Taxonomic identity of Gracilariaceae (Rhodophyta) species tolerant to hot summers: An integrative morphological and molecular assessment

Abstract

Gracilariaceae species are among the most economically important seaweeds, with a wide range of applications. Large-scale cultivation of Gracilariopsis lemaneiformis has already been established along the eastern coast of China. However, as global demand for Gracilariaceae species rises, it is crucial for China to expand large-scale cultivation of these species to other coastal regions. Although the South China Sea harbors rich macroalgal resources, including Gracilariaceae, large-scale cultivation of these species has yet to be implemented in the region. To identify heat-tolerant Gracilariaceae species suitable for large-scale cultivation in the South China Sea, we conducted surveys between June and August from 2021 to 2024. Several heat-tolerant species were identified. Taxonomic identity was confirmed through detailed morphological examination and molecular analysis of rbcL and cox1 gene sequences. We identified eight species of Gracilariaceae, including one Gracilariopsis (Gp.) species and seven Gracilaria (G.) species. Morphologically, the species were characterized as follows: Gp. heteroclada (long secondary branches with short or spiny tertiary branches), G. salicornia (club-shaped segments), G. vermiculophylla and G. tenuistipitata (slender-branched), G. edulis (broom-like appearance with red-tinged branch bases), G. firma (highly constricted branch bases), and two unclassified species, Gracilaria sp.1 and Gracilaria sp.2. This study contributes to the taxonomic knowledge of Gracilariaceae and provides valuable information for the development of heat-tolerant species suited for large-scale cultivation in the South China Sea.