Search

This thesis investigates the potential of computer modeling techniques to elucidate the life history and population-level features of Dosidicus gigas

Analysing movement is essential for understanding population dynamics and spatial distributions and has strong implications for the design of natural reserves. In coral reef systems movement patterns of fishes are particularly important as they are an essential part of the ecosystem and many fish species undertake diel migrations using different habitats. However, guidance mechanisms of these movements are not yet well understood. In this study we thus aim to elucidate potential causal mechanisms and spatiotemporal patterns of reef fish movements. To this end, we simulate the movement decision-making of the parrotfish Chlorurus sordidus by linking it with two main functional landscape features (food availability and predation risk) in a novel approach combining individual-based modelling (IBM) with potential field methods. Model results indicate that populations are more irregularly distributed among coral reef patches the more the coral reef habitat becomes fragmented and reduced. The spatial configuration of the seascape thus influences spatial exploitation of microhabitats, which may have far-reaching consequences on the ecosystem. By shaping individual space use patterns, the physical features of the environment may also impact encounter rates between individuals and thus the overall social structure of a population. Based on our findings we believe our model can provide valuable insights into the spatio-temporal variability of local herbivore fish populations. Moreover, the integration of potential field methods into IBMs seems a promising strategy to represent the complexity of dynamic decision-making of animals in applied models.

Extrinsic/abiotic and intrinsic/biotic factors can influence the connectivity and exploitation of reef fish. Coral reef fish from the genus Acanthurus have evolved different life history characteristics that can affect their connectivity and exploitation. The aim of this thesis is to explore the population genetic structure and growth parameters of Acanthurus triostegus and Acanthurus leucosternon in the Indian Ocean, to determine the influence of biotic and abiotic factors on the connectivity and exploitation of coral reef species. First, a 491bp fragment of cytochrome b and microsatellite loci was used to show that the long pelagic larval duration of acanthurids can confer widespread genetic connectivity to A. leucosternon in the Eastern Africa region. Although the global AMOVA (Analysis of Molecular Variance) involving all A. leucosternon Eastern African population is significant, the hierarchical AMOVA and STRUCTURE does not show any genetic breaks consistent with known Eastern African oceanographic and biogeographical barriers to dispersal. Second, a mitochondrial DNA fragment spanning the ATPase8 and ATPase6 gene regions is used to demonstrate that the genetic differentiation of A. triostegus is correlated with geographic distance throughout the Indo-Pacific. In addition, this study shows that populations of A. triostegus are significantly differentiated in the Indian Ocean (Western Indian Ocean and East Indian Ocean), but not in the Pacific Ocean (West, Central, and East Pacific). Third, using syntopic sampling of the spawning aggregating A. triostegus and monogamous pairing A. leucosternon this study determined the influence of mating behaviour on the connectivity of these two Acanthurus species. Contrary to expectations, DAPC (discriminant analysis of principal components), hierarchical AMOVA, and pairwise comparisons showed that the divergent mating behaviour does not lead to differences in the connectivity patterns of A. leucosternon and A. triostegus, but the two species experienced differences in their demographic history. A detailed analysis in BEAST (Bayesian Evolutionary analysis Sampling Trees) showed iv that A. leucosternon which is often restricted to coral reef habitats had a faster and more recent demographic expansion than the habitat generalist A. triostegus. Finally, the growth parameters and mortality of A. triostegus and A. leucosternon were estimated, to determine whether differences in mating behaviour can lead to differences in exploitation rate. Consistent with expectations, the length-based stock assessment showed that the A. triostegus, the species that often forms spawning aggregation has a higher exploitation rate than the monogamous pairing A. leucosternon, supporting previous studies indicating that spawning aggregation may increase the susceptibility of coral reef fish to fishing.

Small-scale fisheries are essential livelihood and protein providers for coastal communities in developing countries. On the semi-autonomous island state Zanzibar (Tanzania) and, in particular, in Chwaka Bay, located on the east coast of the island, the dependency on small-scale fisheries is very high. Perceived decreases in individual catches and the use of destructive gears and small mesh sizes has led to concerns for an unsustainable use of the baya s fisheries resources. Particularly, the increasing use of the destructive dragnets has led to resource concerns and to strong conflicts between fishermen. However, the lack of knowledge on the state and dynamic of the fishery strongly impedes the potential for the development of proper management plans. The aim of the present dissertation is, therefore, to assess the status of Chwaka Baya s ecosystem and its fishery, as well as to evaluate potential use scenarios for a sustainable fisheries management. Furthermore, using Chwaka Bay as a reference site, the dissertation aims at approaching the answer to the question of the sustainability of Zanzibara s nearshore fisheries. The approach used in this dissertation is twofold: 1) length-based stock assessments were conducted for six of the main target species; and 2) a trophic flow model of the bay was constructed using Ecopath with Ecosim/Ecospace. The data used in both approaches were collected through an extensive field survey conducted over an annual cycle in 2014. A review of the literature about the state of Zanzibara s fisheries reveals that no fisheries assessments have been conducted after 2000. Analyses of the annual reported landings between 1990 and 2014 suggest that, except for clupeioids, none of the target groups of the fishery can be classified as overfished. Most studies aimed at evaluating the status of Zanzibara s resources have been focusing on ecological surveys and fishermena s perception. None of the ecological surveys appropriately link fishing effort and/or fishing pattern with resource state nor provide tangible thresholds for management. The stock assessment of the key target species of Chwaka Bay suggests that the exploitation rate of three out of the six target species exceeds recommended levels (E0.1). Despite high juvenile retention rates and length at first capture being below optimum length at first capture, fishing mortalities are highest for adults. Due to the nursery characteristics and the topography of the bay, juveniles might occur in higher abundances and larger fish may concentrate further outside the bay area. Consequently, an increase in mesh size only seems economically viable, if the radius of the fishery was increased to capture larger specimens outside the shallow bay area. The trophic model indicates that the Chwaka Bay ecosystem is comparatively mature. The bay is strongly bottom-up driven, with biomass concentrations around the first and second trophic level and a low overall fish biomass. The strongest impact on the ecosystem is exerted by dragnets and traps. Both gears potentially destabilize the ecosystem by reducing the biomass of top-down controlling species. Together with handlines, dragnets and traps are the least selective fishing methods. In addition, traps exert the highest fishing pressure on 4 out of the 6 selected key species. While the dragnet fishery is the least profitable, it also provides the highest number of jobs for the community, as it is a labor-intensive fishing method. Simulations of different use scenarios suggest that the elimination of dragnets would lead to the highest increase in overall fish biomass and profits. Nevertheless, this scenario would leave 58 % of fishermen without job and is, therefore, not feasible under the current lack of alternative livelihoods and the high dependency on fisheries resources. The complete reallocation of dragnets is likewise not feasible, since current effort is already high, and a further increase will lead to strong biomass reductions of target species and losses in individual profits of fishermen. Without compromising individual profits (-20 %) and biomass structure of the ecosystem (-30 %), only a part of the dragnet fishermen can be reallocated, leaving 37 % of fisher without jobs. In conclusion, the fishery of Chwaka Bay is fully exploited with some groups experiencing overfishing and does not provide scope for further expansion. Emperor fish together with similar vulnerable target resources such as Serranidae might be unsustainably harvested throughout the island. The lack of recognition for the capacity of dragnet boats to absorb surplus labour and their marginalization is likely hindering the development of feasible management plans aimed at regulating their use. In order to stop the use of dragnets on Zanzibar, management should focus on an effort control of this gear, while investing in the diversification of livelihoods.

Due to its uniqueness and protected status the marine ecosystem of the Galapagos Marine Reserve (GMR) is of particular interest. As a result of its equatorial location and upwelling-influenced waters, the Galapagos archipelago hosts a diverse and productive marine ecosystem, and this is especially true of marine macroalgae. Macroalgal ecology in the archipelago has not been comprehensively studied. This work, which includes a synthesis of historical knowledge, a large-scale description of macroalgal community variation across the archipelago based on standardized surveys, large and fine-scale estimates of macroalgal ecotrophic parameters, and the foundation for studying the phylogenetics and behavior of Caulerpa in the GMR, was completed with the hope that this information will be useful for the continued management and conservation of the unique and fragile marine ecosystems of the Galapagos archipelago.

Marine ecosystems are known to be climatea dependent, and impacts from progressing global climate change are increasingly observed and anticipated to intensify in the course of the 21st century. Under continuously high anthropogenic greenhouse gas emissions, drivers such as ocean warming, ocean acidification, and deoxygenation will increasingly affect marine ecosystems and the provision of marine ecosystem services to human societies. Environmental drivers affect organismal processes directly, but also have indirect effects through biotic interactions. Human societies are dependent on the ecosystem services provided by the oceans, and have limited adaptive capacities to changes in ecosystem service provision. An integrated evaluation of marinea human systems is thus necessary to understand coming changes, and is increasingly pursued by recent ecosystema based and integrated assessment and management approaches. The uncertainty of future climate change impacts and the interactions with the increasing anthropogenic pressures on marine systems need to be addressed. Ecological models are important tools to provide this integration of data and processes, as they can put experimental and observational data into context, and enable us to move beyond simple extrapolations of future states and experiences, creating an understanding of the changes in marine ecosystems anticipated in the future. While a wide variety of modeling approaches is available to answer specific ecological questions, a quantitative integration over different hierarchical levels, and different types of data and knowledge, is rarely achieved. The presented thesis revolves around a case study from the Barents Sea, which is among the marine regions with the earliest impacts of ocean acidification and warming expected and already observed, providing an integrative view of the impacts of these drivers on marine ecosystems and the provision of ecosystem services in the focus region. The work was built upon a thorough general analysis of available modeling approaches for modeling climate change impacts on marine fish populations (Paper 1). This analysis assessed capacities of the existing modeling approaches and recent applications, and revealed processes which need to be incorporated better in the light of recent experimental and observational results. A modeling framework to address the specific questions in the Barents Sea region was developed based on participation of stakeholders gained during personal interviews and two workshops (Paper 2). This served to incorporate their concerns and knowledge into the model structure and identify potential adaptation options for the stakeholder groups. To address one specific scientific question of high importance and uncertainty, the anticipated impacts on fish stock recruitment, an early life stage model was developed which incorporates the experimentally quantified effects of ocean acidification and warming on Atlantic cod eggs and larvae (Paper 3). This model offers a new approach to integrating empirical data on environmental and food-web drivers into recruitment projections of marine fish. Finally, an integrative fooda web model based on the structure developed in the stakeholder work and on current processa based understanding was parameterized with empirical data and estimates of organismal rates, to simulate the dynamic fluctuations in the Barents Sea food web and explore potential shifts in composition and dynamics under ocean warming and ocean acidification (Paper 4). In the thesis discussion, the papers are summarized and put into context, and the implications for the user groups in the region and possible societal adaptation options to the projected changes are highlighted. Impacts on fisheries, cultural and recreational ecosystem services, associated adaptation options for stakeholder groups, and interactions with other uses of the ocean system and expected changes under climate change are delineated. To advance ecosystema based governance in the area, the limitations in adaptation options of some user groups point to the need to better consider these groups in decisions and regulations concerning fisheries and marine areas. The Barents Sea study thus exemplifies the possibilities to integrate experiments, observations and stakeholder input into integrative assessments of marine ecosystems under climate change. Based on the insights gained from processa based modelling and stakeholder participation, it is described how understanding and projections of climate change impacts on marinea human systems can be advanced, pointing out the importance of improved interdisciplinary cooperation and communication and an integrative perspective to link across scales and subsystems a tasks to which purposefully designed models can contribute substantially.

The potential of simulation models to provide insights on ecological questions that are crucial for the management of marine resources has become more relevant in light of the apparent demise of coral reefs. Multiple coral reef stressors can interact in nonlinear ways, confounding ecological interpretation through field studies alone. Theoretical computer modelling offers a platform to test ecological hypotheses about multiple stressors and their systemic impacts. The main purpose of this thesis was to use coral reef ecological theory to create a model as a basis for a scientifically sound, user-friendly decision support tool for the local management of coral reefs. Four major objectives were established: (1) develop a local coral reef model representing the impacts of simultaneous stressors on key ecological groups, (2) turn it into a user-friendly decision-support tool to explore different management options, (3) collect qualitative and quantitative information on the artisanal fishery of Spermonde (Indonesia) to help understand its social drivers, and (4) apply the model to real case scenarios to project the trajectory of selected coral reef response variables. Chapter two contains the description of SEAMANCORE (Spatially Explicit simulation model for Assisting the local MANagement of COral REefs) and its development. The model has two distinct compartments, benthos and fish, which run at different spatiotemporal scales and are affected by each other and by the three modelled stressors: fishing, bleaching and nutrients. Chapter three outlines an assessment of the coral reef fishery in Spermonde, focusing on the role of the patron-client system in the fishing behaviour of individual fishermen. This study contributes to the body of scientific literature on social drivers influencing fishing behaviour by empirically showing catch and behavioural differences between fishermen within the patron-client system and independent fishermen. Quantitative data on catches obtained in this study were used to parameterize fishing scenarios in Spermonde for a real case application of the model. Chapter four stems from the previous studies and adds ecological field collected data to parameterize SEAMANCORE. First, basic scenarios of nutrients and fishery were run under standardized conditions to appraise the stressorsa effects on the modelled response variables. Fishery scenarios included a fishery ban, subsistence fishery, commercial fishery, and commercial combined with destructive fishing practices. In the second part, ten-year simulations were run for four sites in Spermonde (Indonesia) exposed to varying degrees of human impacts and different initial conditions to project their local coral reefa s trajectories. Chapter 5 summarizes the contributions of this dissertation, highlighting the limitations of the modelling approach, and provides recommendations on research directions for modelling local coral reefs and management of their associated artisanal fisheries.

The Ethiopian fishery serves as the main source of affordable protein-rich food and essential macro-nutrients, and is the primary source of livelihood for many households, particularly for those who are residing in the vicinity of major water bodies. Despite its importance, the resources are facing multifaceted challenges including high fishing pressure, use of destructive fishing methods, influences arising from land-based activities, and limited scientific information for proper fishery management. Lake Koka, an important lake for the Ethiopian fishery, has been subjected to intensive fishing over the decades, yet little is known about the present state of fishery target resources. Therefore, this study aims to provide baseline information for proper management of the Lake Koka fishery resources that allows sustainability for both the fish stocks and the society. This dissertation is comprised of eight chapters an introductory chapter, six chapters organized in the form of scientific publications that include both populationa and ecosystem-based fisheries assessment and addresses the research questions highlighted in the 1st chapter, and a chapter which gives a synopsis of the major findings and outlooks.

This study uses an agent-based model (ABM), called KohTaoSim, to represent the complex dynamics of a dive-tourism related social ecological system (SES), using the island of Koh Tao, Thailand as a case study. The results of testing KohTaoSim under different environmental and management scenarios indicate that from an ecological perspective, large scale environmental disturbances, especially mass mortality events (e.g. bleaching), play a dominant role in coral degradation. Local stressors will however compound and exacerbate the effects of global stressors. From a social-economic perspective, visitor numbers are the most important factor affecting the incomes of dive schools results suggest that these are to a large extent self-regulating. Waste water treatment and reforestation are the management actions that will bring most benefits, both from an ecological and an economic perspective. Agent-based modelling was found to be an appropriate option for analysis of this coral-based dive tourism SES. Firstly, it enabled the spatial and temporal dynamics of the system to be captured and analyzed. Second it enabled empirical data from social research to be integrated into the model, to show the effects of social dynamics on ecological processes and vice versa. Thirdly, the freedom to define agents of different types and acting at different scales facilitated cross-disciplinary and cross-scale analysis. Finally, and most importantly, the ABM allowed local stakeholders to become fully involved in the iterative modeling procedure, and provided a platform for them to formulate their own management proposals.

This thesis aims to better understand how changes in primary production, temperature and fishing intensity within a biogeographic regional influence the trophic structure and the diversity and distribution of key species In the Galapagos Marine Reserve. Changes in the marine ecosystem influenced by El Nino and fisheries have been extensively evident in Galápagos. However, alterations resulting in the food chain such as changes in energy flows, trophic interactions and system structure influenced by these factors have been poorly described. Trophic models for the period 2004-2008 were constructed using the "Ecopath with Ecosim" software to describe differences between the three major biogeographic regions in the Galápagos Marine Reserve: the west cold upwelling system - Bolivar Channel, the south-central mixed system - Floreana and the far-north tropical system - Darwin and Wolf. Information required for the construction of these trophic models were mainly based on five years of underwater ecological surveys, oceanographic monitoring and population censuses carried out by the Charles Darwin Foundation and the Galapagos National Park. Additional information was obtained from other sources such as literature, reports and other trophic models. The description of differences in the system structures, energy flows and ecological characteristics of each biogeographic region were based on quantitative ecosystem parameters estimated by Ecopath. Additionally, the effects of artisanal fisheries and El Nino on the Galápagos ecosystems were explored with Ecosim to understand the mechanisms behind the observed changes in the ecosystem dynamics. In conclusion, the three systems compared in this study showed clear differences in their oceanographic settings as well as in their fishery impacts. The selectivity of target species by the local artisanal fishery plays an important role in structuring the benthic community. However, direct effects are spatially variable, depending in part on the proximity to fishing ports. Conservation strategies need to take into account the biogeographic functionality and structural differences of each system to improve the effectiveness of the actual spatial management plan in the Galápagos Marine Reserve. In addition, further studies are recommended to improve the models for future exploration of management strategies. The current fishing-monitoring program must be evaluated and adapted to produce better geo-referenced data, which will provide a robust input to evaluate the fishing effect in the Galápagos Marine Reserve.

The crucial importance of the reef fisheries to the livelihoods of communities associated with coastal areas in developing countries cannot be overemphasised. However, these important resources are increasingly threatened by destructive human activities and continued overexploitation. Therefore, understanding how the degradation of fisheries resources increases the vulnerability of the livelihoods of coastal households, and the coping strategies employed by them, is critical for planning sustainable livelihoods. This thesis looks at how households currently residing in coastal villages of the Mtwara district in southern Tanzania an area with a history involving dynamite-fishing activities sustain their livelihoods. In particular, it examines the existing livelihoods strategies, the ways these strategies are developed in response to changing socio-ecological conditions, and how livelihood trajectories of the households can be conceptualised and interpreted in that context. Further, through scenario planning, it examines whether current coping strategies predispose the community to adapt more easily to unprecedented threats of environmental change, more specifically the effects of climate change to their livelihoods. Drawing on perspectives of sustainable livelihoods, and the ideas of political ecology and scenario planning, the study examines the changing nature of livelihood strategies in coastal areas. By combining insights from political ecology and the thinking around sustainable livelihoods, it links a critical review of the degradation of natural resource discourse and policy with micro-level studies, and thus provides an enhanced understanding of the processes of human environment interactions. The fieldwork was carried out in two phases: phase one from February to July 2012, and phase two from November 2012 to January 2013. A mixed-method approach, involving qualitative and quantitative methodology for data collection, was adopted. The main techniques for primary data collection were household survey, key informant interviews, participant observation, focus group discussions and life history interviews. A sample of 297 household heads and 46 key informants were interviewed, and 58 people participated in focus-group discussions. Secondary data were obtained through documentary review. Data were analysed both qualitatively and quantitatively. The findings demonstrate that the majority of study respondents are driven to the trajectory of livelihood diversification for subsistence where gradual improvements in the livelihoods are interspersed with more abrupt declines. It is clear that, despite significant constraints linked to destructive fishing activities, coastal households seem to retain a very high level of agency, which allows them to pursue their own, sometimes contested, economic and political objectives. Different social networks and local village groups appear to play a key role in facilitating this process, however, they offer less evidence in understanding the opportunities that households and individuals have to cope and transform their livelihoods. By presenting scenarios for the future of livelihoods, the thesis argues that although households constantly adjust their adaptive strategies to survive, their coping strategies in their current form are weak in terms of being able to transit to climate-resilient livelihoods. This situation calls for efforts that take more determined approaches towards sustainable livelihoods with particular focus on the role and viability of a natural-resource base to manage risk and build resilience in a changing social, environmental, institutional and political conditions. The results contribute to our understanding of how households negotiate livelihoods under conditions of rapid socio-environmental change and increased vulnerability.

Coral reefs, rainforests of the sea, are of greatest ecological and economical importance. Although they cover just a small fraction of sea floor, they provide indispensable functions for the associated flora and fauna, and invaluable services for livelihoods of large human populations in tropical coastal regions. Within the last few decades coral reefs have been increasingly endangered for various reasons, which can be directly or indirectly ascribed to anthropogenic influence. Chronic stresses can undermine the resilience of coral reefs, which then become more susceptible to the effects of pulse stresses, like hurricanes or thermally induced bleaching. Such an event may then diminish relevant ecosystem properties beyond a threshold, and thus trigger a sudden shift to an alternative state, which may not be in favour of corals but an alternative live form that then achieves dominance. In my thesis I developed a spatially explicit individual-based model to simulate a benthic reef community, typical for a reef in the Western Indian Ocean region. The application was then used to explore key variables and -processes for resilience and to identify potential triggers for phase shifts. Several coral species with contrasting life histories and algae compete for space under different environmental influences. Evoked by direct neighbourhood-interactions and individual responses to environmental conditions, the system performs dynamic self-organisation, and properties of superordinate hierarchical levels (population, community) emerge as a consequence. In multiple scenarios I tested the influences of (i) two different perturbation types (bleaching and mechanical disturbances), -intensities and frequencies, as well as (ii) various levels of grazing and recruitment on the dynamics of coral reef communities. As the results show, perturbations can generate heterogeneous outcomes. While extreme temperature events render a disadvantage for more susceptible branching coral species, these species can dominate under high frequencies of mechanical disturbance events, because they recolonize empty space faster, due to their faster growth rates. Low disturbance levels always benefit the dominance of massive growth forms and a combination of both perturbations at intermediate levels leads to high evenness in the community composition. The results additionally confirm, that herbivory and recruitment are crucial processes for the resilience and persistence of coral reefs. This study also highlights the importance of a diversified analysis of coral reef dynamics to understand the full magnitude of consequences, caused by environmental change. The presented application renders an excellent tool (a) to integrate current knowledge, which can be kept up to date with little effort and (b) can be coupled with other modelling systems that operate on different spatial and temporal scales. Complexity and non-linear dynamics of coral reef functioning can thus be simulated and analysed with a high level of detail and informative value.