Studies On The Allelopathic Effects Of Enteromorpha Linza On Heterosigma Akashiwo

Inhibitory effects of Enteromorpha linza, Cladophora sp., Codium fragile, Gelidium amansii, Symphyocladia latiuscula, Ahnfeltiopsis flabelliformis, Grateloupia filicina, Gracilaria bursa-pastoris, Halymenia floresia, Gymngongrus flabelliformis, Polysiphonia japonia, Plocamium telfairiae, Chondrus ocellatus, Sargassum kjellmanianum, Sargassum thunbergii on the growth of microalga Heterosigma akashiwo are evaluated using coexistence culture systems, and compared with that of Ulva pertusa, in order to screen the macroalgae whose inhibitory effects are stronger than that of U. pertusa. As a result, the inhibitory effect of Enteromorpha linza is the same strong as that of U. pertusa. The test selects Enteromorpha linza as the object of allelopathy study.Allelopathic effects of the macroalga Enteromorpha linza on the microalga Heterosigma akashiwo are preliminarily studied under stable experimental conditions, in order to find out a means of biological control of harmful algae blooms. Allelopathic effects of fresh tissue and dry powder of Enteromorpha linza on Heterosigma akashiwo are studied using coexistence culture systems. The results of the coexistence assays show that the growth of Heterosigma akashiwo is strongly inhibited by fresh tissue and by dry powder of Enteromorpha linza. At a threshold level of 1.2 g-dryl~-1 of dry powder and 1.0 g-wet 1~-1 of fresh tissue of Enteromorpha linza, H. akashiwo cells are completely killed when their initial density is lower than 1×10~5 cells ml~-1. The effects of the macroalga culture medium filtrate on the Heterosigma akashiwo are also investigated to confirm the existence of allelochemicals. The growth of H. akashiwo is not significantly (p > 0.05) lowered by macroalga culture medium filtrate under initial filtrate addition. On the contrary, the growth of H. akashiwo is strongly inhibited by macroalga culture medium filtrate under semicontinuous filtrate addition. It is speculated that continuous addition of allelochemicals is important to effectively control the growth of H. akashiwo.Heterosigma akashiwo is not inhibited when inoculated in the boiled macroalga culture filtrate, which suggestes that allelochemicals from the fresh tissue of Enteromorpha linza are unstable and degradable at higher temperature. These assays prove that Enteromorpha linza has allelopathic effects on H. akashiwo.Influence of the environmental factors such as temperature, salinity and light intensity on allelopathic activity of Enteromorpha linza against Heterosigma akashiwo are preliminarily studied, in order to provide some theoretical proof for biological control of harmful algae blooms. The growth of Heterosigma akashiwo is strongly inhibited by inoculation concentrations (0.3, 0.45 g-wet I"1) of macroalga fresh tissue when temperature is above 15°C. Allelopathic effects of inoculation concentrations 0.45 g-wet I"1 of E. linza are the strongest at temperature 25 °C, light intensity 50001x, salinity 30. However, allelopathic activity of unit weight of E. linza is the best at temperature 25°C, light intensity 30001x, salinity30. It is speculated that allelochemical production is comparatively large at temperature 25 °C, light intensity 30001x, salinity30.