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The Ecology of the Attached Diatoms and Other Algae in a Small Stony Stream

Barbara Douglas
Journal of Ecology
Vol. 46, No. 2 (Jul., 1958), pp. 295-322
DOI: 10.2307/2257397
Stable URL: http://www.jstor.org/stable/2257397
Page Count: 31
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The Ecology of the Attached Diatoms and Other Algae in a Small Stony Stream
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Abstract

Methods are described for estimating populations of attached algae, particularly diatoms, on stones, rock and bryophytes in a stream. The errors of these methods are considered. Populations at eleven stations in a small stony stream were followed for four years by periodic sampling. Standard chemical analyses; temperature measurements at the sampling stations; total light in the open, and the approximate shading at each station; daily rainfall records; and comparisons of the fauna at two stones stations, are included. The distribution and the factors controlling the periodicity of Achnanthes species group are given in detail. Populations reached several million cells per sq. cm. on the permanent rock, and several hundred thousand on the stones. High populations developed at all the rock and moss stations, but only the lower two stones stations. Poor growth in the upper reaches may be due to a peaty deposit on the substratum. An increase down the stream of the stones populations may be due to the washing-off of cells in the upper reaches and their deposition lower down. Populations on the stones and rock increased at all times of the year. There is no evidence of differences in light intensity or temperature having any effect, except possibly on the populations on the moss. Stones populations were sharply reduced by floods in the stream, rock populations to a less extent, and epiphytic populations only with very severe flooding. In high-water periods stones populations remain low owing mainly to the instability of the substratum, and rock populations increased. In low-water periods stones populations increased; rock populations declined, sometimes after an initial increase. Severe drought caused a stones population to decline also. Epiphytic populations remained fairly steady, apart from increases in late spring and early summer. A negative correlation, suggesting a grazing effect, was found between the populations of Achnanthes and the larvae of the caddis Agapetus fuscipes at the lower two stones stations. Similar population changes were shown by Gomphonema and Synedra species groups, although their populations were lower. Eunotia pectinalis var. minor and Cocconeis placentula were mainly epiphytic, the latter not growing in the upper zone of the stream. Other diatom species which formed small growths, or were occasionally present, are mentioned. The principal diatom species were unable to withstand desiccation. Certain blue-green and red algae also formed considerable growths.

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