Blooms of surf-zone diatoms along the coast of the Olympic Peninsula, Washington. X. Chemical composition of the surf diatom Chaetoceros armatum and its major herbivore, the Pacific razor clam Siliqua patula

The surf diatom Chaetoceros armatum T. West, collected from its natural habitat along the Washington coast (USA), had a large inorganic component in the form of a clay coat (consisting of clay minerals, illite and montmorillonite) surrounding the cell chains: 63% of the dry weight of the natural material collected in November was inorganic. The organic fraction was composed of 67.6% lipid, 29.7% protein, and 1.3% carbohydrate. Culture cells were likewise high in protein and lipid and low in carbohydrate. Traces of chitin found in field samples were probably a contaminant, since chitin was absent from cultured cells. This diatom species serves as a major food source throughout the year for the Pacific razor clam Siliqua patula Dixon, which inhabits these same beaches. Protein constituted 47% and lipid 42% of the dry weight of razor clam tissue. The fatty acid distribution in the diatom lipid resembled that previously reported for other diatom species; similarly, the fatty acid distribution of the clam lipid was similar to that previously reported for other bivalve molluscs. The clam fatty acids differed in chain length and degree of saturation from those extracted from its food source, indicating an active fatty acid metabolism in the clam.