185-5 When a Cold Seep Becomes a Hot Spot: Determining Spatial Relationships Between Substrate, Water Quality, and Fauna Distributions at Southern Hydrate Ridge, Oregon Continental Margin

Session: New Advances and Voices in Geobiology (Posters)

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Southern Hydrate Ridge (SHR), an active gas hydrate system, is the local peak of an anticlinal thrust ridge within the Cascadia Accretionary Wedge, positioned approximately 90 km offshore of Newport, Oregon. This site hosts abundant gas hydrates, active fluid and gas venting, extensive authigenic carbonates, and a robust chemosynthetic community of bacteria and clams. Considerable variation in geomorphology and substrate composition (including seep-associated cobbles, carbonate slabs, clam beds, and bacterial mats) across SHR gives rise to local habitat heterogeneity, which is often assumed to support the anecdotally observed “hotspot” of megafaunal density and diversity at SHR. Like most Cascadia methane seeps, however, a formal description of SHR megabenthos and their ecological relationships with the geologic environment does not yet exist. To fill this knowledge gap and support environmental management, this work analyzes seafloor imagery spanning the pinnacle of SHR, collected by ROV ROPOS in 2011 and 2022 as part of the University of Washington-NSF-OOI VISIONS cruises. Object recognition modelling was applied to this imagery to assist annotation, generating spatial data for mapping distributions of fauna and substrate in ArcGIS and statistically investigating ecological associations. 

This study provides the first detailed account of the SHR megafaunal community and begins to constrain local relationships between seafloor geology, water quality, and megafauna. Commercially relevant taxa were abundant, including Sebastolobus spp., Sebastes spp., Eptatretus spp., Lithodes couesi, and Chionoecetes tanneri. Sea stars (Asteroid spp.), octocorals (Heteropolypus ritteri), and deep sea sole (Embassichthys bathybius) often co-occurred with high fluid flow environments, indicating a residential relationship to the seep. Octocorals likely exhibit this pattern because seep-associated carbonates provide suitable attachment structures that may be otherwise scarce. Highly mobile taxa such as rockfish (Sebastolobus and Sebastes spp.) and crabs (L. couesi and C. tanneri) did not exhibit a clear spatial pattern, suggesting a vagrant relationship to SHR. Still, these species consume seep-derived nutrition and some were frequently observed utilizing seep-associated carbonates as shelter. As documented in this study, presence of gas hydrates and their associated geology has substantial impact on SHR megafaunal diversity, distribution and abundance, with implications for fisheries. As study of seep megafauna continues at SHR and throughout Cascadia, this study also provides a crucial point of reference to identify megafaunal community variation with depth, latitude, and time. 

Geological Society of America Abstracts with Programs. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8310

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