Phytoplankton community composition was assessed using chemotaxonomic pigments (including all chlorophyll types, accessory and photoprotective pigments) measured with high performance liquid chromatography (HPLC). Water samples from 7 depths spanning the euphotic zone were collected using a CTD-rosette during the five Lagrangian experimental cycles conducted during Salp Particle expOrt and Ocean Production (SalpPOOP), from October to November 2018 in the vicinity of the Chatham Rise (New Zealand). Depths varied according to experimental cycle, as it was adjusted based on PAR profiles to span the depth to 0.1% of surface irradiance. Chemotaxonomic pigments of phytoplankton in the water column were filtered onto GF/F filters (2L), then immediately flash-frozen in liquid nitrogen, and shipped frozen to Instituto Español de Oceanografía, Centro Oceanográfico de Gijón, where they were extracted for High-performance liquid chromatography (HPLC) analyses following established protocols (doi:10.4319/lom.2014.12.46). For this study, 2 profiles from each experimental cycle were analyzed, and vertically integrated to obtain areal estimates for each cycle. Pigment contributions were normalized by total chlorophyll a (Chl a) to account for potential losses and low yield, and are thus presented as integrated percentages per cycle. These proportions do not always sum to 100 because ancillary pigments/other compounds that cannot be positively identified are not included.

This study was funded by the Ministry for Business, Innovation and Employment (MBIE) of New Zealand, NIWA core programmes Coast and Oceans Food Webs (COES- COES1901) and Ocean Flows (COOF-COOF1902), the Royal Society of New Zealand Marsden Fast-track award to Moira Décima, and NSF award #OCE-1756610 to Michael R. Stukel and Karen E. Selph.