Structure of Deep-sea Food Webs at Two Submarine Canyons and Adjacent Slope Habitats: from Trophic Niches to Isoscapes

Amanda W Demopoulos, U.S.G.S., Wetland and Aquatic Research Center, Gainesveille, FL, United States, Jennifer McClain-Counts, USGS, Wetland and Aquatic Research Center, United States, Jill R Bourque, Wetland and Aquatic Research Center, Gainesville, FL, United States, Jason D Chaytor, USGS Coastal and Marine Science Center Woods Hole, Woods Hole, MA, United States, Sandra Brooke, Florida State University, Coastal and Marine Lab, Tallahassee, FL, United States, Steve W Ross, University of North Carolina, Wilmington, Center for Marine Science, Wilmington, NC, United States, Brian J Smith, USGS, Wetland and Aquatic Research Center, Gainesville, FL, United States and Furu Mienis, Royal Netherlands Institute for Sea Research (NIOZ), Department of Ocean Systems, Texel, Netherlands
Submarine canyons are dynamic environments, where complex morphology, powerful currents, and variable nutrient conditions influence food supply. However, few studies have examined the trophic pathways of deep-sea canyon communities relative to those on the adjacent slopes. In this study, we sampled fish and invertebrates, sediments and water for stable isotope analysis (SIA) and utilized standard ellipse areas (SEA) to examine food-web structure and trophic niches in Baltimore and Norfolk Canyons and their adjacent slopes along the U.S. mid-Atlantic margin. Linear mixed-effect models (LMMs) were used to predict isotope variation across each site based on seafloor terrain (e.g., slope, rugosity) and feeding group. Model-predicted isotope data combined with seafloor terrain were then used to develop deep-sea isoscapes (geospatially-explicit isotope data) for the region. Communities were composed of isotopically diverse feeding groups, encompassing ~ 5 trophic levels, with phytoplankton-derived carbon providing the basal food resource. Canyon consumers were significantly depleted in 13C relative to consumers on the adjacent slopes. The large spread in consumer δ13C values indicate that the isotopic composition of particulate organic matter changes, which may be a function of location within canyon and slope environments. Niche widths (SEA) indicated little overlap between paired groups found in canyons compared to slopes, possibly due to differences in food selection and habitat association. Important terrain variables identified through LMM analysis included slope, aspect, and depth. Isoscapes for benthic and suspension feeders were distinct, possibly due to the consumption of isotopically different organic matter (fresh = suspension feeders, old = benthic feeders). The geology and geomorphology of canyon environments shape isotopic patterns and modeled isoscapes, influencing sediment dynamics, local hydrodynamics, and, consequently, food supply and quality.