Research On The Status Of Oyster Reef And Resource Restoration In Kenli,Dongying

Oyster reef is a natural reef formed by long-term accumulation of oysters,which is mainly distributed in the temperate estuary.Oyster reefs can not only provide efficient economic and medicinal value,but also play an important role in maintaining the stability of the ecosystem and providing ecological functions such as purifying water quality,providing habitats and stabilizing the coastline.In recent years,owing to environmental pollution and overfishing,the global oyster reef area has declined significantly,and the stability of ecosystem has been destroyed.Therefore,the investigation of oyster reef status and resource restoration is imminent,and it has attracted great attention from domestic and abroad scholars.In this study,Crassostrea ariakensis were sampled in Dongying Kenli area,and the distribution profile and ecological status of the oyster reef were analyzed.The oyster resource restoration was carried out by building reinforced concrete reef;at the same time,oyster reef seedlings were supplemented by constructing the techniques of larval cultivation and intermediate cultivation,so the results of this study will initially reveal the habitat and survival status of Crassostrea ariakensis in the sea area of Dongying Kenli,and provide a scientific basis for the restoration of Crassostrea ariakensis resources in the north of China.The main results are as follows:1)Distribution characteristics of oyster reef in Kenli,DongyingThe distribution of oyster reef patches is relatively concentrated in the waters of Dongying Kenli area,with a total area of 0.24 km²,and the main reef area accounts for about95.8%.The side-scan sonar display clearly shows that the bottom of the oyster reef is covered with fishing net trawls,which indicates that the oyster reef was affected by a large number of trawling operations.The oyster shell length ranged from 16.40 to 29.32 cm,and the average shell length was 22.83 cm;the shell height ranged from 7.60 to 12.10 cm,and the average shell height was 9.75 cm.Most of the Crassostrea ariakensis were buried at the bottom of the sea,with an average buried depth of 12.23 cm.However,juvenile oysters were not found in the process of oyster collection.The mitochondrial 16 Sr DNA sequence analysis showed that the species was Crassostrea ariakensis in Dongying Kenli oyster reef.Compared with the results in other sea areas,it can be seen that this oyster reef is composed of a single species.This study determined the fatness of the oyster in spring?April?and autumn?September?in Dongying oyster reef.The results showed that the average fatness in spring and autumn was21.80%and 21.66%respectively,and the difference was not significant in spring and autumn fatness?P>0.05?.2)Current situation of biotope in reef area and non-reef area of Kenli,DongyingSurface water and sediment samples were tested from 11 stations in the oyster reef area and non-reef area of Dongying Kenli in spring and autumn.The results showed that the suspended substance concentration ranged from 124.44 to 239.64 mg/L at each station in spring,with an average of 183.48 mg/L.The autumn range was 85.56-128.66 mg/L,with an average of 97.13 mg/L,and the average content of suspended solids in spring was higher than that in autumn at each station.Among the components of dissolved inorganic nitrogen?DIN?in spring,the average proportions of nitric acid nitrogen?NO₃^--N?,nitrite nitrogen?NO₂^--N?and ammonia nitrogen?NH₄⁺-N?were 72.99%,2.18%and 24.83%,and the proportions in autumn were 80.51%,6.55%and 12.94%.Therefore nitrite nitrogen?NO₃^--N?is the main form of dissolved inorganic nitrogen?DIN?in this sea area.The ranges of DIN from 0.154 mg/L to0.276 mg/L at each station in the spring and autumn,which meets the national second-class water quality standard.The average contents of DIN,silicate salts(SiO₃^2--Si)and phosphate salts(PO₄^3--P)in the reef area were lower than those in the non-reef area in spring and autumn,which indicated that oyster reef could reduce the concentrations of DIN,SiO₃^2--Si and PO₄^3--P effectively.According to the particle size composition of the sediment,the type of sediment in the reef area is silt while in non-reef area is sandy silt,which indicates that the sediment grain size in the oyster reef area is smaller than that in the non-reef area.The macro-benthos are mainly mollusks and polychaetes in this sea area,there was no significant difference in biomass and abundance of each station in April and September?P>0.05?.The average values of shannon-wiener index,species richness index and species evenness index of reef area were higher than those of non-reef area,indicating that the diversity index of reef area was higher than that of non-reef area.There was no significant difference between the Shannon-Wiener index and the species evenness index in the reef and non-reef areas in April,and the species richness index was significantly different.The Shannon-Wiener index and the species richness index were significantly different in September,and the species uniformity index was not significant.The number of dominant species in reef area was more than that in non-reef area.Notably,Musculus senhousei and Gammaridea were more dominant than other species.Cluster analysis of the macrobenthos community structure in this sea area showed that the state of macro-benthos community at each station was unstable in April and September.3)Artificial breeding and restoration of oyster reef in Kenli,DongyingThe juvenile and intermediate cultivation techniques of Crassostrea ariakensis were constructed.The conditioning of broodstock of Crassostrea ariakensis was conducted for 2months,when the gonad of the oysters got mature,the zygote was obtained by artificial insemination.It was found that the D-larvae appeared after 22 hours of fertilization and the D-larvae developed to eye-spot stage in 18th day when the temperature was around 26.5?,with a shell height of 270?m.The eye-spot larvae can settle on the Crassostrea ariakensis shell successfully,the density of eye-spot larvae was 2-3 ind/mL and the attachment ratio was up to68%.It was found that the growth rate of larvae shell height from eye-spot larvae to juveniles was 7.12%,which was higher than that of from D-larvae to eye-spot larvae with a value of6.07%.The growth rate of the intermediate cultivation was 1.83%,meanwhile,the growth rate of artificial oyster seedlings is 1.06%in the reef area.Thirty reinforced concrete reefs with a size of 60×40×35 cm³ were artificially constructed and placed in the oyster reef area.The subsidence depth of the reef body was found to be about 7 cm,the average density of barnacles,oysters and seasnail was 3.43×10³ ind/m²,83.33 ind/m² and 20.68 ind/m² respectively on the surface of the artificial reef.The results show that reinforced concrete structure can provide habitat environment for barnacle and oyster.In conclusion,the distribution,environmental factors condition of oyster reefs in Dongying Kenli sea area were investigated.This study has revealed the distribution and resource status,habitat characteristics of oyster reefs in this study,and constructed the recruitment technique which combines the artificial breeding and reinforced concrete reefs technique.The results are expected to provide scientific basis for the resources assessment and artificial remediation of Crassostrea ariakensis resources in the north area of China.