Planktonic System Research Articles

Carbon budget of the planktonic food web in an atoll lagoon (Takapoto, French Polynesia)

The structure and functioning of the planktonic food web were characterized in the lagoon of Takapoto Atoll (French Polynesia). Several variables were estimated over several weeks in April 1996 and 1997: carbon stocks of different planktonic compartments, phytoplankton particulate net production (PPNP), release of dissolved organic carbon (DOC) from phytoplankton, bacterial production and metabolic activity, and sinking of particles. The carbon stocks and flows were used to build up a quantitative description of the planktonic food web. The heterotrophic bacterial community was characterized by high biomass, low production and a small proportion of actively respiring cells. This was consistent with the observed low consumption of bacteria by protozoa. The relatively high PPNP was mostly due to cyanobacteria <1 μm in size. DOC release from phytoplankton represented, on average, 48% of the total photoassimilated carbon. The planktonic food web was characterized by a high biomass of small protozoa (82% were ≤14 μm). The contribution of metazoa to the carbon stock of zooplankton was smaller than that of protozoa, but their rates of production and ingestion were high. Detritus had a high sinking rate and were largely consumed by metazoan plankton. The carbon budget of the planktonic system shows that 70% of phytoplankton total net production (PTNP: particulate and dissolved) is lost through heterotrophic respiration. This moderate value, for oligotrophic warm waters, is due to the low activity of bacteria. The remaining 30% of the PTNP is exported from the planktonic system through food-web transfers and sinking of detritus (20 and 10% of PTNP, respectively). It follows that the lagoonal planktonic food web, despite the small size of primary producers, is quite efficient at exporting biogenic carbon. Protozoan grazers play a key role in carbon export, as they exert a strong grazing pressure on phytoplankton, and are themselves largely consumed by metazoan zooplankton.

A transplant experiment to identify the factors controlling bacterial abundance, activity, production, and community composition in a eutrophic canyon‐shaped reservoir

We performed a transplant experiment in eutrophic Sau reservoir to assess the factors that control bacterial abundance, activity, growth rate, and community composition. Samples from the lacustrine and the riverine ends of the reservoir were incubated in dialysis bags placed in situ and transplanted to the other side of the reservoir and also incubated after 1 µm filtration to measure predator effects. The bags were sampled at 12‐h intervals to estimate bacterial abundance, whole community activity, activity structure (by flow cytometry), and phylogenetic composition (by in situ hybridization with group‐specific phylogenetic probes). Bacterial production was always regulated by nutrient supply, but abundance and activity were differently regulated at both sites. The riverine bacteria were limited by predator activity, whereas the lacustrine were regulated by a combination of predation and nutrient supply. Therefore, even in the same environment, different modes of control can act simultaneously. Bacterial activity structure was also regulated in the same way. Abundance of high DNA bacteria and cells hybridizing with the universal EUB338 probe were well correlated. In the lacustrine sample, bacterial community structure did not change significantly, whereas in the riverine sample, Α‐ and Δ‐Proteobacteria reduced their growth when transplanted, whereas Β‐Proteobacteria were stimulated by the presence of predators. Members of the Cytophaga/Flavobacterium phylum grew only when incubated in situ in the absence of predators. This different behavior in the different bacterial groups resulted in strong changes in bacterial assemblage composition, evident already after 24 h. The experiment demonstrates that, together with the effect of predators, nutrient supply affects bacterial community properties and that a complex regulation involving both types of control can occur in a single heterogeneous planktonic system.

Modelling and the monitoring of mesocosm experiments: two case studies

Mesocosm experiments have played an important role over the last decade in increasing our understanding of marine ecosystems. Many studies use these controlled environments to examine ecosystem responses to factors such as nutrient addition and light limitation. A few studies have been able to successfully model mesocosm experiments using carefully designed and comprehensive models and experimental design. Nevertheless, it is rare for such models to be compared with oceanic studies, and to consider the sulphur cycle as well as the carbon and nitrogen budgets. Here we take an ecosystem model, including a dimethylsulphide loop, that has been successfully used in modelling the evolution of the planktonic system in a Lagrangian field experiment in the North Atlantic-the PRIME cruise of 1996-and apply it to two mesocosm experiments. These were operated by two different groups of scientists, but in the same field station in a Norwegian fjord. The experiments were not explicitly designed with the data requirements of any model in mind. We show that the model is best able to simulate mesocosm data using model parameters taken from the real ocean. However, most sensitivity tests are significantly less successful in the mesocosm environment than the real ocean, especially if the model parameters are allowed to vary in a best fit sense. The limitations of the model-mesocosm match highlight the importance of comprehensive monitoring of mesocosms if they are to be useful for validating models suitable for the open ocean.

Effect of coagulation on a model planktonic food web

Observations have shown that aggregates (“marine snow”) are an important fraction of the organic matter vertical flux in the ocean. There has been a separation in biological models describing this flux, with coagulation models focused on phytoplankton blooms for which particle concentrations are high and grazing is low and neglectable and with plankton models focused on food web interactions neglecting coagulation dynamics. This separation has partly resulted from the difficulty in describing the interactions among the multiple particle sources using a coagulation model for a food web. New approaches for describing particle dynamics now make it possible to do so. The present study examines the effect of combining the food web model of Fasham et al. (1990. Journal of Marine Research 34, 591–639) with a coagulation dynamics model and applying the combined model to describe the annual cycle of an oligotrophic plankton system. As part of the model formulation, the coagulation kernels had to be altered to include both the case of fractal particles interacting and the case of smaller particles being faster settling. Results show that coagulation can have an important effect on particle flux even in the low particle concentration oligotrophic environment by increasing average particle settling speed and by increasing the ratio of maximum to minimum daily vertical flux over the course of a yearly cycle. As part of this, coagulation forms large, rapidly sinking particles. Grazing and the accompanying formation of fecal pellets can compete with coagulation for particles, but the fecal pellets can also participate in the formation of large aggregates. Among the variables that can influence export rates are phytoplankton size and concentration as well as depth of the surface mixed layer. The results provide evidence for the importance of coagulation processes in enhancing particle export even in central ocean regions.

The formation of mixed culture biofilms of oral species along a gradient of shear stress.

A chemostat mixed culture system was used to produce two distinct ecological states, state-1 (caries-like microcosm) and state-2 (periodontal-like microcosm). Eleven bacterial species (Streptococcus gordonii, Strep. mitis I, Strep. mutans, Strep. oralis, Actinomyces naeslundii, Lactobacillus casei, Neisseria subflava, Fusobacterium nucleatum, Porphyromonas gingivalis, Prevotella nigrescens, Veillonella dispar) were used to inoculate the planktonic system. A flow cell, designed to produce convergent flow with increasing shear stress, was attached to the chemostat system, and the resultant biofilms developed from the state-1 and state-2 microcosms along the shear stress gradient were examined and compared using image analysis and viable counts. The biofilm produced from state-1 showed a lower shear stress tolerance (0.146 Pa) than the state-2 biofilm (0.236 Pa). The biofilm compositions did not vary along the gradient of shear stress and were dependent on the initial inoculum conditions. Gram-positive species were predominant in the state-1 biofilm, while Gram-negative species were predominant in state-2.

On the mathematical formulation and parameter estimation of the Norwegian Sea plankton system

Abstract The mathematical description of the oceanic plankton system is often characterised by a simple structure where the major components of the system are governed by the dissolved nutrient concentration N, the phytoplankton biomass P, and the zooplankton biomass Z (also known as the NPZ model). The flows between the variables can be formulated in a variety of ways that, in general, alter the time development of the model. In this study we investigate how the numerical value of model parameters that are hard to determine experimentally can be estimated from in situ field observations. By that, we can assign parameter values to each model formulation such that they should follow a prescribed time development that is consistent with data. Accordingly, this gives us a tool to compare model formulations in a consistent way. The study emphasises the importance of analysing the model with respect to stability and multiple solutions. The study is exemplified using observations from Ocean Weather Station Mike (66°N, 2°E) in the Norwegian Sea, illustrating the need for a proper model formulation in order to reproduce measurements.

Trophic efficiency of the planktonic food web in a coastal ecosystem dominated by Phaeocystis colonies

The trophic efficiency of the planktonic food web in the Phaeocystis-dominated ecosystem of the Belgian coastal waters was inferred from the analysis of the carbon flow network of the planktonic system subdivided into its different trophodynamic groups. A carbon budget was constructed on the basis of process-level field experiments conducted during the spring bloom period of 1998. Biomass and major metabolic activities of auto- and heterotrophic planktonic communities (primary production, bacterial production, nanoproto-, micro- and mesozooplankton feeding activities) were determined in nine field assemblages collected during spring at reference station 330. In 1998, the phytoplankton spring flowering was characterised by a moderate diatom bloom followed by a massive Phaeocystis colony bloom. Phaeocystis colonies, contributing 70% to the net primary production, escaped the linear food chain while the early spring diatom production supplied 74% of the mesozooplankton carbon uptake. The rest of mesozooplankton food requirement was, at the time of the Phaeocystis colony bloom, partially fulfilled by microzooplankton. Only one-third of the microzooplankton production, however, was controlled by mesozooplankton grazing pressure. Ungrazed Phaeocystis colonies were stimulating the establishment of a very active microbial network. On the one hand, the release of free-living cells from ungrazed colonies has been shown to stimulate the growth of microzooplankton, which was controlling 97% of the nanophytoplankton production. On the other hand, the disruption of ungrazed Phaeocystis colonies supplied the water column with large amounts of dissolved organic matter available for planktonic bacteria. The budget calculation suggests that ungrazed colonies contributed up to 60% to the bacterial carbon demand, while alternative sources (exudation, zooplankton egestion and lysis of other organisms) provided some 30% of bacterial carbon requirements. This suggests that the spring carbon demand of planktonic bacteria was satisfied largely by autogenic production. The trophic efficiency was defined as the ratio between mesozooplankton grazing on a given source and food production. In spite of its major contribution to mesozooplankton feeding, the trophic efficiency of the linear food chain, restricted to the grazing on diatoms, represented only 5.6% of the available net primary production. The trophic efficiency of the microbial food chain, the ratio between mesozooplankton grazing on microzooplankton and the resource inflow (the bacterial carbon demand plus the nanophytoplankton production) amounted to only 1.6%. These low trophic efficiencies together with the potential contribution of ungrazed Phaeocystis-derived production to the bacterial carbon demand suggest that during spring 1998 most of the Phaeocystis-derived production in the Belgian coastal area was remineralised in the water column.

Effects of fish on plankton dynamics: a theoretical analysis

We present an expansion of a classical minimal Daphnia-algae model to account for effects of fish as a top predator. Our analyses suggest that in most situations, the plankton should show hysteresis in response to predation pressure by fish. Thus, there exist two distinct regimes, one in which Daphnia is controlled (overexploited) by fish and phytoplankton biomass is high and another in which Daphnia is relatively unaffected (underexploited) by planktivores and algae are controlled by Daphnia. Switches from one regime to the other occur abruptly at a critical fish density. This is in line with field observations and experimental results. Our model predicts that the critical fish density for Daphnia collapse is higher in systems with higher ambient nutrient concentrations. The model also shows how intrinsic predator-prey oscillations in the planktonic system can facilitate the switch to the algal-dominated regime where Daphnia is controlled by fish. In terms of dynamical systems theory, this switch happens through a homoclinic bifurcation. In biological terms, Daphnia collapses due to food limitation and is subsequently overexploited by fish. This is indeed the sequence of mechanisms observed at the end of the spring clearwater phase in lakes where Daphnia is absent during the summer when the biomass of young-of-the-year planktivorous fish becomes high.

A model for the plankton system of the Broa reservoir, São Carlos, Brazil

In this paper a model, called ELLOBO running in STELLA II, was set to describe the plankton system of the Broa reservoir (SP). The three state variables of the model are: phytoplankton, zooplankton, and the fish Astyanax fasciatus. The forcing variables are: temperature, nitrate, phosphorus and solar radiation. The model did not consider the cycling of nutrients inside the reservoir. The results show that: temperature is the principal forcing variable in the phytoplankton dynamic and in the subsequent evolution of the whole system. The zooplankton predation was described by Odum’s equation, and there is a strong random component in zooplankton grazing, which was essential for the model, because zooplankton estimates have high variance. One must collect data in a short space of time (maybe daily) to better explain the zooplankton and phytoplankton variation. Validation was performed using simple statistics (arithmetic mean, standard deviation) and the results show concordance between observed and simulated values. Overhead was used to calibrate some parameters and to validate the model. The highest overhead value (5%) imply in the better accordance between estimated and observed state variables values. We believe this approach in Broa reservoir will provide an useful tool for future research and it could be used comparatively in other continental aquatic ecosystems.

Carbon flow patterns in the planktonic food web of the Gulf of Riga, the Baltic Sea: a reconstruction by the inverse method

We used the inverse method to reconstruct a carbon flux model for the planktonic food web of the southern part of the Gulf of Riga, the Baltic Sea. The model was based on data from three field campaigns (3–12 May 1995; 28 June–7 July 1994; 26 August–3 September 1993). The carbon flow model indicated very different channelling of gross primary production (GPP) in the three different periods. In spring 55% of GPP was channelled to detritus, while in summer 35% was exudated and channelled to dissolved organic carbon (DOC). In autumn, 42% of GPP was channelled to the zooplankton compartments. The model suggested high bacterial respiration rates and low bacterial growth efficiencies (6%) in spring and autumn. During these periods large decreases in DOC were anticipated to occur due to bacterial respiration. In summer the model suggested that bacterial respiration rate was low and that the bacterial growth efficiency was high (60%). During this period a net accumulation of DOC apparently occurred. Respiration was the most important loss of organic carbon in all seasons, corresponding on average to 152, 59 and 391% of GPP daily in spring, summer and autumn, respectively. Daily sedimentation rates of particulate organic carbon (POC) were consistently low (<3% d −1), removing 13–29% of GPP daily. The sedimented material consisted mainly of amorphous detritus. This indicates that in spite of the relatively high level of eutrophication, the planktonic system in the Gulf of Riga has a high short-term carbon retention and recycling capacity, and little POC is lost from the upper water column through sedimentation.

Characterization of the planktonic food web of Takapoto Atoll lagoon, using network analysis.

The planktonic food web of Takapoto Atoll lagoon was studied using network analysis. This analysis includes four types of indices dealing with bilateral interactions of compartments, the trophic structure, biochemical cycles, and the topology of the flows. We found numerous parallel carbon pathways of similar importance, indicating a highly complex system compared to other marine ecosystems. Other characteristics were trophic levels not ranked in the same order as the size classes, the domination of system activity by processes at the first trophic level (and especially by herbivory), and cycling processes that involve many pathways. This is the first use of network analysis to describe completely a planktonic food web, and also the first comprehensive description of the trophic structure of the planktonic system in an atoll lagoon.

Phosphorus distribution in three crustacean zooplankton species

The distribution of phosphorus (P) was assessed in homogeneously 33P-labeled Daphnia magna, Daphnia galeata and Eudiaptomus gracilis. The specific P contents were 1.48, 1.41, and 0.50% of dry weight (DW), respectively. The results support the view of low intraspecific variability in P : DW ratios in crustacean zooplankton. The fraction of P allocated to nucleic acids, phospholipids, and other P compounds was assessed in D. galeata and E. gracilis. In both species, the major pool, 35–69% of the total P content, was associated with nucleic acids. This fraction decreased with both body size (age) of D. galeata and E. gracilis and with the reproductive rate of D. galeata. D. magna and D. galeata revealed similar patterns of P allocation between body, carapace, and eggs. The carapace contained approximately 14% of the total P content. If most P is not reabsorbed from the exoskeleton prior to molting, the molting will result in a substantial P drain both from the individual and, at times, from the entire planktonic system.

Bivalve carrying capacity in coastal ecosystems

The carrying capacity of suspension feeding bivalves in 11 coastal and estuarine ecosystems is examined. Bivalve carrying capacity is defined in terms of water mass residence time, primary production time and bivalve clearance time. Turnover times for the 11 ecosystems are compared both two and three dimensionally. Fast systems, e.g., Sylt and North Inlet, have turnover times of days or less, while, slow systems, e.g., Delaware Bay, have turnover times of months and years. Some systems, Marennes-OlSouth San Francisco Bay and North Inlet, require a net influx of phytoplankton in order to support their bivalve populations. Three systems, Carlingford Lough, Chesapeake Bay and Delaware Bay, have very long bivalve clearance times due to small or reduced bivalve filter feeder populations. Carlingford Lough stands out because it is a naturally planktonic system now being converted to bivalve culture with an adherently stronger benthic-pelagic coupling. Existing models of bivalve carrying capacity are reviewed. The Herman model is utilized as an appropriate ecosystem level model to examine carrying capacity because it includes the three major turnover time elements of water mass residence time, primary production time and bivalve filter feeder clearance time. The graphical analysis suggests that massive and successful bivalve filter feeder populations are found in systems with relatively short residence times ( 40 days) and short primary production times ( 4 days) in order to sustain a high bivalve biomass with its associated rapid clearance times. Outlier systems are constrained by long water mass residence times, extended primary production times, and long clearance times.

Virtual plankton: A novel approach to the investigation of aquatic predator‐prey interactions

Small‐scale zooplankton swimming behaviors can affect aquatic predator‐prey interactions. Difficulties in controlling prey swimming behavior however, have restricted the ability to test hypotheses relating differences in small‐scale swimming behavior to frequency of predation by fish. We report here a Virtual Plankton (VP) system that circumvents this problem by allowing the observation of fish “preying"on computer‐generated prey images whose size, shape, color and swimming behavior can be precisely controlled. Two experiments were performed in which bluegill sunfish (Lepomis macrochirus) were given a choice of either two VP images, one of which moved twice as fast as the other, or six VP, one of which moved either faster (1.25 x, 1.5 x or 2 x ) or slower (0.5 x) than the other five. Current predator‐prey models based on encounter probabilities and prey visibility predict that moving faster increases predation risk and conversely, moving slower decreases predation risk. In agreement with existing predator‐prey models, in both experiments, fish chose faster moving VP significantly more often than their slower moving neighbors. Contrary to the predictions of existing models, in the second experiment with six VP, the rate at which fish chose a prey image moving half as fast as the five surrounding images did not differ significantly from the rate predicted by chance(l/6). These results suggest that current fish‐zooplankton predation models would benefit by the incorporation of small‐scale swimming behavior and assessments of its influence on overall prey visibility.

Competition, Herbivory, and Enrichment: Nutrient-Based Models for Edible and Inedible Plants

Simple models representing nutrient-dependent growth of plant prey are used to study herbivores and edible and "inedible" plants. Three types of inedible plants are considered: those that have no direct interaction with herbivores, those that interfere with the ingestion of edible plants but are not themselves consumed, and those that are consumed but provide no nutritional benefit to herbivores. A necessary condition for coexistence at equilibrium applies for all types of inedible plants, which requires that edible plants be better competitors than inedible plants in the absence of herbivores but worse in their presence. All models predict compensatory changes in relative densities of edible and inedible plants at equilibrium as herbivore loss rate changes. If inedible plants do not interact with herbivores, then only inedible (not edible) plant biomass increases with nutrient supply; otherwise, biomasses of both edible and inedible plants increase with nutrient supply. If inedible plants interfere with ingestion of edible plants but are not consumed, then equilibria are stable in the parameter space examined, for a parameterized model of a planktonic system. In the other cases examined, equilibria are unstable in most of the parameter space examined.

The influence of the structure and function of the marine food web on the dynamics of contaminants in Arctic Ocean ecosystems

This paper examines some features of arctic marine ecosystems that may render them vulnerable to airborne pollutants. These features include the seasonal and spatial focus of primary productivity, the allocation of a relatively large proportion of the newly fixed carbon to the benthos, the prevalence of large mammals as apex consumers, and relatively high lipid levels in many arctic species. Sea ice is an important factor, since pollutants falling onto the ice surface during the winter months can be concentrated in epontic particulate matter (at the ice/seawater interface), or, more likely, be released through melting of the ice and enter the planktonic system in spring, reaching the benthos via sedimentation. Two ecosystems are discussed in which these processes are likely to be important — the highly productive Chirikov Basin of the northern Bering Sea and the sea ice-associated community north of Svalbard. There is evidence that pollutants are accumulating in arctic marine ecosystems. However, our predictive ability is constrained by the inability to delineate the sites of deposition.

Plankton Distribution Patterns in a Mediterranean Dilution Basin: Amvrakikos Gulf (Ionian Sea, Greece)

Abstract. The present work describes Amvrakikos Gulf (Ionian Sea, Greece) as a dilution basin and provides information concerning the relationships between the hydrology and plankton composition and distribution.Amvrakikos Gulf is characterized by a differentiated planktonic system which is apparently directly influenced by the input of the rivers located at the northern part of the gulf.

Population Regulation in Theory and Practice

Population regulation is a fundamental process related to most phenomena in ecology, including evolutionary ecology. I review the conceptual basis for defining regulation as bounded fluctuations in abundance, in contrast to the unbounded fluctuations of random—walk populations. Regulation arises as a result of potentially stabilizing density—dependent processes, even when brought about by “non—equilibrium” mechanisms. Although the phenomena is unambiguous in theory, detecting regulation by finding evidence for density dependence in a series of population estimates faces unsolved statistical problems. So, while there is growing evidence for widespread regulation, severe detection problems remain. I illustrate these with data from bird populations. Whether regulation is typically achieved by local stabilizing mechanisms or via metapopulation dynamics remains to be determined. I summarize recent studies on a particularly well—regulated system–red scale (Aonidiella aurantii) and its controlling parasitoid, Aphytis melinus. We tested and failed to find evidence for eight hypotheses that might account for the system's stability, including spatial heterogeneity in attack rates, a refuge, and metapopulation dynamics. We also failed to find evidence for density—dependent parasitism, but such density dependence might be still be present. Recent laboratory and modeling studies have uncovered a number of other potentially stabilizing mechanisms centering on the response of individual Aphytis to their size—structured host. This plethora of size— and stage—dependent interactions leads naturally to a consideration of the factors controlling Aphytis' size—dependent behavioral decisions, and consequently to the elaboration of size—structured models. The latter provide a vehicle for bringing together investigations of selection of life histories, and population dynamics. This is illustrated by a model of Aphytis and red scale dynamics that can explain a dramatic case of competitive displacement. The red scale/Aphytis system exemplifies a particularly challenging problem in population regulation, namely to account for the co—occurrence of stability and severe suppression of the prey population. A potentially generic solution is to assume stabilizing density dependence in the parasitoid or predator population; however, this has the consequence of increasing the host or prey population equilibrium. My colleagues and I have shown that observed prey densities in a plankton system are too low for such a mechanism to be operating. Further work is needed to test this and other hypotheses.

Feeding habits of pasiphaeid shrimps close to the bottom on the Western Mediterranean slope

The composition of the diet and daily cicle of predatory activity of pasiphaeid shrimps in the Northwestern Mediterranean were established; special attention was focussed on nocturnal feeding habits close to the bottom. Daily activity in both species was studied in two continuous 24-h sampling periods. Samples were obtained using bottom trawls between 1988 and 1990. Both species fed on benthic prey items at night. The nocturnal diet of Pasiphaea multidentata consisted of gammarid amphipods, isopods (Cirolana borealis) and macruran decapods (Calocaris macandreae). Nocturnal feeding activity was carried out only by large specimens (cephalothorax length >28 mm), which stayed close to the bottom during the nighttime. In contrast, the specimens collected during the daytime exhibited highly digested remains of pelagic prey (hyperiids, fishes, euphausiids, chaetognaths) ingested as a result of predatory higher activity in the water column the night before. The feeding strategy of P. sivado was parallel to that of P. multidentata. At night large specimens were located near the bottom and fed on suprabenthic gammarid amphipods. This nocturnal feeding activity by both these mesopelagic pasiphaeid species furnishes evidence of energy transfer from the benthos to the planktonic system in bathyal communities. Changes were observed in the diet of P. multidentata with depth. Crustaceans made up a larger share of the diet of P. multidentata on the lower slope than on the upper middle slope, probably because of changes undergone by bathyal communities with increasing depth. The feeding rate was higher in the submarine canyons, where the diet is also more specialised. Dietary overlap between the two pasiphaeids was very low, due to the different size range of prey exploited.

Ecosystem Functioning in the German Bight under Continental Nutrient Inputs by Rivers

The functioning of the German Bight ecosystem is determined largely by nutrient fluxes in and out of the system, namely by the advection of nutrients from the central and southern North Sea, including the influence of the Rhine River; by nutrient inputs through direct continental river runoff into the German Bight (Elbe, Weser, and Ems rivers); and by atmospheric nutrient inputs originating from land. The nutrient situation in the German Bight and the entire North Sea is assessed by estimating these fluxes from available nutrient data. The advective inflowes are based also on simulated water transports. The circulation system in the North Sea is divided into a northern and a southern cell, with only little net water exchange. The nutrient inflow into the southern North Sea from the north is also small, with no effect on the continental coastal areas. For the entire North Sea, the total input of phosphorus increased by 7.7% an nitrogen by about 11.4% from 1950 to 1980. The percentage of Atlantic input of phosphorus into the entire North Sea decreased from 91% to 85%, while river input increased from 2% to 13%. In the continental coastal strip the total inputs increased by 80%. The share of river input increased to 52%, both for phosphorus (1950: 14%) and nitrogen (1950: 20%). Of the winter nutrient content of the upper 30 m of the entire North Sea 33.5% of phosphate and 16.1% of nitrate are taken up by algae until summer. About 50% of total new production is generated in the coastal areas, with 32.8% of the volume and 34.4% of the area of the North Sea. The ratio of new to regenerated production ranges from 2.8 to 12, depending on the method of derivation. In the German Bight, phosphate and nitrate concentrations increased during the last four decades. At Helgoland the five-year-medians of phosphate and nitrate increased by a factor of 1.7 and 2.5, respectively. As the nutrient inputs by river discharges are only slightly larger than advective contributions, the nutrient concentrations rose comparatively slowly. Diatoms stagnated, while flagellates increased 10-fold. Common winter values in the early 1980s resemble those during summer blooms in the early 1960’s. The German Bight ecosystem has changed drastically on all time scales under the anthropogenic nutrient inputs during the last 40 years; the plankton system is no longer in an annual quasiperiodic state.