Vertical distribution of the salt marsh invader Spartina alterniflora and native halophytes on the west coast of Korea in relation to tidal regimes

Smooth cordgrass (Spartina alterniflora Loisel.), an aggressive non-native species worldwide, colonized tidal flats on the west coast of Korea in two regions differing in tidal amplitude between 1990–2004. By the time of our study in 2015, expansion had occurred both clonally and through formation of new patches, providing an opportunity to determine intertidal range, which is a key component of understanding the threat posed by S. alterniflora through competition with native halophytes or transformation of unstructured mudflat. At Ganghwa (5.69 m tidal range), S. alterniflora ranged from 3.52 to 1.34 m above Mean Sea Level (MSL). At Jindo (2.02 m tidal range), S. alterniflora ranged from 1.57 to -0.18 m relative to MSL. Thus, a wider absolute intertidal range was occupied by S. alterniflora at the megatidal vs mesotidal region, but the lower limit of S. alterniflora did not extend below MSL under megatidal conditions, a pattern that now appears to emerge consistently in both the native and introduced range. In both study regions, S. alterniflora occurred at the same elevations as other salt marsh plants, occupying an upper zone with Phragmites australis (non-native) and middle zone with several native species including Suaeda japonica. S. alterniflora occurred below native marsh vegetation at all sites, which would result in transformation of the extensive mudflats along the Korean coast.