Deciphering the lithological consequences of bottom trawling to sedimentary habitats on the shelf

- First study to classify the lithological signatures caused by bottom trawling
- High-resolution spatial bottom trawling intensity data for NW Iberia
- Core locations are presented in conjunction with bottom trawling frequencies.
- Sediment mixing is analyzed with a novel hydrocarbon fingerprinting method.
- Bottom trawling affects sediment up to roughly 35 cm depth.

Widespread bottom trawling on the NW Iberian shelf causes chronic sediment and habitat disturbance. The few studies that have investigated vessel-modified sedimentary-structure and texture of the seabed have typically classified their results as being either impacted by trawling or not. This study indicates that bottom trawling can result in a sequence of vastly different effects to the lithology of seabed sediment, which have in turn different ecological consequences. Here, we combined very high-resolution spatial bottom-trawling data with sedimentological (grain size, porosity) and geochemical datasets (excess 210Pb, 3D petroleum fingerprinting) to study sediment disturbance, including sorting and mixing. Our results were used to develop five conceptual disturbance scenarios: minimal seabed effects, sediment overturning, complete sediment mixing, sediment grading and layering, and loss of sediment. Considering that bottom trawling is a widespread and growing global fishing technique, such impacts need to be considered in the management of habitat conservation as well as in the reconstruction of late Holocene climate history from shallow-water deposits, not just on the NW Iberian shelf, but also globally.