Changes of the Macrobenthos Community with Non-native Mangrove Rehabilitation (Kandelia obovata) and Salt Marsh Invasion (Spartina alterniflora) in Ximen Island, Zhejiang, China

Macrobenthos organisms are vital ecological components of intertidal wetlands. This work studied effects of non-native mangrove rehabilitation (Kandelia obovata) and salt marsh invasion (Spartina alterniflora) on macrobenthos communities in Ximen Island (Zhejiang, China). The macrobenthos communities were compared between rehabilitated K. obovata forests of five different stand ages (2-, 8-, 11-, 16-, and 60-year-old) and adjacent S. alterniflora marsh and non-vegetated mudflat. Compared to the mudflat, S. alterniflora increased the abundance, Shannon–Wiener diversity index (H’), and Margalef's richness index (d’) of macrobenthos. Gastropoda abundance was high in the S. alterniflora marsh, whereas, malacostraca biomass was low. Within mangrove forests, macrobenthos abundance was positively correlated with the stand age of mangroves (Spearman Correlation, P < 0.05), but the corresponding H’, d’ and Pielou's evenness index (J’) showed negative correlations. Gastropoda dominated over macrobenthos in the younger stands (2–11 years in age), whereas, phascolosomatidea and bivalvia were more abundant in the older stands (16 and 60 years in age). Noticeably, the highest biomass for malacostraca was recorded from the 11-year-old stand. Macrobenthos communities differed among habitats, with the divergence in community structure between the S. alterniflora marsh and mangrove stands increasing with mangrove stand age, to be significantly different for stands planted over 16 years ago. Since the 16-year-old stand exhibited similar macrobenthos features to the 60-year-old stand, we speculated that, in the case of macrobenthos, a rehabilitated K. obovata forest can reach its maturity level at a time period of about 15 years in Ximen Island.