Interspecies competition between Scrippsiella acuminata and three marine diatoms: Growth inhibition and allelopathic effects

Interactions between Scrippsiella acuminata and three diatoms, Chaetoceros curvisetus, Phaeodactylum tricornutum , and Skeletonema dohrnii , were investigated using bi-algal co-cultures and cell-free and sonicated-cell filtrates in this study. Volatile aldehydes in sonicated filtrates of the three diatoms were analyzed by GC/MS. Furthermore, effects of 2E, 4E-decadienal (2,4-D) on the growth and the photosynthetic efficiency of the four microalgal species were studied. The growth of Sc. acuminata was significantly inhibited by the three diatoms in all co-cultures, and the inhibitory effects were higher under nutrient-rich conditions. Both cell-free and sonicated-cell filtrates of the three diatoms showed significant inhibitions on the growth of Sc. acuminata , which highlighted that diatoms produce allelopathic compounds not only to the surrounding environments but also inside the cells. Fifteen aldehydes were detected in the sonicated-cell filtrates of the three diatoms, and 5, 5, and 12 types of aldehydes were detected in C. curvisetus, P. tricornutum , and Sk. dohrnii , respectively. Polyunsaturated aldehydes (PUAs) composition differed among the three diatom species. Phenylglyoxal (C 8 H 6 O 2 ) dominated in C. curvisetus , 2,4-D (C 10 H 16 O) predominated in P. tricornutum , and high proportions of 2-hexenal (C 6 H 10 O), 2E, 4E-heptadienal (C 7 H 10 O), and 2,4-D were detected in Sk. dohrnii . 2,4-D showed significantly inhibitory effects on the growth of algal cells including diatoms themselves in a dose-dependent manner, and photosynthetic efficiency was significantly decreased as well. Sc. acuminata was the most sensitive species. The 96 h EC 50 values of 2,4-D on the growth of the four microalgae were 1.64 μmol/L for Sc. acuminata , 3.09 μmol/L for C. curvisetus , 4.93 μmol/L for P. tricornutum , and 8.54 μmol/L for Sk. dohrnii , respectively. The results suggest that PUAs produced by diatoms may help them to take the competitive advantages in phytoplankton community, and thus to sustain diatom-dominated community structure in nutrient rich coastal waters.