The Synergistic Change Rule Between Target Species And Keystone Species In Marine Ranching

Marine ranching is an important means to conserve aquatic biological resources and restore the ecological environment of the waters,which is mainly based on habitat restoration and stock enhancement as the main construction pathway,and has been proposed as a promising solution to manage the depleted coastal fishery ecosystem in recent decades across China.It is usually small in spatial scale,such as national marine ranching demonstration areas are mostly 3-6 km²,and in such small-scale marine ranches are usually affected by multiple anthropogenic activities,while it’s an important guarantee of sustainable output to predict the response characteristics of biological community structure and ecosystem characteristics under the influence of anthropogenic effects in marine ranching.Therefore,in this study,based on the biological community structure and functional characteristics of typical marine ranching ecosystems in the south and north of China,we established a synergistic change assessment technique of marine ranching stocking target species and keystone species based on the Ecosim model by constructing a temporal dynamic ecosystem model to simulate and evaluate the effects of stocking on the dynamics of marine ranching biological community structure.This study was based on the seasonal biological resource surveys conducted in November2020 and March 2021 in the Laizhou Bay marine ranching,Shandong Province,using Ecopath with Ecoism software to construct an Ecopath model of marine ranching in Laizhou Bay containing 27 functional groups,assess the ecosystem function and structure of Laizhou Bay,and combine the topological network model to comprehensively determine the keystone species in Laizhou Bay.A time-dynamic,ecosystem model was constructed using Ecopath with Ecosim for the Laizhou Bay（Bohai Sea）marine ranching ecosystem in the nearshore waters of northern China.Two sedentary target species with potential for stock enhancement,i.e.,the carnivorous red snail Rapana venosa and the detritivorous sea cucumber Apostichopus japonicus,were selected to simulate and estimate their ecological carrying capacities.Ecological carrying capacity was defined as the maximum standing stocks of the target species that would not cause“unacceptable”impacts on the ecosystem function and resilience,i.e.,not cause any other group’s biomass to fall below 10%of its original biomass.We project their overall effects on the ecosystem and explore of the synergistic change pattern between the target species and keystone species of marine ranching enhancement by extracting the time series data.In addition,we constructed an Ecosim model in the southern tropical recreational fishery Wuzhizhou Island marine ranching,Hainan Province.The orange-spotted grouper Epinephelus coioides and the sea cucumber Stichopus monotuberculatus were selected as two economically important target species for marine ranching enhancement in Wuzhizhou Island,simulated and explored the synergistic change between target species and keystone species Cephalopholis boenak in southern tropical recreational fishery marine ranching.The results of the study indicate that:1.The biomass magnitude span of the taxa in the Ecopath model estimated by the PREBAL diagnostics was 6,and the slope of the biomass（on a logarithmic scale）from the highest to the lowest TL declined by 8.5%,the Ecopath model Pedigree（P index）was 0.602,the trophic levels of some functional groups estimated based on stable isotopes were significantly and positively correlated with those estimated by the Ecopath model（R²=0.7576,n=10,P<0.01）,above analysis generally shows that the quality of the model is reliable,indicating that the quality of the model is high.2.The current total system throughput（2020）in the marine ranching ecosystem of Laizhou Bay is 25110.08 t·km^-2·year^-1.The sum of all production was 8270.54 t km^-2 year^-1.the ratio of TPP/TR was 1.01,the ratio of TPP/TB was 9.59,and the ratio of TB/TST was 0.02.the FCI and FML of the marine ranching ecosystem in Laizhou Bay were 24.19%and 5.141,respectively.the connectance index（CI）was 0.178,and the system omnivory index（SOI）was 0.148.The results of the overall characteristics of the ecosystem in Laizhou Bay indicate that the current system in Laizhou Bay is large in scale,with relatively high maturity and stability,but the relationship between the functional groups of the ecosystem is not close,the food web structure is relatively simple,and the resistance of the ecosystem to natural and anthropogenic disturbance factors is weak.3.Based on the keystone species determination results of the Laizhou Bay Ecopath model,phytoplankton,Sebastes schlegelii,and Charybdis japonica,the three functional groups,ranked in the top three of the keystone indexes,with-0.0742,-0.0754,and-0.0804,respectively,and the relative total impact index the top four functional groups were Crassostrea gigas（1）,phytoplankton（0.903）,S.schlegelii（0.846）,and C.japonica（0.807）.Based on the topological network indicators(D,D_out,D_in,BC,CC,IC,K_i,K_b,K_t,TI¹,TI⁷),S.schlegelii,C.giga,Lateolabrax maculatus,Sparus macrocephalus,C.japonica were the keystone species in the Laizhou Bay marine ranching ecosystem.The keystone species in the marine ranching ecosystem of Laizhou Bay were identified by combining the two methods,namely,Sebastes schlegelii.4.The ecological carrying capacities estimated for R.venosa and A.japonicus in the Laizhou Bay marine ranching based on Ecosim model were 623.46 and 200.57 t·km^-2,respectively.The variation patterns of synergistic responses of keystone species in Laizhou Bay under different target species enhancement scenarios were distinctly different.The relative biomass of keystone species showed varying degrees of decline（-62.02%to-56.89%）under the R.venosa enhancement scenario,while in contrast,the A.japonicus enhancement had a relatively weak effect on keystone species and its relative biomass showed a small increasing trend（+4.5%）at the end of the simulation.The scenarios simulating an increase in the biomass of the A.japonicus showed an overall increasing trend in the ecosystem scale indicators（total system flow（TST）,total system biomass（B）,primary production（PP）,respiration（R）,and total system production（P））;however,the Finn’s cycle index,which characterizes system maturity and stability indicators,showed a decrease（FCI:-10.74%～-1.89%）,while the change of system biodiversity index Q（Kempton’s Q）was relatively stable.In contrast,the simulated scenario of increasing R.venosa biomass showed a significant decrease in FCI characterizing system maturity（-35.14%～-18.68%）and a significant decrease in the system biodiversity index Q（-25.99%～-8.53%）,despite the increase in ecosystem size.Compared with the changes in ecosystem characteristics indicators,the A.japonicus stocking was better than the optimization of ecosystem function.5.The ecological carrying capacities estimated for E.coioides and S.monotuberculatus in the western national marine ranching demonstration area of Wuzhizhou Island based on Ecosim model were 105.43 t·km^-2 and 102.22 t·km^-2,respectively.Interspecific differences existed in the synergistic response variation of keystone species C.boenak under different target species enhancement scenarios.The relative biomass of keystone species varied from-51.51%to 204.6%under the E.coioides enhancement scenario,while the response of keystone species varied more（13.92%to 379.25%）under the S.monotuberculatus enhancement scenario.The ecosystem size（TST,B,PP,R,P）increased for the E.coioides and the S.monotuberculatus scenarios,but the FCI,which characterizes the maturity of the system,decreased to different degrees（E.coioides:-21.9%to-14.69%;S.monotuberculatus:-38.48%to-14.71%）.Based on the Kempton’s Q values,the S.monotuberculatus enhancement scenario was more beneficial to maintain the biodiversity of the system（S.monotuberculatus:-7.57%to 8.63%;E.coioides:-13.41%to 6.92%）.This study established the keystone species identification technology based on the ecological model and topological network method,and the evaluation technology for the synergistic changes between the target species and keystone species based on the Ecosim model,and simulated and evaluated the impact of enhancement on the structure and function of the ecosystem.The results of the study can provide technical support for the optimization of marine ranches augmentation and release patterns,ecological capacity estimation,and ecological risk prevention before implementing management strategies.