The Community Characteristics And Ecological Functions Of Artificial Oyster Reef At Xiangyun Bay Marine Ranching

Marine ranching development is an important direction of the marine fishery upgrade in China,which follows the principle of building with nature,and prioritizes environmental restoration and fishery resource conservation.Artificial oyster reef,composed of colonized organisms such as oysters and artificial structures,has a variety of ecological functions and plays an essential role in marine ranching development.Our study was conducted at Xiangyun Bay marine ranching.We aimed to verify the community characteristics and ecological functions of artificial oyster reef through plate experiment,diving sampling and deploying cage net,so as to lay the foundation for modern marine ranching development.The main results were as follows:1.Community characteristics of artificial oyster reefA total number of 16 colonized organisms,belonging to 6 different taxa,were identified at Xiangyun Bay marine ranching.The Mollusca Crassostrea gigas,Mytilus edulis and Arthropod Caprella penantis accounted for more than 95%of total density and biomass,which all had some ecological functions and could promote the formation of a stable and diverse healthy ecosystem.In depths shallower than 6 m,the total biomass of colonized organisms of artificial oyster reefs increased with water depth.The C.gigas biomass at bottom layer was significantly higher than the middle and surface layers.Significant negative correlation existed between M.edulis and C.penantis biomass.The C.gigas biomass at different water depths could be influenced by larva photopathy,food resource and biological competition between other organisms.The artificial oyster reefs at Xiangyun Bay marine ranching had an excellent biological colonization effects.The C.gigas density was 276 ind.m^-2,average shell height was42.63 mm,and the proportion in the range of 30-40 mm was 42.53%.The deployment of artificial oyster reef was conducive to the conservation and reconstruction of natural oyster reef ecosystem.But the structure of reef was too primitive,which could be improved by modifying the reef size,increasing attaching areas and water flowing at the base of reef.2.Environmental effects of artificial oyster reefWithin 5 m from the artificial oyster reef,the total organic matter of surface sediment declined with the distance from it,while the median grain size presented increasing tendency.The existence of artificial oyster reef could change the surrounding flow field,which further facilitated the deposition of smaller particle size material,and the main source of organic matter at the base of reef could come from the colonized organism detritus and filter-feeding bivalve pseudo-feces.That C/N and C/Chl-a values of surface sediment around artificial oyster reef were significantly higher than control areas,which also indicated that the organic matter at the base of reef could come from biological detritus more than fresh phytoplankton.Meiofauna community structure is always included in the ecological assessment of marine environment,because of its sensitivity to benthic environment disturbance.A total of 8 main meiofaunal taxa were identified at Xiangyun Bay marine ranching,including Nematoda,Polychaeta and Copepoda.Meiofauna community showed a high spatial variation,since the total abundance and biodiversity indices were significantly different at diverse sites.Within5 m from the artificial oyster reef at each station,meiofaunal abundance declined with the distance from it,and the total organic matter had a significant positive correlation with the abundance.The increase of meiofaunal abundance could provide more food resource for high-trophic marine organisms,which also indicated that artificial oyster reef could increase the potential of fishery production.3.Resource effects of artificial oyster reefThe total number of fishery species at artificial oyster reef areas and control areas were 31 and 30,while the fish species at artificial oyster reef areas were 50%higher than control areas.The difference of fishery species between reef areas and control areas indicated that artificial oyster reef could provide better living environment for fish.There was no significant difference in biodiversity indices between artificial oyster reef areas and control areas,while the catch per unit of effort?CPUE?was significantly higher at artificial oyster reef areas.The dominant species at Xiangyun Bay marine ranching were Chaeturichthys stigmatias,Charybdis japonica and Sebastes schlegelii.We concluded that the development of artificial oyster reef could benefit the fishery production at Xiangyun Bay marine ranching.Because the colonized oyster made the reef surface structure more complex,promoting conservation and growth of other marine organisms,and the filter-feeding bivalves played an important role in linking the primary productivity and higher trophic organisms.Besides,the facts that the CPUE of dominant species at artificial oyster reef areas was much higher than control areas and C.gigas showed positive effects for Rapana venosa production further demonstrated that artificial oyster reef development could improve fishery conservation.However,artificial oyster reef could not totally replace the role of other essential ecosystems,like mangroves,seagrass beds and salt marshes.We should avoid damaging the spawning ground and feeding ground of key species caused by blind deployment of reefs.