05). The growth of P. donghaiense was suppressed very significantly in the co-culture from LGS onwards, and its cell densities at EGS and SGS were 75 × 104 and 36 × 104 cells mL− 1, only approximately 13% and 3% of those in monoculture(P < 0.0001) ( Figure 1c). When the initial cell densities of both

P. tricornutum and P. donghaiense were set at 1.0 × 105 cells mL− 1, the growths of both P. tricornutum and P. donghaiense in the co-culture INK 128 were significantly inhibited, their cell densities being about 63% and 15% of those in the monoculture at SGS (P < 0.0001) (Figure d). Several studies have hinted that the composition and dynamics of algal communities may be influenced by allelopathy among algal species (Legrand et al. 2003). The earlier studies on allelopathy among algae concentrated on field observations. For example, Keating (1977) observed the allelopathic influence of successors and their predecessors on the blue-green bloom sequence in Linsley Pond, a eutrophic lake, over a period of three years. In eutrophic lakes, diatom bloom populations varied inversely with the levels of the preceding blue-green algal populations, and blue-green algal dominance could be attributed to the allelopathic

effects (Keating 1978). In the current study, we conducted laboratory experiments under controlled conditions to exclude the effects of environmental factor variation. Besides, in order to reveal the growth and interactive effects between P. tricornutum and P. donghaiense, Sirolimus chemical structure we used their axenic strains. That is because previous bi-algal culture experiments indicated that bacteria were either directly or indirectly associated with algal toxin production, and that bacteria exerted some influence in the interaction between microalgal species ( Tarutani et al. 2000). Nagasaki et al. (1994) showed that bacterial attack

and viral infection might play a role in the algal bloom initiation, succession or termination. Therefore, in our study, the allelopathic activity of microalgae might be the most likely explanation for the stimulatory or inhibitory effects of Doxacurium chloride one species on the other co-cultured one. Our laboratory results showed that the growth and interactive effects between P. tricornutum and P. donghaiense were dependent on the initial cell density of each species: a higher initial cell density generally resulted in stronger allelopathic effects between them. In addition, when the initial cell densities of P. tricornutum and P. donghaiense were set at 1.0 × 104 and 1.0 × 105 cells mL− 1 respectively, growth promotion effects of P. tricornutum on P. donghaiense were detected at LGS, implying that allelopathic interactions were very complex and also time-dependent. We did not attempt to delve into the nature of this stimulation, but it could be assumed that some stimulatory compounds were excreted by P. tricornutum and that P.