MEPS 383:1-9 (2009)  -  DOI:

Coupling between phytoplankton growth and microzooplankton grazing in dilution experiments: potential artefacts

Andrés Gutiérrez-Rodríguez1, Mikel Latasa1,3,*, Baptiste Mourre1, Edward A. Laws2

1Institut de Ciències del Mar-ICM (CSIC), Passeig Marítim de la Barceloneta 37–49, 08003 Barcelona, Spain
2Department of Environmental Sciences, School of the Coast and Environment, Louisiana State University, Baton Rouge, Louisiana 70803, USA
3Present address: Centro Oceanográfico de Gijón (IEO), Avda. Príncipe de Asturias 70 bis, 33213 Gijón, Spain
*Corresponding author. Email:

ABSTRACT: Phytoplankton distribution is relatively constant in large areas of the surface ocean. In order to maintain this apparent stability, phytoplankton production and losses have to be balanced. Indeed, growth (μo) and grazing (g) rates obtained simultaneously with the dilution technique are often tightly coupled. One problem with this approach is that growth and grazing are not independent in the ecological model on which the method is based (net growth rate = μog). We evaluated to which extent this methodological artefact may influence the correlation between μo and g estimated using the dilution technique. Following a Monte-Carlo approach, we show that the methodological correlation can be substantial depending on: (1) the % error in the measurement of the state variable ND (e.g. chlorophyll a) and (2) the range (± SD) of the μo and g considered. As long as the error of ND is small (< 10%), the measured correlation between growth and grazing closely reflects a true ecological relationship. For large errors, the dilution technique can yield a substantial correlation between both variables, regardless of their ecological relation. The influence of this methodological correlation decreases as the range of growth and grazing rate values increases. We developed a procedure to evaluate the ecological versus the methodological nature of the correlation observed between μo and g. The application of this procedure to a data set obtained from a coastal site revealed that the high correlation observed (rS = 0.881, p < 0.0001) reflected a true ecological relationship.

KEY WORDS: Dilution technique · Phytoplankton growth · Microzooplankton grazing · Coupling · Monte-Carlo simulation

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Cite this article as: Gutiérrez-Rodríguez A, Latasa M, Mourre B, Laws EA (2009) Coupling between phytoplankton growth and microzooplankton grazing in dilution experiments: potential artefacts. Mar Ecol Prog Ser 383:1-9.

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