Spatially-resolved taxon-specific phytoplankton production and grazing dynamics in relation to iron distributions in the Equatorial Pacific between 110 and 140°W

Selph, Karen E.; Landry, Michael R.; Taylor, Andrew G.; Yang, Eun Jin; Measures, Christopher I.; Yang, Jingjing; Stukel, Michael R.; Christensen, Stephanie; Bidigare, Robert R.

doi:10.1016/j.dsr2.2010.08.014

Cited by 66 publications

(73 citation statements)

References 90 publications

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“…Even under this model construction that did not allow direct sinking of picodetritus, however, picophytoplankton were responsible for producing 18% of the exported carbon (three-fourths of the percentage predicted by the proportionality argument and half their contribution to carbon biomass). A strong growth-grazing balance for picophytoplankton populations, with protists applying essentially all of the grazing pressure, follows directly from the experimental measurements Selph et al 2010) and is a consistent feature of both forms of our model and minimization schemes. Thus, unlike the Richardson et al (2004,2006) analyses, the export of picophytoplanktonbased production cannot be said to be unrealistically enhanced by a large fraction escaping consumption in the microbial food web and passing directly to detritus.…”

Section: Discussionmentioning

confidence: 80%

“…These experiments were incubated for 24 h in seawater-cooled deck incubators at light levels representing 0.1%, 0.8%, 5%, 8%, 13%, 31%, 52%, and 100% of incident solar irradiance, corresponding to light levels at the depth of sample collection. Taxonspecific rates were determined by either high-pressure liquid chromatography pigment analysis (divinyl chlorophyll a [Chl a] was considered representative of Prochlorococcus, fucoxanthin of diatoms, and monovinyl Chl a of total eukaryotic phytoplankton) or flow cytometry samples (Prochlorococcus and Synechococcus; Selph et al 2010). Pigment-derived rates were corrected for systematic changes in cellular pigment content during incubation using the initial and final experimental samples to assess the changes in the mean ratios of accessory pigment to microscopical assessments of phytoplankton biomass (e.g., fucoxanthin : diatom C).…”

Section: Methodsmentioning

confidence: 99%

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Contribution of picophytoplankton to carbon export in the equatorial Pacific: A reassessment of food web flux inferences from inverse models

Stukel

Landry

2010

Limnology & Oceanography

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The paradigm that carbon export is derived almost exclusively from the primary production of large phytoplankton has been challenged by inverse ecosystem modeling studies that suggest that most carbon export in the open ocean is fueled by picophytoplankton. To readdress this hypothesis, we use an inverse model to synthesize the planktonic rate measurements from a pair of recent cruises in the equatorial Pacific. The analysis based on this new experimental data, which crucially include vertically integrated taxon-specific production and grazing estimates, largely resolve the unexpected results of the previous inverse studies, including unbalanced growth and grazing processes and the dominance of production by picophytoplankton. While this very small size class does not produce the majority of phytoplankton carbon that is eventually exported to depth (only 23%, vs. 73% from a previous analysis of Joint Global Ocean Flux Study Equatorial Pacific data), our base model supports the conclusion that the role of picophytoplankton in vertical carbon flux is largely proportional to their contribution to net primary productivity (though neither is proportional to biomass). We show, however, that export-production proportionality is sensitive to the model representation of the detrital pool such that the relative export role of picophytoplankton declines substantially for an alternate model with size-structured detritus. A definitive assessment of the role of picoplankton in vertical carbon flux will thus require detailed experimental examination of the origin, composition, and fate of euphotic zone detrital material.

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Section: Discussionmentioning

confidence: 80%

Section: Methodsmentioning

confidence: 99%

Contribution of picophytoplankton to carbon export in the equatorial Pacific: A reassessment of food web flux inferences from inverse models

Stukel

Landry

2010

Limnology & Oceanography

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“…Of particular relevance is the work of Landry et al (2011a) and Selph et al (2011), which include experiments from the same cruise as used here as well as a 2004 cruise to the same region. Those studies focused on taxonomic-based rates generated from HPLC pigment concentrations and flow cytometry data instead of size-based rates.…”

Section: Application To Field Datamentioning

confidence: 99%

“…Given the observed relative constancy of growth and grazing rates and community composition among stations (Landry et al 2011a;Selph et al 2011), combining data sets is expected to highlight rather than mask the underlying size dependencies. Once the data were pooled, the cells were divided into bins with edges of 0.45, 0.65, 1.25, 2.75, and 4.00 µm.…”

Section: Application To Field Datamentioning

confidence: 99%

“…Given that the size-dependent dilution method worked well under the steady-state conditions of the complex modeled ecosystem, the application of the method to the relatively stable conditions of the equatorial Pacific seemed appropriate. As described in detail elsewhere (Selph et al 2011), two-treatment dilution experiments were conducted at 8 depths at each of 14 stations along a transect at 0.5°N, with one station at 140°W and the rest approximately 2° apart between 132.5 and 123.5°W. For the present analysis, we used only experiments conducted with surface mixed-layer water (collected in early morning CTD casts, ~0300-0400 hour local time) and incubated for 24 h in calibrated seawater-cooled deck incubators at a 31% of surface irradiance, the conditions for maximum phytoplankton growth (Landry et al 2011b).…”

Section: Application To Field Datamentioning

confidence: 99%

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Estimating size‐dependent growth and grazing rates and their associated errors using the dilution method

Taniguchi

Franks

Landry

2012

Limnology & Ocean Methods

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Size-dependent properties are pervasive in nature but difficult to measure for natural communities. Here, we develop a technique to estimate size-specific phytoplankton growth and grazing rates based on the two-point dilution method, enhanced by the acquisition of the size spectra of the phytoplankton in the samples. We describe a way to estimate standard deviations associated with the rate estimates, which can be applied either to the size-dependent or total community rates. We tested the accuracy of rates estimated using the size-dependent dilution method by applying it to dilution experiments simulated using a complex size-structured ecosystem model. The strong agreement between model and size-dependent dilution method rates (two-sample Kolmogorov-Smirnov test, P = 1) supports the accuracy of this new technique. Because size-dependent rates vary with the size interval over which they are calculated, we display the size-dependent growth and grazing rates and their standard deviations as a function of the size interval. This technique easily allows the assessment of rates for any size class of interest. Finally, we apply the size-dependent dilution method to data collected in the equatorial Pacific. There is a general agreement between size-based and previously published taxonomic-based rates, with differences reflecting the extent to which size classes are mixtures of taxa. The use of the size-dependent dilution method will provide new insights into the structure and dynamics of planktonic communities. Future applications of this method to other natural communities will help in assessing the size-dependencies of phytoplankton growth and grazing rates in their environments.

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Size‐specific grazing and competitive interactions between large salps and protistan grazers

Stukel

Décima

Selph

et al. 2021

Limnology & Oceanography

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We investigated competition between Salpa thompsoni and 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 > 1.4 μm (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 > 5.9 μm 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: Clearance()ESD=φ∙TLψ×min(),trueESDθ×TLγ20.16+trueESDθ×TLγ1×Q10()T−12°normalC/10 where ESD is prey equivalent spherical diameter (µm), TL is S. thompsoni total length, φ = 5.6 × 10−3 ± 3.6 × 10−4, ψ = 2.1 ± 0.13, θ = 0.58 ± 0.08, and γ = 0.46 ± 0.03 and clearance rate is L d‐1 salp‐1. We discuss the biogeochemical and food‐web implications of competitive interactions among salps, krill, and protozoans.

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Spatially-resolved taxon-specific phytoplankton production and grazing dynamics in relation to iron distributions in the Equatorial Pacific between 110 and 140°W

Cited by 66 publications

References 90 publications

Contribution of picophytoplankton to carbon export in the equatorial Pacific: A reassessment of food web flux inferences from inverse models

Contribution of picophytoplankton to carbon export in the equatorial Pacific: A reassessment of food web flux inferences from inverse models

Estimating size‐dependent growth and grazing rates and their associated errors using the dilution method

Size‐specific grazing and competitive interactions between large salps and protistan grazers

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