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 cocultures, and the inhibitory effects were higher under nutrient-rich conditions. Both cell-free and sonicatedcell 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 (C8H6O2) dominated in C. curvisetus, 2,4-D (C10H16O) predominated in P. tricornutum, and high proportions of 2-hexenal (C6H10O), 2E, 4E-heptadienal (C7H10O), 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 EC50 values of 2,4-D on the growth of the four microalgae were 1.64 mu mol/L for Sc. acuminata, 3.09 mu mol/L for C. curvisetus, 4.93 mu mol/L for P. tricornutum, and 8.54 mu mol/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.