Selection Of Substrates And Optimization Of Culture Conditions For Caulerpa Lentillifera

Caulerpa lentillifera is an edible and multifunctional macroalgae with rich nutrition and a broad economic market.The development and utilization of this alga has been a hot spot in the world’s fisheries,especially in the area of algal cultivation.At present,large-scale cultivation of C.lentillifera is faced with several hindrances.The low yield of C.lentillifera led to a significant markup in price.Existing research places strong emphasis on increasing the total yield of C.lentillifera,while few studies have been conducted on biological characteristics of thllus,changes of nutritional components and comparison of attachment effects of different substrates for C.lentillifera.The key objective of this study is to explore the best substrate and cultivation conditions of C.lentillifera by changing different substrates types,particle sizes of sea sand and air inflation.This study further analyzes the effects of different substrates on the biological characteristics,nutritional components,photosynthetic characteristics and attachment effects of C.lentillifera in order to cultivate high-quality and high-yield Caulerpa,which shall lay the foundation for an uplift in both production and quality.The main results are as following:1.Effects of different substrates on growth and attachment effect of C.lentillifera.The results showed that the length and number of the new thllus increased significantly（P<0.05）,and the ratio of fresh weight to mass length was the largest（P<0.05）in vertical sand burial treatment.Compared with the algae cultivated with plastic net and nylon net,the ratio of fresh weight and weight length of new thllus increased by more than 200%,while no attachment treatment was not conducive to the growth of C.lentillifera.The growth of rhizoid of algae cultivated in sand was the best,and the rhizosphere coefficient and attached grain weight increased significantly under horizontal sand burial（P<0.05）,which was 3 times as much as that under net attachment treatment,indicating that horizontal sand burial treatment could significantly enhance the attachment ability of algae,followed by vertical sand burial.In addition,the maximum photoenergy conversion efficiency（F_v/F_m）and the actual photochemical efficiency Y（Ⅱ）of each group decreased first and then was on the increase.After 24 hours,the F_v/F_mand Y（Ⅱ）of vertical sediment buried algae was the quickest in terms of recovering to its the original level,which were 0.856μmol·m^-2·S^-1and 0.851μmol·m^-2·s^-1,significantly higher than those in the rest groups（P<0.05）.The soluble sugar content of algae in horizontal and vertical sand burial treatment decreased by 34.24%and 33.93%respectively,and there was no significant difference among the other groups（P>0.05）,while vertical sand burial treatment significantly promoted the protein synthesis of algae.2.Effects of different particle sizes of sea sand on growth and attachment effect of C.letillifera.The results showed that the small gravel substrate（0.12～0.42mm）was more suitable for the growth of the thllus of the algae,and the length,fresh weight and diameter of the new ramuli increased remarkably by 571.92%,623.64%and 139.52%respectively（P<0.05）compared with the control group.The length,number and the attached grain weight of the rhizoid in the small gravel substrate were the best,which increased by 221.46%,523.65%and 453.33%respectively compared with the control group.In addition,the soluble sugar content and protein content of the algae in the small gravel substrate were significantly increased（P<0.05）.3.Effects of different ways of air inflation on growth and attachment effect of C.letillifera.The results demonstrated that the attached substrate combined with aeration device had no significant effect on the specific growth rate and the growth of thllus（P>0.05）.Under the treatment of plastic net combined with aeration device,the stolon length and fresh weight of algae in direct contact with air bubbles increased by123.14%and 122.22%（P<0.05）,and the number and length of rhizoids increased by 2.49 times and 1.18 times,respectively（P<0.05）4.Effects of different depths on growth and photosynthetic characteristics of C.letillifera.The results showed that when cultured in a basket with sands inside,the growth of C.letillifera was the best in the surface layer group（10 cm deep）and the middle layer group（40 cm deep）（P<0.05）,and its specific growth rate was the highest,which was 4.49%·d-1 and 4.40%·d-1 respectively.Compared with the deep layer group（70 cm deep）,the growth rate of Caulerpa letillifera increased by127%and 125%respectively.The fresh weight of thllus and diameter of ramuli in the middle layer group were remarkably increased（P<0.05）,which were 1.13 and1.14 times of those in the deep layer group,and the Fv/Fm and Y（Ⅱ）values in the surface layer group significantly decreased,while those in the middle and deep layer groups were on the increase,but the effect was not significant,which indicated that the cultivation of algae at water level of 10 cm was not conducive to photosynthesis.