Marine Intertidal Cobble: Partially Exposed

Cobble habitats are relatively unstable environments, suffering frequent overturning by waves, and also are hybrid environments because cobbles are virtually always mixed with, or overlie, other substrata. Beaches visually dominated by cobbles, rather than being a clear mix of substrate types, are put into this category. However, all the cobble beaches censused had underlying sand. The organisms characteristic of this habitat include two types:  epibiota — the plants and animals living on or hiding just under the cobbles, and infauna — the animals living in the sand or other substrata under the cobbles.  Only areas exposed to moderate wave action are placed in the “cobble” category, since more exposed areas tend toward pure sand, and more protected areas tend toward “mixed-coarse” substrates where the cobbles are not the dominant feature.  Defining diagnostic species for this habitat type is difficult because species composition varies dramatically with degree of exposure, amount of silt in the sand, slope of the beach, etc.

Diagnostic Species

Littorina spp., Hemigrapsus nudus, Macoma inquinata, Mysella tumida.

Common Associates

The alga Mastocarpus papillatus, barnacles (especially Balanus glandula and Chthamalus dalli), the isopods Exosphaeroma spp., the mussel Mytilus edulis, the clams Protothaca staminea, Macoma balthica, and Transennella tantilla; cirratulid polychaetes, Cancer productus and porcelain crabs (Petrolisthes spp.), the seastar Leptasterias hexactis, and the brittle star Amphipholis squamata.  Beach seines at one site produced quantities of Pandalus danae, Crangon spp., and Cancer magister.  Low zones often have finer substrata and may contain ghost shrimp or mud shrimp.  Herring spawn on seaweeds on some cobble beaches.  Tidepool, calico, and mosshead sculpins, northern clingfish, and penpoint and high cockscomb gunnels use these habitats.

Sites Surveyed

Partridge Point (Whidbey Island), North Beach (Quimper Peninsula), Morse Creek and Slip Point (Strait of Juan de Fuca).


Long, 1983; Webber, 1980; Nyblade, 1979a,b; Smith and Webber, 1978; Webber, 1989.