A TESTATE RHIZOPOD ASSEMBLAGE IN AN EXTREME ENVIRONMENT: THE ANTARCTIC PERMANENTLY ICE-COVERED LAKE HOARE (TAYLOR VALLEY)

The McMurdo Dry Valleys comprise the largest relatively ice-free area in Antarctica and are characterized by low precipitation rates. Perennial ice cover on the dry valley lakes decreases the amount of solar radiation reaching the water column, thereby reducing the interaction between the atmosphere and the water column. However, the ice partly shelters the lake ecosystems from the harsh Antarctic climate. Two cores, collected from Lake Hoare in the Taylor Valley in 1995, contained testate rhizopods (mostly Arcella ) that have only chitinous organic tests with no agglutinated material, unlike other testate rhizopods that use detrital material to build a test. Additionally, a limited number of possible ostracod carapaces and possible rotifer resting-stage remains were present. The testate rhizopod concentration is generally higher in layers containing abundant bacterial/algal-mat fragments. This reflects the local sedimentation pattern in which layers of alternating mat growth and sediment accumulation on the ice surface subsequently fall to the lake bottom.