Functional characteristics of zooplankton bioregions along the cross-shelf gradient

The use of trait-based approaches complements taxonomic community analysis by linking species distributions with organismal traits. For marine zooplankton, traits are used to identify functional similarities between species and to quantify the roles of zooplankton in the food web and biogeochemical cycles. Efforts in understanding the functional biogeography of zooplankton have generally focused on copepods and the latitudinal gradient, while investigations on the wider zooplankton community and the cross-shelf gradient are limited. The objective of this study was to test whether taxonomically distinct zooplankton communities along the cross-shelf gradient are functionally distinct based on multiple functional characteristics. Two decades of zooplankton monitoring data from the Northeast subarctic Pacific Ocean were synthesized with a zooplankton trait database that provides a more extensive set of traits compared to previous functional biogeography studies. The 163 species of crustacean and soft-bodied zooplankton were first categorized into ten functional groups. The Offshore, Deep Shelf, Nearshore, and Deep Fjord bioregions were found to significantly differ in the relative composition of functional groups, community total trait values, community weighted means of traits, and functional diversity metrics. This study additionally explored assemblages with similar functional characteristics that are found in multiple bioregions and described the regional differences in the relationship between functional diversity and ecosystem functioning for zooplankton. The functional characterization of the bioregions provides a foundation for explaining how oceanographic drivers influence the functional characteristics of zooplankton communities and for improving predictions on how environmental changes would influence the distribution of traits and community-level functioning.