Marine ecosystems throughout the Indo-Pacific region are highly threatened by anthropogenic stressors, yet the faunal interaction between different component habitats remains poorly understood. This information is vital as stress on one inter-connected habitat may have cascade effects on other habitats. The present study focused on the impact of inter-habitat connectivity on seagrass fish assemblages, specifically between seagrass, mangrove and reef habitats. Fish were sampled using a seine net within 3 seagrass habitats (seagrass near to reef, seagrass near to reef and mangrove, and seagrass near to mangrove) within eastern Indonesia. Visual surveys were also conducted within mangrove habitats. Fish abundance and species richness in seagrass beds in close proximity to mangroves was at least twice that found in seagrass beds that were distant from mangrove habitat. The trophic structures of seagrass fish assemblages change from being dominated by predators and omnivores close to the reef, to assemblages high in planktivores and herbivores close to mangroves. We found that mangroves enhance the fish assemblages of nearby seagrass beds probably by increasing the availability of shelter and food provision. This study indicates that Indo-Pacific seagrass beds play an important fish nursery role, which is influenced by the availability of nearby reef and mangrove habitats. Our research supports the need for ecosystem-level management of shallow water tropical habitats, but also suggests that successful management requires local-level knowledge of habitat interactions to successfully enhance or conserve fish assemblages. © Inter-Research 2008

Indo-Pacific mangrove swamps and seagrass beds are commonly located in close proximity to each other, often creating complex ecosystems linked by biological and physical processes. Although they are thought to provide important nursery habitats for fish, only limited information exists about their usage by fish outside of estuaries. The present study investigated fish assemblages in non-estuarine intertidal habitats where mangroves and seagrass overlap (the mangrove-seagrass continuum). Three habitats (mangrove, mangrove edge, seagrass) were sampled at 4 sites of the Wakatobi Marine National Park, Indonesia, using underwater visual census. Ninety-one species of fish were observed at a mean density of 130.1 ±37.2 ind. 1000 m -2 . Predatory fish (fish that feed on invertebrates and/or fish) were the most dominant feeding groups in the mangroves, whilst omnivores dominated on the mangrove edge and in the seagrass. Although the habitats along the mangrove-seagrass continuum were observed to be important for many fish, only 22 of the 942 coral reef species known within the area utilised mangroves as nursery habitat and only 15 utilised seagrass. Despite finding evidence that nursery grounds in mangroves and seagrass may not directly support high coral reef fish diversity, many of the coral reef nursery species found in this study are likely to be key herbivores or apex predators as adult fish on local coral reefs, and thus highly important to local fisheries. Although mangroves are not permanently inundated by the tide, this study highlights their importance as fish habitats, which at high tide support a greater abundance of fish than seagrass beds. In the light of the high rate of destruction of these habitats, their role in supporting fish assemblages requires consideration in marine resource management programs. © Inter-Research 2009