, Longipedia spp. were more abundant in the cast areas. For the copepods these findings support models which state that natural disturbances create a mosaic of patches that have different species compositions depending on their states of recovery.     

The impact of implanted whale carcass on nematode communities in shallow water area of Peter the Great Bay (East Sea)

In May, 2007 we sank the remains of a Minke whale (Balaenoptera acutorostrata) in the East Sea, Peter the Great Bay, at 30 m of water near the coast of Big Pelis Island. In the present study we describe the nematode communities in sediments under the implanted whale carcass. Abundance of nematodes increased with the distance from the carcass. Dominant trophic group was non-selective deposit feeders. The highest values of indexes of a specific diversity and evenness were noted in sediments under the whale, while domination index occurred at the highest distance from the whale. The suggestion is made that the cause of low density of nematodes in sediments under the whale is an extreme increase in number of macrofaunal animals, and predation and food competition between macro- and meiofauna. The changes noted in nematode assemblages living in an implanted whale in shallow waters are similar to those in deep-sea assemblages.     

Nematode species distribution patterns at the Håkon Mosby Mud Volcano (Norwegian Sea)

The Håkon Mosby Mud Volcano (HMMV) is a methane seep that is densely populated by the bacteria Beggiatoa spp. as well as by tubeworms of the Family Siboglinidae. Analyses of samples from seven stations located in five different habitats (bare sediments, bacterial mats, siboglinid fields, sediments with small patches of siboglinids and areas of ‘normal’ sea floor) revealed differences in the density and species‐level diversity of nematode communities. Total densities increased from stations inside the mud volcano and on its rim towards the ‘normal’ areas outside the volcano. Nematode species diversity was similar in samples from the siboglinid fields and the bare HMMV sediments. However, the sediment with patches of siboglinids collected outside the volcano was characterised by a diverse nematode community comprising 47 species, whereas the control sediments without siboglinids yielded only 27 species. The nematode assemblage at the bacterial mat site included only two identified species, Halomonhystera disjuncta and Sabatieria ornata, with H. disjuncta being strongly dominant. Terschellingia distlamphida, S. ornata and Aponema ninae dominated nematode communities at the siboglinid fields and in bare HMMV sediments. Species dominating at stations inside the caldera were found in comparable low densities in the sediment with siboglinid patches collected outside the volcano, but were missing in the background samples, where species of Endeolophos, Acantholaimus and Desmoscolex were dominant. Species diversity generally decreased with sediment depth. A subsurface‐dwelling nematode community was observed in the siboglinid fields and the bare sediments. Background sediments showed a sharp decline with 18–20 species at 0–2 cm versus three species at 3–5 cm sediment depth. The trophic composition of the nematode fauna at the HMMV showed a prevalence of deposit feeders at almost all stations, whereas background sediments exhibited a uniform distribution of non‐selective and selective deposit feeders and epistrate feeders. The high percentage of deposit feeders inside the mud volcano could be related to the grain‐size distribution and the significantly higher bacterial biomass compared to the control sediments.     

The distribution of meiofauna on back‐reef sandy platforms in the Maldives (Indian Ocean)

The Maldivian archipelago comprises some of the most characteristic and significant world atoll systems, but the meiobenthic assemblages of these islands continue to be largely unknown. To investigate variations in meiofaunal spatial distribution and biodiversity in back‐reef platforms, three transects were studied, two at Felidhoo (the north and east sides) and one at South Malé. The sedimentological features of the samples obtained were also analyzed to further current knowledge on the relationships that exist between sediments and meiofauna. Our results reveal that the meiofaunal assemblage at these locations is well diversified and includes 20 major taxa. Nematodes and copepods are dominant, together forming 68% of the total meiofauna, followed by platyhelminthes, polychaetes and ostracods. The nematode assemblage is very rich and composed of 34 families and 123 genera – 96 of which (78%) set new records for the Maldives. The structures of the meiofaunal and nematode assemblages are relatively similar on the ‘large‐scale’ level (i.e. when the different platforms are compared) and reveal a low β‐diversity. However, significant dissimilarities were detected within each platform, emphasizing that such ‘small‐scale’ differences are the main factors determining the structure of the meiofauna and, in particular, the nematode assemblages. Although significant differences were not detected between the transects, greater levels of dissimilarity were recognized at North Felidhoo. Here, the building of inclined deposit layers plays a significant role in increasing the heterogeneity of the platform habitats and sediments, confirming the great importance of sediment granulometry as an environmental variable. Indeed, a close relationship is observed between meiofauna (especially for the nematodes) and grain size, which appears to control the structure, diversity and trophic composition of the Maldivian meiofauna assemblages, thus highlighting the high biodiversity existing in the medium‐coarse sands.     

Vertical Distribution of Meiobenthos in Bathyal Sediments of the Eastern Mediterranean Sea: Relationship with Labile Organic Matter and Bacterial Biomasses

Abstract. Quantitative information on the vertical distribution of meiofaunal abundances and biomass were obtained from samples collected at 3 bathyal stations in the Eastern Mediterranean Sea located at the same depth but characterized by different food supply. Vertical distribution patterns of nieiofauna were investigated in relation to the biochemical composition of the sediment organic matter (proteins, carbohydrates, and lipids) and compared to benthic bacterial standing stocks. No significant relationship between bacteria and meiofauna was found, whereas a significant relationship between protein and lipid concentrations and total meiofauna density was observed. These data suggest that labile organic matter. considered as material readily aVdihbk to benthic consumers, may be an important factor regulating meiofaunal abundance and vertical distribution in deep-sea sediments.     

莱州湾和牟平近海夏季小型底栖生物群落组成及环境状况分析

为探究莱州湾和牟平近海小型底栖生物群落组成及影响因子,作者于2016年7月在这两个海域采集了沉积物样品,并结合沉积环境因子进行了小型底栖生物群落组成分析。结果表明,在莱州湾和牟平近海各仅检获了7个小型底栖生物类群,且莱州湾的小型底栖生物平均丰度和生物量均明显低于牟平近岸海域。莱州湾线虫和桡足类平均丰度分别占小型底栖生物的91.9%和6.3%,牟平近海分别占92.1%和4.2%。对两个海域小型底栖生物群落组成与环境因子进行Pearson相关性分析,结果显示:小型底栖生物丰度与底层水溶解氧含量呈显著正相关;表层小型底栖生物丰度比与沉积物中叶绿素a含量、脱镁叶绿素含量、沉积物有机质含量以及水深呈显著正相关,与中值粒径和底层水温度呈显著负相关。本研究显示,基于不同沉积物类型中的参考比值,线虫和桡足类丰度比值(N/C)可用于莱州湾和牟平近海沉积环境有机污染状况的评估。研究还发现,牟平海域的小型底栖生物丰度和生物量呈现由近岸向外海增加的异常趋势,且小型底栖生物的数量和类群多样性较十年前显著降低,显示沉积环境受到了明显干扰。     

Sediment-related distribution patterns of nematodes and macrofauna: two sides of the benthic coin?

We investigated the sediment-related distribution of both nematodes and macrofauna on the Belgian part of the North Sea (Southern Bight of the North Sea) in order to evaluate whether both faunal groups reflect similar patterns in community composition and diversity. Fine-grained sediments (median grain size <200μm) were inhabited by nematode communities characterised by a low diversity and dominated by non-selective deposit-feeding nematodes. Nematode communities from coarser sediments were significantly different in terms of community composition and diversity. Moreover, all nematode feeding types were present in coarser sediments. These differences were explained by the contrasting biogeochemical processes prevailing in both sediment types, rather than granulometry and food availability per se. Macrofaunal distribution patterns were different from those of the nematode communities and seem to be related to water column processes (SPM loading, food availability, hydrodynamic stress) that promote the establishment of diverse communities in the coarser sediments but not in the finest sediments. This suggests that data on nematodes and macrofauna reveal different, complementary aspects of the factors structuring the benthic ecosystem that can be of importance in assessing the ecological status of the seafloor.     

Recovery of meiofauna communities following mudflat disturbance by trampling associated with crab-tiling

The provision of artificial shelters for the collection of crabs, known as crab-tiling, and the subsequent harvesting of the soft "peeler" crabs for angling bait, are associated with trampling disturbance of intertidal mudflats in the United Kingdom. Recovery of meiofauna communities following crab-tiling activity was investigated on an intertidal mudflat in SW England. Harvesting of experimental plots was reproduced six times over a 2-week period. Meiofauna was collected at low tides 12h, 36 h and 144 h after treatment. Meiofaunal and nematode abundance, and nematode species number, was significantly greater in controls compared to crab-tile stations at 12h. At 36 h and 144 h there were no significant differences between treatments, indicating recovery had occurred in 12-36 h. Multivariate analysis showed nematode assemblage composition from control plots to be significantly different from crab-tile plots at 12h. No significant differences were observed between sediment physical parameters with treatment. Results suggest that the predominant effect of disturbance may be vibration-induced burial, which causes nematodes to bury deeper into the sediment, beyond the depth sampled, and explains the rapid recovery.     

Effects of the invasive polychaete Marenzelleria spp. on benthic processes and meiobenthos of a species-poor brackish system

The effects of the invasive polychaete Marenzelleria spp. on sediment processes and meiobenthos with an emphasis on free-living nematodes of the Vistula Lagoon (southern Baltic Sea) were investigated in a laboratory microcosm experiment. Marenzelleria occupies an open niche and its deep burying behaviour and feeding strategy represent a new function in the study area. Halos of oxidized sediment along Marenzelleria burrow walls indicated oxygen penetration into the burrows but the polychaete had no significant effect on porewater nutrient concentrations. The results showed, however, the density dependent effects of Marenzelleria on ammonium transport. An enhanced ammonium efflux was recorded at high polychaete densities (2000 ind. m^− 2) but not at low polychaete densities (300 ind. m^− 2).There was no observable impact of the polychaete on total meiobenthic numbers. There was, therefore, no indication that Marenzelleria caused meiofauna mortality. On the contrary, the polychaete significantly affected vertical distribution of meiofauna facilitating the colonization of deeper sediment depths and thus extending the habitat to be used by meiobenthos. In addition, Marenzelleria had a positive impact on the survival of turbellarians.Nevertheless, there was no effect of Marenzelleria on nematode assemblage structure and diversity, indicating that neither the physical presence nor the biological activity of the worm affected the nematode community. This suggests either 1. the limited impact of Marenzelleria on nematodes, resulting from the creation of simple, narrow and un-branched burrows, 2. poor response of nematode community resulting from their low abundance and diversity in the study area, or 3. the overriding role of the harsh chemical environment typical of sediments of the Vistula Lagoon, masking the effect of the bioturbator.     

Meiobenthic communities of seagrass beds (Zostera capricorni) and unvegetated sediments along the coast of New South Wales,Australia

Seagrass beds have higher biomass, abundance, diversity and productivity of benthic organisms than unvegetated sediments. However, to date most studies have analysed only the macrofaunal component and ignored the abundant meiofauna present in seagrass meadows. This study was designed to test if meiobenthic communities, especially the free-living nematodes, differed between seagrass beds and unvegetated sediments. Sediment samples from beds of the eelgrass Zostera capricorni and nearby unvegetated sediments were collected in three estuaries along the coast of New South Wales, Australia. Results showed that sediments below the seagrass were finer, with a higher content of organic material and were less oxygenated than sediments without seagrass. Univariate measures of the fauna (i.e. abundance, diversity and taxa richness of total meiofauna and nematode assemblages) did not differ between vegetated and unvegetated sediments. However multivariate analysis of meiofaunal higher taxa showed significant differences between the two habitats, largely due to the presence and absence of certain taxa. Amphipods, tanaidacea, ostracods, hydrozoans and isopods occurred mainly in unvegetated sediments, while kinorhyncs, polychaetes, gastrotrichs and turbellarians were more abundant in vegetated sediments. Regarding the nematode assemblages, 32.4% of the species were restricted to Z. capricorni and 25% only occurred in unvegetated sediments, this suggests that each habitat is characterized by a particular suite of species. Epistrate feeding nematodes were more abundant in seagrass beds, and it is suggested that they graze on the microphytobenthos which accumulates underneath the seagrass. Most of the genera that characterized these estuarine unvegetated sediments are also commonly found on exposed sandy beaches. This may be explained by the fact that Australian estuaries have very little input of freshwater and experience marine conditions for most of the year. This study demonstrates that the seagrass and unvegetated sediments have discrete meiofaunal communities, with little overlap in species composition.     

厦门凤林红树林湿地自由生活海洋线虫群落的研究

2004年冬季在集美凤林类似底质类型、盐度和潮位的海湾地段4个断面,就不同红树植物林中的小型底栖动物数量和自由生活海洋线虫群落进行了研究。结果表明:海洋线虫是凤林红树林中小型底栖动物中的绝对优势类群,占到小型底栖动物的76.1%~96.3%;从丰度来看,旧区白骨壤(Avicennia marina)林中小型底栖动物的数量较少,有污水流过的光滩数量较大;4个断面共鉴定出海洋线虫37种(分类实体单元),其中新区秋茄(Kandelia candel)林中的生物多样性指数较低,旧区白骨壤林中群落具有较高的物种多样性;从出现的物种来看,新区秋茄林、旧区白骨壤林和光滩上出现的优势种和摄食功能群的类型各不相同。从4个断面13个站位进行的聚类分析和MDS标序分析结果推断自由生活海洋线虫的群落结构与不同的红树植物形成的沉积物有关。     

青岛湾有机质污染潮间带底栖生物研究 Ⅱ.小型底栖动物生态特点

用大型底栖动物为指标来指示、监测和评价海洋有机质污染,国内外已有许多研究报道。但是,由于大型底梄动物世代时间较长,对中低度及非急性致死污染的反应迟缓,不够灵敏迅速,因此这方面的工作至今还未见令人满意的结果。随着小型底栖生物学,尤其是生态学在最近几十年的发展,给人们应用底栖生物来指示和监测海洋污染提供了新的科学依据。小型底牺生物的分布广,野外取样方便,世代周期短,保守的生殖策略,对环境的变化反应更灵敏迅速,因此使其在污染监测研究中有着更大的潜力(Moore & Bett，1989)。作为小型底栖生物的最优势类群一自由生活海洋线虫,因其具有极高的丰度和多样性,以及身体较坚硬不易破碎等优点,而成为污染监测的研究重点(Ferris et al.,1979; Heip et al.,1985)。有关污染环境中小型底栖生物的研究,国外已有许多报道，迄今为止,国内还研究甚少。 青岛湾东侧海滩主要接纳青岛市市南区排放的生活污水和混合废水,近年来大规模截污后,张志南等(1993)曾在此做过小型底栖动物群落的研究,发现线虫密度与小头虫(Capitella Capitata)有着相似的分布特点,并根据线虫群落多样性指数、线虫的取食特性及桡足类的相对丰度,对比Wu Boling et al..(1988)和孙道元等(1978)的研究,得出该湾有机质污染程度正在减轻的结论。但到目前为止,尚缺乏对该海区有机质污染状况及其变化的综合的系统研究。 作者于1991年4月-1992年3月在青岛湾东侧进行了底栖生物调査,本文试图通过对该有机质污染环境中小型底栖生物生态特点的研究,探讨污染指示种、主要类群的丰度、线虫与桡足类的比值(N/C)、线虫群落的多样性指数和种类组成等诸项生态学参数在有机质污染监测中的适用性和优缺点,为海洋污染监测及环境质量评价提供依据和最优选择。     

Meiofauna and chlorophyll associated with Beggiatoa mats of a natural submarine petroleum seep

Previous studies at the Isla Vista oil seep have suggested that meiofauna, particularly nematodes, might be an important factor in explaining macrofaunal enrichment by making bacterial biomass available to the benthic food web. To explore this possibility, we analyzed meiofaunal abundance and microalgal pigments inside and just outside of bacterial mats at this natural oil seep.The bacterial mats occur where crude oil and natural gas are actively seeping out of the sediment; cores from within the mats contained a great deal of crude oil (up to 50 %). Meiofaunal abundances were the same in and out of the bacterial mats (averaging 1·-9 × 10⁶ individuals m^-2). However, dramatic changes in community structure were noticed. Harpacticoids made up 19 % of the fauna outside the mats but only 1 % inside. Pigment concentrations were also the same in both sites with phaeophytin dominating chlorophyll (120 compared to 29.8 mg m^-2). The variance of both microalgal pigments and meiofauna was much greater inside than outside, suggesting that the bacterial mats are a more heterogeneous environment.Although the effect of crude oil toxicity is not clear, the high abundances of microbial and meiofaunal biomass support the hypothesis of benthic enrichment via microbes and meiofauna.     

Spatial variability of meiofaunal communities at areas of contrasting depth and productivity in the Aegean Sea (NE Mediterranean)

The abundance and community structure of metazoan meiofauna were studied in deep-sea sediments from the north and south Aegean Sea (Eastern Mediterranean) in summer 1997 and spring 1998. The two areas varied in their surface primary productivity with the northern area being more productive. Meiofaunal densities displayed strong spatial variability while no temporal changes were observed. Total metazoan density ranged from 128 to 1251 ind./10 cm², with significantly higher values in the north. Meiofaunal biomass ranged from 27 to 391 μgC/10 cm² with higher values also in the north. At all stations nematodes dominated the community, comprising on average more than 91% of the total abundance. On a broad scale, meiofaunal densities displayed a positive correlation with food availability (sediment-bound chloroplastic pigments, carbohydrates and lipids); carbon mineralization (an indicator of organic matter turnover) was significantly higher in the northern Aegean, providing evidence of high organic-matter input and intense benthic-pelagic coupling. The spatial structure of the nematode community indicated that the two areas were similar in terms of their dominant genera (Halalaimus, Acantholaimus, and Thalassomonhystera).     

夏、秋季南黄海小型底栖动物空间分布格局及其环境影响因素

为研究南黄海小型底栖动物的空间分布格局及其环境影响因素,于2020年8月（夏季）和11月（秋季）对南黄海进行了两个航次的野外观测和采样,对小型底栖动物的类群组成、丰度、生物量、垂直分布、群落结构及其与环境因子的关系进行了研究。结果显示,共鉴定出小型底栖动物类群15个,其中自由生活海洋线虫为最优势类群,在两个航次中分别占小型底栖动物总丰度的75.6%和84.6%。其他较重要的类群还包括底栖桡足类、轮虫类和枝角类等。夏季和秋季小型底栖动物的平均丰度分别为（514.9±32.1）ind./(10 cm2) 和（350.8±30.7）ind./(10 cm2),平均生物量（干质量）分别为（651.7±98.0）μg/(10 cm2)和（589.2±37.1）μg/(10 cm2)。小型底栖动物在时空分布上存在差异。在季节分布上,小型底栖动物丰度和类群组成存在极显著差异。结合环境因子分析结果可知,沉积物中值粒径是引起差异的主要环境因子。在空间分布上,夏季小型底栖动物丰度和类群组成在不同水深间存在极显著差异,秋季小型底栖动物丰度和类群组成在不同水深间差异不显著。推测黄海冷水团是影响夏季小型底栖动物空间分布差异的主要因素。本研究中小型底栖动物的数量和类群多样性相较于国内其他对南黄海小型底栖动物的研究较低,其中沉积物叶绿素a含量及有机质含量是引起南黄海小型底栖动物丰度变化的重要因素。海洋线虫与桡足类的丰度比值（N/C比值）评估显示秋季该区域存在有机污染,这一结果与应用大型底栖动物对同一区域进行环境评价的结果不一致,对于应用N/C比值评价环境质量还需要进一步的研究。