Modelling the dynamics of the North Sea's Mesozooplankton

A simple biomass-only zooplankton submodel is presented, describing the dynamics of copepods and carnivorous zooplankton in the North Sea. This submodel together with the other process-oriented submodels (viz. phytoplankton dynamics, the microbial food web, benthic processes, fish dynamics and large-scale advective transport) forms a spatially resolved simulation model of the North Sea ecosystem, the European Regional Seas Ecosystem Model (ERSEM). A large set of field measurements of zooplankton abundance has been assembled against which to compare the ERSEM's performance. These data are not only internally consistent, but have also gathered at the large spatial scales appropriate to the ERSEM. In addition to the spatially resolved, monthly estimates of zooplankton abundance, several instantaneous, in situ estimates of the carbon fluxes between different components of the planktonic web in the northern North Sea are presented. Simulated dynamics are in good agreement with the data only during the mid-summer to mid-winter period. During the latter part of the winter and throughout the spring period zooplankton abundance is underpredicted and the simulated zooplankton growth rate is overpredicted during spring. The excessive decline of mesozooplankton biomass during winter may be caused by failing to capture many of the behavioural/physiological changes which zooplankton manifest during winter. It is suggested that the excessive spring growth is a consequence of a. a failure to properly distinguish between somatic and population growth, b. an inadequate representation of the small scale processes which influence feeding success, and c. an excessive spring phytoplankton bloom. The large phytoplankton bloom is, in part at least, a consequence of the excessively low simulated standing crop of omnivorous zooplankton in spring.     

Segregation of herring larvae from inshore and offshore spawning grounds in the north-western North Sea — Implications for stock structure

Herring larvae hatching from spawning sites around the Scottish coast are dispersed by water currents during the weeks following hatching. Hydrographic data, observations on the distribution of caesium-137 and measurements of current velocities by moored meters and drifting buoys, suggest that larvae from offshore spawning sites around the north of Scotland should be more rapidly dispersed than those hatching in inshore areas. This has been confirmed by direct observations on the advection of herring larvae in different regions of the north western North Sea. The conclusion is that larvae hatching in inshore areas, especially in the Moray Firth, are most likely to contribute to nearby juvenile populations, whereas larvae from offshore spawning sites should be widely dispersed over the North Sea.Tagging and parasitology investigations have shown that adult herring spawning in the north-western North Sea have been widely dispersed in the North Sea and adjacent waters as juveniles (six months — one and a half years old). However, a high proportion of adult fish caught at inshore spawning sites and in the Moray Firth were found to have been recruited from more local areas. Taken together with the observations on larval drift, these observations suggest that the stock structure of herring in the northern North Sea may in part be a consequence of the physical oceanography of the area.     

Simulations of the north sea circulation,its variability,and its implementation as hydrodynamical forcing in ERSEM

The rationale is given of how the gross physical features of the circulation and the stratification of the North Sea have been aggregated for inclusion in the ecosystem box model ERSEM. As the ecosystem dynamics are to a large extent determined by small-scale physical events, the ecosystem model is forced with the circulation of a specific year rather than using the long-term mean circulation field. Especially the vertical exchange processes have been explicitly included, because the primary production strongly depends on them. Simulations with a general circulation model (GCM), forced by three-hourly meteorological fields, have been utilized to derive daily horizontal transport values driving ERSEM on boxes of sizes of a few 100 km. The daily vertical transports across a fixed 30-m interface provide the necessary short-term event character of the vertical exchange.For the years 1988 and 1989 the properties of the hydrodynamic flow fields are presented in terms of trajectories of the flow, thermocline depths, of water budgets, flushing times and diffusion rates. The results of the standard simulation with ERSEM show that the daily variability of the circulation, being smoothed by the box integration procedure, is transferred to the chemical and biological state variables to a very limited degree only.     

Flatfish selection by herring gulls Larus argentatus and lesser black-backed gulls Larus fuscus scavenging at commercial beamtrawlers in the southern North Sea

Flatfish selection by scavenging herring gulls and lesser black-backed gulls was studied onboard a commercial beamtrawler in the southern North Sea, June2 -August 1993. Dab (median total length 18 cm), plaice (23 cm), sole (22 cm) and solenette (10 cm) dominated the flatfish discard fraction of the catch. The overall consumption amounted to 30.5% of the discarded flatfish. Flatfish were selected on the basis of fish width rather than length or species, with very low consumption rates (percentage consumed of number offered) of flatfish >8 cm width. All discarded solenette, 98% of all sole and 92% of all dab were of suitable size for these gulls, whereas only 12% of all discarded plaice were small enough to be consumed. Consumption rates of discarded flatfish of ‘suitable size’ for herring gulls and lesser black-backed gulls (<8 cm width) ranged from 25.9% (plaice) to 40.5% (dab). Success indices and selected size classes of flatfish in scavenging herring gulls and lesser black-backed gulls feeding on flatfish were similar, but the first were more efficient than the latter and lost fewer flatfish as a consequence of kleptoparasitism. In contrast to earlier suggestions (based on dietary studies in colonies), there was no evidence that herring gulls were outcompeted by lesser black-backed gulls when feeding on discarded fish.     

The European regional seas ecosystem model,a complex marine ecosystem model

This paper presents an overview of the concept, structure and implementation of the European Regional Seas Ecosystem Model (ERSEM). The model dynamically simulates the biogeochemical seasonal cycling of carbon, nitrogen, phosphorus and silicon in the pelagic and benthic food webs of the North Sea, and is forced by irradiance, temperature and transport processes.The model has a coarse spatial resolution into ten boxes, the ICES boxes, of which the five deepest have been resolved into surface (0 to 30 m) and deep (30 m to bottom) boxes.At the open boundaries, time series are prescribed for dissolved and particulate nutrients. River loads of nutrients for the rivers discharging into the North Sea are prescribed at monthly intervals. A general circulation model has been used to aggregate the exchange volumes across the box boundaries into daily in- and outflows. From these, the horizontal transports of dissolved and suspended constituents are calculated. Vertical transport is in the form of sinking and sedimentation for particulates and in the form of turbulent diffusion for dissolved constituents.The physical model contains all information specific to the area to be modelled, whereas the biological/chemical submodels have been constructed not to be site-specific.The biological variables are represented as functional groups expressed in units of organic carbon and the chemical variables as the internal pools in the biological variables and as the dissolved inorganic pools in water and sediment, expressed in units of N, P and Si.The model runs in a software environment (SESAME) developed for enabling the development of large and complex models in a modular way by a consortium of institutes, each focusing on different. aspects of the ecosystem, translating these into modules within the model. With the exception of fish populations, where size- and age-structure are explicity represented, all the other biological components have been modelled as unstructured populations aggregated into functional groups. This approach is shown to be appropriate for taxa having short generation times in relation to the annual cycle and for taxa which do not span more than one trophic level during their lifetime.     

The mechanism of energy allocation over reproduction and somatic growth in female North Sea plaice,Pleuronectes platessa L.

The mechanism of surplus production allocation over reproduction and somatic growth was studied in female plaice using market sampling data, tagging data and a tank experiment. Somatic growth peaked between March and October and main gonad growth occurred between October and January. However, an estimated 50% of the gonad growth was subsidized from body reserves built up during the growing period. Therefore processes of somatic growth and the building up of energy reserves for gonad growth take place simultaneously.Market sampling data and a tank experiment showed that pre-spawning energy reserves were positively correlated with somatic growth but also indicated that a twofold increase in somatic growth only results in an increase in energy reserves of less than 10%. Analysis of the relation between back-calculated somatic growth and reproductive investment in individual females did not reveal a significant effect of somatic growth on size-specific fecundity, gonad weight and pre-spawning body weight. It is concluded that size-specific reproductive investment is not, or only slightly, enhanced by an increase in surplus production. In the tank experiment females, which did not grow by more than 20% of the initial body weight, did not develop their gonads, but this phenomenon of skipping a spawning season does not seem to occur in the North Sea population.The results of this study are summarized in a hypothetical model of the mechanism of surplus production allocation that is based on physiology and can be tested with tank experiments. The model postulates that surplus production is used to maintain body energy reserves at a threshold level that increases from a post-spawning low to a pre-spawning high. Surplus production exceeding the demands for maintaining body energy reserves at the threshold level is channeled into somatic growth. Implications of the mechanism for the changes in biological parameters in relation to reproductive strategies are discussed.     

Changes in growth of plaice Pleuronectes platessa L. and sole Solea solea (L.) in the North Sea

The changes in growth of plaice and sole between 1957 and 1988, as estimated from samples of the commercial fishery and pre-recruit surveys, were analysed in order to study possible density dependent effects. Indices of potentially competitive biomasses of plaice and sole, based on Lloyd's index of mean crowding, were estimated from the average spatial distribution of various age groups during the summer growing period and from the population age structure as estimated by virtual population analysis.Growth of all age groups of sole increased in the 1960s and was stable in the 1970s and 1980s. In plaice only age groups 1 to 3 showed a similar increase in the 1960s, whereas the growth of 1-year-old plaice tended to decrease in the 1980s. Growth did not show a negative correlation with mean crowding, except in age group 1 of plaice and in age group 3+ of sole. It is concluded that these negative correlations do not provide unequivocal evidence for density dependent growth in plaice and sole, since they could equally well be caused by parallel but unrelated trends in time of one or more other factors. The simultaneous increase in growth in the 1960s of age groups of sole and plaice in the southern North Sea, and the absence of such an increase in age groups in the central North Sea, suggests that food availability must have increased in the Southern North Sea. This inference is supported by several macrobenthos studies. Whether the reduced growth of 1-group plaice in the 1980s, when recruitment was well above the average level, is caused by density dependent growth or to a reduced food availability remains an open question.     

A structure and methodology for marine ecosystem modelling

Comprehensive ecosystem models involve aspects from each of the biological, chemical and physical sciences. Consequently such models, for example the European Regional Seas Ecosystem Model (ERSEM), are often based on computer code written by a number of different research groups each with a well-defined area of responsibility. To construct a meaningful integrated model capable of combining the expertise from each of these disciplines requires a formalized ecosystem structure that provides a template for model development. Assumptions made at this stage will to a large extent determine the qualities of the resulting model. Essential too is a system of quality management that assures a correct and consistent end product. Such a system, however, requires the flexibility to allow the various contributors the freedom to pursue individual and novel representations of ecosystem function, if the model is to be ground breaking. The system adopted by the ERSEM group, which should have a wider applicability than marine ecosystem modelling, is described here. Finally, the methodology used to gauge the relative merits of alternative ecosystem representations is described.     

Nutrient dynamics in the North Sea: Fluxes and budgets in the water column derived from ERSEM

Nutrient dynamics for phosphate, nitrate, ammonium and silicate have been simulated with ERSEM, the European Regional Seas Ecosystem Model. From the model results budgets for the dissolved inorganic nutrients and the corresponding particulate fractions have been calculated. The annual cycles of the nutrients phosphate and silicate compare quite well with the observed ranges of variability. This does not hold for ammonium and nitrate. Biologically mediated transformations such as nutrient uptake and pelagic and benthic mineralization are the dominant processes in changing the nutrient concentrations with the horizontal advective contributions playing a minor role during the productive season.Vertical advection and vertical diffusion have a clear seasonal signal, with a maximum in February. The decay of the advective nutrient transport in summer is caused by the depletion of the upper layer of dissolved inorganic nutrients by algal uptake. The inflow of nutrients in the northwest is almost balanced by the outflow in the northeast, without causing large nutrient transports into the shallower areas from the north. However, from the coastal areas there is a nutrient flow towards the central North Sea, enhancing primary production in the central area.     

The benthic biological submodel in the European regional seas ecosystem model

The submodel describing benthic biology including a bioturbation module as incorporated in the European Regional Seas Ecosystem Model (ERSEM) is discussed. It is linked to a nutrient dynamic model. The structure of the benthic model food web is presented. There are four macrobenthic functional groups, meiobenthos and aerobic and anaerobic bacteria. The modelling uses ‘standard organisms’ as basic building blocks. The choice of parameter values is discussed. The results demonstrate the dependence of the benthic system on the pelagic system. The importance of features such as predation within functional groups for stability of the system is investigated. Detritus input from the pelagic system and detritus recycling is most important in the benthic food web. The web of carbon and nutrient fluxes through the system is analysed. On the basis of the food web analysis, the trophic positions of the functional groups are calculated. Besides the benthic biology, the mathematical formulation of the bioturbation and diffusion enhancement is discussed. Macrobenthic presence and activity enhance diffusion in the sediment and contribute essentially to vertical transport of particulate matter. This is of great importance for the vertical distribution of detritus, and as a consequence, for microbial activity in the sediment layers.     

North Sea Scyphomedusae; summer distribution,estimated biomass and significance particularly for 0-group Gadoid fish

Data on the by-catch of Scyphomedusae from pelagic trawls was collected during the routine ICES International 0-group Gadoid Surveys of the North Sea, in June and July of the years 1971–1986 (except 1984). These data are used to describe the distributions, abundances and biomasses of three common North Sea Scyphomedusae: Aurelia aurita (L.), Cyanea capillata (L.) and C. lamarckii (Péron & Lesuer). Information is also presented on inter-annual variability, size (umbrella diameter) frequencies and, for the Cyanea species, umbrella diameter: wet weight relationships. The general role and ecological significance of Scyphomedusae is discussed and, given the well known ‘shelter’ relationships between Scyphomedusae and certain 0-group fish, whiting (Merlangius merlangus) and haddock (Melanogrammus aeglefinus), in particular. The data were examined for evidence of such relationships.Aurelia aurita, although fairly widespread in the northern North Sea was virtually absent from the central North Sea but very abundant in coastal waters. This species was particularly abundant off the Scottish east coast and especially in the Moray Firth.Cyanea lamerckii was most abundant in the southern and eastern North Sea. More widespread than Aurelia, this species was also most abundant in coastal regions, particularly off the Danish west coast.Cyanea capillata, with a more northern distribution was also more widely distributed and abundant offshore. This species was most abundant in the area between the Orkney/Shetland Isles and the Norwegian Deep and in shelf waters of the north west approaches to the North Sea. As with C. lamarckii it was also, in some years, abundant off the Scottish east coast and west of Denmark.The abundance and the size frequency of the jellyfish show considerable inter-annual variability, and variability between regions of the North Sea. It is considered that hydrographic variability and differences in food supply to both medusae and to their sessile benthic polyps, are the major causes of the observed differences between years and areas.The impact of Scyphomedusae on fishing and recreational activities is discussed.     

Cyclic organochlorines in the hermit crabs Pagurus bernhardus and P. pubescens from the North Sea. A comparison between winter and early summer situation

The body burdens of 5 cyclic organochlorine compounds were determined in abdomens of Pagurus bernhardus and P. pubescens from the North Sea during two seasons. The seasonal bioaccumulation of ΣPCB (as the sum of concentrations of 24 individual components) is influenced by the substances associated with food originated from the spring plankton bloom and the resuspended sediments during the winter.The patterns of individual PCB congeners depended on the weight of the abdomens, and the geographical position of sampling. In offshore samples, the findings indicated a relationship between the weight of the abdomen (roughly the age) and the bioconcentration of higher chlorinated biphenyls. The results from the coastal areas demonstrated that the uptake by food determines the steady state concentration of the higher chlorinated congeners in the hermit crab. Pagurus pubescens probably possesses a mixed-function oxygenase (MFO)-system different from that of Pagurus bernhardus because the congeners 2,2′, 3,3′, 4,5,6′-heptachlorobiphenyl (174) and 2,2′, 3,3′, 4′, 5,6-heptachlorobiphenyl (177) were absent in all samples of the former species but were always present in the latter.The geographical differences between concentrations of ΣPCB reflect the general mean-routes of water and suspended particular matter transport through the North Sea: the Southern Bight and the continental coasts were more polluted with PCBs than the central North Sea. Maximum concentrations of p-p′-DDE were found in the southern parts and parts of the central North Sea. Samples from the German Bight showed the highest concentrations of Lindane. The results indicate that the atmospheric transport of lower chlorinated biphenyls, HCB, α-HCH and Lindane may be important in the distribution of these components, because they only showed slight gradients or even none at all in the area investigated.     

Using data on biomass and fishing mortality in stock production modelling of flatfish

Stock production modelling was used to estimate population parameters such as the carrying capacity (B_∞), as well as management parameters such as maximum sustainable yield (MSY), the instantaneous rate of fishing mortality at MSY (F_MSY) and the sustainable biomass at MSY (B_MSY). The input data were not catch and effort data, which usually require adjustments for changes in catchability, but biomass and catch (or fishing mortality), which are frequently available from cohort analysis or direct surveys. The model does not require the assumption of stock equilibrium for estimating parameters.The model was applied to data from the Alaska plaice, Pleuronectes quadrituberculatus, and yellowfin sole, Limanda aspera stocks in the eastern Bering Sea, and the Pacific halibut, Hippoglossus stenolepis, stock in the Gulf of Alaska and Bering Sea. All three stocks are characterized by separation of nursery area and exploitable population. There are at least five age groups present in nursery areas and ten or more in the exploitable stock so that recruitment levels and exploitable stock sizes are well-buffered.Predictions from the surplus production model provided reasonable fits to the biomass time series for all three stocks examined, given the sources of uncertainty in the biomass estimates available. It appears that the stock dynamics for the three species can be described by a relatively simple density-dependent model assuming instantaneous responses in stock biomass via recruitment and growth.     

The importance of rivers as nursery grounds for 0- and 1-group flounder (Platichthys flesus L.) in comparison to the Wadden sea

From May 1988 to June 1989 selected areas of the German Wadden Sea, the Ems, Weser, Elbe and Eider estuaries as well as in Elbe tributaries were sampled for 0- and 1-group flounder (Platichthys flesus L.). Estuarine and Wadden Sea sampling was conducted on board commercial shrimp vessels equipped with beam trawls. The Elbe river system was sampled on board a research boat equipped with a similar 3-m beam trawl. Density indices were calculated for the various areas. To estimate the importance of rivers as nursery areas for flounder, river surface area was compared to the area of tidal flats in the Wadden Sea.In all surveys, there was no relationship between fish densities and tow directions with respect to tide. In the Elbe river system flounder densities were not correlated to substrate types but increased significantly with decreasing salinity. Abundances were always lowestt in polyhaline habitats and increased up to 10-fold in mesohaline estuarine areas. In the limnetic tidal sections of the Elbe river and its tributaries densities increased again by factors of 3 to 10. The succession of 1-group modal lengths from limnetic to polyhaline habitats demonstrated that smaller fish preferred less saline waters. 0-group specimens lagging behind in growth did not leave the limnetic river section in winter. The onset of the spawning migration in November was determined by monitoring the length-frequency distributions throughout the year.The possible sources of bias are discussed and gear efficiency is estimated from literature sources. The contribution of rivers to the 0- and 1-group flounder population on the tidal flats of the Wadden Sea is estimated at about 35.1%.     

Significance of tintinnid grazing during blooms of Phaeocystis pouchetii (haptophyceae) in Dutch coastal waters

Extremely dense populations of tintinnids (24 000 to 118 000·dm⁻³) were found during the spring bloom of the alga Phaeocystis pouchetii in the Dutch Wadden Sea and coastal North Sea. Microscopic observations showed that these Protozoa grazed on the single-cell stage of the colony-forming Phaeocystis. At the end of the bloom, the biovolume of the tintinnid population equalled or even exceeded that of the Phaeocystis population, indicating that microfaunal grazing prevented further growth of the Phaeocystis spring bloom.     

水稻叶色变化动态的模拟模型研究

定量描述叶片颜色变化的动态过程是植物生长数字化和可视化的重要内容。本研究通过对不同水稻品种和不同水氮处理条件下主茎和分蘖不同叶位叶色变化过程的连续观测和定量分析，构建了水稻叶片颜色随生长度日变化的动态模拟模型。水稻叶片颜色变化的基本过程可以用3个阶段的SPAD值分别表达，第一阶段为基于幂函数的伸长期，叶色逐渐增强，第二阶段为相对稳定的功能期，叶色基本不变，第三阶段为基于二次曲线的衰老期，叶色逐渐减弱；并基于二次曲线方程分别描述了叶片含氮量和含水量对叶色变化过程的调控效应。在此基础上，进一步建立了叶片SPAD值与叶色组分（RGB）值的关系模型。利用独立的水稻田间试验资料对所建模型进行了测试和检验，显示主茎不同叶位叶色变化3个阶段模拟值的均方根差分别为2.58、3.69和3.82，4个分蘖不同叶位叶色变化模拟值的均方根差分别为4.65、4.39、3.51和4.25；SPAD值与叶色组分间模拟值的均方根差分别为2.98和3.25。表明本模型可较好地模拟不同生长条件下水稻不同茎蘖上不同叶位叶色的动态变化过程，从而为实现水稻生长系统的数字化模拟和可视化显示奠定了基础。     

Two Types Modules for the Boiler Attached to 330 MW Unit

Boiler is an important facility in power plant , the safety and economy of unit is affected by it. Studying the dynamic of boiler can improve the knowledge about boiler , which is important for. Features of MMS are introduced based on MMS simulation setting, and the real time capable module and non real time capable module are compared from principle. Real time capable dynamic model of boiler and non real time capable dynamic model of boiler of 330 MW unit are established . The experimental results show that the dynamic process of two type model accords with the mechanism of the object , at the same time, the validity of real time capable module is discussed .     

西藏茶巴朗湿地外来种大鳞副泥鳅的年龄与生长

[目的]通过探究茶巴朗湿地内的外来物种大鳞副泥鳅的年龄结构与生长特性,为控制和治理包括大鳞副泥鳅在内的外来鱼入侵提供基础参数。[方法]取微耳石作为年龄鉴定材料,对299尾大鳞副泥鳅样本进行了研究。[结果]结果表明,大鳞副泥鳅已在茶巴朗湿地形成了自然种群,个体体长范围为5.13 cm ~16.92 cm,体重范围为1.22 g ~49.89 g;种群由2龄~8龄共7个年龄组成,优势年龄组为4龄~6龄;相关分析表明雌雄的体长与体重无显著性差异,其种群体长体重表达式为：W=0.010L2.917 ,呈匀速生长;逻辑斯谛生长方程为：Lt=12.740/(1+e0.803-0.530*t),Wt=16.740/(1+e0.803-0.530*t)2.917,拐点年龄为3.5龄,对应的体长与体质量分别为9.44 cm,6.99 g。[结论]与平原地区相比,茶巴朗湿地大鳞副泥鳅在年龄结构上表现为高龄个体增多;在生长特征上表现为个体减小,生长指标下降,这些变化可能是该外来物种为了更好的适应高原低温水环境。     

The processing and interpretation of north sea CZCS imagery

A series of CZCS scenes of the North Sea has been processed. The atmospheric correction of the scenes has been carried out after the scheme suggested by Gordonet al. (1983a) and also by the interactive technique of Arnone & Laviolette (1984). The processing techniques are described in relation to problems encountered in a case II water area such as the North Sea with yellow substances, suspended sediments and large coccolithophore blooms. Examples of atmospherically corrected colour images are evaluated.