Hydrostatic pressure and temperature affect the tolerance of the free-living marine nematode Halomonhystera disjuncta to acute copper exposure

Abstract

Potential deep-sea mineral extraction poses new challenges for ecotoxicological research since little is known about effects of abiotic conditions present in the deep sea on the toxicity of heavy metals. Due to the difficulty of collecting and maintaining deep-sea organisms alive, a first step would be to understand the effects of high hydrostatic pressure and low temperatures on heavy metal toxicity using shallow-water relatives of deep-sea species. Here, we present the results of acute copper toxicity tests on the free-living shallow-water marine nematode Halomonhystera disjuncta, which has close phylogenetic and ecological links to the bathyal species Halomonhystera hermesi. Copper toxicity was assessed using a semi-liquid gellan gum medium at two levels of hydrostatic pressure (0.1MPa and 10MPa) and temperature (10°C and 20°C) in a fully crossed design. Mortality of nematodes in each treatment was assessed at 4 time intervals (24 and 48h for all experiments and additionally 72 and 96h for experiments run at 10°C). LC values ranged between 0.561 and 1.864mg CuL and showed a decreasing trend with incubation time. Exposure to high hydrostatic pressure significantly increased sensitivity of nematodes to copper, whereas lower temperature resulted in an apparently increased copper tolerance, possibly as a result of a slower metabolism under low temperatures. These results indicate that hydrostatic pressure and temperature significantly affect metal toxicity and therefore need to be considered in toxicity assessments for deep-sea species. Any application of pollution limits derived from studies of shallow-water species to the deep-sea mining context must be done cautiously, with consideration of the effects of both stressors.

Biogeochemical Regeneration of a Nodule Mining Disturbance Site: Trace Metals, DOC and Amino Acids in Deep-Sea Sediments and Pore Waters

“…Trace metal input would, however, be considerably enhanced when metals would diffuse from the suboxic pore water after removal of the Mn-oxide rich layer due to deep-sea mining (Table 3). Nevertheless, metals do not reach concentrations potentially toxic to animals, e.g., Cu release 0.3 µmol * m −2 * month −1 compared to lowest LC 50 values of 8.85 µmol/L (Mevenkamp et al, 2017). The trace metal concentrations and fluxes in the upper cm are already reduced after 5 weeks, as the data from the EBS track shows (Figure 8).…”

“…Since some heavy metals could potentially reach toxic concentrations with detrimental effects for the fauna, sediment disturbance and potential metal release is a serious issue to be considered with respect to deep-sea nodule mining. Ecotoxicological experiments showed that LC 50 values for animals subjected to colder temperatures and higher pressures, to simulate deep-sea environmental conditions, for dissolved Cu ranged between 8.85 and 29.4 µmol/L for nematodes (Mevenkamp et al, 2017) and 380-420 µmol/L for shrimp (Brown et al, 2017a). LC 50 values for Cd ranged between 521 and 548 µmol/L for shrimp (Brown et al, 2017a).…”

“…LC 50 values for Cd ranged between 521 and 548 µmol/L for shrimp (Brown et al, 2017a). Experiments are usually carried out with spiked Cu and Cd concentrations in the µmol/L range (Auguste et al, 2016;Martins et al, 2017;Mevenkamp et al, 2017). Trace metals are an important part of the biogeochemical cycle of the surface sediment and should be well understood before mining commences.…”

Identifying Toxic Impacts of Metals Potentially Released during Deep-Sea Mining—A Synthesis of the Challenges to Quantifying Risk

“…Similar results were found in an acute copper toxicity study with the experimental model organism Halomonhystera disjuncta GD1 (Mevenkamp et al, 2017); a nematode that is phylogenetically closely related to the deep-sea species H. hermesi (Van Campenhout et al, 2014;Tchesunov et al, 2015) that inhabits cold-seep ecosystems. In H. disjuncta GD1, cold temperatures (10 • C) reduced copper toxicity, whilst toxicity was increased when nematodes were exposed to high hydrostatic pressure (10 MPa) (Mevenkamp et al, 2017).…”

“…In H. disjuncta GD1, cold temperatures (10 • C) reduced copper toxicity, whilst toxicity was increased when nematodes were exposed to high hydrostatic pressure (10 MPa) (Mevenkamp et al, 2017).…”