Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
• Data Files
• Related Publications
• Related Datasets
• Parameters
• Instruments
• Deployments
• Project Information
• Funding

Note: A less condensed dataset containing all particle size, volume, and converted biomass values from each FlowCam run is also available in the related dataset "FlowCam Particle Sizes" (https://www.bco-dmo.org/dataset/881563).

Samples were collected during October and November 2018 on R/V Tangaroa cruise TAN1810 ("SalpPOOP" cruise) in the Chatham Rise (subtropical and subantarctic waters off the coast of New Zealand). Samples were collected from Niskin bottles of CTD deployments to the base of the mixed layer and the deep chlorophyll maximum. 250 mL subsamples were concentrated by gravity filtration to 10 mL over a 2 µm 47 mm filter, and 2 mL of this concentrate was imaged using a FlowCam's 10X objective lens to quantify the larger (>3 µm) phytoplankton (Sieracki et al. 1998).

FlowCam image analyses were conducted using FlowCam's dedicated classification software VisualSpreadsheet (v. 4.18.5). First, duplicate images resulting from parabolic flow within the flow cell were manually removed. The particles within the remaining images were then classified based on the quality with which VisualSpreadsheet detected their outlines. For particles where the outline appeared to provide good estimates of length and width (classes "Other", "Pennates", "Chaeto", and "Ciliate"), size was calculated for a prolate spheroid using the minimum feret as width and maximum feret as length.

Four categories of particles imaged by the FlowCam proved problematic due to poorer outline quality and had to be treated specially. For such pennate diatoms (class "BadPen"), we manually measured the caliper width of every such pennate diatom in the first CTD cast of each of the four cycles to derive the average pennate width for that cast, and applied this average retroactively to all poorly detected pennates within that cycle. Equivalent spherical diameter (ESD) and biovolume (BV) for the resulting prolate spheroid were then calculated as normal. For semi-transparent dinoflagellates (class "ClearDino"), we recalculated the width using the recorded length and mean aspect ratio for well-detected dinoflagellates in the first CTD cast of each cycle and then calculated ESD and BV normally. For Chaetoceros (class "BadChaeto") we recalculated the length and width of these particles using the recorded aspect ratio and area. Each Asterionelopsis colony (class "Aster") was saved as an individual image file, and representative single cells within a colony that were parallel to the camera’s field of view were manually analyzed using ImageJ (v. 1.52a). This procedure was repeated for all colonies in the first cast of each cycle and the mean width and length taken to produce an "average" Asterionelopsis cell. We then manually counted the number of individual cells present in each image and applied them to the averaged cell sizes to estimate the total biovolume.

The biomass of ciliates (class "Ciliate") was estimated as 0.19 pg C µm⁻³ Putt and Stoecker 1989). The biomass of diatoms (classes "Chaeto", "BadChaeto","Pennate", "BadPen", and "Aster") was estimated allometrically as 0.288*Biovolume^0.811 while other protists and unidentified particles (classes "Other" and "ClearDino") were estimated using 0.216*Biovolume^0.939 (Menden-Deuer and Lessard 2000).

Data Processing:
This dataset was achieved by splitting the particles in the companion dataset "FlowCam Particle Sizes" for a given FlowCam run into discrete size bins (see Related Dataset https://www.bco-dmo.org/dataset/881563). To calculate "X-Y Abundance", the sum of the particles larger than X and smaller than Y within a run was divided by the "Fluid Volume Imaged" for that run multiplied by 25 (to account for the 250 mL concentration down to 10 mL). This was then divided by the bin width, or Y-X. The resulting columns represent the Normalized Abundance Size Spectrum, or NASS. Biomass was similarly calculated with the exception of rather than summing the particle counts from “FlowCam Particle Sizes”, we sum the converted carbon biomass (column "Biomass" in "FlowCam Particle Sizes"). The result is the Normalized Biomass Size Spectrum, or NBSS.

BCO-DMO Processing:
- started with file named "FlowCam_ReducedV2.xlsx" received February 2023;
- renamed fields to comply with BCO-DMO naming conventions;
- rounded Lat and Lon fields to 4 decimal places.

NSF Award Abstract:
Salps are unique open-ocean animals that range in size from a few millimeters to greater than twenty centimeters, have a gelatinous (jelly-like) body, and can form long chains of many connected individuals. These oceanic organisms act as oceanic vacuum cleaners, having incredibly high feeding rates on phytoplankton and, unusual for consumers of their size, smaller bacteria-sized prey. This rapid feeding and the salps' tendency to form dense blooms, allows them move substantial amounts of prey carbon from the surface into the deep ocean, leading to carbon dioxide removal from the atmosphere. However, salps are often considered a trophic dead-end, rather than a link, in the food web due to the assumption that they themselves are not consumed, since their gelatinous bodies are less nutritious than co-occurring crustacean prey. Along with this, salp populations are hypothesized to be increasing due to climate change. This proposal addresses these questions: 1) Do salps compete primarily with crustaceans (as in the prevailing paradigm) or are they competitors of single-celled protists, which are the dominant grazers of small phytoplankton? 2) Do salp blooms increase the efficiency of food-web pathways from tiny phytoplankton to fisheries production in nutrient-poor ocean regions?

This project will support the interdisciplinary education of a graduate student who will learn modeling and laboratory techniques in the fields of biological and chemical oceanography and stimulate international collaborations between scientists in the United States and New Zealand. Additionally, several Education and Outreach initiatives are planned, including development of a week-long immersive high school class in biological oceanography, and education modules that will serve the "scientists-in-the schools" program in Tallahassee, FL.

It is commonly assumed that salps are a trophic sink. However, this idea was developed before the discovery that protists (rather than crustaceans) are the dominant grazers in the open ocean and was biased by the difficulty of recognizing gelatinous salps in fish guts. More recent studies show that salps are found in guts of a diverse group of fish and seabirds and are a readily available prey source when crustacean abundance is low. This proposal seeks to quantify food web flows through contrasting salp-dominated and salp-absent water parcels near the Chatham Rise off western New Zealand where salp blooms are a predictable phenomenon. The proposal will leverage previously obtained data on salp abundance, bulk grazing impact, and biogeochemical significance during Lagrangian experiments conducted by New Zealand-based collaborators. The proposal will determine 1) taxon- and size-specific phytoplankton growth rate measurements, 2) taxon- and size-specific protozoan and salp grazing rate measurements, 3) compound specific isotopic analysis of the amino acids of mesozooplankton to quantify the trophic position of salps, hyperiid amphipods, and other crustaceans, 4) sediment traps to quantify zooplankton carcass sinking rates, and 5) linear inverse ecosystem modeling syntheses. Secondary production and trophic flows from this well-constrained ecosystem model will be compared to crustacean-dominated and microbial loop-dominated ecosystems in similarly characterized regions (California Current, Costa Rica Dome, and Gulf of Mexico).

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.