The Fauna of the Algal Zone of the Swan River Estuary. 67 
istics there can be little doubt that it is a Melita,. The generic distinctions 
.are in agreement with those given for Melita by Stebbing (1906) and by 
Barnard (1941). 
Leander intermedins Stimpson, 1860. 
Serventy (1938) states that he found Palaemonetes australis } Dakin 
(1915) only, in the Swan estuary. I am not aware whether any of his 
specimens came from Freshwater Bay, but he does mention taking some in 
Crawley Bay, some way upstream. The nature of Crawley Bay differs from 
that of the area investigated in being predominantly sandy with scattered 
pieces of rock and continuing out as a. shallow shelf much further than is 
the case in Freshwater Bay. All the specimens taken amongst the algae 
were Leander intermedins. Each specimen was dissected to make certain. In 
each case the mandible bore a distinct large palp, the absence of which 
distinguishes Palaemonetes from Leander. Besides those recorded in Table 1 
extra specimens were taken from the algal area. (Kemp (1925) gives an 
excellent key and descriptions.) All proved to be L. intermedins ; the specific 
■characters were definitely those of intermedius, not of the marine serenus. 
It was noted that a shrimp occurred on the shallow sandy portion of 
the bay just down-stream from the rock-algae area. Specimens of these 
were taken, and proved to lack a palp to the mandible and were identified 
as Palaemonetes australis. 
It seems then that both these shrimps occur in the estuary in different 
habitats, L. intermedins among the algae, and P. australis in the sandy 
shallows. Distribution : South Australia, Tasmania, Coekburn Sound. 
SUMMARY. 
The fauna occurring in six species of algae was investigated. The 
species of algae varied in abundance and none was present in all ten months 
of the survey. Some 52 species of animals were recorded as members of 
the algal community. These occurred in varying abundance at different 
times of the year. The maximum number of species occurring in any month 
was 33, the minimum six. Population density and species density are shown 
for each species of alga. Population density, species density, amount of 
diatoms present, and abundance of algae were all lowest in August - 
September. The dominant species in each month are listed. The nature of 
the species present changed as the salinity dropped during heavy winter 
rains. As summer returned the summer members of the fauna returned 
with the increasing salinity, Caprella spp. being the only species common in 
late summer collections which had not returned by December. It was found 
that the top four inches or so of the algae were not favoured, but most 
species were taken between four inches and two feet. A list of occasional 
intruders into the algal community is given. Added are ecologie and systematic 
notes on the chief species. A graph (text fig. 1) summarises the variation in 
population density. Besides the figures for each species of alga an estimated 
mean is given which is the average reading of the different algae present; 
at the time, their relative abundance being ignored except at the point A. 
The reading at this point represents the figure for Cladophora pencillata 
only since this was in vast abundance, whereas the other species recorded 
at this time were present in extremely small widely-scattered clumps. The 
reading for Cladophora thus gives a much more accurate picture of the 
algal fauna. 
