Habitat connectivity and spatial complexity differentially affect mangrove and salt marsh fish assemblages

Coastal salt marshes and mangroves are both intertidal habitats that, relative to unvegetated habitat, provide increased food, shelter and a nursery function to fish. Patch structural complexity and connectivity can influence assemblage structure across multiple spatial scales, and should be taken into account when assessing the effectiveness of marine reserves. We tested the hypothesis that fish assemblage density and species richness of the 2 habitats would be strongly associated with similar patch complexity-, connectivity- and physically-based variables (37 variables assessed) in a replicated investigation of 10 Indonesian mangrove and 9 European salt marsh habitats. Salt marsh and mangrove fish assemblage density and species richness (4.95 and 111.5 ind. 100 m(-2); 13 and 64 species for salt marshes and mangroves, respectively) showed significant variation between patches, and were influenced by different spatial variables. Patch shape (increased circularity) was the most highly influential variable in both habitats associated with enhanced fish species richness and density. Prop root density and number of mangrove patches within 1 km radial extent were strongly positively correlated with mangrove fish species richness, and patch isolation was negatively correlated with density. Salt marsh fish assemblage structure was negatively correlated with intertidal mudflat extent, patch seaward edge length and patch depth. The role of habitat mosaics was less important in structuring salt marsh fish than mangrove fish assemblages. Different spatial factors must be integrated when considering the role of coastal fringing habitats as fish nursery sites, and to maximize their conservation value, salt marsh and mangrove habitats may require different management approaches.