High connectivity of Indo-Pacific seagrass fish assemblages with mangrove and coral reef habitats

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.