Bottom fishery impact generates tracer peaks easily confused with bioturbation traces
Abstract. In the process of reworking sediments and thus shaping biogeochemical processes, marine bottom dwelling animals are thought to play a pivotal role in many benthic environments. This aspect of bioturbation (particle reworking) is often partitioned into short distance local and non-local transport acting over relatively longer distances. Here we document that subsurface peaks, such as those typically attributed to biological particle transport in sediments, may equally be generated by otter boards in bottom trawling fishery. Boards can generate tracer peaks whereby they scoop sediment from the surface, flip it over and deposit it onto the adjacent sea floor. These peaks are indistinguishable from those (presumably) generated by benthic fauna in a process whereby. We demonstrate this for the particle tracer chlorophyll a in silty sand from the Western Baltic Sea with fauna that generally does not burrow deep in a global comparison. Our inability to distinguish the driving processes generating the peaks indicates limits to our understanding of magnitude and spatial extend of bioturbation traces in this environment. It also poses a problem to the assessment of fishery resource use and benthic ecosystem services. However, we can clearly identify macrofauna and not otter boards as the cause for peaks at the sites investigated here.
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