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Here, we communicate a point of departure in the development of aquatic ecosystem models, namely a new community-based framework, which supports an enhanced and transparent union between the collective expertise that exists in the communities of traditional ecologists and model developers. Through a literature survey, we document the growing importance of numerical aquatic ecosystem models while also noting the difficulties, up until now, of the aquatic scientific community to make significant advances in these models during the past two decades. Through a common forum for aquatic ecosystem modellers we aim to (i) advance collaboration within the aquatic ecosystem modelling community, (ii) enable increased use of models for research, policy and ecosystem-based management, (iii) facilitate a collective framework using common (standardised) code to ensure that model development is incremental, (iv) increase the transparency of model structure, assumptions and techniques, (v) achieve a greater understanding of aquatic ecosystem functioning, (vi) increase the reliability of predictions by aquatic ecosystem models, (vii) stimulate model inter-comparisons including differing model approaches, and (viii) avoid 're-inventing the wheel', thus accelerating improvements to aquatic ecosystem models. We intend to achieve this as a community that fosters interactions amongst ecologists and model developers. Further, we outline scientific topics recently articulated by the scientific community, which lend themselves well to being addressed by integrative modelling approaches and serve to motivate the progress and implementation of an open source model framework. © 2011 Springer Science+Business Media B.V.

1. We studied the effect of size-selective predation on the outcome of competition between two differently sized prey species in a homogenous environment.2. Using a physiologically structured population model, we calculated equilibrium food concentrationsfor a range of predation scenarios defined by varying maximum predation intensity and size-selectivity, the latter being characterized by the neutral selection length (NSL), where negativeselection of small prey size-classes turns into positive selection of larger prey. We parameterized the model according to the well-studied example of fish predation on two differently sizedcladoceran species, Daphnia pulicaria and Daphnia galeata.3. Although the larger D. pulicaria was principally the better competitor for food, competitive superiority shifted to the smaller D. galeata under certain predation scenarios. The lowest predationintensity needed to induce a shift from D. pulicaria to D. galeata was found at NSL values in between the sizes at maturity of both species.4. Analysing the per capita mortality rates as a result of the underlying parameters of the mortality model, NSL and maximum predation intensity, revealed that the tolerable mortality rate of daphnids decreased as NSL increases towards values close to the size at maturity. This effect was most pronounced in D. pulicaria, thus explaining a higher vulnerability of the larger speciesto size-selective predation.5. A reduction of the size at maturity in the smaller species (D. galeata) as a phenotypic response to the presence of fish resulted not only in an increased capability to withstand predation, butalso in competitive dominance shifts over the larger D. pulicaria at lower predation intensities and a much wider range of NSL as a trait-mediated indirect effect.6. Overall, our results demonstrate that shifts in dominance of differently sized herbivores under size-selective predation regimes may be facilitated by the demonstrated alteration in competitivecapacities and thus might not be exclusively caused by direct predation effects.

1. The zebra mussel (Dreissena polymorpha) is one of the most successful invasive species; it has colonised many aquatic systems in Europe and North America with strong impacts on various ecosystem processes. The effect of D. polymorpha filtration on pelagic seston concentrations has been quantified in several studies, but the magnitude and stoichiometry of the transfer of sestonic biomass into benthic detritus by D. polymorpha and the accompanying enrichment of the benthic habitat is still under-investigated.2. We studied biodeposition by zebra mussels in two series of laboratory experiments with the food algae Cryptomonas erosa and Scenedesmus obliquus. We also measured the year-round biodeposition rate under natural conditions in the oligotrophic Lake Constance.3. In all experiments, zebra mussel biodeposition was linearly related to seston concentration. In the field, the relationship changed with a seasonal shift in algal composition and lower biodeposition rates during the spring algal bloom.4. For both algal species in laboratory experiments, biodeposited material was depleted in phosphorous at an algal concentration ≤0.6 mg ash-free dry mass L-1, but not at higher concentrations. This effect was not observed in the field, probably because of high variation in C : N : P stoichiometry.5. By mediating the transfer of pelagic resources into the benthos zebra mussels provide a sufficient amount of detritus for benthic invertebrates, especially during summer. Thus, material biodeposited by the mussels might increase benthic secondary production from pelagic resources, and zebra mussels are important mediators of this flux of organic matter from the pelagic zone into the benthos.

Lake Constance is among the largest lakes in central Europe and represents the most important drinking water reservoir in southwestern Germany. About 4 million people depend on this lake for their drinking water supply, and considerable efforts have been made to protect its high water quality (STABEL 1998). In addition to a drinking water supply, the lake is the receiving water body of numerous waste-water plants within its catchment and is moreover used for recreational purposes and fisheries. To improve water quality management of the lake, a research project (see www.bodenseeonline.de) was initiated to develop a model-based decision support system. The model system consists of a coupled hydrodynamic ecological model that can be either run in a 1D-setting (DYRESM-CAEDYM) or a 3D setting (ELCOM-CAEDYM). The establishment of the model systems requires the adaptation of the ecological model CAEDYM to Lake Constance, achieved by long-term simulations and comparison to historical data. The main goal of this study is to adapt the ecological model to reflect the physiological properties of the planktonic community, particularly for phytoplankton, which shows a great functional diversity. This diversity needs to be taken into account (REYNOLDS et al. 2002, SOMMER et al. 1986) for phytoplankton succession to be represented properly.

We studied costs and benefits of life history shifts of water fleas (genus Daphnia) in response to infochemicals from planktivorous fish. We applied a dynamic energy budget model to investigate the resource allocation patterns underlying the observed life history shifts and their adaptive value under size selective predation in one coherent analysis. Using a published data set of life history shifts in response to fish infochemicals we show that Daphnia invests less energy in somatic growth in the fish treatment. This observation complies with theoretical predictions on optimal resource allocation. However, the observed patterns of phenotypic plasticity cannot be explained by changes in resource allocation patterns alone because our model-based analysis of the empirical data clearly identified additional bioenergetic costs in the fish treatments. Consequently, the response to fish kairomone only becomes adaptive if the intensity of size selective predation surpasses a certain critical level. We believe that this is the first study that puts resource allocation, energetic costs, and adaptive value of predator induced life-history shifts – using empirical data – into one theoretical framework.

Plankton succession during spring/early summer in temperate lakes is characterised by a highly predictable pattern: a phytoplankton bloom is grazed down by zooplankton (Daphnia) inducing a clear-water phase. This sequence of events is commonly understood as a cycle of consumer-resource dynamics, i.e. zooplankton growth is driven by food availability. Here we suggest, using a modelling study based on a size-structured Daphnia population model, that temperature and not food is the dominant factor driving interannual variability of Daphnia population dynamics during spring. Simply forcing this model with a seasonal temperature regime typical for temperate lakes is sufficient for generating the distinctive seasonal trajectory of Daphnia abundances observed in meso-eutrophic temperate lakes. According to a scenario analysis, a forward shift of the vernal temperature increase by 60 days will advance the timing of the Daphnia maximum on average by 54 days, while a forward shift in the start of the spring bloom by 60 days will advance the Daphnia maximum only by less than a third (17 days). Hence, the timing of temperature increase was more important for the timing of Daphnia development than the timing of the onset of algal growth. The effect of temperature is also large compared to the effect of applying different Daphnia mortality rates (0.055 or 0.1 day-1, 38 days), an almost tenfold variation in phytoplankton carrying capacity (25 days) and a tenfold variation in Daphnia overwintering abundance (3 days). However, the standing stock of Daphnia at its peak was almost exclusively controlled by the phytoplankton carrying capacity of the habitat and seems to be essentially independent of temperature. Hence, whereas food availability determines the standing stock of Daphnia at its spring maximum, temperature appears to be the most important factor driving the timing of the Daphnia maximum and the clear-water phase in spring.

Die Simulation von Seeokosystemen hat innerhalb der Limnologie eine verhaltnismasig lange Tradition, die bis in die 1970er Jahre zuruckreicht [1]. Das Interesse an der Entwicklung von okologischen Modellen fur Standgewasser kam dabei gleichermasen aus der Grundlagenforschung als auch von der angewandten Limnologie bzw. dem Gewassermanagement. Aus wissenschaftlicher Sicht sind Seen verhaltnismasig abgeschlossene Oko systeme, die somit gut studierbar sind und hervorragend als Modellsysteme geeignet sind. Aus der Perspektive des Gewassermanagements spielen okologische Prozesse eine zentrale Rolle, weil die Wasserqualitat eines Wasserkorpers masgeblich durch okologische Zustandsgrosen beeinflusst wird (z. B. Phytoplanktonbiomasse, toxische Algen, Nahrstoffkonzentration en). Geeignete Modellsysteme zur Simulation der Okosystemdynamik stellen daher wichtige Instrumente dar, um Auswir kun gen von anthropogenen Stressoren oder anderen Umweltfaktoren zu untersuchen bzw. vorherzusagen. Klassische Ein satz bereiche solcher Modelle sind Gewas sereutrophierung oder Gewassersanierung. Neue Anwendungsfelder richten sich auf die Auswirkungen des globalen Klimawan dels, der Invasion exotischer Arten oder die Effekte fortschreitender Reoligotrophierung. Im Rahmen des Verbundprojektes BodenseeOnline wurde eine ganz andere, neuartige Anwendung eines okologischen Modells angestrebt: Die Kurzfrist-Prognose der okologischen Prozesse im Rahmen des BodenseeOnline-Systems (s. a. Lang et al. [2] in diesem Heft der WasserWirtschaft). Hierbei liefern Modelle Prognosen uber Zeitraume von wenigen Tagen, die als Entscheidungsunterstutzung im Ge wassermanagement des Bodensees herangezogen werden konnen. Die Anwendung eines okologischen Models auf derartig kurzen Zeitskalen ist bisher selten realisiert worden, was sehr wahrscheinlich darauf zuruckzufuhren ist, dass viele elementare okologische Prozesse eher auf Zeitskalen von Wochen (z. B. Planktonsukzession) bis mehreren Monaten (z. B. Nahrstoffkreislaufe, Zirkulation) ablaufen. Eine sinnvolle Beurteilung der Simulationsergebnisse von okologischen Modellen muss deshalb uber langere Zeitraume stattfinden, im besten Fall uber mehrere aufeinanderfolgende Jahre, um auch Prozesse des saisonalen Wechsels von Stratifikation, d. h. Schichtung, und Durchmischung sowie langDas Okosystem Bodensee ist aus ethischer, okologischer und wasserwirtschaftlicher Sicht eine wertvolle Ressource. Die nachhaltige Nutzung und ein sinnvoller Schutz des Bodensees setzen ein elementares Verstandnis der Okosystemdynamik des Bodensees voraus. Im Rahmen des Verbundprojektes BodenseeOnline wurde die Anwendung des 1-D-Modellsystems DYRESM-CAEDYM auf den Bodensee realisiert, welches wertvolle Einsichten in die Funktionsweise des Okosystems liefert und somit das Fundament fur Kurzund Langzeitprognosen fur den Bodensee bildet. Das okologische Modell des Bodensees: Konzept, Simulation und Test an Langzeitdaten

The simecol package provides an open structure to implement, simulate and share ecological models. A generalized object-oriented architecture improves readability and potential code re-use of models and makes simecol-models freely extendable and simple to use. The simecol package was implemented in the S4 class system of the programming language R. Reference applications, e.g. predator-prey models or grid models are provided which can be used as a starting point for own developments. Compact example applications and the complete code of an individual-based model of the water flea Daphnia document the efficient usage of simecol for various purposes in ecological modeling, e.g. scenario analysis, stochastic simulations and individual based population dynamics. Ecologists are encouraged to exploit the abilities of simecol to structure their work and to use R and object-oriented programming as a suitable medium for the distribution and share of ecological modeling code.

1. We present data with a high spatio-temporal resolution from a 72-h field survey in Bautzen Reservoir (Saxony, Germany). The aims of this survey were to observe hydrophysical processes during a period of unstable stratification in spring and investigate the effect of wind-induced internal waves on the vertical distribution of zooplankton.2. Wind velocities up to 10 m s)1 caused a strong downwelling event of warm water at the sampling site and led to the generation of internal waves with an amplitude of 4 m.3. The zooplankton community, which was dominated by Daphnia galeata, inhabitedepilimnetic waters. Downwelling enlarged the thickness of the epilimnetic layer and, hence, led to high zooplankton abundances down to relatively deep water strata indicating lateral transport of zooplankton. As a consequence, area-specific zooplankton abundances increased considerably (max. fourfold) during downwelling.4. We conclude that classical limnological field sampling, such as for monitoring purposes, can lead to severely biased estimates of zooplankton abundance due to the interfering effects of hydrophysical processes like internal waves.5. Backscattering strengths measured by a simultaneously deployed Acoustic Doppler Current Profiler (600 kHz) were found to be correlated with estimated zooplankton abundances based on plankton samples.

Seen und Talsperren sind dynamische Systeme, die gleichermasen durch externe wie interne Prozesse gesteuert werden. Das Verstandnis dieser Dynamik ist ein zentrales Anliegen der Limnologie und Grundvoraussetzung fur zielfuhrendes und kreatives Management. In diesem Zusammenhang sind komplexe dynamische Seenmodelle (KDS) ein unentbehrliches Hilfsmittel zum Systemverstandnis geworden. Dieser Beitrag gibt eine Einfuhrung in den Stand der okologischen Modellierung von Standgewassern und liefert Einblicke in unterschiedliche Modelle. Gleichzeitig werden auch Probleme und Limitationen von komplexen Seenmodellen erortert. Keywords: BELAMO; Bodensee; KDS; Nahrstoffbilanzierung; Okosystemmodell; PROTECH; SALMO; Seemodell; Simulation; Systemanalyse; Unsicherheitsanalyse