Effects of forest width on fish use of fringing mangroves in a highly urbanised tropical estuary.

The size and shape of a habitat patch can influence patterns of species utilisation. The present study examined how the width of fringing mangrove habitats affects the composition and use patterns of the fish assemblage using mangrove edge habitats on the flooding tide. Underwater cameras surveyed fish approaching mangrove habitats, ranging from a thin fringe 5 m wide to forests over 75 m wide, in a highly modified tropical estuary. The fish assemblage composition was similar across all mangrove widths, although the temporal patterns of use varied among mangrove widths for some species. The mean maximum number of individuals in the field of view was similar among mangrove widths, but fish were visible for a significantly greater proportion of time in videos from narrow (,20 m) than wide (≥20 m) mangrove stands (15 v. 3% respectively). At least some fish were visible in the field of view in narrow mangrove fringes throughout the first hour of the flood tide, whereas in wide mangroves areas the presence of fish declined over time. The findings suggest that estuarine fish are using mangrove edge habitat regardless of width, making narrow mangroves viable habitats for estuarine fish. [ABSTRACT FROM AUTHOR]