Aim To evaluate the potential of habitat connectivity to promote the effectiveness of marine reserves. We used heterogeneous reef seascapes as a model system to examine the potential interaction of reserves and mangrove-reef connectivity and compared the magnitude of these effects across the western Pacific Ocean. Location The tropical and subtropical western Pacific, including the Solomon Islands, Great Barrier Reef and Moreton Bay, Australia. Methods We quantified fish densities on coral reefs (38 sites) and in mangrove forests (19 sites) across seven marine reserves and twelve unprotected control locations. Fish assemblages were in seascapes supporting either adjacent reefs and mangroves or isolated reefs. For each reserve-control comparison, we evaluated the potential interactive effects of habitat connectivity on species richness and densities of harvested species, functional groups, families and individual species. We then examined the influence of spatial variation in reserve attributes, seascape heterogeneity and latitude on the magnitude of reserve-connectivity effects. Results Snappers (Lutjanidae) and rabbitfish (Siganidae) were more abundant on reserve reefs close to mangroves in all regions. These interactive effects also enhanced the abundance of sweetlip (Haemulidae), bream (Sparidae), harvested fish, herbivores and piscivores and species richness in two of the three regions examined. Spatial variation in the magnitude of reserve-connectivity effects was explained by differences among reserves in seascape variables (i.e. area of mangroves and reef, duration of mangrove inundation and distance to rivers) but not by reserve attributes (i.e. age, size, poaching) or latitude. Main conclusions Habitat connectivity improved the effectiveness of reserves across the western Pacific Ocean. We recommend that heterogeneous landscapes with high-habitat connectivity should be viewed as high priorities for conservation. By improving our understanding of connectivity, and through its explicit incorporation into conservation, we may have greater success in restoring biodiversity and functioning of ecosystems.