The gastropod Tegula funebralis (A. Adams, 1855) is confined to the intertidal. At Mukkaw Bay, Washington, it typically occurs in patches of characteristic individual size structure. Various energy flow parameters have been determined for a high intertidal (+ 1.8 to +0.9 m) and a low intertidal (+0.6 to −0.15 m) subpopulation; these values were then combined in a 3:1 ratio to generate a composite population.Direct and indirect calorimetry and direct observation on the natural population suggest the following: Tegula spawns once per year; the dry weight‐shell diameter relationships for males and females can be expressed by a single regression; different caloric values characterize immature (5.2 kcal/ash‐free g), mature males (5.4), intermediately mature females (5.8), and fully mature females (6.1); rates of aquatic and aerial respiration are different (at 13.5C an average low intertidal individual, 211 mg dry wt, respires at a rate of 75 µl O2/hr in water and 43 µl/hr in air).The energy budget, in which ingestion was obtained by summation, suggests an assimilation efficiency of about 70%, a gross efficiency of growth of 16.7%, and an ecological efficiency of predators of 4.9%. Other efficiencies are discussed. In Tegula, 60% of energy transferred to other levels is to decomposers. Comparison of the rate of annual consumption by Tegula, 1,071 kcal m− 2 yr−1, and net primary production estimated by cropping, 1,167 kcal m−2 yr−1, indicate a near balance. Importation of primary production may be necessary to the maintenance of the rocky intertidal community at Mukkaw Bay.