Renjun Wang

Allelopathic effects of Ulva pertusa, Corallina pilulifera and Sargassum thunbergii on the growth of the dinoflagellates Heterosigma akashiwo and Alexandrium tamarense

The allelopathic effects of fresh tissue, dry powder and aqueous extracts of three macroalgae, Ulva pertusa, Corallina pilulifera and Sargassum thunbergii, on the growth of the dinoflagellates Heterosigma akashiwo and Alexandrium tamarense were evaluated using coexistence culture systems in which concentrations of the three macroalga were varied. The results of the coexistence assay showed that the growth of the two microalgae was strongly inhibited by using fresh tissue, dry powder and aqueous extracts of the three macroalga; the allelochemicals were lethal to H. akashiwo at relatively higher concentrations of the three macroalga. The macroalgae showing the most allelopathic effect on H. akashiwo and A. tamarense using fresh tissue were U. pertusa and S. thunbergii, using dry powder were S. thunbergii and U. pertusa, and using aqueous extracts were U. pertusa and C. pilulifera. We also examined the potential allelopathic effect on the two microalgae of culture filtrate of the three macroalga; culture medium filtrate initially exhibited no inhibitory effects when first added but inhibitory effects became apparent under semi-continuous addition, which suggested that continuous release of small quantities of rapidly degradable allelochemicals from the fresh macroalgal tissue were essential to effectively inhibit the growth of the two microalgae.

Allelopathic growth inhibition of Heterosigma akashiwo by the three Ulva spcieces (Ulva Pertusa, Ulva Linza, Enteromorpha intestinalis) under laboratory conditions

Allelopathic effects of several concentrations of fresh tissue, dry powder and dry tissue of three bloom-forming green macroalgae Ulva pertusa, Ulva linza and Enteromopha intestinalis on the red tide microalga Heterosigma akashiwo were evaluated in microcosms systems. The effects of macroalgae culture medium filtrate were investigated on H. akashiwo using initial or semi-continuous filtrate addition. Preliminary studies on the algicidal effects of one aqueous and four organic solvent extracts from the macroalgae on the microalga were carried out to confirm the existence of allelochemicals in the tissue of these macroalgae. The dry powder of U. pertusa was extracted with methanol, and the methanol extracts were partitioned to petroleum ether phase, ethyl acetate phase, butanol phase and distilled phase by liquid-liquid fractionation. The bioassays of the activity of every fraction were carried out on H. akashiwo. The resultant microcosms assay showed that the growth of H. akashiwo was strongly inhibited by using fresh tissues, dry powder or dry tissue of these three macroalgae, while aqueous and methanol extracts of both macroalgae had strong inhibitory effects on the growth of H. akashiwo, and the EC50 values for methanol extract of U. pertusa, U. linza or E. intestinalis were 0.016, 0.028×10−12 or 0.033×10−12, respectively. While the other three organic solvent extracts (acetone, ether and chloroform) had no apparent effect on its growth, this suggests that the allelochemicals from these three macroalgae had relatively high polarities. The activity of petroleum ether phase, ethyl acetate phase, butanol phase and distilled phase of U. pertusa methanol extract was carried out on H. akashiwo indicating that petroleum ether phase and ethyl acetate phase had stronger algicidal effect on H. akashiwo. The inhibition effect of the ethyl acetate phase was not as strong as that of petroleum ether phase, and effective concentration of petroleum ether phase was 17 mg/L for H. akashiwo. However, no significant algicidal effects were observed on the butanol phase and distilled water phase. These three macroalgae’s culture medium filtrate exhibited no apparent growth inhibitory effect on the microalga under initial filtrate addition whereas the growth of H. akashiwo was significantly inhibited under semi-continuous filtrate addition, which suggests that continuous release of small quantities of rapidly degradable allelochemicals from the fresh tissue of both macroalgae was effective in inhibiting the growth of H. akashiwo.

Identification of the toxic compounds produced by Sargassum thunbergii to red tide microalgae

The inhibitory effects of methanol extracts from the tissues of three macroalgal species on the growths of three marine red tide microalgae were assessed under laboratory conditions. Extracts of Sargassum thunbergii (Mertens ex Roth) Kuntz tissue had stronger inhibitory effects than those of either Sargassum pallidum (Turner) C. Agardh or Sargassum kjellmanianum Yendo on the growths of Heterosigma akashiwo (Hada) Hada, Skeletonema costatum (Grev.) Grev, and Prorocentrum micans Ehrenberg. Methanol extracts of S. thunbergii were further divided into petroleum ether, ethyl acetate, butanol, and distilled water phases by liquid-liquid fractionation. The petroleum ether and ethyl acetate fractions had strong algicidal effects on the microalgae. Gas chromatography-mass spectrometry analyses of these two phases identified nine fatty acids, most of which were unsaturated fatty acids. In addition, pure compounds of four of the nine unsaturated fatty acids had effective concentrations below 5 mg/L. Therefore, unsaturated fatty acids are a component of the allelochemicals in S. thunbergii tissue.

Effect of anthracene on the interaction between Platymonas helgolandica var. tsingtaoensis and Heterosigma akashiwo in laboratory cultures

Two species of marine phytoplankton, Platymonas helgolandica var. tsingtaoensis and Heterosigma akashiwo, were cultivated in bi-algal cultures to investigate the effect of anthracene (ANT) on the interaction between them. Without ANT, H. akashiwo out-competed P. helgolandica at low initial biomass ratios (P. helgolandica (P): H. akashiwo (H) = 1:4 and 1:1), but not at the highest (P:H = 4:1). This observation was consistent with the description in Lotka-Volterra two species competition model. It was found that P. helgolandica was excluded at low initial biomass ratios, while the unstable equilibrium between two species was predicted at the highest. For both species, carrying capacity and maximal specific growth rate decreased in bi-algal cultures compared to those in monocultures. H. akashiwo exhibited a higher sensitivity to ANT than P. helgolandica. This resulted markedly in a reduced cell density of H. akashiwo but an increased cell density of P. helgolandica. Carrying capacity of P. helgolandica was consistently higher in bi-algal cultures with ANT than those without ANT, suggesting that ANT, through the elimination of H. akashiwo, generated the dominance of P. helgolandica independently of initial biomass ratios. This study showed a density-dependent effect of harmful alga (H. akashiwo) on dietary alga (P. helgolandica), and indicated that ocean pollutant ANT could induce the succession of marine phytoplankton.

Effects of Inoculation Proportions and UV-B Radiation on the Growth Competition between Two Red Tide Algae Alexandrium Tamarense and Skeletonema Costatum

The potential danger from the influence and injury of UV radiation on marine organisms has been increasing. In this study, for the first time we investigated the responses of the interspecies competition between two red tide algae, Alexandrium tamarense (At) and Skeletonema costatum (Sc) to different inoculation proportions and UV-B radiation enhancement by co- culture method. Our results demonstrated that the different inoculation proportions of A. tamarense and S. costatum had apparent effects on interspecies competition between the two red tide algae. When the inoculation proportion of A. tamarense and S. costatum was Af:Sc = 1:4, S. costatum was dominant in competition. In contrast, A. tamarense was dominant when Af:Sc = 1:1 and Af:Sc = 4:1. In addition, the UV-B radiation treatment could change the nature of the competition between A. tamarense and S. costatum, and promote the competitive dominance of S. costatum. We observed that the competitive dominance of S. costatum changed more remarkably when Af:Sc=l:4, and was in predominance when Af:Sc =1:1 under UV-B radiation treatment.