Linking copepod functional traits to diel vertical migration at the Patagonian shelf-break

Abstract

Copepod diel vertical migration (DVM) is a significant phenomenon with implications for the biological pump andpelagic food webs; nevertheless, its drivers and ecological significance are not fully understood. This study analyzed thedaytime and nighttime vertical density of females, males, and developmental stages of copepods to investigate the roleof functional traits, such as spawning strategy, body size, trophic group, and feeding mode, in DVM at the Patagonianshelf-break (44ºS–47ºS and 60ºW–61ºW). Only females and late copepodites exhibited a normal DVM at oceanic stations,showing their weighted mean depth (WMD) near the surface during the nighttime and at greater depths during thedaytime. Fourteen dominant species (the most densely and frequently) were identified based on a relative importanceindex (RII). Females that are sac-spawners, detritivores, carnivores, omnivores, and/or cruise-feeders exhibited normalDVM, such as Clausocalanus brevipes, Oithona atlantica, Ctenocalanus vanus, Clausocalanus laticeps, Scolecithricellaminor, Aetideus armatus, Haloptilus oxycephalus, Metridia lucens, and Candacia longimana, presenting their WMD nearthe surface and at the fluorescence maxima at nighttime, and below the thermocline at daytime. Conversely, females thatare broadcasters, large-sized, herbivores, and/or current-feeders did not exhibit consistent DVM patterns, such as Calanussimillimus, Rhincalanus gigas, and Subeucalanus longiceps, presenting their WMD above the thermocline and at the fluorescencemaxima during both daytime and nighttime. Copepod depth selection appears to be influenced by a combinationof morphological, physiological, behavioral, and life history traits, that, in each case, would optimize predator avoidance,foraging, and reproduction opportunities.