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Abstract We investigated competition betweenSalpa thompsoniand protistan grazers during Lagrangian experiments near the Subtropical Front in the southwest Pacific sector of the Southern Ocean. Over a month, the salp community shifted from dominance by large (> 100 mm) oozooids and small (< 20 mm) blastozooids to large (~ 60 mm) blastozooids. Phytoplankton biomass was consistently dominated by nano‐ and microphytoplankton (> 2 μm cells). Using bead‐calibrated flow‐cytometry light scatter to estimate phytoplankton size, we quantified size‐specific salp and protistan zooplankton grazing pressure. Salps were able to feed at a > 10,000 : 1 predator : prey size (linear‐dimension) ratio. Small blastozooids efficiently retained cells > 1.4μm (high end of picoplankton size, 0.6–2 μm cells) and also obtained substantial nutrition from smaller bacteria‐sized cells. Larger salps could only feed efficiently on > 5.9μm cells and were largely incapable of feeding on picoplankton. Due to the high biomass of nano‐ and microphytoplankton, however, all salps derived most of their (phytoplankton‐based) nutrition from these larger autotrophs. Phagotrophic protists were the dominant competitors for these prey items and consumed approximately 50% of the biomass of all phytoplankton size classes each day. Using a Bayesian statistical framework, we developed an allometric‐scaling equation for salp clearance rates as a function of salp and prey size:urn:x-wiley:00243590:media:lno11770:lno11770-math-0001where ESD is prey equivalent spherical diameter (µm), TL isS. thompsonitotal length,φ = 5.6 × 10−3 ± 3.6 × 10−4,ψ = 2.1 ± 0.13,θ = 0.58 ± 0.08, andγ = 0.46 ± 0.03 and clearance rate is L d‐1salp‐1. We discuss the biogeochemical and food‐web implications of competitive interactions among salps, krill, and protozoans.
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This content will become publicly available on October 3, 2026
A prototype submersible sheathless flow cytometer designed for autonomous platforms
Abstract Development of submersible flow cytometers has allowed for continuous, in situ measurements of natural assemblages of phytoplankton cells. Here we introduce DeepCyte, a sensitive prototype submersible flow cytometer developed for deployment on autonomous platforms. DeepCyte continuously collects multidimensional characteristics of individual phytoplankton cells (~0.5–10 μm in diameter), includingProchlorococcus, and transmits this data in real‐time to remote observatories via a network connection. DeepCyte utilizes a virtual sample core technology and an open flow system, enabling direct measures from the surrounding environment without the use of a clean carrier fluid. The primary surfaces of excitation and collection optics are exposed to the outside of the instrument, and the only fluid path is a 6 mm diameter length of silicon tubing. These design features allow for simple maintenance of optical surfaces and minimize sampling downtime due to clogs or air bubbles. An innovative arrangement of the optical system means the instrument fits within a volume of 0.017 m3, and our selection and design of low power electronics yield power consumption of 36 watts when operated as a standalone instrument with integrated pump. The DeepCyte is characterized by high optical sensitivity, low power consumption, compact size, and low maintenance. This technology will provide a continuous view of the dynamics and structure of the smallest phytoplankton populations, aligning with and expanding upon other continuous measurements such as chlorophyll‐afluorescence, temperature, and salinity.
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- Award ID(s):
- 2022843
- PAR ID:
- 10647320
- Publisher / Repository:
- Limonology and Oceanography
- Date Published:
- Journal Name:
- Limnology and Oceanography: Methods
- ISSN:
- 1541-5856
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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