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221.
全球河口海域屡屡爆发褐潮,但我们对致因种抑食金球藻和浮游桡足类之间的营养关系还不甚清楚。我们就浮游桡足类火腿伪镖水蚤摄食抑食金球藻中国株的单种或混合饵料时的摄食行为和生长、发育等表现进行了研究。研究发现:火腿伪镖水蚤的无节幼体、桡足幼体和成体摄食单种抑食金球藻饵料时,摄食率和食物浓度之间的关系符合米氏方程。较之桡足类幼体和成体,无节幼体摄食抑食金球藻时的Imax(最大摄食率)值最大,同时大于其摄食中肋骨条藻的Imax值。通常情况下,火腿伪镖水蚤在摄食抑食金球藻和中肋骨条藻的混合饵料时避食抑食金球藻,但于无节幼体,这种情况并不明显。无节幼体摄食单种抑食金球藻饵料在无节幼体期末期死亡,无法进入桡足类幼体期,与饥饿状态下的个体相似。但是,饵料中抑食金球藻的存在对桡足幼体的生长无明显效应,但却极大地减少了成体的生殖率。我们的研究表明火腿伪镖水蚤无节幼体,在褐潮的控制中有潜在作用,然而,这种潜在控制作用由于桡足类种群的衰落难以持续。 相似文献
222.
Effect of temperature and irradiance on growth and reproduction of Enteromorpha prolifera that bloomed offshore along the Qingdao coast in summer 2008, was studied. It was showed that E. prolifera propagated mainly asexually with specific growth rate (SGR) of 10.47 at 25℃/40 μmol m^-2s^-1. Under this condition, gametes with two flagellate formed and released in 5 days. At the beginning of the development, the unicell gamete divided into two cells with heteropolarity, and then the apical cell developed into thalli primordial cells, whereas the basal cell developed into rhizoid primordial cells. In 8-day culture, the monoplast gamete developed into juvenile germling of 240 μm in length. Unreleased gametes can develop directly within the alga body. E. prolifera could either reproduce through lateral branching or fragmenting except apomixis revealed by Microscopic observation. On aged tissue of E. prolifera, although the degraded pigments partially remained in faded algal filaments, numerous vegetative cells could still divide actively in the algal tissues. 相似文献
223.
采用室内培养和野外实地观测的方法,研究了鼠尾藻的生长发育和有性生殖过程,并在此基础上进行了有性生殖人工育苗实验。结果表明,鼠尾藻在海水温度高于22℃时,生殖托开始发育,海水温度超过23℃以后,生殖托的生长速度加快,海水温度超过24℃时,生殖托生长速度最快并迅速成熟,在海水温度达到26℃时,观察到了卵的集中排放挂托现象。鼠尾藻卵的排放较为齐整且有一定的先后顺序,生殖托基部的卵最先排出,中部次之,最后是顶部,雄托排精时间要稍晚于雌托排卵时间。受精卵大约在受精1h后进行第一次细胞分裂,分裂面与长轴垂直,大约2h后进行第二次分裂,下端细胞的分裂面平行于第一次分裂方向,而上端细胞的分裂面则垂直,随后大约每2—4h细胞分裂一次。从卵挂托到幼胚脱落一般需要24—48h。观察发现,生殖窝不仅存在于生殖托上,在部分生殖枝上也有分布。在鼠尾藻的人工育苗的实验中,胚苗在苗帘上的生长状态良好。 相似文献
224.
以采自厦门沿岸的中华盒形藻(BidduphiasinensisGreville)为实验材料 ,通过培养研究了光对该藻有性生殖的影响。结果表明 ,光诱导该藻有性生殖发生的临界日长为16h,且其性分化反应随光照时数的延长而增强 ;该藻性分化反应的有效光照强度范围为40~80μmol/(m2·s) ,高峰出现在70μmol/(m2·s) ;光照强度低于光合补偿点的延长光 (8h光期 )无论置于主光期(8h)之前或之后均能引起精原孢囊的形成 ,白光作为延长光的诱导效果最为明显 ,蓝光其次 ,红光有效但不明显 ,远红光无效。由上得知 ,中华盒形藻有性生殖过程存在光周期现象 ,属长日植物 ,具有“光控”反应特征 ,但不典型 ,该藻可能同时存在蓝光和红光2种光信号受体 相似文献
225.
226.
《Geoforum》2015
Since the mid-1980s, liberalization has motivated numerous water supply reforms. Among these, privatization has received the most attention. Yet, its actual scope has been limited. Beyond privatization, the territorial expansion of municipally owned water corporations into new service areas can be witnessed in countries as diverse as Italy, South Africa, Canada, Colombia and the Netherlands. Generally, the activities of public water corporations are analyzed through the lens of commercialization. This framework is central to understanding recent shifts in water supply. Yet, while it addresses the effects of commercialization on service quality and access, it rarely integrates the influence of shifts in social reproduction and collective consumption in structuring reform. Drawing on theories of urban entrepreneurialism, I attempt to advance a broader analytical framework that is more amenable to integrating the diversity of processes involved, including but not limited to commercialization. At the same time, the territorial expansion of municipally owned water corporations suggests ways to rethink urban entrepreneurialism: it is not only commercial, it is also social, and it is Schumpeterian. To make these points, this article examines the efforts of two public water corporations to go international: EPM of Medellín, Colombia and WMD of Drenthe, the Netherlands. 相似文献
227.
This paper deals with vegetative reproduction by multicellular propagules in Rhodophyta. An extensive examination of the relevant literature shows that this phenomenon in Rhodophyta is not well known. A propagule is here defined as a vegetative multicellular structure which spontaneously detaches from the parent thallus and gives rise to a new individual. The origin and morphological features of multicellular propagules are examined in the various known propagule‐forming species. The importance of multicellular propagules as both overwintering and resting organs and as a taxonomic feature is also shown. Their role in increasing local populations and/or for long‐distance dispersal is discussed. The relative abundance of vegetative reproduction by multicellular propagules versus sexual reproduction, as well as the advantages of this additional mode of reproduction, are shown and discussed. The production of multicellular propagules may contribute to the capacity of species to increase populations, to weather unpredictable environmental changes, to survive in conditions that would be lethal for entire thalli, and to reach new habitats. As resting organs, they may also be responsible for long‐distance dispersal and may account for the introduction of some alien species. Accordingly, propagule‐forming species are probably more competitive than taxa that do not produce such propagules. These considerations should be taken into account in future studies of the biology, ecology and demography of Rhodophyta. 相似文献
228.
Alessandra Gallo Francesco Silvestre Annunziata Cuomo Fabrizia Papoff Elisabetta Tosti 《Marine Ecology》2011,32(2):222-231
Environmental pollution due to anthropogenic activities may exert an adverse impact on the reproductive mechanisms of animals. In particular, environmental chemicals introduced into seawater are able to disrupt the normal development and function of the reproductive system of marine animals. In this study, we have used the whole‐cell voltage clamp technique to examine the effects of four metals – lead, cadmium, mercury, and zinc – on reproductive mechanisms of the marine ascidian Ciona intestinalis (tunicates). In particular, we measured the effect of metals on plasma membrane electrical properties, the steady‐state conductance, the fertilization current in the mature oocyte, and larval development. Results show that oocyte voltage‐gated sodium currents are significantly reduced by all four metals, steady‐state conductance is affected only by zinc, and post‐fertilization contraction is inhibited only by lead. The fertilization current is suppressed in the presence of zinc and mercury. Embryo development up to larval stage is inhibited by zinc and mercury exposure with a reversible effect; however, a long‐term effect on larval morphology was observed. After exposure to cadmium, fertilization occurs but gives rise to abnormal larval development. These findings highlight the point that exposure to metals represents a significant risk factor for the physiology of reproduction of marine species and suggest a possible role of the C. intestinalis as a bioindicator for marine pollution monitoring. 相似文献
229.
230.
Some populations of gelatinous zooplankton appear to be increasing and causing ecological disruptions during large bloom events. The goal of this study was to investigate the life history and population dynamics of the small, invasive Moerisia sp. and its potential ecological impacts in the upper San Francisco Estuary, California. Medusae and polyps were collected from 8 and 2 sites, respectively, during 2007 and 2008. Polyps emerged from a resting stage during June. Asexual reproduction of medusae buds was positively correlated with temperature and negatively related to salinity. The production of polyp buds was positively correlated with dissolved oxygen and water transparency levels. Sexual reproduction, defined by the presence of eggs, was related to the size of medusae. Cessation of reproduction of both polyps and medusae occurred in October, when temperatures dropped below 17 °C. This life history is similar to other hydrozoans and allows Moerisia sp. to reach large numbers seasonally in the San Francisco Estuary, possibly contributing to the recent declines of pelagic fish and zooplankton. 相似文献