The Macrobenthic Community Characters And Its Response To Seasonal Hypoxia Of Muping Marine Ranch During 2015-2017

Seasonal hypoxia occured at Muping marine ranch during from 2015 to 2017,which caused a large number of deaths of local economic organisms and had a serious impact on the local benthic esosystem.The main aims of this work was to understand:(1)the current status of macrobenthos community and the spatial-temporal changes of macrobenthos community at Muping marine ranch based on the 16 field survey;(2)the effect of hypoxia on macrobenthos community and biodiversity.The main results are shown as bellows.The macrobenthic community was researched based on data carried out 16 surveys from 2015 to 2017.The results showed that 364 macrobenthic species were obtained,most of them belong to Polychaeta(155),Crustacea(112),Mollusca(70),Echinodermata(14)and other animals(13).A total 261 species were found in 2015.199 species were found in2016.160 species were found in 2017.The dominant species were polychaetes.15 dominant species were found during spring,summer and autumn 2015,they were Lumbrineris latreilli,Glycinde gurjanovae,Magelona cincta,Lumbrineris cruzensis Hartman,Nephtys oligobranchia,Capitella capitate,Sternaspis sculat,Haploscoloplos elongates,Sigambra bass,Heteromastus filiformis,Notomastus latericeus,Eunice sp.,Paranthura japonica,Endopleura lubrica,Semelangulus miyatensis.6 dominant species were found and they were Lumbrineris latreilli,Mediomastus sp.,Sternaspis sculata,Endopleura lubrica during spring,summer and autumn 2016.7 dominant species were found and they were Lumbrineris latreilli,Nephtys oligobranchia,Glycera onomichinensis,Mediomastus sp.,Sternaspis sculata,Sigambra bassi,and Endopleura lubrica during spring,summer and autumn 2017.In 2015,the total mean macrobenthic abundance was 928 ind/m~2,and the total mean biomass was 8.5 g/m~2.In 2016,the total mean abundance was 1380 ind/m~2,and the total mean biomass was 9.0 g/m~2.In 2017,the total mean abundance was 1112 ind/m~2,and the total mean biomass was 9.8 g/m~2,the main contributor to abundance and biomass belonged to Polychaeta.The main value of richness index,evenness index and Shannon-Wiener diversity index were respectively 2.76±0.69?0.73±0.13?3.10±0.67 during 2015.The main value of richness index,evenness index and Shannon-Wiener diversity index were respectively 2.21±0.65?0.67±0.22?2.60±0.92 during 2016.The main value of richness index,evenness index and Shannon-Wiener diversity index were respectively 2.47±0.61?0.68±0.17?2.80±0.79 during 2017.Abundance/Biomass Comparison Curves(ABC)indicated that the macrobenthic community was in a state of moderate disturbance during the spring and summer 2015 and was seriously disturbed during autumn 2015.The macrobenthic community was seriously disturbed during spring,summer and autumn 2016.The macrobenthic community was seriously disturbed during the spring,and in a state of moderate disturbance during the summer and autumn 2017.To analysis the effects of hypoxia on the community structure of macrobenthos,the macrobenthic samples were collected at the Muping marine ranch during August 2015,2016,and 2017.The results showed that the dissolved oxygen(DO)<3 mg/L in most of the bottom water and the lowest dissolved oxygen was 1.02 mg/L during August 2016.The number of macrobenthic species during August was:culture zone(56)>marginal area of hypoxic zone(38)>offshore zone(36)>hypoxic zone(33),There were the least dominant species and polychaetes accounted for the largest proportion in the hypoxic zone compared to other sea areas.The species richness index,evenness index and Shannon Wiener diversity index were the lower in the hypoxic zone,1.81,0.5,and 1.84,respectively.The lower values of dissolved oxygen correspond to the higher values of abundance and biomass.The SIMPER and NMDS analysis showed that the macrobenthic community structure changed significantly during 2015-2017.The results of PCA analysis showed that dissolved oxygen,temperature and salinity were the main reasons for the changes of macrobenthic community during August 2016.The results of ABC curve show that the macrobenthic community was seriously disturbed in hypoxic zone compared other zones.The results of AMBI and M-AMBI index evaluation showed that the habitat condition of macrobenthos during August 2016 was lower than that during June and September 2016.The main conclusions of this paper were as follows:(1)the number of macrobenthos decreased during 2015-2017.The number of dominant species decreased,the composition of macrobenthic community became singler.The species showed a trend of miniaturization(2)Hypoxia significantly changed the community structure of macrobenthos,low value of dissolved oxygen correspond to high biomass and abundance.Species diversity decreased;sensitive species decreased,opportunistic species Lumbrineris latreilli increased.