MEPS 604:99-120 (2018)  -  DOI: https://doi.org/10.3354/meps12742

ABSTRACT: Accurately assessing the diversity and abundance of marine zooplankton is greatly confounded by the interactions of biological and physical processes that vary in space and time. This study simultaneously assessed biological and physical sources of zooplankton assemblage variation with multidisciplinary methods. Autonomous underwater vehicles (AUVs) and shipboard plankton net sampling were used to document a seasonal shift that occurred during a typical fall transition period in northern Monterey Bay, California. Intrusion of low salinity offshore waters into our study region was associated with decreased stratification of the water column. Morphological taxonomy and high-throughput DNA sequencing (HTS), involving mitochondrial cytochrome oxidase subunit-I (COI) and large subunit (28S) nuclear ribosomal RNA, were used to document zooplankton communities in 36 vertical plankton tows collected during the fall transition. Increased copepod diversity and delivery of species associated with warmer southern waters corresponded with the intrusion of offshore waters. Echinoderms and barnacles also increased in abundance. Conversely, species of polychaetes and gastropods decreased in diversity and abundance. Onshore-offshore spatial shifts also occurred between August and October sampling periods. Primary insights contributed by newer methods included high resolution documentation of environmental variation (i.e. AUV data) and increased taxonomic resolution for some zooplankton groups (e.g. polychaetes and gastropods; HTS data) compared to the morphological assessment. Together, the AUV environmental data, morphological assessments and HTS zooplankton identifications provided a compelling picture of how water mass variation typical of the fall season can affect zooplankton assemblages in northern Monterey Bay, California.

KEY WORDS: Marine zooplankton · Biological oceanography · Plankton ecology · Upwelling shadow · Monterey Bay · California Current