St Helena Bay (southern Benguela) then and now: muted climate signals,large human impact

The development of suitable reference states for ecosystem-based management requires documentation of changes in structure and functioning of marine ecosystems, including assessment of the relative importance of bottom-up and top-down processes as drivers of change. We used monitoring data available from St Helena Bay, the most productive bay and an important nursery area situated on the west coast of South Africa, during 1950–2010 to reveal changes in the abiotic and biotic components. St Helena Bay in the 1950s showed similarities to 2000–2010 in terms of wind patterns, hydrology and phytoplankton. Upwelling, oxygen and nutrient concentrations in subthermocline water displayed pronounced decadal-scale variability. Primary production in St Helena Bay is variable, but consistently higher than that on the adjacent Namaqua shelf. Zooplankton size composition and biomass in August have changed markedly since the 1950s. During 2001–2010, mesozooplankton biomass in autumn was considerably lower than in summer, probably due to predation by small pelagic fish. Pelagic fish catch patterns and distributions have altered dramatically. Conservation measures, implemented to reverse past negative human impact, have benefitted marine mammals, the abundance of which has increased in the area, but additional conservation measures are necessary to reverse the decline in African penguins Spheniscus demersus. St Helena Bay shows a muted response to long-term change in the southern Benguela, with marked decadal variability but no clear long-term trend in oceanography and biogeochemistry. Changes in ecosystem boundary conditions and fishing pressure cannot be ignored as important drivers of change in the southern Benguela since the 1950s.     

胶州湾浮游植物初级生产力粒级结构及固碳能力研究

根据2006年3月-2007年2月逐月对胶州湾浮游植物分粒级初级生产力的调查研究,分析了该海湾初级生产力的季节变化和空间分布、粒级结构特征以及碳流途径,计算了胶州湾浮游植物光合作用固碳量以及其对富营养化物质氮、磷的净化能力.结果表明:胶州湾的初级生产力平均为408.8 mgC*m-2d-1,存在明显的季节差异和空间分布的不均匀性;微微型浮游植物(Picophytoplankton)对总初级生产的贡献率最高(42.14%),小型浮游植物(Microphytoplankton)和微型浮游植物(Nanophytoplankton)贡献率相当(分别为27.81%和30.03%);浮游植物光合作用固定的碳超过50%通过微食物环再向高营养级传递并入经典食物链,微食物环在胶州湾生态系统碳循环中具有重要作用;胶州湾海域每年通过浮游植物光合作用固碳量为52 809.1 tC,按照Redfield比值(C∶N∶P=106∶16∶1)每年吸收N和P的量值分别为9 299.7 t和1 287.0 t,浮游植物对大气CO2的吸收及对富营养化物质的净化均具有重要作用.     

Nitrogen isotopic fractionation of particulate organic matter production and remineralization in the Prydz Bay and its adjacent areas

During the 29th Chinese National Antarctic Research Expedition, spatial variations in nitrogen isotopic composition of particulate nitrogen (δ15N_PN) and their controlling factors were examined in detail with regard to nitrate drawdown by phytoplankton and particulate nitrogen (PN) remineralization in the Prydz Bay and its adjacent areas. To better constrain the nitrogen transformations, the physical and chemical parameters, including temperature, salinity, nutrients, PN and δ15N_PN in seawater column were measured from surface to bottom. In addition, the nitrogen isotopic fractionation factor of nitrate assimilation by phytoplankton in the mixed layer, and the nitrogen isotopic fractionation factor of PN remineralization below the mixed layer were estimated using Rayleigh model and Steady State model, respectively. Our results showed that suspended particles had its lowest δ15N_PN in the surface layer, which was due to the preferential assimilation of 14N in nitrate by phytoplankton. The δ15N_PN in the mixed layer of the Prydz Bay and its adjacent areas decreased from the inner shelf to the outer basin, ascribing to the effect of isotope fractionation during phytoplankton assimilation. In mixed layer, the spatial distribution of δ15N_PN associated with particulate organic matter (POM) production can be well interpreted according to Rayleigh model and Steady State model. The nitrogen isotope fractionation factor during phytoplankton assimilating nitrate was estimated as 10.0‰ by Steady State model, which was more reasonable than that calculated by Rayleigh model. These results validate the previous reports of fractionation factor during nitrate assimilation by phytoplankton. Increasing δ15N_PN with depth below the euphotic zone correlated with the decreasing PN contents, and it was attributed to preferential remineralization of 14N in PN by bacteria. In subsurface and deep layer, the δ15N_PN distributions also conformed to Rayleigh model and Steady State model during PN remineralization, with a fractionation factor of about 3.6‰ and 3.2‰, respectively. It is the first time to estimate the fractionation factor during POM production and remineralization in the Prydz Bay and its adjacent areas. Such fractionation may provide a useful tool for the follow-up study of the nitrogen dynamics in the Southern Ocean.     

胶州湾北部水层生态动力学模型与模拟 Ⅰ.胶州湾北部水层生态动力学模型

建立了一个包括浮游植物、浮游动物、无机氮和磷、溶解态与悬浮有机物及溶解氧七状态变量的浅海水体生态动力学箱式模型,并且考虑了海面太阳辐照度变化、海水与底泥温度变化以及营养盐海底溶出和陆源流入的影响。初步分析了在胶州湾北部浮游生态系统演变的几个特征时期动力学方程中的物流动态特征。结果是比较合理的。     

Microheterotrophic pathways in the southern Benguela upwelling system

During the 1980s, there was a major shift in the understanding of the structure of marine foodwebs. As a result, the microbial loop has been incorporated into the classical concept of the planktonic food chain. Heterotrophic bacteria and Protozoa have been shown to be important components of the plankton biomass in many parts of the world's oceans, and their role in the trophic dynamics of pelagic foodwebs has been studied intensively. In the southern Benguela, field, laboratory and modelling studies have been combined to calculate carbon and nitrogen fluxes through the microheterotrophic portion of the pelagic foodweb. A size-based simulation model incorporating recent hypotheses on the structure and functioning of the pelagic foodweb after upwelling predicts rapid growth of a phytoplankton community dominated by netphytoplankton and chain-forming nanophytoplankton cells. After nitrate-depletion the bloom declines, to be followed by a bloom of single nanophytoplankton cells dependent upon regenerated nitrogen. During conditions of high nitrate availability and a netphytoplankton-dominated community, mesozooplankton ingest 44 per cent of the total primary production through herbivory and 1,4 per cent through carnivory. During periods of low nitrate availability and a nanophytoplankton-dominated community, mesozooplankton ingest 0,6 per cent of the total primary production through herbivory and 5 per cent through carnivory. Food chains are longer and microheterotrophs are an important link between primary producers and the larger heterotrophs. Simulation results show that microheterotrophs are an important component of the pelagic foodweb, primarily as regenerators of nitrogen, which sustains phytoplankton growth, and as a food source for larger heterotrophs of the metazoan foodweb during the nanophytoplankton-dominated bloom.     

Sediment organic matter composition and dynamics in San Francisco Bay, California, USA: Seasonal variation and interactions between water column chlorophyll and the benthos

Sediment and water column data from four sites in North, Central and South San Francisco Bays were collected monthly from November 1999 through November 2001 to investigate the seasonal variation of benthic organic matter and chlorophyll in channel sediments, the composition and quality of sediment organic matter (SOM), and the relationship between seasonal patterns in benthic organic matter and patterns in water column chlorophyll. Water column chlorophyll peaked in the spring of 2000 and 2001, characteristic of other studies of San Francisco Bay phytoplankton dynamics, however an unusual chlorophyll peak occurred in fall 2000. Cross-correlation analysis revealed that water column chlorophyll at these four channel sites lead sediment parameters by an average of 2 to 3 months. Sediment organic matter levels in the San Francisco Bay channel showed seasonal cycles that followed patterns of water column production: peaks in water column chlorophyll were followed by later peaks in sediment chlorophyll and organic matter. Cyclical, seasonal variations also occurred in sediment organic matter parameters with sediment total organic carbon (TOC) and total nitrogen (TN) being highest in spring and lowest in winter, and sediment amino acids being highest in spring and summer and lowest in winter. Sediment chlorophyll, total organic carbon, and nitrogen were generally positively correlated with each other. Sediment organic matter levels were lowest in North Bay, intermediate in Central Bay, and highest in South Bay. C:N ratio and the ratio of enzyme hydrolyzable amino acids to TOC (EHAA:TOC) data suggest that SOM quality is more labile in Central and northern South Bay, and more refractory in North Bay and southern South Bay.     

A nitrogen and phosphorus dynamic model of mesocosm pelagic ecosystem in the Jiaozhou Bay in China

A nitrogen and phosphorus dynamic model of mesocosm pelagic ecosystem was established according to the summary and synthesis of the models available, in which seven state variables （DIN, PO4-P, DON, DOP, phytoplankton, zooplankton and detritus） were included. Logically it had five modules--phytoplankton, zooplankton, dissolved inorganic nutrients, dissolved organic nutrients and detritus. The results showed that this model could simulate the variations of DIN, PO4-P, DON, DOP, POC and phytoplankton biomass in pelagic ecosystem in mesocosm properly, based on the site experiment data in the Jiaozhou Bay in the autumn of 1999 and the summer of 2000. Not only the logical structure but also the model parameters were feasible, and about 20 parameters were made to fit for the Jiaozhou Bay during the simulation. All of these are necessary to study the control mechanism of nutrients biogeochemical cycling in the Jiaozhou Bay and other China＇ s coastal waters.     

胶州湾北部水层-底栖耦合生态系统的动力数值模拟分析

基于胶州湾1995年5航次的生态动力学综合实验观测，建立了一个水层－底栖生态系耦合的动力学箱式模型，其中水层亚模型包括浮游植物、浮游动物、无机氮、无机磷以及DOC、POC和溶解氧7变量，底栖部分包括大型、小型底栖生物、细胞、碎屑及无机氮和磷6变量。模型考虑了海面太阳辐照度变化、海水及底泥温度变化，以及营养盐与DOC陆源流入的影响，利用该模型成功地模拟了胶州湾北部各生态变量的季节变化特征。同吴增茂等（1999）水层模型模拟结果相比可以看出，耦合模型的结果更加合理。     

Distribution and vertical dynamics of planktonic communities at Sofala Bank, Mozambique

Coastal ecosystem processes are largely influenced by the interaction of different factors operating at various temporal and spatial scales, specifically those responsible for primary production patterns that modulate zooplankton and subsequent trophic levels. Hydrological processes, such as tidal cycles and coastal currents, nutrients availability, phytoplankton groups (studied through algal pigment signatures analysed by HPLC), and zooplankton abundance and distribution were investigated at the Sofala Bank (Mozambique), with special emphasis on their horizontal distribution and vertical dynamics (48 h). Horizontal distribution has shown inshore–offshore gradients in all analysed parameters, as well as inshore waters intrusion probably related to Zambezi River delta runoff. Tidal currents were responsible for major hydrological vertical variations and for horizontal and vertical advection of phytoplankton biomass in the surface and deepest layers, respectively. Nutrient concentrations were typical from oligotrophic regions, and nutrient ratios were strongly influenced by depleted nitrate + nitrite concentrations, indicating low estuarine discharges typical from the dry season. The very low N:P ratio obtained suggests strong nitrogen limitation to phytoplankton communities, supporting the low phytoplankton abundance observed. Both phytoplankton pigments and zooplankton were found mainly near the bottom (40 m depth), despite the latter displayed vertical migrations triggered by light variations. Phytoplankton community was dominated by microflagellates, specifically prymnesiophyceans, and behaved as a whole, except Cyanobacteria that displayed vertical distribution movements different from other phytoplankton groups, being mainly concentrated at mid-water column depths (10–20 m). This investigation enhances physico-chemical phenomena and their importance determining the planktonic communities vertical dynamics at Sofala Bank, a tropical coastal ecosystem of the Western Indian Ocean where planktonic dynamics are still poorly described and understood.     

南极普里兹湾及其邻近海域悬浮颗粒有机物的碳同位素组成及其影响因素

依托中国第29次南极科学考察航次开展了南大洋普里兹湾及其邻近海域悬浮颗粒有机物碳同位素组成(δ13CPOC)的研究,结合温度、盐度、营养盐和溶解CO_2的数据,揭示了影响研究海域颗粒有机物碳同位素组成的主控因素,计算出混合层中浮游植物吸收无机碳过程的碳同位素分馏因子。结果表明,普里兹湾及其邻近海域的δ13CPOC介于-28.5‰~-21.1‰,平均值为-24.6‰,表现出湾内大于湾外的特征。浮游植物同化吸收CO_2过程的碳同位素分馏是影响研究海域混合层δ13 CPOC的主要因素,根据δ13CPOC和1/[CO_2(aq)]的线性拟合关系,计算出浮游植物同化吸收CO2过程的碳同位素分馏因子εp为23.4‰。δ13CPOC的垂直分布随深度增加而增大,反映出颗粒有机物垂向输送过程中颗粒有机物再矿化过程同位素分馏作用的影响。     

Phosphorus and nitrogen cyclings in the pelagic system of hiroshima bay: Results of numerical model simulation

A numerical ecosystem model expressing both phosphorus and nitrogen cyclings in the pelagic system of Hiroshima Bay, Japan, was developed in order to investigate the seasonal variations of these elements and their annual budgets. Based on the geophysical and chemical structures of the bay, Hiroshima Bay was divided into northern and southern boxes, themselves divided into two layers of an upper 5 m and a lower layer according to the stratification of the water column. The model consists of equations representing all relevant physical and biological processes. The results revealed that the internal regeneration of materials was an important source of bioavailable nutrients for phytoplankton growth in the water column. The incorporation of phytoplankton aggregation improved the accuracy of the outputs in comparison to the observed data, especially during the stratified summer season. The results also indicated that phosphorus limitation of phytoplankton growth occurs in the upper layer during summer while light limitation occurs in the lower layer. In addition, physical processes such as diffusion and advection were also important as they ensured that most of regenerated nutrients in the lower layer were transported to the upper layer. Thus, these processes might support the high primary production and the production of oysters that are extensively cultured in this bay. Considering the informative results obtained, the model used in this study provides a sound basis and tool to describe the dynamics of phosphorus and nitrogen cyclings in Hiroshima Bay.     

浮游植物生物量研究 Ⅰ.浮游植物生物量细胞体积转化法

在海洋生态动力学研究过程中,采用浮游植物细胞数量来估算浮游植物丰度可以说是不够精确的,因为不同种的浮游植物细胞大小差别很大,只有浮游植物的生物量才能正确反映海洋生态系中的能量分布.本文以拟合浮游植物细胞相似体积方法,基于胶州湾生态动力学研究所获资料,计算了87种中国近海常见浮游植物的细胞体积、鲜重、碳含量、氮含量.     

Carbon and nitrogen flow through pelagic microheterotrophic communities

The significance of the microheterotrophic community of bacteria and Protozoa in marine systems is reviewed. In surface waters, bacterial production may be linked to cycles of photosynthetically produced dissolved organic matter released from living phytoplankton. The bacteria then form a principal food resource for grazing Protozoa which are themselves potentially available for exploitation by higher trophic levels. Recent data suggest that the interaction between Protozoa and their bacterial prey may be a good deal more complicated than this simple predator-prey relationship implies. Ciliates may show either "steady-state" or strongly cyclical relationships with their bacterial prey, whose community may in turn be supported to a large extent by the release of dissolved organic matter by the ciliate population. This implies that the low standing stocks of bacteria commonly recorded in many pelagic systems may be sustained, as well as exploited, by bacterivorous Protozoa. In other systems, bacterial production may enter the larger zooplankton directly without involvement of the bacteria-Protozoa-bacteria loop. However, the microheterotrophic community of bacteria and Protozoa in general represents a competitive pathway down which a significant proportion of carbon from primary production may be channelled, compared with that flowing directly into the grazing zooplankton and thence to fish. Despite the high primary production which characterizes temporally unstable areas such as the southern Benguela upwelling system, the carrying capacity for fish may therefore be considerably less than that which might be anticipated for a simple herbivore-dominated food chain.     

海洋浮游植物初级生产力及碳生物量的检测技术研究进展

浮游植物是海洋生态系统中的主要初级生产者，构建海洋食物网、生物泵和元素循环（包括碳循环、氮循环和硅循环等）的基石。因此，海洋生态系统中的元素循环和能量流动均与浮游植物的生长和代谢息息相关。海洋碳循环是全球碳循环的关键环节，也是全球生态系统中生物地化循环的重要组成部分。尽管浮游植物在海洋碳循环中起着至关重要的作用，但是直接测定浮游植物的初级生产力和碳生物量依旧受到传统技术和方法的限制。本文详细介绍了有关浮游植物初级生产力和碳生物量检测的各种技术和方法，列举了其各自的优缺点。目前，测定海洋浮游植物初级生产力的主要方法有黑白瓶法、遥感估算法、碳同位素测定、快速重复率荧光法；测定海洋浮游植物碳生物量的主要方法有细胞体积转换法、流式细胞术、电子探针X射线显微分析、分位数回归模型估算法。通过对比分析发现碳同位素与快速重复率荧光法相结合可以更高效测定出初级生产力，而最具优势与应用前景的碳生物量检测方法是基于分位数回归模型估算法。其中，基于分位数回归模型估算法具有拟合异常值、测定结果准确等优势，能够实现现场浮游植物群落以及各个功能群碳生物量的估算，并能够与卫星遥感技术手段相结合，可以应用于大尺度和长时间序列的海洋浮游植物碳生物量估算。通过本文的综述，一方面为海洋浮游植物初级生产力和碳含量的研究提供一个基本和系统的认识，另一方面为深入研究浮游植物在海洋碳循环以及全球碳循环中的作用提供参考。     

Variation of dissolved organic matter and fluorescence characteristics before,during and after phytoplankton bloom

The variation of dissolved organic matter (DOM) and fluorescence characteristics during the phytoplankton bloom were investigated in Yashima Bay, at the eastern part of the Seto Inland Sea, Japan. We found significant accumulations of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), chromophoric dissolved organic matter (CDOM) fluorescence, and UV₂₆₀ during the phytoplankton bloom period in 2005, although lower accumulations of DOC and DON and only increases of CDOM fluorescence were observed during the bloom period in 2006. Little or no correlation between DOM and phytoplankton abundance might be due to the composition of DOM, which is a complex mixture of organic materials. The 3D-EEM results revealed that the DOM produced around the phytoplankton bloom period contained tyrosine, tryptophan, and humic-like substances. Our results showed that the occurrence of phytoplankton bloom contributed to the production of DOM in coastal water but the DOM accumulation depended on the type of phytoplankton bloom, the phytoplankton species in particular. From our results, we concluded that phytoplankton have a great role in the dynamics of DOM as a producer in a coastal environment.     

渤海浮游植物群落结构时空分布及其影响因素

浮游植物群落结构的时空变化对生物地球化学循环、全球气候及渔业资源具有重要的影响。本文采用ROMS-CoSiNE高分辨率数值模拟结果,分析了渤海浮游植物生物量和群落结构的时空分布特征,讨论了浮游植物群落结构时空差异的主要影响因素。结果表明,渤海表层叶绿素浓度和甲硅藻比在冬季最低、夏季最高。叶绿素浓度呈条带状分布,甲硅藻比呈斑块状分布。冬季、春季和秋季浮游植物群落结构均以硅藻占绝对优势,夏季以硅藻和甲藻共同占优。不同因素对浮游植物群落结构的影响具有时空差异性。在辽东湾、渤海湾、莱州湾和渤海中部,各个季节浮游植物群落结构差异分别受磷酸盐、氮磷比、硅氮比、溶解无机氮的影响最大。在冬季、夏季和秋季,各个区域浮游植物群落结构差异均受溶解无机氮的影响最大,在春季则受硅氮比的影响最大。总体上,营养盐浓度及结构是浮游植物群落结构时空差异的主要影响因子。     

海洋中碱性磷酸酶及其活性的研究进展

为加深对海洋生物地球化学循环过程和海洋生态系统功能的认知,并为相关研究提供科学依据,文章综述海洋中碱性磷酸酶及其活性的研究进展,并提出展望。研究结果表明：碱性磷酸酶主要来源于浮游植物、浮游动物和细菌,通常根据滤膜孔径等进行分类,对于海洋碳、氮、磷循环和调节生物群落组成具有重要意义;碱性磷酸酶活性通常采用水解荧光模拟底物法定量研究,并在全球海洋范围具有一定的水平、垂直和季节分布特征,影响碱性磷酸酶活性的典型环境因子包括太阳辐射、海水温度、河流输入、上升流、溶解态有机磷、溶解态无机磷、溶解态无机氮、金属离子以及病毒裂解、浮游动物捕食和排遗作用等。     

胶州湾围隔浮游生态系统氮、磷营养盐迁移-转化模型研究

通过对目前生态动力学模型的总结和综合,以生态系统中氮、磷营养盐循环为主线,建立了适用于海洋围隔浮游生态系统的多变量的营养盐迁移-转化动力学模型.该模型包括浮游植物、浮游动物、溶解无机态营养盐、溶解有机态营养盐和生物碎屑5个模块,涉及溶解无机氮、磷酸盐、溶解有机氮、溶解有机磷、浮游植物、浮游动物和生物碎屑7个状态变量.分别利用1999年秋季和2000年夏季胶州湾围隔生态实验数据进行了模型和验证工作,成功地模拟了富加营养盐条件下围隔浮游生态系统中氮、磷营养盐生物化学迁移-转化过程,并确定了20余个参数的量值.     

A Linked Physical and Biological Framework to Assess Biogeochemical Dynamics in a Shallow Estuarine Ecosystem

The littoral zone of Chesapeake Bay contains a mosaic of shallow vegetated and nonvegetated habitats with biotic components that are sensitive to changes in biological and physical driving factors. Static and dynamic modelling frameworks provide an integrative way to study complex hydrodynamic and biogeochemical processes in linked estuarine habitats. In this study we describe a spatial simulation model developed and calibrated relative to a specific littoral zone, estuarine ecosystem. The model consisted of four distinct habitats that contained phytoplankton, sediment microalgae, Zostera marina (eelgrass), and Spartina alterniflora. There was tidal exchange of phytoplankton, particulate and dissolved organic carbon and dissolved inorganic nitrogen between the littoral zone ecosystem and the offshore channel. Physical exchange and biogeochemical transformations within the habitats determined water column concentrations in each habitat. Predicted subtidal water column concentrations and Z. marina and S. alterniflora biomass were within the variability of validation data and the predicted annual rates of net primary production were similar to measured rates. Phytoplankton accounted for 17%, sediment microalgae 46%, the Z. marina community 24% and S. alterniflora 13% of the annual littoral zone primary production. The linked habitat model provided insights into producer, habitat and ecosystem carbon and nitrogen properties that might not have been evident with stand-alone models. Although it was an intra-ecosystem sink for particulate carbon, the seagrass habitat was a DOC source and responsible for over 30% of the littoral zone carbon and nitrogen primary production. The model predicted that the Goodwin Islands littoral zone was a sink of channel derived POC, but a source of DOC to the surrounding estuary. The framework created in this study of estuarine ecosystem dynamics is applicable to many different aquatic systems over a range of spatial and temporal scales.