Inter-tidal Zonation — BEVERIDGE and CHAPMAN 
193 
Fig. 4. Algal zonation in a gully to the west of 
Lion Rock. At the top there is a well-marked 
zone of Gigartina alveata, below a belt of Pachy- 
menia himantophora and below that Gigartina 
tnarginifera. 
menu, flourishing especially on the flat tops 
of boulders in strong surge. 
9. Durvillea-Mytilus association 
Range: E.(H).L.W.N. to E.L.W.S. 
Durvillea antarctica (d) 
Mytilus canaliculus (d) 
Gigartina tnarginifera (1) 
The association occurs in the form of con- 
sociations dominated either by Durvillea or 
by Mytilus , because the two species appear 
to be antagonistic to each other. The upper 
limit of the Durvillea is clearly defined but 
the lower plants seem to thin out gradually 
with decreasing power of the surf. The spe- 
cies is essentially surf loving, and in this re- 
spect is like Postelsia of California. The 
Mytilus consociation is better developed in 
the more sheltered areas. 
10. Mytilus-attached algae association 
Range: M.L.WN. to M.L.W.S. 
Mytilus canaliculus (d) 
Porphyra columbina (d) 
Ulva rigida (d) 
Viva linza (d) 
Scytothamnus australis (d) 
Gigartina atropurpurea ( d ) 
Gigartina alveata (o) 
Splachnidium rugosum (o) 
Laurencia sp. (o) 
Corallina sp. (o) 
Centroceras clavulatum (o) 
Glossophora kunthii (o) 
The association is found on the shallowing 
floors of small caves, on flat shelves, and on 
boulders in moderately sheltered areas. The 
attached algae form colonies on the Mytilus, 
though both Viva and Porphyra are capable 
of colonising the bare rock. 
11. Gigartina association 
Range: M.L.W.N. to M.L.W.S. 
Gigartina atropurpurea (d) 
Gigartina marginifera (d) 
Mytilus canaliculus (o) 
Viva rigida (la) 
Laurencia gracilis (f) 
Champia novae-zelandiae 
Corallina spp. (1) 
Plocamium spp. (1) 
The association occurs in moderately shel- 
tered areas, G. marginifera tending to dom- 
inate seaward and G. atropurpurea shore- 
ward. Shifting sand constantly buries parts 
of the association temporarily and removes 
the plants by scour. On re-exposure to air 
Viva quickly recolonises the area but is re- 
placed later by the dominants. 
LOCAL COMMUNITIES OF THE 
MID-LITTORAL 
12. Nemastoma oligarthra society 
Range: M.H.W.N. to M.S.L. 
The Nemastoma society was noted but 
once in a large gully. It disappeared in 
winter. 
