MEPS 290:193-205 (2005)  -  doi:10.3354/meps290193

ABSTRACT: Mangroves and mudflats are a conspicuous element of temperate estuaries in south-eastern Australia, but our understanding of their use by fish is poor. A combination of experimental and survey methods were used to investigate (1) the utility of pop nets in sampling fishes and (2) patterns in fish assemblages among mangrove zones (forest, edge, mudflat) in 2 large embayments between October 2003 and January 2004. In the experimental assessment of pop net artefacts, there were no statistically significant differences (p >> 0.05) in assemblage structure, species richness (number of species) or abundances of fish among net disturbance treatments regardless of structure (seagrass or unvegetated sand). These results were not simply due to type II errors. The statistical power to observe an effect of net disturbance on fish abundances and species richness generally exceeded 80%. In the pop net survey of fish using mangrove zones, only 15 species of fish (9 families) were caught, but assemblages varied strongly among zones. Small (<30 mm) benthic gobiids, such as Pseudogobius olorum Sauvage 1880 and Mugilogobius paludis Whitley 1930, and juveniles of the atherinid Atherinasoma microstoma Gunther 1861 dominated catches in the forest. The sillaginid Sillaginodes punctata Cuvier 1829, the tetraodontid Tetractenos glaber Freminville 1813 and a further 2 species of gobiid, Arenigobius frenatus Gunther 1861 and Favonigobius lateralis Macleay 1881, dominated catches along the edge and over the mudflat, but these species were more abundant along the edge. Fish densities were significantly lower (p < 0.05) in the mudflats (0.37 ± 0.05 fish m^–2) than in the forest (1.98 ± 0.36) or at the edge (1.42 ± 0.43); species richness was greater along mangrove edges (0.25 ± 0.19 species m^–2) than in the forest (0.17 ± 0.06) and in the mudflats (0.12 ± 0.02); biomass was greater (but not significantly) at the edge (4.64 ± 2.09 g m^–2) and in the mudflats (4.06 ± 1.79) than in the forest (1.20 ± 0.38). Seine nets caught fewer individuals (0.95 ± 0.17 fish m^–2) and species (0.03 ± 0.01 species m^–2), and lower biomass (1.15 ± 0.21 g m^–2) than pop nets (see above) in mudflats. Differences in the fish assemblage structure among zones suggest that overall fish biodiversity may increase in fragmented mangrove landscapes as relative amounts of edge to area increase, but this could detrimentally affect abundances and species richness of resident mangrove fishes.

KEY WORDS: Mangroves · Mudflat · Intertidal · Pop nets · Survey · Zonation