Seagrass beds, mangroves, and coral reefs are often located adjacent to one another, but few studies have focused on the influence that their proximity may have on their fish assemblages. Juvenile fish assemblages of seagrass beds, differing according to their adjacent habitats, were investigated in the Caribbean island of Guadeloupe. We tested whether adjacent habitats influence (i) the structure and composition of juvenile fish assemblages and (ii) the size class distribution of fishes using analysis of variance (ANOVA) and multivariate permutation tests. Significant differences in species richness, abundance, and size were identified between the two types of seagrass beds. Close to the reef, daytime fish assemblages were constituted of seagrass beds resident species, while at night, indicator species of seagrass beds belong to reef families. Near coastal mangroves, the shift between day and night is less evident. Fish size class distributions confirm the sequential use of the two types of seagrass beds by juvenile fishes.