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PACIFIC SCIENCE, Vol. IV, October, 1950 
Nearly all of the subordinate algal species 
are epiphytic, chiefly because of the almost 
continuous covering of the substrate by the 
coralline turf, and most of them vary season- 
ally in abundance. 
Caulerpa Clan 
Within the limits of the above association, 
Caulerpa sedoides grows in isolated, cushion- 
like clumps between M.L.W.N. and M.L.W.S. 
The plant mass is so compact that other 
species are generally excluded, and hence the 
community is given the rank of clan (see 
p. 35 6). 
6. Encrusting Coralline Association 
Vertical range: 1.7-0. 2 feet. Between 
M.L.W.S. and 0.4 feet below E.L.W.S. 
Exposure: 3-0.2 per cent. 
Corallina officinalis (basal portion) (d) 
Peysonelia atropurpurea (f) 
Laurencia thyrsifera (o) 
Elminius modestus (o) 
Melobesia sp. (d) 
Acrosorium decumbens (o) 
Chamaesipho columna (o) 
On most steep rock faces which descend 
below low water mark, a pink band of en- 
crusting algae separates the Corallina — Hor- 
mosira association from that dominated by 
species of Carp op by llum and Ecklonia. The 
most prevalent alga here is the basal, encrust- 
ing portion of Corallina officinalis. Growing 
with it are round or oval crusts of a species 
of Melobesia, which will readily colonize 
other surfaces besides rock, including shells 
of molluscs, and even smooth pieces of glass. 
Intermixed with these species is a darker red, 
hard crust with a slimy exterior, which ap- 
pears to be Peysonelia atropurpurea. In shaded 
crevices, the delicate fronds of Acrosorium 
decumbens are sometimes to be found. 
Carpophyllum and Ecklonia have their 
average upper limit (0.4 feet) in the Encrust- 
ing Coralline association. When growing at 
this level, holdfasts and stipes of the large 
brown algae may be exposed during a low 
spring tide, but the fronds usually escape 
desiccation by trailing in the water below. 
7. Mytilus — Attached Algae Community 
Vertical range: 0.7-0.2 feet. From E.L. 
W.S. to 0.4 feet below that level. 
Exposure: 0.5-0.0 per cent. 
Mytilus canaliculus (d) 
Caulacanthus spinellus (Id) 
Elminius modestus (a) 
Corallina officinalis (d) 
Ulva lactuca (1) 
This community, which is of doubtful eco- 
logical status, is present locally where wave 
action is greater than usual for such a shel- 
tered locality. It occurs at the extreme sea- 
ward end of St. Leonard’s Point, both on the 
concrete sewer and on the rock ledges adja- 
cent. During periods of exposure by the tide 
it is kept moist by surge from the constant 
swell or by spray if the wind is onshore. Un- 
der optimum conditions the principal dom- 
inant, Mytilus canaliculus, constitutes a closed 
community in which other members are 
forced to live as epiphytes on its shells. 
Elminius modestus is enabled to widen its 
vertical distribution in the inter-tidal region 
by colonizing the mussel shells. 
Mytilus dominates in one other area — on 
a group of rocks outcropping from the sub- 
marine continuation of Narrow Neck Reef 
about 500 yards from the shore and 300 yards 
from the end of the Main Reef. Even on a 
calm day there is a considerable swell round 
these rocks. Associated with Mytilus here are 
dense clumps of Ulva lactuca, which does not 
occur on the Main Reef. 
Sublittoral Brown Kelp Formation 
8. Carpophyllum — Ecklonia Association 
Vertical range: 0.4 feet- From E.L.W.S. 
to below the reach of all tides. 
Exposure: 0. 3-0.0 per cent. 
Carpophyllum maschalocarpum (d) 
Carpophyllum plumosum (d) 
Ecklonia radiata (d) 
