Ecological succession, palaeoenvironmental change, and depositional sequences of Barremian–Aptian shallow-water carbonates in northern Oman     

Bernard Pittet  Frans S. P. Van Buchem  Heiko Hillgärtner  Philippe Razin†  Jürgen Grötsch‡  Henk Droste§ 《Sedimentology》2002,49(3):555-581

Abstract Barremian and Aptian shallow‐water carbonate facies (uppermost Lekhwair, Kharaib and Shuaiba Formations) are described from outcrops in northern Oman. Based on facies analysis and bedding pattern, three orders of depositional sequences are defined (third to fifth order) and correlated between sections. Over the course of three third‐order sequences, covering the Barremian to Lower Aptian, a third‐order depositional pattern is documented that consists of a succession of three distinct faunal assemblages: discoidal orbitolinids and calcareous algae were deposited during early transgression; microbialites and microencrusters dominate the late transgressive to early highstand facies; and a rudist‐ and miliolid‐dominated facies is typical of the highstand. This ecological succession was controlled largely by palaeoenvironmental changes, such as trophic level and clay influx, rather than sedimentological factors controlled by variations in accommodation space. Orbitolinid beds and carbonates formed by microbialites and microencrusters seem to be the shallow‐water carbonate response to global changes affecting Late Barremian to Aptian palaeoclimate and palaeoceanography.  相似文献   

Importance of diffuse nutrient loading and lake level changes to the eutrophication of an originally oligotrophic boreal lake: a palaeolimnological diatom and chironomid analysis     

Jarmo J. Meriläinen  Juhani Hynynen  Arja Palomäki  Pasi Reinikainen  Anssi Teppo  Kaj Granberg 《Journal of Paleolimnology》2000,24(3):251-270

The recent environmental history of Lake Lappajärvi in western Finland (63°00 N, 23°30 E, area 149 km²), a humic, brown water lake with an average phosphorus content of ca. 20 g l^–1, was studied from short core sediment samples taken from the two main basins of the lake. Based on the stratigraphy of diatoms and chironomids and the sediment quality it was possible to distinguish four developmental stages during the past century: (1) a pre-industrial stage covering the time up to about 1935; (2) a stage of increasing nutrient loading (ca. 1936–1960); (3) a stage of pronounced erosion from lake level regulation and extensive ditching of the catchment area (ca. 1960–1970); and (4) a meso-eutrophic stage from ca. 1970 onwards.Acidophilous Aulacoseira distans coll. and other species typical of dystrophic, nutrient-poor lakes characterized the diatom assemblages during the first stage, and the profundal zoobenthic assemblages, characterized by Heterotrissocladius subpilosus and Micropsectra, indicated good hypolimnetic oxygen conditions and a low sedimentation of organic matter (approx. less than 50 g m^–2 a^–1). The increased loading rapidly led to changes both in diatoms and chironomids (e.g., to an early extinction of H. subpilosus in the 1950s). The process finally led to eutrophication with a successive proliferation of diatom species such as Asterionella formosa followed by Aulacoseira ambigua, Fragilaria crotonensis, and finally Melosira varians. The relative proportion of alkaliphilous species reached a maximum in the final stage and the original profundal chironomid fauna was replaced by Chironomus anthracinus gr. and C. plumosus which are typical of profundal areas suffering from temporal oxygen deficit. It is notable that the considerable decrease in waste water loading from the point sources (80–86% ) during the past two decades has not led to a recovery in the lake. This highlights the importance of diffuse loading from agriculture, forestry and other human activities even to this comparatively large lake.  相似文献   

Small pelagics in upwelling systems: patterns of interaction and structural changes in "wasp-waist" ecosystems     

Cury  Philippe; Bakun  Andrew; Crawford  Robert J. M.; Jarre  Astrid; Quinones  Renato A.; Shannon  Lynne J.; Verheye  Hans M. 《ICES Journal of Marine Science》2000,57(3):603-618

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Abundance, Biomass, Production and Trophic Roles of Micro- and Net-Zooplankton in Ise Bay, Central Japan, in Winter     

Shin-Ichi Uye  Naoki Nagano  Tetsuya Shimazu 《Journal of Oceanography》2000,56(4):389-398

We investigated the geographical variations in abundance and biomass of the major taxonomic groups of micro- and net-zooplankton along a transect through Ise Bay, central Japan, and neighboring Pacific Ocean in February 1995. The results were used to estimate their secondary and tertiary production rates and assess their trophic roles in this eutrophic embayment in winter. Ise Bay nourished a much higher biomass of both micro- and net-zooplankton (mean: 3.79 and 13.9 mg C m^–3, respectively) than the offshore area (mean: 0.76 and 4.47 mg C m^–3, respectively). In the bay, tintinnid ciliates, naked ciliates and copepod nauplii accounted for, on average, 69, 18 and 13% of the microzooplankton biomass, respectively. Of net-zooplankton biomass, copepods (i.e. Acartia, Calanus, Centropages, Microsetella and Paracalanus) formed the majority (mean: 63%). Average secondary production rates of micro- and net-zooplankton in the bay were 1.19 and 1.87 mg C m^–3d^–1 (or 23.1 and 36.4 mg C m^–2d^–1), respectively, and average tertiary production rate of net-zooplankton was 0.75 mg C m^–3d^–1 (or 14.6 mg C m^–2d^–1). Available data approximated average phytoplankton primary production rate as 1000 mg C m^–2d^–1 during our study period. The transfer efficiency from primary production to zooplankton secondary production was 6.0%, and the efficiency from secondary production to tertiary production was 25%. The amount of food required to support the zooplankton secondary production corresponded to 18% of the phytoplankton primary production or only 1.7% of the phytoplankton biomass, demonstrating that the grazing impact of herbivorous zooplankton was minor in Ise Bay in winter.  相似文献   

Predatory impact of an epiphytic hydrozoan in an upwelling area in the Bay of Coliumo (Dichato, Chile)     

C. Orejas  J. -M. Gili  V. Alv  W. Arntz 《Journal of Sea Research》2000,44(3-4)

The natural diet of the epiphytic hydrozoan Obelia geniculata has been studied in an upwelling area in the Bay of Coliumo (Dichato, Chile) during two 24-h cycles. Number of prey per predator and predatory density have been measured. In both cycles more than 78% of the diet consisted of eggs of invertebrates and faecal pellets. Compared with other species of hydrozoans studied in a similar way, O. geniculata had a heterogeneous diet and a capture rate which was scarcely related to the peaks of abundance of its prey. This catch rate was between 632×10³ and 10 393×10³ prey m⁻² day⁻¹, which corresponds to a mean ingestion rate of 113% of the hydranth biomass per day. These results indicate the importance of small-sized benthic suspension feeders in upwelling systems.  相似文献   

渤、黄、东海高营养层次重要生物资源种类的营养级研究   总被引：47，自引：0，他引：47  

张波  唐启升 《海洋科学进展》2004,22(4):393-404

利用2000年和2001年2次大面调查所收集的11970个胃含物样品分析结果,计算了黄海和东海生态系统高营养层次35个重要生物资源种类的营养级,同时,结合对渤海和黄海39个种类营养级历史数据的修正,讨论研究了我国海洋高营养层次生物资源种类营养级的研究策略和计算方法。主要研究结果为：(1)渤海重要生物资源种类营养级的变化范围为3．12～4．9,黄海为3．2～4．9,东海为3．29～4．55。近年来各海域高营养层次的营养级呈下降趋势,如渤海从1959年的4．1下降到1998～1999年的3．4,黄海从1985～1986年的3．7下降到2000～2001年的3．4;(2)高营养层次营养级波动主要是由于群落种类组成变化及单种类营养级年间波动引起的,而单种类营养级年间波动又直接与群体个体变小以及摄食食物的低营养层次化有关。因此,高营养层次的营养级变化是认识海洋生态系统生物生产动态的重要指标,需要对其进行长期和系统的监测;(3)建议在今后的研究中,根据简化食物网的概念,对占生物量绝对多数的重要生物资源种类的营养级进行重点研究并采用国际通用的标准划分计算营养级。  相似文献   

南海大眼金枪鱼(Thunnus obesus)摄食生态研究     

李波  阳秀芬  王锦溪  易木荣  何雄波  陶雅晋  冯波  颜云榕 《海洋与湖沼》2019,50(2):336-346

根据2011年12月—2013年2月于我国南海海域采用金枪鱼延绳钓以及灯光罩网调查捕获的大眼金枪鱼(Thunnusobesus)的各项基础生物学以及胃含物的数据,对其摄食生态进行了分析研究。结果表明:(1)南海海域大眼金枪鱼的食物组成包括鸢乌贼、帆蜥鱼、金色小沙丁鱼、飞鱼、竹荚鱼、鲐鱼、小公鱼属、圆鲹属以及不可辨别的鱼类与虾类,其主要饵料生物为鸢乌贼(%IRI=45.21),其次为金色小沙丁鱼(%IRI=21.36)和帆蜥鱼(%IRI=13.72);(2)空胃率与平均饱满指数随季节变化明显,空胃率在春季时会达到顶峰(37.9%),秋季时最低(16.7%),呈先下降后上升趋势,同时平均饱满指数也在春季达到最高值(0.33),随季节下降并稳定于0.1,空胃率随性腺成熟度的提高有明显上升趋势,平均饱满度指数在性成熟度Ⅰ期与Ⅵ期均呈现高值(1.18、1.04);(3) Shannon-Weiner多样性指数H′和Pielou均匀度指数J随季节变化呈现出明显的变化,Shannon-Weiner多样性指数H′随叉长组基本在1.52—1.72之间变化, Pielou均匀度指数J随性腺成熟度的提高有逐步下降的趋势;(4)营养长度(NR)较高,说明其摄食的饵料成分多、氮来源较复杂,基础食物来源(CR)和生态位总空间(TA)的冬季指标值近乎夏季指标的两倍;通过δ15N稳定同位素法计算大眼金枪鱼的平均营养级为4.73。总体上,南海海域大眼金枪鱼主要以头足类和鱼类为食,其摄食习性与季节和个体发育相关,在食物链中处于较高营养位置。  相似文献   

New insights on the trophic ecology of bathyal communities from the methane seep area off Concepción,Chile (~36° S)     

Germán Zapata‐Hernández  Javier Sellanes  Andrew R. Thurber  Lisa A. Levin  Frédéric Chazalon  Peter Linke 《Marine Ecology》2014,35(1):1-21

Studies of the trophic structure in methane‐seep habitats provide insight into the ecological function of deep‐sea ecosystems. Methane seep biota on the Chilean margin likely represent a novel biogeographic province; however, little is known about the ecology of the seep fauna and particularly their trophic support. The present study, using natural abundance stable isotopes, reveals a complex trophic structure among heterotrophic consumers, with four trophic levels supported by a diversity of food sources at a methane seep area off Concepción, Chile (~36° S). Although methanotrophy, thiotrophy and phototrophy are all identified as carbon fixation mechanisms fueling the food web within this area, most of the analysed species (87.5%) incorporate carbon derived from photosynthesis and a smaller number (12%) use carbon derived from chemosynthesis. Methane‐derived carbon (MDC) incorporation was documented in 22 taxa, including sipunculids, gastropods, polychaetes and echinoderms. In addition, wide trophic niches were detected in suspension‐feeding and deposit‐feeding taxa, possibly associated with the use of organic matter in different stages of degradation (e.g. from fresh to refractory). Estimates of Bayesian standard ellipses area (SEA_B) reveal different isotopic niche breadth in the predator fishes, the Patagonian toothfish Dissostichus eleginoides and the combtooth dogfish Centroscyllium nigrum, suggesting generalist versus specialist feeding behaviors, respectively. Top predators in the ecosystem were the Patagonian toothfish D. eleginoides and the dusky cat shark, Bythaelurus canescens. The blue hake Antimora rostrata also provides a trophic link between the benthic and pelagic systems, with a diet based primarily on pelagic‐derived carrion. These findings can inform accurate ecosystem models, which are critical for effective management and conservation of methane seep and adjacent deep‐sea habitats in the Southeastern Pacific.  相似文献   

The characteristics of the nematode faunas in subtidal sediments of a large microtidal estuary and nearshore coastal waters differ markedly   总被引：1，自引：0，他引：1  

M. Hourston  I.C. PotterR.M. Warwick  F.J. Valesini 《Estuarine, Coastal and Shelf Science》2011,94(1):68-76

The present study examines traditional paradigms regarding the differences between faunas in estuaries vs coastal waters. The ecological characteristics of the free-living nematode faunas of nearshore, subtidal sediments in downstream and upstream areas of the large, microtidal Swan River Estuary are compared with those similarly recorded seasonally in subtidal sediments along an adjacent part of the coast of temperate south-western Australia. Overall, the nematode species richness recorded in the upstream (38) and downstream estuarine areas (58) and from throughout the estuary (61) were substantially less than in marine waters (75). In addition, the value for Simpson’s diversity index was marginally less in the estuary and the dominance of the most abundant species greater. In contrast, the mean nematode species richness and diversity in individual cores followed the reverse trend, reflecting a combination of less variability among the species compositions and far greater densities in the cores from estuarine sediments. Furthermore, the mean density (numbers 10 cm⁻²) was far higher in both upstream (341) and downstream (903) areas of the estuary than in marine waters (87). Although the compositions of the assemblages in upstream and downstream estuarine areas differed markedly from each other at the species, genus and family levels, these differences were less pronounced than those between either of these areas and marine waters. The trophic compositions at the moderately sheltered and fully exposed marine sites differed from that in both areas of the estuary, whereas that at the most sheltered marine site was similar to that in the downstream estuarine area, with both containing substantial proportions of epistrate-grazing species. The variations among the species richness, diversity, densities and taxonomic and trophic compositions of nematode assemblages in the sediments of the two estuarine areas and nearby marine waters appear to reflect differences in 1) salinity regimes, 2) extents of exposure to wave action and its related effects and 3) amounts and types of food available to nematodes.  相似文献   

Assessment of benthic trophic status of marine coastal ecosystems: Significance of meiofaunal rare taxa     

Antonio Pusceddu  Silvia BianchelliCristina Gambi  Roberto Danovaro 《Estuarine, Coastal and Shelf Science》2011

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