Community structure and trophic role of ciliates and heterotrophic nanoflagellates in Rhone River diluted mesoscale structures (NW Mediterranean Sea)

Abstract

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 57:263-277 (2009) - DOI: https://doi.org/10.3354/ame01339 AME Special: 'Rassoulzadegan at Villefranche-sur-Mer: 3 decades of aquatic microbial ecology' Community structure and trophic role of ciliates and heterotrophic nanoflagellates in Rhone River diluted mesoscale structures (NW Mediterranean Sea) Urania Christaki1,*, Claude Courties2, Fabien Joux3, Wade H. Jeffrey4, Jacques Neveux3, Jean-Jacques Naudin3 1Univ Lille Nord de France, ULCO, LOG, CNRS, UMR 8187, 32 Avenue Foch, 62930 Wimereux, France 2UMPC Univ Paris 06, FRE 3247, MBCE, CNRS, Observatoire Océanologique, 66651 Banyuls-sur-mer, France 3UMPC Univ Paris 06, FRE 3247, MBCE, LOBBCNRS, UMR 7621, Observatoire Océanologique, 66651 Banyuls-sur-mer, France 4Center for Environmental Diagnostics and Bioremediation, 11000 University Parkway, University of West Florida, Pensacola, Florida 32514, USA *Email: urania.christaki@univ-littoral.fr ABSTRACT: Studies of the Rhone River plume, and in particular its diluted mesoscale structures, have shown over recent years that low salinity water (LSW) is characterised by both high primary and high secondary productivity. Here we compare the structure and grazing activity of the hetorotrophic community (nanoflagellates, ciliates) in the LSW and the surrounding marine water (MW) of the northwestern Mediterranean Sea. Furthermore, we report on the temporal variability of these characteristics all along a Lagrangian track in the LSW. In May 2006, salinity of the LSW ranged from 31.41 to 38.25 down to a depth of 35 m, and surface chlorophyll a concentration reached 15.5 µg l–1. The ciliate community structure was similar in both the LSW and the MW, characterised by the dominance of the mixotrophic ciliates Laboea strobila and Myrionecta rubra. The ciliate biomass was approximately 6 times greater in the LSW, compared to the MW. This difference was due to the mixotrophic ciliates, which were about 4- to 5-fold more important in terms of abundance and biomass in the LSW, while heterotrophic ciliates only increased by a maximum of 2-fold. M. rubra was the most abundant species reaching 4600 cells l–1, while L. strobila was dominant in terms of biomass, accounting for 47% of total biomass in the LSW. Ciliates, in particular mixotrophs, were very active in the LSW where they grazed on phytoplankton at rates near their maximum clearance capacities. Mixotrophic and heterotrophic ciliates in LSW consumed about 50 and 10% of the nanophytoplankton stock per day, respectively. The mixotrophic ciliate L. strobila was found to be an efficient grazer of nanophytoplankton. In contrast to the ciliates, the biomass of heterotrophic nanoflagellates was similar in both the LSW and the MW; thus, we suggest that the transfer of bacterial biomass in the LSW towards higher trophic levels was moderate. KEY WORDS: Bacterivory · Grazing · Mixotroph · Laboea strobila · Picoeucaryotes · Rhone River plume Full text in pdf format PreviousNextCite this article as: Christaki U, Courties C, Joux F, Jeffrey WH, Neveux J, Naudin J (2009) Community structure and trophic role of ciliates and heterotrophic nanoflagellates in Rhone River diluted mesoscale structures (NW Mediterranean Sea). Aquat Microb Ecol 57:263-277. https://doi.org/10.3354/ame01339 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 57, No. 3. Online publication date: November 24, 2009 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2009 Inter-Research.