黄海中华哲水蚤繁殖、种群补充与生活史研究

中华哲水蚤是黄、东海浮游动物关键种，连接初级生产与较高营养级，在海洋生态系统中占据核心地位。在以往研究基础上，依据2006年3月至2007年8月黄海9个航次、胶州湾11个航次现场调查数据以及大量室内实验数据，本文研究了中华哲水蚤的繁殖、种群补充以及油脂积累的季节变化，期望初步阐明中华哲水蚤在黄海的种群动态及驱动因素、并构建其生活史概念模型。 3、4月份，黄海与胶州湾中华哲水蚤的生殖腺普遍发育成熟、产卵率较高，中华哲水蚤种群进入繁殖、种群补充的活跃期，恰好可以利用此时较好的食物条件。5、6月份，中华哲水蚤在黄海近岸海区仍表现出较高的产卵率，而陆架海区的中华哲水蚤生殖腺成熟度、产卵率逐渐降低，种群逐渐表现出度夏特征—C5占优势、积累大量脂类。整个夏季，中华哲水蚤的繁殖率、种群补充率在整个黄海都较低，尤其在黄海冷水团区：中华哲水蚤生殖腺停滞于未成熟的GS1－GS2期，产卵率为零。10月，中华哲水蚤在冷水团边缘潮汐锋区的繁殖、种群补充活跃，或许可以解释秋、冬季近岸种群的恢复。11月之后，随着垂直混合的加强，黄海冷水团逐渐消失，此时陆架区的中华哲水蚤种群结束度夏过程，并以较低的繁殖率进行种群补充，直到次年3、4月份食物环境转好，中华哲水蚤种群出现新一轮繁殖、补充高峰。本文依据中华哲水蚤雌体密度、产卵率、孵化率等计算了中华哲水蚤的种群潜在补充率，我们发现，陆架区种群仅在3、4月份出现较强补充以及冬季的微弱补充，而近岸海区除夏季外，于各个季节均可进行比较活跃的种群补充，其中春季种群补充规模、强度最大；整体来看，春季是黄海中华哲水蚤种群补充的最重要时期。 本文详细研究了中华哲水蚤的繁殖与各种环境、雌体自身因素之间的关系：1、统计结果表明，中华哲水蚤的产卵率与海区食物条件（浮游植物生物量、纤毛虫丰度）之间具有紧密联系，而与油囊体积无关；在饥饿培养条件下，中华哲水蚤只能维持3－6天的产卵，而添加食物2－7天内，即可逐渐恢复产卵；体内积累油脂在饥饿过程中有所消耗，不过仍然不能阻止产卵率的下降；这些结果表明中华哲水蚤繁殖的能量所需主要来自于近期摄食，而体内储存脂类可能主要用于代谢所需，是应对不利条件的一种能量缓冲。2、统计分析表明：产卵率与雌体前体长间具有一定的正相关性，这可能由于体长较长的雌体往往具有较高的怀卵量；产卵率与温度之间没有显著的统计关系，温度可能通过调节中华哲水蚤的代谢率、体长等间接影响到产卵率。3、值得一提的是，本文发现中华哲水蚤的产卵率与其生殖腺成熟度之间具有非常紧密的统计关系，这为通过保存样品估算产卵率以及长期历史样品、数据间的比较提供了可能。 春季硅藻水华是黄海及其邻近海域的重要季节性特征。本文针对硅藻水华与中华哲水蚤繁殖的关系进行了多次现场研究，我们发现，硅藻水华因其发生海区、硅藻优势种类不同而对中华哲水蚤繁殖具有复杂多样的影响。2006年3月，胶州湾东部海区发生中肋骨条藻（Skeletonema costatum）水华，中华哲水蚤的产卵率显著增高，但其孵化率相对较低（50%左右）；2007年2月，胶州湾东部发生环纹劳德藻（Landeria annulata）水华，中华哲水蚤卵的孵化率在各种处理下均接近100%；2006年4月，黄海东北部发生太平洋海链藻（Thalassiosira pacifica）水华，产卵率与孵化率均处于调查海区的中等水平；2007年4月，黄海中部海区发生中肋骨条藻水华，中华哲水蚤在此次调查海区平均产卵率高达27.8 卵/雌体/天，远远高于以往同时期的调查结果，孵化率、幼体存活率也普遍较高；此次硅藻水华对于黄海陆架区中华哲水蚤的种群补充具有积极的促进作用。综上，硅藻水华对中华哲水蚤繁殖的影响表现出种类、海区特异性，其具体机理仍需进一步研究。 本文研究了黄海中华哲水蚤C5期油脂积累的区域、季节变化，并探讨了油脂积累对中华哲水蚤的生理、生活史的可能作用。黄海近岸区的C5期油囊体积常年较小，而陆架区则表现出明显的季节差异。在陆架区，C5期是中华哲水蚤度夏种群的主要组成部分，其油囊体积与度夏过程有密切联系：最大油囊体积（可占前体部体积的30%以上）出现于度夏准备期（5、6月），随着度夏过程的进行，油囊体积因代谢而不断消耗，至12月时，油囊体积降低到与近岸种群无异。次年4月以后，油脂积累可能随食物条件转好而再次开始积累。我们认为黄海中华哲水蚤所积累油脂除了可以为休眠提供能量以克服较长时期食物缺乏之外，还可能是休眠的诱导因素，对其生活史具有重要意义。 黄海近岸海区与陆架海区在水团特征、中华哲水蚤种群丰度与结构、繁殖特征、种群补充、油脂储存策略等方面具有显著差异，因此，本文分别讨论了这两个区域中华哲水蚤的生活史。黄海陆架海区中华哲水蚤在全年共有4－5个世代：11月末，中华哲水蚤结束度夏过程，种群中占优势的C5期个体开始蜕皮为成体、逐渐成熟、繁殖，由此产下的子代可称之为G0，此世代在食物条件较差的冬季发育成熟后可以产下G1；G1于3月初发育成熟，恰逢春季较好的食物条件，于是在3月初－5月中旬很可能发育G2、G3两个世代；假若陆架区食物环境适宜，5月中旬后很可能产生新的世代—G4；G3与G4两个世代的混合种群共同进入度夏过程，期间，一小部分C5蜕皮为成体，大部分C5保持滞育状态；至12月冷水团消退后，G3、G4世代C5蜕皮、成熟，开始新的生活周期。中华哲水蚤生殖腺成熟度、油囊体积的季节变化与上述概念模型具有较好的对应关系，另外，这两个参数简单易用、对环境变化敏感，可以尝试应用于气候变化与桡足类关系等长期研究中。 以往的研究更多的关注于黄海陆架区的中华哲水蚤种群，对近岸种群的关注较少，本文初步探讨了近岸种群的种群补充、世代情况。相对于陆架区，黄海近岸区中华哲水蚤的生活史更为复杂，区域差异较大。近岸海区中华哲水蚤产卵率、种群周转率较高；同时，近岸海区是多种鱼类的产卵场、索饵场，该区域的各营养级间的能量流动对黄海海洋生态系统的结构功能至关重要。因此，在将来的研究中，近岸海区中华哲水蚤种群的生态学、生活史应该受到同样的重视。

The combined effects of temperature and food supply on Calanus sinicus in the southern Yellow Sea in summer

The effects of temperature and food availability on the life history strategy of the planktonic copepod Calanus sinicus in the southern Yellow Sea in summer were studied in this paper. The fifth copepodite stage (CV) dominates the population in the central part of the southern Yellow Sea, where the Yellow Sea Cold Water Mass (YSCWM) occurs below the thermocline. Incubation experiments were conducted on CV C. sinicus caught from the YSCWM to examine the effects of temperature and food availability. Temperature at the surface (27degreesC) is lethal to CVs regardless of food availability. At the temperature in the middle of the thermocline (18degreesC), survival time of the specimens depends on food availability, being similar to20 days in treatments without extra food supply. At the temperature in the YSCWM (9degreesC), most animals survive at the end of 27 day incubation even in treatments without food supply. Developmental rate of CVs at 9degreesC without extra food supply is extremely low. The increase of either temperature or food supply promotes the developmental rate of CVs. According to these results, the surface layers with high temperature and low food abundance are detrimental for the survival and reproduction of C. sinicus. Low temperature and low food availability in the YSCWM help CV to maintain a much lower developmental rate and higher survival rate. The ecological trait of C. sinicus in the southern Yellow Sea in summer cannot be sufficiently explained solely by the effects of temperature.

Diel vertical migration of zooplankton following optimal food intake under predation

A model is developed to investigate the trade-offs between benefits and costs involved in zooplanktonic diel vertical migration (DVM) strategies. The 'venturous revenue' (VR) is used as the criterion for optimal trade-offs. It is a function of environmental factors and the age of zooplankter. During vertical migration, animals are assumed to check instantaneously the variations of environmental parameters and thereby select the optimal behavioral strategy to maximize the value of VR, i.e. taking up as much food as possible with a certain risk of mortality. The model is run on a diel time scale (24 h) in four possible scenarios during the animal's life history. The results show that zooplankton can perform normal DVM balancing optimal food intake against predation risk, with the profile of DVM largely modified by the age of zooplankter.

Application of Neomysis awatschensis as a standard marine toxicity test organism in China

The small mysid crustacean Neomysis awatschensis was collected in the west coast of Jiaozhou Bay, Qingdao, China in 1992 and acclimated and cultured in laboratory conditions since then. Standard acute toxicity tests using 4-6 d juvenile mysids of this species were conducted and the results were compared with Mysidopsis bahia, a standard toxicity test organism used in the US in terms of their sensitivities to reference toxins, as well as their taxonomy, morphology and geographic distributions. Because of its wide distribution along the Chinese coast, similar sensitivity to pollutants as M. bahia, short life history, small size and the case of handling, this study intended to use N. awatschensis as one of the standard marine organisms for toxicity testing in China. The species were applied to acute toxicity evaluations of drilling fluid and its additives I organotin TPT and toxic algae, and to chronic ( life cycle) toxicity assays of organotin TPT and a toxic dinofalgellate Alexandrium tamarense, respectively. Using N, awatschensis as a standard toxicity testing organism in marine pollution assessment in China is suggested.

Feeding resumption, morphological changes and mortality during starvation in Japanese flounder larvae

Japanese flounder Paralichthys olivaceus larvae established first feeding 3 days after hatching (DAH) at c. 17degreesC. Non-fed fish reached irreversible starvation at age 5 DAH. Non-fed fish showed similar feeding rate and feeding intensity as the fed fish when they were provided with prey before 5 DAH, after which the starved larvae did not feed even when prey became available. None of the six morphological measurements examined (total length, body height, eye height, head height, gut height and myotome height) showed significant differences between the non-fed and fed larvae until 5 DAH. Normal development continued only in the fed group, and the non-fed larvae showed reverse growth or body collapse after 5 DAH. Owing to the shrinkage and collapse at the top of head due to starvation, head height could be a sensitive indicator of starvation in Japanese flounder larvae. In the fed treatments, high mortality occurred from first feeding (3 DAH) to irreversible starvation (5 DAH), accounting for about two-thirds to three-quarters of the overall mortality (46-52%) throughout the experiments. This mortality was not prey density or larval density dependent. Mortality during the same period in the non-fed larvae accounted for about a third of the overall mortality (100%). (C) 2002 The Fisheries Society of the British Isles. Published by Elsevier Science Ltd. All rights reserved.

Feeding behaviour of Japanese flounder larvae under laboratory conditions

Tank-reared Japanese flounder larvae, Paralichthys olivaceus, had a major feeding peak in the morning and a secondary peak in the afternoon throughout the larval development, with light being the primary factor regulating their feeding activity. The larvae consumed rotifers in preference to Artemia for up to 10 days, after which the food preference shifted to Artemia. Feeding rates of the larvae prior to 10 days post-batch depended on prey density, but in the old larvae, feeding rates were independent of prey density. Maximum feeding rate occurred at 19 degrees C. The occurrence of the attack posture, after its onset at first feeding (2 days post-hatch), increased up to 25 days, began to decrease when the larvae prepared to settle down, then disappeared after settlement. The occurrence frequency of the attack posture was positively related to fish density, but inversely related to starvation duration, and occurred most frequently at 19 degrees C. This posture depended on prey density in larvae prior to 10 days post-hatch, but became independent of prey density as the larvae developed. It was obvious that, for flounder larvae, attack posture was a behavioural character closely related to feeding and subject to larval development and environmental factors. (C) 2000 The Fisheries Society of the British Isles.

Immune condition of Apostichopus japonicus during aestivation

Aestivation is an indispensable state in the life history of sea cucumbers, Apostichopus japonicus. The immune characteristics of the coelomic fluid of A. japonicus, were investigated during aestivation. Samples were collected between July and November 2006 from a coastal pond located off the Yellow Sea in Jiaonan, Shandong Province, China. The total coelomocytes counts (TCC), total superoxide dismutase (T-SOD), catalase (CAT), myeloperoxidase (MPO), and lysozyme (IZM) in the coelomic fluid were measured. The activities of catecholamines, [adrenaline (AD), noradrenaline (NA), and dopamine (DOP)] were estimated. TCC decreased from July to September, indicating weakness of the cellular immune activity at that time. Activities of SOD, CAT, MPO, and LZM changed significantly from July to October. Catecholamines AD and NA in coelomic fluid were significantly higher on August 21 and November 27. There was no significant variation in DOP during the sampling period. Thus, immune characters in coelomic fluid of A. japonicus changed significantly during aestivation. Water temperature was significantly and negatively correlated with TCC, and salinity was significantly and positively correlated with AD and NA. The mechanism of aestivation in A. japonicus is complex and might not be attributed only to environmental changes, such as temperature and salinity, as shown in previous studies. (C) 2008 Elsevier B.V. All rights reserved.

Viewing DVM via general behaviors of zooplankton: A way bridging the success of individual and population

In this paper, we viewed the diel vertical migration (DVM) of copepod in the context of the animal's immediate behaviors of everyday concerns and constructed an instantaneous behavioral criterion effective for DVM and non-DVM behaviors. This criterion employed the function of 'venturous revenue' (VR), which is the product of the food intake and probability of the survival, to evaluate the gains and losses of the behaviors that the copepod could trade-off. The optimal behaviors are to find the optimal habitats to maximize VR. Two types of VRs are formulated and tested by the theoretical analysis and simulations. The sensed VR, monitoring the real-time changes of trade-offs and thereby determining the optimum habitat, is validated to be the effective objective function for the optimization of the behavior; whereas, the realized VR, quantifying the actual profit obtained by an optimal copepod in the sensed-VR-determined habitat, defines the life history of a specific age cohort. The achievement of a robust copepod overwintering stock through integrating the dynamics of the constituent age cohorts subjected to the instantaneous behavioral criterion for DVM clearly exemplified a possible way bridging the immediate pursuit of an individual and the end success of the population. (c) 2005 Published by Elsevier Ltd.

Inbreeding depression for various traits in two cultured populations of the American bay scallop, Argopecten irradians irradians Lamarck (1819) introduced into China

This paper examines the effect of inbreeding level of population on the magnitude of inbreeding depression expressed by comparing them between two cultured populations (A and B) in the hermaphroditic animal of the bay scallop Argopecten irradians irradians. Population A is expected to have less genetic variations and higher inbreeding level due to longer cultured history (20 generations) and less "ancestral" individuals (26 individuals) than population B due to shorter cultured history (4 generations) and more "ancestral" individuals (406 individuals). Two groups within each population were produced, one using self-fertilization and one using mass-mating within the same population. Selfed offspring (AS and BS) from two populations both had lower fitness components than their mass-mated counterparts (AM and BM) and exhibited inbreeding depression for all examined traits, e.g. lower hatching, less viability and slower growth, indicating that inbreeding depression is a common feature in this animal. Fitness components in all traits of offspring from population A significantly differed those from population B and the magnitude of inbreeding depression for all traits in population A with higher inbreeding level was significantly smaller than that in population B with lower inbreeding level, indicating that both fitness components and magnitude of inbreeding depression were significantly affected by inbreeding level of populations and genetic load harbored in population A may be partially purged through inbreeding. Moreover, the magnitude of inbreeding depression in the two populations both varied among traits and life history stages. The present results support the partial-dominance hypothesis of inbreeding depression. (C) 2008 Elsevier B.V. All rights reserved.

Response of Polygonum viviparum species and community level to long-term livestock grazing in alpine shrub meadow in Qinghai-Tibet Plateau

Grazing by domestic herbivores is generally recognized as a major ecological factor and an important evolutionary force in grasslands. Grazing has both extensive and profound effects on individual plants and communities. We investigated the response patterns of Polygonum viviparum species and the species diversity of an alpine shrub meadow in response to long-term livestock grazing by a field manipulative experiment controlling livestock numbers on the Qinghai-Tibet Plateau in China. Here, we hypothesize that within a range of grazing pressure, grazing can alter relative allocation to different plant parts without changing total biomass for some plant species if there is life history trade-offs between plant traits. The same type of communities exposed to different grazing pressures may only alter relative species' abundances or species composition and not vary species diversity because plant species differ in resistant capability to herbivory. The results show that plant height and biomass of different organs differed among grazing treatments but total biomass remained constant. Biomass allocation and absolute investments to both reproduction and growth decreased and to belowground storage increased with increased grazing pressure, indicating the increasing in storage function was attained at a cost of reducing reproduction of bulbils and represented an optimal allocation and an adaptive response of the species to long-term aboveground damage. Moreover, our results showed multiform response types for either species groups or single species along the gradient of grazing intensity. Heavy grazing caused a 13.2% increase in species richness. There was difference in species composition of about 18%-20% among grazing treatment. Shannon-Wiener (H') diversity index and species evenness (E) index did not differ among grazing treatments. These results support our hypothesis.