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

Abstract

Copepod diel vertical migration (DVM) is a significant phenomenon in marine ecosystems that could have implications for the biological pump and pelagic food webs. DVM has been reported in many regions of the global ocean; nevertheless, their drivers and ecological meaning are not fully understood. This study focused on the daytime and nighttime vertical abundance of select species (and developmental stages) to investigate the role of functional traits such as spawning strategy, body size, trophic group, and feeding mode in DVM at the Patagonian shelf-break (44ºS–47ºS and 60ºW–61ºW). Only females and late copepodites exhibited a normal DVM, being more abundant near the surface during the nighttime and below the thermocline during the daytime. Those species that are sac-spawners, detritivores, carnivores, omnivores, herbivores-omnivores, and cruise-feeders, such as Clausocalanus brevipes, C. laticeps, Aetideus armatus, and Oithona atlantica, were more abundant near the surface during the nighttime and below the thermocline during the daytime. Conversely, those species that are broadcasters, large-sized, herbivores, and filter-feeders, such as Calanus simillimus, Rhincalanus gigas, and Subeucalanus longiceps, did not show consistent DVM patterns, and were more abundant above the thermocline and at the fluorescence maxima, during both daytime and nighttime. Copepod depth selection appears to be influenced by a combination of morphological, physiological, behavioral, and life history traits.