A Study On Farming Techniques Of Sargassum Thunbergii And Application In Integrated Multi-tropic Aquaculture

Sargassum thunbergii belongs to Phaephyta and considered as important economic algae in coastal region of china. It is widely used in sea cucumber, abalone feed industry.There was a growing trend of demand of S. thunbergii with the development of sea cucumber culture. As wild resources could’t meet the demand, mariculture of S. thunbergii become important. Integrated Multi-trophic Aquaculture based on seaweed is a kind of research hot, by this way, it could reduce environmental stress and improve aquaculture production. Currently, there are still a lots of problem for the longline culture of S. thunbergii, which need to be deal with.Experiments were impleted in Sungo Bay, Shangdong province. The growth characteristics, biofouling controlling technique, higher efficiency longline culture technique were studied. And its application efficience in IMTA mode of finfish cage + bivalve+seaweed was studied. The mainly results were as follows: 1. Investigation on fouling organisms and growth characteristics of S. thunbergii aquacultured in Sanggou BayIn order to set-up the efficiency maricultural technique, the growth characteristics of long-line culture seaweed S. thunbergii was measured in Sanggou Bay during April-June, 2014. Meanwhile, the species and biomass of biofouling attaching on the seaweed were investigated. The results showed:(1) S. thunbergii could survive and grow well in Sanggou Bay and the maximal SGR(specific growth rate) reached to 6.10%·d-1 at the temperature 10~17℃; The optimum growth temperature was 14.9℃ according to the relationship between the temperature and SGR;(2) At 10 May, the reproductive branches could be found and most of mature sexual reproduction were appeared when the sea water temperature reached to 20.4℃;(3)At these stage, the maximum thallus length of S. thunbergii could reached to 187.05 cm, and maximum average length was 112.31cm; The ratio of wet-to-dry weigtht rised from 0.147( at May) to 0.189( at June); the total production per acre estimated to be 2.93 t wet weigth, equal to 0.55 t dry weight;(4) 16 species of macro-biofouling were identified and the dominant species were the Pachychalina variabilis, Ciona intestinalis and eggs of Ablennes anastomella; Biomass of biofouling increased with temperature increasing. It is feasible for S. thunbergii large-scale longline culture in Sanggou Bay and benefit of up to 4000 yuan per mu. 2. The effect of different initial length of seedling、water deep and seedlings separation to the growth of S. thunbergiiIn order to achieve the farming techniques of S. thunbergii in north of china, we studied the effect of different initial length、water deep and separated seedings to the trial trial culture of S. thunbergii in shallow sea of Ailian Bay. The experiment started from April to August in 2014,we set three different initial length group(Initial length was: 103.67±36.43cm、49.03±11.81cm、20±6.37cm)、two different deep water(Water deep:0m、1m)、separated seedings and non-separated seedings. The results show:(1)Different initial length didn’t significantly effected the wet weight and dry weight after growing of two months(P>0.05);(2)Culturing under water significantly increased dry weight production(P < 0.05);(3)Separated seedings had sigificantly increased SGR(specific growth rate)(P<0.05),and didn’t effect the N content of algae(P>0.05).(4) The relevant equations of specific growth rate(y)(%·d-1) and density(x)(wet weight of 1m rope) was y=2.8674e-24.087x(R2=0.8904),which meaned SGR no more than 1% when density reach to 2.3kg. Although S. thunbergii grew well in Ailian Bay, S. thunbergii was easily restricted by the factor of density, we could improve the growth status through changing water deep and separating seedings, and increased production in final. 3. Effects of freshwater stress on chlorophy II fluoresence parameters and survival rate of Sargassum Thunbergii and fouling algaesBy using chlorophy chlorophy II fluoresence kinetics technology, we studied the chlorophy II fluoresence parameters and survival rate of S. thunbergii、Ceramium rubrum、Ulva linza under freshwater press to explor the method of fouling algae prevention in S. thunbergii cultivation.The result shows:(1) The tolerance of freshwater to algae was different, Ceramium rubrum was most sensitive, S. thunbergii followed, last was U. linza.(2) Chlorophy II fluoresence parameters(Fv/Fm 、α、r ETRmax) won’t significantly(P>0.05) decrased within 10 h of S. thunbergii. Death appeared after 6h, the survival rate declined to 0 after 24 h. Chlorophy II fluoresence parameters significantly(P<0.05) decrased after 0.5h of C. rubrum. the survival rate declined to 0 after 1h. Chlorophy II fluoresence parameters significantly(P<0.05) decrased after 48 h of U. linza. Death appeared after 40 h.(3) The effects of freshwater bath were different from species of algae. 1h freshwater bath won’t damage the S. thunbergii, but killed all of the C. rubrum. 4. Application efficience of S. thunbergii in IMTAIn order to explore the ecological potential of application in fish–shellfish-algae breeding mode of S. thunbergii, We studied the fix capacity of carbon and nitrogen in the conditions of single breeding(contrast) and integrated farming, evaluated the effects of S. thunbergii shedding detritus to Chlamys Scallop in Shell tissue carbon sources using isotope techniques.The results showed:(1) S. thunbergii as the primary producers in the ecosystem, in addition to the absorption of nutrients in aquaculture water, seaweeds may provide some food for Scallop in detritus;(2) Integrated farming can significantly(P < 0.05) improve the S. thunbergii harvest(dry weight), S. thunbergii in integrated farming removed N 21.98% more than the contrast, removed C 42.12% than the contrast, the carbon sequestration rate was significantly(P < 0.05) higher than the contrast in the rapid growth phase;(3) After 3 months of integrated farming, Chlamys Scallop in Shell carbon source, 26% from S. thunbergii, 26% from the cage system, 48% from POM. The purpose of this paper is to provide a theoretical basis for the comprehensive cultivation technology for seawater.