Dynamics of microbial planktonic food web components during a river flash flood in a Mediterranean coastal lagoon
David Pecqueur; Francesca Vidussi; Eric Fouilland; Emilie, L.F.oc'h; Sebastien Mas; Cecile Roques; Christian Salles; Marie-George Tournoud; Behzad Mostajir
Hydrobiologia 673(1): 13-27
ISSN/ISBN: 0018-8158 DOI: 10.1007/s10750-011-0745-x
Episodic river flash floods, characteristic of Mediterranean climates, are suspected to greatly affect the functioning of microbial food webs. For the first time, the abundance, biomass and diversities of microbial food web components were studied before and during 4 consecutive days after a flash flood that occurred in November 28, in the surface waters of five stations along a salinity gradient from 2 to 36 in the Thau lagoon. Eukaryotic pico- and nanophytoplankton were discharged from the river into the lagoon and increased by 3- and 7-fold, respectively. Bacteria increased by only 2-fold in the lagoon, from around 4 8 16 cells ml?1, probably benefiting from river nutrient input. Chlorophyll a increased 4-fold, and pigment biomarkers showed that the dinophyceae, prasinophyceae and prymnesiophyceae were sensitive to the flood perturbation, whereas the bacillariophyceae, cryptophyceae and chlorophyceae were resistant and/or transported to the lagoon from the river. Predator responses were more complex as total heterotrophic flagellate abundance decreased slightly, whereas those of specific naked ciliates increased, particularly for Uronema sp. The flood also induced a specific change in diversity, from a community dominated by Strobilidium spiralis to a community dominated by Uronema sp. The tintinnid community was particularly sensitive to the flood event as the abundance of all species decreased greatly. The high increases in biomass, mainly brought by the river during the flood, could have eventually sedimented to the benthic layer and/or been transported further into the lagoon, supporting the pelagic food web, or have even been exported to the Mediterranean Sea.