Abstract. The lethal concentration of cadmium was determined for the mysid Leptomysis lingvura G.O. Sars, a Mediterranean species from surface coastal waters, and the effect of sublethal doses on respiration, ammonia excretion, and feeding efficiency at different temperatures, and on activities of 19 hydrolases was tested. Experiments were carried out on individuals collected in spring 1987 near Marseille. At 18 °C, respiration rate was significantly affected only by concentrations > 0.05 mg Cd 1-1. At 0.1 mg Cd 1-1, respiration rate was more significantly depressed at 20 °C than at 10 °C. There was a concomitant decrease in the Qlo rate (by 23 to 59%, according to the particular experiment), indicating a strong synergistic effect of temperature. Ammonia excretion was likewise affected by cadmium, also with a concomitant decrease in the Qlo rate (by 34%). Daily faecal pellet production was maximum at 18 °C; it was inhibited by cadmium at temperatures between 14 and 20 °C, and enhanced at extreme temperatures (10 and 22 °C). The assimilation efficiency of contaminated individuals was reduced by 9%. These decreases in faecal pellet production and assimilation efficiency reflect a significant decrease in energy (by about 43%) which could rapidly lead to an unbalanced energy budget with a consecutive lowering of the reproductive potential. Generally, hydrolase activities usually increased initially in the presence of 0.2rag Cd1-1, but after 48 h they declined, reaching very low values at 72 h. Most physiological processes are therefore affected by exposure to cadmium and the unbalanced energy budget arises from the inability to utilize environmental food. These results are consistent with the literature data on cadmium contamination in marine organisms. Physiological and biochemical changes appear to be very informative in studies of in vitro sublethal effects ofmicropollutants and in situ environmental modifications.

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Replacement o~ Sphaeroma serratum by S. hookeri in Etang de Berre by means o/its desalincttionThe inflow of the river Durance into the Etang de Berre has resulted in a great change in hydrological conditions. Air photographs of this fresh-water influx and the rapid decrease in salinity explain a most important change in ecological factors. Salinity values are about 9 to t3~ The observed variations are caused by water flow and meteorological conditions, especially wind. Populations of the genus Sphaeroma in the Etang de Berre were notably affected by the decrease in salinity. Sphaeroma serratum has completely disappeared and S. hookeri has taken its place. This substitution of species is not due to interspecific competition, since S. hookeri has moved into the habitats which S. serratum has left. This change of milieu observed in the Etang de Berre Iepresents a remarkable natural experiment, in which sMinity separates 2 distinct ecological niches.

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