| A nutrient budget describing the flow of organic carbon (OC), nitrogen (N) and phosphorus (P) through four polyculture ponds (jellyfish-shellfish-fish-prawn) in Donggang Liaoning province from 2013 to 2014 was produced base on the principles of biology and ecology in this paper. The research includes water quality, community structure of plankton, sediment and structure of suspended particles, the food sources of the food web structure, nutrient (OC, N, P) budgets in ’Rhopilema esculentum-Sinonovacula constricta -Paralichthys olivaceus-Fenneropenaeus chinensis’ polyculture ponds, and nutrient (OC, N, P) budgets in a’Rhopilema esculentum-Sinonovacula constricta-Paralichthys olivaceus-Marsupenaeus japonicus’ polyculture pond. The effects of suspended particles on the clearance rate and absorption efficiency of Sinonovacula constricta was investigated by adopting the measures of experimental ecology in the laboratory. Aim to clarify the structure and function of this ecosystem, analyze the characteristics of this culture model and its benefits, and to provide a reference for the water quality management and sustainable development of aquaculture. The main results are listed as follows:1. Characteristics of water environment in ’R. esculentum-S. constricta -P. olivaceus-F. chinensis’polyculture pondsDuring the culture period, the DO were (6.14±2.34) and (6.96±1.82) mg/L; pH were (7.4±0.3) and (7.5±0.5); Salinity were 21.2±4.4 and 19.6±4.0; water temperature were (23.8±4.3)℃ and (23.9±4.3)℃; transparency were (0.61±0.11) and (0.58±0.17) m; TN were (1.42±0.37) and (1.35±0.11)mg/L; TP were (0.45±0.24)and (0.32±0.14)mg/L; TOC were (7.31±1.35) and (6.42±1.20) mg/L:the chl-a of phytoplankton were (5.20±1.23) and (5.49±1.16)μg/L; the gross primary production of phytoplankton were (2.69±1.23) and (3.33±2.48) gO2/(m~2×d); the density of bacteria were (2.65±0.96)×107 and (2.10±0.85)×107 cells/ml. There were 48 species of phytoplankton were found in experimental ponds, the density of phytoplankton were (26.71±4.69)×105 and (26.29±5.76)×105 ind./L; the biomass of phytoplankton were (0.72±0.19) and (1.07±0.28) mg/L; the dominant species of phytoplankton were Chlorella sp. and Chroomonas acuta; the equivalent spherical diameter of phytoplankton were 11.94μm/cell; and the density of phytoplankton at<20μm was comparatively higher than those at>20μm. There were 24 species of zooplankton were found in experimental ponds, the density of zooplankton were (93.69±39.68) and (69.41±26.61) ind./L; the biomass of zooplankton were (0.57±0.25) and (0.45±0.18) mg/L; the dominant species of zooplankton were Codonellopsis mobilis and Mesodinium rubrum; the equivalent spherical diameter of zooplankton were 141.09μm/ind.; and the density of zooplankton at<200μm was comparatively higher than those at>200μm.2. Structure of suspended particles matter and its organic carbon distribution in ’R. esculentum-S. constricta-P. olivaceus-F. chinensis’ polyculture pondsThe concentration of total suspended particles matter was (67.12±6.03) mg/Land (70.05±7.63) mg/L in the two experimental ponds; the percentage of organic suspended particles in total suspended particles matter was 27.43and 24.51. The average concentration of total organic carbon (TOC) was (7.31±1.51) mg/Land (6.42±1.31) mg/L in the two experimental ponds; the percentage of particles organic carbon (POC) in total organic carbon (TOC) was 23.67 and 29.44. The concentration of total suspended particles matter in polyculture ponds had a higher level, and the inorganic suspended particles was the most important component of the total suspended particles matter, bacteria and detritus was the main components of the organic particles, and the results indicated bacteria and detritus play a very important role in nutrient cycling and energy flow.3. The effects of low concentration of suspended particles on the clearance rate and absorption efficiency of S. constrictaThe results were as follow, the suspended particles had significant effect on clearance rate of Sinonovacula constricta (P<0.05). Clearance rate of Sinonovacula constricta increased with concentration rise of suspended particles. Maximum clearance rate value of S. constricta was detected when the concentration of suspended particles was 160 mg/L, and the minimum value was detected when the concentration of suspended particles was 50 mg/L after 6h test stage. The suspended particles had significant effect on absorption efficiency of S. constricta (P<0.01). Absorption efficiency of S. constricta decreased with concentration rise of suspended particles.4. Sedimentation of particle matter and organic carbon in ’R. esculentum-S. constricta-P. olivaceus-F. chinensis’polyculture pondsIn the two experimental ponds, the average values of sedimentary flux for total particulate matter were (124.84±100.98) g/(m~2·d) and (92.36±26.34) g/(m~2·d), the average values of sinking velocity for total particulate matter were (1.89±1.33) m/d and (1.53±0.51) m/d. the average values of S/T were (0.28±0.04) and (0.31±0.12), the average values of real sediment particulate matter were (10.44±6.56) and (7.53±3.44) g/(m~2·d), respectively. The average values of particle organic carbon (POC) in sediment were (2.62±1.65)% and (2.39±1.36) mg/L, the average values of sedimentary flux for particle organic carbon (POC) were (2.51±1.58) g/(m~2·d) and (2.36±1.72)g/(m~2·d).respectively.5. Food web structure and trophic level of organism in ’R. esculentum-S. constricta-P. olivaceus-F. chinensis’polyculture pondsThe food sources of the main economic animals and trophic levels of biotic communities from an optimization culture model (R. esculentum-S. constricta-P. olivaceus -F. chinensis) in experimental pond were studied using the stable carbon and nitrogen isotopes technique. The results indicated that the values of δ13C range from (-27.28±0.35)‰ to (-16.65±0.20)‰ and the values of δ15N range from (3.68±0.23)‰ to (13.91±0.26)‰. Bait fish had the greatest contribution to R. esculentum, S. constricta and F. chinensis; F. chinensis had the greatest contribution to P. olivaceus, followed by the E. carincauda. The trophic level of the biotic communities under that optimization culture model in a sea water pond was 3.54, in which P. olivaceus was in the fourth level (3.54); F. chinensis, Synechogobius hasta, Ablennes anastomella, E. carincauda, Clupanodon punctatus, Chelon haematocheilus were in the 3rd trophic levels; R. esculentum, Engraulis japonius, S. constricta and zooplankton (1.00) in the 2rd trophic levels, suspended matters (0.15) including phytoplankton, bacteria, humus, etc. were in the end trophic levels.6. Nutrient budgets in ’R. esculentum-S. constricta-P. olivaceus-F. chinensis’ polyculture pondsA budget describing the flow of organic carbon (OC), nitrogen (N) and phosphorus (P) through in the two polyculture ponds was produced. The results indicated that the total input of organic carbon were 3107.44 and 3358.25 kg/ha, the total output were 1759.38 and 1324.96 kg/ha; the total input of nitrogen were 363.75 and 439.37 kg/ha, the total output were 354.00 and 342.32 kg/ha; the total input of phosphorus were 75.40 and 66.48 kg/ha, the total output were 74.31 and 64.77 kg/ha, respectively. Feed was the main input of N and P (78-81% and 79-80%); the primary production of phytoplankton was the major input of total OC (49-56%). The harvest was the main output of N and P (50-73% and 49-52%), and the respiration was the major output of OC (43-61%). The feed conversion ratio were 1.14 and 1.51 in the two experiment ponds, and OC, N and P utilization efficiency of all harvest economic animals in the two experimental ponds were 30.30 and 21.03%,70.19 and 46.95%,50.14 and 46.47%, respectively. S. constricta had greater utilization efficiency of nutrient than those of other culture animals. On the contrary, the utilization efficiency of F. chinensis was the lowest.7. Organic carbon and nitrogen budgets in ’R. esculentum-S. constricta-P. olivaceus-M. japonicus’ and ’R. esculentum-S. constricta-P. olivaceus-F. chinensis’polyculture model pondsOrganic carbon (OC), nitrogen (N) and phosphorus (P) budgets in ’R. esculentum- S. constricta -P. olivaceus- M. japonicus’and ’R. esculentum- S. constricta -P. olivaceus- F. chinensis’polyculture ponds were produced in 2014. The results indicated that the total input of organic carbon were 3508.63kg/ha and 4799.16 kg/ha, the total output were 1209.87 kg/ha and 1440.20 kg/ha in the two experimental ponds; the total input of nitrogen were 235.36 kg/ha and 212.37 kg/ha, the total output were 206.61 kg/ha and 190.65 kg/ha, respectively, the total input of phosphorus were 36.02 kg/ha and 34.81 kg/ha, the total output were 37.10 kg/ha and 36.60 kg/ha. Feed was the main input of N and P (N were 85.23% and 81.52%, P were 75.46% and 68.34%); the primary production of phytoplankton was the major input of total OC (68.32% and 75.49%) in the two polyculture ponds. The harvest was the main output of N and P (N were 74.17% and 66.98%, P were 47.28% and 38.06%), and the respiration was the major output of OC (65.52% and 69.99%). The feed conversion ratio were 0.5 and 0.7 in the two experimental ponds, and OC utilization efficiency of all harvest economic animals in the ponds were 20.57% and 12.39%; N utilization efficiency were 66.69% and 60.05%, P utilization efficiency were 41.78% and 35.04%, respectively. P. olivaceus had greater utilization efficiency of OC and N than those of other culture animals, S. constricta had greater the utilization efficiency of P than those of other culture animals.8. Analysis on aquaculture benefits of jellyfish-shellfish-fish-prawn polyculture modelThe aquaculture benefits of four ’jellyfish-shellfish-fish-prawn’ polyculture ponds were analyzed in Donggang, Liaoning Province from 2013 to 2014, and clarified the features of this culture model, pointed out the problem and proposed related suggestions during the practical production period. The results shown that the net profits was (3.16～7.25)×10~4 yuan per ha under this polyculture model, the feed conversion rate (FCR) was 0.5～1.5 in the four ponds. The utilization of OC, N and P were (12.4～30.3)%. (47.0～70.2)%. and (35.0～50.1)%. respectively. Compared with other culture model, it indicated higher economic and ecological benefits. The features of this polyculture model include that:(1) short culture period (only 4-6 month), quick gains, and less risk; (2) high space utilization efficiency, high yield per unit area, high utilization efficiency of nutrition, and there was significant culture profits under this culture model; (3) in this culture system, prawn shown the lowest survival rates, and fish-P. olivaceus shown the highest survival rates, which had the greatest contribution to the cultural profits composition; (4) the wild species was also the main part of culture profits composition. The problem and proposed related suggestions:(1) the high contents of inorganic suspended particles were found in culture ponds, therefore the water quality management method should be strengthen; (2) genetical characterization decline of culture animals was one of the problem during the practical production, the screening of excellent germplasm was necessary; (3) aquaculture management methods had direct impact on the culture profits, so the scientific management method should be taken. |
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