Meiobenthos in estuary part of ha long bay (gulf of tonkin, south china sea, vietnam)

The distribution of the taxonomical composition and the density of meiobenthos depending on some factors of environment has been studied in bottom sediments of the northern estuary part of Ha Long Bay (Cua Luc estuary). The basic factor of influence on meiobenthic community structure was the granulometric composition of sediment. The greatest taxonomic diversity is noted in the silted sands, lowest — in the silty sediments. The density of meiobenthic community was higher in the silty sediments. Slightly expressed correlation between the density of nematodes and the percentage of silty particles in the sediments is detected (Spearman rank correlation coefficient was 0.49±0.21, p=0.035). The nematodes were dominant at all stations. In total, representatives of 66 species of nematodes belonging to 17 families and 52 genera were identified.     

Features of the soft-bottom subtidal macrobenthos in Nha Trang Bay (Vietnam, South China Sea)

General characteristics of macrobenthos of the muddy sediments of the subtidal (19–24 m) zone in Nha Trang Bay (South Vietnam) were described based on the survey performed in April–May 2002. The mean abundance of organisms was 637 ind/m² and the mean biomass was 2.3 g/m². Sixty-seven macrobenthic species were found during the study. The main structural features of the macrobenthos were high species diversity, low species recurrence, and high eveness of the species structure with the absence of clearly manifested dominants. The number of species encountered regularly increased with the increase in the total area sampled from 210 to 5000 cm², though the relation did not reach saturation. The similarities and differences between the macrobenthos structures in Nha Trang Bay and those in some tropical and boreal soft-bottom communities are discussed.     

Quantitative distribution of the meiobenthos in Baidaratskaya Bay (Kara Sea)

The quantitative characteristics and spatial distribution of the meiobenthos in Baidaratskaya Bay (Kara sea) were analyzed based on data collected in 1994–2007. The extremely high density of the meiobenthos (up to 8121 ind/10 cm², average 2318 ind/10 cm²) makes it possible to consider Baidaratskaya Bay among the most productive Arctic regions. The spatial distribution of the meiobenthos was mostly determined by the depth and sediment properties in the subtidal zone of the bay. The density of meiobenthic organisms decreased with depth, and with the increase of the small sediment fraction. The difference in the meiobenthic densities between the two coastal areas of the bay (Yamal and Jugora CAs) is also revealed. Such difference caused by the combined effects of small-scale and mesoscale factors, mainly by the grain size. Opposite changes in the meio- and macrobenthic biomass with depth is shown.     

Composition and distribution of meiobenthos in amursky bay (peter the great bay, the east sea)

Qualitative and quantitative composition of meiobenthos was studied in Amursky Bay (Peter the Great Bay, the East Sea). Ten taxonomic groups were found, where nematodes were dominant. Density of meiobenthos in ground sediments of the Bay were not uniform, and the average density was measured at 126.4±62.3 ind. m^-2. 56 species of nematodes were detected, and dominant species wereSabatieria palmaris, Paracanthonchus macrodon, Sphaerolaimus limosus, S. gracilis andOncholaimium ramosum. Five taxocenes of nematodes were allocated based on the results of cluster analysis and species domination according to density. Low diversity in species composition of nematodes was noted in the northwestern part of the Bay, which is a zone of desalination, and in the eastern part, which is exposed to household drains.     

Distribution and Variability of the Meiobenthic Assemblages near the Korean Polymetallic Nodule Claim Area of the Clarion-Clipperton Fracture Zone (Subequatorial NE Pacific)

This study was carried out as part of a baseline long-term environmental project in the proposed mining areas for an environmental impact assessment of future mining in the Clarion-Clipperton Fracture Zone (CCFZ). The community structure and distributional pattern of meiobenthos were investigated in the deep-sea bottom of the Clarion-Clipperton Fracture Zone of the northeastern Pacific in July 1998, 1999, 2001, 2003 and August 2004, 2005. Twenty one meiobenthic groups were found at the stations in the study area. The most abundant meiobenthos comprised nematodes followed by benthic foraminiferans and harpacticoid copepods. The maximum density of meiobenthos was 306 ind/10 cm² at the station located at 11°N (water depth, 4833 m), and the minimum density was 6 ind/10 cm² at the station located at 14°N (water depth, 5037 m). Oligotrophic conditions in the CCFZ seem to directly reflect the lower standing stocks of meiobenthos in the CCFZ compared to other deep-sea plains of similar depth. The latitudinal distribution pattern of meiobenthos in the study area seemed to be related with surface water primary productivity, which was connected to the water circulation pattern of the Pacific Ocean near the Equator, diverging at 8ºN latitude and converging at 5°N. The horizontal distribution of meiobenthic organisms in the study area showed high densities at the stations within 135–136°W. The densities of meiobenthic organismas within the CCFZ were high at stations with few manganese nodules on the sediment surface at low-latitude sites. In 1998, the observed relative high values of meiobenthic abundance were at stations from 5° to 6°N. Other stations from 7° to 10°N showed no significant fluctuations during the interannual sampling periods. It is considered that the inter-annual fluctuation of meiobenthos abundance is intimately related with a regime shift that may have occurred in the north Pacific between 1998 and 1999, the El Niño period. Vertical distribution of meiobenthic organisms showed the highest individual numbers in the surface sediment layers of 0～2 cm depth and a steep decreasing trend as sediment becomes deeper at the stations of high latitude located in 16～17°N. Size distribution analyses showed that organisms that fit into the sieve mesh size of 0.063 mm were abundant.     

Experiments on rain-induced incipient motion of noncohesive sediment

Laboratory studies of artificial raindrops demonstrate the importance of rain in sedimentation processes in the shallow intertidal zone. Drop-formed vortex rings are hypothesized to be a mechanism for transfering kinetic energy to bottom sediments. Vortex rings initiated sediment motion in shallow water at least 22.5-cm deep. Although rings were able to move very coarse sand, they were more efficient in moving the finer-sand sizes. The probability of drops initiating sediment motion decreased from 94 to 11% with increasing depth from 2.5 to 22.5 cm. Ring-induced bottom shear stresses were estimated in excess of 11 dynes cm^–2.     

北黄海小型底栖生物丰度和生物量时空分布特征

分别于2006年7月和2007年1,4和10月在北黄海陆架浅海水域进行小型底栖生物调查.结果表明,4个航次的小型底栖生物平均丰度分别为(1 099±634),(664±495),(1 601±837)和(524±378) ind·10 cm-2;平均生物量分别为(1 446.34±764.66),(428.63±294.84),(1 580.53±1 041.23)和(793.50±475.83) μg·dwt·10 cm-2.共鉴定出18个小型底栖生物类群,按丰度,自由生活海洋线虫为最优势类群,4个航次的优势度分别为72%,90%,85%和74%,其他优势类群依次是桡足类、多毛类、动吻类和介形类;按生物量依次是线虫、桡足类、多毛类、介形类和双壳类.97%的小型底栖生物分布在0～5 cm的表层沉积物内,线虫和桡足类分布在0～2 cm沉积物的比例分别为86%和87%.二因素方差分析(two-way ANOVA)表明:小型底栖生物丰度和生物量在由4个航次所代表的春、夏、秋、冬各季节之间存在显著差异(春、夏高于秋、冬),在4个航次的5个相同取样站位之间也有显著差异.小型底栖生物的丰度和生物量与水深和底盐呈负相关性.北黄海冷水团对小型底栖生物丰度和生物量时空分布有一定的影响.     

Community Structure of Free-living Marine Nematodes in the Area of Agar-Producing Alga Ahnfeltia To b u c h i e n s i s Field (Starka Strait,Peter the Great Bay,East Sea)

The structure of the nematodes communities has been studied in the sediments on two sites located outside and under the layer ofAhnfeltia tobuchiensis (Kanno and Matsubara 1932; Makijenko 1970). Bottom sediments at the stations were represented by sands with a different degree of silting. Specific structure of nematodes at the stations was significantly different under the similar environmental conditions (water depth, dissolved oxygen saturation, salinity, temperature of the bottom layer and organic carbon content inside of the sediment). Nematodes dominated (75.7 %) in meiobenthos community under the layer of A.tobuchiensis where concentration of silt particles was 12 %. Representatives of the family Comesomatidae were dominant. Low index of species diversity and high Simpson domination index were detected in this community. Under a layer ofA. tobuchiensis with the thickness of 30 cm concentration of the silt particles was 5.39 %; nematodes density was low and made 32.1 % of the general density of meiobenthos. Species of the families Xyalidae and Monoposthiidae were dominant. Outside of A.tobuchiensis, field percentage of silt particles was minimal (3.1 %) and representatives of families Cyatholaimidae and Axonolaimidae dominated. The specific structure of nematodes in this type of the ground is characterized by high index of species diversity and low level of domination.     

Intertidal meiofauna of Jeju Island,Korea

For the first time, the structure of the meiobenthos community and marine nematodes in particular was investigated in the different intertidal zones of Jeju Island (South Sea of Korea). A relationship was found between the density of meiobenthic communities and the type of the bottom sediment. In addition, in the silty sediments, nematodes were dominant, while in the sandy sediments harpacticoids and ostracods were dominant groups. Sixty eight species belonging to 60 genera and 19 families of nematodes were found in the whole area. Four different nematode taxocenosis were distinguished using a cluster analysis. Dominant feeding groups were omnivores (2B) and epistratum-feeders (2A). The highest number of non-selective deposit-feeders (1B) was detected in the lagoon with the bottom silty sediments.     

A New Video Controlled,Hydraulically Damped Corer for Sediment/Water Interaction Studies

Abstract

A new box-corer is described. Placement and penetration of the box-corer is video-assisted to secure a sample representative of the bottom. The box itself is constructed of fully transparent polycarbonate which allows for video control observation of the sediment/water interface during sampling. The box is open during the descent towards the seabed but closes when the release is triggered. The box-corer is hydraulically damped so that the box after landing is very gently pushed into the seabed to a predetermined depth. A sediment sample with a total length of about 35 cm and with a surface area of 400 cm² (20.0x20.0 cm) is collected in the box together with the near bottom water to a height of about 10 cm above the bed. The box-corer height is 180 cm and the total weight about 200 kg. The legs can be dismounted which makes transportation easy. The box-corer has been operated with success both in coarse sand and in soft silt and clay dominated sediments.     

中国多金属结核开辟区东、西两小区小型底栖动物的空间分布

利用 1 998年“大洋一号”调查船 DY95 - 8航次在中国多金属结核开辟区东、西两小区用多管取样器采集的沉积物样品 ,对小型底栖动物的组成、分布及其与环境因子的关系进行了研究。结果表明 :(1 )东、西两小区共有 1 6个类群的小型底栖动物 ,其中线虫类占居显著优势 ,在东、西两小区各占总栖息密度的 71 %和 6 4 %,其次为猛水蚤类和蜱螨类。 (2 )东、西两小区小型底栖动物类群平均栖息密度分别为 3 2 .47ind/1 0 cm2 和 1 8.0 5 ind/1 0 cm2 ,东小区高于西小区。小区各站位间的栖息密度平面分布差异显著。 (3 )东、西两小区小型底栖动物类群栖息密度的垂直分布趋势明显 ,由表层向底层 ,栖息密度逐渐降低。 (4)东、西两小区小型底栖动物空间分布与底质沉积物、结核覆盖率和底层流等环境因子密切相关 ,底质较硬、结核覆盖率较高以及底层流较强都不利于小型底栖动物的栖息。     

Influence of anthropogenic pressure and seasonal upwelling on coral reefs in Nha Trang Bay (Central Vietnam)

The growing coastal development, dredging and dumping activities, overfishing and expansion of marine cage culture in Nha Trang Bay (NTB) of Central Vietnam since the beginning of the 2000s have resulted in a dramatic decrease of live coral cover. Surveys conducted in April–May 2013 and the same period in 2014 revealed that with an increase in distance from the outer part of the bay towards the mainland, the rivers’ influxes and dredged areas, coral cover decreased from 75% to 0.6% and species richness from 63 to 5, while the abundance of macroalgae increased from 0% to 56%. These changes correlate with differences in the concentration of suspended sediments on the same gradient. The abundance of the crown‐of‐thorns starfish Acanthaster planci and of the echinoid Diadema setosum significantly increased between the first estimation in 1998 and the survey in 2014, from 0 to 1.7 individuals (ind.) per 100 m^?2 and from 50.8 to 94.5 ind. per 100 m^?2, respectively, contributing to coral loss and intensive bioerosion of the reef framework in the bay. The large sizes of adult colonies of tabulate Acropora on the remote stations with negligible sedimentation and eutrophication loads were inconsistent with the assumptions that temperature‐induced coral bleaching or cyclones could be the major impacts in Nha Trang Bay. Analysis of the 16‐year thermal history of the bay did not reveal any instances in which the coral thermal bleaching threshold had been exceeded up to the present study. Seasonal upwelling, which occurs annually in the vicinity of Central Vietnam, may contribute to mitigation of thermal anomalies within NTB and to the maintenance of healthy coral communities on the remote reefs with relatively low anthropogenic impact.     

Characteristics of resuspended sediment from Georges Bank collected with a sediment trap

A sediment trap was deployed 3 m from the bottom at a water depth of 62 m on the southern flank of Georges Bank (41°02·2′N, 67°33·5′W) from 30 September 1978 to 10 March 1979 to qualitatively determine the size of sediments resuspended from the bottom by winter storms and to determine if seasonal changes in the phytoplankton could be observed in the trapped sediment.Bulk X-ray analyses of the trapped sediment showed layers of distinctly different textures preserved in the collection vessel. The median grain size of sampled layers ranged from 2·7 to 6·5 φ (fine sand to silt), but all layers contained a pronounced mode in the 3 φ (fine sand) range. Nine layers containing relatively large amounts of sand were present. The sand content was 75% in the coarest layers and about 32% in the fine layers. The median grain size of bottom sediments at the deployment site was considerably coarser than the trap samples, although the dominant grain size was also 3 φ.Average bottom-current speeds during the deployment period were about 30 cm s^?1 with a range of 10 to 50 cm s^?1. Bottom stress, computed from the observed currents and waves, suggest that 11 storms caused sufficient stress to resuspend 3 φ-sized sediments, in good agreement with the nine layers of relatively coarse sediments collected in the trap. Surface waves had to be included in the calculation of bottom stress because the bottom currents alone were insufficient to cause the resuspension of 3 φ-sized sediment.The trapped sediments contain numerous diatoms and coccoliths that are typical of late fall and winter assemblages. No clear seasonal difference in the flora was noted among sampled layers, probably due to the large influx of resuspended material and a reduced primary flux during this period. An undescribed species of Thalassiosira (G. Fryxell, personal communication), and siliceous scales of unknown systematic position were observed at all levels.     

台湾海峡中北部海域春季小型底栖生物丰度和生物量

2009年4月14～16日在台湾海峡中北部海域进行了小型底栖生物调查研究.结果表明,研究海域的小型底栖生物平均丰度为21.11±16.29 ind/cm^2;平均生物量为20.97±4.96μg/cm^2（以干重记）.研究海域共鉴定出13个小型底栖生物类群,按丰度,最优势类群为自由生活海洋线虫其丰度为19.23±15.49 ind/cm^2,占小型底栖生物总丰度的91.10%,其他优势类群依次为底栖桡足类和多毛类,分别占小型底栖生物总丰度的2.77%和2.64%;分布在0～5 cm的表层沉积物内的小型底栖生物约为83.18%,线虫和底栖桡足类分布在0～2 cm的比例分别为57.66%和62.96%.小型底栖生物的生物量低于大型底栖生物,但由于其繁殖快,生命周期短,因此,其生物量约为大型底栖生物的445倍,年平均生产量约为大型底栖生物的1.39倍.     

厦门浔江湾小型底栖生物数量分布及生态意义

本文首次报道 1 998年 5月厦门浔江湾水域 5个测站小型底栖生物调查的初步结果。小型底栖动物的平均密度为 5 9.6 5个 /cm2 ,自由生活的海洋线虫是优势类群 ,占总密度的 89.2 8% ;其次 ,底栖桡足类占 2 .76 % ;其它类群所占比例较少。小型底栖生物的丰度分布为湾口区底 ,湾中部高。文中分析了小型底栖生物具有高类群优势度和低类群多样性特征 ,以及线虫与桡足类的丰度比率与环境的关系 ,提出浔江湾水域环境状况应引起重视。     

Composition of the organic matter of the water,suspended matter,and bottom sediments in Nha Trang Bay in Vietnam in the South China Sea

Research has been conducted in Nha Trang Bay (Southern Vietnam, the South China Sea) at the section from the estuary of the Cai River to the marine part of the bay, as well as in the area of coral reefs. The objects of the studies are the river and sea waters, the suspended matter, and the bottom sediments. Data on the dissolved organic carbon and the total nitrogen in the water are obtained. The organic carbon content is estimated in the suspended matter; the organic carbon and the molecular and group composition of the n-alkanes are determined in the bottom sediments. The molecular and group composition of the n-alkanes in the bottom sediments of the landfill have made it possible to identify three types of organic matter (OM): marine, mixed, and of mainly terrigenous origin. All the types of OM are closely related to the specificity of the sedimentation and the hydrodynamics of the waters in this water area.     

长江河口近底层悬沙和沉积物的交换过程研究

大河河口的动力沉积过程一直是陆海相互作用研究的核心内容,其中水体泥沙的垂向交换是河口动力-沉积机制分析中的关键环节。基于2011年12月对长江河口及其邻近海湾采集的大范围、高密度的近底层悬沙、海床表层1~2cm(表层沉积物)和垂向向下约2~10cm的沉积物(次表层沉积物)同步3组303个样品,利用经验正交函数方法,对河口地区的悬沙和沉积物交换过程进行研究。结果表明:近底层水体悬沙的空间分布模式主要以粉砂粒级为主,空间分布差异性不大;表层及次表层沉积物的空间分布模式相似,但较近底层水体悬沙的分布复杂,存在明显的区域性特征,其中南汇边滩水域中部辐散区的沉积物表现为粗粉砂-细砂模式,其他区域由粉砂组分模式组成。近底层水体悬沙、表层和次表层沉积物的第一模态主要反映了粒径较细的泥沙运动,第二模态主要反映了粒径较粗的泥沙运动。在近底层水体悬沙与表层沉积物的垂向交换中,主要交换粒级为粉砂组分粒级。在表层沉积物与次表层沉积物的垂向交换中,南汇边滩中部辐散区的主要交换粒级为粗粉砂-细砂组分粒级,其他区域主要为粉砂组分粒级。     

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。     

Accumulation rate and heavy metal pollution in Osaka Bay sediments

The accumulation rates of sediment cores in Osaka Bay have been determined by using²¹⁰Pb dating technique. In the upper 10 cm²¹⁰Pb_ex contents show a constant value with depth. The accumulation rates below the homogeneous layer of sediments ranging from 0.12 to 0.61cm y^–1 (0.067–0.34 g cm^–2 y^–1) were obtained. The higher contents of Zn, Cu, Pb and Cr were observed in the upper 10 to 30 cm of sediments. Assuming that the increment of heavy metal content in sediments is due to anthropogenic origin, the amount of anthropogenic input of heavy metals into sediments were estimated to be 1,300–2,700g cm^–2 for Zn, 150 – 480 for Cu, 360 – 410 for Pb and 320 – 480 for Cr. The increment appears to start about 100 years ago. In surfical sediments most of heavy metal contents exceeded the background content, and then most part of Osaka Bay is polluted by heavy metals.     

Long-term changes in the meiobenthos of the eastern part of the Black Sea

The results of meiobenthic surveys undertaken in 1991, 1999, and 2005 off the Caucasian coasts of the Black Sea are presented. During the period of 1991 to 1999, the number of free-living nematodes increased significantly at all the sampling stations. The mean nematode abundance values grew from 85 ind./10 cm² in 1991 to 1167 ind./10 cm² in 1999. Proportionally, the total metazoan meiofauna density increased from 171 to 1283 ind./10 cm². The abundance of other meiofaunal groups including harpacticoid copepods did not change significantly. As a result of these changes, the ratio of nematodes to copepods (the nematodes-copepods index) increased from 2.5: 1 in 1991 to 26: 1 in 1999 and to 70: 1 in 2005. The number of foraminifers increased twofold. In 1991, they were found only at five stations out of 25. In 1999, foraminifers were presented at all ten stations with a mean density of 212 ind./10 cm². Such changes in the meiobenthic communities could have resulted from cascade transformations of the ecosystem leading to among other changes to a decline in the macrobenthos biomass and the release of nonutilized organic matter in the bottom ecosystems. The differences in the procedures of the sampling and the samples’ processing in the different years may be responsible for the 20–30% variation in the assessment of the meiobenthos’ number.