Studies On The Methods Of Removing Attached Ulva L. Green Algae From Pyropia Rafts

Laver aquaculture which is one of the representatives of Chinese aquacultureindusty has a long history in China. In the late90s laver breeding in China witnessed asignificant increase, and then overtook Japan became the seaweed farming superpowerin2000. However, green algae attaches to breeding rafts has become one of theimportant factors that restrict the laver breeding healthy development of our country.Therefore, how to effectively remove these algae has become an important issues to besolved. This paper used the composing species of green algae communities in Jiangsucoastal seaweed farming sea area for investigation, studied the inhibit effect of twoantioxidants on the green algae.1. First, we used attached Ulva L. green algeafor investigation, studied the effects ofsodium hypochlorite on chlorophyll composition, fluorescence characteristics andphotosynthetic rate of Ulva L. by Chlorophyll extract, chlorophyll fluorescencetechnology and liquid oxygen electrode. The results showed that with the NaClOconcentration increased, the chlorophyll content and fluorescence characteristics ofUlva L. are gradually decreasing. After10.0mmol/L NaClO treatment, Chla and Chlbrespectively reduced to0.030mg/g and0.039mg/g.0.00~6.00mmol/L NaClO havesignificant influence on the fluorescence characteristics of the algae. Thephotosynthetic rate of Ulva L. decreased to36%of the control group with2.00mmol/L NaClO treatment. According to the result of the determination of residual rateof sodium hypochlorite, the available cholrine content has a negative correlationrelationship with illumination time and temperature.2. Then we invested the effects of sodium hypochlorite on chlorophyll content,fluorescence characteristics and photosynthetic rate of Ulva prolifera by Chlorophyllextract, chlorophyll fluorescence technology and liquid oxygen electrode. The resultsshowed that after sodium percarbonate treated, the content of Chla and Chlb were bothdeclining, and with concentration of sodium percarbonate increased, and along withthe higher concentration of sodium percarbonate, Chla and Chlb content decreasing.After50mmol/L sodium percarbonate soaked, the content of Chla decreased by53.8%,Chlb decreased by55.8%, and the whole chlorophyll content decreased by54.5%.With sodium percarbonate soaked for5min, Fv/Fm (fluorescence characteristics) hada slow decline, but, after96h recovery cultivated, Fv/Fm of those algae with10,20, 30mmol/L treated has returned to normal level, while the Fv/Fm of algae of40、50mmol/L was undetectable. As for the photosynthetic rate of Ulva prolifera, we foundthat after10mmol/L sodium percarbonate treated, the rate was only1/3of controlalgae, and there was no significant difference from20to50mmol/L. The ratio ofphotosynthetic rate and respiration rate decreased obviously. According to the result ofthe determination of residual rate of sodium percarbonate, its decomposition rate has anegative correlation relationship with illumination time and temperature, in thecondition of20℃and8h illumination, the decomposition rate reachede90%.3. The results of outdoor experiment showed that both0.6%sodium hypochloriteand100mmol/L sodium percarbonate can remove the algae that attached on thebreeding rafts effectively. Compared with sodium percarbonate, the algaecide effectand the cost of sodium hypochlorite was better and lower than sodium percarbonate.However, sodium percarbonate can almost decompose in3h. After comprehansiveconsideration of all aspects, we considered sodium percarbonate as algaecide not onlycan effectively remove the algae but also can prevent the secondary pollution to themirane.