Publications

Deep-sea vertical walls are characterized by enhanced hydrodynamics and hard substrates, making them particularly suitable habitats for suspension feeders, including vulnerable marine ecosystems (VMEs) indicator taxa, like cold-water corals (CWC) and sponges. These species enhance the complexity of the abiotic background and the retention of trophic resources increasing habitat availability for other organisms. While some areas of vertical walls present a high density of VMEs, others are mostly bare rock. However, the habitat characteristics that favor the presence of CWC and sponges within vertical walls at a fine-scale (under 1 m) are still poorly understood despite their ecological importance. Owing to technological limitations, fine-scale terrain variables (e.g., orientation, curvature, verticality, roughness, slope) have seldom been quantified in deep-sea habitats. These terrain variables can represent proxies of community structuring factors (e.g., hydrodynamics conveying food, sedimentation rates) important to understand habitat selection of VME indicator species. In this study, we investigate the fine-scale habitat selection and niche differentiation of CWC and sponges on vertical walls of the Charlie-Gibbs Fracture Zone. Structure-from-motion photogrammetry was employed to create high-resolution 3D models of three vertical walls based on remotely operated vehicle (ROV) videos (at 1060-1901 m depth). The 3D models were used to derive terrain variables at fine-scale and geotag corals and sponges. Using ecological niche factor analysis, we reveal that corals and sponges selected habitat features that significantly differ from the average habitat available. The corals and sponges studied showed large or complete niche partitioning. Solenosmilia sp. had total niche separation with Geodia spp. and globular sponges and partial separation with Hertwigia spp., while Scleralcyonacea showed partial niche separation with Geodia spp. and globular sponges. Conversely, the niches of closely related sponges were more similar. This research advances our understanding of the processes enabling species co-existence among these organisms and the factors influencing habitat preferences of VME indicator species on steep underwater landscapes.

The resistance of hard corals to warming can be negatively affected by nitrate eutrophication, but related knowledge for soft corals is scarce. We thus investigated the ecophysiological response of the pulsating soft coral Xenia umbellata to different levels of nitrate eutrophication (control = 0.6, medium = 6, high = 37 μM nitrate) in a laboratory experiment, with additional warming (27.7 to 32.8 °C) from days 17 to 37. High nitrate eutrophication enhanced cellular chlorophyll a content of Symbiodiniaceae by 168%, while it reduced gross photosynthesis by 56%. After additional warming, polyp pulsation rate was reduced by 100% in both nitrate eutrophication treatments, and additional polyp loss of 7% d−1 and total fragment mortality of 26% was observed in the high nitrate eutrophication treatment. Warming alone did not affect any of the investigated response parameters. These results suggest that X. umbellata exhibits resistance to warming, which may facilitate ecological dominance over some hard corals as ocean temperatures warm, though a clear negative physiological response occurs when combined with nitrate eutrophication. This study thus confirms the importance of investigating combinations of global and local factors to understand and manage changing coral reefs.

Skates are a diverse group within the chondrichthyans and comprise a large component of the bycatch in many demersal fisheries. The distribution of the Deepsea Skate, Bathyraja abyssicola, is presently known to be limited to the northern temperate Pacific Ocean. We filmed B. abyssicola from a remote operated vehicle during surveys undertaken on a seamount located north of Darwin Island within the Galapagos Marine Reserve in 2015. This sighting represents the first record of B. abyssicola in the Galapagos Marine Reserve and the first record of the species from anywhere in the tropical eastern Pacific Ocean. The large range extension of this species to tropical low-latitude waters of the Pacific Ocean is a critical contribution to conservation biology of this poorly known species, especially since deepwater skates and rays are generally over-exploited. This new record also highlights our limited knowledge of unique deepwater ecosystems in general and those of the Galapagos Islands in particular.