46 
PACIFIC SCIENCE, Vol. VI, January, 1952 
the basalt is often the indirect basis of other 
environmental variations. The scoria shores, 
the broken surfaces of which provide pockets 
of shelter, are likely ' to show a mosaic of 
climax and serai communities. 
General texture may be involved (Fig. 3). 
An unbroken surface favours Saxostrea glomer- 
ata. At lower levels, an unbroken surface 
favours Codium adhaerens and a broken one the 
Corallina-Hormosira association. The Carpo- 
phyllum-Ecklonia association requires a solid 
substrate for the attachment of the large 
dominants. Boulders on an exposed shore 
appear to favour a zonation of Scytothamnus 
australis^ Splachnidium rugosum, and Glosso- 
phora kunthii. 
Physical exposure appears to be reduced by 
a flat shore so that a habitat, such as the top 
of a lava flow, results in the development of 
the Hormosira hanksii consociation, while 
Saxostrea glomerata occurs on slopes. Further, 
Codium adhaerens tends to dominate on ver- 
tical surfaces (Fig. 3), while CoraUina officinalis 
and Hormosira hanksii are best developed on 
flatter shores. Again, vertical surfaces in the 
upper sublittoral bear Mytilus canalictdus, 
tunicates, and some Ecklonia in place of the 
usual Carpophyllum-Ecklonia association. 
Finally, differences in shade tolerance pro- 
duce some variations. Carpophyllum maschalo- 
carpum is reduced in shade, while Ecklonia is 
more tolerant. In the shade of the kelps, 
CoraUina officinalis is reduced to its basal fila- 
ments, while Aeodes nitidissima is eliminated. 
Codium adhaerens is favoured by shade to the 
extent of frequent dominance in the levels of 
the Corallina-Hormosira association on the 
southern sides of rocks. It is probable that 
the discoloration of sheltered waters by sedi- 
ment in suspension, with subsequent light 
reduction, operates in excluding at least some 
of the species associated with physical ex- 
posure. 
Tidally Controlled Variations. It must be 
noted that not only seasonal climatic con- 
ditions but also seasonal variations in tidal 
behaviour may be responsible for the fluctua- 
tions of some species. Thus the occurrence 
in the autumn of the maximum periods of 
continuous submergence of the lower littoral 
levels for the year may have been responsible 
for the establishment of Colpomenia sinuosa and 
the disappearance of Splachnidium rugosum in 
that season. Similarly, the spring maximum of 
the Enteromorpha bulhosa—Monostroma crepid- 
inum aspect might be associated with the fact 
that the maximum periods for the year of 
continuous emergence in the upper littoral 
occurred at that time. 
SUMMARY 
An attempt has been made to classify the 
communities of inter-tidal plants and animals 
at Rangitoto Island. The climax communities 
appear to fit into the general, basic, rocky- 
shore zonation for New Zealand. 
The causal factors in vertical zonation at 
Rangitoto, namely, those determining the 
upper and lower limits of species, have been 
related to tidal phenomena. Attention has 
been given to the behaviour relative to tide 
levels of Hormosira hanksii. The variables, 
which produce variations in the vertical limits 
of species and in species composition, have 
been sought in environmental factors other 
than tidal. 
REFERENCES 
Beveridge, A. E., and V. J. Chapman. 1950. 
The zonation of marine algae at Piha, New 
Zealand, in relation to the tidal factor. 
(Studies in inter-tidal zonation 2.) Pacific 
Sci. 4 (3): 188-201. 
Chapman, V. J. 1946. Marine algal ecology. 
Bot. Rep. 12 (10): 628-672. 
1950. The marine algal communities 
of Stanmore Bay, New Zealand. (Studies 
in inter-tidal zonation 1.) Pacific Sci. 4 (1): 
63 - 68 . 
Stephenson, T. A. 1939. The constitution of 
the inter-tidal fauna and flora of South 
Africa. Part I. Linn. Soc. London, Jour., 
Zool. 40: 
