A comparative study of responses in plankton food web structure and function in contrasting European coastal waters exposed to experimental nutrient addition

Ôlsen, Yngvar; Agustı́, Susana; Andersen, Tom; Duarte, Carlos M.; Gasol, Josep M.; Gismervik, Ingrid; Heiskanen, Anna-Stiina; Hoell, E.; Kuuppo, Pirjo; Lignell, Risto; Reinertsen, Helge; Sommer, Ulrich; Stibor, Herwig; Tamminen, Timo; Vadstein, Ôlav; Vaqué, Dolors; Vidal, Montserrat

doi:10.4319/lo.2006.51.1_part_2.0488

Cited by 50 publications

(54 citation statements)

References 39 publications

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“…We then ran 100,000 simulations, during which we allowed the inputs to vary simultaneously by drawing them randomly from their respective distributions to generate confidence intervals for all model outputs. When possible, we utilized the full-rank inverse solution; where not, we followed the method of Olsen et al (2006), selecting the highest-rank solution that satisfied the constraints.…”

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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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: 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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“…Concentrations of chlorophyll a (Chl) in the upper 10 m of the lagoon at the time of the experiment ranged from 0.5 to 2.4 mg m −3 , corresponding well to the typical average summer concentrations for this lagoon (between 1-3 mg m −3 , Olsen et al, 2006).…”

Section: Study Areamentioning

confidence: 99%

“…We mimicked the natural nutrient input by manually adding nutrient to the enclosed mesocosms, using nitrogen concentrations that compensated for the loss of N caused by sedimentation and Redfield ratios for phosphorus and silicon additions as described in previous studies (Sommer et al, 2005;Olsen et al, 2006). Such nutrients additions maintained the low natural phytoplankton concentrations yet avoided accumulation of unrealistically high concentrations of phytoplankton biomass (Børsheim et al, 2005).…”

Section: Mesocosmsmentioning

confidence: 99%

“…Mesocosms enclose part of an in situ water column allowing manipulations of target parameters. Mesocosms are large enough to host a reasonably complex food web (e.g., including microand mesozooplankton) (Wassmann et al, 1996;Svensen et al, 2001;Sommer et al, 2004;Stibor et al, 2004;Olsen et al, 2006;Stange et al, 2017) while still allow controlled manipulations of parameters such as nutrients, ballast minerals, turbulence, and phytoplankton and zooplankton community composition.…”

Section: Introductionmentioning

confidence: 99%

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Copepods Boost the Production but Reduce the Carbon Export Efficiency by Diatoms

et al. 2018

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The fraction of net primary production that is exported from the euphotic zone as sinking particulate organic carbon (POC) varies notably through time and from region to region. Phytoplankton containing biominerals, such as silicified diatoms have long been associated with high export fluxes. However, recent reviews point out that the magnitude of export is not controlled by diatoms alone, but determined by the whole plankton community structure. The combined effect of phytoplankton community composition and zooplankton abundance on export flux dynamics, were explored using a set of 12 large outdoor mesocosms. All mesocosms received a daily addition of minor amounts of nitrate and phosphate, while only 6 mesocosms received silicic acid (dSi). This resulted in a dominance of diatoms and dinoflagellate in the +Si mesocosms and a dominance of dinoflagellate in the −Si mesocosms. Simultaneously, half of the mesocosms had decreased mesozooplankton populations whereas the other half were supplemented with additional zooplankton. In all mesocosms, POC fluxes were positively correlated to Si/C ratios measured in the surface community and additions of dSi globally increased the export fluxes in all treatments highlighting the role of diatoms in C export. The presence of additional copepods resulted in higher standing stocks of POC, most probably through trophic cascades. However it only resulted in higher export fluxes for the −Si mesocosms. In the +Si with copepod addition (+Si +Cops) export was dominated by large diatoms with higher Si/C ratios in sinking material than in standing stocks. During non-bloom situations, the grazing activity of copepods decrease the export efficiency in diatom dominated systems by changing the structure of the phytoplankton community and/or preventing their aggregation. However, in flagellate-dominated system, the copepods increased phytoplankton growth, aggregation and fecal pellet production, with overall higher net export not always visible in term of export efficiency.

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“…Picocyanobacteria (PCY) are ubiquitous prokaryotic autotrophic organisms that often represent a major fraction of the phytoplankton biomass (Johnson & Sieburth 1979, Waterbury et al 1979 and are major contributors to primary production in both marine and freshwater communities (Stockner 1988, Olsen et al 2006. Extensive research efforts have been made to study PCY biomass and their seasonal variations in marine and freshwater systems.…”

Section: Introductionmentioning

confidence: 99%

Trophic cascades mediated by copepods, not nutrient supply rate, determine the development of picocyanobacteria

Sundt-Hansen¹,

Ôlsen²,

Stibor³

et al. 2006

Aquat. Microb. Ecol.

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We studied the effect of nutrient supply rate (resources) and concentrations of copepods (top predator) on picocyanbacteria (PCY) in experimental ecosystems (mesocosms) using gradients of both nutrients and predators. The biomass and production of PCY, and the biomass and predation rates of their predators were determined by epifluorescence microscopy, X-ray microanalysis (XRMA), the 14 C method, and cell counting by microscopy. PCY biomass did not change significantly with increased supply of nutrients, but it was positively correlated with copepod biomass. A lack of variation in PCY growth rates, and nutrient saturation of cells as suggested by nutrient analysis and XRMA measurements, indicate that PCY grew close to their maximum growth rate during the experiment. Appendicularia and ciliates were the main predators on PCY when copepod biomass was normal or low, whereas heterotrophic nanoflagellates were significant predators on PCY when copepod biomass was high. Based on a negative effect of copepod biomass on the biomass of PCY predators, we conclude that predation had a stronger effect on the development of PCY than did nutrient supply rate. The only effect of nutrient supply was negative and indirect, implemented through stimulation of predatory ciliates. Copepods had a profound effect by structuring the food web, and thus directly and indirectly regulating the abundances of predators of PCY (top-down control). Therefore, copepods indirectly controlled the abundance of PCY through trophic cascades.

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A comparative study of responses in plankton food web structure and function in contrasting European coastal waters exposed to experimental nutrient addition

Abstract: AcknowledgmentsThanks to our colleague Egil Sakshaug for his efforts with this manuscript. We also thank Stephen V. Smith and two anonymous reviewers for their constructive comments and help to improve our manuscript.

Cited by 50 publications

References 39 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

Copepods Boost the Production but Reduce the Carbon Export Efficiency by Diatoms

Trophic cascades mediated by copepods, not nutrient supply rate, determine the development of picocyanobacteria

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