The Zonation of Marine Algae at Piha, New Zealand, in Relation to the 
Tidal Factor' (Studies in Inter-tidal Zonation 2) * 2 
W. A. Beveridge and V. J. Chapman 3 
INTRODUCTION 
This paper forms part of an inquiry into 
the operation of tidal factors in determining 
littoral zonation, and provides a comparison 
with work performed on the east coast of the 
Auckland Province (unpublished). There is 
still considerable confusion concerning the 
terminology that should be used in these eco- 
logical investigations. One of us (Chapman, 
1947) has suggested that the time is now 
ripe for the application of ecological terms 
in the sense used by land workers. This view- 
point has been contested recently by Wo- 
rn ers ley (1947) but on grounds that scarcely 
seem adequate. In view of this confusion, 
however, it is still desirable to define the 
terms used, and in the present investigation 
they are as follows: 
The littoral region is regarded as all that 
part of the shore between highest wash and 
the lowest level of spring tides. This defini- 
tion is also adopted by Oliver (1923) and 
by Cranwell and Moore (1938). 
Formation is a unit of vegetation formed 
by the habitat and expressed by distinctive 
life forms (Tansley, 1944), e.g., the Lami- 
narian formation of Europe and the giant 
kelp formation of the north Pacific. (Owing 
to the small area studied formations have not 
been considered in this paper.) 
x This paper is a resume of work carried out by 
the first author for a Master of Science degree at 
Auckland University College, Auckland, and has 
been prepared for publication by the second author. 
2 For Studies in Inter-tidal Zonation 1, see Pa- 
cific Science 4(1): 63—68, 1950. 
3 Forest Officer in the Malayan Forest Service 
and Professor of Botany, Auckland University Col- 
lege, respectively. Manuscript received March 29, 
1949. 
Association is the largest unit of the plant 
formation dominated by more than one spe- 
cies and with at least some subordinate spe- 
cies, the dominants having the same ecologi- 
cal requirements. 
Consociation is a community characterised 
by a single major dominant. 
Society is a subordinate community within 
an association or consociation and character- 
ised by a locally dominant subsidiary species. 
Belt ( zone of some authors) is a horizon- 
tally extended association which may be con- 
tinuous round the coast, or which may be 
interrupted by another community, the pres- 
ence of which depends on slightly different 
local conditions. 
Aspect society is a seasonal community 
locally dominant. 
Clan is a small aggregation of subordinate 
species. 
Fasciation is a modification of the associa- 
tion in which a secondary species becomes a 
dominant or co-dominant. 
Exposure can mean one of two things — 
exposure to the air during low tide periods 
or exposure to strong wave action. These 
two different types of exposure will be desig- 
nated in the text by the terms air and wave 
exposure, respectively. 
In this paper the viewpoint is adopted that 
the biome of the rocky sea shore represents 
a physiographic climax, since it is dependent 
upon the tide rather than upon the climate. 
LOCALITY 
Piha is situated about 7 miles north of the 
Manukau Heads on the west coast of New 
Zealand, where there is exposure to the waves 
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