Characterization of Natural and Anthropogenic Seabed Features in the Southwestern Baltic Sea

The marine environment faces threats from human activities that can disturb the seabed and may threaten the proper functioning of marine ecosystems. A sustainable balance between human uses and seabed integrity requires knowledge of the seabed's physical characteristics, benthic habitat distribution, and the extent of human impacts. Seabed pressure assessments typically rely on large-scale proxy data, overlooking actual impacts and the long-term effects of human activities on the seafloor. Also, while habitat mapping provides the basis for characterizing seafloor conditions, identifying the nature of features can be challenging, particularly for circular features.

The southwestern Baltic Sea is a region with a heterogeneous seafloor, where intense human pressures converge in a shallow, confined marine setting. This work integrates findings from various seabed mapping investigations in the area to provide a comprehensive seafloor characterization. It also explores relationships between substrate properties and habitat distribution by applying a geological marine habitat classification approach. This approach enables the identification of essential parameters across scales that reflect seabed characteristics relevant to marine spatial planning and conservation.

Circular seabed structures were classified to distinguish human from natural origins based on sedimentology, morphology, and acoustic signatures. Anthropogenic traces were identified in 36% of the mapped area, with trawl marks accounting for over 91% of the footprint, primarily on muddy substrates. Seabed pressure results derived from hydroacoustic data and from other spatial data types used in large-scale assessments were compared to highlight the significance of hydroacoustic data in evaluating physical seabed pressure.

This thesis advances the understanding of natural seafloor characteristics and human impacts through harmonized habitat mapping, a refined classification scheme, and the investigation of anthropogenic features. The results highlight the importance of detailed characterization through multi-method approaches for comprehensive environmental assessment and provide a foundation for future monitoring and management strategies with implications for seafloor integrity.