On database biases and hypothesis testing with dilution experiments: Response to comment by Latasa

Landry, Michael R.

doi:10.4319/lo.2014.59.3.1095

Cited by 9 publications

(6 citation statements)

References 11 publications

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“…The large variability observed at stations on the plateau was mainly due to the remarkably low values obtained at Station 21 (minimum rates across the study, μ 0 = 0.09, grazing = 0.18), where the dilution experiment rendered nonsignificant relationship between apparent growth and dilution factor ( R 2 = 0.02, Table ). Although the exact magnitude of these rates should be regarded with caution, we consider that the low rates obtained represent a valid experimental outcome that can contribute meaningfully to the broader interpretation of growth and grazing variability in this region (Landry, ; Latasa, ). Taken together, photo‐physiological measurements and growth rates estimated at stations on the plateau suggested a physiological improvement of phytoplankton relative to waters off the plateau.…”

Section: Discussionmentioning

confidence: 92%

Decoupling Between Phytoplankton Growth and Microzooplankton Grazing Enhances Productivity in Subantarctic Waters on Campbell Plateau, Southeast of New Zealand

et al. 2020

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The Subantarctic zone is one of the largest High‐Nutrient Low‐Chlorophyll zones of the Southern Ocean. Despite widespread iron limitation, phytoplankton accumulation (chlorophyll a (chla) > 0.3 mg m−3) often occurs near islands and bathymetric features such as on the Campbell Plateau, southeast of New Zealand. To investigate the processes responsible for localized increases in chla commonly observed by satellites, we characterized phytoplankton biomass structure, production, and microzooplankton grazing on Campbell Plateau and surrounding waters in austral autumn (March 2017). Chla on the plateau tended to be higher, more variable (0.52 ± 0.38 mg chla m−3, mean ± standard deviation), and characterized by larger phytoplankton forms (22 ± 27%chla > 20 μm) than surrounding waters (0.29 ± 0.12 mg chla m−3, 5 ± 2%). The increased contribution of diatoms, together with higher photosystem II maximum photochemical efficiency (Fv/Fm = 0.45 ± 0.05) and lower effective absorption cross‐section (σPSII = 774 ± 90 Å RCII−1) on the plateau, suggests an alleviation of iron stress relative to surrounding waters (Fv/Fm = 0.37 ± 0.04, σPSII = 974 ± 89 Å RCII−1). Phytoplankton growth (μ0 = 0.42 ± 0.20 day−1) and production rates (6.1 ± 3.2 mg C m−3 day−1) were also higher compared to surrounding waters (0.27 ± 0.04 day−1, 3.5 ± 1.9 mg C m−3 day−1). While microzooplankton grazing (g = 0.28 ± 0.18 day−1) balanced phytoplankton growth off the plateau (g:μ0 = 1.13 ± 0.18), the imbalance observed on Campbell Plateau (g = 0.25 ± 0.25 day−1) allowed a substantial proportion of primary production to escape microzooplankton grazing control (g:μ0 = 0.48 ± 0.31). Overall, the degree of coupling tended to decrease with the depth of the mixed layer (R2 > 0.6, p < 0.001). We hypothesize that the entrainment of deeper water into the mixed layer regulates the onset and fate of the autumn bloom by altering nutrient supply and microzooplankton grazing pressure.

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Section: Discussionmentioning

confidence: 92%

Decoupling Between Phytoplankton Growth and Microzooplankton Grazing Enhances Productivity in Subantarctic Waters on Campbell Plateau, Southeast of New Zealand

et al. 2020

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“…[ 13 – 15 , 18 , 22 ]) or suggested to overestimate the impact of grazing. Indeed, a recent meta-analysis found that many studies erroneously applied tests that assessed the significance of mortality rates based on whether they were greater than or less than zero, rather than strictly greater than zero [ 23 , 24 ]. Other studies have also suggested that grazing rates may be overestimated due to changes within the grazer communities [ 25 ].…”

Section: Discussionmentioning

confidence: 99%

Disentangling niche competition from grazing mortality in phytoplankton dilution experiments

Beckett

Weitz

2017

PLoS ONE

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The dilution method is the principal tool used to infer in situ microzooplankton grazing rates. However, grazing is the only mortality process considered in the theoretical model underlying the interpretation of dilution method experiments. Here we evaluate the robustness of mortality estimates inferred from dilution experiments when there is concurrent niche competition amongst phytoplankton. Using a combination of mathematical analysis and numerical simulations, we find that grazing rates may be overestimated—the degree of overestimation is related to the importance of niche competition relative to microzooplankton grazing. In response, we propose a conceptual method to disentangle the effects of niche competition and grazing by diluting out microzooplankton, but not phytoplankton. Our theoretical results suggest this revised “Z-dilution” method can robustly infer grazing mortality, regardless of the dominant phytoplankton mortality driver in our system. Further, we show it is possible to independently estimate both grazing mortality and niche competition if the classical and Z-dilution methods can be used in tandem. We discuss the significance of these results for quantifying phytoplankton mortality rates; and the feasibility of implementing the Z-dilution method in practice, whether in model systems or in complex communities with overlap in the size distributions of phytoplankton and microzooplankton.

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“…However dilution experiments done in large numbers can be used to describe the process interactions and relationships in natural systems (Landry 2014). This study shows strikingly different responses 5 in predator-prey coupling between eutrophic and oligotrophic systems.…”

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confidence: 99%

Temporal variation of phytoplankton growth and grazing loss in the west coast of Peninsular Malaysia

Lim

Lee

Kudo

2015

Environ Monit Assess

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Phytoplankton growth (µ) and grazing loss (g) rates were measured monthly by the Landry-Hassett dilution method over a two-year period at both estuarine (Klang) and study, grazing loss was coupled to phytoplankton growth and the ratio of g : μ or grazing pressure which estimates the proportion of primary production grazed was 50% at Klang and lower than at Port Dickson (68%) (t = 2.213, df = 36, p < 0.05). We found that the higher growth rates in an eutrophic system i.e. Klang were not matched by higher grazing loss, and this may have implications for the biogeochemical cycling in coastal waters.

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On database biases and hypothesis testing with dilution experiments: Response to comment by Latasa

Abstract: Response

Cited by 9 publications

References 11 publications

Decoupling Between Phytoplankton Growth and Microzooplankton Grazing Enhances Productivity in Subantarctic Waters on Campbell Plateau, Southeast of New Zealand

Decoupling Between Phytoplankton Growth and Microzooplankton Grazing Enhances Productivity in Subantarctic Waters on Campbell Plateau, Southeast of New Zealand

Disentangling niche competition from grazing mortality in phytoplankton dilution experiments

Temporal variation of phytoplankton growth and grazing loss in the west coast of Peninsular Malaysia

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