Reverse vertical migration and hydrographic distribution of Anomalocera ornata (Copepoda: Pontellidae) in the US South Atlantic Bight

Abstract

The vertical and horizontal abundance of juvenile and adult stages of the pontellid copepod Anomalocera ornata was determined on cruises of the 'Oregon II' during February 1991 and 1994 at coastal, shelf and Gulf Stream-influenced stations in Onslow Bay, North Carolina, USA. The presence and patterns of diel vertical migration (DVM) in this species, as well as its hydrographic habitat, were inferred from these data. Juveniles exhibited twilight vertical migration with residence in the upper water column at night, whereas adults had a reverse vertical migration pattern with residence in surface water during the day. The hydrographic distribution of A. ornata is primarily limited to the colder waters of coastal and shelf regions, with very few copepods present in warmer water influenced by the Gulf Stream. Given the hydrographic structure of Onslow Bay during the winter months, undergoing any DVM pattern could aid in retaining this species inshore.