Relationships Between the Abundance of Benthic Organisms and Near-Bottom Food Availability in Mesophotic Coral Habitats off the Coast of the Southern USA

Hard bottom coral habitats in the mesophotic zone are ecologically and economically important systems, yet questions remain about the relative abundances of benthic organisms and trophic resources available to them. As part of the Deepwater Horizon Natural Resource Damage Assessment Mesophotic and Deep Benthic Communities Habitat Assessment and Evaluation project, downward—facing imagery along ROV transects was used to estimate percentage cover of major benthic organism groups across the Mississippi—Alabama continental shelf (MS—AL shelf, 6 dives) and at 2 sites within the Flower Garden Banks National Marine Sanctuary on the Texas—Louisiana continental shelf (TX—LA shelf). Benthic cover was analyzed relative to depth and the availability of water—borne food as living particulate organic carbon (LPOC) and dissolved organic carbon (DOC) using unpaired water column seawater samples (MS—AL shelf) and paired seawater samples taken above the benthos (TX—LA shelf). Over a limited depth range at MS—AL shelf sites, percentage cover significantly changed with bottom depth but accounted for only 5.1% of the variation. Water column DOC ranged from 69−284 μmol C/L and was variable across depth while LPOC ranged from 6−36 μg C/L and was influenced by sampling time and depth. At the TX—LA shelf sites, benthic cover significantly changed with transect depth, accounting for 25% of the variation (p < 0.01), and both LPOC and DOC overall decreased as bottom depth increased but differed by site. The trends in benthic organism abundance reported herein align with limited previous studies for this region and provide new data on food availability near the benthos.