Description: The widespread decline of anadromous Atlantic salmon (Salmo salar L.) populations makes it imperative to research the underlying cause and to develop mitigation measures. One of the most vulnerable phases in the life-cycle of salmon is the fry stage in early spring. Survival rates of juveniles emerging from the gravel of riverbeds are related to the three-dimensional complexity of bottom morphology and hence the variety of microhabitats within the nursery area. However, anthropogenically increased sediment supply due to changes in agricultural land-use reduces complexity, especially the roughness of the streambed. This study used a series of controlled manipulative field experiments conducted in a purpose built raceway system, to provide quantitative data on the impact of sediment pollution on salmon production in freshwaters. The comparison of in-stream habitat with an increased sediment load and control (i.e. simulated natural) situations revealed that increased sedimentation drastically reduced the salmon fry carrying capacity of a stream. A modest increase in sand bed load (15%) in semi-natural streams reduced the fry density by 50% ten days after stocking with unfed fry. Emigration patterns of fry from sedimented habitat and control habitat were significantly different. Fry from both habitat types showed unusual active upstream migration which compensated for densities exceeding the carrying capacity. Riverine habitat was optimised on a reach scale to complement the raceway results and to provide a temporary mitigation measure. The in-stream habitat of a mill leat was manipulated to build the first Eco-Hatchery for salmon in the UK based, on results from the raceway and on an extensive literature review. The hatchery achieved high survival rates of salmon juveniles throughout their freshwater life stages. Furthermore, in-stream sediment traps were developed to offer effective protection for key fry nursery habitat from excess sand bed load. The data provided by the raceway system and the Eco-Hatchery inform riparian management plans. However, addressing sedimentation related issues in salmon rivers is a politically sensitive issue and will take time. Stocking with unfed fry is being used in the interim to temporarily enhance or restore populations. But stocking programmes based on conventional hatchery methodology as a response to declining stocks have frequently failed in both respects. A semi-natural incubator for salmon eggs, the Bamberger-box, was developed to address extremely low survival of newly stocked fry from conventional hatcheries. The new incubator mimics a natural salmon redd and aims in essence to produce wild fish in a hatchery environment. The results of five years field experiments using genetically different broodstock were encouraging. There was a significant increase in the average length and body mass of fry emerging from Bamberger-boxes and the mean eyed-egg-to-fry survival was 93% - greatly exceeding published data for egg-to-fry survival in the wild. Fry from Bamberger-boxes showed a significantly different and more natural rheotactic behaviour, and fewer fry had deformities when compared with fry incubated in conventional hatchery troughs. Seasonal and diurnal emergence patterns from Bamberger-boxes correlated with natural emergence patterns. A potentially crucial advantage of this new semi-natural incubation system was to ensure larvae survival during environmental extremes when all juveniles incubated in conventional hatchery troughs did not survive. Large-scale commercial incubators based on the same principles as the Bamberger-Box were developed and proved equally effective in producing ecologically viable fry. Low costs of production and operation render the new incubators an economically viable alternative to traditional incubation systems. Exploratory research on the influence of hyporheic invertebrates abundance on fry size at emergence was carried out as a next step in continuously improving semi-natural incubation technology.

Description: This Doctorial Thesis investigates the fundamental problem of flow and deposition processes of unsteady, inertial flows of granular media and elucidates its implications for the behaviour of pyroclastic flows formed in explosive volcanic eruptions. A three-fold approach is followed including laboratory experiments, their theoretical analysis, and field work on the pristine pyroclastic flow deposits of the 1975 eruption of Mt. Ngauruhoe (New Zealand). The experiments are based upon the physical problem of the sudden collapse of vertical columns of granular media onto a base and their subsequent spreading behaviour. Through investigations of the pyroclastic flow deposits of the 1975 eruption of Mt. Ngauruhoe, first complete data sets of the internal structure and grain-size distribution and the morphology of the upper free surface of small-volume pyroclastic flow deposits as a function of travel distance, underlying slope and topographic confinement are presented. This detailed data set is interpreted using the experimental findings on the propagation of an internal interface, and a qualitative time- and space-dependent model on transport, segregation and deposition is developed for pyroclastic flows.

Description: Die Arbeit beschäftigt sich mit der Reaktion von Nahrungsquantität und -�qualität sowie Umweltfaktoren wie Temperatur und Salzgehalt auf die Reproduktion, das Überleben und die Verbreitung von calanoiden Copepoden. Diese Experimente wurden mit Organismen aus der Nord- und Ostsee sowie unter Labor- also auch unter Freilandbedingungen durchgeführt. Hierbei waren die calanoiden Copepoden Acartia clausii, A. tonsa, A. longiremis und Temora longicornis in Kombination mit Rhodomonas sp.(Chrypthophycea), Thalassiosira weissflogii (Bacillariophycea), dem heterotrophen Dinoflagellaten Oxyrrhis marina, sowie einem oligotrichen Ciliaten Strombidium conicum untersucht worden. Rhodomonas sp. verändert seine Nahrungsqualität unter Stickstoffmangel. Copepoden wie Acartia clausii und A. tonsa reagieren darauf mit einer Erhöhung der Eiproduktion. Wenn heterotrophen Protisten wie O. marina (Dinoflagellat) bzw. S. conicum (Ciliat) im Vergleich zu nur Rhodomonas sp. gefüttert wurden, dann war die Eiproduktion signifikant höher. Aber zwischen den beiden Versuchsansätzen mit den heterotrophen Protisten gab es keinen Unterschied. Durch Versuche mit Freilandtieren an verschiedenen Orten in der Ostsee lässt sich schlussfolgern, dass der Salzgehalt, die Temperatur und die Nahrungskonzentration einen großen Einfluss auf die Populationsdynamik dieser Art haben. Die Messung der Reproduktion von Freilandtieren auch in der Nordsee haben gezeigt, dass die Temperatur nicht der einzige Kontrollfaktor bei der Reproduktion von marinen Copepoden ist. Stattdessen lässt sich schlussfolgern, dass die Quantität der Nahrung und die Qualität der Nahrung ein dominierender Faktor im saisonalen Verlauf bei der Reproduktion von Temora longicornis eine Rolle spielen kann.

Description: This study explores life-history strategies of recent fishes based on a data set that is two orders of magnitude larger than those used in previous studies. Trophic level, size and productivity were taken as key traits and proxies for many other closely related traits. Size was strongly correlated with most life-history traits of fishes and also with morphological characters, behaviour, and preferred environmental conditions. Size was also a good predictor of placement on the r-K continuum. Productivity was derived from growth, age at maturity, maximum age, and fecundity data. It was positively correlated with metabolism and level of activity and was also an indicator for placement of species on the r-K continuum. It was strongly correlated with most life-history traits of fishes and also with morphological characters, behaviour, and preferred environmental conditions. It was negatively correlated with status of threat. The position of species in the food web was shown to restrict life-history options. The addition of trophic level as an orthogonal axis on the r-K continuum revealed unoccupied regions such as the combination of small size and high productivity with either herbivory or top-predatory, and the combination of very large size and very low productivity with herbivory. Discrete classes of size, trophic level and productivity were used to define 80 life history strategies. Only 50 of these strategies were used by recent species, with an exponential decline in species’ numbers from the most to the least used strategies. This decline is interpreted as an exponential increase in constraints associated with less-used strategies. Analysis of trade-off or constraint curves in life-history space revealed unoccupied areas as well as local maxima, i.e., areas occupied by more species than the surrounding space. Such a local optimum was occupied by very large top predators with very low productivity. Low-level predators of small to medium size and medium to high productivity were the three strategies used by altogether 60% of the species. Strategies used in extreme environments such as the deep and polar seas or high-altitude lakes were not ‘specialist strategies’ but rather among the 10 most-used strategies, suggesting that constraints imposed by extreme environments excluded strategies that had a high degree of inherent constraints. The number of strategies used by phylogenetic, environmental, morphological or behavioural groupings of fishes was highly predictable from the number of species in the respective groups. A preliminary chronology of life-history strategies showed that over 2/3 of recent strategies were invented only 200-150 million years ago during several radiations of the Actinopterygii, including small size, very large size (invented in parallel by Elasmobranchii), high productivity, and true herbivory. Phylogeny restricted the life-history options available to species with respect to size, place in the food web and productivity. There was evidence for a non-overlap of preferred life-history strategies between the two largest recent Classes, with Elasmobranchii tending towards large size and low to very low productivity, and Actinopterygii tending towards medium size with medium to high productivity. Nine selection theories were tested as to their ability to correctly predict adaptation of life-history traits in response to environmental conditions such as salinity, climate, zoogeographic realm, ocean basin, and habitat type. Predictions were 88 – 100% correct when cases where different theories predicted different adaptations were excluded. In conflicting cases, predictions by temperature theory usually prevailed over those by r-K and succession theories. Life-history strategies were examined with respect to their correlations with body shape, brain size, reproductive guild, migratory behaviour and status of threat. Productivity increased with body shape from eel-like to short and/or deep, with brain size from very small to normal and large, and with migratory behaviour from catadromous to amphidromous and non-migratory. Size decreased with migratory behaviour from catadromous to non-migratory, and with parental care from nonguarders to bearers (in Actinopterygii). Trophic level decreased with increase in brain size. Several life-history strategies were only used by migratory species. Non-threatened fishes had significantly higher productivity than threatened fishes. Life history-strategies that combined large size and low productivity contained proportionally more threatened species than other strategies. Independent estimates of abundance and distributional range of species were used as indicators of success of life-history strategies. Species showed preferences for strategies that were associated with high abundance or small to medium ranges. When abundance and range were combined into a single measure of success (Impact), most strategies were associated with impacts that were not significantly different from the overall mean. Only medium-sized low-level predators and omnivores with high productivity had significantly higher impact; these two strategies were used by 39% of the species.

Description: Aim of this study was the investigation of the vertical dis-tribution of N2O and the factors influencing this distribu-tion. Dissolved and atmospheric N2O was measured in the North Atlantic Ocean and the Baltic Sea. These data, in com-bination with physical and chemical parameters, were used to determine sources and sinks of N2O. Possible production pathways were investigated using the relationship between N2O and relevant production parameters, and their relation to physical processes in the oceans. The hypothesis whether N2O concentrations increased by oceanic iron fertilization via enhanced substrate supply for microbial respiration, was tested during the European Iron Fertilization Experi-ment (EIFEX) in the subpolar South Atlantic. The vertical structure of bacterial communities in the subtropical North Atlantic was investigated, with the intention to find corre-lations between the community structure of bacteria and the distribution of N2O. In summary, this study presents a de-tailed picture of the distribution of N2O in the North At-lantic Ocean and the Baltic Sea and adds 80 profiles of the Atlantic and 26 profiles of the Baltic Sea to the database.

Description: For decades, ecologists have studied trophic interaction in aquatic systems, and described the food web structure of dominant ecological groups based on gut content analyses. The conception of these interactions may, however, be biased by the lack of couplings to the microbial food web and direct errors in diet analyses (e.g. differences in digestion rate between food types). In this thesis, I examined the planktonic food web by analyzing the trophic structure (i.e. trophic levels) with an alternative technique, the abundances and fractionation of stable isotope. I used natural abundances of stable isotopes of nitrogen (delta15N) and carbon (delta13C) to describe the food web structure of mesozooplankton communities in the Central Baltic Sea (Bornholm Basin, Gdansk deep and Gotland Basin) and Southern North Sea (German Bight). I focused on assessing spatial and seasonal isotopic variation with respect to trophic levels of the dominant mesozooplankton species in both marine systems. The stable isotopes of nitrogen and carbon provide powerful tools for assessing trophic levels of and carbon flow to consumers in the food web.

Description: Species invasion is a conspicuous phenomenon in today’s human-dominated biosphere. With the changing configuration of marine ecosystems, the barriers limiting the range of species are changing, too. Studing species invasions allows scientists to observe and measure many ecological processes (such as spatial distribution, genetic changes) directly, which are difficult to study with long-established native species. Therefore the study of invasion ecology gained the name of “an experiment in nature” (Grinnel 1919 as referred in Sax et al. 2005). Because the frequency of gelatinous zooplankton increases globally, their future ecological role is a matter of concern for marine invasion ecologists. The Baltic Sea is a recipient of species from several different donor systems and referred to as ‘a sea of invaders’ by Leppaekoski et al. (2002). The recent invasion by the comb jelly Mnemiopsis leidyi became a topic of major concern after its appearance in the Baltic Sea because of the vast ecological and economic impacts it had in its previously invaded habitats such as the Black Sea. In the first chapter, we established a morphological key to distinguish Mnemiopsis leidyi from Bolinopsis infundibulum. Both species are very similar. This key enabled us to identify this species from time series data of Helgoland Road station where B. infundibulum naturally occurs. A permanent weekly sampling in the Western Baltic Sea provided the basic knowledge on M. leidyi seasonal dynamics and ability of being established. In chapter II we show the late summer outbreak in 2007 with a 10 fold increase in abundance in a short time that coincided with high reproduction activity. The drop of mesozooplankton prey in late spring was due to predatory control of fish larvae and no seasonal overlap between M. leidyi and fish eggs or larvae could be detected. We have also provided data on the main environmental conditions which might trigger the outbreaks of M. leidyi population in the Western Baltic Sea. In chapter III, we simulated the drift pattern of M. leidyi during its first year of observation in 2007 by using a hydrographical model. The model illustrated the possible advection route of M. leidyi through the Baltic Sea. It is hardly possible that M. leidyi has penetrated from Kategat Skagerak as a single source of spread. Instead ballast water release and the subsequent spread away from different recipient harbors might have led to the concentration of its population in the deep basin of North and Central Baltic Sea. In the last chapter we show the predatory impact of M. leidyi on mesozooplankton population of Western Baltic Sea was measured. During cold season this species showed a high preference for small sized and slow swimming prey. Copepods were preferred just for a short time in August. The most abundant prey in summer were planula larvae of the other gelatinous carnivore in the Baltic Sea, Aurelia aurita. However adults of M. leidyi got their major energy intake via cannibalism on their own larvae.

Description: Conventional production systems used in aquaculture such as ponds, raceways, net cages or recirculating systems have in common that they release large amounts of feed nutrients either in dissolved or particulate form. The efficient removal of suspended solids is a key factor for the successful operation of recirculating aquaculture systems (RAS). The here presented thesis utilised the solid wastes from modern aquaculture recirculating system for carnivorous fish for the secondary production of detritivorous organisms (Common ragworm, Nereis diversicolor and European brown shrimp, Crangon crangon). In an experimental integrated recirculating system, fish were cultured for a period of 684 days. During the complete growth period of the fish, polychaete worms were cultivated as exclusive consumer of the excreted particulate waste. The excreted dissolved inorganic nutrients of both fish and polychaetes were utilized either by algae to produce additional harvestable biomass. Water replacement rate during two long term experiments was around 0.8 % / d (system volume). With increasing fish biomass the nutrient and energy supply of the polychaetes could be met to enable them to grow and finally to reproduce. Till the end of the experimental period a self-sustaining worm population up to the fourth generation could be achieved. The growth experiments of the European brown shrimp revealed the potential of the crustacean as detritivorous organisms for integrated aquaculture. The results of this thesis were used for the development of nutrient budget models.