Sometimes in science, unforeseen events can lead to unexpected discoveries. Such was the case on board the RV Pelagia on a North Sea research expedition focused on measuring the impact of fisheries disturbance on the seafloor. When an impending storm threatened to derail the campaign, little did we know that it would open the door to observing and comparing anthropogenic and natural disturbances in the same area and timeframe.

Anxiety gripped the room as we scrutinized the oncoming weather forecast. What had begun as a tranquil and sunny research cruise was quickly evolving into an unexpected summer storm. To compound our worries, the main objective of this research campaign was to carry out extensive field manipulations to measure the biogeochemical effects of bottom trawling. Alarmingly, the storm was predicted to take place shortly after the scheduled trawling operations, casting a shadow of uncertainty over our experimental plans. Almost a year of planning and a large portion of PhD research, hung precariously in the balance.

Despite the storm looming, we pushed forward with our field experiments. Collaborating closely with the skipper of a commercial fishing vessel, we commenced operations early in the morning before the storm intensified. This fleeting window of opportunity proved invaluable and allowed us to perform multiple tasks before stormy weather would render them impossible. This included deploying moorings during the bottom trawl activity, collecting sediment samples pre- and post-fishing, and deploying our prized in-situ benthic landers within the trawled area. This turned into a race against time as all the work needed to be finished before stormy conditions would make it too dangerous to work on deck. The heavy equipment we deployed would suddenly turn into wrecking balls and swing uncontrollably as the waves increased in size. We cheered as the last of our equipment, the second benthic lander, was deployed safely amidst escalating sea conditions.

Our strategy was to leave our in-situ equipment – a pair of benthic landers and a mooring – at  sea, to retrieve them after the storm had diminished. We hoped to recover information from the fishing activities and possibly capture some data from the storm itself. Little did we know what kinds of insights awaited us in the aftermath of the storm.

By the time the waves relented, our focus shifted to retrieving our valuable equipment from the sea. Locating the mooring was more challenging under the still choppy waves but it was eventually collected intact. As for the landers, we soon discovered that the most expensive devices used during the expedition were partially buried in the thick mud due to the storm.

With great effort, the crane on board the vessel, was able to lift the first lander from the seafloor. When it was hoisted on deck, we saw that one of its ‘feet’ had snapped off in the mud. Attempts to pull out the second lander proved futile as it was too deeply entrenched. Each lander is equipped with floats and could normally be released remotely to float to the surface by dropping the heavy weight that lets the lander sink. In a last-ditch effort, the RV Pelagia crew devised a bold plan to use the research vessel itself to try and pull the lander out of the seafloor by hooking onto it with a thick metal wire, tilt it sideways to dislodge it from the from the muddy entrapment, and hope it floats to the surface. Anxious anticipation turned into sheer elation as the last lander breached the surface.

Despite sustaining some structural damage during the storm and subsequent retrieval, most of the measurement equipment remained intact. Upon inspection of the data, we were surprised to discover that not only had we successfully gathered information from the bottom trawl field experiments^1,2, but we had also effectively captured the effects of the storm. What was once a source of concern turned out to be quite valuable for our research.

By comparing data on turbidity and oxygen in the water column, we found that sediment resuspension from bottom trawling coincided with declines in water column oxygen. However, turbidity from the storm quickly surpassed levels recorded during the bottom trawl experiments and eventually reaching an order of magnitude higher. Intriguingly, oxygen did not decrease with turbidity caused from the storm but instead rapidly increased throughout the storms duration. Particles were transported up to 60 km towards the northeast and into deeper waters supporting previous hypotheses about the role of storms in the annual transport and distribution of North Sea sediments³.

The storm caused an influx of mixed and less saline water masses from the south displaying reduced silicate levels and higher phosphate concentrations, suggesting the arrival of more coastal waters likely influenced by land based pollutants. The increasing fluorescence in the water may indicate increased decomposition of organic matter as seen in other studies measuring post-storm impacts^4,5.

Perhaps one of the most notable findings from our study was the seemingly large effect of the storm compared to the bottom trawl disturbance on sediment resuspension. However, it is important to interpret these results within a broader context. Our studies in the area have also revealed that the effect of bottom trawling on fresh organic matter in the sediments as well as the total sediment metabolism was more pronounced compared to the storm impact^1,2,6. This leads us to believe that storms can easily have a larger spatial impact compared to a single trawler but that the localized impact from trawling on the seabed can be more substantial.

Ironically, these findings would not have been possible had we been able to continue with our original plan to retrieve our in-situ equipment shortly after the trawling experiments. The inclement weather necessitated that we leave the instruments in the water until calm conditions resumed. What began as a mission to study the effects of fishing on the seafloor, evolved into an unexpected chance to witness and compare the effects of natural and anthropogenic forces at play. As we reflect on these events, we are reminded that it is often amidst tempests of uncertainty that discoveries are made.  

1. Tiano, J. C., Witbaard, R., Bergman, M. J. N., van Rijswijk, P., Tramper, A., van Oevelen, D., & Soetaert, K.  Acute impacts of bottom trawl gears on benthic metabolism and nutrient cycling. ICES J. Mar. Sci. https://doi.org/10.1093/icesjms/fsz027 (2019).
2. Tiano, J. C., van der Reijden, K. J., O'Flynn, S., Beauchard, O., van der Ree, S., van der Wees, J., Ysebaert, T., & Soetaert, K. Experimental bottom trawling finds resilience in large-bodied infauna but vulnerability for epifauna and juveniles in the Frisian Front. Marine Environmental Research. https://doi.org/10.1016/j.marenvres.2020.104964 (2020).
3. Baars, M. A. et al. The ecology of the frisian front observations on a biologically enriched zone in the North Sea between the Southern Bight and the oyster ground. ICES J. Mar. Sci. 1991 L: 25, (1991).
4. Lao, Q. et al. Characteristics and mechanisms of typhoon-induced decomposition of organic matter and its implication for climate change. J. Geophys. Res. Biogeosci. 128, e2023JG007518 (2023).
5. Zhou, X. et al. Effects of typhoon mujigae on the biogeochemistry and ecology of a semi-enclosed bay in the Northern South China Sea. J. Geophys. Res. Biogeosci. 126, e2020JG006031 (2021).
6. ICES. Report of the Working Group on Electric Trawling (WGELECTRA).
   ICES Scientific Report. WGELECTRA 2018 17 - 19 April 2018. IJmuiden, the Netherlands. (2018).