Reuter, Hauke

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Reuter, Hauke
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Reuter, Hauke

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    Connectivity and exploitation of Acanthurus triostegus and Acanthurus leucosternon in the Indian Ocean : Application of genetics and single stock assessment to aid coral reef management
    (2018-11-02)
    Otwoma, Levy Michael
    ;
    Reuter, Hauke
    ;
    Zimmer, Martin
    ;
    Reuter, Hauke
    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.
    Dissertation
      446  248
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    How do fragmented seascapes influence fish movement behaviour? Insights from an individual-based model (IBM) using potential fields
    (2019-12-12)
    Kruse, Maren
    ;
    Wolff, Matthias
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    Reuter, Hauke
    ;
    Reuter, Hauke
    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.
    Dissertation
      405  201
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    Agent-based model on the effects of dive tourism in coral related social-ecological system
    (2016-08-24)
    Wang, Fei
    ;
    Wolff, Matthias
    ;
    Reuter, Hauke
    ;
    Reuter, Hauke
    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.
    Dissertation
      510  184