Marine Intertidal Mixed-Fines: Semi-Protected and Protected

This habitat type (or its estuarine equivalent) occurs in most bays and harbors in the Pacific Northwest. Protection from waves allows finer sediments to accumulate, and the substratum is relatively stable.  The beaches tend to be accretional.  The mixed-fine sediments include sand and mud with patches of gravel (especially in the higher intertidal).  Few marine (but many estuarine) sites in this category have been surveyed.  Species are generally a mix of those found in sand and in mud habitats.  Birds and fish using these areas are described under the counterpart Estuarine habitat.  Drift algae and seagrass may be abundant.

Common Species

Zostera marina (low zones) and Z. japonica (higher), with the red alga Gracilaria pacifica, and green ulvoids on the beach surface in spring and summer. Commonly found are the clams Macoma nasuta and balthica, Tresus capax, Clinocardium nuttallii, and Cryptomya californica. In areas with some gravel, hard shell clams (Protothaca staminea, Saxidomus giganteus) are characteristic.  The phoronid worm Phoronopsis harmeri is very patchy in distribution.  Other organisms include the crabs Hemigrapsus oregonensis, Cancer magister, and C. productus, ghost shrimp, and the polychaetes Lumbrineris sp., Axiothella rubrocincta, and Owenia fusiformis. Representative fishes include juvenile Pacific tomcod and lingcod, tube-snout, bay pipefish, shiner perch, snake prickleback, saddleback gunnel, silverspotted sculpin, sharpnose sculpin, Pacific staghorn sculpin, tidepool sculpin, sturgeon poacher, Pacific sanddab, surf smelt, juvenile English sole, and starry flounder.

Sites Surveyed

False Bay, other sites in the San Juans.


Pamatmat, 1966; Kozloff, 1983; Webber, 1989; Long, 1983; H. Wilson unpubl. data.