. 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.
We proposed an approach to calculate estuarine habitat suitability and habitat fragmentation by integrating various environmental factors. Based on fuzzy logic method, water depth, salinity, and fluctuation rate of salinity were integrated into a Habitat Suitability Index (HSI) to map suitable habitat pattern of target species in estuaries. Then the HSI is used to calculate Habitat Aggregation Index (HAI) that represents the degree of habitat fragmentation. The proposed method was applied to the Yangtze River Estuary which has experienced long term land reclamation activities during the past two decades including the transformations of coastal wetlands to urban infrastructures and the deep-water channel construction. We selected Chinese mitten crab (Eriocheir sinensis) as a target species in this study, the results indicated that under the impact of land reclamation in the Yangtze River Estuary the isoclines of low salinity moved seaward and the optimum salinity range for Chinese mitten crab has been compressed. The suitable habitat for Chinese mitten crab decreased 325.4 km 2 and the HAI has also decreased 2% during the first stage of land reclamation (scenario 1 to scenario 2) with a transformation of 237.2 km 2 coastal *Correspondence author.: Tao Sun
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