Ismar, Stefanie M. H. (2017) Marine food webs and ecological traits of their communities under global anthropogenic change. (Professorial dissertation), Christian-Albrechts-Universität Kiel, Kiel Germany, IV, 615 pp.

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Abstract

Marine food webs are under multi-factorial directly or indirectly human-caused impacts, which can affect their trophic levels and fluxes individually, through multiple pathways by first order effects, or interactively. This thesis cumulatively presents investigations of different categories of anthropogenic impacts, assessing their effects on marine food web compartments in three distinct sections: (1) the primary producers, as these provide the food web basis, crucial for all higher trophic levels (Chapters 1-3), (2) lower level consumers, as these tightly couple primary productivity to productivity of higher trophic levels, by providing a crucial link of matter and energy flux (Chapters 4-9), and (3) seabirds as exemplary marine top predators, as apex predators can reflect systemic changes in a cumulative manner, and depict such changes strongly in their population trajectories, driven by K-strategic slow recovery from decline (Chapters 10-26). The sections are linked by chapters assessing grazing impacts on primary producers (Chapter 3), diet effects on lower level consumers (Chapters 4,5), and food web links between lower level consumers and top predators (Chapters 10, 12). In doing so, the work collated here applies established food web quantification tools and spatial ecology assessment technology, and implements these with novel approaches in genetic (transcriptomics, qPCR), biochemical tracer (simultaneous triplestable isotope measurements), or biologging (μGPS, miniaturized radio telemetry) methodological adaptations, when required to provide the sought-after answers to the posed research questions. In an extract, the findings highlight the interactive nature of the environmental factors warming, nutrient availability and ocean acidification on primary producer and lower level consumer species and communities, and strongly indicate species-specifity of effects on community-dominating key-players. Biotic effects of grazing and epigrowth are also assessed and put into context of climate change related other factors. At the top predator level, enigmatic and rare species are assessed, and community assemblages are quantified particularly with regards to relief from the impacts of invasive predators, concluding with a rarely available baseline comparison of a littledisturbed community, which has largely foregone anthropogenic disruption (Chapter 26). Future research is envisaged to assess marine food web properties and structural traits which are associated with sustaining ecosystem services and the survival of rare and threatened marine species.

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