A review of the NEMURO and NEMURO.FISH models and their application to marine ecosystem investigations

The evolution of the North Pacific Ecosystem Model for Understanding Regional Oceanography (NEMURO) family of models to study marine ecosystems is reviewed. Applications throughout the North Pacific have shown the models to be robust and to be able to reproduce 1D, 2D and 3D components of nutrient, carbon cycle and biogeochemical cycles as well as aspects of the lower trophic levels ecosystem (phyto- and zooplankton). NEMURO For Including Saury and Herring, an extension that includes higher trophic levels, can be run uncoupled or coupled to NEMURO. In the uncoupled mode, the growth and weight of an individual fish is computed using plankton densities simulated by NEMURO but with no feedback between fish consumption and plankton mortality. In the coupled mode, the feeding, growth and weight of a representative fish are computed, and prey removals due to feeding by fish appear as mortality terms on the prey. The NEMURO family of models continues to evolve, including effects of the microbial loop and iron limitation at lower trophic levels, and full life cycle, multi-species and multi-generational simulations at higher trophic levels. We outline perspectives for future end-to-end modeling efforts that can be used to study marine ecosystems in response to global environmental change.     

Ecosystem structure and resilience—A comparison between the Norwegian and the Barents Sea

Abundance and biomass of the most important fish species inhabited the Barents and Norwegian Sea ecosystems have shown considerable fluctuations over the last decades. These fluctuations connected with fishing pressure resulted in the trophic structure alterations of the ecosystems. Resilience and other theoretical concepts (top-down, wasp-waste and bottom-up control, trophic cascades) were viewed to examine different response of the Norwegian and Barents Sea ecosystems on disturbing forces. Differences in the trophic structure and functioning of Barents and Norwegian Sea ecosystems as well as factors that might influence the resilience of the marine ecosystems, including climatic fluctuation, variations in prey and predator species abundance, alterations in their regular migrations, and fishing exploitation were also considered. The trophic chain lengths in the deep Norwegian Sea are shorter, and energy transfer occurs mainly through the pelagic fish/invertebrates communities. The shallow Barents Sea is characterized by longer trophic chains, providing more energy flow into their benthic assemblages. The trophic mechanisms observed in the Norwegian Sea food webs dominated by the top-down control, i.e. the past removal of Norwegian Spring spawning followed by zooplankton development and intrusion of blue whiting and mackerel into the area. The wasp-waist response is shown to be the most pronounced effect in the Barents Sea, related to the position of capelin in the ecosystem; large fluctuations in the capelin abundance have been strengthened by intensive fishery. Closer links between ecological and fisheries sciences are needed to elaborate and test various food webs and multispecies models available.     

Hydrological and biogeochemical features of the Northern Adriatic Sea in the period 2003–2006

This paper reports on the main biogeochemical properties of the Northern Adriatic Sea in the period May 2003–November 2006 within the framework of the European program INTERREG III Italy‐Slovenia. Spatial and temporal distributions of water density, dissolved oxygen, nutrients (nitrogen, phosphorous and silicon) and chlorophyll a are presented. Multivariate methods such as fuzzy k‐means, self‐organising maps and cluster analysis were used to identify the different water masses and to characterise the temporal and spatial variability of the main biogeochemical features present in the area. The results confirm that the Po River outflows and the meteorological forcing factors are the main components triggering the alternation of stratification and mixing of the water column and that strongly affect the trophic state of the basin. In general, oligotrophic conditions dominate, and were more pronounced offshore, but mesotrophy occurred episodically in May 2004 and July 2005, when phytoplankton blooms were observed concomitant with vertical stability of the water column. A marked interannual variability was also observed, supporting the importance of maintaining long‐term observations of the basin.     

黄茅海浮游生物及其粒径结构的潮汐变化特征研究

河口区浮游生物作为食物链的重要组成部分,在海洋生物地球化学循环中起到重要作用。为了解黄茅海河口浮游生物及其粒径结构的时空分布特征,于2017年8月17日至21日对黄茅海河口区域微微型浮游生物（pico-,<2 μm）,微型浮游生物（nano-,2-20 μm）及小型浮游生物（micro-,20-200 μm）及其粒径结构进行观测。结果显示,河口外侧总叶绿素a浓度最高,为19.34μg/L,且大粒径浮游生物占比最高。底层水体受上溯海水影响较为明显,表现出盐度及营养盐浓度随潮汐呈现显著的周期性变化。潮汐过程对不同粒径的浮游生物影响不同,对微微型浮游生物影响较小,对大粒径浮游生物影响较大。涨潮时,表层标准化浮游生物粒径谱（NBSS）斜率增大,大粒径浮游生物占比增多。落潮时,NBSS斜率减小,小粒径浮游生物占比增多。潮汐过程及由其引起的营养盐、温度和可利用光强的改变是影响黄茅海河口浮游生物分布的主要因素。研究可为河口区浮游生态系统以及海洋生物地球化学循环过程等的研究提供重要依据。     

Structure and function of contemporary food webs on Arctic shelves: A panarctic comparison: The pelagic system of the Kara Sea – Communities and components of carbon flow

After a short introduction to the physical setting and the history of biological research the pelagic ecosystem of the Kara Sea is described. Main emphasis is on regional aspects of the plankton communities and their seasonal dynamics using mostly data collected between 1996 and 2001. In the zooplankton, for which most data were available, four regional aggregations were separated: (1) the rivers and estuaries of the Southern Kara Sea, (2) the south-western and (3) the central Kara Sea, and (4) the northern troughs and slope. The phytoplankton communities had a similar distribution. To provide components for detailed carbon budgets the regional dynamics of bacterial, phytoplankton and zooplankton biomass and production are described and carbon requirements of bacteria and zooplankton are estimated. For completeness a short literature review on higher trophic levels is included. Finally, recent observations of the pelago-benthic coupling are considered. Estimates of the carbon requirements from the plankton and benthos reveal a large underestimation of primary production, which to date, together with seasonal aspects, shows the largest gap in our knowledge.     

Abrupt transitions of the top-down controlled Black Sea pelagic ecosystem during 1960–2000: Evidence for regime-shifts under strong fishery exploitation and nutrient enrichment modulated by climate-induced variations

Functioning of the Black Sea ecosystem has profoundly changed since the early 1970s under cumulative effects of excessive nutrient enrichment, strong cooling/warming, over-exploitation of pelagic fish stocks, and population outbreak of gelatinous carnivores. Applying a set of criteria to the long-term (1960–2000) ecological time-series data, the present study demonstrates that the Black Sea ecosystem was reorganised during this transition phase in different forms of top-down controlled food web structure through successive regime-shifts of distinct ecological properties. The Secchi disc depth, oxic–anoxic interface zone, dissolved oxygen and hydrogen sulphide concentrations also exhibit abrupt transition between their alternate regimes, and indicate tight coupling between the lower trophic food web structure and the biogeochemical pump in terms of regime-shift events.The first shift, in 1973–1974, marks a switch from large predatory fish to small planktivore fish-controlled system, which persisted until 1989 in the form of increasing small pelagic and phytoplankton biomass and decreasing zooplankton biomass. The increase in phytoplankton biomass is further supported by a bottom-up contribution due to the cumulative response to high anthropogenic nutrient load and the concurrent shift of the physical system to the “cold climate regime” following its ∼20-year persistence in the “warm climate regime”. The end of the 1980s signifies the depletion of small planktivores and the transition to a gelatinous carnivore-controlled system. By the end of the 1990s, small planktivore populations take over control of the system again. Concomitantly, their top-down pressure when combined with diminishing anthropogenic nutrient load and more limited nutrient supply into the surface waters due to stabilizing effects of relatively warm winter conditions switched the “high production” regime of phytoplankton to its background “low production” regime.The Black Sea regime-shifts appear to be sporadic events forced by strong transient decadal perturbations, and therefore differ from the multi-decadal scale cyclical events observed in pelagic ocean ecosystems under low-frequency climatic forcing. The Black Sea observations illustrate that eutrophication and extreme fishery exploitation can indeed induce hysteresis in large marine ecosystems, when they can exert sufficiently strong forcing onto the system. They further illustrate the link between the disruption of the top predators, proliferation of new predator stocks, and regime-shift events. Examples of these features have been reported for some aquatic ecosystems, but are extremely limited for large marine ecosystems.     

Trophic relationships in tidepool fish assemblages of the tropical Southwestern Atlantic

Trophic studies are fundamental to understanding the dynamics of assemblages and functional roles of species within ecosystems, contributing to the identification of factors responsible for the organization and structure of communities. This study aimed to analyse the trophic organization of tidepool fish assemblages in the tropical Southwestern Atlantic, based on the underlying idea that food resources are not limiting and that trophic guild formation is not driven by food competition. Diets were based on feeding index values of food categories for 12 representative species collected in six tidepools (20º49′ S, 40º36′ W) at quarterly intervals (2005 to 2007). The main food categories were small crustaceans, polychaetes and macroalgae. Multivariate techniques evidenced two multispecific trophic guilds: small‐prey carnivores, including Bathygobius soporator, Bathygobius geminatus, Malacoctenus delalandii and Halichoeres poeyi, and herbivores, including Sparisoma axillare and Acanthurus bahianus. Other species presented significantly different diets and were classified into the following guilds: omnivores feeding on filamentous algae and copepods (Abudefduf saxatilis); large‐prey carnivores (Labrisomus nuchipinnis); omnivores feeding on polychaetes and filamentous algae (Stegastes fuscus); and polychaete feeders (Ahlia egmontis). Gymnothorax funebris and Gymnothorax moringa were classified as carcinophagores and piscivores, respectively. Trophic organization appears related to species convergence toward the use of abundant food resources, driven by a combination of factors allowing some resource partitioning through inter‐specific differences in consumer size, microhabitat, behavior, and trophic specialization.     

Impacts of elevated CO2 on particulate and dissolved organic matter production: microcosm experiments using iron-deficient plankton communities in open subarctic waters

Response of phytoplankton to increasing CO₂ in seawater in terms of physiology and ecology is key to predicting changes in marine ecosystems. However, responses of natural plankton communities especially in the open ocean to higher CO₂ levels have not been fully examined. We conducted CO₂ manipulation experiments in the Bering Sea and the central subarctic Pacific, known as high nutrient and low chlorophyll regions, in summer 2007 to investigate the response of organic matter production in iron-deficient plankton communities to CO₂ increases. During the 14-day incubations of surface waters with natural plankton assemblages in microcosms under multiple pCO₂ levels, the dynamics of particulate organic carbon (POC) and nitrogen (PN), and dissolved organic carbon (DOC) and phosphorus (DOP) were examined with the plankton community compositions. In the Bering site, net production of POC, PN, and DOP relative to net chlorophyll-a production decreased with increasing pCO₂. While net produced POC:PN did not show any CO₂-related variations, net produced DOC:DOP increased with increasing pCO₂. On the other hand, no apparent trends for these parameters were observed in the Pacific site. The contrasting results observed were probably due to the different plankton community compositions between the two sites, with plankton biomass dominated by large-sized diatoms in the Bering Sea versus ultra-eukaryotes in the Pacific Ocean. We conclude that the quantity and quality of the production of particulate and dissolved organic matter may be altered under future elevated CO₂ environments in some iron-deficient ecosystems, while the impacts may be negligible in some systems.     

From microscope to management: The critical value of plankton taxonomy to marine policy and biodiversity conservation

Taxonomic information provides a crucial understanding of the most basic component of biodiversity – which organisms are present in a region or ecosystem. Taxonomy, however, is a discipline in decline, at times perceived as ‘obsolete’ due to technical advances in science, and with fewer trained taxonomists and analysts emerging each year to replace the previous generation as it retires. Simultaneously, increasing focus is turned towards sustainable management of the marine environment using an ecosystem approach, and towards conserving biodiversity, key species, and habitats. Sensitive indicators derived from taxonomic data are instrumental to the successful delivery of these efforts. At the base of the marine food web and closely linked to their immediate environment, plankton are increasingly needed as indicators to support marine policy, inform conservation efforts for higher trophic organisms, and protect human health. Detailed taxonomic data, containing information on the presence/absence and abundance of individual plankton species, are required to underpin the development of sensitive species- and community-level indicators which are necessary to understand subtle changes in marine ecosystems and inform management and conservation efforts. Here the critical importance of plankton taxonomic data is illustrated, and therefore plankton taxonomic expertise, in informing marine policy and conservation and outline challenges, and potential solutions, facing this discipline.     

A STUDY ON THE PLANKTON COMMUNITIES IN THE SOUTH HUANGHAI SEA AND THE EAST CHINA SEA

The South Huanghai Sea and the East China Sea lie on the east continental shelf ofChina. These areas are generally under the effects of river, coastal currents, and coldwater in the Huanghai Sea, as well as the branches of Kuroshio. Therefore, obviously, thephysical oceanography, chemical elements and plankton distribution in these areas areconsiderably complicated. As for plankton composition, there are temperate neriticspecise, brackish water and estuarine species, coastal species and also tropical pelagicspecies. Each community of the plankton occupies a distributional area of its own.Among the communities there exists a transitional area caused by horizontal andvertical mixing of water masses which effect this area in different degrees. All commu-nities and the transitional area are more or less relatively stable, except for seasonal varia-tion.     

海洋酸化对浮游植物生理生态影响的研究进展

当前全球气候变化下的上层海洋变暖与酸化对以浮游植物为主的海洋生态系产生了重大影响,理解此背景下的海洋浮游植物生理生态响应,对我们理解和抑制全球气候变化具有重要意义。在全球大气二氧化碳分压（pCO₂）升高情景下,浮游植物通过光合作用、微生物循环等过程,通过不同功能群对海洋生源要素循环模式的改变,进而影响区域及全球海洋的生物地球化学循环。研究全球浮游植物对海洋酸化生理生态的响应使得我们对生物地球化学系统的认识更加全面、系统。     

Iron fertilization and the structure of planktonic communities in high nutrient regions of the Southern Ocean

In this review article, plankton community structure observations are analyzed both for artificial iron fertilization experiments and also for experiments dedicated to the study of naturally iron-fertilized systems in the Atlantic, Indian and Pacific sectors of the Southern Ocean in the POOZ (Permanently Open Ocean Zone) and the PFZ (Polar Frontal Zone). Observations made in natural systems are combined with those from artificially perturbed systems, in order to evaluate the seasonal evolution of pelagic communities, taking into account controlling factors related to the life cycles and the ecophysiology of dominant organisms. The analysis considers several types of planktonic communities, including both autotrophs and heterotrophs. These communities are spatially segregated owing to different life strategies. A conceptual general scheme is proposed to account for these observations and their variability, regardless of experiment type. Diatoms can be separated into 2 groups: Group 1 has slightly silicified fast growing cells that are homogeneously distributed in the surface mixed layer, and Group 2 has strongly silicified slowly growing cells within discrete layers. During the growth season, Group 1 diatoms show a typical seasonal succession of dominant species, within time windows of development that are conditioned by physical factors (light and temperature) as well as endogenous specific rhythms (internal clock), and biomass accumulation is controlled by the availability of nutrients. Group 1 diatoms are not directly grazed by mesozooplankton which is fed by protozooplankton, linking the microbial food web to higher trophic levels. Instead, successive dominant species of Group 1 are degraded via bacterial activity at the end of their growth season. Organic detritus fragments feed protozooplankton and mesozooplankton. The effective silicon pump leads to the progressive disappearance of silicic acid in surface waters. In contrast, Group 2 is resistant to grazing due to its strong silicification, and its biomass accumulates continuously but relatively slowly throughout the productive period. Group 2 diatoms are concentrated at or near the seasonal pycnocline and thus benefit from upward nutrient fluxes by diapycnal mixing. The decrease in light and the deep convective mixing in the fall produce both light and nutrient limitation leading to a massive carbon export of Group 2 diatoms, a major annual event of the biological pump. This scheme describes the seasonal evolution of plankton communities in surface waters of the Southern Ocean. The scheme could probably be extended to ecosystems that are characterized by a seasonal bloom under influence of iron or other nutrients.     

Nutrient dynamics in the Sylt-Rømø Bight ecosystem,German Wadden Sea: An ecological network analysis approach

Carbon, nitrogen, and phosphorus flow networks, consisting of 59 compartments, were constructed for the Sylt-Rømø Bight, a large shallow sea in the German Wadden Sea. These networks were analysed using ecological network analysis. Each network depicts the standing stock of each component in the ecosystem, and the flows between them. The trophic efficiency by which material is utilised in the Bight increase from 3%, to 6% to 17% for C, N and P, respectively. The number of cycles though which these elements pass increase from 1 197 for carbon, to 414?744 and 538?800 for nitrogen and phosphorus, respectively. The Finn Cycling Index, reflecting the amount of material recycled as a fraction of the total system activity, TST, increases from 17% for carbon, to 43% for nitrogen, to 81% for phosphorus. Other system level attributes such as the Average Path Length, the Average Internal Mutual Information, Relative Ascendancy, Relative and Normalized Redundancy, show an increase from the carbon to the nitrogen to the phosphorus networks. Phosphorus is tightly cycled over longer pathways than the other two elements, and also has the longest residence time in the Bight. Postulated differences between the behaviour of energy (or carbon) and biogeochemical networks in coastal ecosystems are evident from the results obtained from ecological network analysis.     

Topological redundancy and ‘small‐world’ patterns in a food web in a subtropical ecosystem of Brazil

According to graph theory, the frequency distribution of trophic interactions within a food web has deep structural implications, as it can highlight the presence of patterns associated with the web and indicate whether the properties of the web are independent of its size. A hypothesis is that ‘small‐world’ food webs are sensitive to the loss of species with the highest values. Therefore, the present work aimed to evaluate the degree to which a subtropical food web in Southern Brazil displays small‐world patterns and their resistance. As part of the assessment, we evaluated the topological redundancy values of species in the food web and then we simulated the exclusion of these species (such as sharks and sea birds), and also the exclusion of high centrality species (such as squids Loligo sp., portunid swimming crabs and the cutlassfish Trichiurus lepturus). The food web showed a ‘broad‐scale’ distribution of connections by node, and a small‐world pattern. As expected, a simplification of the network was observed after elimination of some species with high centrality. However, the food web was resistant to the loss of species with low topological redundancy, probably because these species occupy a high trophic level and do not participate in lots of routes within the food web. We highlight however, the importance of the application of multiple analyses to evaluate the importance of components in food webs, and fisheries management plans should consider both species of high centrality values and species with low topological redundancy.     

The trace element geochemistry of marine biogenic particulate matter

Plankton samples have been carefully collected from a variety of marine environments for major and trace-chemical analysis. The samples were collected and handled under the rigorous conditions necessary to prevent contamination of the trace elements. Immediately after collection, the samples were subjected to a series of physical and chemical leaching-decomposition experiments designed to identify the major and trace element composition of the biogenic particulate matter. Emphasis was placed on the determination of the trace element/major element ratios in the various biogenic phases important in biogeochemical cycling.The majority of the trace elements in the samples were directly associated with the non-skeletal organic phases of the plankton. These associations include a very labile fraction which was rapidly released into seawater immediately after collection and a more refractory component which involved specific metal-organic binding. Calcium carbonate and opal were not significant carriers for any of the trace elements studied. A refractory phase containing aluminum and iron in terrigenous ratios was present in all samples, even from remote pelagic environments. This non-biogenic carrier contributed insignificant amounts to the other trace elements studied.The plankton samples were collected from surface waters with a wide range in the dissolved trace element/nutrient ratios, however, the same elemental ratios in the bulk plankton samples were relatively constant in all these environments. The bulk compositions and the rapid release of the metals and nutrient elements (specifically phosphorus) from the plankton after collection were used to examine the systematics of depletions of the dissolved elements from surface waters. These elemental ratios were combined with known fluxes of the major biogenic materials to estimate the significance of the plankton in the vertical flux of the trace elements. In parallel with the major surface ocean cycles of carbon and nitrogen, significant fractions of the trace elements taken up by primary producers must be rapidly regenerated in order to explain the observed elemental compositions and fluxes.     

牛山湖浮游生物群落DNA指纹结构与物种组成的关系

利用RAPD及DGGE指纹技术揭示牛山湖5个采样点浮游生物群落的DNA多态性,并定性地探讨其与物种组成的关系.结果如下:(1)从40条随机引物中筛选出9条引物,共获得93条谱带,多态率为58%;各采样点所得谱带平均为67条,其中Ⅰ站最少,为61条,Ⅴ站最多,为74条;(2)PCR-DGGE指纹图谱共含102条谱带,其中原核生物56条,真核生物46条,谱带总数以Ⅲ站、Ⅳ站和Ⅴ站较多.Ⅰ站和Ⅱ站较少;(3)5个采样点共观察到62种/类浮游生物,其中Ⅰ站和Ⅱ站种类较少.Ⅲ站、Ⅳ站和Ⅴ站种类较多,分布概率在100%的种类达19种.多维尺度(MDS)分析表明:基于RAPD指纹和DGGE指纹,Ⅰ站和Ⅱ站最相似,Ⅲ站、Ⅳ站和Ⅴ站最相似;基于物种组成.Ⅳ站和Ⅴ站相似性最高,Ⅲ站和Ⅳ站次之,相对RAPD指纹和DGGE指纹,Ⅰ站和Ⅱ站相似性较低.研究表明:浮游生物群落DNA指纹结构与物种组成有一定的相关性,可能因部分物种信息的缺失导致些许偏差.     

Discovery of prolific natural methane seeps at Gullfaks, northern North Sea

The Gullfaks and Kvitebjørn fields are located on the North Sea Plateau (135 m water depth), and on an ancient beach (135–190 m) deposited during the sea-level lowstand during the Last Glacial Maximum (LGM). There are several continuous seeps of mainly methane gas, where large patches of Beggiatoa bacterial mats occur. The ‘Heincke’ seep area, which is named after the German research vessel Heincke, has been targeted by scientists studying seep-associated processes and microbiology. The Gullfaks area has a long history of shallow gas and seepage. In 1980, well no. 34/10–10 had a blowout from a reservoir located 230 m below seafloor. The active Heincke seep location has no topographic expression, probably because the seabed consists of dense sand and gravel. Extensive bacterial mats (Beggiatoa sp.) are found on the seafloor at this seep site. Organisms such as hermit crabs were seen ingesting pieces of such mat, indicating ‘trophic bypass,’ where carbon derived directly from seeping methane is evidently feeding directly into higher trophic organisms. Ongoing and future research at this seep location in the North Sea can answer some important questions on the environmental impact of natural methane seeps on continental shelves.     

New insights on the trophic ecology of bathyal communities from the methane seep area off Concepción,Chile (~36° S)

Studies of the trophic structure in methane‐seep habitats provide insight into the ecological function of deep‐sea ecosystems. Methane seep biota on the Chilean margin likely represent a novel biogeographic province; however, little is known about the ecology of the seep fauna and particularly their trophic support. The present study, using natural abundance stable isotopes, reveals a complex trophic structure among heterotrophic consumers, with four trophic levels supported by a diversity of food sources at a methane seep area off Concepción, Chile (~36° S). Although methanotrophy, thiotrophy and phototrophy are all identified as carbon fixation mechanisms fueling the food web within this area, most of the analysed species (87.5%) incorporate carbon derived from photosynthesis and a smaller number (12%) use carbon derived from chemosynthesis. Methane‐derived carbon (MDC) incorporation was documented in 22 taxa, including sipunculids, gastropods, polychaetes and echinoderms. In addition, wide trophic niches were detected in suspension‐feeding and deposit‐feeding taxa, possibly associated with the use of organic matter in different stages of degradation (e.g. from fresh to refractory). Estimates of Bayesian standard ellipses area (SEA_B) reveal different isotopic niche breadth in the predator fishes, the Patagonian toothfish Dissostichus eleginoides and the combtooth dogfish Centroscyllium nigrum, suggesting generalist versus specialist feeding behaviors, respectively. Top predators in the ecosystem were the Patagonian toothfish D. eleginoides and the dusky cat shark, Bythaelurus canescens. The blue hake Antimora rostrata also provides a trophic link between the benthic and pelagic systems, with a diet based primarily on pelagic‐derived carrion. These findings can inform accurate ecosystem models, which are critical for effective management and conservation of methane seep and adjacent deep‐sea habitats in the Southeastern Pacific.