96 The Queensland Naturalist November, 1940 
soever, while that of Goat Island is relatively quite rich 
and varied, consisting of 64 species in six communities. 
The various communities observed may be arranged 
as follows : — 
1. MARINE VEGETATION, with four communi- 
ties — 
A. The Z ostera nana — Halophila ovalis community. 
This community is developed on the muddy area off Bird 
Island at about and just below low water mark. The pri- 
mary condition for the establishment of the community 
appears to be a certain amount of mud in the substrate. 
Once established, the plants (both of which possess creep- 
ing rhizomes) stabilise the substrate and gradually raise 
it by collecting further mud, until eventually mangroves 
( Avicennia officinalis) establish themselves. This estab- 
lishment of mangroves is not realised on Bird Island, but 
the succession is plainly to be seen near Myora on Strad- 
broke Island. 
B. A mixed Algal community on the reef near the 
above but somewhat to the south thereof, from just above 
low water mark to at least 2 feet below. This is where 
the majority of species was collected. Pkaeophyceae pre- 
dominate in species and individuals. The species observed 
were Cystophylluni micricatum , Dictyota clichotoma , 
Sargassum sp. (subgen. Eusargassum), and Padina 
pavonia (Phaeophyceae) ; C aider pa racemosa (fairly 
common) and Halimeda macroloba (Chlorophyceae) 
Polysiphonia sp. (epiphytic on Dictyota) and Laurencin 
sp. (Rliodophyceae). 
G. An Algal community associated with living coral 
to the west of the south end of Goat Island. Cystophylluni 
muricatum and Padina pavonia are almost the sole mem- 
bers of this community and are very numerous in indivi- 
duals. Halimeda is occasional. Lithothamnion sp. occurs 
here and between this and the former community. 
D. Between the two islands, at slightly above low 
water mark, there is a community of numerous individuals 
belonging to two species. One of these, belonging to an 
unidentified genus of the Bhodophyceae , is slightly 
calcified and brittle, and invariably occurs attached to the 
shell of a certain living lamellibranch ( Mytilus sp.). The 
other, Blossevillea sp. {Phaeophyceae) , though occasionally 
found attached to this shell, is most often attached to 
coralline fragments. 
