Marine influence on Maryland's juvenile lagoon fish community was examined under varied levels of internal and external forcing. In 2009, stable isotope analysis showed increasing marine carbon dependency by bay anchovy with decreasing distance to the marine inlet. Following large seagrass losses, no similar trend was detected in 2012. Weakfish showed no structured dependence on marine carbon in either year. Diet contents lacked corresponding year-to-year changes in pelagic versus benthic prey items. In 2009, serial changes with distance to the inlet occurred in species assemblage, which may have been associated with internal seagrass structure. No gradient occurred in 2012. Analysis of a 24-year survey indicated a shift from marine-pelagic to structure-oriented species, associated with increased seagrass and tide level, and decreased North Atlantic Oscillation index. In Maryland's northern lagoon, the strength of marine influence on juvenile assemblages depended on the interplay between internal bay structure and external marine forcing.