Ecological Impacts of Deep-Sea Mining Waste on Marine Algae and Copepod Tigriopus californicus

With growing global interest in critical metals, large-scale
operations
are increasingly proposed by some for mining across deep-sea ecosystems,
raising concerns about environmental impacts on and beyond the seafloor.
Discharges of mining-derived sediments and effluent into the pelagic
zone can spread contamination beyond benthic environments, particularly
via diel vertically migrating species, affecting epipelagic and mesopelagic
communities. This study investigates the effects of sediments from
the Clarion–Clipperton zone (CCZ) on representative phytoplankton
and zooplankton under laboratory conditions, focusing on nutrient
availability, metal toxicity, and reproductive impacts. Sediment particles
stimulated the growth of nitrogen- or metal-limited diatoms (Thalassiosira weissflogii, Phaeodactylum
tricornutum, Skeletonema costatum), coccolithophores (Emiliania huxleyi), and cyanobacteria (Synechococcus sp.) by releasing
nutrients (N, Co, Cu, Fe, Mn, Ni, and Zn). However, a reduced growth
of the diatom T. weissflogii in metal-replete
seawater and a limited response of cyanobacteria Synechococcus were observed, likely due to metal toxicity. The marine copepod Tigriopus californicus exhibited dose-dependent reductions
in growth and reproduction to the CCZ sediment (2–50 mg L–1) and significant reductions in mating success, pregnancy
rates, and offspring viability were also observed following exposure
to the sediment from the North Pacific abyss. While the test species
primarily inhabit surface waters, they were selected as established
models to elucidate mechanistic responses to deep-sea sediment exposure.
These findings provide one of the first assessments of ecological
vulnerabilities to deep-sea mining waste discharges that are broadly
relevant across pelagic ecosystems and could inform regulatory decisions
by the International Seabed Authority or any individual nations seeking
to mine the deep-sea beyond national jurisdiction.