长江口桡足类数量分布与变动

于1999年枯水期(2～3月份)、丰水期(8月份)、2000年枯水期(2～3月份)对长江河口浮游动物桡足类采样调查,研究了长江河口桡足类的数量分布与变动.结果表明:1999年枯水期,桡足类在整个长江河口区的平均数量相对不大,为76ind/m3,但却占同期浮游动物平均数量的95.61%;1999年丰水期桡足类平均数量为254ind/m3,占同期浮游动物平均数量的84.29%;2000年枯水期桡足类平均数量为97ind/m3,占同期浮游动物总数量的84.46%.从优势度看,1999、2000年枯水期主要优势种为华哲水蚤(Sinocalanus sinensis);1999年丰水期主要优势种为火腿许水蚤(Schmackeria poplesia).虫肢歪水蚤(Tortanus vermiculus)、真刺唇角水蚤(Labidocera euchaeta)则在枯、丰水期均为优势种.从种类数看,桡点类在1999年、2000年枯水期均为14种,1999年丰水期为枯水期的近2倍,达25种.对于长江河口主要桡足类而言,华哲水蚤的季节变化明显,适宜生活在盐度较低水域.虫肢歪水蚤数量年际变化较大,其适盐范围比华哲水蚤较宽、较高.真刺唇角水蚤的适盐范围与虫肢歪水蚤相似且更高一些,但该种在枯水期数量较少,丰水期数量较多,变化显著,更适宜在较高温时生长.火腿许水蚤适盐范围宽,能适应很大范围盐度变化,枯水期数量少,丰水期数量大,较高温度生长良好.     

两种桡足类短期热冲击的高起始致死温度值

于2007年4月研究了亚热带海域近海种桡足类中华哲水蚤(Calanus sinicus Brodsky)和真刺唇角水蚤(Labidocera euchaeta Giesbrecht)在不同驯化温度下热冲击15、30、45 min后的24 h高起始致死温度(upper incipient lethal temperature,24-h UILT50).结果表明:(1)在相同驯化温度下,两种桡足类短期热冲击24-h UILT50随暴露时间的延长而降低;(2)在相同暴露时间下,两种桡足类短期热冲击24-h UILT50随驯化温度的上升均有不同程度的上升,但这种升高的趋势会随驯化温度的上升而变缓,且趋于一固定值后不再上升;(3)中华哲水蚤在暴露时间为15、30、45 min的24 h最高起始致死温度(ultimate upper incipient lethal temperature,24-h UUILT50)分别为31.7、31.0、30.3℃,真刺唇角水蚤在暴露15、30、45 min时的24-h UUILT50分别为36.5、36.0、35.4℃;(4)在相同驯化温度和暴露时间条件下,真刺唇角水蚤对短期热冲击的耐受性显著强于中华哲水蚤.     

附着基对分叉小猛水蚤(Tisbe furcata)种群密度及水体化学要素的影响

以分叉小猛水蚤(Tisbe furcata)为研究对象, 对比室内养殖条件下添加附着基与否对分叉小猛水蚤的种群密度的影响, 并同步分析水体化学要素(亚硝态氮、硝态氮、氨氮和磷酸盐)与桡足类种群密度的关系。研究结果表明, 加入附着基并未达到增加桡足类种群密度的效果, 反而有一定的抑制作用。对水体三氮一磷的分析表明亚硝态氮、硝态氮和磷酸盐含量均与桡足类种群密度呈极显著正相关, 而氨氮浓度与桡足类种群密度间没有相关性, 这与之前研究结果一致, 进一步验证了现有养殖方法的可靠性。此外, 添加附着基养殖池中快速升高的亚硝氮含量可能抵消了附着基的积极作用, 因此, 后续相关研究需要综合考量上述因素。     

水体化学要素对分叉小猛水蚤(Tisbe furcata)和小拟哲水蚤(Paracalanus parvus)室内养殖种群密度的影响

以分叉小猛水蚤(Tisbe furcata)和小拟哲水蚤(Paracalanus parvus)为研究对象, 对比室内养殖条件下两种桡足类的种群密度差异, 并分析水体化学要素亚硝态氮、硝态氮、氨氮和磷酸盐与桡足类种群密度的关系。结果表明: 分叉小猛水蚤较小拟哲水蚤种群密度优势明显(P<0.01), 更适合北方室内养殖, 盐度可能起主要作用; 水体亚硝态氮最为重要, 在桡足类种群的快速增长期, 其浓度与两种桡足类的种群密度均呈极显著正相关性; 水体磷酸盐浓度与两种桡足类的种群密度均呈极显著正相关性; 通过部分换水的方式可以实现分叉小猛水蚤的可持续培养, 换水量不要超过水体总量的1/3; 本研究所采用复合饲料和养殖方式可以实现分叉小猛水蚤的北方室内大规模、高密度和可持续养殖。     

脂肪酸对中华哲水蚤摄食两种海洋微藻的指示作用

在室内以饥饿培养为对照,以海洋原甲藻(Prorocentrum micans)和中肋骨条藻(Skeletonema costatum)培养中华哲水蚤(Calanus sinicus),研究了各脂肪酸标记对中华哲水蚤摄食不同饵料的指示作用。结果显示,海洋原甲藻中18 ∶ 4ω3、22 ∶ 6ω3含量较高,中肋骨条藻中16 ∶ 1ω7、20 ∶ 5ω3的含量较高。二者分别表现出典型的甲藻门和硅藻门的脂肪酸组成特征。中华哲水蚤的脂肪酸组成有两个特点:(1)20 ∶ 5ω3和22 ∶ 6ω3的含量均较高;(2)其体内表征桡足类浮游植物食性、由桡足类自身合成的20 ∶ 1和22 ∶ 1脂肪酸占有相当的比例。虽然中华哲水蚤对不同脂肪酸的吸收和转化效率不同,但以脂肪酸作为标记还是成功的指示了中华哲水蚤对微藻的摄食。在饥饿培养中,首先消耗的是那些浮游动物自身不能合成的多不饱和脂肪酸,而结构脂肪酸都表现出了较高的保守性。结合各脂肪酸标记变化趋势和Pearson相关性分析的结果认为,18 ∶ 4ω3、18 ∶ 4ω3/16 ∶ 1ω7、∑18/∑16能较好的指示中华哲水蚤对海洋原甲藻的摄食,仅16 ∶ 1ω7/18 ∶ 4ω3能指示中华哲水蚤对中肋骨条藻的摄食。     

三座南亚热带大型水库敞水区桡足类群落结构比较

于2000-2002年对南亚热带三座大型水库:新丰江水库、公平水库和飞来峡水库敞水区桡足类进行了定性定量采样.三座水库桡足类种类数较少,共检出桡足类4科10属14种,其中8种哲水蚤,5种剑水蚤和1种猛水蚤.主要分布在广东省水库的我国特有种舌状叶镖水蚤(Phyllodiaptomus tunguidus)和广布性种类右突新镖水蚤(Neodiaptomus schmackeri)是出现频率较高的哲水蚤种类,温中剑水蚤(Mesocyclops thermocyclopoides)、台湾温剑水蚤(Thermocyclops taihokuensis)和博平近剑水蚤(Tropocycl opsbopingi)是出现频率较高的剑水蚤种类.水库的流域面积、滞留时间、鱼类捕食和营养状态是影响水库桡足类种类组成和数量的重要因素.三座水库桡足类种类数与水库流域面积大小存在正相关关系.随着水库营养水平的升高,桡足类密度和生物量也相应增加,但是大型哲水蚤的优势度降低,而剑水蚤和桡足类幼体的优势度上升.水力滞留时间很短是引起飞来峡水库桡足类种群波动的主要因素.水库捕食性鱼类对甲壳浮游动物的选择性捕食,对桡足类种类影响较小,对桡足类成体密度影响较大.由于地区差异和鱼类捕食强度等因素的影响,桡足类种类多样性与水体营养状态之间存在不确定性.     

重金属对海洋桡足类的影响研究进展

桡足类是海洋浮游动物种群的主要组成部分和重要的初级消费者,重金属污染对其影响可通过食物链传递到其他海洋生物甚至人类。综述了近20 a来重金属对桡足类影响的研究进展,包括重金属对桡足类的毒性和生理效应,重金属在桡足类体内蓄积及桡足类体内重金属的食物链(网)传递。并指出今后的研究重点:桡足类体内致毒重金属的存在形式,重金属食物暴露对桡足类生理生化影响机理,以及重金属对桡足类生活史的影响。     

海洋酸化对日本虎斑猛水蚤抗氧化性指标和繁殖发育的影响

本文选取海洋桡足类日本虎斑猛水蚤(Tigriopus japonicus)为模式生物,采用生化测定和实验生态学方法,研究不同酸化胁迫对桡足类体内抗氧化性指标[超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、谷胱甘肽硫转移酶(GST)和脂质过氧化(LPO)]、幼体发育时间、世代发育时间和产后代数的影响。结果表明:海水酸化可显著诱导桡足类的抗氧化性酶(SOD和CAT)的活性,而GST活性不受酸化影响,同时酸化可显著提高桡足类的LPO水平,可见该桡足类可通过SOD和CAT活性的提高来抵抗酸化胁迫引起的氧化胁迫;另外,酸化显著缩短桡足类的幼体发育时间和世代发育时间,并显著抑制其产后代数,提示酸化可以影响海洋桡足类的种群补充和动态;酸化引起该桡足类氧化胁迫的出现,继而对细胞生物大分子(如蛋白质、核酸等)造成氧化损伤,最终影响到该动物的个体水平和种群动态(如缩短发育时间和抑制繁殖力)。     

长江口南北支浮游甲壳动物的比较及南水北调工程影响预测

南水北调东线、中线工程实施后将给长江口水生生物的生态环境带来影响.2005年秋季和2006年春季,对长江口南、北支浮游甲壳动物进行了2航次的调查.调查区域从长江口徐六径至河口 50号灯标,全长181.8 km,自西向东江面宽由约5.7 km扩展为约90km,平面形态呈扇形分布,设立3个断面14个调查采集点.采集到浮游甲壳动物共23科37属54种,其中枝角类6科8属15种,桡足类17科29属39种;秋季种类数多于春季,北支桡足类种类数多于南支;平均总密度为9.10 ind·L-1,平均总生物量为0.1179 mg·L-1,以桡足类为主;北支Ⅲ断面的现存量远远高于南、北支其他断面;长额象鼻溞、简弧象鼻溞为优势枝角类;中华华哲水蚤、汤匙华哲水蚤、球状许水蚤、广布中剑水蚤为优势桡足类.文中还对长江口南、北支浮游甲壳动物的总体水平及时空分布、南水北调对浮游甲壳动物的影响进行了分析.     

湛江港湾浮游桡足类群落结构的季节变化和影响因素

2009年2月、5月、8月和11月分别对湛江港湾浮游动物进行了季度月调查,并对该海域浮游桡足类群落结构的季节变化及影响因素进行了分析.结果共鉴定出桡足类72种,其中冬季36种,占浮游动物种类数的29.5％;春季33种,占浮游动物种类数的39.3％;夏季24种,占浮游动物种类数的29.6％;秋季19种,占浮游动物种类数的40.4％.主要优势种为中华哲水蚤Calanus sinicus、强额拟哲水蚤Paracalanus crassirostris、短角长腹剑水蚤Oithona brevicornis、亚强真哲水蚤Eucalanus subcrassus、刺尾纺锤水蚤Acartia spinicauda和桡足类幼体.季节变化模式为:夏季丰度最高,达960.0个/m3,春季次之为421.0个/m3,冬季为303.4个/m3,秋季最低仅为252.8个/m3.平面分布冬春季丰度内湾高,往湾口逐渐降低,夏季内湾低往湾口逐渐增大,而秋季分布较均匀.调查海区桡足类丰度与水温、叶绿素a和浮游植物细胞丰度呈极显著的正相关,与DIN和PO3-4呈显著的负相关,与盐度、pH值和活性硅酸盐相关性不明显.     

Accumulation of mercury in estuarine food chains

To understand the accumulation of inorganic mercury and methylmercury at the base of the estuarine food chain, phytoplankton (Thalassiosira weissflogii) uptake and mercury speciation experiments were conducted. Complexation of methylmercury as methylmercury-bisulfide decreased the phytoplankton uptake rate while the uptake rate of the methylmercury-cysteine and -thiourea complexes increased with increasing complexation by these ligands. Furthermore, our results indicated that while different ligands influenced inorganic mercury/methylmercury uptake by phytoplankton cells, the ligand complex had no major influence on either where the mercury was sequestered within the phytoplankton cell nor the assimilation efficiency of the mercury by copepods. The assimilation efficiency of inorganic mercury/methylmercury by copepods and amphipods feeding on algal cells was compared and both organisms assimilated methylmercury much more efficiently; the relative assimilation efficiency of methylmercury to inorganic mercury was 2.0 for copepods and 2.8 for amphipods. The relative assimilation is somewhat concentration dependent as experiments showed that as exposure concentration increased, a greater percentage of methylmercury was found in the cytoplasm of phytoplankton cells, resulting in a higher concentration in the copepods feeding on these cells. Additionally, food quality influenced assimilation by invertebrates. During decay of a T. weissflogii culture, which served as food for the invertebrates, copepods were increasingly less able to assimilate the methylmercury from the food, while even at advanced stages of decay, amphipods were able to assimilate mercury from their food to a high degree. Finally, fish feeding on copepods assimilated methylmercury more efficiently than inorganic mercury owing to the larger fraction of methylmercury found in the soft tissues of the copepods.     

Phosphorus limitation and excess carbon in zooplankton

Organisms rely on a series of chemical reactions, which are constrained by the availability of key chemical elements, such as carbon (C), nitrogen (N), and phosphorus (P). Ecological stoichiometry provides a tool for analyzing how the balance of elements required by organisms affects food-web dynamics. Ecological stoichiometric theory suggests that the balance between supply and demand of elements is determined by the conversion efficiency from resources to organisms.Autotrophs and heterotrophs commonly face unequal access to and uptake of elements. The stoichiometric variability of autotrophs is based on their ability to maintain the balance of elements required for growth. This creates a challenge for their grazers. Phytoplankton can adjust their P content to ambient nutrient concentrations, while zooplankton cannot store excess nutrients. Ecological stoichiometric theory thus suggests that zooplankton have relatively fixed stoichiometry compared with phytoplankton.Nutrient limitation is common in aquatic systems. Stoichiometric imbalances between phytoplankton and zooplankton mean that zooplankton rarely find optimal food sources, and phytoplankton production is in excess. P availability potentially limits zooplankton growth, because of the high C:P ratio in phytoplankton relative to zooplankton demand. Based on the Liebig minimum principle, organisms are normally limited by a single nutrient, while everything else is in excess. Under P deficiency, excess C cannot be allocated to zooplankton somatic growth, and the net intake of C must balance the C:P ratio of zooplankton. Thus, when zooplankton encounter nutritionally imbalanced foods the elements in excess are released in order to maintain homeostasis. Excess C, released by zooplankton results in two biochemical challenges: (1) to sequester the limiting element and (2) to either store or dispose of the element in surplus.Zooplankton must resort to various physiological solutions to cope with these challenges. As a first option, zooplankton can reduce their C assimilation efficiency but maintain their P assimilation efficiency. Alternatively, after assimilation, excess C may be stored in C-rich compounds. Finally, assimilated excess C could also be disposed of through respiration or extracellular release. Excess C released by zooplankton reduces C transfer efficiency and sequestration in aquatic ecosystems.In aquatic ecosystems, C sequestration largely depends on the balance between uptake and demand for key nutrient elements. These feedback mechanisms have arisen only because organisms must obey stoichiometric rules at the cell and body levels, which greatly constrain the range of element values in ecosystems. Thus, the fate of C in ecosystems is determined by the absolute and relative demands for N and P of each organism. Limiting elements are utilized for growth and transferred in food chains with high efficiency, while non-limiting elements must be disposed of. Therefore, low C:P phytoplankton communities subject to high turnover rates and high productivity are selectively channeled into zooplankton. When zooplankton face high C:P foods, excess C is returned to the environment. Hence, nutrient-deficient phytoplankton constitute poor food, influencing the entire food web and adversely affecting secondary production at all levels.Excess C processed by zooplankton has far-reaching implications for ecosystem food-web functioning and C sequestration. Studies of the fate of excess C in zooplankton would increase the understanding of energy flow and material cycling in aquatic ecosystems. This paper reviews the reasons for P limitation and excess C in zooplankton, principal routes for the disposal of excess C, and the ecological effects of this. In addition, the paper aims to provide insight and a theoretical foundation for related studies in China.     

Variation in nutrient limitation of lotic and lentic algal communities in a Texas (USA) river

Nutrient limitation of periphyton and phytoplankton was assessed in the Upper Guadalupe River, Texas USA. Nutrient-diffusing substrates with added nitrogen (N) and phosphorus (P) were used to identify the limiting nutrient for lotic algae at three river sites in summer, fall, and winter. Pots enriched with P had significantly higher chlorophyll a concentrations for 7 of 9 trials. Added N alone did not significantly increase algal standing crops, although it was found to be secondarily limiting on one (and possibly two) occasions. Flow-through enrichment experiments were conducted in order to quantify the concentration of P needed to significantly increase algal standing crops. Response to enrichment was rapid when ambient P concentration was low (< 0.010 mg L^–1), but more moderate when ambient P levels were higher (0.015–0.025 mg L^–1). Nutrient limitation of phytoplankton in small surface-release reservoirs varied throughout the study, but N was either primarily or secondarily limiting in 6 of 8 trials; shifts in the limiting nutrient were correlated with fluctuations in flow into the reservoirs. Our enrichment studies show that algal response to nutrient addition was unpredictable as phytoplankton tended to be N-limited while periphyton was mainly P-limited. Further, while discharge apparently dictated the nutrient-biomass relationship for phytoplankton in reservoirs, ambient nutrient level is an important determinant of lotic periphyton response to enrichment.     

Responses of Two Coastal Algae (Skeletonema costatum and Chlorella vulgaris) to Changes in Light and Iron Levels1

Iron (Fe) is essential for phytoplankton growth and photosynthesis, and is proposed to be an important factor regulating algal blooms under replete major nutrients in coastal environments. Here, Skeletonema costatum, a typical red-tide diatom species, and Chlorella vulgaris, a widely distributed Chlorella, were chosen to examine carbon fixation and Fe uptake by coastal algae under dark and light conditions with different Fe levels. The cellular carbon fixation and intracellular Fe uptake were measured via ¹⁴C and ⁵⁵Fe tracer assay, respectively. Cell growth, cell size, and chlorophyll-α concentration were measured to investigate the algal physiological variation in different treatments. Our results showed that cellular Fe uptake proceeds under dark and the uptake rates were comparable to or even higher than those in the light for both algal species. Fe requirements per unit carbon fixation were also higher in the dark resulting in higher Fe: C ratios. During the experimental period, high Fe addition significantly enhanced cellular carbon fixation and Fe uptake. Compared to C. vulgaris, S. costatum was the common dominant bloom species because of its lower Fe demand but higher Fe uptake rate. This study provides some of the first measurements of Fe quotas in coastal phytoplankton cells, and implies that light and Fe concentrations may influence the phytoplankton community succession when blooms occur in coastal ecosystems.     

Grazing rates and behaviors of Neocalanus plumchrus: implications for phytoplankton control in the subarctic Pacific

Grazing rates and behaviors of the copepod Neocalanus plumchrus were investigated in shipboard experiments during the first SUPER Program cruise (May, 1984). N. plumchrus can exploit cells in the 2 to 30 m size range with equal clearance efficiency but displays considerable flexibility in responding to changes in concentration and size composition. Its functional response helps to stabilize phytoplankton at low densities. In 60-liter microcosms, a density of one copepod liter^–1 was sufficient to maintain the ambient abundance and structure of the phytoplankton community for a week. In the absence of the copepod, phytoplankton bloomed to unnaturally high levels, and the community composition was dramatically altered. Despite its grazing potential, N. plumchrus was not present in sufficient density to control phytoplankton blooms in the subarctic Pacific. However, the copepod may have an important role in regulating the abundance of smaller grazers and the size structure of the phytoplankton community.Contribution No. 2002 from Hawaii Institute of Geophysics, University of Hawaii, Honolulu, HI 96822     

Agronomic improvements through the genetic and physiological regulation of nitrogen uptake in wheat (Triticum aestivum L.)

Nitrogen (N) uptake is the first step in nitrate assimilation, and efficient N uptake is essential for plant growth, especially for protein biosynthesis and photosynthetic activities. In cereals, improved N uptake is closely coupled with an increase in nitrogen use efficiency (NUE) and yield improvements. Because wheat (Triticum aestivum L.) is a leading crop worldwide, a better understanding of N uptake regulation in wheat is vital to improving NUE and developing sustainable agricultural systems. However, detailed information regarding the biological mechanisms that are responsible for the more efficient uptake of ambient N by wheat is limited. This review presents recent developments in the biological mechanisms of N uptake in wheat, including plant growth regulations, fundamental roles of root systems, interactions between N species, and genetic controls. Specifically, this paper provides a number of potential strategies that can be used to increase wheat N uptake. The information provided here may guide N fertilizer management during wheat production and further elucidate the plant regulatory mechanisms that are involved in N uptake, which can thereby increase wheat NUE.     

东海原甲藻与中肋骨条藻的种间竞争数值模拟

研究探讨了两个零维箱式模型在东海典型赤潮藻东海原甲藻和中肋骨条藻竞争与演替研究中的应用。模型在采用不同接种密度下的单种培养实验数据进行参数校正后,被用来模拟不同N/P条件下单种培养实验以及两藻种共培养竞争实验,并以实验数据对其结果进行了验证。模拟结果表明,在单种培养条件下,模型能够较好地重现两种藻在不同N/P环境中的生长及对营养盐的利用;共培养实验的模拟结果显示,在所有初始细胞密度比例条件下,中肋骨条藻的最终密度均会超过东海原甲藻,且PO4的消耗主要源于中肋骨条藻的利用,与实验结果一致,表明模型能够很好地体现两种藻的竞争结果及对营养盐的竞争关系;由于模型不足以模拟除营养盐竞争以外的藻间相互作用,模拟结果未体现东海原甲藻细胞数迅速衰减这一现象,有待进一步研究。     

Phosphorus physiological ecology and molecular mechanisms in marine phytoplankton

Phosphorus (P) is an essential nutrient for marine phytoplankton and indeed all life forms. Current data show that P availability is growth‐limiting in certain marine systems and can impact algal species composition. Available P occurs in marine waters as dissolved inorganic phosphate (primarily orthophosphate [Pi]) or as a myriad of dissolved organic phosphorus (DOP) compounds. Despite numerous studies on P physiology and ecology and increasing research on genomics in marine phytoplankton, there have been few attempts to synthesize information from these different disciplines. This paper is aimed to integrate the physiological and molecular information on the acquisition, utilization, and storage of P in marine phytoplankton and the strategies used by these organisms to acclimate and adapt to variations in P availability. Where applicable, we attempt to identify gaps in our current knowledge that warrant further research and examine possible metabolic pathways that might occur in phytoplankton from well‐studied bacterial models. Physical and chemical limitations governing cellular P uptake are explored along with physiological and molecular mechanisms to adapt and acclimate to temporally and spatially varying P nutrient regimes. Topics covered include cellular Pi uptake and feedback regulation of uptake systems, enzymatic utilization of DOP, P acquisition by phagotrophy, P‐limitation of phytoplankton growth in oceanic and coastal waters, and the role of P‐limitation in regulating cell size and toxin levels in phytoplankton. Finally, we examine the role of P and other nutrients in the transition of phytoplankton communities from early succession species (diatoms) to late succession ones (e.g., dinoflagellates and haptophytes).     

不同小麦品种氮效率与氮吸收对氮素供应的响应及生理机制

以具有典型特征的不同氮效率小麦品种为材料,研究了低氮和高氮条件下小麦的生物学性状、生理参数和氮同化代谢酶活性.结果表明:低氮条件下,不同氮效率小麦品种根系干质量、茎叶干质量、植株氮累积量基本上为氮高效品种>中效品种>低效品种.低氮条件下,氮吸收高效品种（冀97-6360）的根系活跃吸附面积、TTC还原力、叶片硝酸还原酶活性和叶片NO₃^-含量最大;生理高效品种(石新5418)具有较高的叶片亚硝酸还原酶活性和谷氨酰胺合成酶活性,较低的植株全氮含量、叶片NO₃^-含量和硝酸还原酶活性.低氮条件下植株氮利用效率与氮吸收系数显著相关.不同小麦品种在高氮条件下的生物学性状、生理参数和氮同化代谢酶活性与低氮条件下不尽一致.     

Heterotrophic utilization of extracellular products of phytoplankton in a tropical estuary

Bacterial uptake of algal exudates has been estimated in a tropicalestuary, Dona Paula, where the seasonal fluctuations in hydrographicand nutrient parameters as well as dissolved organic matterconcentrations and phytoplankton species composition are dominatedby the monsoon regime. A close coupling existed between algaland bacterial trophic levels. Algal exudation products wererapidly assimilated with short turnover times. An average 80%of the excreted material was removed by heterotrophic bacteriaand there was a significant correlation between algal extracellularproduction and net bacterial uptake of algal exudates.