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Abstract

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.