Preliminary Study Of Allelopathic Effects Between Marine Algae

Red tides have become one of the most serious marine disasters due to the eutrophication of the coastal areas. Harmful algae blooms (thereafter HABs) even cause direct economic loss as much as 1 billion yuan every year. On the other hand, "green tides" also need to be controlled which comes from Chlorophyta such as Ulva pertusa's out breaking growth. How to control red tides in a quick and effective way and at the same time, benign to the environment is becoming a hot spot in marine science field. There are some promising methods have been developed to control this, including the use of yellow losses to sediment red tide organisms, chemical agents such as copper sulfate, hydrogen peroxide, and some biological controls in the form of viruses or bacteria. However, they may have potentially dangerous environmental consequences; therefore there are very limited investigations of a direct and specific control of marine harmful algal blooms with few environmental side-effects.In this study, we tried to utilize the interaction among aquatic organisms to control the growth of red tides microalgae. Two red tides species S. coatatum and H. akashiwo and a macroalgae Ulva pertusa were involved in this study. The experiments of two microalgae in bialgal culture and in each other's culture filtrate were conducted under laboratory conditions. The effects of macroalgae Ulva pertusa on the growth of the two microalgae in co-culture and aqua-extract conditions were also performed. The data was simulated by the Logistic and Lotka-Volterra model to predict the following situation. By using different organic solvents to extract and doing biological assay, this study wanted to make sure the chemical property and structure. The main objectives of this study were to provide proof of the allelopathic effects between microalgae and macroalgae on microalgae, to gain an insight into the chemical interactions among aquatic organisms in coastal areas, and to present evidence for the feasibility of using biological way to control the growth of red tide microalgae.Results show that:Both microalgae:Skeletonema coatatum and Heterosigma akashiwo were inhibited in each other's culture filtrates. According to the simulated processing, the inhibited factor of S. coatatum on H.akashiwo was 6.56, the factor of H. akashiwo on S.coatatum was 0.04. Macroalgae fresh leaves had inhibition effect on microalgae and this effect increased with the amount of fresh leaves. H. akashiwo was more vulnerable than S. coatatum which may due to the transparent structure easily absorbing allelopathic compounds. From the result of extract and bioassay experiment, it can be concluded that the bioactive compound or responsible mixture is non-polar and easy to volatilizing. The accurate composition and mechanism need more research.