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Anthropogenic Disturbances in the Deep Sea

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Front. Mar. Sci. | doi: 10.3389/fmars.2018.00059

Has phytodetritus processing by an abyssal soft-sediment community recovered 26 years after an experimental disturbance?

  • 1Department of Estuarine and Delta Systems, Royal Netherlands Institute for Sea Reseach (NIOZ), Netherlands
  • 2Marine Biology Research Group, Ghent University, Belgium
  • 3The Lyell Centre for Earth and Marine Science and Technology, Heriot-Watt University, United Kingdom

The potential harvest of polymetallic nodules will heavily impact the abyssal, soft sediment ecosystem by removing sediment, hard substrate and associated fauna inside mined areas. It is therefore important to know whether the ecosystem can recover from this disturbance and if so at which rate. The first objective of this study was to measure recovery of phytodetritus processing by the benthic food web from a sediment disturbance experiment in 1989. The second objective was to determine the role of holothurians in the uptake of fresh phytodetritus by the benthic food web. To meet both objectives, large benthic incubation chambers (CUBEs; 50 × 50 × 50 cm) were deployed inside plough tracks (with and without holothurian presence) and at a reference site (holothurian presence, only) at 4100 m water depth. Shortly after deployment, 13C- and 15N-labelled phytodetritus was injected in the incubation chambers and during the subsequent three-day incubation period, water samples were taken five times to measure the production of 13C-dissolved inorganic carbon over time. At the end of the incubation, holothurians and sediment samples were taken to determine biomass, densities and incorporation of 13C and 15N into bacteria, nematodes, macrofauna and holothurians. For the first objective, the results showed that biomass of bacteria, nematodes and macrofauna did not differ between reference sites and plough track sites when holothurians were present. Additionally, meiofauna and macrofauna taxonomic composition was not significantly different between the sites. In contrast, total 13C uptake by bacteria, nematodes and holothurians was significantly lower at plough track sites compared to reference sites, though the number of replicates was low. This result suggests that important ecosystem functions such as organic matter processing has not fully recovered from the disturbance that occurred in 1989. For the second objective, the analysis indicated that holothurians incorporated 2.16×10-3 mmol labile phytodetritus C m-2 d-1 into their biomass, which is one order of magnitude less as compared to bacteria, but 1.3 times higher than macrofauna and one order of magnitude higher than nematodes. Additionally, holothurians incorporated more phytodetritus carbon per unit biomass than macrofauna and meiofauna, suggesting a size-dependence in phytodetritus carbon uptake.

Keywords: Stable isotopes, DISCOL, C/N-ratio, stoichiometry, Carbon limitation, Holothuroidea, Pacific Ocean, deep-sea mining

Received: 18 Sep 2017; Accepted: 09 Feb 2018.

Edited by:

Ricardo Serrão Santos, University of the Azores, Portugal

Reviewed by:

Nikolaos Lampadariou, Hellenic Centre for Marine Research, Greece
George A. Wolff, University of Liverpool, United Kingdom  

Copyright: © 2018 Stratmann, Mevenkamp, Kvassnes Sweetman, Vanreusel and Oevelen. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Ms. Tanja Stratmann, Royal Netherlands Institute for Sea Reseach (NIOZ), Department of Estuarine and Delta Systems, Den Burg, Netherlands, tanja.stratmann@nioz.nl