Is the distribution of Prochlorococcus and Synechococcus ecotypes in the Mediterranean Sea affected by global warming?

Daniella Mella-Flores (1) , S. Mazard (2, 3) , Florian Humily (1) , Frédéric Partensky (1) , Frédéric Mahé (1) , L. Bariat (4) , C. Courties (4) , Marie Dominique (1) , J. Ras (5) , R. Mauriac (6) , Christian Jeanthon (1) , El Mahdi Bendif (1) , M. Ostrowski (3, 2) , D. J. Scanlan (2) , Laurence Garczarek (1)

1 MAPP - Procaryotes Phototrophes Marins = MArine Phototrophic Prokaryotes
2 University of Warwick [Coventry]
3 Department of Chemistry and Biomolecular Sciences
4 OOB - Observatoire océanologique de Banyuls
5 LOV - Laboratoire d'océanographie de Villefranche
6 COM - Centre d'océanologie de Marseille

Biological communities populating the Mediterranean Sea, which is situated at the northern boundary of the subtropics, are often claimed to be particularly affected by global warming. This is indicated, for instance, by the introduction of (sub) tropical species of fish or invertebrates that can displace local species. This raises the question of whether microbial communities are similarly affected, especially in the Levantine basin where sea surface temperatures have significantly risen over the last 25 years (0.50 +/- 0.11 degrees C in average per decade, P < 0.01). In this paper, the genetic diversity of the two most abundant members of the phytoplankton community, the picocyanobacteria Prochlorococcus and Synechococcus, was examined during two cruises through both eastern and western Mediterranean Sea basins held in September 1999 (PROSOPE cruise) and in June-July 2008 (BOUM cruise). Diversity was studied using dot blot hybridization with clade-specific 16S rRNA oligonucleotide probes and/or clone libraries of the 16S-23S ribosomal DNA Internal Transcribed Spacer (ITS) region, with a focus on the abundance of clades that may constitute bioindicators of warm waters. During both cruises, the dominant Prochlorococcus clade in the upper mixed layer at all stations was HLI, a clade typical of temperate waters, whereas the HLII clade, the dominant group in (sub) tropical waters, was only present at very low concentrations. The Synechococcus community was dominated by clades I, III and IV in the northwestern waters of the Gulf of Lions and by clade III and groups genetically related to clades WPC1 and VI in the rest of the Mediterranean Sea. In contrast, only a few sequences of clade II, a group typical of warm waters, were observed. These data indicate that local cyanobacterial populations have not yet been displaced by their ( sub) tropical counterparts.

Domaines: Sciences du Vivant [q-bio]; Sciences de l'environnement

Daniella Mella-Flores, S. Mazard, Florian Humily, Frédéric Partensky, Frédéric Mahé, et al.. Is the distribution of Prochlorococcus and Synechococcus ecotypes in the Mediterranean Sea affected by global warming?. Biogeosciences, 2011, 8 (9), pp.2785-2804. ⟨10.5194/bg-8-2785-2011⟩. ⟨hal-01218507⟩