Size-fractionated incubation dilution experiments
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| Microzooplankton grazing, size-fractionated |
|---|
| Approach: dilution method with FCM or HPLC tracking of size-class phytoplankton |
| Context: incubation |
| Spatial scale: point sample |
| Temporal scale: hours (one diel cycle) |
| Units: d-1 |
| Community captured: size-fractionated phytoplankton (FCM populations or HPLC pigment groups) |
| Co-measurements: temperature, simulated or in situ PAR, depth of collection |
Method Overview
This is the size-fractionated variant of the Incubation dilution experiments method, in which phytoplankton growth and grazing rates are resolved for distinct size classes or taxonomic groups rather than the bulk community. The dilution procedure is identical to the standard method: whole seawater is diluted with particle-free (0.2 µm) filtrate across a dilution series. Rather than tracking bulk chlorophyll-a, phytoplankton biomass in distinct populations is measured by flow cytometry (resolving Prochlorococcus, Synechococcus, picoeukaryotes, nanoeukaryotes) or by HPLC pigment analysis[1]. Separate µ and g values are derived for each resolvable population, revealing which phytoplankton groups are most heavily grazed.
Scale of measurement
Point sample; 24 h incubation. Multiple populations resolved within a single dilution series provide a more complete picture of community trophic dynamics than bulk Chl tracking alone.
Data generated
Population-specific phytoplankton growth rates (µ, d-1) and microzooplankton grazing rates (g, d-1) for each FCM-resolvable population or HPLC-derived taxon group.
Units & currency
Units are d-1. The currency is Chl-a or cell counts.
Sample size
Typical samples are 1–2 L per dilution treatment.
Repositories & databases
Limitations
Same assumptions apply as for the bulk dilution method. FCM populations must be optically distinct; overlapping populations cannot be separated. HPLC pigment markers require taxon-specific pigment:Chl ratios for biomass conversion.
Example Applications & Protocols
Classic examples
- Morison & Menden-Deuer (2017) Doing more with less? Balancing sampling resolution and effort in measurements of protistan growth and grazing rates [1]
Recent applications
- Marrec & Menden-Deuer (2024) Changes in phytoplankton size-structure alter trophic transfer in a temperate, coastal planktonic food web [2]
Common calculations/conversions
- As for the bulk dilution method, applied separately to each FCM population or pigment group.
References
- ↑ 1.0 1.1 Morison, F., & Menden-Deuer, S. (2017). Doing more with less? Balancing sampling resolution and effort in measurements of protistan growth and grazing rates. Limnology and Oceanography: Methods, 15, 794–809. https://doi.org/10.1002/lom3.10200
- ↑ Marrec, P., & Menden-Deuer, S. (2024). Changes in phytoplankton size-structure alter trophic transfer in a temperate, coastal planktonic food web. Limnology and Oceanography Letters, 9(5), 624–633. https://doi.org/10.1002/lol2.10410