[Thermal anomaly in waters of the Gulf of Marseilles during the summer of 1999. A partial explanation of the mortality of certain fixed invertebrates?]. / Anomalie thermique dans les eaux du golfe de Marseille durant l'été 1999. Une explication partielle de la mortalité d'invertébrés fixés?

During summer 1999, a massive mortality of attached benthic invertebrates was reported at several points along the French Mediterranean coast, east of the Rhône River. Such a wide geographical extension suggested the occurrence of a climatic anomaly as a direct or an indirect cause of this phenomenon. The systematic observations of surface water temperature (1 record/30 min) and vertical thermal structure from 0 to 55 m (semi-monthly frequency) performed by the service of observation of centre d'océanologie de Marseille since 1994 in the Gulf of Marseilles (northwestern Mediterranean) compared with historical data obtained for the summer periods (June till October) indicates a thermal anomaly during summer 1999. Although the surface temperatures do not strictly show exceptional values, the stability during long periods of high temperatures (24.1 degrees C +/- 0.5 in September, n = 1,018) and the thermal structure of the water column are remarkable. The vertical temperature profiles of 1999 reflect a general warming of 2-3 degrees C in the water layer overlying the thermocline, accompanied by its deepening (up to 30-40 m). This situation can be explained by the scarcity of NW winds with a marked drop of their relative frequency during July and October 1999 (13-27% versus 42%, mean value calculated from the previous 12 years) and the short duration of these windy periods (between 30 min and 5 h as a mean). Parallel to this, a large number of no wind registrations (125-250 h/month as a mean) were observed during this period. A similar thermal stratification, of lesser amplitude, associated with comparable meteorological conditions was also observed in 1997. The hypothesis that this summer 1999 temperature anomaly could constitute a partial explanation for the recorded massive mortality is discussed.

[Toxic effect of four heavy metals on the growth of unicellular marine algae]. / Action toxique de quatre métaux lourds sur la croissance d'algues unicellulaires marines.

The growth inhibition of phytoplankton, resulting from Cd, Cu, Hg and Pb in sea water, has been studied on 18 monospecific strains belonging to different taxonomic groups. Data obtained pointed out that all species are very susceptible to Hg, and slightly to Pb. Effects of Cu and Cd vary with species, but Cu appears to be more toxic with dinoflagellates than with diatoms. In the authors' opinion, these results, obtained under laboratory conditions, cannot immediately be extended to the natural environment.