Marine, intertidal, boulder, semi-protected, eulittoral

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, where there is not enough freshwater input for sites to be categorized as Estuarine. Siltation, desiccation, and temperature stresses all take their toll on rocky-shore organisms in these areas. Communities on tops and sides of boulders are similar to those on bedrock, but the spaces on the lower edges and beneath boulders provide additional spatial complexity; these microhabitats tend to be shadier (and thus cooler) and less exposed to wave disturbance. Boulder habitats thus often have very high species diversity.