Marine Intertidal Gravel: Partially Exposed

Gravel beaches, like cobble beaches, are seldom one uniform grain size; most surveys report some sand mixed in with gravel.  Some partially exposed habitats in the Strait of Juan de Fuca have nearly uniform gravel, and have very low biological diversities.  Due to the instability of the substratum, the exposed habitats are relatively unproductive with virtually no plant life, and are occupied solely by mobile burrowing animals or epibenthic forms such as shrimp. Protected habitats with gravel intermixed with sand fall under “mixed-coarse.” Gulls sometimes forage in these habitats, and oystercatchers may nest in high intertidal gravel areas.

Diagnostic Species

Gammarid amphipods:  Paramoera mohri, and P. serrata n.sp., Traskorchestia traskiana.

Common Associates

Oligochaete and nemertean worms, and the crustaceans Allorchestes angusta and Exosphaeroma spp. are the only other infauna.  Beach seines contain Crangon spp, Cancer magister and C. productus, Archaeomysis spp. A variety of fish use these beaches and the areas just offshore:  shiner perch, juvenile tomcod and English sole, starry flounder, crescent gunnels, and sculpins (great, tidepool, padded, staghorn, and buffalo).  Surf smelt spawn here, and larvae of sand lance use these habitats.

Sites Surveyed

Outer Dungeness Spit, Twin Rivers (Straits), West Beach and Ebey’s Landing on Whidbey Island, Deadman Bay on San Juan Island.


Nyblade, 1979a,b; Cross et al., 1978; Webber, 1980; Long, 1983; C. Simenstad and C. Staude, unpubl. data.