Environmental DNA reveals how the absolute dominant zooplankton species affects the community

Zooplankton play a crucial role in marine ecosystems. In recent years, the East China Sea (ECS) has recorded the highest levels of pollution among China's marine areas, leading to a trend toward homogenization of the dominant zooplankton species. Environmental degradation has triggered various ecological responses, but how these responses further impact community structure requires more investigation. In this study, we employed a combined approach of morphological identification and environmental DNA (eDNA) metabarcoding to analyze the effects of seasonal variation and dominant species on zooplankton communities. The results indicated that an absolute dominant species, Calanus sinicus, emerged in the ECS, significantly occupying ecological resources. As seasons changed, C. sinicus showed a trend of migrating from offshore to coastal areas. The high abundance of C. sinicus in the sub-regions led to a regional decline in zooplankton community diversity and interspecies cooperation, while the community also experienced stronger dispersal limitations. Furthermore, the spring zooplankton community exhibited higher alpha and beta diversity, as well as a more stable co-occurrence network compared to summer. However, the level of interspecies cooperation in spring was lower than in summer. In conclusion, the high abundance of C. sinicus has a significant impact on zooplankton communities, and this impact shows a lag effect.