PROTOZOAN COMMUNITIES IN CHALK STREAMS

The population densities of the main,groups of protozoa in the principal protozoan habitats in a chalk stream were surveyed over period of a year or more. These data were used to estimate the mean biomass and annual production of flagellates, ciliates and amoebae in the different habitats, and to make comparisons with the estimated production of macrophytes, algae and bacteria in the stream. Protozoa epiphytic on macrophytes accounted for about 30% and protozoa in soft sediments about 45% of the overall protozoan production. Lesser amounts were attributed to protozoa in stony sediments, those epizoic on insects and crustaceans, and least to protozoa in the water column. Ciliates contributed about 75% of the protozoan production, flagellates 15% and amoebae 10%. The total annual production by protozoa was estimated to be approximately 16 g dry wt m-2 stream floor, which was equal to about 20% of the bacterial and about 1% of the algal production. However, protozoan production was of the same order of magnitude as that by Gammarus, and more than the production by fish.