GO 
J. M. Thomson. 
Analysis of Collections. 
Appended at the end of this paper is a table (Table 1) setting out the 
monthly mean results. The quantities are expressed, as explained under 
“ Estimation of population/’ in terms of the number of animals per amount 
of algae displacing 100 c.c. of water. The total number of animals in any 
column then represents the population density per 100 c.c. for that type 
of algae. 
From the table it is evident that no species of alga was present- during 
all 10 months, although Enteromorpha was completely absent only in 
August. The following list shows the species of alga present from month 
to month and their relative abundance. 
(a) — abundant; (b) — well distributed; (c) — isolated stands. 
March — Cystopliyllum (a), Enteromorpha (a), Ulva (b). 
April — Cystopliyllum (a), Enteromorpha (a). 
May — Cystopliyllum (a), Enteromorpha (a). 
June — Cystopliyllum (b), Enteromorpha (a), Ulva (a). 
July — CystophyUum (c), Enteromorpha (b), Ulva (a), Chaetomorplia 
(c). 
August — Ulva (a), Chaetomorplia (b). 
September — Cystopliyllum (c), Enteromorpha (b), Cladophora (c). 
October — Enteromorpha (c), Cladophora (c), Ectocarpus (a). 
November — Enteromorpha (a), Cladophora (a), Ectocarpus (a). 
December — Enteromorpha (c), Cladophora (a), Ectocarpus (c), Ulva 
(e). 
Animal Distribution. 
From March to September CystophyUum muricatum provided the most 
favoured habitat for the algal fauna. From October to December Ectocarpus 
conf ervoides was favoured as long as it was thriving, but in December when 
it was decaying Cladophora penicillata became the chief habitat. Ulva at all 
times provided the least utilised substratum, being most densely inhabited 
in March when the fronds were of great size and much convoluted. There 
can be little doubt but that it is the character of the plant that causes the 
differences rather than environmental conditions. It is noticeable that 
Cystopliyllum muricatum, Cladophora penicillata and Ectocarpus c'onf ervoides 
provided the best substrata for the colonial diatoms. 
Seasonal Changes. 
Almost assuredly associated with the change in salinity is the change 
in the species making up the algal communities. No species was recorded 
in all ten months. Tanais cavolinii, while absent only in October, was repre- 
