High resolution seafloor photogrammetry indicates long-term persistence of a sulphophilic community on a whale fall in the NE Pacific

Deep-sea whale falls serve as biodiversity hotspots and pass through distinct successional stages, with the duration of the sulphophilic stage remaining controversial. We conducted a 15-year time-series study of a blue or fin whale skeleton on the edge of the Oxygen Minimum Zone at 1288 m depth on the Clayoquot Slope, Cascadia Continental Margin, using ROV surveys and high-resolution 3D photogrammetry to assess long-term ecosystem changes. The skeleton, consisting of skull bones and 23 caudal vertebrae, showed minimal structural degradation, based on 3D models from 2012 and 2023, with vertebrae decreasing in length by only 1.4% and mandibles showing the greatest erosion at 7.8%. Quantitative analysis revealed that bacterial mat coverage significantly increased from 39.9% to 48.6% on vertebrae and from 27.0% to 30.7% on skull bones between 2012 and 2023, indicating an expanding sulphophilic stage. The benthic megafaunal community in 2023 comprised 31 taxa, including characteristic sulphophilic species: 33 vestimentiferan tube worms (Lamellibrachia cf. barhami), live vesicomyid clams, provannid gastropods, and over 100 accumulated vesicomyid shell valves. Notably present in 2009 but absent in 2023 were bone-eating Osedax worms, suggesting transition from the enrichment opportunist to sulphophilic stage. The Clayoquot Slope whale fall also served as a nursery habitat, with 36 Neptunea cf. amianta egg mass towers observed on skull bones in 2023. Our findings demonstrate that the sulphophilic stage has persisted for at least 21 years on this whale fall, similar to the decadal time scales observed for whale falls off southern California in slightly more oxygenated waters. The slow degradation of lipid-rich skull and caudal vertebrae, combined with expanding bacterial mat coverage and persistent chemosynthetic fauna, suggests that sulphophilic communities can persist for multiple decades at oxygen levels of 0.38 - 0.49 ml l-1, providing important stepping stones for deep-sea biodiversity along continental margins. We discuss our findings in light of the continued oxygen minimum zone (OMZ) expansion in the Northeast Pacific due to climate change, with predictions of substantial loss of whale fall habitats impacting whale fall ecosystem function and biodiversity (possible exclusion of ecosystem engineer Osedax species).