Even short deep sea mining tests can cause lasting damage to marine ecosystems. 

A two-hour deep sea mining test conducted off the coast of Japan in 2020 may have caused damage to the local ecosystem that persisted for over a year, according to international research findings.

Recent research involved extracting cobalt crusts from the Takuyo-Daigo seamount, a deep-sea mountain, to mine cobalt for electric vehicle batteries. 

Researchers analysed data from one month before, one month after, and one year after the mining activity. The results revealed a concerning decline in fish and shrimp populations, with a 43 per cent drop in density within the areas affected by sediment pollution from the mining operation.

Interestingly, the negative impact was not limited to the directly mined zones. 

Surrounding areas also experienced a 56 per cent decrease in fish and shrimp density, indicating that the mining's influence extended beyond the immediate vicinity. 

The study suggests that the mining test may have contaminated fish food sources, contributing to the reduction in marine life.

Although the study did not detect major changes in less mobile organisms like corals and sponges, researchers cautioned that long-term mining operations could still harm these species. 

The team says multiple years of data should be collected prior to mining tests to account for natural variations in ocean animal communities.

Lead author Travis Washburn, a benthic ecologist affiliated with the Geological Survey of Japan, expressed surprise at the magnitude of the impact resulting from the short test duration. 

Seamounts, known as biodiversity hotspots in deeper waters, are increasingly targeted for mining valuable minerals. 

The study's unique focus on mobile animals highlights the link between sediment plumes generated by mining operations and their impact on marine organisms. 

The results underscore the vulnerability of seamount communities to mining and emphasise the need for a cautious approach until a thorough understanding of the ecosystem impacts is achieved.

The full study is accessible here.