Marine Intertidal Mixed-Coarse Sediments: Semi-Protected to Protected

Mixed-coarse sediments are those where no one grain size occupies more than 70 percent of a stretch of beach. Instead, the beach is a mix (in variable quantities) of a few boulders, with cobble, gravel, and sand.  Few marine sites (but many estuarine) qualifying as mixed-coarse have been surveyed.  Data on dominant species are limited.  Drift algae may accumulate in these habitats seasonally, creating anaerobic sediments beneath them but providing food and habitat for a variety of small organisms.

Diagnostic Species

Fucus gardneri, Mytilus edulis, Protothaca staminea.

Common Associates

Ulvoid algae (Ulva, Enteromorpha, Monostroma), Balanus glandula, the clams Tapes philippinarum, Saxidomus giganteus, Macoma spp. especially M. inquinata, Mya arenaria, and Tresus capax, the burrowing shrimp Upogebia pugettensis and Callianassa spp.; the anemones Anthopleura artemisia and Urticina coriacea, and the polychaetes Naineris dendritica, Neoamphitrite robusta, Eunice kobiensis, Saccocirrus eroticus, and nereids.

Sites Surveyed

Turn Island, Partridge Point (Whidbey Island), and parts of False Bay (San Juan Island).


Smith and Webber, 1978; Pamatmat, 1966; H. Wilson, R. Shimek, and R. Anderson unpubl. data.