Zooplankton functional and taxonomic diversity: Linking functional traits and springtime environmental gradients at the Patagonian shelf-break front

Abstract

Zooplankton is a key component in energy transfer within marine ecosystems. We combined taxonomic and functional diversity approaches to characterize the spatial patterns of zooplankton at the Patagonian shelf-break front (PSBF), using functional groups (FGs) and diversity indices to assess the relationships between functional traits and environmental gradients. Four assemblages were identified: the outer shelf (OS), the PSBF, the upper Malvinas waters (UMW), and the deeper Malvinas waters (DMW), each defined by indicator taxa. Some species shared functional traits but inhabit distinct environmental conditions, highlighting the importance of taxonomic identity in delineating assemblages. Functional diversity increased offshore, associated with the higher salinity of the Malvinas Current and the presence of carnivores and omnivores (FG C), detritivores (FG B), and herbivores (FG A) in the PSBF, UMW, and DMW. These assemblages exhibited broader functional space than the OS, which was dominated by functionally similar herbivores and omnivores from FG A. Trade-offs between growth, reproduction, and survival would define distinct ecological strategies driven by particular combinations of functional traits: herbivorous broadcasters in the upper layers maximize energy acquisition under high food availability, while detritivorous and carnivorous sac-spawners in deeper layers adopt strategies that would balance the cost of lower food density with reduced predation risk. These life-history compromises revealed a depth-related partitioning of functional roles, suggesting enhanced energy transfer and a significant contribution to vertical carbon export and sequestration.