04 Sep 2023
 | 04 Sep 2023
Status: this preprint is currently under review for the journal BG.

Bottom fishery impact generates tracer peaks easily confused with bioturbation traces

Stefan Forster, Claudia Runkel, Josephin Lemke, Laura Pülm, and Martin Powilleit

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.

Stefan Forster et al.

Status: open (until 27 Oct 2023)

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Stefan Forster et al.

Stefan Forster et al.


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Short summary
During an investigation on the effects that bottom-trawling, we found that otter boards that keep the nets open, burry surface sediment at a few centimeters sediment depth. This is also done by animals living in the sediment and the process is considered very important for sediment ecosystem integrity. We try to differentiate between the two and estimate that natural bioturbation is much more likely than otter board sediment reversal in OUR sediment areas.