William G. Ambrose

Predation by infaunal and epibenthic predators is often an important determinant of marine soft‐bottom community structure. The role of the predatory, benthic‐dwelling fish, the wrymouth ( Cryptacanthodes maculatus ), in the soft‐bottom food web has received little attention. The purpose of our study was to examine spatial and temporal variability in diet and trophic position of wrymouth at two lower intertidal sites in eastern Maine, USA. Wrymouth, their potential prey, and primary producers were collected in the spring and summer of 2013 in Machiasport and Beals, Maine. Stable isotope analysis was used to determine trophic position of the fish and its potential diet. Wrymouth δ 13 C signatures were influenced by location and ranged from −12.6‰ to −11.5‰, whereas δ 15 N signatures varied little (12.3‰–12.7‰) between locations or seasons. Wrymouth trophic position ranged from 3.02 to 3.48, indicating that they are tertiary consumers. The intertidal zone consisted of two distinct clusters of taxa, characterized by the presence of either macroalgae (mostly fucoids) or eelgrass ( Zostera marina ). Wrymouth diet consisted primarily of predatory polychaetes. Stable carbon and nitrogen isotope signatures varied across seasons and locations for multiple species, including our base species, Mya arenaria . Results suggest wrymouth are generalist feeders with limited seasonal and spatial variation in diet. Bottom‐up processes, however, are fundamentally different between the two study sites and influence their trophic structure. This result highlights the importance of collecting baseline data and evaluating trophic interactions at multiple spatial scales within small regional areas in coastal systems.