Effects Of Environmental Factors On The Growth Of Gracilaria Arcuate

Macroalgae are important aquaculture species worldwide,accounting for 27%of the global production from aquaculture.Gracilaria arcuata,belonging to the genus Gracilaria of the Rhodophyta,is a typical tropical coral reef macroalgae,which plays an important role in the agar industry,food industry,pharmaceutical industry,biotechnology,aquaculture feed and cosmetics.It has the potential to be cultivated on a large-scale cultivation,which can absorb nutrients in water,improve eutrophication water quality,increase dissolved oxygen concentration in water,maintain the stability of mariculture system and improve marine biodiversity.However,there are few studies on the environmental adaptability and nutrient uptake characteristics of G.arcuata.In this research,wild G.arcuata in the Xisha Islands of China was used as experimental material.The effects of different environmental factors about temperature,salinity,light quality,and light intensity on the growth,photosynthetic pigment content and photosynthetic physiology of G.arcuate were studied.Besides,the effects of temperature and light intensity on the growth,photosynthetic pigment content,and photosynthetic physiology of G.arcuate were investigated under the superposition of temperature and light intensity in a tropical marine environment.In terms of nutrients,the absorption characteristics and capacity of G.arcuate to different nitrogen and phosphorus sources were studied,and to explore the effects of under different the ratio of nitrogen and phosphorus on growth,photosynthetic pigment content and photosynthetic physiology of G.arcuate were explored,as well as the nutrient uptake.On this basis,we explored the methods of indoor culture and field cultivation of G.arcuate,recorded the changes of biomass of G.arcuate during indoor culture and field cultivation,established the most suitable culture method,and provided technical basis and guidance for the large-scale cultivation and culture of G.arcuate.Firstly,the collected species was identified morphologically and molecular biologically,and the species was confirmed to be G.arcuate.The results are as follows:1.Effects of temperature,salinity and light on the growth rate,photosynthetic pigment content,and photosynthetic physiology of G.arcuateThe experimental results show that G.arcuate is a macroalgae that can adapt to high temperature and high light growth environments.The suitable temperature for growth is 22～30℃,and the suitable salinity for growth is 20～40‰,the suitable light intensity was 100～300μmol·m^-2·s^-1,the suitable light quality was green light,white light and red light.Among them,the optimal for growth temperature is 26～30℃,the optimal for growth salinity is 30～35‰,and the most suitable for growth light intensity is 150～200μmol·m^-2·s^-1,the most suitable light quality for growth is green light and white light.G.arcuate has a relatively high growth rate under suitable environmental conditions,at which time the phycobiliprotein content,fat-soluble pigment content,soluble protein content and Fv/Fm are relatively high Under the combinations of temperature and light intensity,G.arcuate has a strong adaptability to high temperature and high light.Although the growth of algae is inhibited,the content of phycobiliprotein content and fat-soluble pigment content is high.2.Characteristics of nitrogen and phosphorus nutrient uptake and growth response of G.arcuateThe Michaelis-Menten equation model is suitable for evaluating the absorption capacity of algae to nutrients,which could better describe the relationship between nutrient concentration and its uptake rate.G.arcuate has remarkable absorption efficiency on three nutrients,nitrate nitrogen,ammonium nitrogen and phosphate,respectively,especially ammonium nitrogen and nitrate nitrogen.The maximum absorption rates V_max of G.arcuate for nitrate nitrogen,ammonium nitrogen,and phosphate are 14.59,10.91,and 5.02μmol·g^-1·h^-1,respectively,and the absorption semi saturation constant K_m are 305.6,64.41,and 9.410,respectively.At a concentration of150μmol·L^-1,the relative growth rate of G.arcuate was faster than other concentrations like 25、50、100、200μmol·L^-1.At the same concentration of ammonium nitrogen and nitrate nitrogen,G.arcuate preferentially absorbs ammonium nitrogen.Compared with nitrate and ammonium nitrogen,G.arcuate has a poor absorption efficiency on phosphate uptake.The relative growth rate of G.arcuate was the highest when the phosphate concentration was 5μmol·L^-1 than at other concentrations(2.5、10、20、30μmol·L^-1).The optimal the ratio of nitrogen and phosphorus was 10:1 and30:1,respectively,under these two ratios,G.arcuate could grow better and absorb nitrogen more quickly.3.The cultivation experiment of G.arcuateG.arcuate can attach to coral stone and produce secondary attachment structure,which is beneficial to the increase the yield of alga and in situ remediation the of algal resources.During indoor culture,aerated culture greatly increased the growth rate of the algae,which was better than static culture.In the field cultivation experiments using different culture methods,all three cultivation methods were able to achieve rapid growth of G.arcuate under suitable environmental conditions,with the relative growth rate of 2.24±0.04%·d^-1 for the coral-rock seedling method being higher than that of the net bag hanging method and the net curtain spreading method.