| Identifying the main factors influencing spatial differences of Yesso scallop net growth rate in culture systems is crucial for effective aquaculture management and development.Coupling a three-dimensional ecosystem model with a dynamic energy budget model for scallops,a Yesso scallop culture ecosystem model（Ye SCEM）was presented to simulate scallop growth ability.Based on scenario simulation,the spatial-temporal differences of growth ability of bottom-cultured scallop in Changhai sea area were analyzed,and the indicator factors for predicting the annual difference of scallop growth ability were explored.The production carrying capacity of bottom-cultured Yesso scallop was evaluated,and the maximum aquaculture profit and the best scallop density were determined,to provide scientific support for the aquaculture planning of the Changhai sea area.Ye SCEM has reasonably simulated the environmental variation and scallop growth process in the Changhai sea area.There were significant spatial-temporal differences in bottom water temperature,salinity,food concentration,dissolved oxygen,and p H.Except for bottom water temperature and food concentration,other factors had no significant effect on the growth of scallop.The bottom water temperature is controlled by temperature gradient and convection and changes greatly（>2℃）in the tidal cycle.Under different Representative Concentration Pathway（RCP）,the growth rate of bottom water temperature is different.The seasonal distribution of food concentration was controlled by the primary production process,which was higher nearshore and lower far shore in the whole year,the lowest in January,and the highest in April.However,the interannual variation of food accumulation is very small,only showing phenological changes.The spatial distribution of the growth ability of the bottom-cultured Yesso scallop high in the north and low in the south of the Changhai sea area.Due to the gathering of food by current,a high-value area of biomass is formed near islands.The food concentration in the northern study area is high,but the growth of scallops is restricted by water temperature.Although the water temperature in the southern study area is suitable for scallop growth,the lack of food makes the growth of scallops slower.The net growth rate of the scallop is slow in winter and midsummer,which is mainly restricted by temperature;it grows faster from spring to early summer and autumn and is mainly controlled by food.In other words,scallops grow rapidly when the water temperature and the food are matched,while scallops grow slowly or even lose weight when the water temperature and the food are unmatched.The spatial difference of the growth ability of the Yesso scallop is affected by the timing of suitable growth days.The interannual differences in the growth ability of the bottom-cultured Yesso scallops in the Changhai Sea are obvious,with the lowest in 2009-2010 and the highest in 2013-2014.Since the interannual difference in the accumulation of food is small,the interannual difference in growth ability is mainly controlled by the unsuitable growth days when the water temperature in winter is less than 0℃.The potential biomass of bottom-cultured scallops at the end of the year can be predicted by the sea surface temperature in early winter（November to next January）,and the abnormally cold winter corresponds to the next year as a lower level of biomass.The initial seeding scallop density corresponding to the maximum aquaculture profit after considering the condition index of the Yesso scallop is the optimal seeding scallop density,and the biomass of scallops at the end of the year is the production carrying capacity.Estimation of the Ye SCEM shows that there are obvious spatial-temporal differences in the production carrying capacity and the optimal seeding scallop density of Yesso scallop in the Changhai Sea area,ranging from 2.99-67.00 g m-2 and 3-27 ind m-2,respectively.Based on the results of the cluster analysis of the standardized maximum aquaculture profit and the interannual differences,the Changhai sea area is divided into four regions.The high-profit bottom culture area is located between Zhangzi Island and Changshan Island and extends to the northeast of the Changhai sea area,the timing of suitable growth days is significantly higher than in other seas.The middle-profit bottom culture area is located in the northwest and central part of the Changhai sea area.Due to the limitation of the bottom water temperature in the northwest of Changhai sea area,the plumpness of the Yesso scallops is insufficient and belongs to the low-profit bottom culture area.The area in the central part of the Changhai sea area which is near the unsuitable bottom culture area also belongs to the low-profit bottom culture area because of food restriction.The unsuitable bottom culture area is located in the south of the Changhai sea area（>50 m）,and the main reason is the lack of food,which causes the growth of scallops to be restricted.The relationship between the recommend seeding scallop density and the maximum aquaculture profit in each region shows that just blindly increasing the seeding scallop density cannot achieve the effect of increasing production and profit.Under the background of global warming,with the increase of bottom water temperature,the timing of unsuitable growth days will increase.Under the RCP2.6scenario,there is no significant difference in the bottom water temperature and the biomass of the Yesso scallop in each period of the Zhangzi island;under the RCP4.5scenario,the bottom water temperature will increase about 1.3℃by 2090s,and the biomass will decrease by 10%;under the RCP8.5 scenario,the bottom water temperature increased by 3.3℃in 2090s,and the biomass decreased by 28%.In other words,the higher the greenhouse gas emission,the more obvious the restriction on the growth of the bottom-cultured Yesso scallop.In conclusion,the Yesso scallop culture ecosystem model which is composed of a three-dimensional hydrodynamic model,ecosystem model,and individual growth model can study the response of aquaculture resources to environmental change in the open sea area and can play an important role in mariculture carrying capacity assessment and marine ranch planning. |
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