Zooplankton collected with a 1.4-m2 frame, 500-μm mesh Multiple Opening/Closing Net and Environmental Sensing System (MOCNESS) aboard Palmer LTER annual cruises off the coast of the Western Antarctic Peninsula, 2009-2017

Zooplankton are a morphologically and taxonomically diverse group of animals. Many zooplankton feed on phytoplankton in surface waters and thus provide a link between primary producers and higher trophic levels. Other zooplankton reside in the mesopelagic zone and feed on detritus or on other animals. Depth-discrete density of zooplankton taxa was determined at process study stations on the annual Palmer LTER cruises along the western Antarctic Peninsula. Samples were collected with a 1.4-m2 frame, 500-μm mesh Multiple Opening/Closing Net and Environmental Sensing System (MOCNESS) towed obliquely to the surface from a depth of typically 500 m. MOCNESS tows were conducted in consecutive day-night pairs at each process study station. Zooplankton depth distributions vary between day and night as these animals conduct diel vertical migrations. Depth distributions also vary among zooplankton taxa based on species feeding ecology and life history traits. Zooplankton diel vertical migration contributes to the export of carbon and nutrients from the surface ocean to the mesopelagic zone.