La diversite des dinoflagelles symbiotiques de 7 especes de corail occupant le meme ecosysteme a ete etudie a l'aide d'outils moleculaires. Le gene codant la petite sous-unite ribosomale (ADNr 18S) a ete choisi et 26 sequences originales de dinoflagelles symbiotiques ont ete obtenues.Les pourcentages de similarite, les signatures et les analyses phylogenetiques des sequences montrent que nos echantillons de dinoflagelles symbiotiques appartiennent au genre Symbiodinium et qu'ils correspondent a au moins six souches differentes et trois nouvelles especes. Le niveau taxonomique des sequences de l'ADNr 18S n'etant pas toujours determine, six phylogroupes Symbiodinium ont ete definis. Nos resultats suggerent 1) la possibilite d'echanges de phylogroupes Symbiodinium similaires entre des especes de corail differentes ; 2) la presence d'association plus specifique pour deux especes de corail ; 3) le rejet du concept de co-evolution.Symbiotic Dinoflagellates are unicellular microalgae associated with scleractinian corals. This symbiosis is necessary for life and growth of reef communities. The diversity of symbiotic Dinoflagellates from seven coral species (Fungia scutaria, Fungia paumotensis, Leptastrea transversa, Pavona cactus, Pocillopora verrucosa, Montastrea curta and Acropora formosa) was studied in a restricted geographical area, the lagoon of Arue in Tahiti (French Polynesia). Symbiotic Dinoflagellates are difficult to maintain in vitro, and their diversity was explored using ribosomal small subunit gene (18S rDNA) sequences. 18S rDNAs from 15 symbiotic Dinoflagellates samples were amplified by PCR and sequenced. All the 26 sequences found were original compared to published Symbiodinium sequences. Phylogenetic analysis proved that symbiotic Dinoflagellates studied belonged to the genus Symbiodinium and may correspond to at least 6 strains and three new species. Similary percentage, sequence signature and monophyletic clusters allowed to define six phylogroups Symbiodinium. In this restricted geographical area, one Symbiodinium phylogroup could be associated with several coral species.Phylogroup Symbiodinium I was found in Fungia scutaria, Fungia paumotensis, leptastrea transversa, Pavona cactus, Pocillopora verrucosa, and Acropora formosa suggesting the possibility of symbiotic Dinoflagellates flux in this area. A single Symbiodinium phylogroup could be associated with only one coral species, as Montastrea curta which contained Symbiodinium IV phylogroup, suggesting that specific mechanisms could be involved in the establishment of a symbiosis. One coral species could be associated with more than one Symbiodinium phylogroups, as Pocillopora verrucosa which contained two Symbiodinium phylogroups.