Studies in the Ecology of Rivers: IV. Observations on the Growth and Distribution of the Sessile Algae in the River Hull, Yorkshire

Abstract

INTRODUCTION THE algae which inhabit natural waters may be conveniently studied as two separate groups. The first group consists of those which are suspended in the water and usually termed plankton: the second group of those which are growing on the bottom or on any submerged objects such as stones, rocks, living plants or dead bodies. This second group has been variously called benthos, the littoral algae or the sessile algae. Plankton has been extensively studied; in the sea where it is all-important, and in lakes, reservoirs and small ponds. Little attention however has been paid to it in moving waters and quantitative data is very sparse. Still less information is available about the growth and distribution of the bottom-living and shore living algae. Geitler (1927) and Fritsch (1929) studied the algae on the bed of the small streams in Austria and Devon respectively but in neither case were quantitative data presented. In 1932 the view was put forward (Butcher, 1932 b) that as far as plankton and benthos in small shallow rivers were concerned, the plankton represented a pale image of the benthos from which it was almost entirely derived. Additional results in the river Tees (1937) and the Thames (Rice, 1938) support this view though, on the other hand, Southern & Gardiner (1938) have shown that the plankton of the Shannon approaches to a certain extent the plankton of the lakes in the same watershed but even in the figures these authors give, some organisms clearly derived from bottom growths are present. This type of limnetic plankton in moving waters is apparently rare. In most cases water comes out of a lake as a stream in which the flow is obvious and the limnetic organisms are immediately destroyed. In some cases they are filtered out by the tufts of river-plants (1937) and in other instances they are probably pounded to death and their place is taken by algae derived from the river bed (Butcher et al. 1937). Conversely it has been found (Metropolitan Water Board, 1938) that the plankton of a large reservoir consists of species totally different from and unrelated to those in the supply water derived from the river Thames. With all this evidence of the secondary role played by the plankton and the importance of the bottom-living or sessile algae in the rivers of the type usually found in Britain, it is natural that where studies of the flora and fauna have been carried out, work has been concentrated on the sessile algae and the plankton has been ignored.