The biosecurity problem represented by the biological invasion of alien species has become a major global environmental concern (Haubrock et al. 2022). The intensification of globalization and the expansion of introduction channels and trade patterns have disrupted natural barriers to potential alien invasive species, leading to an increase in the rate of invasion (Seebens et al. 2018; Kaiser et al. 2021). The threat of new invasive species emerging in the 21st century is widespread, with 17% of the world’s land area (excluding Antarctica and the Greenland glaciers) and 16% of global biodiversity hotspots vulnerable to invasion (Early et al. 2016). China is the third largest country in the world. Diverse climatic and environmental conditions in China enable most species, especially invasive alien plants, to find habitats that are suitable for their survival, where they can successfully establish populations and further propagate and spread, thus forming a biological invasion (Wang et al. 2021). According to the 2020 China Ecological Environment Bulletin issued by the Ministry of Ecology and Environment of China in 2021, more than 660 invasive alien species have been found throughout the country. Among them, 71 species are or may potentially pose a threat to natural ecosystems and are included in the list of invasive alien species in China. A total of 219 species have invaded national nature reserves.
Spartina alterniflora is a perennial salt marsh herbaceous plant of the Gramineae family (Liu 2018). It has well-developed roots, strong adaptability, salt tolerance, flooding tolerance and a fast reproduction speed. It can be used to prevent the coast from being eroded by wind and waves and increase the land area. The species was introduced from the United States as an important ecological engineering material in 1979 (Xie and Han 2018). Since its introduction, the ecological harm caused by S. alterniflora has been identified. It occupies the niche of native plants (Jie et al. 2020), destroys the habitat of offshore organisms, changes the elevation of tidal flats (Qing et al. 2006), affects the structure and function of the tidal flat ecosystem, threatens the biodiversity of tidal flats, causes the loss of habitat for migratory birds (Li et al. 2008), and causes negative effects such as the siltation of estuary channels and ‘competition’ with tidal flats aquaculture (Li et al. 2005). It has become the most important malignant invasive plant on China’s coastal tidal flats (Jie et al. 2020). In 2015, S. alterniflora occurred in all coastal provinces in China except Taiwan and Hainan, with a total area of 54579.9 ha (Li 2021). China began to comprehensively control S. alterniflora in 2022 and aims to achieve effective management in 2025. However, whether the management process has an impact on the tidal flat ecosystem remains unknown.
At present, studies on the control of S. alterniflora have been reported in Asia, North America, Europe and Africa, especially in China and the United States (Li et al. 2008; Adams et al. 2016; Taylor and Hastings 2004; Gao et al. 2014). Chemical control is the main method outside China, while physical control is the main method inside China (Cheng et al. 2020). In recent years, China has explored a variety of methods to control S. alterniflora. The chemical method uses herbicides for treatment, but the use of herbicides usually leaves residual toxicity, which can cause harm to the ecological environment (Paveglio et al. 1996; Kilbride and Paveglio 2001). Chemical methods have not been widely used in China, and the impact of herbicides on ecosystems needs to be further studied (Xie and Han 2018). Physical methods include manual removal, cutting, flooding and other measures, usually as a pre-treatment to biological alternatives (Xie and Han 2018). Biological replacement is an ecological control technology that replaces invasive plants with native plants according to the principles of plant community succession (Taylor and Hastings 2004; Gao et al. 2014; Knott et al. 2013; Tan et al. 2022; Wang et al. 2017). However, effective and safe alternative species in specific areas are still difficult to find. At present, most of the research uses reeds and mangrove plants as substitutes. The aim of the various control methods is to limit the growth and reproduction of S. alterniflora to control diffusion or completely remove the species (Xie and Han 2018). However, owing to the successful invasive and competitive properties of S. alterniflora, economical and effective ways to control its diffusion are still lacking. China has carried out much research on S. alterniflora, but this has mostly focused on the analysis and prediction of regional and general data, and it lacks the basic data from field investigations and field tests. There is no detailed research on the impact of S. alterniflora on the local biological and environmental conditions, nor on the response of organisms in the recovery process.
As an important part of the tidal flat ecosystem, macrobenthos plays a key role in material circulation and energy flows, and helps to maintain the health and integrity of marine ecosystem (Lv et al. 2018). The biodiversity, community structure and species composition of macrobenthos can indicate the status of the ecological environment of the region (Harrel and Smith 2002). Through a comprehensive investigation of the macrobenthic community, we can better understand their response to environmental changes. In turn, their response will reflect the effect of restoration on the beach ecosystem, and provide a basis for judging the implementation success of the restoration project. Some scholars have studied the community composition and ecological characteristics of macrobenthos in the intertidal zone of Hangzhou Bay (Fan et al. 1996; Shou et al. 2012; Yan et al. 2021), especially the resources and population changes of macrobenthos after the implementation of several large-scale marine projects in Hangzhou Bay (Zhou et al. 2009; Li et al. 2007; Luo et al. 2007). However, a study comparing specific habitat types has not been undertaken. Different habitats have different effects on the composition of macrobenthic communities owing to the differences in hydrodynamic conditions (Zheng et al. 2011), physical factors such as water depth (Cai et al. 2012), physical and chemical factors such as water quality (Wang et al. 2005) and biological factors such as competition and predation (Holland et al. 1980).
To explore the impact of S. alterniflora management on organisms and the restoration of the tidal flat ecosystem, this study carried out a survey of macrobenthos in the mudflat recovery area (MRA), natural mudflat area (NMA), S. alterniflora area (SAA) and Scirpus mariqueter area (SMA) in June 2022, 1 year after S. alterniflora management measures were undertaken in the ecological restoration area on the south bank of Hangzhou Bay. A large amount of S. alterniflora originally grew in the MRA, which gradually recovered to mudflats after the implementation of the control project. By comparing the species composition, quantity and distribution of macrobenthic communities in different habitats and the differences in biodiversity, the study identified the distribution changes of macrobenthic communities and the impact of ecological restoration projects on macrobenthic communities. The findings provide a theoretical basis and practical experience for the prevention and control of S. alterniflora in the future.