Abstract
This study was conducted to assess the diversity of Gracilariaceae species across various coastal ecosystems in Zhanjiang, Guangdong Province, China, and identify species suitable for large-scale cultivation in the southern coastal waters of China. The diversity and seasonal and spatial distribution patterns of Gracilariaceae species in different ecosystems were systematically analyzed, and taxonomic studies were performed on species with disputed taxonomic identities using morphological and multi-gene marker techniques to clarify their classification status. Species richness was higher, but individual species coverage was lower in open ecosystems (e.g., tidal pools) compared to enclosed ecosystems (e.g., mangroves, seagrass beds, saltwater ponds), and both factors showed significant seasonal variation. Conversely, enclosed ecosystems had lower species richness, higher species coverage, and minimal seasonal variation. The presence of Gracilaria fisheri in China was recorded for the first time, and the taxonomic status of G. hainanensis was systematically evaluated. Based on taxonomic evaluations and a review of the literature, G. changii and G. firma were proposed to be synonymous. In total, eight Gracilariaceae species were identified during the survey. Among them, Gracilariopsis heteroclada, G. fisheri, G. edulis, and G. hainanensis were identified as potential candidates for large-scale cultivation in the southern coastal waters of China. This study advanced the understanding of the taxonomy and ecology of Gracilariaceae species in the Zhanjiang region and provided a scientific foundation for the conservation and industrial development of Gracilariaceae resources.