Ecological Functioning in Two Mid–Atlantic Bight Submarine Canyons: Macrofauna Community Trends and the Role of Canyon Specific Processes

Craig Robertson1, Jill R Bourque2, Andrew J Davies3, Gerard Duineveld4, Furu Mienis5, Sandra Brooke6, Steve W Ross7 and Amanda W Demopoulos2, (1)Bangor University, Bangor, United Kingdom, (2)U.S.G.S., Wetland and Aquatic Research Center, Gainesveille, FL, United States, (3)University of Rhode Island, Bangor, United Kingdom, (4)Royal Netherlands Institute for Sea Research, Den Burg, Netherlands, (5)Royal Netherlands Institute for Sea Research, Den Burg, 1790, Netherlands, (6)Florida State University, Coastal and Marine Lab, St Teresa, FL, United States, (7)University of North Carolina, Wilmington, Center for Marine Science, Wilmington, NC, United States
Abstract:
Submarine canyons are complex systems, acting as major conduits of organic matter along continental shelves and promoting gradients in food resources, turbidity flows, habitat heterogeneity, and areas of sediment resuspension and deposition.

In the western North Atlantic, a large multidisciplinary program was conducted in two major Mid-Atlantic Bight (MAB) canyons (Baltimore and Norfolk canyons). This Atlantic Deepwater Canyons project was funded by BOEM, NOAA, and USGS. Here we investigate the ‘canyon effect’ on benthic ecosystem ecology and functioning of two canyon systems by defining canyon specific processes influencing MAB shelf benthic community trends.

Sediment cores were collected in 2012 and 2013 with a NIOZ box corer along the main axes (~180-1200m) of Baltimore and Norfolk Canyon and at comparable depths on the adjacent continental slope. Whole community macrofaunal (>300 μm) abundance and biomass data provided insight into community trends across depth and biogeochemical gradients by coupling diversity metrics and biological trait analyses with sediment biogeochemistry and hydrodynamic data. The canyons exhibited clear differences in sediment profiles, hydrodynamic regimes and enrichment depocenters as well as significantly distinct infauna communities. Interestingly, both canyons showed bimodal distributions in abundances and diversity of infauna and a shallowing of species maxima which was not present on adjacent slopes. We hypothesize that physical canyon processes are important regulators in the depth of observed species maxima and community functioning on the MAB shelf, on local and regional scales.

Unique sediment dynamics, organic enrichment, and hydrographic conditions were significant factors in structuring benthic community differences in MAB canyons The study provides a complete benthic infaunal appraisal of two canyon systems in the western Atlantic, incorporating biogeochemistry and oceanography to increase our understanding of canyon ecosystem ecology and provide baseline information on canyon functioning.