Some Experiments with Fucus to Determine the 

 Factors Controlling its Vertical Distribution 



Floyd W. Gail 

 University of Idaho, Moscow 



Even a casual observation convinces one that Fucus is rarely found 

 below the low-tide line, certainly rarely if ever reaches the high-tide line, 

 and occupies rather a small portion of the area between its upper and 

 lower limits which one would expect it to cover. During the summer of 

 1918, at the Puget Sound Biological Station, the writer attempted to de- 

 termine some of the factors governing the local distribution of Fucus 

 evanescens Agardh. This is by far the most common species of the re- 

 gion, in fact, except in rare cases, the only one in the immediate locality. 



Studies were made on San Juan Island, Brown Island, some of the 

 Sucia Islands and Turn Rock. My observations showed that the lower 

 and upper limits of the Fucus zone were very variable on exposures in 

 different directions. The lower limit is higher and the upper limit lower 

 on north, northwest and northeast exposures. Thus the zone is compara- 

 tively narrow, and indeed is usually wanting on high and steep north 

 shores. The upper limit of the Fucus zone on the south, southeast, east 

 and southwest exposures is often almost a straight line parallel to the 

 high-tide line. The upper limit of barnacles was taken as the high-tide 

 line. The Fucus zone on these exposures often almost reaches this upper 

 limit. The lower limit of the zone on south exposures is usually about the 

 zero tide-line. Some Fucus is found below this, but only a little, and only 

 near that line. 



Turn Rock is an oblong reef composed entirely of rock and is about 

 40 by 100 meters at a -1.1 tide. A ridge about 6 meters above a —1.1 

 tide extends from the southeast to the northwest. According to the water 

 marks on the concrete base of the lighthouse, the high-tide line was one 

 meter above its highest point. The lower limit of the Fucus zone was % 

 meters above this —1.1 tide. There were only a few scattered plants at 

 the low-tide line, and below this practically none. The northwest half 

 of the rock had much less Fucus growing upon it than the southeast half. 

 The north third of the rock was practically destitute of this plant. The 

 Fucus that did grow on the northwest half was just over the top of the 

 ridge and on the south and southeast sides of the higher projections. 



These observations led the writer to measure the vertical space oc- 

 cupied by the Fucus zone on various shores. Measurements were made 

 for some distance north and south of the Station laboratory and also on 

 the southeast and northeast exposures about Point Caution. The shores 



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