Mangroves are opportunistic tree species, coming from 16 families that colonize the intertidal zone of tropical coastlines to create some of the most productive of marine habitats (Wester, 1981). These forests are important components of low-latitude coastal ecosystems, making up more than 60% of tropical and sub-tropical coastal habitats (Duke 1992). Mangroves were introduced to Hawaii in 1902, and now three introduced species maintain viable populations on all the major Hawaiian Islands. Mangroves are dramatically altering the Hawaiian coastal ecosystem (Demopoulos, 2004; Demopoulos et al., 2007), and may provide a habitat for other invasive species. To determine whether mangroves harbor distinct megafaunal assemblages and provide footholds for invasive species in Hawaii, I used crab traps and drop nets to sample megafaunal invertebrates and fishes in mangrove and non-mangrove habitats. Replicate mangrove and sandflat sites on the southern coast of Molokai were sampled a total of 11 times by day and 3 times by night over a three-year period. Mangroves contained greater species richness and larger population densities than non-mangrove sandflats. In addition, patterns of body size for animals collected in mangroves showed significantly smaller individuals than in the sandflats, which was consistent with the hypothesis that mangroves can act as juvenile or nursery habitat. The results also suggest that mangroves may provide open niches for invasive species. In particular, mangroves supported significantly higher abundances of the introduced mantis shrimp Gonodactylaceus falcatus, the molly Poecilia sp., and the Samoan crab Scylla serrata. Overal1, mangroves may produce positive effects in Hawaii by providing a nursery habitat for native juvenile megafauna, but they may also have the negative effect of facilitating the invasion of non-native species.