56 
J. M. Thomson. 
is, however, a marked seasonal variation in salinity (Serventy 1938). In 
summer, conditions in the estuary are marine. In winter, the water is greatly 
diluted and after heavy rains becomes quite fresh at least In shallow water 
near the banks. This dilution is greatest during July and August. 
During part of the year there is a regular daily rise and fall in the 
waters of the estuary, generally of about four to six inches. This appears 
to be due, not so much to tidal influence, but to the regular alternation of 
land and sea breezes. An easterly (land) breeze drives the waters of the 
adjacent ocean away from land, depressing the level of waters along the 
coast and consequently in the drowned valley of the estuary. A westerly 
(sea) breeze piles water against the coast and raises the water level. If the 
westerly continues for several days, as may happen during a storm, the level 
of water is raised several feet. Similarly when an easterly continues for 
an abnormal period, the water level may drop a few feet and as a result 
expose some of the algal beds which otherwise are not out of water. 
The area under investigation is under direct illumination from the sun 
from early morning till late afternoon, when the high cliffs shut off the direct 
rays of the sun. 
No measurements of temperature were taken, but, as was to be expected, 
in depths of only a few inches the water was considerably warmer than in 
deeper water, if there had been practically no water movement for some 
time and the sun was particularly hot. 
The currents in the estuary are practically confined to the deeper 
channels. Shallow areas such as the one under consideration are more in- 
fluenced by the surface drift produced by winds. Though normally incon- 
siderable, waves of up to two feet may be raised during strong winds, thus 
laying the shallows open to some battering. 
There is always a considerable amount of organic matter and soil in 
the water, but usually the bottom can be seen at several feet depth. How- 
ever, after heavy rains greatly increased quantities of material occur sus- 
pended in the water and it may be impossible to see the bottom even at a 
depth of 1 ft. Gin. Photosynthesis in the algal zone must be considerably 
impeded during such periods. 
Algal Zone. 
The rock bottom on which the algae occurs is a ledge of shallow depth 
along the bank, extending outwards for a width of 7ft. to 16ft. Most of the 
algae occurs from surface level to a depth of 5ft., though occasionally 
patches were found at 7ft. 
Methods. 
The method of collection consisted simply of plucking the algae from 
the substratum and transferring to a collecting jar. In the case of larger 
algae, such as Cystophyllum muricatum it was sometimes necessary to cut- 
off only part of the stem or only branches. At first the transference of 
material was made under water with a control jar of water to ascertain 
whether there was any free-swimming population to influence results. Later 
trials, however, showed that no significant loss occurred if the algae were 
lifted out of the water and then transferred. As this method was more 
rapid and more easily accomplished it was adopted. 
