Deep-sea fauna at a former red-mud disposal site (Cassidaigne Canyon, NW Mediterranean)

Abstract

After 50 years, the dumping of red mud at the head of Cassidaigne Canyon (Southern France) was stopped in 2015. The area was surveyed in 2021 with an ROV at depths of 440–630 m. Biological findings reported here (images, sampling) have been obtained during a single ROV transect in the heavily impacted zone. In spite of the industrial waste deposit, a diverse faunal assemblage has persisted at the canyon head. Bioconstruction comprising large deep-sea oyster shells, scleractinian corals and hexactinellid sponge skeletons provides elevate and complex substrates for other organisms. Among the more significant findings, three live specimens of Neopycnodonte zibrowii Gofas, C. Salas & Taviani, 2009, previously only known as dead shells in that canyon, were documented and the rarely observed stenopodid shrimp Odontozona edwardsi (Bouvier, 1908) has been sampled (first record in the Mediterranean) and DNA barcoded.