Context dependence masks the long-term harm of Spartina alterniflora invasion on macrobenthos in China

The invasion of Spartina alterniflora poses a significant threat to the biodiversity of tidal wetlands, including mangroves, native saltmarshes, and mudflats. However, its impact on macrobenthos, a key group within these ecosystems, remains a subject of debate. In a meta-analysis of 2411 data points from 105 studies on macrobenthos in China's tidal wetlands, we found that at the coastal scale of mainland China, S. alterniflora invasion did not significantly affect the abundance or diversity of macrobenthos. However, single-factor analysis showed strong spatiotemporal variation in the invasion's effects on macrobenthos, which obscured the negative effects of S. alterniflora in specific local areas. Key factors such as habitat type, temperature, tidal strength, seawater chemistry, and invasion duration play a critical role in shaping the extent of the invasion's impact. Our predictive model, which integrates these factors, suggests that 19.63% of China's tidal wetlands could experience dual losses in macrobenthos abundance and diversity within just one year of S. alterniflora invasion. This proportion increases to 34.03% after 10 years, and rises to as high as 61.85% after 20 years. These findings suggest that the negative effects of S. alterniflora on macrobenthos are often masked by context dependence. Therefore, it is crucial to identify and prioritize the protection of tidal wetlands at higher risk of invasion to safeguard macrobenthos communities and maintain their essential ecosystem services.