Responses of an abyssal meiobenthic community to short-term burial with crushed nodule particles in the south-east Pacific

Increasing industrial metal demands due to rapid technological developments may drive the prospection and exploitation of deep-sea mineral resources such as polymetallic nodules. To date, the potential environmental consequences of mining operations in the remote deep sea are poorly known. Experimental studies are scarce, especially with regard to the effect of sediment and nodule debris depositions as a consequence of seabed mining. To elucidate the potential effects of the deposition of crushed polymetallic nodule particles on abyssal meiobenthos communities, a short (11 d) in situ experiment at the seafloor of the Peru Basin in the south-east Pacific Ocean was conducted in 2015. We covered abyssal, soft sediment with approx. 2 cm of crushed nodule particles and sampled the sediment after 11 d of incubation at 4200m water depth. Short-term ecological effects on the meiobenthos community were studied including changes in their composition and vertical distribution in the sediment as well as nematode genus composition. Additionally, copper burden in a few similar-sized but randomly selected nematodes was measured by means of micro X-ray fluorescence (mu XRF). At the end of the experiment, 46 +/- 1% of the total meiobenthos occurred in the added crushed nodule layer, while abundances decreased in the underlying 2 cm compared to the same depth interval in undisturbed sediments. Densities and community composition in the deeper 2-5 cm layers remained similar in covered and uncovered sediments. The migratory response into the added nodule material was particularly seen in polychaetes (73 +/- 14 %, relative abundance across all depth layers) copepods (71 +/- 6 %), nauplii (61 +/- 9 %) and nematodes (43 +/- 1 %). While the dominant nematode genera in the added nodule material did not differ from those in underlying layers or the undisturbed sediments, feeding type proportions in this layer were altered, with a 9% decrease of non-selective deposit feeders and an 8% increase in epistrate feeders. Nematode tissue copper burden did not show elevated copper toxicity resulting from burial with crushed nodule particles. Our results indicate that burial with a 2 cm layer of crushed nodule particles induces changes in the vertical structure of meiobenthos inside the sediment and an alteration of nematode feeding type proportions within a short time frame of 11 d, while nematode tissue copper burden remains unchanged. These findings considerably contribute to the understanding of the short-term responses of meiobenthos to physical disturbances in the deep sea.