Marine Intertidal Rock: Semi-Protected and Protected

Many areas in the northern Puget Trough receive neither oceanic swell nor extensive wind fetch, but retain their rocky character due to steepness of the shore or currents that sweep away most sediment. Examples are the inside waters of the San Juan Islands. Siltation, desiccation, and temperature stresses all take their toll on rocky-shore organisms in these areas, and diversity is correspondingly relatively low.

Diagnostic Species

The brown rockweed Fucus gardneri (= distichus), the red algae Porphyra spp. and Mastocarpus papillatus, the snails Littorina spp. (all high zones), and the whelk Nucella lamello.

Common Associates

The brown algae Fucus spiralis and Leathesia difformis, the reds Endocladia muricata, Iridaea splendens, the barnacles Semibalanus cariosus, Balanus glandula, and Chthamalus dalli, limpets, Katharina tunicata, the mussel Mytilus edulis, the periwinkle Lacuna spp., the seastar Leptasterias hexactis. Coralline algae are absent except in pools.  Fish resemble those in more exposed areas.

Surveyed Sites

Variety of sites in the San Juan Islands.


Smith and Webber, 1978; Mauzey, 1965 and 1967; Nyblade, 1979a; Houghton, 1973; Muenscher, 1916; Dethier pers. obs.