The Fauna of the Algal Zone of the Swan River Estuary. 55 
4— THE FAUNA OF THE ALGAL ZONE OF THE 
SWAN RIVER ESTUARY. 
A PRELIMINARY SURVEY OF FRESHWATER BAY 
WITH NOTES ON THE CHIEF SPECIES. 
By 
J. M. Thomson, B.Sc., 
Hackett Research Scholar, University of Western Australia. 
Read 14th March, 1944. 
INTRODUCTION. 
The primary aims of this investigation were, firstly to learn the nature 
of the fauna inhabiting’ the algae, and secondly to follow the seasonal change 
in this fauna. From the data gathered various other observations have been 
made, such as the species density and population density of various algal 
species. 
Adequate ecological study requires a team of workers. A lone worker 
can hope only to make a general survey of the situation. Especially is this 
so when, besides collecting and the laborious and time-expending work of 
separation it is necessaray to identify species which are quite unfamiliar. 
As a result a number of species have only been identified as far as the genus, 
and some remain assigned only to the family. However, all those which can 
be described as dominant have been specifically identified except for an 
immature Gammarid which occurred at times. 
Acknowledgment is due to Professor G. E. Nicholls and to Dr. A. G. 
Nicholls for advice on literature and aid in other ways; and to Miss A. M. 
Baird and Mr. G. G. Smith, of the Botany Department for aid in identifica- 
tion of the higher algae. 
Collections were made somewhat irregularly, due either to the number 
of species requiring identification, or to other unavoidable circumstances. 
PRELIMINARY SURVEY OF FRESHWATER BAY. 
Physiography. 
Accounts of the Swan River estuary have been given by Somerville 
(1919) and by Aurousseau and Budge (1921). It need only be added that 
the main area of investigation was situated in Freshwater Bay at the part 
marked “C” in the map given by Somerville (op. cit. p. 17). The rocky 
bottom under the high cliffs at this point provides an admirable substratum 
for the algae. 
Physical Conditions. 
The Swan estuary differs in type from those upon which a fairly 
abundant literature exists (Alexander 1936; Bassindale 1938; Milne 1940, 
etc.). Along the coast in this region there is practically no tide; as a result 
there is no daily alteration of fresh and salt water in the estuary, nor are 
there areas of mudflats daily exposed as is the case in tidal estuaries. There 
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