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© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 28 Jun 2019

Submitted as: research article | 28 Jun 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Biogeosciences (BG).

Effects of the arrival of fresh organic matter on eroded and nutrient-depleted trawling grounds (Gulf of Castellammare, SW Mediterranean)

Sarah Paradis1, Antonio Pusceddu2, Pere Masqué1,3,4,5, Pere Puig6, Davide Moccia2, Tommaso Russo7, and Claudio Lo Iacono6,8 Sarah Paradis et al.
  • 1Institut de Ciència i Tecnologia Ambientals, Universitat Autònoma de Barcelona, Bellaterra, 08193, Spain
  • 2Dipartimento di Scienze della Vita e dell’Ambiente, Università degli Studi di Cagliari, Cagliari, 09126, Italy
  • 3Departament de Física, Universitat Autònoma de Barcelona, Bellaterra, 08193, Spain
  • 4School of Natural Sciences, Centre for Marine Ecosystems Research, Edith Cowan University, Joondalup, WA 6027, Australia
  • 5School of Physics and Oceans Institute, University of Western Australia, Crawley, WA 6009, Australia
  • 6Marine Sciences Institute, Consejo Superior de Investigaciones Científicas, Barcelona, 08003, Spain
  • 7Laboratory of Experimental Ecology and Aquaculture, Department of Biology, University of Rome Tor Vergata, Rome, 00133, Italy
  • 8National Oceanography Centre, University of Southampton Waterfront Campus, Southampton, SO14 3ZH, UK

Abstract. Bottom trawling in the deep sea is one of the main drivers of sediment resuspension, eroding the deep seafloor and altering the content and composition of sedimentary organic matter (OM). The physical and biogeochemical impacts of bottom trawling on the seafloor were studied in the continental slope of the Gulf of Castellammare, Sicily (Southwestern Mediterranean) through the analysis of two triplicate sediment cores collected in trawled and untrawled sites (~ 550 m water depth) during the summer of 2016. Geochemical and sedimentological parameters (excess 210Pb, excess 234Th, 137Cs, dry bulk density, and grain size), elemental (organic carbon and nitrogen) and biochemical composition of sedimentary OM (proteins, carbohydrates, lipids), as well as its freshness (phytopigments) and degradation rates were determined in both coring locations. The untrawled site had a sedimentation rate of 0.15 cm yr−1 and presented a 6-cm thick surface mixed layer that contained coarser sediment with low excess 210Pb concentrations, possibly resulting from the resuspension, posterior advection, and eventual deposition of siltier and older sediment from adjacent trawling grounds. In contrast, the trawled site was characterized by highly eroded and compacted century-old sediment, as shown by the lack of excess 210Pb and high dry bulk densities. The continuous erosion in the trawled site has led to the depletion of OM, which were between 20 % and 60 % lower than those in the untrawled site, as well as to statistically significant differences in the biochemical composition of OM. Nevertheless, the upper 2 cm of the trawled site consisted of recently accumulated sediments, enriched in excess 234Th, excess 210Pb, and phytopigments, which had similar OM contents to surface sediments from the untrawled core. The arrival of fresh sediment in a chronically-trawled deep-sea site that is generally deprived of OM was associated with an enhancement of remineralization rates, reflected by protein turnover rates of 0.025 d−1, which doubled the rates quantified in surface sediments of the untrawled site. We conclude that the detrimental effects of bottom trawling can be temporarily and partially abated by the arrival of fresh and nutritionally-rich OM, which stimulate the response of benthic communities. However, these ephemeral deposits are likely to be swiftly eroded due to the high trawling frequency over fishing grounds, highlighting the importance of establishing management strategies to mitigate the impacts of bottom trawling.

Sarah Paradis et al.
Interactive discussion
Status: final response (author comments only)
Status: final response (author comments only)
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Sarah Paradis et al.
Sarah Paradis et al.
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Short summary
Chronic deep bottom trawling in the Gulf of Castellammare (SW Mediterranean) erodes large volumes of sediment, exposing over a century-old sediment depleted in organic matter. Nevertheless, the arrival of fresh and nutritious sediment recovers superficial organic matter in trawling grounds and leads to high turnover rates, partially and temporarily mitigating the impacts of bottom trawling. However, this deposition is ephemeral and it will be swiftly eroded by the passage of the next trawler.
Chronic deep bottom trawling in the Gulf of Castellammare (SW Mediterranean) erodes large...