The Pacific Oyster (Magallana gigas) – a recent reef builder in the Wadden Sea

This thesis investigates the Pacific oyster Magallana gigas as a recent reef builder in the European Wadden Sea and integrates geoscientific and biological perspectives to quantify growth dynamics, evaluate structural stability, and assess the potential of these reefs to form long term biosedimentary geoarchives. Two intertidal oyster reefs in the central Wadden Sea were studied through seasonal spatial and population surveys conducted from 2019 to 2022, combining high resolution terrestrial laser scanning, unmanned aerial vehicle derived orthomosaics, biological population monitoring, and micropalaeontological microhabitat analyses. The terrestrial laser scanning data reveal median vertical growth rates of 17.5 to 19.8 mm yr⁻¹, exceeding current local rates of sea level rise. Vertical reef growth is elevation dependent and directly linked to temperature driven recruitment pulses and seasonal shell growth, providing a process based baseline for evaluating reef resilience under combined pressures of climate change and sea level rise. Complementary lateral reef scale analyses based on orthomosaics show that present reef morphologies partly reflect legacy patterns of former Mytilus edulis beds. While central reef areas remain structurally stable, reef margins are persistently shaped by erosion, burial, and re exposure, highlighting hydromorphodynamic processes as key controls on long term reef persistence. By synthesising vertical and lateral reef dynamics, this thesis establishes a high resolution baseline to improve our understanding of biogenic reef formation and future development trajectories in the dynamic intertidal environment of the Wadden Sea. It identifies key areas for future research, including the systematic classification of M. gigas reefs across the broader Wadden Sea, the extension of temporal frameworks to detect long term trends, and core based assessments of biosedimentary preservation and carbonate production. Together, these perspectives highlight the emerging geoscientific relevance of non native oyster reefs at a global scale.