THE DEPTH DISTRIBUTION OF RECENT MARINE OSTRACODA FROM THE SOUTHERN STRAIT OF MAGELLAN

From 16 sediment samples collected from the Chilean part of the Strait of Magellan, 2338 Ostracoda were recovered. These represent 61 specie s belonging to 45 genera and 16 families. Previous work in the Tierra del Fuego Province has shown the faunas to be highly endemic, resultin g from the relative isolation of the region and its particular climati c and oceanographical characteristics. The fauna of the Strait of Mage llan is similar to those previously described with one notable excepti on: the occurrence of deep-water, psychrospheric species at shallow de pths. Species of Bradleya, Agrenocythere, Poseidonamicus, Bythoceratin a, and Legitimocythere, usually recorded from bathyal to abyssal depth s of more than 1000 m, were found together in the same samples with a typical, shelf fauna. Such unusual depth distribution of psychrospheri c species may have resulted from the extremely cold temperature and lo w salinity of the water in the southern Strait of Magellan, coupled wi th the upwelling of cold, deep water masses.