Are rice fields less diverse and more invaded by non-native species than less impacted habitats? A test with wetland microcrustaceans

Freshwater ecosystems are subject to multiple human stressors, which can make them more susceptible to invasions. Even protected areas established to safeguard freshwater wetlands can be vulnerable to invasions, particularly when they include disturbed environments such as rice fields, which function as colonization pathways for invasive aquatic organisms. In this study, we compared the microcrustacean communities across three habitat types (rice fields, marshes and limnocrenes) in two protected Mediterranean wetlands during summer and winter seasons, using PERMANOVA, dbRDA and indicator value analyses. We studied the species diversity (alpha and gamma), composition and frequency of microcrustaceans, focusing on invasive taxa. We found 92 microcrustacean species, 16 of which were considered invasive. Although we expected higher microcrustacean diversity in marshes and limnocrenes than in rice fields due to human impact, the latter stood out as more diverse than less disturbed habitats. Invasive species played a significant role in accounting for microcrustacean diversity, and they were present across all habitats, in similar proportions. Species composition remained relatively stable between winter sampling campaigns but varied in summer and among habitats. Although more invasive species were selected as indicators of rice fields, their presence in less disturbed environments challenged expectations. Despite the absence of seasonal and habitat differences in the proportion of invasive species found, our study underscored the potential of rice fields as invasion pathways for protected wetlands and the capacity of invasive species to colonize less impacted environments. Addressing microcrustacean invasions is crucial for wetland conservation and ecosystem function, even if their ecological impacts are not fully understood. Integrated management strategies should focus on prevention and early detection to safeguard native species persistence and the ecosystem integrity of protected wetlands.