Abundance of terrestrial gymnamoebae at a northeastern U. S. site: a four-year study, including the El Niño winter of 1997-1998.

The abundance, sizes, and when appropriate, diversity of gymnamoebae were documented at approximately monthly intervals for four years (1995-1998) at a grassy, terrestrial site slightly upslope from a freshwater pond. Soil samples were analyzed for viable gymnamoebae using a standard laboratory culturing protocol. The mean density of gymnamoebae based on the total data set was ca. 1,600/g (s.e.+/-190). Minimum densities of gymnamoebae (156/g) occurred in January 1995, and a maximum for the sampling period (5,838/g) occurred in July 1997, when a rainy period followed an extended period of drought. Among the environmental variables monitored (precipitation, soil moisture, organic content, and temperature) only precipitation correlated significantly with abundance of gymnamoebae (r = 0.34, p = 0.02). During the mild, moist El Niño winter of 1997-1998, a larger than usual number of gymnamoebae was recorded at the site (approximately 3,800/g) compared to a mean density of approximately 900/g for comparable periods in preceding years. The mean sizes were also larger. Since gymnamoebae are increasingly recognized as major members of soil microbial communities enhancing soil fertility through nutrient mineralization, it is important to document environmental variables that influence their abundance and activity in terrestrial ecosystems.