首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
2001/2002年夏季南极普里兹湾及其邻近海域的浮游植物   总被引：15，自引：4，他引：15       下载免费PDF全文
报道了 2 0 0 1 /2 0 0 2年夏季南极普里兹湾邻近海域 3 7个大面测站浮游植物的调查结果。经初步鉴定共有浮游植物 3门 3 7属 86种 ,其中硅藻在种类和细胞丰度上占绝对优势 ,其次为甲藻。主要优势种为克格伦拟脆杆藻 (Fragilariopsiskerguelensis)、细条伪菱形藻 (Pseu do nitzschialineola)、短拟脆杆藻 (Fragilariopsiscurta)和赖氏束盒藻 (Trichotoxonreinboldii)等南极特有种类和常见种类。调查区浮游植物分为两个群集 ,分布在 6 7°S以南的普里兹湾内的群集主要以克格伦拟脆杆藻、短拟脆杆藻、胡克星脐藻 (Asteromphalushookeri)和南极弯角藻 (Eu campiaantarctica)等南极特有种类和常见种类为主 ;分布在 6 7°S以北的大洋海域的群集主要以细条伪菱形藻、赖氏束盒藻、拟膨胀伪菱形藻 (Pseudo nitzschiaturgiduloides)和羽状环毛藻(Corethronpennatum)等南极常见种为主。调查区浮游植物的平均细胞丰度为 (8796± 2 92 85 )ind/L ,细胞多分布于海水的表层 ,密集区分布在 6 7°S以南的普里兹湾内 ,浮游植物的细胞丰度同硝酸盐的浓度密切相关。调查区浮游植物的多样性程度是低的。  相似文献   

2.
2006年秋季长江口及其邻近水域浮游植物群集   总被引：1，自引：0，他引：1  
赵冉  孙军  白洁 《海洋科学》2010,34(4):32-39
根据2006年11月在长江口及其邻近水域(30°30′N～32°30′N,121°E～123°30′E)39个测站采集的浮游植物水样研究了该水域浮游植物群集特征。调查区浮游植物以硅藻和甲藻为主,此外还有少量的金藻、蓝藻和绿藻。浮游植物细胞丰度介于0.13～59.69个/mL之间,平均为4.39个/mL,主要优势物种为圆海链藻Thalassiosira rotula和骨条藻Skeletonema spp.,调查区两个细胞丰度密集区分别出现在靠近口门以及外海水域。浮游植物细胞在20m层出现最大值。调查区两个典型断面的浮游植物分布特征分别由骨条藻和圆海链藻所刻画。固氮蓝藻铁氏束毛藻Trichodesmium thiebautii主要出现在调查区东部水域表层。根据浮游植物物种和细胞丰度进行聚类分析后,发现存在调查区东部与近岸2个浮游植物分区。  相似文献   

3.
2001—2002年粤东柘林湾浮游动物的生态学研究   总被引：25，自引：3，他引：25  
2001年4月-2002年4月,利用生态学方法对粤东柘林湾浮游动物进行的周年调查结果表明,粤东柘林湾浮游动物有桡足类34属60种,枝角类3属3种,及端足类、磷虾、糠虾、多毛类、毛颚类、被囊类、水母和各种浮游幼体虫.浮游动物的群落构成小型化趋势明显,因为体长不足0.6 mm的小型优势种强额拟哲水蚤(Paracalanus crassirostris)、短角长腹剑水蚤(Oithona brevicornis)和鸟喙尖头(氵蚤)(Penilia avirostris)在浮游动物总个体数中所占比例合计高达57.1 %.浮游动物的种类数、总个体数和生物量的平面分布模式大体相似,即湾外大于湾内,外侧大于内侧,东部大于西部.总个体数与生物量的周年变化曲线与水温的变化趋势非常相似,高峰位于高温季节的8-9月,低谷位于冬季2月.调查期间柘林湾浮游动物非常丰富,年均总个体数达15.8×103 ind/m3,生物量达227.8mg*dW/m3.在单一调查年度内,浮游动物丰度与水温、浮游植物细胞数呈显著正相关关系.在不同年份,浮游动物丰度与浮游植物密度则表现为负相关的趋势.  相似文献   

4.
This study has determined the ways in which the density, number of species, species composition and trophic structure of free-living nematode assemblages in the subtidal waters of a large southern hemisphere microtidal estuary change spatially and seasonally, and has explored whether those four biotic characteristics are related to certain environmental factors. Based on data derived from samples collected seasonally at 12 sites throughout the estuary, the densities and number of species of nematodes decreased progressively with distance from estuary mouth, to reach a minimum at sites where salinities were most variable, and then increased slightly in the uppermost part of the estuary where salinities were least. Densities were also generally greatest in spring, due largely to increases in the abundance of epistrate-grazing species at this time and thus when the amount of primary food (microphytobenthos) peaked. The spatial distribution of the composition of the nematode assemblages was closely correlated with salinity and, to a lesser extent, grain-size composition and amount of particulate organic material (%POM) in the sediment. Although species composition changed sequentially along the estuary, the change was particularly pronounced between sites above and below the area where salinities started to decline markedly and become more variable and %POM increased markedly. This reflected, in particular, far greater abundances of Spirinia parasitifera at the six downstream sites and of Theristus sp. 1 at the six sites further upstream. Species composition underwent pronounced seasonal cyclical changes at all sites, presumably reflecting interspecific differences in the timing of peak reproduction and thus of recruitment. The trophic structure of the nematode assemblages changed both spatially and temporally in relation to the relative abundance of different food sources. Thus, for example, non-selective deposit feeders, such as Theristus sp. 1, dominated samples in the upper estuary, where %POM was by far the greatest, and was rare or absent at downstream sites. Conversely, epistrate grazers, such as species of the Chromadoridae, were most abundant at downstream sites in spring, when the density of the microphytobenthos reached its maximum.  相似文献   

5.
Surgeonfish and parrotfish play an important role in structuring the benthic communities of coral reefs. However, despite their importance, little is known about their distribution patterns in the north sector of the Mesoamerican Reef System. This study evaluated the distribution of these fish in 34 sites in four habitats (lagoon, front, slopes and terrace) along a depth gradient (c 0.5–20 m). These herbivorous fish were assessed by visual censuses. Species dominance was evaluated for each habitat using SIMPER analysis. Habitat characteristics data were collected to determine the relationship between habitat conditions and spatial variations in herbivorous fish (using abundance and biomass as a proxy) via redundancy analysis. The herbivorous fish assemblage had a low density (fish per 100 m2) and biomass (g·100 m?2) in comparison with assemblages in similar studies. In contrast, species richness was high compared with other studies in the Caribbean. Spatial variation of the abundance, biomass and size of herbivorous fish was strongly related to coral and seagrass cover, as well as to depth and rugosity. These four variables were critical in controlling the distribution patterns of the herbivorous fish assemblages. No associations were found between fish and macroalgae or any other benthic group. The present study indicates that the species richness of surgeonfish and parrotfish was not regionally affected by the dominance of macroalgae in the habitats studied. Seagrass beds and the coral reef matrix need to be preserved for the herbivorous fish assemblages to remain healthy and capable of controlling excess macroalgae growth.  相似文献   

6.
Sandy beach/surf‐zone ecosystems are unique environments that, despite the harsh and highly variable hydrodynamic conditions, present a diverse and heterogeneous fauna. However, the dynamics of these ecosystems are currently poorly understood. In this study we tested the hypothesis that surf‐zone assemblages vary with temporal factors such as time of day, tide and tidal height. To test this hypothesis, the surf‐zone community of Bastendorff, a Southern Oregon sandy beach was sampled during the summer of 2006. Samples were collected to (i) describe the smaller, benthic and larger swimming assemblages, (ii) determine whether assemblage compositions, densities, species richness and diversity vary with time of day, tide and tidal height, (iii) explore potential reasons for the variation by correlating environmental factors to the assemblages, and (iv) identify particular species that most strongly exhibit these variations. A hyperbenthic sledge, a sediment corer and a beach seine were used to collect the smaller swimming, benthic and larger swimming fauna, respectively. Sampling occurred during day and night, spring and neap tide, and high, mid and low tide. A total of 76,743 individuals belonging to 105 species were collected. Ninety‐one invertebrate (72,904 individuals), 15 invertebrates (2234 individuals), and 19 invertebrate and vertebrate species (1605 individuals) were collected with the sledge, corer and seine, respectively. Nine species of fish were caught, 98% of which were juveniles. The smaller and larger swimming assemblages varied most strongly with the time of day, suggesting certain species will actively move to the shallow surf‐zone at night. The three assemblages also varied with the tide, potentially due to the larger waves and higher abundance of detached macrophytes observed during spring tides when compared to neap tides, which could push individuals into the surf zone. The benthic assemblage most strongly varied with tidal height and sand grain size, confirming the presence of different faunal zones within Oregon sandy beaches. Finally, several variables of the swimming assemblages varied with temperature and salinity, suggesting that downwelling favorable conditions may have transported species close to shore. Bastendorff presents a complex and diverse surf‐zone community that appears to be influenced by diel species movements, environmental variables such as wave height and abundance of detached macrophytes, and regional oceanographic conditions.  相似文献   

7.
通过1999年和2010年夏季同期7月在白令海(169°E~166°W,50°N~67°N)获取的94份浮游植物样品分析,获得了近十年的始末两个时间节点的浮游植物群落结构与时空变化,探讨了浮游植物群落动态及其与环境因素的关联。研究结果显示,共鉴定浮游植物(>10μm)5门58属153种,分为3个生态类群。硅藻是浮游植物的主体,种类多丰度高,占总种类数目的66.7%,占总丰度的95.2%。鉴于样品属性和空间范围的不同,物种组成有细微差别,丰度有较大差异且空间分布明显不同,高丰度区受控于上层营养盐供给和表层环流系统。优势种从北方温带大洋性硅藻演变为广温广盐性与冷水性硅藻,1999年以西氏新细齿状藻为第一优势种,柔弱伪菱形藻次之;2010年以丹麦细柱藻为第一优势种,冷水性的诺登海链藻次之并在陆架和陆坡占优。浮游植物群落结构较为稳定,由深水群落和浅水群落组成。深水群落分布于太平洋西北部和白令海盆,种类组成以温带大洋性的西氏新细齿状藻、长海毛藻、大西洋角毛藻和广布性的菱形海线藻、扁面角毛藻、笔尖根管藻为主,丰度低,种间丰度分配均匀,优势种多元化,物种多样性高;浅水群落分布于白令海陆坡和陆架,主要由冷水性的诺登海链藻、叉尖角毛藻、聚生角毛藻和广布性的丹麦细柱藻、旋链角毛藻组成,丰度高,种间丰度分配不均匀,优势种突出,物种多样性低。白令海夏季浮游植物种类组成及丰度变化直接受控于表层环流、营养盐、春季冰缘线等环境因素。  相似文献   

8.
本研究依据2006—2007年与2016—2017年各个季节在厦门海域采样获得的蟹类样品数据,对比分析了其种类组成、资源密度及其多样性指数。结果表明：厦门海域蟹类的种类组成有较大变化,种类更替率为55.32%,伴随着在两次调查中扇蟹科、方蟹科和关公蟹科等物种的新出现及梭子蟹科和长脚蟹科物种的消失,同时蟹类丰度(d)有所减少;均匀度(J)、种类多样性指数(H′)和资源密度变化较小;蟹类的群落结构变得更单一,容易遭到破坏;研究期间拟穴青蟹(Scylla paramamosain)资源出现一定程度的恢复,蟹类资源的平均个体质量有所增加,其中秋季蟹类个数密度增长较为明显。本研究建议在保证严格禁渔等管理的同时,加强对其海洋栖息地的管理和恢复。  相似文献   

9.
The northern Pacific seastar, Asterias amurensis, was first collected in southeast Tasmania in 1986. Mistaken for the endemic asteroid Uniophora granifera, its true identity was not realised until 1992. It is now a conspicuous predator in soft sediment habitats in this region, and is considered a major threat to native assemblages and commercial species. We examined the structure of soft sediment assemblages at different spatial scales in southeast Tasmania, and correlated spatial variation in community composition with seastar abundances. We found that the structure of soft sediment assemblages is highly variable at a range of spatial scales from metres to tens of kilometres. Clear differences in the composition of assemblages and abundances of major taxa were detected between areas with and without seastars and between areas with low and high seastar densities. However, the nature of these patterns suggests that they are more likely due to differences in sediment characteristics than due to impacts of the seastar. Thus, spatial differences in soft sediment assemblages might have been erroneously attributed to seastars without detailed information on important physical factors such as sediment characteristics. A second survey, using larger sampling units (1 m2) but across a more limited spatial extent, targeted bivalves and heart urchins that were identified as important prey of the seastar in observations of feeding and in experimental studies. Large-scale patterns of abundance and size structure were consistent with seastar effects anticipated from small-scale experimental and feeding studies for some, but not all, species. While the field survey ultimately provided evidence about the presence or absence of seastar impacts at large-scales, the identification of key ecological variables in experimental and feeding studies proved crucial to both the design and interpretation of patterns observed in the large-scale surveys. Overall, this work highlighted the necessity to consider multiple lines of evidence rather than relying on a single ‘inferential’ test, in the absence of pre-impact data.  相似文献   

10.
The effect of environmental variables on the vertical structure of larval fish assemblages in a tropical coastal lagoon was analyzed. Ichthyoplankton samples were collected from the near-bottom and surface strata near the mouth of a subtropical lagoon during contrasting seasonal conditions of temperature, photoperiod, light intensity, and tidal heights. During summer, larval fish assemblages had high species richness (R) and were dominated by tropical species. During winter, assemblages had lower R values and were dominated by subtropical and temperate species. Vertical distribution patterns of the taxa were determined by the interaction of environmental variables and behavior of each species to maintain their position in a stratum in the water column, or to achieve vertical migrations induced by environmental stimuli that, in this case, were thermal gradient, column water stratification, and intensity of light. Depth position and vertical migration of fish larvae, coupled with the flood and ebb tide conditions, played an important role in their retention and displacement toward the lagoon. Fish larvae with distribution restricted to the inner part of the inlet, such as Achirus mazatlanus, Etropus sp., and several gobies, were more abundant in the near-bottom stratum during the ebb tide, allowing them to avoid exportation, whereas those that could spawn outside, but depended on the inlet as a nursery area, were more abundant near the surface during flood tide, such as Abudefduf troschelii and Stegastes rectifraenum.  相似文献   

11.
The purpose of this paper was to study the community structure, in terms of species composition, abundance and spatial distribution, of fish larvae in a wide coastal area of Sicily facing the Southeastern Tyrrhenian Sea, extending for 2300 km2 from Cape Cefalù to the west, to Cape Rasocolmo in the east. This study analyses how species are assembled in relation to an inshore–offshore gradient and also how environmental conditions, determined by surface circulation patterns occurring in the Central Mediterranean at the local scale, determine the distribution patterns. Samples from 39 stations were collected using a 60‐cm Bongo net during an ichthyoplanktonic survey carried out in June 2006. In all, 62 taxa, representing 32 families, were identified. Cyclothone braueri (59.6%), Engraulis encrasicolus (9.2%) Lampanyctus crocodilus (4.3%) and Lampanyctus pusillus (4.1%) were the most abundant species. The results showed that the highest abundance value (14830.6 fish larvae per 10 m2 sea surface) was observed in the western part of the study area. MDS, SIMPER and CCA analyses revealed well defined groups of stations and assemblages of larvae in accordance with an inshore–offshore gradient. The results of this study could have implications for the management of marine resources because the investigated area has already been identified as a nursery area for many pelagic and coastal fishes and a natural habitat for many species of high commercial interest.  相似文献   

12.
Epifaunal invertebrate species, such as amphipods and isopods, have been shown to play key but varying roles in the functioning of seagrass habitats. In this study, we characterized patterns in the poorly known epifaunal communities in eelgrass (Zostera marina) beds in San Francisco Bay as a first step in understanding the individual and collective importance of these species, while testing predictions on spatial patterns derived from previous studies in other regions. Surveys conducted at five beds across multiple time periods (April, June, August and October 2007) showed that San Francisco Bay eelgrass beds varied strongly in epifaunal community composition, total, and relative abundance, and that abundance differed markedly among time periods. In contrast to findings by others, morphologically complex flowering shoots frequently harbored greater numbers of epifauna (>2× and up to 10× more individuals) than vegetative shoots, but not different species assemblages. Similar to previous studies, several abiotic factors did not explain patterns in distribution and abundance among beds. The proportion of introduced species was very high (>90% of all individuals), a finding unique among seagrass epifaunal studies to date. Defining numerical patterns in epifaunal communities will inform related efforts to understand effects of epifaunal species and assemblages on eelgrass growth dynamics, seed production, and higher order trophic interactions over space and time.  相似文献   

13.
Environmental variables have been measured and sampling for ichthyoplankton has been conducted monthly, since April 2001, at three stations, located at the inner (1), middle (2) and outer (3) shelf of the central Cantabrian Sea. This paper presents the results of the study of the ichthyoplankton collected from July 2001 to June 2004. Fish larvae from 99 species, belonging to 37 families, were identified. Families with higher number of species were Gadidae, Sparidae and Labridae. The larval fish assemblage was dominated by pelagic fish species, with Sardina pilchardus, as the most abundant. There was a pronounced spring peak in larval abundance, dominated by S. pilchardus. A smaller peak, dominated by S. pilchardus and Micromesistius poutassou, was recorded in late winter at Stns 2 and 3. This pattern was evident for the three-year study. Results also indicate that this study was limited to the coastal larval fish assemblage inhabiting the central Cantabrian Sea shelf. This assemblage was temporally structured into other three assemblages: winter, late winter–spring and summer–autumn. Temperature was apparently a key factor in larval fish assemblage succession. In a scenario of global warming, this study constitutes a basis to evaluating the ongoing changes in the pelagic coastal ecosystem of the central Cantabrian Sea.  相似文献   

14.
通过对中国第1~4次北极考察在西北冰洋采集的表层沉积物中底栖有孔虫丰度及其优势种分布特征与环境因素关系的综合研究发现,楚科奇海区低的底栖有孔虫丰度主要受较高的陆源物质输入的稀释作用影响;楚科奇海台和阿尔法脊较高的底栖有孔虫丰度主要受到暖而咸的大西洋中层水的影响;受碳酸钙溶解作用影响的门捷列夫深海平原和加拿大海盆底栖有孔虫丰度较低,并且水深3 597 m的站位出现了似瓷质壳的Pyrgo williamsoni和Quinqueloculina orientalis,说明该区的CCD深度大于3 600 m。根据底栖有孔虫7个优势属种的百分含量分布特征可以划分出5个区域组合:南楚科奇海陆架-白令海峡组合以优势种Elphidium excavatum和Buccella frigida为特征,可能反映受白令海陆架水影响的浅水环境;阿拉斯加沿岸-波弗特海组合以优势种Florilus scaphus和Elphidium albiumbilicatum为特征,可能反映受季节性海冰融化,低盐的阿拉斯加沿岸流以及河流淡水输入的低盐环境;大西洋中层水组合以优势种Cassidulina laevigata为特征,可能反映高温高盐的大西洋中层水影响的环境;北极深层水组合以优势种Cibicides wuellerstorfi为特征,可能反映水深大于1 500 m低温高盐的北极深层水环境;门捷列夫深海平原组合以优势种Oridorsalis umbonatus为特征,可能反映低营养的底层水环境。  相似文献   

15.
This study examines species composition and abundance of appendicularians in the northwestern coastal waters of South China Sea based on in situ data obtained by 169 μm planktonic nets during summer and winter, and discusses the influence of environmental factors on their distribution and assemblages. A total of 19 appendicularian species (including one unidentified species) was collected. Species richness is higher in summer than in winter, and it increases from inshore to offshore waters. Average abundance of appendicularians is 103.1 (±198.1) and 54.6 (±111.1) ind. m−3 in summer and winter, respectively. The abundance distribution of appendicularians is generally high around inshore waters during summer and winter, and with a higher abundance assemblage along the eastern coast from Leizhou Peninsula to Hainan Island, especially at the eastern mouth of Qiongzhou Strait in summer. Oikopleurids accounted for 97.5% and 99.6% of total appendicularians abundance in summer and winter, and the region of high values was the same to that of total appendicularians abundance. Oikopleura longicauda, Oikopleura rufescens, and Oikopleura fusiformis are dominant species during summer and winter. Results showed that spatial distribution of species richness of appendicularians is considered to be the result of physical factors such as temperature and salinity in summer and winter, while variations in abundance of appendicularians are affected by the combination of physical and biological factors. In particular, variations of appendicularians abundance are affected by food availability in summer.  相似文献   

16.
Macroalgae are useful organisms to monitor the environmental quality and to detect impacts due to anthropogenic activities. However, it is very important to identify the scales of variation in natural assemblages, particularly for the detection of environmental impacts. Otherwise, changes due to anthropogenic impacts may be confused with differences due to natural temporal variability. Another important task is to determine the appropriate level of taxonomical effort needed to detect changes in the assemblage structure. Many taxonomical surrogates, at higher taxonomic levels than that of species, have been proposed but, the consistence in space and time of the results produced by surrogates with those obtained at specific level should be tested. The objectives of this study are to identify the seasonal patterns of tidepool macroalgal communities using objective procedures and to test the consistence between the patterns obtained considering data at the species level and functional groups. Results showed that the seasonal pattern obtained using functional groups and species was consistent. Tidepool macroalgal assemblages showed a seasonal pattern with significant differences between spring–summer and autumn–winter. This pattern can be explained by changes in environmental variables and the seasonal development of the dominating species. Ulva spp. and the non-indigenous species Grateloupia turuturu were the species responsible for this pattern due to their high seasonality in terms of biomass. Finally, the abundance and species diversity within the corticated functional group was proposed as indicator of environmental impacts due to its relatively constant abundance and its sensitivity to environmental impacts.  相似文献   

17.
This study compares the fish assemblages of the permanently open cool-temperate Olifants and warm-temperate Breede estuaries on the west and south coasts of South Africa respectively, and their responses to altered freshwater flows. Both estuaries have experienced a >35% reduction in mean annual runoff (MAR) from a historical reference condition to the present day with a >60% reduction possible under future flow scenarios. With the exception of species that have both marine and estuarine breeding populations, the Olifants Estuary fish assemblage has experienced an overall 20% decrease in abundance from reference (pristine state) to the present day and will gradually decline to 55% of reference with a predicted future 60% reduction in MAR. Consequently, future reductions in flow are likely to result in the Olifants Estuary progressing towards a low biomass, low diversity, marine-dominated system. In contrast, reduced freshwater flows in the Breede Estuary are likely to experience an overall reduction in the abundance of species that breed only in estuaries, and in freshwater and catadromous species. Collectively, entirely estuarine-dependent fish will increase in abundance, but considered individually some important exploited species such as Argyrosomus japonicus and Pomadasys commersonnii will collapse to 50% of historical numbers once there has been a 64% reduction in MAR. Overall, fish abundance in the estuary has increased by 6% from reference to the present day and is likely to increase to 115% of reference with future reductions in flow. Some species with a preference for fresh and brackish water will be all but lost from the system, but overall diversity is likely to increase with the range expansion of warm-temperate and subtropical marine species westward. In all, the fish assemblage of the Breede Estuary will experience a gradual change from a relatively high-diversity, low-abundance, freshwater rich system under historical flow conditions to a high diversity, high-abundance, marine-dominated system with future reductions in flow.  相似文献   

18.
The ecology and diversity of the shallow soft‐bottom areas adjacent to coral reefs are still poorly known. To date, the few studies conducted in these habitats dealing with macroinvertebrate fauna have focused on their abundance spatial patterns at high taxonomic levels. Thus, some aspects important to evaluate the importance and vulnerability of these habitats, such as species diversity or the degree of habitat specialization, have often been overlooked. In this study we compared the crustacean assemblages present in four different habitats at Magoodhoo Island coral reef lagoon (Maldives): coral rubble, sandy areas and two different seagrass species (Thalassia hemprichii and Cymodocea sp.). Forty‐two different crustacean species belonging to 30 families and four orders were found. ‘Site’ was a significant factor in all of the statistical analyses, indicating that tropical soft‐bottom habitats can be highly heterogeneous, even at a spatial scale between tens and hundreds of meters. Although traditionally it has been considered that seagrass beds host greater species diversity and abundance of organisms than adjacent unvegetated habitats, no differences in the univariate measures of fauna (abundance of organisms, number of species and Shannon diversity) were observed among habitats. However, sandy areas, coral rubble and seagrass beds exhibited different species composition of crustacean communities. The percentage of taxa considered as potential habitat specialists was 27% and the number of species exclusively occurring in one habitat was especially high in seagrass beds. Thus, degradation of this vegetated habitat would result in a great loss of biodiversity in tropical shallow soft‐bottom habitats.  相似文献   

19.
Abstract. A two year benthic sampling program of a 2000 km2 area, covering 22 stations, showed a dominance of deposit-feeding polychaetes. The quantitative structure of the three infaunal assemblages was related to a salinity gradient: the inner and outer regions were inhabited by, respectively, mixohaline and euhaline associations, both quantitatively related to granulometric facies of sediment. Species diversity was very low in the inner region, although abundance of opportunistic species was high. In the outer region, abundance and diversity were more stable, with an increasing number of species. A comparison of species number and abundance with Species-Abundance-Biomass curves from enriched environments showed that the inner region of Bianca Bay may be considered as an organically enriched environment. Scoloplos, a species associated with organic enrichment, and dense terebellid belts were present in great abundances in front of sewage outflows. The spatial distribution of heterotrophic bacteria and the bivalves Corbula and Nucula also followed this pattern.  相似文献   

20.
We studied diatom assemblages and CaCO3 contents of methane-derived authigenic carbonates from the eastern margin of the Sea of Japan and assessed the formation time of these samples. Radioactive 14C date was determined in selected samples to obtain the maximum age of the time. The results of our study suggest mass formation of carbonate nodules in a glacial period within ∼40 ky, consistent with a published U/Th dating result of carbonate nodules in the study area. Diatom assemblages and contents in the carbonate nodules (abundance of ∼106/g, dominance of neritic-littoral species, warm/cold water species ratio lower than ∼25) differ from the near-seafloor sediments in the study area, which have characteristics of Holocene sediments in the Sea of Japan, and suggest cementation of glacial sediments. Laminated sediments in some nodule samples are glacial sediments because laminations are records of a low sea level period in the semi-enclosed ocean. Similarity of diatom assemblages and contents in all carbonate samples is another evidence of glacial sediments in nodules. Glacial sediments with oceanic cold water species as low as Holocene sediments restricts the sediment age to before 20 cal. ky BP. Carbonate contents higher than 78 wt% suggest the cementation of poorly compacted sediments near the seafloor, and the date of carbonate cementation is, therefore, close to that of the cemented sediments. Most carbonate nodule samples in this study were formed in a glacial period and detection of 14C restricts this period to within ∼40 ky.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号