Spring copepod functional diversity associated with the oceanographic fronts of the Southwestern Atlantic Ocean

Abstract

Studies on species’ functional traits are increasingly used to explore the links between zooplankton community structure and ecosystem functioning. This study investigates copepod diversity across the main frontal types along the continental shelf and shelf break of eastern South America (32°S-55°S), using taxonomic and functional diversity approaches. We analyzed 53 copepod species grouped by five key traits, comparing adult copepod diversity, functional traits, diversity indices, and functional space between frontal systems and surrounding control regions. Contrary to expectations, no significant differences in functional or taxonomic diversity were observed between frontal systems and control regions. Instead, a distinct latitudinal pattern in functional group distribution emerged, shaped by reproductive mode, myelination, feeding traits, and body size. This pattern revealed a decline in species richness, taxonomic diversity, functional richness, and functional space toward southern regions. The findings suggest spatial filtering of specific trait combinations: larger and medium-sized broadcasters and herbivore-omnivore current feeders dominate colder southern systems, while warmer northern systems support a broader array of functional groups, including small-sized sac-spawners, omnivores-detritivores, carnivores, ambush feeders, and cruise feeders. The transition from heterogeneous northern waters—populated by species from the Malvinas Current, subtropical, and subantarctic shelf waters—to colder, less heterogeneous subantarctic waters in the south likely accounts for the greater functional diversity in northern latitudes. These results underscore the role of environmental heterogeneity, species interactions, and ecosystem functioning in shaping copepod communities along the eastern South American continental shelf.