Spartina anglica settlement and effect on macrofauna in the west coast of Korea

Abstract

Spartina anglica, an invasive perennial marsh grass, brings changes in ecosystem of tidal flat causing sediment stabilization. It has been identified as invasive species in foreign countries such as USA, Canada, and China. S. anglica was first discovered in Ganghwa Island in Incheon, Korea in 2012 and designated as Invasive alien Species by the Ministry of Environment in 2016. However, there are a few studies on the S. anglica settlement and its effect on the tidal flats in Ganghwa Island. I conducted outdoor experiment to identify the factors for the S. anglica seed settlement and S. anglica patch effects on macrofauna. Additionally, an indoor experiments was performed to determine the factors influencing germination rate of S. anglica. Average of the seed number of S. anglica in S. japonica vegetation was 7.1 ± 1.31 m-2 and in mudflat was 0.6 ± 0.26 m-2. The seed number of S. anglica per unit area (m2) was higher in S. japonica vegetation than mudflat. However, Spearman correlation analysis among density, coverage, height, underground biomass of S. japonica, and number of seeds of S. anglica showed no correlation. To identify a certain inundation time germinating S. anglica seeds, germination experiment was conducted. The Cox Proportional-Hazard Model suggested that inundation treatment had no significant effect on germination probability. It indicated inundation time might not have effect on seed settlement. First result suggests that S. japonica vegetation play a role as a trap for S. anglica seed. The second study was carried out to examine the difference of S. anglica patch structure along invasion history within 5 years and the effect of S. anglica on benthic macrofauna. The survey area was divided into 2 sections by habitats, S. japonica vegetation from 0 to 60 m away and mudflat 60 to 90 m away from the embankment. The patch size of S. anglica was categorized into small (1 – 4 m2), medium (5 – 11 m2), and large (13 – 40 m2) in area with four replicates for each habitat. The mean of live leaf and rhizome biomass in small size patch of S. anglica was significantly higher than in medium and large size patch of S. anglica, indicating more resource allocation to be underground in small size patch. After S. anglica invasion in Dongmak-ri, macrofauna richness (70%), diversity (80%), and abundance (67%) were decreased. However, infaunal spartina feeder Perinereis linea and epifauna Batillaria cumingi and Lactiforis takii may be increased by S. anglica. In CCA analysis for macrofauna assemblages, Mudflat where S. anglica invaded was not mixed with S. japonica vegetation where S. anglica invaded. However, Mudflat and S. japonica vegetation with no invasion were mixed. It suggested that habitat with S. anglica invasion may change the macrofauna assemblages with negative effect and the result differs depending on the habitat.