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Observations of deep-sea fishes and mobile scavengers from the abyssal DISCOL experimental mining area

Abstract. Industrial interest in deep-sea mineral extraction began decades ago, and
today it is at an all-time high, accelerated by global demand for metals.
Several seafloor ecosystem disturbance experiments began in the 1970s,
including the Disturbance and Recolonization experiment (DISCOL) conducted
in the Peru Basin in 1989. A large seafloor disturbance was created by
repeatedly ploughing the seafloor over an area of ∼10.8 km2. Though a number of studies in abyssal mining regions have
evaluated megafaunal biodiversity and ecosystem responses, few have included
quantitative and detailed data on fishes or scavengers despite their
ecological importance as top predators. We used towed camera transects
(1989–1996, 2015) and baited camera data (1989–1992) to evaluate the fish
community at the DISCOL site. The abyssal fish community included 16 taxa
and was dominated by Ipnops meadi. Fish density was lower in ploughed habitat at 6 months and 3 years following disturbance but thereafter increased over time.
Twenty-six years after disturbance there were no differences in overall total
fish densities between reference and experimental areas, but the dominant
fish, I. meadi, still exhibited much lower densities in ploughed habitat, likely
avoiding these areas and suggesting that the fish community remains affected
after decades. At the scale of industrial mining, these results could
translate to population-level effects. The scavenging community was
dominated by eelpouts (Pachycara spp.), hermit crabs (Probeebei mirabilis) and shrimp. The large
contribution of hermit crabs appears to be unique amongst abyssal scavenger
studies worldwide. The abyssal fish community at DISCOL was similar to that
in the more northerly Clarion–Clipperton Zone (CCZ), though some species have only
been observed at DISCOL thus far. Also, further species-level
identifications are required to refine this assessment. Additional studies
across the polymetallic nodule provinces of the Pacific are required to
further evaluate the environmental drivers of fish density, diversity and
species biogeographies. This information will be important for the
development of appropriate management plans aimed at minimizing human impact
from deep-sea mining.
