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PACIFIC SCIENCE, Vol. IV, July, 1950 
Level and percentage of air exposure 
per month (Fig. 6) 
It will be noted that between + 7 and 
+ 10 feet there is an increase in air exposure 
in spring and autumn, this rise being most 
marked at the 10-foot level. 
Level and continuous air exposure 
and submergence 
This factor may operate either through the 
total period to which an organism is exposed 
or through the occurrence of an extensive 
period at a critical stage in development. Sig- 
nificant changes in the length of the max- 
imum periods occur at -f- 3 feet and +10 
feet. There is also a slight increase in the 
total air exposure above the 11 -foot level and 
percentage continuous (non-tidal) exposure per 
month. Lcnver. Relationship between level and 
percentage continuous (non-tidal) submergence 
per month. 
gence at high tides. Lower. Percentage monthly 
exposure at low tides. 
an increase in total submergence at + 3 feet. 
Level and percentage of continuous air expos- 
ure and submergence per month ( Fig. 7 ) 
There are significant changes in continuous 
air exposure at both the 9- and 10- foot levels. 
The short periods of continuous air exposure 
occurring in August and September at the 
9-foot level may also be important in deter- 
mining the upper limits of some of the more 
sensitive species. At the 2-foot level long 
submergences occur from February to May 
but toward winter there is a rapid decrease 
in length of submergence which may be of 
significance. 
Percentage of monthly submergences 
and exposures (Fig. 8) 
From the data given here it may be con- 
