Early Invasion of Common Cordgrass (Spartina Anglica) Increases Belowground Biomass and Decreases Macrofaunal Density and Diversity in a Tidal Flat Marsh

Spartina anglica is an invasive perennial marsh grass causing significant negative impacts on tidal flat ecosystem. There have been only a few studies focusing on the patch structure of S. anglica according to size and its effects on macrofauna. A field experiment was conducted to identify effects of S. anglica patches where they have been introduced no later than 5 years after invasion occurred on macrofauna assemblages. The survey area was divided into two sections according to vegetation: (1) Suaeda japonica vegetation from 0 to 60 m away from the embankment, and (2) bare mudflat from 60 to 90 m away from the embankment. The patch sizes of S. anglica were categorized into small (1–4 m2), medium (5–11 m2), and large (13–40 m2) in area with four replicates for each section. The biomass ratio of the belowground and aboveground in the small size patch of S. anglica was significantly higher than those in the medium and large size patch of S. anglica. It indicated that more resource was allocated to rhizomes in small size patch with short invasion history (1 ~ 2 years). After S. anglica invaded, macrofauna richness (70%), Shannon-Wiener diversity (80%), and density (67%) were decreased. However, infaunal deposit-feeding polychaete Perinereis linea and epifaunal gastropods Batillaria cumingi and Lactiforis takii increased by S. anglica. Ordination of macroinvertebrate assemblages separated the habitat with S. anglica invasion from the adjacent uninvaded tidal flat and Suaeda japonica habitats. This study offers a significant insight into early invasion strategies of an aggressive plant invader, S. anglica for management of coastal wetlands and its impacts on macrofaunal assemblages.