An ecological study of Pozos Colorados marine brine was carried out between January an August 1987. Although the two sampled stations were greatly different to each other in genera the dynamics of the ecosystem were apparently controlled by salinity, which varied between 7 and 341 °/oo; its increase, accompanied by a decrease of the water level, possibly generated temperature increament and a decrease of the dissolved oxygen, ranging between 26,3 an 41 °C for the first and between 0 and 5,4 mg/l for the latter. Although the average pH wa neutral (7,5), this reductive environment, also characterized by the abundance of organi matter, ocassionaily generated a slight acidity (6,7). The net primary production was negative i most cases, as a result of an intense respiratory activity. Therefore, the system behaved a heterotrophic, using organic matter as subsidiary energy. The species dynamics was possibl determined by rain and ionic change relations, showing a succesion dominated initially b benthic cyanophites and Dunaliella viridis; an increase in salinity was followed by the appear ance of Dunaliella salina, which dominated in high salinities, before the total dominance of red and pink bacteria began.