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Polar regions are projected to experience faster and stronger impacts of climate change than the rest of the planet. It is crucial to investigate how climate change drivers may affect polar ecosystems, potentially causing pressures on biodiversity and ecosystem functioning. Specifically, seaweed is considered the primary beneficiaries of the loss of sea ice in polar seas, as some species have increased in bathymetric extent, density and biomass. However, the loss of protective sea ice and increased storm frequency has increased detached seaweed in polar coastal systems. Thus, detached seaweed could represent a connecting vector between rocky and sedimentary habitats in polar regions. Nevertheless, research on the effects of detached seaweed on benthic communities is still limited. Some studies suggest that detached seaweed may provide a food supplement, modify biotic interactions and disturb the benthos by mechanical action on the sedimentary substrate. This thesis aims to investigate the mechanisms by which biotic drivers modify the structure and functioning of coastal sedimentary communities at the poles. In Publication I, I investigated the effects of detached seaweed on the structural and functional traits of species assemblages in soft-bottom intertidal habitats. For this, manipulative experiments based on simulation of detached seaweed patches were conducted for comparative purposes between intertidal sites in the Arctic. I found that patches with seaweed compared to unmanipulated areas reduced the abundance of individuals at both sites and the biomass at one of the intertidal sites. In addition, detached seaweed strongly modified the structure and functioning of the soft-bottom species assemblages at both intertidal sites. Thus, I suggest that the detected effects are possibly the result of seaweed-driven changes in environmental conditions and physical disturbances as underlying processes. Publication II assessed the magnitude and direction of the effects of predation on the diversity and structure of Arctic benthic communities. The effects of predation on the benthic communities studied were contrasted with the predictions of the environmental stress model (ESM), which predicts that predation as a community regulating factor decreases at higher levels of environmental stress. To this end, a caging experiment was conducted in which consumers were excluded from plots in two intertidal sedimentary sites in the Arctic. Unmanipulated areas were used as treatment controls, and partial cages were used to estimate cage artefacts. In both sites, predator exclusion changed the species composition of the communities but did not affect univariate ecological responses. This study suggests that consumers have limited effects on the structure and functioning of Arctic intertidal communities, thus providing empirical support for ESM under high environmental stress. In Manuscript II. Detached seaweed accumulated on the seabed could provide food and shelter for epibenthic predators, increasing the density of consumers and indirectly causing more predation pressure on the benthic community. Manipulative field experiments were conducted to assess the combined effect of detached seaweed and predation on the dynamics and structure of the subtidal soft-bottom benthic community at the poles. Seaweed plots, predator exclusion cages and a combination of seaweed patches and exclusion cages were installed at these sites. In the Arctic, I discovered that seaweed patches with access to predators and seaweed patches without access to predators reduced species diversity and abundance of individuals compared to unmanipulated areas. Also, seaweed plots with access to predators in Antarctica and seaweed plots without predators decreased species richness compared to unmanaged areas. Furthermore, the results indicate that predation seems to play a minor role in subtidal soft-bottom benthic communities. Based on the results, I suggest that detached seaweed themselves affect the dynamics and structure of soft-bottom benthic communities at both poles. Overall, the results highlight the importance of research on the effects of biotic drivers on coastal marine ecosystems and of using manipulative field experiments to move towards predictive ecology, even more so in polar regions highly affected by global warming.

Macrofaunal bioturbation is an important mechanism for the enhancement of remineralization and biogeochemical cycling in marine sediments. Reduction of bioturbation activity may accordingly have far-reaching negative implications for general ecosystem performance. This is especially the case for shallow shelf seas, such as the German Bight, which account for 50% of global benthic remineralization, although they cover only 7% of the total sea surface. Increasing anthropogenic activities (e.g. wind farm construction) in these shallow shelf seas have intensified the need for reliable quantifications and predictions of macrofaunal bioturbation activities and resulting biogeochemical processes. The aim of this thesis was,thus, to develop easily applicable concepts that allow for the quantification of sediment reworking and the prediction of bioirrigation. In order to simplify the quantification of sediment reworking, which can so far only be assessed experimentally, I compared two of the most commonly applied methods (sediment profile imaging (SPI) and standard slicing technique (ST)). In addition, the time-saving and easily applicable SPI method was tested for its suitability to assess sediment reworking from cylindrical multi-corer samples (Manuscript I). The results suggested that SPI is suitable and even more accurate than ST for the investigation of sediment reworking activity. This omits the previously necessary need for timeconsuming slicing or the complex transfer into rectangular aquaria. These findings will facilitate studies on spatiotemporal patterns of sediment reworking activity in the German Bight. Such studies are of special interest as the bioturbation potential (BPc), which was previously often applied to estimate the potential of communities to rework the sediment, does not correlate with actual sediment reworking rates (Manuscript II). Surprisingly BPc, which includes sediment reworking traits (i.e. mobility and reworking mode) but no specific bioirrigation traits, rather correlated with bioirrigation activity and nutrient fluxes of silicate, ammonium, nitrate, and nitrite (Manuscript II). To overcome ambiguity of BPc, I developed the irrigation potential (IPc), as an adaptation from BPc (Manuscript III). By incorporation of bioirrigation effect traits (i.e. burrow type, feeding type, injection pocket depth), IPc was specifically designed to predict bioirrigation and its influence on biogeochemical processes (Manuskript III). I could demonstrate that, in contrast to BPc, the modified index provides an accurate quantitative measure of macrofaunal bioirrigation for both single species and entire communities of various infaunal species, if the index is calculated with ash free dry body mass. IPc provided better estimations of phosphate, silicate, ammonium, nitrate and nitrite fluxes than BPc (Manuscript IV). The estimation of silicate, ammonium, nitrate, and nitrite fluxes may be further increased if IPcis calculated in wet body mass instead of ash free dry body mass. Wet body mass thereby serves as a proxy of the irrigated sediment volume. In general, IPc could become a valuable tool to support ecosystem management and future investigations on the effects of anthropogenic activities on biogeochemical turnover in shallow shelf seas. Findings of Manuscript IV however also demonstrated that IPc is a crucial but insufficient parameter for the modelling of sediment biogeochemical processes because these also dependent on environmental conditions (e.g. temperature, sediment organic matter content, permeability). A newly proposed temperature term (IcT) (Manuscript III) may provide a tool to identify spatiotemporal variations in macrofaunal bioirrigation activity. There is however a need to determine further how IPcor IcT relate to biogeochemical cycling under different environmental conditions as well as how the respective macrofaunal traits are affected by environmental parameters.

Marine ecosystems are subjected to an unprecedented range of natural and anthropogenic disturbance with an increasing frequency of occurrence over recent decades. Among others, rising sea water temperature, ocean acidification, and coastal water pollution have resulted in alteration of habitats and subsequent changes in the structures of species assemblages. In the face of these challenges, ecological research needs to predict responses of assemblages to global change, a requisite for the adequate prevention of further environmental degradation. However, predicting assemblage responses requires a thorough understanding of ecological processes and of the structure and functioning of assemblages. The present thesis comprises four manuscripts which address in detail a) the temporal variability of benthic macrozoobenthos assemblages and the relative role of different environmental drivers of abundance variations in the North Sea, b) the functional diversity and the dominant functional characteristics of benthic species of the southern North Sea, c) the temporal variations in the functional trait composition, the contribution of different biotic and abiotic predictors to the variation in ecological functioning, the relationship between species diversity and functional diversity and the extent of functional redundancy within benthic communities and d) the degree of functional homogenization and the identification of dynamically-dominant-traits that likely have the greatest effect on biodiversity and ecosystem function. In Manuscript I, the model results revealed that temperature and anomalies of the North Atlantic Oscillation Index (NAOI) play a distinct role in controlling the temporal variation of the benthic assemblages. The results also showed substantial variation in the composition of macrozoobenthos assemblages in the North Sea at decadal and sub-decadal scales. Species react differently to environmental disturbances with generalist species being dominant in the region. Manuscript II and Manuscript III on the functional characteristics of macrozoobenthos assemblages revealed that changes in trait composition were more similar among monitoring sites than changes in the taxonomic composition, emphasizing the role of environmental disturbances in the determination of trait associations in the North Sea system. The relationship between species richness and functional diversity indicates a relatively high functional redundancy within benthic assemblages of the southern North Sea. Manuscripts II - IV showed that some trait modalities such as small body size, high dispersal potential, interface- and deposit-feeding were relatively common in the North Sea benthic assemblages. In fact, this suite of traits represents an adaptive strategy enabling species to survive and thrive in a stressful environment. The replacement of specialist species by generalist species (Manuscripts I and III), less site-specific temporal variations in functional composition as compared to the taxonomic composition (Manuscript III) and a high degree of functional niche overlap (Manuscript IV), imply functional similarity among species assemblages. An increased spatial similarity of assemblages, in turn, generated functional homogenization in the North Sea benthic system. In contrast to the considerable temporal variation in species abundance, the temporal development of functional diversity was relatively stable with only two incidental inconsistencies coinciding with extreme events (i.e. cold winter 1995/96 and extreme negative NAO winter of 2009/10) in the North Sea. Following the temporary changes, the functional diversity rebounded to previous levels after almost one year. The rapid recovery of functionality after disturbance may be attributed to the high functional redundancy in the ecosystem. The results of the present thesis contribute to the understanding of the structural and functional processes of macrozoobenthos in the southern North Sea. The study highlights that a comprehensive understanding of long-term dynamics of benthic ecosystems requires a combined analysis of functionality and taxonomic structure.

Mangroves are considered as an important source of nutrition to aquatic consumers, which, in return, sustain the fish population. However, there is still controversy about the importance of mangroves to fish communities, and furthermore, not all mangroves fulfill every function ascribed to them. The Persian Gulf presents the northernmost mangroves in the Indo-Pacific region, thriving under extreme environmental conditions such as very low rainfall and high salinities. Very few studies have addressed fish distribution patterns of mangroves in this arid region. The main objective of this study is to describe and compare the fish community structure and food web dynamics of mangrove and non-mangrove intertidal creeks in a low-rainfall system in Qeshm Island, Persian Gulf, Northern Indian Ocean (26.8°N, 55.75°E). Therefore, this thesis addresses temporal changes in mangrove fish assemblages related to the tidal and diel cycles in the meso-tidal mangrove of Qeshm Island. Also, the food web s dynamics were studied to determine the role of mangroves in fish food webs. Moreover, due to the arid climate along the northern Indian Ocean, many neighboring creeks are devoid of mangroves but still provide habitat for fish. This provided the necessary conditions for a natural experiment to compare fish assemblage structures and trophic diversity between creeks that are mangrove lined, and creeks without mangroves across seasons. For that, fish were collected with respect to the different combinations of tidal amplitude (and lunar phase) and day light conditions as well as seasons (winter, summer). Also, various potential food sources were collected for à ´13C and à ´15N measurements from both habitats across seasons. The findings show the impact of environmental variables (e.g. tide and temperature) in structuring fish assemblages in Qeshm intertidal creeks. The interaction between tide and time of day emerged as an important factor in organizing mangrove fish assemblages in this meso-tidal arid region. The highest fish biomass, abundance, and diversity were observed during spring tide night. High inundation during spring tides coinciding with the darkness provided the most favorable conditions for fish. When mangrove fish communities were compared with the non-mangroves, seasonality appeared as a more important factor than habitat. Extreme summer water temperatures (>33°C) likely limit the fish abundances and biomass. Fish assemblages of mangrove and non-mangrove intertidal creeks were equally diverse and dominated by the same fish families (e.g. Mugilidae). Small-sized fish dominated catches in both habitats. Also, there were no consistent differences in fish abundance and biomass for mangrove vs. non-mangrove fish collections. Community trophic diversity, measured with size-corrected standard ellipse areas (SEAc), also showed no significant difference across habitats. Instead, strong seasonal patterns were observed for the food sources and fish communities isotopic niche sizes. These findings demonstrate that the structuring effect of seasonality is more important than habitat in determining the fish distribution patterns in this region. Mangrove-derived organic matter contributed to a maximum of 36% to the fish tissue, whereas organic matter produced by microphytobenthos and plankton plays a major role in the diets of the most abundant fish species, with contributions of 64 - 100%. Thus, the fish food web s support of mangrove and non-mangrove intertidal creeks seems to be energetically driven by pelagic and benthic food pathways in this study area. Furthermore, the dominance of detritivores in both mangrove and non-mangrove intertidal creeks suggests the importance of benthic food webs in the intertidal creeks at Qeshm Island. The outcomes of this dissertation contribute to the global understanding of the importance of mangrove and non-mangrove intertidal creeks for fish food webs and fisheries support in a low-rainfall coastal ecosystem. The findings imply some potentially interesting consequences on habitat conservation and indicate that the abundance of small fish is not always higher in complex vegetation. Like mangrove creeks, the bare creeks are utilized by a wide variety of fish, suggesting greater attention should be drawn to these habitats.

The artisanal fi shery for Spondylus has a very long tradition in Ecuador but developments in recent years have made it an excellent example of the rapid overharvesting of a Latin American shellfi sh fi shery. In reaction to the declining population status, the Ecuadorian government enacted an offi cial ban on the fi shery in October 2009. The ban is intended to be kept in place at least until there is scientifi c information regarding stock status and basic population parameters that are necessary for a sustainable use of the resource. This study aims to provide the necessary knowledge base to develop a sustainable management program for Ecuadorian Spondylus stocks in the future. Our fi ndings suggest that current population densities will not allow for a recovery without additional measures to support such recuperation. Nevertheless, the parameters we have calculated for growth and fecundity suggest that exploitation of Spondylus as a resource is generally possible when undertaken with caution. Under a precautionary approach it is crucial for a future management program to monitor densities of individuals closely, as this study identifi ed recruitment failure as the main factor that has contributed to the collapse of the fi shery in the past. Restoration efforts would be of high value for the local ecosystem as this study has also shown that Spondylus contributes signifi cantly to the native biodiversity. Their shells provide a three dimensional habitat for a variety of drilling and non-drilling species that are not present without them, thus making Spondylus an important foundational species. Artisanal fi sheries make a signifi cant contribution to satisfying the increasing global demand for protein. It is dangerous to assume, that these fi sheries operate sustainably per se and it is crucial to ensure that they do in the future. Sustainable solutions for artisanal overfi shing are urgently needed, because tropical coastal communities are highly dependent on their local resources for their livelihoods and nutrition. The tools for successfully managing a common pool resource such as Spondylus through a comanagement system are known – we hope these are used in the future in conjunction with the fi ndings of this study to prevent this iconic genus from disappearing.

Carbon dioxide concentration (pCO2) in the ocean is steadily increasing causing a drop of pH, consequently turning the surface seawater more acidic. Due to possible adaptation mechanisms some marine organisms can cope better with high pCO2 and low pH than others. The ocean quahog Arctica islandica is widely distributed in the North Atlantic region. Populations of this species are also well established in the high fluctuating environment of the Kiel Bight in the Western Baltic Sea and show high tolerance to environmental parameters like salinity, temperature and low oxygen levels. In my thesis I am interested in the performance of A. islandica from Kiel Bight to build and maintain its shell in a high pCO2 environment and the general aspects of bivalve shell properties as well as the site of calcification within the bivalve as a prerequisite for a mechanistic understanding of the biomineralization process. This thesis summarizes i) A. islandica from Kiel Bight populations is resistant and most likely pre-adapted towards elevated pCO2 over a short period of time (90 days) and contributes to the fundamental understanding of ii) single organic shell-compounds identified as pigment polyenes, that are not habitat related and may contribute to shell formation and iii) the calcification process itself is not happening inside the bulk EPF but rather within a supersaturated microsite created by active ion pumping by the OME. Understanding the biomineralization process and all components involved is crucial and thus the next challenge in order to estimate the robustness of A. islandica and other marine calcifiers in a high pCO2 world.

The German Bight is dominated by sandy and muddy sediments whilst rocky terrain is rare. The only rocky intertidal is present on the island of Helgoland. However, thousands of ship wrecks are distributed in the German Bight. Such wrecks have only recently become part of investigations into species settlement and the underwater ecosystem. During the next 30 years 5000 wind power foundations are planned to be built in the German Bight as part of the German renewable energy program. Twelve foundations are completed and 197 in progress. The knowledge of the impact such constructions have on the German Bight underwater ecosystem is poor. Prognoses are the only form of estimation. The present study was conducted at the research platform FINO 1 and different ship wrecks which are located in the German Bight. Consistent with FINO1 it is expected that 4,300 kg biofouling will inhabit the wind power foundations. This means that the foundations can be interpreted as hotspots with 35 times more macrozoobenthos biomass than there was prior to the construction. The 5,000 wind power foundations mean an increased biomass of 0.8% for the entire German Bight. In addition, at least half of this biomasses will be produced at the foundations and leave the foundations on a yearly basis. What impact the increased production and high biomass concentration will have on the energy flow in the North Sea remains unknown. Other scenarios are more obvious. Changes include the increased food supply for species, such as crabs, fish and seals as well as the proliferation of the mussel Mytilus edulis. The number of Mytilus edulis inhabiting all wind power foundations will be the same as half of the amount of mussels currently living in German Wadden Sea. The mussel shell litter fall may lead to changing sediments and additional reefs. The mussels will also add to the significant increase of the filtration of sea water with the possible result of clearer waters. The mussels are seen as the main contributor to changes taking place in the German Bight following the introduction of wind power foundations. The increased number of mussels as well as the effects such increasing numbers of Mytilus edulis on the ecosystem will be titled Mytilusation. The introduction of wind power foundations into the German Bight will also mean an increase in rocky shallow waters and intertidal zones in the German Bight. The result will be a proliferation and the development of exotic species, such as the pacific oyster (Crassostrea gigas) which relies on low water depths. Whilst wind power foundations will be colonized by a similar range of species, they will be inhabited by a smaller number than ship wrecks. 2.0 Million brown crabs (Cancer pagurus) which will inhabit the wind power foundations will be added to the already existing number of 2.3 Million living at the 1,300 ship wrecks. Ship wrecks also provide an ideal environment for the endangered European lobster (Homarus gammarus). No lobsters were sighted at the already existing wind power foundations and it is yet to be seen whether the foundations will add to the spread of this species. Behaviour observations of the striped bristletooth surgeonfish (Ctenochaetus striatus) in the Indo-Pacific Coral Reefs revealed that he swept 18% of the sediment. Reef Sweeping as well as the bioerosion entail two major ecological functions of that fish. Ctenochaetus striatus therefore plays a major role in the preservation of coral reefs. Ongoing studies will show how certain species, such as the edible crab, which inhabit the new wind power foundations, influence the faunal community and surrounding areas. As with the striped bristletooth surgeonfish it is recommended to use behavioural investigations as fauna quantifications and community analyses do not provide satisfying results regarding the relationship between the various species and their environment. As part of the present study, techniques and materials were developed to activate or minimise certain functions of the wind power foundations, i.e., to increase or decrease the development of species at such foundations. Individual techniques are described in detail. Whether to activate wind power foundations or to make them passive, whether the reef effects are positive, negative or neither depends on the interpretation of the individual. The qualitative data reveals that the thousands of future wind power foundations will indeed transform the German North Sea ecosystem. The on-going scientific research is necessary to analyse the extent of such changes and to lead the pathway of renewable energy into the right direction.

Bivalve shells are often used to reconstruct past environmental conditions at the time of carbonate formation. The aim of this thesis is to optimize the process of reconstructing environmental history of marine ecosystems from bivalve shells (Arctica islandica) and to contribute to a better understanding of the correlations between shell chemistry and environmental parameters. In two chapters I examine how sample preparation and data collection may affect the outcome of subsequent trace element analyses in A. islandica shells. The other two chapters of the thesis focus on the applicability of specific trace element to calcium ratios in A. islandica shells to reconstruct the recent environmental history of the German Bight (North Sea). I analyzed Pb/Ca ratios as a tracer of anthropogenic lead pollution as well as Ba/Ca and Mn/Ca ratios as indicators of the pelagic primary production of the German Bight.

The Humboldt Current System is a highly productive ecosystem supporting one of the world's largest fisheries. The oceanographic characteristics with year-round upwelling, low seasonality, and comparably low latitudinal changes allow wide distributional ranges of species. One of these species is the hairy crab Cancer setosus (Molina 1782) with a distributional range from 2 13'S to 46 00'S, which corresponds to a temperature range from ~10 to ~20 degree Celsius. The relatively temperature stable habitat is subjected to the El Nino Southern Oscillation, which might lead to drastic temperature changes of up to 10 degree Celsius. Temperature is one of the most important determining factors of species distribution. The early ontogeny of brachyurans was detected to be the bottleneck for survival, as the early life stages are especially sensitive to temperature changes. The pelagic phase presents the dispersal stage of the life cycle and influences biology, ecology, evolution and recruitment of a species. This study analyzed the influence of temperature changes on different levels of biological organisation at different simulated habitat temperatures ranging from 12 degree Celsius (LN temperature) to 24 degree Celsius (EN temperature). Results of this thesis show that C. setosus Zoeal instars react highly sensitive to temperature changes which is reflected in the whole organism function as well as in lower levels of organism complexity.

In order to understand the present, environmental knowledge from the past is important. Observational records of environmental data are spatiotemporally incomplete and extremely scarce prior to AD 1860. Large scale environmental variability can be well represented by integrating data from a limited number of geographically scattered indicators or 'proxies' of past climate. This is partly achieved by the analysis of tree rings and of marine sediments cores. Long term environmental reconstruction with high resolution can be achieved by the calcareous skeleton of long lived invertebrates. In the last decade the ocean quahog Arctica islandica has attracted increasing interest among marine biologists owing to its extremely long life span approaching 400 y, and occurrence along the entire North Atlantic Ocean margins. But even more important is that its calcareous shell archives information on past environmental conditions in the morphological growth patterns and biogeochemical properties. The Ocean quahog A. islandica may become an important proxy in environmental change research, although until now the full capabilities of this species have not yet been fully realised.This thesis is an attempt to achieve deeper insight of the environmental proxy A. islandica, in terms of its environment, biology as well as population dynamics and evolutionary history. In order to achieve this goal, a number of approaches targeting six different sites of the North East Atlantic Ocean (i.e. Norwegian coast, Kattegat, Kiel Bay (Baltic Sea), White Sea, German Bight (North Sea) and off North East Iceland) were developed: (i) A general metabolic model which allows calibration of individual metabolic rates of A. islandica from five populations to body mass, water temperature, age and site. (ii) Growth and energy budget models of A. islandica at six different sites allowed a better understanding of the ecological role of the bivalve in its environment and to enable a linkage of the dynamics of A. islandica populations to environmental drivers (iii) Morphological and genetic comparison confirm differences between populations of A. islandica and revealed whether the morphological differences are driven by the environment or underlying genetic differences.Between different populations, environmental temperature is found to be the prime driving force that exerts distinct site specific effects on respiration rate. Respiration of A. islandica is significantly below the average of 59 bivalve species when temperature and mass are taken into account. In addition, growth rates of A. islandica are very low. A. islandica populations differ distinctly in maximum lifespan (40 y Kiel Bay, to 197 y Iceland). Lifespan is the principal determinant of the relationship between energy budget parameters, whereas temperature affects net growth efficiency only. Genetic results indicate a fairly mixed assemblage over the North East Atlantic area. Morphometric and genetic patterns appear to be unrelated and confirm morphological differences between populations of A. islandica, morphometrics appear to be driven by the environment (e.g. temperature and salinity) rather than underlying genetic differences between populations. Therefore this study enhances our understanding of the relationship between environmental conditions and the population biology such as growth, metabolism as well as population dynamics and evolutionary history of A. islandica. In addition, different models may enable the coupling of regional oceanographic temperature models as an environmental proxy of past environmental variabilities. Further, a geographically more extensive data set is necessary to apply A. islandica as a proxy and eliminate uncertainties related to its biological and evolutionary history.

Marine organisms are influenced by environmental variability and fishery and cephalopods are especially plastic in their response to exogenous factors. Underlying mechanisms of interactions are often unclear and complex. The ommastrephid jumbo squid (Dosidicus gigas) is an important component in the ecosystems of the Eastern Pacific Ocean and like other cephalopods rapidly changes abundances of its populations and their size structure. Results of the present work show that the morphological and life history traits of D. gigas respond highly variable to changing environmental conditions. Fishery impacts indirectly and rather positive through the reduction of competitors and predators. A synchronous change in the state of expression of traits occurred after the strong La Nina/El Nino-sequence 1996 to 1998. The elevated energetic requirements of the new states compared to those before the shift lead to the conclusion that the changes in traits follow an energy optimization strategy that allows jumbo squid to adjust to changing availability of prey and emphasize either in survival of the population or the increase of individual fitness.

The stock of humpback whales in the Gulf of St. Lawrence (GSL) was severely depleted by whaling in the 18th and 19th century and started to recover later in the 20th century than other stocks in the North Atlantic. A long-term study of humpback whales by the Mingan Island Cetacean Study in the GSL, using photo-identification and biopsy techniques, started in 1980 and is still ongoing. The data set from 1980 to 2005 was evaluated in this thesis to estimate population parameters, such as sex ratio, calving rates, survival rate and population trend for this stock for the first time. The estimates were compared with other populations and stocks, and used to assess the current conservation status of humpback whales in the GSL.

Segara Anakan is a large lagoon located along the southern coast of Java, Cilacap district, Indonesia, fringed by the only large estuarine-mangrove forest left in Java. This thesis evaluates the changes in the Segara Anakan lagoon (SAL) ecosystem by using a trophic modelling approach based on data derived from the identification and evaluation of habitat and resource abundance changes in the SAL over the last 25 years. Complementary datasets i.e. satellite images, field data and secondary data were used to determine these changes. The SAL ecosystem was mapped from 1978 through 2004 using satellite images and a GIS package to determine coastal habitat changes. The main changes involved the conversion of a large part of the estuary to new land (2966.8 ha) and mangrove area (3497.2 ha), and the subsequent conversion of these areas, and of older sections of the mangrove forest, to rice agriculture, semi-intensive fishponds, new settlements and other land uses (11315.6 ha). The major changes have occurred in the western area of the SAL (Ujung Alang, Ujung Gagak, Klaces and Penikel), both in extent and spatial distribution of some vegetation classes, with large area increases in rice fields, dry land agriculture, aquaculture and settlement area, and decreases in mangrove cover, mud flat and lagoon area. In the eastern area (Kembang Kuning, Sapuregel and Donan), changes are less extensive, but some of the trends verified in the western area can also be identified such as decreases in mangrove area and increases in aquaculture, settlement and industrial areas. Trophic flow models of the SAL system were developed in order to evaluate the changes in the ecosystem between the decades of 1980 and 2000. The models were structured by defining 21 functional trophically linked groups of the ecosystem including commercially important fish groups, shrimps and bivalves. The mass-balanced models for the two periods show how the different groups of the system were affected by the habitat transformations. Estimates of biomass per trophic level, mixed groups impact, ecotrophic efficiency, ascendancy and several other ecosystem attributes derived from the trophic modeling analysis show that trophic functioning as well as average catches of the SAL ecosystem differed between the two periods. Model biomass and mean annual production of commercially important fish and shrimp groups were smaller in the 2000s as were the total catches. Primary production required to sustain catches in SAL ecosystem was 250.19 t km-2 y-1 in the 1980s and 391.74 t km-2 y-1 in the 2000s. Developing a trophic flow model for the sustainable management of the SAL lagoon�s living resources requires an integrated understanding of ecosystem functions and their changes related to human activities and environmental change. These results indicate (i) high temporal and spatial changes of coastal habitat and its resources and (ii) changes in trophic functioning as well as average catches in the SAL ecosystem. The observed changes are both due to human activities (such as mangrove conversion, resources exploitation, and pollution) and environmental impact in the study area (mainly through the filling of the lagoon with riverine sediments derived from the hinterland). Management measures of the lagoon�s resources applied for many years suffer from the lack of an integrated ecosystem understanding, and hence, had little success. The results of this study are expected to contribute to a more sustainable management and conservation of the SAL ecosystem.

The Northern Humboldt Current Ecosystem (NHCE) is one of the most productive in the world. Wind-driven coastal upwelling brings cool, nutrient-rich water to the photic zone where rich plankton communities develop. This high productivity supports large populations of small plankton-grazing pelagic fish, which are an important food source for many higher predators and support a large fish meal industry. The NHCE is subject to strong interannual environmental variability from the El Nino Southern Oscillation (ENSO), which has direct and indirect effects on the biotic components of the ecosystem. This complex mixture of environmental, trophic, and human influences calls for a holistic approach for management. This thesis contributes to our understanding of the NHCE by shedding light on the changes in energy flow that occur during strong "El Nino" events (warm phase of ENSO) as well as differentiating between the relative importance of environmental, trophic, and human influences in reproducing historical changes in fisheries resources. Methods included the application of time-series and trophic modeling analyses for two NHCE subsystems of different scale: i) the nearshore benthic ecosystems of Independencia Bay and Sechura Bay (2 models, include the area of

Tidal Inlets are the links between the Wadden Sea and the open shore. So their benthic communities are influenced by both sides. Export- and import processes along tidal inlets were discussed on specific species by e.g. BOSSELMANN (1989), HERTWECK (1995), and SMTDT (1951). Additionally DÖRJES&HOWARD 1992, DÖRJES et al. 1970, DÖRJES&REINECK 1977, PARKE&HAUSMANN 1971, SCHUSTER 1951, STECHER&DÖRJES 1993a,b. They show main differences between benthic communities of tidal flats and shore faces of the open sea. Investigations of the links, the tidal inlets, are still missing. The benthos- and the according driftfauna of Tidal Inlet of the Otzumer Balje were investigated in close relationship with the hydrographical investigations (KRÖGEL 1995) to answer following questions: Are the benthic associations of Tidal Inlets a mix of Wadden Sea and Shore Face communities ? Are the Tidal Inlets a reservoir of species, which will settle on the Tidal Flats ? Can exchange processes be documented between the Wadden Sea and the Open Sea ? In which way are benthic associations of Tidal Inlets influenced by morphodynamic processes ?

Antarctic minke whales (AMW) have a circum-antarctic distribution and are known to occur in both open and ice-covered waters of the Southern Ocean (SO). They are a pagophilic species and are regularly observed in heavily sea-ice covered areas. Because of this, current knowledge about Antarctic minke whales is scarce and limited to austral summer and ice-free regions where the majority of visual survey data have been collected. Hence, very little is known on their winter distribution in high latitude waters and to what extent the wintering individuals that are occasionally observed in Antarctic waters represent single observations or a structurally present behavioral trait of the species. Likewise, AMW population structure is poorly known. As most baleen whale species, AMWs are known to undertake annual migrations between high latitude feeding areas and low latitude breeding areas. However, available data to date suggest that for AMWs, migrations seem more protracted and complex than in other baleen whale species. The recent identification of vocalizations produced by AMWs (“bio-duck call”) now makes it possible to also use passive acoustic technology to study occurrence patterns and behavior. Passive acoustic monitoring (PAM) offers a versatile technology with which long-term archival data can be collected on sound-producing species using autonomous recording units. Acoustic observation has the additional advantages that it can continue data collection independent of light conditions and under poor weather conditions. Furthermore, it can monitor large areas at the same time, since it collects data omnidirectionally, and it can collect data over extended periods (i.e., multi-year time scales) through the use of autonomous devices. In the scope of this doctoral thesis, I analysed passive acoustic data from high and low latitudes collected in the Atlantic Ocean sector of the Southern Ocean (Weddell Sea) and southern Atlantic Ocean, to investigate spatio-temporal patterns in the acoustic presence and vocal behaviour of AMWs. In Chapter I, I investigate year-round spatial- temporal patterns in AMW occurrence in ice-covered areas. Our analysis was based on a 9-year passive acoustic dataset (2008- 2016) from 21 locations throughout the Weddell Sea (WS). AMW bio-duck calls were detected acoustically at all mooring locations from May to December, with the highest presence between August and November (bio-duck calls present at more than 80% of days). At the southernmost recording locations, bio-duck calls were present up to 10 months of the year. We identified a substantial inter-annual variation in the seasonality of vocal activity correlated to variation in local ice concentration. Our analysis indicates that part of the AMW population stays in the Weddell Sea during austral winter. In Chapter II, I used PAM data from 6 positions located along the WS during 2013 as well as three consecutive years of PAM data (2015-2016-2017) recorded at the stationary coastal acoustic observatory PALAOA to study both spatial and inter-annual variability in the acoustic behavior of AMWs. During 2013, between May and December throughout the WS, we detected 11 different bio-duck call types. The comparative analyses of the AMW bio-duck call repertoire throughout the WS showed that these 11 call types can be attributed to four call type groups. Furthermore, multi-year data from PALAOA on AMW repertoire composition showed an inter-annual difference in bio-duck call type usage. The observed patterns in AMW vocal behavior show that AMW vocal behavior matches the definition of song, exhibiting regional differences and highly dynamic revolutions over time. This study provides new information to potentially explore stock structures and movement patterns using passive acoustic methods. In Chapter III, my work addressed the occurrence of the AMW through bio-duck acoustic detections in the Santos Basin, South-Southeastern Brazil (22º and 28º S / 42º and 48º W), recorded between 12 November and 19 December 19, 2015, utilizing advanced passive acoustic technologies, i.e., an autonomous underwater vehicle (SeaGlider), for sampling. AMW calls were detected during 12 days. We detected and classified 9 different bio-duck calls in Brazilian coastal waters, evidencing a highly diverse acoustic behavior on this potential Antarctic minke whale breeding ground. Finally, in Chapter IV, our study investigated the temporal patterns of acoustic occurrence of baleen whales in a presumed baleen whale breeding area off Namibia. Our results show seasonal acoustic presence of humpback whales, fin whales and Antarctic minke whales from November to January and from June to August. Their acoustic absence from February to May possibly indicates that most animals migrated to other areas (presumably in higher latitudes) in austral summer to feed. Our findings support the presumed ecological importance of the oceanic area off Namibia, providing (part of) a suitable cetacean wintering and, possibly, breeding range or migratory corridor. Furthermore, the occurrence of Antarctic blue and minke whales off Namibia, concurrent with their reported acoustic presence in high-latitude feeding areas, adds to growing evidence that baleen whale migration is not obligate but much more dynamic than previously assumed. Overall, this PhD thesis highlights the significance of using long-term and large-scale datasets for the investigation of distribution patterns, habitat preferences, behavior and the effects of environmental variation on AMW distribution. The results present new information about fundamental and ecological knowledge of AMWs that can be implemented for the conservation and management of populations and ecosystems.