Research On Plankton Community Structure In Low Salinity Integrated Aquaculture Ponds Of Litopenaeus Vannamei

In order to understand the effects of polyculture on plankton community structure in low-salt(2-3.2) ponds of Litopenaeus vannamei, sampling were taken respectively in molocultureponds and polyculture ponds from June to August,2011and in polyculture ponds whichmainly stereoscopic cultivation was carried out in Dongyi Pond from May to August,2012inAndong Town, Cixi City, Zhejiang Province, to investigate the physical and chemical factorsand plankton of the ponds.Multivariate statistical analysis was applied, PCA of physical andchemical factors was conducted to extract the main factors of each pond, then Spearmancorrelation analysis of the main factors was carried out to find out the linkages between them.Quantity and biomass of plankton was analysed to identify the dominant species and itsvariation. Planktonic algal was classified into different functional groups, then RDA ordinationwas conducted with the primary functional groups and the main physical and chemical factorsto identify the physical and chemical factors which impacted on phytoplankton communitystructure variation.The results showed:(1) In2011, the average feed coefficient of polyculture Aristichthys nobilis and Carassiusauratus in Litopenaeus vannamei pond was1.31, significantly lower than the monoculturemode,1.51(p<0.05); Average value of polyculture shrimp output is4342.9kg.hm-2,significantly higher than monoculture style which is3600kg.hm-2(p<0.05); Incidence ofpolyculture ponds was30%, significantly lower than53.7%of the monoculture style.(2) June to August2011, the average value of total soluble nitrogen, total solublephosphorus, ammonia nitrogen and reactive phosphorus content in polyculture ponds wassignificantly lower than that in monoculture ponds, value of the soluble chemical oxygendemand, total soluble nitrogen, total soluble phosphorus, ammonia nitrogen and reactivephosphorus content in polyculture ponds was significantly lower than that of monocultureponds(p<0.05)in the later period of investigation. The soluble nitrogen and phosphorus ratioshowed a gradual decrease trend in monoculture and polyculture pond. Spearman correlationanalysis showed that the concentration of chlorophyll a was significantly negative correlatedwith the soluble nitrogen and phosphorus ratio(p<0.01), and significantly positive correlatedwith the total soluble nitrogen and total soluble phosphorus(p<0.01). Value of chlorophyll a in polyculture ponds was significantly smaller than that in monoculture pond(p<0.05) late in thecultivation.(3) June to August2011, a total of48phytoplankton species which belonded to32generaof5phyla were identified in two shrimp ponds. The main dominant species of phytoplanktonwere Spirulina sp., Planktolyngbya limnetica and Oocystis lacustris and so on. A total of19zooplankton species were identified in two shrimp ponds. The main dominant species ofzooplankton were Brachionus angularis, B. calyciflorus, Asplanchna sp., Strombidium sp.,Acanthocystis sp. and Tintinnidium sp. and so on. The average biomass of planktonic algalin polyculture ponds(22.7mg/L) was lower than that of monoculture ponds(33.9mg/L).Biomass of Cyanophyta species accounted for46.4%of total biomass in polyculture ponds,lower than68.1%of the monoculture shrimp ponds, but the biomass of Chlorophyta andCryptophyta species showed the opposite trend.(4) May to August2012, the phosphorus content of feeding water had reached about0.6mg/L in the early period, and dramatically dropped to0.02mg/L in the later period ofinvestigation in Dongyi Pond, the amplitude of variation was big. Variation in theconcentration of chlorophyll a varied between60.45ug/L to309.75ug/L, varation wassignificant in the later period(p<0.05), the main physical and chemical factors that determinethe concentration of chlorophyll a were light and phosphorus content. The average value ofsoluble nitrogen and phosphorus ratio was6.35, and reached a peak value of25.06in August15th.(5) May to August2012, a total of90phytoplankton species which belonded to63genera of6phyla were identified in Dongyi Pond, they included24Cyanophyta species,37Chlorophyta species,15Bacillariophyta species,12Euglenophyta species,1Dinophytaspecies and3Cryptophyta species.The main dominant species of phytoplankton werePeridinium sp., Raphidiopsis sp., Gonium sociale and Microcystis sp. and so on. A total of30zooplankton species were identified, they included13Protozoa species,13Rotiferia species,2Cladocera species and2Copepoda species,12Euglenophyta species,1Dinophyta species and3Cryptophyta species. The main dominant species of zooplankton were Trichocerca sp.,Filimia sp., Polyarthra sp., Halteria sp., Vorticella sp., Didinium sp. and Acanthocystis sp. andsoon.