Distribution and germination of viable diatom resting stage cells in sediments of the East China Sea

The abundance and temporal patterns of viable diatom resting stage cells in sediments of the East China Sea in 2006 have been investigated. The abundance of viable resting stages was enumerated with the most probable number (MPN) technique. Overall, 25 diatom species (including varieties) belonging to 16 genera were detected. Viable resting stage cells were common, on the order of 10³ to 10⁶ cells/g dry mass. The abundant taxa included Skeletonema marina, S. dohrnii, Chaetoceros curvisetus and Thalassiosira spp., with Skeletonema accounting for 83.3% of the cell. The effects of temperature (10, 15, 20, 25℃), salinity (20, 25, 30, 35 psu) and light intensity (0, 300, 4 000, 8 000 lux) on the germination of resting stages in sediment samples were also determined. The results showed that light intensity had a significant positive effect on the germination of diatom resting stage cells (p <0.01) and that diatoms could not germinate in darkness. Temperature and salinity had no noticeable effects on the germination. The present study suggests that there are abundant diatom resting cells in sediments of the East China Sea, which could serve as a "seed bank" in the phytoplankton population succession and contribute to the initiation of algal blooms.     

大亚湾大鹏澳海域表层沉积物中浮游植物休眠体集群的季节变化

于2007年4月至2008年3月对大亚湾大鹏澳海域表层沉积物中浮游植物休眠体进行了每月1次的周年调查.本调查分析鉴定出浮游植物休眠体79种,包括甲藻孢囊50种,硅藻休眠体26种.浮游植物休眠体丰度没有明显的季节变化规律,变化范围为217～6 764 cells/cm3,平均为1 376 cells/cm3;鱼类养殖区休眠体丰度较高,平均丰度为1 999 cells/cm3.浮游植物休眠体在数量上以硅藻为主,甲藻次之,而在鱼类养殖区也出现了较高的蓝藻休眠体.硅藻休眠体的平均丰度为783 cells/cm3,百分比含量为56.9%,从而反映了该海域硅藻型浮游植物群落结构.甲藻孢囊丰度的变化范围在79～1 237 cells/cm3,位于湾口对照区丰度较高,年平均为733 cells/cm3,而鱼类养殖区和贝类养殖区平均值分别为502、388 cells/cm3.异养型甲藻孢囊的种类和数量均比较丰富,其百分比含量为26.7%～82.4%.研究结果显示,在富营养化程度较高的养殖区海域,硅藻休眠体和异养型甲藻孢囊百分率均较高,而鱼类养殖区还出现了较高蓝藻孢子丰度.本次调查中还出现了易碎藻和艉杆藻等在本海域浮游植物调查中未记录种类的孢囊,有毒有害赤潮生物的休眠体如亚历山大藻、链状裸甲藻、旋沟藻、巴哈马梨甲藻孢囊等也在此次调查中频繁出现,说明大亚湾海域存在较大的有毒有害赤潮发生的风险.     

模拟水动力对湖泊浮游动物群落演替的实验研究

湖泊的浮游动物在种群演替和数量变化方面都有极明显的周期性(Chen et al., 1987)。浮游动物的周期性变化，除受湖泊环境温度、光照的周期性变化等因素外，同时还受到水体的水动力作用影响(陈伟民等，1998)。 王家楫等(1965)对东湖的轮虫数量进行了研究，陈受忠(1965)阐述了东湖近邻剑水蚤(Cyclops vicinus)、广布中剑水蚤(Mesocyclops leuckarti)、汤匙华指水蚤(Sinoialanub dorrii)、特异荡镖水蚤(Neutrodiaptomus incongreus)等都有显著昼夜垂直移动。Evans(1988)等在有关浮游动物的数量变动与水环境关系方面做了研究。但就水动力作用对浮游动物群落演替的实验研究较少见报道。 为研究水动力作用对浮游动物群落的种类数量变化，利用大型生态模拟槽，探讨不同水动力过程对浮游动物种类组成、数量变化过程和作用途径等，本文作者用模拟水动力的方法对湖泊浮游动物群落演替进行了实验研究，为今后的湖泊生态修复提供了科学依据。     

Enzyme activities in the water column and in shallow permeable sediments from the northeastern Gulf of Mexico

The activities of extracellular enzymes that initiate the microbial remineralization of high molecular weight organic matter were investigated in the water column and sandy surface sediments at two sites in the northeastern Gulf of Mexico. Six fluorescently labeled polysaccharides were hydrolyzed rapidly in the water column as well as in permeable sediments. This result contrasts with previous studies carried out in environments dominated by fine-grained muds, in which the spectrum of enzymes active in the water column is quite limited compared to that of the underlying sediments. Extracts of Spirulina, Isochrysis, and Thalassiosira were also used to measure hydrolysis rates in water from one of the sites. Rates of hydrolysis of the three plankton extracts were comparable to those of the purified polysaccharides. The broad spectrum and rapid rates of hydrolysis observed in the water column at both sites in the northeastern Gulf of Mexico may be due to the permeable nature of the sediments. Fluid flux through the sediments is sufficiently high that the entire 1.5 m deep water column could filter though the sediments on timescales of a few days to two weeks. Movement of water through sediments may also transport dissolved enzymes from the sediment into the water column, enhancing the spectrum as well as the rate of water column enzymatic activities. Such interaction between the sediments and water column would permit water column microbial communities to access high molecular weight substrates that might otherwise remain unavailable as substrates.     

A potential source of recruitment of Acartia pacifica nauplii: viable benthic resting eggs

1 Introduction M any estuarine and coastal copepods that havepreviously been classified as holoplankton m ightbestbe described as adultm eroplankton since they actuallyspend a portion oftheir life cycle in the seabed as rest-ing eggs [review ed by G rice and M arcus (1981) andM arcus (1996)]. R esting eggs can be extrem ely abun-dant (106 m ) in bays and estuaries especially w here -2w aterdepths are less than 20 m (M arcus,1989).Theyare likely to profoundly influence the dynam ics ofpel…     

Impact of oxygen-depleted water on the vertical distribution of chaetognaths in the northeastern Arabian Sea

The influence of a thick layer of oxygen-depleted water (<0.2 ml l⁻¹) on the abundance and distribution of chaetognaths was investigated in the northeastern Arabian Sea (NEAS), a natural oxygen-deficient system in the global ocean. The species and maturity stage-wise distribution of this group were studied at five discrete depths down to 1000 m. A total of 22 species belonging to four genera were observed, and the genus Sagitta dominated, representing 60% (500-1000 m) to 89% (Mixed layer depth) of the total chaetognath population. Based on their vertical distribution limits, four groups were recognised, as follows: I: species abundant in surface water with a maximum distribution limit up to 300 m; II: species confined mainly to deeper waters (>500 m); III: species present throughout the water column (0-1000 m); and IV: species present in most layers, but with a preference for a specific depth stratum. A positive correlation (P<0.01) was observed in the abundance of chaetognaths and their main prey copepods, emphasising the strong trophic relationship between these groups. It was found that the intensely oxygen-deficient waters of the NEAS play a crucial role in the vertical distribution and abundance of chaetognath species of all four genera. This report presents information on the maturity stages and ontogenetic migration of this important planktonic group in relation to the oxygen-depleted water in the study region for the first time. The results obtained are also important for understanding the biological processes associated with a major oxygen minimum zone (OMZ) in the global ocean.     

Spatial and long-term temporal variation of meiobenthic-hyperbenthic copepods in Lake Pontchartrain,Louisiana

The distribution and abundance of the meiobenthic-hyperbenthic copepods of Lake Pontchartrain (a large, 1630 km², shallow, mean depth of 3·7m, brackish, 0·3–5‰, lake in Southeastern Louisiana) were characterized monthly from August 1978 to August 1979. Ten stations, all with water depth > 2m, were established and sampled quantitatively by removing four benthic subsamples (containing as much as 25 cm overlying water) from replicated box cores. Averaged across stations over time, total copepod densities ranged from 31–89 × 10 cm^?2. A total of only 15 copepod species were identified from benthic samples; 8 harpacticoids, 4 cyclopoids and 3 calanoids. The copepod assemblage in Pontchartrain differs from all other known benthic assemblages in that the species composition is dominated by species which are often associated with the water column; true infaunal species are rare or found in reduced abundance. Four species comprised 90% of all individuals collected. All four are epibenthic or commonly collected as zooplankton and include Scottolana canadensis which comprised 47% of all individuals collected, Halicyclops fosteri which dominated fall collections, Acartia tonsa and Pseudobradya sp. Burrowing species were largely restricted to the more saline eastern stations. The rarity of burrowing species might be related to low salinity, however the highly unstable bottom in Pontchartrain with silty-clayey sediments commonly resuspended into the water column, may also influence burrowers. Cluster analysis reveals diffuse seasonal grouping of stations for all seasons except fall, with spatial groupings from the central and western sides. Physical processes appear to dictate the community structure of benthic-hyperbenthic copepods in Lake Pontchartrain.     

Spatial variability and dynamics of macrobenthos in a Mediterranean delta front area: The role of physical processes

Benthic communities in delta fronts are subject to burial risk because of high riverine sediment discharges and to substrate instability due to deposition of fine sediments at shallow depths. This study examines the spatial distribution of macroinfauna in the subaqueous deltaic depositions of a small river in the eastern Mediterranean (the Spercheios river, Maliakos Gulf, Aegean Sea) in relation to environmental variables in the water column and sediment. Samples were taken at eight stations in January, May, August and November 2000. From late winter to spring enhanced phytoplanktonic biomass, elevated suspended load and poorly sorted sediments showed a simultaneous influence of riverine discharges and hydrodynamics on the benthic system. In contrast, from summer to autumn oligotrophy in the water column and low hydrodynamic regime were observed. Total abundance, biomass and numbers of benthic species were positively correlated with distance from the river but negatively correlated with suspended inorganic particles and sediment skewness. Species from different functional groups, ranging from surface-living opportunists to burrowers and predators, coexisted at each station. However, suspension feeders were numerically suppressed near the river mouth. Non-parametric multivariate regressions showed that the variance in the species data was explained by environmental variables to a level ranging from 53 to 69%. This indicated a strong link between the macrofauna and the delta front environment. The variables used as measures of hydrodynamics and turbidity (i.e. sediment skewness and sorting, suspended material and transparency) displayed great explanatory power. The results of the present study show that the distribution of species is related to fluctuations in hydrodynamic regime that influence substrate characteristics. The study also demonstrates that sediment discharges of small temperate rivers can determine species composition in the delta front and have a detrimental impact on the community at short distances from river outflows.     

珠江口外表层沉积物底栖有孔虫组合及其与环境的关系

对珠江口外CJ14区块250个站位的表层沉积物进行底栖有孔虫分析,共发现底栖有孔虫118种,其中玻璃壳质80种,瓷质壳质21种,胶结壳质17种。有孔虫丰度基本随水深变深而增大。为研究底栖有孔虫分布与沉积环境之间的关系,对底栖有孔虫含量进行Q型因子分析,并选取前4个主因子,分别对应4个有孔虫组合。它们总共解释了总方差的86.2%,基本上反映了沉积物中有孔虫的群落结构。研究表明,水深和盐度是影响珠江口表层沉积物中有孔虫组合分布的控制因素,其他影响因素主要包括沉积物类型、水动力条件和沉积速率。水动力条件主要影响有孔虫的含量;沉积速率主要影响有孔虫的丰度。     

孢囊及其与赤潮爆发关系的研究进展

某些藻类(特别是甲藻),在不适宜生长的恶劣环境条件下能形成休眠孢囊。孢囊下沉到海底,以渡过不良的生存条件。一旦环境条件适宜,孢囊就大量萌发形成浮游细胞和优势群体,从而诱导赤潮的形成。简述了当前国际上对孢囊研究的最新进展,从孢囊和营养细胞相互转化的角度探索了孢囊与赤潮形成的关系,以及分子生物学技术在赤潮生物及其孢囊的定性、定量及赤潮发生监测中的应用。     

Abundance and biomass of meiobenthos in the spawning ground of anchovy (Engraulis japanicus) in the southern Huanghai Sea

1 Introduction Meiofauna is an important group in benthic small food web energetically due to their small size, high abundance and fast turnover rates. The production of meiofauna is equal to or higher than that of macrofau- na in estuaries, shallow waters and deep sea (Gerlach, 1971; Platt and Warwick, 1980; Heip et al., 1985; Zhang et al., 2004). A role of meiofauna may be the recycling of nutrients. Marine nematodes may keep the bacterial colonies on sand grains in active phase of growth …     

北黄海典型水域秋冬季浮游植物群落的昼夜变化

利用冬季(2007年1月)和秋季(2007年10月)在北黄海中部昼夜连续观测所获浮游植物样品,分析了浮游植物群落的昼夜变化.结果表明:浮游植物丰度在各层存在昼夜变化,冬季10～20 m层主要在白天出现高丰度,而20～30 m层和30～底层都是在夜间出现高丰度,冬季丰度垂直分布相对较均匀.秋季各层都主要在夜间出现高丰度,丰度垂直分布是下层水体明显比上层高.2个季节优势种昼夜组成都比较稳定.冬季优势种为具槽帕拉藻(Paralia sulcata),主要分布在下层水体.秋季罗氏角毛藻(Chaetoceros lauderi)和密连角毛藻(Chaetoceros densus)成为优势种,两者分别以下层和上层水体分布较多.冬季浮游植物群落多样性和均匀度昼夜变化都不明显,秋季0～10 m层和20～30 m层多样性和均匀度昼夜变化较明显.从季节变化来看,秋季多样性要高于冬季,均匀度的季节变化不明显.     

壶状臂尾轮虫及其休眠卵的形态学研究

从乳山对虾养殖场池塘底泥中分离出数量较多的一种轮虫休眠卵,经孵化鉴定为壶状臂尾轮虫(Brachionus urceus),对该轮虫休眠卵及孵出的轮虫进行了形态学观察.扫描电镜观察发现,壶状臂尾轮虫休眠卵表面有明显的、不规则的褶皱突起,与已有报道略有差异,这可能是由生活水体盐度的不同引起的;该休眠卵表面附着一些污染物.透射电镜观察显示,壶状臂尾轮虫细胞内线粒体密集、分泌颗粒较多,这是与其代谢旺盛、运动活跃等机能相适应的.     

南海南部活体浮游有孔虫分布特征及其影响因素初探

通过对2002年5月采自南海南部海区11个站位20个垂直分层浮游拖网样品的浮游有孔虫组成和分布特征的初步分析,发现该区表层水体中浮游有孔虫分布广泛,共鉴定属种20种,以热带暖水种占绝对优势,广适应性冷水种有零星出现。深水种Globorotalia menardii在南海南部50 m水层中广泛出现,但壳体相对较小,壳壁较薄。该区0—50m水层活体浮游有孔虫丰度范围为(6 138—64 174)枚.1 000 m-3海水,大致呈西高东低的分布趋势,在西南部浅水区和西北部上升流区丰度最高,与表层水体的营养水平密切相关。将水样浮游有孔虫分布数据与该海区23个站位表层沉积样数据进行对比分析,发现遗壳浮游有孔虫与活体的分布关系密切,虽然在种属丰度以及分布范围等方面有明显差异,但两者具有相似的优势种组合。主要差异在于水体中浮游有孔虫优势种相对丰度差异较大,易溶种Hastigerina pelagica含量较高,而遗壳中浮游有孔虫各种属分布趋向于均匀化。此外,陆源物质的释稀作用对沉积物中的有孔虫丰度分布有明显的控制作用。     

Compositions and transport of lipid biomarkers through the water column and surficial sediments of the equatorial Pacific Ocean

A systematic investigation of fluxes and compositions of lipids through the water column and into sediments was conducted along the U.S. JGOFS EgPac transect from l2°N to l5°S at 140°W. Fluxes of lipids out of the euphotic zone varied spatially and temporally, ranging from ≈0.20 – 0.6 mmol lipid-C m⁻² day⁻¹. Lipid fluxes were greatly attenuated with increasing water column depth, dropping to 0.002-0.06 mmol lipid-C m⁻² day⁻¹ in deep-water sediment traps. Sediment accumulation rates for lipids were ≈ 0.0002 – 0.00003 mmol lipid-C m⁻² day⁻¹. Lipids comprised ≈ 11–23% of C_org in net-plankton, 10–30% in particles exiting the euphotic zone, 2–4% particles in the deep EgPac, and 0.1-1 % in sediments. Lipids were, in general, selectively lost due to their greater reactivity relative to bulk organic matter toward biogeochemical degradation in the water column and sediment. Qualitative changes in lipid compositions through the water column and into sediments are consistent with the reactive nature of lipids. Fatty acids were the most labile compounds, with polyunsaturated fatty acids (PUFAs) being quickly lost from particles. Branchedchain C₁₅ and C₁₇ fatty acids increased in relative abundance as particulate matter sank and was incorporated into the sediment, indicating inputs of organic matter from bacteria. Long-chain C₃₉ alkenones of marine origin and long-chain C₂₀-C₃₀ fatty acids, alcohols and hydrocarbons derived from land plants were selectively preserved in sediments. Compositional changes over time and space demonstrate the dynamic range of reactivities among individual biomarker compounds, and hence of organic matter as a whole. A thorough understanding of biogeochemical reprocessing of organic matter in the oceanic water column and sediments is, thus, essential for using the sediment record for reconstructing past oceanic environments.     

Dispersal and recruitment of blue crab larvae in Delaware Bay,U.S.A.

Results of a three-year survey of the occurrence of Callinectes sapidus larvae in the mouth of Delaware Bay indicated that stage I zoea larvae were most abundant insurface water as compared to mid-depths and near bottom. The major peak in abundance of stage I zoea larvae occurred in early August with a secondary peak in early September. Peaks in abundance of megalopae occurred five weeks after the respective peaks in zoeal abundance. Zoea stages II–VIII were not collected in the bay mouth. Results of sampling every 3 h over consecutive tidal cycles showed that stage I zoea larvae were most common in the water column on ebbing tidal currents. Megalopae were most common in the water column on flooding tidal currents, suggesting a tidally related, vertical migration. It was concluded that stage I zoea larvae are flushed from the estuary and undergo development on the continental shelf. Megalopae are then transported back to inshore waters by a combination of winds and currents and invade the estuary by means of migration into the water column on flooding tidal currents and migration to the bottom on ebbing tidal currents.     

Contribution of benthic and epiphytic diatoms to clam and oyster production in the Akkeshi-ko estuary

The species composition and dynamics of phytoplankton in the water column and its contribution to clam, Ruditapes philippinarum, and oyster, Crassostrea gigas, production were studied in the Akkeshi-ko estuary, eastern part of Hokkaido, Japan. A total 128 taxa of diatoms were identified, with 103 and 102 species occurring on the surface sediments and in the water column, respectively. Amphora sp., Bacillaria paradoxa var paxilifer, Cocconeis scutellum, Navicula sp., Nitzschia sigma, Paralia sulcata, Rhoicosphenia curvata, Synedra ulna and Thalassiosira sp. were most common and dominant in all stations in both water column and surface sediment. Benthic diatoms were most dominant in both water column and surface sediment. The species composition of epiphytes was, in part, similar to diatom assemblage of the water column and also to that of the surface sediment. The benthic and pelagic ratio in the diatom assemblage of the water column was very high. Benthic diatoms were able to resuspend into water column by turbulence stimulated by wind. Chlorophyll a concentration in the water column increased as wind speed increased. Seventy and 67% of the gut contents oysters consisted of benthic diatoms in 2003 and 2004 and also 78 and 87% of clams in 2003 and 2004, respectively. The availability of benthic and epiphytic diatom assemblages contributes significantly to food resources for clam and oyster mariculture due to resuspension by disturbance in the Akkeshi-ko estuary.     

Last glacial emplacement of methane-derived authigenic carbonates in the Sea of Japan constrained by diatom assemblage,carbon-14, and carbonate content

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.     

Water column and recent sediment data on diatoms and coccolithophorids,off Portugal,confirm sediment record of upwelling events

Diatom and coccolithophorid abundance and diatom assemblage composition found in the water column along the Portuguese margin, during upwelling and non-upwelling conditions, are compared to the distribution patterns observed in the recent sediments from the same area. The water column results indicate a one order of magnitude increase in phytoplankton biomass during upwelling conditions (summer), with diatoms being the most important contributors. Coccolithophorids, on the contrary, dominate the phytoplankton in winter (non-upwelling). The comparison of the upwelling and non-upwelling spatial distribution of these phytoplankton groups to their sedimentary record reveals the sediment record as a reflection of the upwelling situation, preserving most of its original spatial variability. The comparison between living and fossil diatom assemblages indicates that from the two genera which dominate the summer biological assemblage, Pseudo-nitzschia and Chaetoceros, Pseudo-nitzschia is not represented in the sediments, while Chaetoceros is the dominant form of the sediment. Thalassiosira, which occurs in the same abundance in both seasons, responding to both river and upwelling nutrient input, can not be a reliable indicator of any single process. However, this genus distribution in the sediments can be used as an indicator of continuous nutrient availability. Such results are of great importance for paleoceanographic reconstructions, since they constitute a good indication that the sediment record, even though somewhat altered with respect to assemblage composition, does reflect the water column characteristics.