Fine-scale environmental heterogeneities of tidal creeks affect distribution of crab burrows in a Chinese salt marsh

Abstract

Tidal creeks are an important structure of salt marshes in estuarine ecosystems, providing valuable ecosystem services to wildlife in the estuary. To determine the effects of environmental heterogeneities within tidal creeks on the features of crab burrows, we divided a typical creek section into four parts (i.e., microhabitats): bottom, slope, edge and flat, investigated the distribution of crab burrows and sediment properties on creek sections in the Yangtze River estuary, and compared the burrow distribution in tidal creeks with that in non-creek areas. Our results showed that from the creek bottom to flat soil water content declined ( F 3, 60 = 93.8, p < 0.001), and the variations of other sediment physical and chemical properties associated with the change of soil water content were significant among the microhabitats on the creek sections ( p < 0.001 for pH, conductivity, and grain size). No crab burrows were found at the creek bottom. The burrows on the slope were smaller in size ( p < 0.001 for burrow opening diameter) while the density was higher than that at the edge and on the flat ( F 2, 45 = 31.2, p < 0.001). Moreover, although the correlations between burrow distribution and sediment properties varied among the microhabitats on the creek sections, crabs generally selected relatively solid sediments to build their burrows. On the slope, there was a significantly negative relationship between burrow density and soil water content ( r 2 = 0.53, p < 0.001). At the edge, the correlation between total burrow opening area and soil water content was significantly negative ( r 2 = 0.44, p < 0.002). The density of small crab burrows (<10 mm) was greater, but that of large burrows (>10 mm) was lower in tidal creeks than in non-creek habitats. Therefore, sediment properties showed a gradual transition from hydrophytic to terrestrial environments on the creek section, which caused significant differences of burrow distribution among the microhabitats. The creeks of tidal salt marshes could affect ecological processes and functioning through affecting crab burrows.