Size-Selective Foraging of Adult Mummichogs, Fundulus heteroclitus, in Intertidal and Subtidal Habitats

Abstract

Intertidal marshes provide an important foraging habitat for resident marsh fishes. However, few studies have considered whether the importance of intertidal foraging is uniform across the adult-size range of marsh fishes or whether size-selective foraging, which has been demonstrated in intertidal habitats, also occurs in subtidal habitats. This study compares diet composition of adult mummichogs (Fundulus heteroclitus) in Hoffler Creek, VA, USA, foraging in intertidal salt marshes with the diet of individuals foraging in the subtidal creek and considers the effect of fish size on gut fullness and consumption of major intertidal and subtidal diet items. Gut fullness was significantly greater in the intertidal salt marsh for small mummichogs (40–60 mm total length), and small mummichogs were significantly more likely than larger individuals to consume several major intertidal diet items, including copepods and ostracods. However, gut fullness was greater in the subtidal creek for large mummichogs (70–90 mm total length (TL)) due to consumption of grass shrimp (Palaemonetes spp.). This diet item was rarely consumed by large mummichogs in the marsh or by smaller mummichogs in either habitat. Modifications to the marsh landscape that affect prey resources for fishes may, therefore, have differing impacts across adult size classes. Although subtidal habitats are not frequently considered important for foraging of marsh fishes, access to shallow, subtidal water may allow larger adults to take advantage of additional prey resources, such as shrimp.