Abstract: Tidal creeks are the main transporting and exchanging channels of nutrient between estuarine wetlands and adjacent waters, and also serve as the key habitats and migration channels for fish and other aquatic animals. It is of great importance to maintain good connectivity of tidal creeks for the sustainable development of fisheries resources in estuarine wetlands and adjacent waters. Compared with the higher-order ones, the lower-order tidal creeks are more ecologically vulnerable. The highly connected areas of the lower-order creeks are preferred habitats for fish. To quantify the connectivity of lower-order tidal creeks in the Dongtang tidal flat, located in the Chongming Island of the Yangtze River estuary, six indicators from two categories (hydrological group and fish migrating behavior group) were chosen, including cross-sectional area (m), β index, diameter (m), total number of connections between nodes, total length of connections between nodes (m), and measures of local centrality. These indicators were used to analyze the effects of creek connectivity on the distribution of fish communities. The habitat preference mechanism of fish communities could be verified in the lower-order tidal creeks of estuarine wetland. The node path set, which was derived from the fish migrating group and represented by three indicators (total number of connections between nodes, total length of connections between nodes, measures of local centrality) had significant differences (P<0.05) in fish abundance and biomass among the tidal creeks, with high, middle, and low connectivity. This result could effectively verify the effects of connectivity on fish community distribution in the lower-order tidal creeks. Since the node path set was mainly composed of indicators quantifying the lateral connectivity of tidal creeks with adjacent patches, the result also suggested that the habitat preference of fish may be mainly correlated with the lateral connectivity of lower-order tidal creeks, but not with the hydrological connectivity of the higher-order tidal creeks. The characteristics of the lower-order tidal creeks with high connectivity were also clarified, which showed higher measures of local centrality (the average measures of local centrality of the network was 11), more total number of connections between nodes (the average number of paths was 6), and wider swimming range (total length of connections between nodes was about 800 m). The larger the range of suitable habitat for foraging and sheltering, the more this kind of tidal creek could attract small fish or juvenile fish, especially the detritivory and strong swimmer species to habitat. Our results can provide a scientific basis for ecological restoration of wetland tidal creeks.

Key words: estuary wetland, lower-order tidal creek, connectivity index, fish community, habitat selection mechanism