Connectivity is now a common consideration in conservation planning, but we need further empirical evidence for the role of connectivity in catalyzing reserve function. We examined whether connectivity improved reserve performance by investigating how isolation between coral reefs and mangroves influenced fish assemblages inside and outside a reserve in Moreton Bay, Australia. Connectivity greatly enhanced reserve performance, with close reserve habitats supporting more harvested fish, and a greater abundance of both piscivores and herbivores than similar nonreserve locations. Close reserve habitats also contained fewer prey fish than nonreserve locations. In contrast, fish abundance in isolated reserve habitats did not differ from similar nonreserve locations. We demonstrate that connectivity can improve the performance of a reserve in promoting fish abundance. We highlight its importance for maintaining ecological processes in reserves and advocate the prioritization of areas of similarly connected habitat for conservation.