Publication

2005-09

English

http://archimer.ifremer.fr/doc/2005/publication-726.pdf (0.19 Mo)

2005 Published by Oxford University Press

Bec Béatrice¹, Husseini Ratrema Julie¹, Collos Yves¹, Souchu Philippe², Vaquer André¹

1 : Univ Montpellier 2, Lab Ecosyst Lagunaires, CNRS, UMR 5119, F-34095 Montpellier, France.
2 : IFREMER, Lab Cotier Del, F-34203 Sete, France.

Journal of plankton research (0142-7873) (Oxford university press), 2005-09 , Vol. 27 , N. 9 , P. 881-894

25

Ecology

Coastal lagoon, NW Mediterranean, Picoeukaryote, Phytoplankton

The dynamics of the phytoplankton community were investigated in a marine coastal lagoon (Thau, NW Mediterranean) from February 1999 to January 2000. Dilution experiments, chlorophyll a (Chl a) size-fractionation and primary production measurements were conducted monthly. Maximum growth and microzooplankton grazing rates were estimated from Chl a biomass fractions to separate pico- from nano- and microphytoplankton and by flow cytometry to distinguish between picoeukaryotes and picocyanobacteria. In spring, the phytoplankton community was dominated by Chaetoceros sp. and Skeletonema costatum, which represented most of biomass (B) and primary production (P). Nano- and microphytoplankton growth was controlled by nutrient availability and exceeded losses due to microzooplankton grazing (g). Picoeukaryote and cyanobacteria growth was positively correlated with water temperature and/or irradiance, reaching maximum values in the summer (2.38 and 1.44 day(-1) for picoeukaryotes and cyanobacteria, respectively). Picophytoplankton accounted for 57% of the biomass-specific primary productivity (P/B). Picophytoplankton was strongly controlled by protist grazers (g = 0.09-1.66 day(-1) for picoeukaryotes, g = 0.25-1.17 day(-1) for cyanobacteria), and microzooplankton consumption removed 71% of the daily picoplanktonic growth. Picoeukaryotes, which numerically dominate the picoplankton community, are an important source of organic carbon for the protistan community and contribute to the carbon flow to higher trophic levels.