Nekton use of intertidal creek edges in low salinity salt marshes of the Yangtze River estuary along a stream-order gradient

Non-vegetated creek edges were investigated to explore spatial nekton use patterns in a low salinity intertidal salt marsh creek network of the Yangtze River estuary along a stream-order gradient with four creek orders. Non-vegetated creek edges were arbitrarily defined as the approximately 3 m extending from the creek bank (the marsh–creek interface) into open water. Nekton was sampled using seine nets during daytime high slack water during spring tides for two or three days each in May through July 2008. Twenty-three nekton species (16 fishes and 7 crustaceans) were caught during the study. Fishes were dominated by gobies (Mugilogobius abei, Periophthalmus magnuspinnatus, Periophthalmus modestus, Synechogobius ommaturus), mullets (Chelon haematocheilus, Liza affinis) and Chinese sea bass (Lateolabrax maculatus). Crustaceans were dominated by mud crab (Helice tientsinensis) and white prawn (Exopalaemon carinicauda). Rank abundance curves revealed higher evenness of nekton assemblages in lower-order creeks compared to higher-order creeks. Fish abundance tended to increase with increasing creek order. Crustacean abundance was higher in the first–third order creeks than in the fourth-order creek. Dominant nekton species displayed various trends in abundance and length–frequency distributions along the stream-order gradient. The spatial separation of nekton assemblages between the first–third order creeks and the fourth-order creek could be attributed to geomorphological factors (distance to mouth and cross-sectional area). These findings indicate that both lower- and higher-order creek edges play important yet different roles for nekton species and life history stages in salt marshes.