Unravelling cumulative effects of human pressures on demersal fish traits using a driver-pressure-state-impact framework

Highly productive shelf seas, like the North Sea, face increasing pressure from climate change and the rapid expansion of offshore renewables alongside chronic human pressures such as fisheries. The extent to which biological communities are impacted largely depends on the species' characteristics, such as behaviour and life-history traits. Understanding the cause-effect relationships between a pressure and species' traits is thus a critical step towards comprehensive assessments and mapping of cumulative effects on key functions of biological communities. In this context, we explored cause-effect pathways among drivers (i.e., human activities and climate change), their pressures, and the trait composition of demersal fish communities in the southern North Sea. We first identified potential cause-effect pathways through a literature review and structured them using the Driver-Pressure-State-Impact (DPSI) framework. Then, we tested these pathways using multivariate statistical analysis of spatial data on drivers, pressures, and demersal fish traits. The DPSI model consisted of six drivers, ten pressures and seven traits. We identified enrichment and the introduction of pollutants as the pressures influenced by the largest number of drivers and having the broadest impacts on fish. The traits sensitive to the selected pressures included not only the typical slow life-history characteristics but also migration, and benthic reproductive strategies. Mapping sensitive trait modalities, such as large size, suggested higher abundances along the UK, German, and Danish coasts, indicating an increased risk of cumulative effects of human activities in shallow and nearshore areas. The cause-effect pathways described here provide a knowledge base for future trait-based cumulative effects assessments and allow for the prioritisation of management strategies.