A Study of the Algal Associations of San Juan Island 



Walter L. C. Muenscher, 

 University of Nebraska, Lincoln. 



The botanists who have visited the San Juan Islands have been 

 impressed with the large number of species and individuals of seaweeds 

 which inhabit the rocky shores. So far little has been done on the 

 distribution of the species of marine algae which are common on the 

 shores of this region. Rigg (13) in his report on kelps includes a 

 map showing the distribution of kelp beds composed of Nereocystis and 

 Macrocystis in Puget Sound. 



It is not the intention of the writer to attempt any new classifica- 

 tion of algal zones and associations in this paper. The botanist who 

 comes to this region for the first time is rather dismayed at the problem 

 which confronts him — that of learning the habitats and distribution of 

 t^ many species of marine algae found here. If the discussions and 

 charts in this brief paper regarding the algal associations of San Juan 

 Island prove to be of any value in helping visiting botanists to get 

 more quickly an idea of the composition and distribution of the algal 

 flora of this island, the writer will feel amply repaid for his efforts. 



The San Juan archipelago consists of over 120 islands, besides 

 numerous rocks and reefs which are uncovered at low tide. It lies in 

 Puget Sound in the northwestern jjart of the State of Washington. 

 It is separated from the mainland on the north by Georgia Strait, and 

 on the east by Rosario Strait. Between the southern boundary and the 

 Olympic Peninsula lies the Strait of Juan de Fuca, while the western 

 shores and Vancouver Island are separated by Haro Strait. 



San Juan Island is located in the southwestern portion of the group. 

 Its position is latitude i8° 30' X., longitude 123° 5' W. In general 

 this island is similar to the others, but conditions for marine shore life 

 are more varied on this than on any other single island, because its 

 southwest coast is exposed to the tidal currents wliich come directly 

 from the Pacific Ocean. The algal flora is therefore much different 

 from that of the more protected inner shores. It is the second largest 

 island of the group. Its greatest length from north to south is about 

 15 miles, while its greatest width from cast to west is about 9 miles. 



The shore line of San Juan Island is quite irregular. Its numerous 

 indentations and points make it about 75 miles in length, not consider- 



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