On intertidal mudflats, invertebrate communities often respond strongly to biogenic species that form emergent structures. This hypothesis was tested by collecting benthic macroinvertebrates from four distinct habitat types, which occurred in a saltmarsh mosaic at an equivalent tidal elevation at Dongtan, Yangtze Estuary, Shanghai, China. Habitat types were: a) Scirpus × mariqueter saltmarsh (hs), b) Phragmites australis saltmarsh (lw), c) Spartina alterniflora saltmarsh (hh), and their contrasting type, d) unvegetated mudflat (ld). Within every habitat type, six quadrats (25cm×25 cm, 20cm deep) were taken from independent patches in late May, 2005 and sieved (1 mm mesh).
Communities in different habitats were compared in terms of numbers of species, total individuals, Shannon-Wiener index value, Margalef index value, mean density and mean biomass (fresh weight) of the macrofauna. All of these values were lowest on unvegetated mudflat. There were significant differences (P<0.05, LSD tests) in the mean macrofaunal density between the three saltmarshes and the ld type, and extremely significant difference (P <0.01, LSD tests) in the mean biomass between patch types hs and ld; CLUSTER showed that the macrofauna in type ld were quite different from those in the three saltmarshes.
In patch types hs, lw and hh, the dominant life forms were all adhering Mollusca, whereas that in patch type ld was caving Crustacea. This difference was reflected in the ratios of group of surface to group of surface below in patch type hs (0.56), lw (0.63), hh (0.63), and ld (0.75). Though the macrofauna in the three saltmarshes were relatively similar, they were distinguished from each other by MDS.
Differences in macrofauna between unvegetated mudflat and the three saltmarshes suggest the obvious effects of saltmarsh on the benthic macroinvertebrate community. These effects may be direct, such as alteration of habitat structure, providing resources of food, or may be indirect through shifts in hydrodynamic and deposition regimes. The saltmarsh is thus an important ecological factor which can influence the benthic macroinvertebrate community in the intertidal zone.