Geographical Variation and Influencing Factors of Spartina alterniflora Expansion Rate in Coastal China

Abstract

Biological invasion poses a huge threat to ecological security. Spartina alterniflora was introduced into China in 1979, and its arrival corresponded with negative effects on native ecosystems. To explore geographical variation of its expansion rate in coastal China, we selected 43 S. alterniflora sites from Tianjin Coastal New Area to Beihai. The area expansion rate, expansion rate paralleling and vertical to the shoreline were analysed based on Landsat images and field survey in 2015. Simple Ocean Data Assimilation (SODA) and climate data were collected to statistically analyse the influential factors of expansion rate. Results showed that significant difference of S. alterniflora area expansion rate among different latitude zones (P < 0.01), increasing from 6.08% at southern (21°N–23°N) to 19.87% in Bohai Bay (37°N–39°N) along latitude gradient. There was a significant difference in expansion rate vertical to shoreline in different latitude zones (P < 0.01) with the largest occurring in Bohai Bay (256 m/yr, 37°N–39°N), and showed an decreasing tendency gradually from north to south. No significant difference and latitudinal clines in expansion rate paralleling to shoreline were observed. Expansion rate had significant negative correlation with mean seawater temperature, the lowest seawater temperature, current zonal velocity and meridional velocity and presented a reducing trend as these biotic factors increased; however, they were not significantly correlated with the highest seawater temperature and mean seawater salinity. We identified significant correlations between expansion rate and annual mean temperature, the lowest temperature in January and annual precipitation, but there was little correlation with annual diurnal difference in temperature and the highest temperature in July. The rapid expansion rate in high-latitude China demonstrated a higher risk of potential invasion in the north; dynamic monitoring and control management should be established as soon as possible.