This alga is common in spring and summer (March through September) as an epiphyte on Odonthalia (bottom picture) and Rhodomela (top picture).  Typically found in mid to low intertidal habitat.  This species has been located in northern Japan and along the Pacific coast from the Bering Sea to Northern Mexico.  Usually, from north to central California, Soranthera is found on Rhodomela and from central California to Alaska this alga is found on Odonthalia.  This is the general rule for the epiphytic associations, but it is possible to find it growing on the other host plant in any particular area. (Gabrielson, 2006) 

Locations on San Juan Island: Dead Mans Bay, Rueben Tarte, Cattle Point, as well as others

Pictures: photographed at Friday Habor Labs Herbarium

Gabrielson, Paul W., Widdowson, Thomas B., Lindstrom, Sandra C.. Keys to the Seaweeds and Sea grasses of Southeast Alaska, British Columbia, Washington and Oregon.  July 2006.