Changes Of Resistant Indexes Under High-and Low-Temperature Stress In Gracilaria Lichevoides And Its Effect On The Growth Of Red Tide Algae

Gracilaria lichevoides is a warm-water alga that is found in the subtropical,temperate intertidal zone or near the low tide line.Currently,the culture of Gracilaria lichevoides introduced from Taiwan was carried out in coasts of Hainan,Guangdong and South Fujian.The alga can be used as bait for abalone and raw materials for agar.It can also absorb large amounts of nutrients such as N and P in seawater,which plays an important role in the purification of seawater and can be used as a biofilter in the offshore marine ecosystem.This paper studied the growth of Gracilaria lichevoides at different temperatures,the changes of resistant indexes under high-and low-temperatures stress,the fatty acid composition of algae,and the effects of unsaturated fatty acids,dried powder and hydroponics fluid of the alga on the growth of red tide algae.1.Changes of growth and resistant indexes under high-and low-temperatures stress in Gracilaria lichevoidesUnder different temperature conditions,the specific growth rate of Gracilaria lichevoides at 24? reached the highest.Under the high temperature stress of 36 ?,the daily growth rate of Gracilaria lichevoides could still maintain 0.92%,but when the stress temperature was 15 ?,12 ?,the growth rate showed a negative value.The effect of low temperature stress on the growth of Gracilaria lichevoides was significantly greater than that of high temperature stress.It was determined that the contents of soluble sugar,proline,MDA,and SOD in Gracilaria lichevoides varied from different degrees in the temperature range of 120C-360C.After 9 days of experiment,soluble sugars increased correspondingly,and there was a positive correlation with temperature change,and soluble sugar content at 12 ? in low temperature stress was higher than that at 36 ? in high temperature stress.The content of free proline first increased and then decreased.Among them,the proline content of cold stress at 12? was 2.4 times higher than that of high temperature stress at 36?.The change trend of MDA showed a downward trend of "V" type first rising and then decreasing.The contents and activity of MDA and free proline under low temperature stress at 12 ? were higher than 36 ?.From the perspective of the specific growth rate and various resistance indicators,the response of Gracilaria lichevoides against low temperature stress is much greater than that under high temperature stress conditions.1.Inhibitory effect of unsaturated fatty acids of Gracilaria lichevoides on red tide algae13 oil components in Gracilaria lichevoides was identified by GC-MS analysis,including 11 saturated fatty acids and 2 unsaturated fatty acids,namely 9z-octadecenoic acid,5z,8z,11z,and 14z-.Eicosatetraenoic acid.Test of algae inhibition showed that 9z-octadecenoic acid had a certain inhibitory effect on Prorocentrum above 80 mg/L,and it came stronger with the increase of concentration.Skeletonema costatum only had a weak inhibitory effect at 320 mg/L,but below this concentration,it shows a growth promoting effect.The inhibitory effects of 5z,8z,11z,14z-eicosatetraenoic acid on two species of red tide algae reached 100%,and their inhibitory effects increased with increasing concentrations.3.Effects of Gracilaria lichevoides powder and hydroponics fluid on the growth of Skeletonema costatumWhen the concentration powder added to the culture medium reached 1.6 g/L,the growth of Skeletonema costatum was effectively inhibited.With the concentration of 3.2 g/L,the inhibition rate on the 1st day reached 100%,its semi-effect inhibition is between 0.8g/L-1.6g/L.Hydropon is fluid from Gracilaria lichevoides on the growth of Skeletonema costatum had no inhibitory effect before 8 days of the experiment,and the inhibitory effects until the 10th day in each group.With the extension of time,the inhibitory effect gradually increased.