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1.
《海洋科学集刊》2017,(0)
海洋中存在着大量的颗粒,包括大型聚合颗粒(即海雪,粒径500?m)、小型聚合颗粒(1~500?m)和亚微米颗粒粒径(1?m)等。颗粒在海水中营造了不同于纯海水的小生境,其中生活着与自然海水中不同的生物。异养细菌、蓝细菌、真核藻类、鞭毛虫、纤毛虫等微食物网生物可以黏附在海洋颗粒上,或生活在颗粒内部,其丰度高于周围水体中的自由生活生物,这可能是由于颗粒提供了更适宜生长的营养环境。本文综述了海洋浮游微食物网生物在海洋颗粒形成和沉降中的作用。微食物网生物在颗粒物的形成过程中起到很重要的作用,它们可以直接促进颗粒形成,也可以彼此结合成颗粒,或微型浮游动物排粪形成颗粒。微食物网生物还可以对颗粒进行转化,影响颗粒的大小、沉降速度、或对颗粒及其黏附生物进行摄食。微食物网生物由于本身较小,沉降较慢,但这些生物和颗粒的结合使得微食物网生物在碳通量中发挥重要的作用。 相似文献
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微食物环是海洋生态系统中重要的物质和能量过程,是传统食物链的有效补充。微食物环研究是当前海洋生态学研究的热点之一,但对其结构的系统研究较少,海洋微食物网结构在2000年才被Garrison提出。尽管微食物网各个类群的丰度在不同海洋环境中有相对变化,但是这些变化都处于一定的范围之内,其丰度结构约为纤毛虫10 cell ml-1、鞭毛虫103 cell ml-1、微微型真核浮游生物104 cell ml-1、蓝细菌104-5 cell ml-1、异养细菌106 cell ml-1、病毒107 particle ml-1。海洋浮游食物链中捕食者和饵料生物粒径的最佳比值为10:1,实际研究中该比值会略低,例如纤毛虫与其饵料的粒径比值为8:1,鞭毛虫为3:1。Pico和Nano浮游植物的丰度比（Pico:Nano）是研究微食物网结构的指数之一,该指数具有不受研究尺度影响的优点,可用于研究区域性和全球性微食物网结构。近年来,学者们从多角度对海洋微食物网的结构开展了研究,不同海区微食物网各类群丰度、生物量的时间和空间变化研究有很多报道,微食物网的结构可受空间、季节、摄食、营养盐等多种因素影响。在对不同空间微食物网的研究中,学者往往研究不同物理性质的水团中各类群生物丰度的不同,以此来表征微食物网结构的不同;同一海区微食物网结构的季节变化也是使用各个类群丰度和生物量的变化来表示,该变化主要受水文环境因素影响。摄食者对微食物网各类生物的影响通过三种途径：1. 中型浮游动物摄食;2. 中型浮游动物摄食微型浮游动物,通过营养级级联效应影响低营养级生物;3. 中型浮游动物通过释放溶解有机物、营养盐影响细菌和低营养级生物。浮游植物通过产生化感物质和溶解有机物影响微食物网结构,而营养盐的浓度及变化则可以对微食物网产生直接或间接影响。 相似文献
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海洋沉积物/颗粒物在生源要素循环中的作用及生态学功能 总被引：2，自引：1，他引：1
海洋沉积物/颗粒物是生源要素循环过程中的关键源与汇，沉积物/颗粒物一方面是海水生源要素的主要归宿，生源要素从溶解态经复杂的生物-化学过程转变为颗粒态，颗粒物质再沉降形成沉积物，另一方面，海洋沉积物/颗粒物经过微生物-浮游动物-底栖生物作用分解形成溶解态的生源要素，并释放到海水中再次被浮游植物利用，进入下一轮循环，所以，海洋沉积物/颗粒物具有异常重要的生态学功能。浮游植物是海水溶解态生源要素的利用者和海源颗粒态生源要素的初始形成者，浮游动物通过摄食浮游植物或其他有机颗粒物可释放出溶解态生源要素或形成更大的颗粒物，颗粒物沉降后形成的沉积物又通过底栖生物摄食-扰动-破碎等过程将颗粒生源要素释放进入水体参与再循环。生态系统不同类群的生物在颗粒生源要素的释放-沉降中所起的作用不同而又相互关联，其中浮游动物-底栖生物的摄食与代谢、微生物参与的分解过程起着非常重要的作用。所以，海洋沉积物/颗粒物生态学功能研究作为支撑海洋环境和资源的持续利用的科学基础，已成为海洋科学的前沿领域，必将获得跨越发展。 相似文献
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《海洋科学集刊》2016,(0)
微食物环是海洋生态系统中重要的物质和能量过程,是传统食物链的有效补充。微食物环研究是当前海洋生态学研究的热点之一,但对其结构的系统研究较少,海洋微食物网结构在2000年才被Garrison提出。尽管微食物网各个类群的丰度在不同海洋环境中存在相对变化,但是这些变化都处于一定的范围之内,其丰度结构约为纤毛虫10cell/mL、鞭毛虫10~3cell/mL、微微型真核浮游生物10~4cell/mL、蓝细菌10~4~10~5cell/mL、异养细菌10~6cell/mL、病毒10~7particle/mL。海洋浮游食物链中捕食者和饵料生物粒径的最佳比值为10︰1,实际研究中该比值会略低,如纤毛虫与其饵料的粒径比值为8︰1,鞭毛虫为3︰1。微微型(pico-)和微型(nano-)浮游植物的丰度比(pico︰nano)是研究微食物网结构的指数之一,该指数具有不受研究尺度影响的优点,可用于研究区域性和全球性微食物网结构。近年来,学者们从多角度对海洋微食物网的结构开展了研究,针对不同海区微食物网各类群丰度、生物量时间和空间变化的研究有很多报道,微食物网的结构受空间、季节、摄食、营养盐等多种因素影响。在对不同空间微食物网的研究中,众多学者往往研究不同物理性质的水团中各类群生物丰度的不同,以此来表征微食物网结构的不同;同一海区微食物网结构的季节变化也是使用各个类群丰度和生物量的变化来表示,该变化主要受水文环境因素影响。摄食者对微食物网各类生物的影响通过3种途径:(1)中型浮游动物摄食;(2)中型浮游动物摄食微型浮游动物,通过营养级级联效应影响低营养级生物;(3)中型浮游动物通过释放溶解有机物、营养盐影响细菌和低营养级生物。浮游植物通过产生化感物质和溶解有机物影响微食物网结构,而营养盐的浓度及变化则可以对微食物网产生直接或间接影响。 相似文献
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海洋微塑料是全球共同面对的环境问题和挑战,然而目前海洋微塑料从源到汇的输运和沉积过程及影响机制尚不明确。已有研究发现微塑料颗粒的垂向沉降过程受到海洋雪等水体悬浮物质的影响,但是目前相关研究只局限于定性的观察分析。在实验室中模拟含有海洋雪的近岸水体环境,使细颗粒微塑料(PS微球、PVC颗粒)与海洋雪产生碰撞、聚集,观测微塑料或微塑料-海洋雪聚集体的沉降过程。研究结果表明,水体中含有海洋雪时,一方面海洋雪会促进微塑料颗粒自身的聚集,形成更大的聚集体;另一方面由于海洋雪包裹微塑料形成松散的聚集体,导致平均沉速减小。50 μm以下的微塑料其沉降过程受海洋雪的影响较大,平均沉速减小35%以上;微塑料密度越大,受海洋雪的影响越小,平均沉速减小10%以下。沉降速率的减缓,意味着微塑料在水柱中的停留时间增加,处于不同深度的水生生物可能有更多时间和概率与微塑料接触,增加了鱼类等水生生物摄入微塑料的风险。 相似文献
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海洋原生生物是微食物环的重要组成部分,在海洋生态系统的物质循环和食物传递中发挥着不可替代的作用;亚洲沙尘颗粒经长距离输运后沉降入黄海,会对海洋生态系统产生显著影响。本研究在黄海南部海域进行了现场模拟培养实验,分析了不同浓度沙尘和P添加对不同粒径、异养类型浮游原生生物生长速率的影响。结果表明,在培养早期,P和沙尘的添加都会促进各营养类型浮游原生生物的生长,特别是对10~20μm自养型生长速率的促进作用最为显著,其在高、低浓度P和高、低浓度沙尘添加组的生长速率分别为1.39、0.96、0.69和0.47 d-1,分别是对照组的5.35、3.69倍和2.65、1.81倍(P<0.05),表明研究海区为P潜在限制海区,沙尘对原生生物的促进作用可能和P的溶出有关;沙尘对异养型和兼养型原生生物早期是抑制作用。在培养后期,沙尘添加对各类群原生生物的生长以促进作用为主,对2~5μm异养型的促进作用最为显著,其在高、低浓度沙尘组的生长速率分别为0.84和0.40 d-1,显著高于对照组的-0.46 d-1(P<0.05)。沙尘沉降早期对大粒径自养型原生生物生长的促进作用会加速富营养海区赤潮的发生,但对异养型的抑制作用会削弱海区物质循环和食物传递的效率;沙沉降对不同粒径和营养类型浮游原生生物生长的影响会改变黄海南部海区微型食物网的结构,影响原生生物在该海区物质转化和食物产出中的生态功能,研究结果可为深入探讨沙沉降对海洋生态系统的作用机制和生态效应提供科学参考。 相似文献
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海洋表层沉积物再悬浮的诱因及其对生源要素循环的影响 总被引：5，自引：0，他引：5
颗粒物质在向海底沉降的同时,在自然因素、生物扰动以及人为因素等作用下,海洋表层沉积物会再悬浮,从而引起生源要素在海水和沉积物中的再分配,进而对生物食物网、初级生产力产生影响。特别是在陆架边缘海,由于海水较浅,再悬浮剧烈,对生源要素的垂直转移及其生物地球化学过程影响严重,由于再悬浮的诱因很多,过程复杂,所以定量研究表层沉积物的再悬浮还有很多困难。作者将主要对表层沉积物再悬浮的诱因及其对生源要素循环的影响进行总结归纳,以期促进这方面的研究。 相似文献
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基于全球海洋及其上空大气中关于有机磷酸酯（OPEs）的数据，分析了目前OPEs在全球海洋及其上空大气的分布特征、影响因素以及当前研究存在的不足。总结发现，海水中的OPEs主要来自河流输送，且浓度分布特征表现为由近及远、由浅及深逐渐递减。磷酸三（2-氯乙基）酯（TCEP）、磷酸三（1-氯-2-丙基）酯（TCPP）和磷酸三（1，3-二氯异丙基）酯（TDCPP）三种卤化OPEs是海水中主要污染物；输入到海水中的OPEs经过颗粒沉降等作用沉积到海洋沉积物中，随之，沉积物中的OPEs可能反析出或直接累积，在海洋沉积物中形成一个大的OPEs储存库。分析北太平洋到北冰洋表层沉积物中OPEs的浓度发现，从白令海峡到北冰洋，随着纬度的增加OPEs的浓度也普遍增加，且相对于非卤化OPEs，卤化OPEs更易被运输到偏远海域。总有机碳（TOC）与大洋沉积物中OPEs的浓度无相关性，但与近海海洋沉积物中OPEs的浓度呈正相关，TCEP和磷酸三异丁酯（TiBP）为海洋沉积物中主要污染物；海洋上空大气与水体中的OPEs是不可分割的，海洋上空大气中的OPEs一部分通过大气沉降进入海水，一部分继续迁移到更偏远区域，气团来源是影响其分布的主要因素。对比OPEs在全球海洋上空大气中的浓度分布发现，南北半球并无明显差异，TCEP和TCPP是海洋上空大气中主要污染物。 相似文献
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寄生性甲藻阿米巴藻Amoebophrya是一类广泛寄生于纤毛虫类、放射虫类、甲藻类等海水浮游生物的原生生物,在北大西洋、北太平洋和地中海等营养盐丰富、宿主密度较高的河口和近海水环境中普遍存在,是海洋浮游食物网的重要组成部分。这类寄生性甲藻能够特异性感染海洋浮游甲藻,在有害藻华(harmful algal bloom,HAB)的发生过程中起下行控制作用,将逃脱了浮游动物摄食的浮游植物补充到微食物环(microbial loop)中去。Amoebophrya在近海海洋生态系统中的独特作用日益受到国际上越来越多研究者的关注和重视,并逐渐成为国际上海洋微型生物研究的新热点之一。近年来,已有初步调查研究表明这类寄生性甲藻在我国近海海域广泛存在;然而,目前我国尚缺乏该类寄生性甲藻的相关研究。本文系统综述了国际上该类寄生性甲藻的研究进展,针对目前研究中存在的问题并结合我国有害藻华发生机制相关研究的现状做出了分析和展望,以期推动我国该类寄生性甲藻的相关研究,为进一步阐释寄生性甲藻等海洋微型生物在有害藻华消长过程和海洋微食物环中的作用奠定基础。 相似文献
11.
海洋浮游细菌生长率和被摄食的研究综述 总被引：2，自引：0，他引：2
海洋浮游细菌利用海水中的溶解有机碳合成自身物质,是海洋浮游生态系统的二次生产者。微型浮游动物是细菌的主要摄食者,也是细菌生产向较高营养级传递的中介。研究海洋浮游细菌的生长率和被(微型浮游动物的)摄食率对理解海洋浮游生态系统的功能具有重要作用。本文综述了利用改变海水中生物类群组成(或功能)的培养方法研究海洋浮游细菌生长率和被摄食率的历程和现状,为我国的同类研究提供借鉴。改变海水中生物类群组成(或功能)进行培养的方法有海水分粒级培养、海水稀释培养和添加选择性抑制剂培养。这些方法各有其局限性,应用并不广泛。细菌及其主要摄食者异养鞭毛虫群落在自然海区和实验室内都有生长周期,鞭毛虫的生长周期落后于细菌,因此细菌的生长率有时会小于被摄食率,有时会大于被摄食率。我国这方面的研究相对落后,应值得引起重视,建议从海水稀释培养法入手开展相关研究。 相似文献
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《Deep Sea Research Part I: Oceanographic Research Papers》2001,48(1):95-123
Observations have shown that aggregates (“marine snow”) are an important fraction of the organic matter vertical flux in the ocean. There has been a separation in biological models describing this flux, with coagulation models focused on phytoplankton blooms for which particle concentrations are high and grazing is low and neglectable and with plankton models focused on food web interactions neglecting coagulation dynamics. This separation has partly resulted from the difficulty in describing the interactions among the multiple particle sources using a coagulation model for a food web. New approaches for describing particle dynamics now make it possible to do so. The present study examines the effect of combining the food web model of Fasham et al. (1990. Journal of Marine Research 34, 591–639) with a coagulation dynamics model and applying the combined model to describe the annual cycle of an oligotrophic plankton system. As part of the model formulation, the coagulation kernels had to be altered to include both the case of fractal particles interacting and the case of smaller particles being faster settling. Results show that coagulation can have an important effect on particle flux even in the low particle concentration oligotrophic environment by increasing average particle settling speed and by increasing the ratio of maximum to minimum daily vertical flux over the course of a yearly cycle. As part of this, coagulation forms large, rapidly sinking particles. Grazing and the accompanying formation of fecal pellets can compete with coagulation for particles, but the fecal pellets can also participate in the formation of large aggregates. Among the variables that can influence export rates are phytoplankton size and concentration as well as depth of the surface mixed layer. The results provide evidence for the importance of coagulation processes in enhancing particle export even in central ocean regions. 相似文献
13.
V. Rousseau S. Becquevort J. -Y. Parent S. Gasparini M. -H. Daro M. Tackx C. Lancelot 《Journal of Sea Research》2000,43(3-4)
The trophic efficiency of the planktonic food web in the Phaeocystis-dominated ecosystem of the Belgian coastal waters was inferred from the analysis of the carbon flow network of the planktonic system subdivided into its different trophodynamic groups. A carbon budget was constructed on the basis of process-level field experiments conducted during the spring bloom period of 1998. Biomass and major metabolic activities of auto- and heterotrophic planktonic communities (primary production, bacterial production, nanoproto-, micro- and mesozooplankton feeding activities) were determined in nine field assemblages collected during spring at reference station 330. In 1998, the phytoplankton spring flowering was characterised by a moderate diatom bloom followed by a massive Phaeocystis colony bloom. Phaeocystis colonies, contributing 70% to the net primary production, escaped the linear food chain while the early spring diatom production supplied 74% of the mesozooplankton carbon uptake. The rest of mesozooplankton food requirement was, at the time of the Phaeocystis colony bloom, partially fulfilled by microzooplankton. Only one-third of the microzooplankton production, however, was controlled by mesozooplankton grazing pressure. Ungrazed Phaeocystis colonies were stimulating the establishment of a very active microbial network. On the one hand, the release of free-living cells from ungrazed colonies has been shown to stimulate the growth of microzooplankton, which was controlling 97% of the nanophytoplankton production. On the other hand, the disruption of ungrazed Phaeocystis colonies supplied the water column with large amounts of dissolved organic matter available for planktonic bacteria. The budget calculation suggests that ungrazed colonies contributed up to 60% to the bacterial carbon demand, while alternative sources (exudation, zooplankton egestion and lysis of other organisms) provided some 30% of bacterial carbon requirements. This suggests that the spring carbon demand of planktonic bacteria was satisfied largely by autogenic production. The trophic efficiency was defined as the ratio between mesozooplankton grazing on a given source and food production. In spite of its major contribution to mesozooplankton feeding, the trophic efficiency of the linear food chain, restricted to the grazing on diatoms, represented only 5.6% of the available net primary production. The trophic efficiency of the microbial food chain, the ratio between mesozooplankton grazing on microzooplankton and the resource inflow (the bacterial carbon demand plus the nanophytoplankton production) amounted to only 1.6%. These low trophic efficiencies together with the potential contribution of ungrazed Phaeocystis-derived production to the bacterial carbon demand suggest that during spring 1998 most of the Phaeocystis-derived production in the Belgian coastal area was remineralised in the water column. 相似文献
14.
Isabel G. Teixeira Francisco G. Figueiras Bibiana G. CrespoSílvia Piedracoba 《Estuarine, Coastal and Shelf Science》2011
The dilution technique, combined with identification and enumeration of pico-, nano- and micro-plankton by microscopy, was used to estimate microzooplankton impact on the microbial community in surface waters of a coastal embayment on the NW Iberian upwelling system. Microzooplankton were important consumers of autotrophic and heterotrophic plankton in this system, feeding up to 93% of standing stock and more than 100% of production of several groups. Heterotrophic bacteria and heterotrophic picoflagellates experienced the highest and constant impact, with 75–84% of their standing stocks and 85–102% of their production being channelled through the microbial food web. Pico- and nano-phytoplankton were also consumed, although maximum grazing occurred on diatoms during upwelling events, coinciding with highest primary production. Predation on pico-nano-heterotrophs was especially relevant under downwelling conditions, when consumption of total carbon and particularly autotrophic carbon was considerably lower than during upwelling. The results suggest that the existence of a multivorous food web, extending from the microbial loop to the herbivorous food web, could be a major feature in this coastal upwelling system. The microbial loop, which occurs as a permanent background in the system, would contribute to sustain the microbial food web during downwelling, whereas the herbivorous food web could coexist with a microbial food web based on large diatoms during upwelling. The multivorous food web would partially divert diatoms from sinking and hence favour the retention of organic matter in the water column. This could enhance the energy transfer to higher pelagic trophic levels in coastal upwelling systems. 相似文献
15.
The plankton food web structure and trophodynamics in the neritic area of Sagami Bay were investigated from January 2003 to
December 2005, based on abundance, biomass, production rate and nutritional requirements of pico- (0.2–2 μm), nano- (2–20
μm), micro- (20–200 μm) and mesoplankton (>200 μm: mainly copepods CI-CVI) at 0–10 m depth. The average carbon biomass of
the total plankton community was higher in spring and summer (1.452 and 1.466 g C m−2, respectively) than in winter and autumn (0.676 and 0.686 g C m−2, respectively). The average values of primary production and of production rate and food requirement of heterotrophic organisms
were higher in summer than in other seasons. During the study period the biomass, production rate and food requirement of
small heterotrophs (i.e. bacteria: BA; heterotrophic nanoflagellates: HNF; microzooplankton: MZ) were much higher than those
of copepod secondary (CSP) and tertiary producers (CTP), indicating that the microbial food web was the main route of carbon
flow from phytoplankton (PP) to CSP and CTP, rather than the grazing food chain. In particular, during summer and autumn the
biomass of pico- and nano-size PP plus BA was greater than that of micro-size PP, suggesting the high prevalence of the microbial
food web (pico-/nanophytoplankton/BA-HNF/MZ-copepods). During winter and spring, the biomass of micro-size PP was greater
than that of pico- and nano-size PP plus BA, suggesting that the indirect route (microphytoplankton-MZ-copepods) probably
prevailed, while the microbial food web might be important. 相似文献
16.
Andrew W. Leising Wendy C. Gentleman Bruce W. Frost 《Deep Sea Research Part II: Topical Studies in Oceanography》2003,50(22-26):2877
The equatorial Pacific is an HNLC (High-Nitrate Low-Chlorophyll) region. Modeling and in-situ process studies have confirmed the importance of microzooplankton grazing in this ecosystem. Unfortunately, both the parameters and functions representing microzooplankton grazing within current ecosystem models are poorly constrained. We used a simple 4-component food web model to test the assumption that a lower grazing threshold, which is common in many models, is necessary to achieve the HNLC condition. Without the grazing threshold, the model did not reproduce the HNLC condition. However, by raising the half-saturation constant within the microzooplankton functional response with no threshold, it was possible to reproduce the critical dynamics of the HNLC condition under both steady and moderate seasonal variability in nutrient input. It was also possible to reproduce the HNLC system using a sigmoidal functional response for the microzooplankton, with results somewhere between the other two forms of the model, although this version had the highest sensitivity to changes in its parameters. The three models predicted similar phytoplankton biomass and primary productivity under steady nutrient input, but diverge in these metrics as the amplitude of nutrient input variability increases. These three functional responses also imply certain important differences in the microzooplankton community. Whereas the threshold model had the least sensitivity to parameter choice, the high half-saturation constant, no-threshold model may actually be a better approximation when modeling a community of grazers. Ecosystem models that predict carbon production and export in HNLC regions can be very sensitive to assumptions concerning microzooplankton grazing; future studies need to concentrate on the functional responses of microzooplankton before these models can be used for predicting fluxes in times or regions where forcing is beyond that used to constrain the original model. 相似文献
17.
《Journal of Sea Research》2000,43(3-4):345-356
During spring blooms 1998 and 1999, three complementary methods were used to evaluate the in situ feeding activities of the dominant copepod species of the Belgian coastal zone: gut pigment content analysis using HPLC, the 14C tracer method, and cell count experiments. The results obtained by all three methods consistently showed that Phaeocystis globosa is not an adequate food source for the spring copepods in the Belgian coastal zone. Our results demonstrated that, among the potential prey, copepods strongly selected diatoms and microzooplankton, and that these types of prey accounted for the major part of the ingested carbon. However, diatoms and microzooplankton ingestion did not always seem sufficient in terms of carbon to avoid food limitation. Comparison of clearance rates exerted on different potential prey types during the P. globosa peak with those before and after the P. globosa peak showed that the copepods' feeding pressure on diatoms was reduced during the P. globosa peak while that on microzooplankton was not. The low grazing pressure on P. globosa, together with the preferential grazing on diatoms, which reduces the competition for nutrients, and the predation on microzooplankton organisms, which reduces the microzooplankton grazing pressure on P. globosa cells, are likely to favour the P. globosa bloom in the Southern Bight of the North Sea. 相似文献
18.
Gordon V. Wolfe Maurice Levasseur Guy Cantin Sonia Michaud 《Deep Sea Research Part I: Oceanographic Research Papers》2000,47(12):687
We adapted the dilution technique to study microzooplankton grazing of algal dimethylsulfoniopropionate (DMSP) vs. Chl a, and to estimate the impact of microzooplankton grazing on dimethyl sulfide (DMS) production in the Labrador Sea. Phytoplankton numbers were dominated by autotrophic nanoflagellates in the Labrador basin, but diatoms and colonial Phaeocystis pouchetii contributed significantly to phytomass at several high chlorophyll stations and on the Newfoundland and Greenland shelfs. Throughout the region, growth of algal Chl a and DMSP was generally high (0.2–1 d−1), but grazing rates were lower and more variable, characteristic of the early spring bloom period. Production and consumption of Chl a vs. DMSP followed no clear pattern, and sometimes diverged greatly, likely because of their differing distributions among algal prey taxa and size class. In several experiments where Phaeocystis was abundant, we observed DMS production proportional to grazing rate, and we found clear evidence of DMS production by this haptophyte following physical stress such as sparging or filtration. It is possible that grazing-activated DMSP cleavage by Phaeocystis contributes to grazer deterrence: protozoa and copepods apparently avoided healthy colonies (as judged by relative growth and grazing rates of Chl a and DMSP), and grazing of Phaeocystis was significant only at one station where cells were in poor condition. Although we hoped to examine selective grazing on or against DMSP-containing algal prey, the dilution technique cannot differentiate selective ingestion and varying digestion rates of Chl a and DMSP. We also found that the dilution method alone was poorly suited for assessing the impact of grazing on dissolved sulfur pools, because of rapid microbial consumption and the artifactual release of DMSP and DMS during filtration. Measuring and understanding the many processes affecting organosulfur cycling by the microbial food web in natural populations remain a technical challenge that will likely require a combination of techniques to address. 相似文献
19.
《Deep Sea Research Part II: Topical Studies in Oceanography》1999,46(11-12):2909-2939
We use inverse analysis to model carbon and nitrogen flows in the upper ocean food web at Ocean Station Papa (OSP; 50°N, 145°W) for winter, spring, and late summer. The seasonal variability in basic physical, chemical, and biological characteristics is low, and the particulate carbon and nitrogen flux at 200 m is remarkably constant. Despite this apparent uniformity, the food web structure undergoes significant seasonal changes. The diversity of trophic pathways is higher during late summer than during the other two periods. The spring ecosystem is not in steady state and undergoes net phytoplankton growth and macronutrient consumption. The microbial loop is well developed only during late summer. Nevertheless, ammonium regeneration by the food web seems insufficient to meet demand by the primary producers. The difference may be due to recycling of dissolved organic nitrogen (urea+free amino acids), a process not represented in the model. The winter food web is the closest to steady state, with nitrate utilisation approximately in balance with export of particulate nitrogen. The inverse analysis suggests two main seasonally invariant features of the NE Pacific ecosystem. First, the major trophic pathway is always from picophytoplankton (0.2–5 μm) to microzooplankton (heterotrophic dinoflagellates and ciliates) to mesozooplankton. This supports the idea of a strong coupling between the microbial and metazoan food webs. Second, much of the primary production (and bacterial production in late summer) is not grazed and is recycled through the detrital pool. Both these features seem to arise from the requirement to conserve nitrogen as well as carbon in the food web. More complete measurements on the microzooplankton 20–200 μm in size, including the small metazoans like nauplii larvae, are required to improve the models presented here. 相似文献