Genotypic diversity and growth responses to temperature and salinity variations of Coolia malayensis (Gonyaulacales, Dinophyceae) in Chinese coastal waters

Coolia malayensis is a benthic dinoflagellate widely distributed in tropical to subtropical coastal waters, with some strains exhibiting cytotoxicity, indicating potential ecological and toxicological roles. This study investigated the genetic diversity and adaptability of C. malayensis strains across diverse environmental conditions in Chinese coastal waters. Three distinct genotypes, Genotype 1 (strain DF553), Genotype 2 (DF630), and Genotype 3 comprising strains DF307, DF316, and DF364, were confirmed by the large subunit (LSU) ribosomal DNA phylogenetic analysis, with a protein profiling by the matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry providing supporting evidence for the phenotypic differentiations. The results of growth experiments conducted under varying temperature (15°C to 30°C) and salinity (15 to 35) conditions demonstrated genotype-specific environmental preferences: strain DF553 exhibited an optimal growth at 25°C and 30 salinity, strain DF630 at 30°C and 30, while strains DF307, DF316, and DF364 displayed a wider range of adaptive capacities. These results emphasized the ecological flexibility and adaptive potential of C. malayensis, indicating its ability to thrive in diverse marine environments. The study underscores the importance of genotypic variation in predicting species responses to environmental fluctuations, offering valuable insights for marine ecosystem management and mitigation of harmful algal blooms.