Photosynthetic activity and productivity of intertidal macroalgae: in situ measurements, from thallus to community scaleReport as inadecuate

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* Corresponding author 1 SBR - Station biologique de Roscoff Roscoff 2 EFEB - Ecogéochimie et Fonctionnement des Ecosystèmes Benthiques ADMM - Adaptation et diversité en milieu marin 3 Station Marine de Wimereux 4 LOG - Laboratoire d-Océanologie et de Géosciences 5 Environmental futures research institute

Abstract : The photosynthetic activity and productivity of four dominant canopy intertidal macroalgae were measured under emersion and immersion, at saturating light levels PAR > 300 μmol photons m−2 s−1, and compared at two sites eastern and western English Channel in spring and summer. The photosynthetic activity of thalli was measured by the electron transport rate ETR using pulse-amplitude modulated PAM fluorescence and the productivity of individuals and of communities was measured by carbon fluxes in closed chambers. Under emersion, when thalli were still hydrated, the uppermost species Pelvetia canaliculata had higher photosynthetic activity mean ETR between 327 and 460 μmol e− m−2 s−1 and individual gross productivity between 60 and 212 μmol C gDW−1 h−1 than the lowermost species Laminaria digitata mean ETR between 24 and 53 μmol e− m−2 s−1 and gross productivity between 2 and 38 μmol C gDW−1 h−1, whatever the site and season. P. canaliculata had higher ETR in air than underwater averaged 146 μmol e− m−2 s−1 and L. digitata had lower ETR in air than underwater averaged 112 μmol e− m−2 s−1, while they exhibited respectively 3 and 5 times higher gross productivity underwater. At the community scale, the low mid-shore zone of Fucus serratus had the highest mean gross productivity under emersion 47 mmol C m−2 h−1 while rates were higher for the uppermost than lowermost zone at the eastern site average 20 and 6 mmol C m−2 h−1 respectively and of the same order of magnitude for both zones at the western site about 30 mmol C m−2 h−1. Finally, the variability of under emersion primary productivity among sites and seasons was reduced when the measurements were performed on entire communities compared to isolated individuals of the dominant species.

Keywords : Primary production Rocky shores Fucoids Kelps

Author: Aline Migné - Gaspard Delebecq - Dominique Davoult - Nicolas Spilmont - Dominique Menu - François Gévaert -



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