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PACIFIC SCIENCE, Vol. IV, July, 1950 
13. Splachnidium rugosum society 
Range: M.S.L. to L.W.N. 
A seasonal community that disappears in 
winter. 
14. Cladhymenia oblongifolia-Schizymenia 
sp. association 
Range: M.L.W.S. to E.L.W.S. 
The association occupies the sublittoral 
where there is a shallowing shore and a mod- 
erate surf. It is to be found from spring to 
autumn and it reaches its maximum devel- 
opment in summer. Champia novae-zelandiae 
and Stenogramme interrupta are common 
associates. 
15. Vidalia-Melanthalia-Pterocladia lucida 
association 
Range: M.L.W.S. to sublittoral. 
An association that occurs in long gullies 
below the Pachymenia belt. Vidalia colensoi 
is the dominant near the mouth but it is 
replaced by Melanthalia abscissa and Ptero- 
cladia near the head. 
16. Brackish water community 
Enteromorpha ramulosa 
Enieromorpha hulbosa 
Enteromorpha flexuosa 
Enteromorpha nana 
Bangia fusco-purpurea 
Calothrix sp. 
Rhizoclonium riparium 
The composition of this community varies 
from place to place. 
17. Seasonal communities 
Scytosiphon lomentarius forms an aspect 
society at L.W.N. during spring but the 
plants are very small. Colpomenia sinuosa, 
together with Myriogloia lindaueri, is also 
abundant in spring and early summer. Ilea 
( Phyllitis ) fascia is another casual occurring 
around L.W.N. during winter and spring. 
Stephenson (1939) in his work on the 
zonation of South African shores distin- 
guished three principal zones in the inter- 
tidal region: (a) Littorina zone; (b) bala- 
noid zone; (c) sublittoral fringe. 
It seems that this concept can be well ap- 
plied to the zonation at Piha. Melaraphe is 
closely allied to Littorina and the balanoid 
zone is well represented by the species of 
Chamaesipho and Elminius. The sublittoral 
fringe can be regarded as extending from 
M.L.W.S. to E.L.W.S. and is occupied by the 
V idalia-Melanthalia-Pterocladia, Cladhyme- 
nia— Schizymenia, Durvillea—Mytilus , and Gi- 
gartina associations according to the nature 
and degree of wave action. 
TIDAL MEASUREMENTS AND PROCEDURE 
As no tidal data were available for Piha 
it was necessary to erect a tide pole and to 
take a series of readings at high and low 
water. The tide pole was erected near Camel 
Rock in a sheltered area with its foundation 
at approximately E.L.W.S.T. Owing to the 
surf and swell, readings were restricted to calm 
days. When the Piha scale had been cor- 
related with the data of the Auckland Har- 
bour Board (A.H.B.) charts, the complete 
records of the Auckland tides could be used 
to calculate the tidal phenomena at different 
levels, especially those that appeared to be 
highly significant in respect of zonation. 
The correlation data showed that on an 
average both high and low water records at 
Piha on the arbitrary tide pole scale were 0.98 
(= 1 foot) foot below the corresponding 
levels at Auckland (A.H.B. datum). This 
indicates also that the tidal range at Piha is 
approximately the same as that at Auckland 
(10 feet at average spring tides). 
The various fundamental tide levels were 
calculated using the actual Auckland mari- 
grams for 1945. M.H.S.W., M.L.W.S., 
M.H.W.N., and M.L.W.N. were obtained by 
averaging the highest and lowest tides, re- 
spectively. The means of the equinoctial high 
and low spring tides gave E.H.W.S.T. and 
E.L.W.S.T., respectively. Similarly the figures 
