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

Xose Anxelu G. Moran

Research output: Contribution to journalArticlepeer-review

49 Scopus citations

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 [pmol photons m-2 s-1]-1) was always higher at depth than at the surface, while the maximum chl a-normalized photosynthetic rate P B m (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.

Original languageEnglish (US)
Pages (from-to)267-279
Number of pages13
JournalAquatic Microbial Ecology
Volume49
Issue number3
DOIs
StatePublished - Nov 29 2007

Keywords

  • Coastal waters
  • Growth rates
  • Photosynthetic parameters
  • Picophytoplankton
  • Primary production
  • Seasonal variability

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Aquatic Science

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