DOI: 10.6076/d17c7j
title: Pico-phytoplankton abundance, growth and grazing rates along 110°E in the eastern Indian Ocean

description: Dilution experiments were conducted on R/V Investigator cruise IN2019v03
 (17 May to 5 June 2019) on a south-to-north transect along longitude
 110°E, west of Australia. Population abundances were measured by flow
 cytometry. Instantaneous rates of growth and grazing mortality were
 calculated from 2-treatment dilution incubations at six light levels.
description: Stations were occupied on successive days, with sampling done on a consistent daily schedule, followed by late-night transit between stations. Experimental water was collected on the evening (~21:00 local) hydrocasts at depths corresponding to 75.6, 31.7, 18.0, 7.6, 2.6 and 1.3% of incident solar radiation (PAR, %Io). For each depth, we prepared a two-treatment dilution experiment, with one polycarbonate bottle (2.7 L) containing unfiltered seawater (100%) and the second (diluted) bottle consisting of ~33% whole seawater with filtered water from the same depth. Each bottle was subsampled for flow cytometry (FCM) analysis (2 mL) for initial population abundances, and the bottles were placed in light-calibrated shipboard incubators corresponding to the light depths of collection and incubated for 24 h, cooled by the ship’s running seawater line. The incubators were covered from deck lighting during nighttime operations and received full solar lighting during the daytime. Picoplankton FCM samples were preserved with 1% paraformaldehyde and frozen at –80°C. Thawed samples were stained with Hoechst 34580 (1 µg mL<sup>-1</sup>) and analyzed at a flow rate of 30 µL min<sup>-1</sup> with a Beckman-Coulter CytoFLEX-S instrument with 4 lasers. Listmode files were analyzed with FlowJo software for abundances of Prochlorococcus (PRO), Synechococcus (SYN), and photosynthetic (pico-)eukaryotes (EUK). Net rates of population growth from initial and final FCM samples in diluted (k<sub>d</sub>) and undiluted (k) treatments were used to compute rate estimates of microzooplankton grazing mortality (m, d<sup>-1</sup>) and instantaneous growth rate (µ, d<sup>-1</sup>) as:  m = (k<sub>d</sub> - k)/(1 - D) and µ = k + m.
description: Parameter Definitions and Units of Measurement         Date = Sampling date (~21:00 local) month/day/year; incubation was during the following day   Lat = Latitude (°S)               Long = Longitude (°E)               %Io = Light depth, % of incident PAR             Depth = Water depth (m) of sample collection           Temp = Temperature (°C) at depth of collection           Abun_Pro = Abundance (cells/mL) of Prochlorococcus          Grow_Pro = Instantaneous rate of growth (d-1) of Prochlorococcus cells in dilution incubation   Graz_Pro = Instantaneous rate of grazing mortality (d-1) of Prochlorococcus cells in dilution incubation Abun_Syn = Abundance (cells/mL) of Synechococcus         Grow_Syn = Instantaneous rate of growth (d-1) of Synechococcus cells in dilution incubation   Graz_Syn = Instantaneous rate of grazing mortality (d-1) of Synechococcus cells in dilution incubation Abun_Euk = Abundance (cells/mL) of photosynthetic (pico-)eukaryotes       Grow_Euk = Instantaneous rate of growth (d-1) of photosynthetic (pico-)eukaryotes in dilution incubation Graz_Euk = Instantaneous rate of grazing mortality (d-1) of photosynthetic (pico-)eukaryotes in dilution incubation Abun_HBact = Abundance (cells/mL) of heterotrophic bacteria         Grow_HBact = Instantaneous rate of growth (d-1) of heterotrophic bacteria cells in dilution incubation Graz_HBact = Instantaneous rate of grazing mortality (d-1) of heterotrophic bacteria cells in dilution incubation -9999 = no data