Maintenance of salt barrens inhibited landward invasion ofSpartinaspecies in salt marshes

Abstract

. 2017. Maintenance of salt barrens inhibited landward invasion of Spartina species in salt marshes. Ecosphere 8(10):e01982. 10. 1002/ecs2.1982 Abstract. Spartina spp. (cordgrasses) often dominates intertidal mudflats and/or low marshes. The landward invasion of these species was typically thought to be restrained by low tidal inundation frequencies and interspecific competition. We noticed that the reported soil salinity levels in some salt marshes were much higher than those at the mean higher high water level, which might inhibit the landward invasion of cordgrass. To test this possibility, we transplanted Spartina alterniflora across an elevational gradient in an invaded salt marsh in the Yellow River Delta National Nature Reserve, where a salt accumulation zone (i.e., salt barren) was previously observed. We found that S. alterniflora was significantly inhibited by the salt barren in high marsh regions, although it performed better at upland and low marsh regions. A common garden experiment further elucidated that S. alterniflora performed best at low salinity levels and that this species is less sensitive to inundation frequency. Our results indicated that the salt barren inhibited the landward invasion of S. alterniflora in salt marshes and provided a natural barrier to protect the upland from invasion. Though field observations suggest that S. alterniflora could propagate along tidal channels, which provide low-salinity corridors for the dispersal of propagules, natural salt barrens can inhibit the landward invasion of Spartina in salt marshes. However, artificial disturbances that break the salt barren band in salt marshes (e.g., artificial ditches) might accelerate the invasion of Spartina spp. This new finding should alert salt marsh managers to pay attention to artificial ditches and/or other human activities when attempting to control Spartina invasion.

Native herbivores enhance the resistance of an anthropogenically disturbed salt marsh to Spartina alterniflora invasion

“…, Qi et al. ). However, our results suggest that anthropogenic ditches break the abiotic resistance of high marshes which facilitate S. alterniflora invasion.…”

“…S. alterniflora is a worldwide coastal invasive species, which has aggressively spread to estuaries in Europe, Australia, New Zealand, Pacific Coast of United States, southern Africa, and Asia (Qi et al 2017). It was first introduced intentionally to China in 1979 to alleviate shoreline erosion (Li et al 2009).…”

“…, Qi et al. ). Importantly, high marshes are facing the increasing and drastic anthropogenic disturbances (e.g., road construction and tidal creek ditching) (Appendix : Fig.…”

“…S. alterniflora rapidly occupied the low marshes, and nowadays, it is showing a trend of landward invasion (Qi et al. ). However, high marshes, which represent salt marshes at elevations between the mean high‐water spring tides and the highest astronomic tides (Adam ), are often resistant to S. alterniflora invasion due to hyper‐stresses such as high salinity (He et al.…”

“…Along the coastlines of China, salt marshes are subject to the invasion by Spartina alterniflora (hereafter S. alterniflora), which was intentionally introduced from the Atlantic and Gulf coasts of the United States to China in the 1970s (An et al 2007, Strong andAyres 2013). S. alterniflora rapidly occupied the low marshes, and nowadays, it is showing a trend of landward invasion (Qi et al 2017). However, high marshes, which represent salt marshes at elevations between the mean high-water spring tides and the highest astronomic tides (Adam 1990), are often resistant to S. alterniflora invasion due to hyper-stresses such as high salinity , Qi et al 2017.…”