Mass mortality of marine invertebrates: an unprecedented event in the Northwestern Mediterranean.

An unprecedented mass mortality event has been observed at the end of the s ummer 1999 along the coasts of Provence (France) and Ligury (Italy). This e vent has severely affected a wide array of sessile filter-feeder invertebra tes from hard-substratum communities, such as sponges (particularly the ker atose sponges Hipposongia and Spongia), cnidarians (particularly the anthoz oans Corallium, Paramuricea, Eunicella and Cladocora), bivalves, ascidians and bryozoans. Along the Provence coasts, the outbreak spread from east to west. Exceptionally high and constant temperatures of the whole water colum n (23-24 degreesC, for over one month, down to 40 m) could have determined an environmental context favourable to the mass mortality event. Like the t hermal anomaly, the mortality is limited in depth. However, rye cannot asce rtain whether temperature had a direct effect on organisms or acted in syne rgy with a latent and/or waterborne agent (microbiological or chemical). Ta king into account the global warming context in the NW-Mediterranean, monit oring programs of physical-chemical parameters and vulnerable populations s hould rapidly be set up. (C) 2000 Academie des sciences/Editions scientifiq ues et medicales Elsevier SAS.