Patterns of microhabitat utilization by mobile megafauna on the southern New England (USA) continental shelf and slope

Video transects from occupied submersibles were used to define associations of mobile megafauna (primarily demersal fishes and crustaceans) with microhabitat features including shell, burrow, biogenic depression, biogenic depression with adjacent burrow, sand wave crest, boulder, and burrowed clay outcrop. Sites were located on low-relief bottoms across the southern New England (USA) continental shelf and slope at depths of 55, 240, and 712 m. No significant diel differences in abundance were found for the 8 taxa censused at the 55 m (inner shelf) site. Non-random distributions and associations with specific microhabitats were found for the 8 taxa from diurnal transects and 6 taxa had non-random distributions from nocturnal transects. Silver hake Merluccius bilinearis and little skate Raja erinacea were associated with particular microhabitats during the day but were randomly distributed at night. These shifts in pattern are attributed to diel differences in feeding behavior. Three of 6 taxa at a 240 m (outer shelf) site and 5 of 6 taxa at a 712 m (slope) site showed non-random distributions and associations with specific microhabitats from diurnal transects. Observations with an ROV (remotely operated vehicle) at inner shelf sites (33 to 55 m) identified a distinction between species which produce biogenic depressions and species which later occupy abandoned depressions. We posit that associations with microhabitat features enhance individual fitness possibly by reducing contact with potential predators and enhancing the ability to capture prey. Use of microhabitat features occurs in assemblages where predators of focal organisms are abundant and possibly where prey density allows ambush predator tactics.