AME 49:267-279 (2007)  -  DOI: https://doi.org/10.3354/ame01151

Annual cycle of picophytoplankton photosynthesis and growth rates in a temperate coastal ecosystem: a major contribution to carbon fluxes

Xosé Anxelu G. Morán*

Centro Oceanográfico de Xixón, Instituto Español de Oceanografía, Camín de L’Arbeyal, s/n, 33212 Xixón, Spain

ABSTRACT: Autotrophic picoplankton (cells <2 µm) have been comparatively little studied in coastal waters. I present here the seasonal variation of picophytoplankton photosynthetic parameters, primary production and growth rates determined using the 14C method at a shelf station in the southern Bay of Biscay sampled monthly during 2003. Picophytoplankton chlorophyll a (chl a) (11.5 ± 1.7 mg m–2, mean ± SE) amounted to a mean of 42% (6 to 63%) of euphotic-layer integrated total values. Although prokaryotic cyanobacteria (Synechococcus and Prochlorococcus) generally outnumbered eukaryotic cells, picoeukaryotes were the greatest contributors to total picophytoplankton biomass (54 to 914 mg C m–2) for most of the year. Mean C:chl a ratios ranged from 7 to 89. The initial slope αB (0.01 to 0.11 mg C mg chl a–1 [µmol photons m–2 s–1]–1) was always higher at depth than at the surface, while the maximum chl a-normalized photosynthetic rate PBm (0.6 to 17.4 mg C mg chl a–1 h–1) was only significantly higher at the surface during summer, with vertical differences positively correlated to stratification. In contrast, maximum growth rates (μmax, 0.1 to 3.1 d–1) were remarkably similar in surface and deep samples, with maxima in spring and minima in summer and autumn. μmax values were significantly correlated with the relative abundance of picoeukaryotes, indicating their prevalence over prokaryotes in coastal ecosystems. Integrated picophytoplankton primary production ranged from 35 to 345 mg C m–2 d–1 and accounted for a mean annual value of 51% (4 to 76%) of total rates, thus confirming the essential role of small cells in the carbon flux of this temperate coastal ecosystem.


KEY WORDS: Picophytoplankton · Photosynthetic parameters · Primary production · Growth rates · Seasonal variability · Coastal waters


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Cite this article as: Morán XAG (2007) Annual cycle of picophytoplankton photosynthesis and growth rates in a temperate coastal ecosystem: a major contribution to carbon fluxes. Aquat Microb Ecol 49:267-279. https://doi.org/10.3354/ame01151

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