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

Abstract

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 4200 m 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 (µXRF). 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.

Distribution of free-living marine nematodes in the Clarion–Clipperton Zone: implications for future deep-sea mining scenarios

“…As mining of mineral resources on land is increasingly burdened with logistic and geopolitical concerns (Petersen et al, 2016), humankind is now looking towards the deep seafloor (∼ 4000-5000 m) as a potential source to meet the global demand for metallic deposits. The abyssal plains of the Clarion-Clipperton Zone (CCZ) in the central eastern Pacific harbour the largest known accumulation of polymetallic nodules, rich in nickel, manganese, copper and cobalt (Halbach and Fellerer, 1980;Mewes et al, 2014). Their occurrence is relatively well-studied and has sparked economic interest from governments and industry.…”

Deconvolving feeding niches and strategies of abyssal holothurians from their stable isotope, amino acid, and fatty acid composition

“…Psychronaetes hanseni is a deposit feeder of the family Laetmogonidae , which has a trophic level of 2.0, low level of heterotrophic re-synthesis of amino acids (∑ V = 1.02) and feeds selectively ( CF gut content = 25.6) on sedimentary detritus particles of a medium grain size of 17.5 μm which is smaller than the medium grain size of the upper 5 cm of sediment (20.8±0.3 μm; Mevenkamp et al, 2019). Based on the biomarkers present in the body wall tissue of the specimen analysed and in its gut content, parts of the sedimentary detritus likely consists of diatom-derived phytodetritus .…”

“…from the family Psychropotidae has an estimated trophic level of 2.8±0.5 and a very high level of heterotrophic re-synthesis of amino acids (∑ V = 7.09±3.70). It feeds with a ‘sweeper’ feeding style (Roberts et al 2000) selectively on smaller sediment particles (medium grain size:13.0 μm) from the surface sediment (medium grain size: 20.8±0.3 μm; Mevenkamp et al, 2019). However, it likely does not or only moderately selects for specifically detritus-enriched particles ( CF gut content = 1.17; CF feces = 1.81±0.53).…”

“…Benthodytes typica belongs to the family Psychropotidae and its trophic level is estimated to be a bit higher (2.9) than the trophic level of Benthodytes sp. This species has a medium level of heterotrophic re-synthesis of amino acids (∑ V = 3.69) and feeds selectively on smaller particles (medium grain size: 14.2 μm) from the ambient sediment (20.8±0.3 μm; Mevenkamp et al, 2019). These smaller particles contain an at least four times higher concentration of PLFAs than the surrounding sediment ( CF feces = 4.44±1.52) and consist partially of diatom-derived phytodetritus .…”

“…as member of the family Deimatidae has an estimated trophic level of 3.5 and a very high level of heterotrophic re-synthesis of amino acids (∑ V = 7.43). This species feeds selectively ( CF gut content = 16.6) with a ‘raker’ feeding style (Roberts et al 2000) and takes up particles with a median grain size of 19.0 μm, which is slightly smaller than the median grain size of sediment particles in the Peru Basin (20.8±0.3 μm; Mevenkamp et al, 2019). The specimen collected in the Peru Basin likely fed on diatom-derived phytodetritus and maybe on bacteria.…”