Site details

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5 stars - Fully protected as a national park or Natura 2000 site by national legislation
LTBR Focal Site

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Gorgonians and red coral on a slightly overhanging cliff. Photo: Harmelin, Jean-Georges

Synoptic description of site:

Uninhabited islands in limestone formations with varied topography including steep cliffs down to >70 m, with rich and diverse ‘coralligenous’ fauna and flora.

Extensive description of site:

The Riou Archipelago, near Marseille, is a group of uninhabited limestone islands with varied topography. The archipelago contains the whole set of sandy and rocky habitats typical of the NW Mediterranean, including vertical cliffs down to more than 70 m and submarine caves.

Habitats present:
Littoral XX
Seagrass bedsX

Description of fauna and flora:

The Archipelago contains a rich and diverse coralligenous fauna and flora, and is rich in Mediterranean endemic species and flagship species such as the red coral and several gorgonians.

Human impact:

The north coasts of the archipelago may be exposed to the effect of treated sewage from Marseille. The south coasts are under the influence of the general east-west current of the North-Western Mediterranean, and are free from obvious pollution. The site is very popular among divers and marine tourists. It is a Natura 2000 habitat.


Facilities are available at the Centre d’Océanologie de Marseille (COM).

Available database and website:

A species inventory for several algal groups and invertebrates (sponges, serpulid polychaetes, bryozoans, crustaceans) is available in the COM. Web site (mostly terrestrial):


Commitment and ongoing research:

The site has been routinely studied by the COM for 50 years. Ongoing studies include monitoring of the coralligenous and cave assemblages, continuous temperature recordings, permanent quadrats, inventories of the cave and cliff fauna, and changes in flora and fauna after a recent temperature-related mortality event.

Additional Information:

Examples of references available: Harmelin J.G., Sartoretto S., Francour P., 1996. Patrimoine biologique marin de l'archipel de Riou : première évaluation. Rapport Direction de l'Environnement et des Déchets, Ville de Marseille, 86 p. Harmelin J.G., Sartoretto S., Francour P., Boudouresque C.F., Bellan-Santini D., Vacelet, J., 1998. Création d’une aire marine protégée dans l’archipel de Riou : élaboration argumentée du projet. Rapport Ville de Marseille, Direction de l’Environnement et des Déchets, 198 pp. Harmelin J.G., Sartoretto S., Francour P., 1999. Mise en place d’une stratégie de suivi de l’ichtyofaune et des peuplements de gorgonaires de l’archipel de Riou. Rapport Ville de Marseille, Direction de l’Environnement et des Déchets, 110 pp. Perez, T., J. Garrabou, S. Sartoretto, J.-G. Harmelin, P. Francour & J. Vacelet 2000. Mortalité massive d'invertébrés marins : un événement sans précédent en Méditerranée nord-occidentale. C. R. Acad. Sci. Paris, Sciences de la Vie 323: 853-865.