Dataset: Plankton size spectra

In situ data were compiled from five field programs (Fig. 1). Datasets from the California Current Ecosystem Long-Term Ecological Research (CCE LTER) Program are derived from eight cruises spanning multiple seasons and years in the southern sector of the California Current System.  This region includes a productivity gradient stretching from a coastal upwelling biome to an oligotrophic offshore domain (Ohman et al. 2013).  Results from the Costa Rica Dome (CRD) are derived from the CRD FLUxes and ZInc Experiments (FLUZIE) cruise in an open-ocean upwelling region of the Eastern Tropical Pacific in July 2010 (Landry et al. 2016).  The Gulf of Mexico (GoM) dataset was collected on two cruises of the Bluefin Larvae in Oligotrophic Ocean Foodwebs, Investigations of Nutrients to Zooplankton (BLOOFINZ-GoM) program in May 2017 and May 2018 that focused on the oligotrophic deepwater spawning grounds of Atlantic Bluefin Tuna (Gerard et al. 2022).  The Salp Particle expOrt and Oceanic Production (SalpPOOP) Expedition investigated the Southern Ocean region near the Subtropical Front and sampled waters of frontal, subtropical and subantarctic origin (Décima et al. 2023).  All of these programs utilized quasi-Lagrangian sampling schemes with Lagrangian experiments that lasted from ~2.25 to ~7.75 days in duration (typical duration = 4.25 days) allowing repeated sampling of plankton communities from bacteria to microzooplankton within distinct water parcels (Landry 2009).  Samples from the North Pacific Subtropical Gyre were collected by the Hawaii Ocean Time-series program, which samples the time-series station ALOHA over ~3 days near Hawai’i with ~monthly frequency (Church et al. 2013; Karl and Church 2014).  Brief descriptions of field methods are given below.  Additional details are available in original publications as cited. 

Microbes – Samples for microbial biomass were collected by Niskin bottles at 6 – 8 depths spanning the euphotic zone.  Picoplankton abundances (heterotrophic bacteria, Prochlorococcus, Synechococcus, and picoeukaryotes) were determined by flow cytometry and converted to biomass using carbon cell-1 conversion factors for their respective regions as determined by the original investigators (Selph et al. 2016; Selph et al. 2021). While conversion factors did vary slightly between regions for some groups, they were generally quite similar.  Nano- and microplankton biomasses were determined by epifluorescence microscopy with proflavin (protein) and DAPI (nucleic acid) staining (Taylor et al. 2012; Taylor et al. 2016).  50-mL samples were filtered through 0.8-µm filters to quantify ~2- to 12-µm cells (imaged at 60X or 63X magnification) and 450-mL samples were filtered through 8.0-µm filters to quantify >12-µm cells (imaged at 20X magnification).  Cells were manually outlined based on proflavin fluorescence and carbon biomass was determined from biovolume using equations in Menden-Deuer and Lessard (2000).  We note that while this approach will accurately quantify most nano- and micro-sized protists (autotrophic, heterotrophic, and mixotrophic), some fragile taxa (e.g., some ciliates) may not survive preservation and hence could be undercounted. 

Mesozooplankton – Mesozooplankton were collected with either a ring net or a bongo net with 202-µm mesh, equipped with a General Oceanics flow meter and a depth sensor.  Double oblique net tows (to a maximum depth between 100 and 210 m) were conducted twice daily (paired day and night tows) during Lagrangian experiments.  Typically three day/night pairs of tows were conducted for each occupation of Station ALOHA in the subtropical North Pacific.  After recovery, samples were split using a Folsom splitter and sequentially filtered through nested sieves (5 mm, 2 mm, 1 mm, 0.5 mm, 0.2 mm).  Sieves were rinsed onto pre-weighed, 47-mm diameter, 0.2-mm mesh filters, rinsed with isotonic ammonium formate, and dried for storage (Décima et al. 2016; Landry and Swalethorp 2021).  On land, samples were weighed to determine dry mass.  Filters from most projects were then subsampled for C/N analyses by elemental analyzer thus providing carbon values for all 5 size classes.  For cruises without direct carbon measurements available, dry weight was converted to carbon using equations in Landry et al. (2001).  On the SalpPOOP cruise, >5-mm salps were removed from the >5-mm sample and individually sized (for all other cruises, no organisms were removed from the large size fraction and it was treated identically to other size fractions).  We estimated salp biomass using allometric relationships in Iguchi et al. (2004) and included it to the >5-mm sample.