The Abundance of Different Peritrich Ciliates on Stone Surfaces in Contrasting Lowland Streams Throughout the Year

Pentrich ciliates attached to small stones from the beds of two streams, one large with hard water, the other small with soft water, were enumerated throughout an annual cycle. Throughout the year, Platycola was the dominant peritrich in both streams, except for a brief period during the spring when Vorticella and Carchesium predominated. Vorticella reached peak levels of 89 ciliates cm 2 of stone surface, and up to 102 Platycola per cm 2 of stone surface were found. Mean volumes of samples of the main species were calculated, and used to estimate the standing stock biomasses. using a standard value of dry weight per unit volume. Published values of the growth rates of representatives of the main genera were used to estimate production values, which totalled about 6.5 g dry weight of peritrich cytoplasm/m 2 of stream bed per annum in the large stream (mean annual density = 8.3 peritrichs/cm 2 of stone surface), and 33 g dry weight/m 2 of stream bed per annum in the small stream (mean annual density = 47 peritrichs/cm 2 of stone surface). Food supply, temperature and predation were the primary factors determining peritrich abundance