Comparison of the Benthic Prey Community and Diet of Adult Mummichogs (Fundulus heteroclitus) Along a Tidal Creek Gradient

Resident salt marsh fishes consume a diversity of intertidal benthic prey whose abundances may be affected by anthropogenic stressors. A generalist feeding strategy in which diet closely matches the benthic community could allow these fishes to flexibly track changes in prey availability, whereas selection for particular prey may put these fishes at risk if preferred resources decline, especially as warming water temperatures increase metabolic demand. This study detected differences between the diet of adult mummichogs (Fundulus heteroclitus) and the benthic prey community at salt marshes along Hoffler Creek in southeastern Virginia, USA, in May through August of 2 years. Polychaetes made up 74.8% of benthic samples but were only 33.9% of benthic prey items identified in diet samples. Compared to benthic samples, mummichog diet contained higher percentages of small arthropods, including ostracods, copepods, amphipods, and Diptera larvae, with substantial variation across months and sites. Consumption of large numbers of arthropods by some individual fish suggests they were taking advantage of patchily abundant prey. Despite these differences, mummichog diet reflected major temporal and spatial patterns in the benthos, including increased consumption of polychaetes in late summer and of ostracods at the upstream site in 2017. These results suggest that mummichogs are not uniformly generalist in their diet but that they may still be fairly robust to variation in prey availability due to their ability to consume large numbers of abundant prey on a small spatial scale and to track changes in the most abundant prey categories through time.