Molluscan assemblages of seagrass-covered and bare intertidal flats on the Banc d'Arguin, Mauritania, in relation to characteristics of sediment and organic matter     

Pieter J.C. Honkoop  Eilke M. Berghuis  Sander Holthuijsen  Marc S.S. Lavaleye  Theunis Piersma   《Journal of Sea Research》2008,60(4):255-263

The Banc d'Arguin, a non-estuarine area of shallows and intertidal flats off the tropical Saharan coast of Mauritania, is characterised by extensive intertidal and subtidal seagrass beds. We examined the characteristics of intertidal seagrass (Zostera noltii) meadows and bare areas in terms of the presence and abundance of molluscs (gastropods and bivalves). To explain observed differences between molluscan assemblages in seagrass and bare patches, some aspects of the feeding habitat (top-5 mm of the sediment) and of food (organic materials) of molluscs were examined. The novelty of this study is that phytopigments were measured and identified to assess source and level of decay (freshness) of organic material in the sediment and to study their importance as an explanatory variable for the distribution of molluscs. Over an area of 36 km² of intertidal flats, at 12 sites, paired comparisons were made between seagrass-covered and nearby bare patches. Within seagrass meadows, dry mass of living seagrass was large and amounted to 180 ±10 g AFDM m^− 2 (range 75–240). Containing twice the amount of silt per unit dry sediment mass, seagrass sediments were muddier than bare areas; the relative amount of organic material was also larger. The total number of species of bivalves and gastropods amounted to 27, 14 of which were found only in seagrass areas, 4 only in bare and 9 in both types of habitat. Among the three numerically most abundant species, the bivalves Anadara senilis, Dosinia hepatica and Loripes lacteus, the first was numerically most abundant in bare and the other two in seagrass-covered areas. Bare intertidal areas had greater mean total biomass of molluscs (80.5 g AFDM m^− 2) than seagrass meadows (30.0 g AFDM m^− 2). In both habitats, the bulk of the biomass was made up by A. senilis. Excluding this species, bare mudflats contained on average only 3.1 g AFDM m^− 2 and seagrass meadows 6.9 g AFDM m^− 2. As compared to previous surveys in 1980–1986, the biomass of A. senilis had increased almost 10-fold and D. hepatica, previously found in very small numbers, had become the most numerous species. However, the total biomass excluding that of A. senilis was similar. Concentrations of phytopigments were similar to those observed at temperate mudflats, indicating that the Banc d'Arguin might not be as oligotrophic as previously thought. Per unit of dry sediment mass, smaller amounts of phytopigments were found in bare than in seagrass areas. Per unit of dry organic material, bare sediments contained most (fresh) phytopigments. This suggests that in seagrass-covered meadows the organic material is more degraded than in bare sediments. Overall, the composition of phytopigments, quite surprisingly, indicated a benthic-diatom-dominated trophic system. Multivariate statistics revealed that patterns of zoobenthic assemblages were correlated with patterns of a combination of four environmental parameters: grain size of the sediment, amount of fresh phytopigments and amounts of leaves and roots of seagrass.  相似文献   

秦皇岛港区春、夏和秋季底栖海藻的研究     

刘剑华  张耀红  杨毓英 《中国海洋大学学报(自然科学版)》1995,(1)

报道秦皇岛港区底栖海藻的群落结构、季节变化、生物量及优势种类等。通过４次定性采样指出：４月和６月的种类数高于８月和１０月，群落组成都以红藻类为优势。平均生物量分布以金山咀最高，灯塔最低，各采样点的优势种是新煤码头为绿藻类的孔石莼、肠浒苔和尾孢藻；灯塔为红藻类的珊瑚藻、鸭毛藻及绿藻类的孔石莼和刺松藻，金山咀为孔石莼、刺松藻、萱藻和蜈蚣藻。  相似文献   

渤海海洋线虫与底栖桡足类数量之比的应用研究   总被引：9，自引：0，他引：9  

郭玉清  张志南  慕芳红 《海洋科学》2002,26(12):27-31

在渤海的22个站位，分3个航次采集未受扰动的沉积物样品，进行了小型底栖动物中两个主要类群自由生活海洋线虫和底栖桡足类数量变动和两者数量之比评价沉积物有机污染环境的研究。结果表明：对于同一航次的不同重复，数量变动差异显著或极显著；在同一个站位24h，6次重复取样，两者数量的变异系数较大；在应用该比值进行沉积物有机污染评价时，在同一站位该比值波动较大。  相似文献   

含澄江动物群地层的Pb-Pb同位素定年   总被引：4，自引：0，他引：4  

常向阳  陈良忠  胡世学  王江海  朱炳泉 《地球学报》2004,25(2):181-184

对含澄江动物群的地层样品进行了Pb同位素定年研究。经测定未受风化作用影响的 2 0个黑色页岩样品给出了5 34± 6 0Ma左右的Pb Pb等时线年龄 ,应代表了澄江动物群的下限年龄。该年龄较以往采用Rb Sr和40 Ar 3 9Ar等定年方法所获得的年龄更为年轻。  相似文献   

山东南部沿海冬季小型底栖生物的初步研究   总被引：1，自引：0，他引：1  

吴绍渊  慕芳红 《海洋与湖沼》2009,40(6):682-691

利用统计法、经验模型和多元聚类分析法和数学分析软件对2006年12月908项目冬季航次山东南部海域(36°15′—36°45′N,120°45′—122°00′E)小型底栖生物调查所获得的数据进行分析,获得该调查海域冬季小型底栖生物的平均丰度为(657.43±214.60)ind/10cm2,平均生物量为(847.15±427.63)μgdwt/10cm2,平均生产量为(7624.32±3848.64)μgdwt/(10cm2·a-1);还对N/C、Simpson优势度指数、Margalef多样性指数、Pielou均匀度指数和香农-威纳指数进行了计算。与2006年8月908项目夏季航次同一海域调查数据进行了比较,得到小型底栖生物的平均丰度及其优势类群线虫丰度冬季明显低于夏季,而生物量和类群多样性与夏季相当。同时,依据丰度指标对山东南部研究海域进行了初步的生态学划分,呈现出较明显的地域性。  相似文献   

Benthic nitrate biogeochemistry affected by tidal modulation of Submarine Groundwater Discharge (SGD) through a sandy beach face, Ria Formosa, Southwestern Iberia     

C. Rocha  J. Ibanhez  C. Leote   《Marine Chemistry》2009,115(1-2):43-58

To investigate both the role of tides on the timing and magnitude of Submarine Groundwater Discharge (SGD), and the effect on benthic nitrogen biogeochemistry of nitrate-enriched brackish water percolating upwards at the seepage face, we conducted a study of SGD rates measured simultaneously with seepage meters and mini-piezometers, combined with sets (n = 39) of high resolution in-situ porewater profiles describing NH₄⁺, NO₃⁻, Si(OH)₄ and salinity distribution with depth (0–20 cm). Sampling took place during two consecutive spring tidal cycles in four different months (November 2005, March, April and August 2006) at a backbarrier beach face in the Ria Formosa lagoon, southern Portugal. Our results show that the tide is one of the major agents controlling the timing and magnitude of SGD into the Ria Formosa. Intermittent pumping of brackish, nitrate-bearing water at the beach face through surface sediments changed both the magnitudes and depth distributions of porewater NH₄⁺ and NO₃⁻ concentrations. The most significant changes in nitrate and ammonium concentrations were observed in near-surface sediment horizons coinciding with increased fraction of N in benthic organic matter, as shown by the organic C:N ratio. On the basis of mass balance calculations executed on available benthic profiles, providing ratios of net Ammonium Production Rate (APR) to Nitrate Reduction Rate (NRR), coupled to stoichiometric calculations based on the composition of organic matter, potential pathways of nitrogen transformation were speculated upon. Although the seepage face occasionally contributes to reduce the groundwater-borne DIN loading of the lagoon, mass balance analysis suggests that a relatively high proportion of the SGD-borne nitrogen flowing into the lagoon may be enhanced by nitrification at the shallow (1–3 cm) subsurface and modulated by dissimilatory nitrate reduction to ammonium (DNRA).  相似文献   

A deep burrowing sipunculan of ecological and geochemical importance     

Mark A. Shields  Monika Kedra 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(11):2057-2064

In late 1980s, a dense network of deep capillary burrows was reported on the Vøring Plateau, Nordic Seas, and associated with a sipunculan belonging to the genus Nephasoma. This sipunculan was responsible for rapid transport of organic matter from the sediment surface down a deep burrow network. Over 460 specimens belonging to the genus Nephasoma were collected from the deep Nordic Seas during four cruises from 2000–2005 and four species identified: Nephasoma abyssorum abyssorum, N. diaphanes diaphanes, N. diaphanes corrugatum and N. lilljeborgi. The species responsible for the deep burrows and rapid subduction of organic matter can now be confirmed as Nephasoma lilljeborgi. Deep burrows associated with N. lilljeborgi were observed on the Vøring Plateau, Bear Island Fan, Svalbard Margin and Yermak Plateau and may be a seabed feature endemic to the Nordic Seas region. N. lilljeborgi could have a significant role in influencing the ecology and geochemistry of the Nordic Seas region. It is recommended that future benthic community studies in the Nordic Seas region confirm the species identity of sipunculan specimens in order to determine the ecological and geochemical importance of the specimens.  相似文献   

Benthic macrofauna and productivity regimes in the Barents Sea — Ecological implications in a changing Arctic     

Sabine K.J. Cochrane  Stanislav G. Denisenko  Paul E. Renaud  Christopher S. Emblow  William G. Ambrose Jr.  Ingrid H. Ellingsen  Jofrid Skarhamar 《Journal of Sea Research》2009,61(4):222-233

Benthic faunal assemblages were analysed from 47 stations in the central and southern parts of the Barents Sea, together with sedimentary and water column parameters, daily ice records and modelled integrated primary productivity. Sampling spanned areas influenced by Atlantic Water (AW) to those lying under Arctic Water (ArW), and included stations with mixed water masses. Ice cover suppressed water column productivity in the northern areas. Three main faunal groups were identified, based on similarity of numerical faunal composition. The northern and southern faunal groups were separated by the northernmost penetration of AW in the bottom water and the third group, the Hopen group, was influenced by modified bank water. Faunal abundances were significantly higher within the southern faunal group relative to the northern group, but the numbers of taxa present were similar. The particularly rich fauna of the Hopen group reflected sediment heterogeneity and tight pelagic–benthic coupling. These results suggest that a retreat and thinning of the ice cover in the Barents Sea likely will result in the northern parts of the Barents Sea becoming more Atlantic in character, with a higher productivity at the sea floor.  相似文献   

泥河湾盆地磁性地层定年与早期人类演化   总被引：26，自引：10，他引：16       下载免费PDF全文

朱日祥  邓成龙  潘永信 《第四纪研究》2007,27(6):922-944

主要评述了近年来泥河湾盆地磁性地层学的研究进展,包括建立泥河湾组的磁性地层年代格架、厘定泥河湾动物群的时代和确定华北地区早期人类活动年代序列.研究表明:第一,泥河湾组河湖相沉积序列记录了高斯正极性时末期以来的地磁极性特征(松山和布容极性时),即沉积时代始于约2.6Ma.早期人类至少在1.66～0.78Ma期间的大约90万年的时间内长期持续地占据高纬度的泥河湾盆地.泥河湾动物群(包括广义和狭义)的时代为2.0～0.8 Ma.第二,华北地区早期人类已经能够适应东亚高纬度地区冬季风增强、夏季风减弱和干旱化趋势增强的复杂环境变化,尤其能适应中更新世气候转型前后中国北方多变而且不稳定气候条件和生态环境.因此,气候和生态环境的多变性与不稳定性是促进人类进化的重要因素.第三,早期人类走出非洲以后,可能沿不同的路径并以较快的速度扩散到东亚地区.向南越过印度尼西亚的赤道地区,向北至少扩散到40°N的泥河湾盆地.  相似文献   

A New Vetulicolian from the Early Cambrian Chengjiang Fauna in Yunnan of China   总被引：7，自引：0，他引：7  

CHEN Ailin  FENG Hongzhen  ZHU Maoyan  MA Dongsheng  LI Ming Department of Earth Science  Nanjing University  Nanjing  Jiangsu  E-mail: feng.h@jlonline.com Nanjing Institute of Geology  Palaeontology  Chinese Academy of Sciences  Nanjing  Jiangsu Chenjiang Fauna National Geological Park  Chengjiang  Yunnan Wang Si''en  Xie Guanglian 《《地质学报》英文版》2003,77(3):281-287

The genus and species Yuyuanozoon magnificissimi gen. et sp. nov., a new fossil vetulicolian, is reported from the Early Cambrian Chengjiang Fauna in Yunnan of China. It has a bipartite body plan and five pairs of chain-formed gill sacs, showing the general characteristics of Ventulicolia. However, the exclusive "atrial cavity" and external gill observed indicate that the new form is different from those previously described as vetulicolians, probably representing a lineage developed within deuterostomes and more primitive than urochordates.  相似文献